SOME NORTHERN CALIFORNIA TERTIARY PALEOCANYON SITES
by
Larry J. Garside
Nevada Bureau of Mines and Geology
Alpha Diggings are located mostly in SW¼ Section 18, T17N, R11E [P197], about 2 km west of Omega Diggings and 5 km west of Diamond Creek placers. There is an extensive area of piles of boulders and cobbles from historic placer operations. Vein quartz clasts (over 1 m diameter) predominate over those of quartzite and quartz-pebble metaconglomerate. A few (approximately 1%) of the clasts are of schorlite-quartz vein matter, probably from the Meadow Lake mining district to the east. The bedrock is vertically foliated slate.
Photos
P197b.JPG Piles of coarse-reject boulders at Alpha Diggings; 3-m long vein-quartz boulder in foreground. Note trees growing between piles.
P197c_41.JPG Looking east from Alpha Diggings toward Omega Diggings.
P197e.JPG Black tourmaline cobble (~20 cm long) at Alpha Diggings.
Bean Hill is an area of relatively extensive hydraulic mining over at least 15 acres (6 hectare) in Center W½ W½ Section 3, T24N, R8E (Meadow Valley 7.5-minute Quadrangle), along the main road about 4 km northwest of Spanish Ranch [P88]. This is shown as a hydraulicking site by Turner (1898) but it is not named. Hietanen (1973, p. 57) reported that two mines, “the Pine Leaf and Little California have been in operation until recently.” The exact areas where these names were applied is unclear; the name Pine Leaf Mine is applied on the Bucks Lake 7.5-minute Quadrangle to a lode mine about 3 km to the east. Preston (1893, p.325) described the Pine Leaf Drift Claim and the nearby Centennial and Topaz Drift Mine; the exact location of these mines it is not clear from his description. However, Cooper (1898) reported that the Pine Leaf Mine was located in Section 11, T24N, R8E; this location plots on the modern topographic map a kilometer or less north of the community of Spanish Ranch, an area not examined in 2003. MacBoyle (1920a) reported that the Bean Hill hydraulic mine was located 2 mi northwest of Spanish Ranch.
Based on the clasts observed in the piles of hydraulicked material, the smooth, well rounded clasts consist of about 80% white vein quartz, and most of the remainder metasedimentary rocks. A few clasts that lie directly on the ultramafic bedrock are derived from that rock type, consisting of a carbonate-rich ultramafic alteration product. One boulder from the bedrock contact consists of a meta- feldspar porphyry. Hietanen (1973, p. 57) reported that pebbles on Bean Creek in the vicinity of this area consist of about 80% vein quartz, 8% gray chert, and 12% quartzite from the Silurian(?) Shoo Fly Formation and that larger pebbles and cobbles consist of 60% vein quartz and 40% Shoo Fly. Locally, one can see blocks of the original conglomerate that hydraulic mining did not completely break up. The cement in these conglomerates is, at least in part, iron oxide minerals (possibly originally pyrite).
Because the gravel has been stripped to bedrock over most of the mined area, it is possible to estimate the channel width and direction. Just east of Bean Hill the channel appears to trend nearly north, but turns to the northeast (to about N30°E) upstream. The channel is only about 100 ,m wide and rises steeply to the northeast, probably about 1000 feet per mile. This channel can not be the main course of an Eocene river, but more likely a side channel or possibly the gutter portion of a much broader channel that has been removed by erosion. Hietanen (1973, p. 57) reported that the clasts of Shoo Fly probably come from Shoo Fly outcrops about 2 km to the northeast, suggesting a southwest transport direction for the paleostream. Similar gravels lie below younger andesitic mudflows both to the northwest and southeast. There is no indication that the gravels at Bean Hill are interandesitic (Miocene) rather than Eocene; certainly there are no Tertiary volcanic clasts in them. However, at least one area of Auriferous stream deposits (Ts) shown by Hietanen (1973, Plate 2) about 1 km to the west in SE¼ NE¼ NW¼ Section 4, T24N, R8E [P89] has rounded clasts of the quartz-pebble conglomerate in float, indicating that there has been local reworking of the original conglomerate in some areas.
Photos
P88a.JPG White quartz cobble with 13 cm pen for scale, Bean Hill workings.
P88d.JPG Rounded 1-m boulder of feldspar porphyry lying on serpentinite bedrock, Bean Hill workings. Hammer is 32 cm.
P88g_63.JPG Dark outcrops of serpentinite bedrock stripped of Auriferous Gravels by hydraulick mining; white pipe clays in distance. Bean Hill workings.
P88i.JPG Flattened 24-in riveted steel pipe, Bean Hill workings.
P88k_59.JPG Iron-stained conglomerate, Bean Hill workings; ruler is 15 cm.
P88n_57.JPG Iron-stained conglomerate, Bean Hill workings; pen is 13 cm.
A thick stack of five Oligocene ash-flow tuffs, ranging in age from 31.1 to 25.1, crops out on and southwest of Black Mountain (Hinz and others, 2003; Wagner and Saucedo, 1990b). The tuffs represent essentially the same sequence observed at Haskell Peak (Brooks and others, 2003) and Dogskin Mountain (Henry and others, 2003). The ash-flow tuffs occupy a paleovalley that has an apparent northerly (upstream) trend at Black Mountain (Hinz and others, 2003), but may be the upstream continuation of a southwest-northeast-trending paleocanyon in the vicinity of the Red Clover creek area. The tuff of Campbell Creek is especially thick near Ferris Creek in the Ferris Creek 7.5-minute quadrangle (Section 36, T26N, 14E) [P182].
Photos
P182a.JPG Nubbly weathering surface of the tuff of Campbell Creek, near Ferris Creek, Black Mountain area.
P182c.JPG Close up of nubbly weathering tuff of Campbell Creek, near Ferris Creek, Black Mountain area.
P183b.JPG Columnar jointed tuff of Campbell Creek, near Ferris Creek, Black Mountain area.
Turner (1897) showed two areas of Auriferous Gravels on the northeast and northwest flanks of Blue Nose Mountain. He speculated that the masses of white quartz gravels could be the continuation of the Hepsidam channel northeast of the Bunker Hill Mine, although he noted they were about 500 ft lower in elevation.
Two areas were checked for Auriferous Gravels at the north end of Blue Nose Mountain, NE¼ NW¼ SE¼ Section 11(PB41), T22N, R10E along U.S. Forest Service road 19, about 500 m northeast of Turkeytown Diggings [P37], and the pass at the north “nose” of the mountain in NE¼ NE¼ NW¼ Section 12(PB42), T22N, R10E [P34]. Both of these areas are near the Tertiary-preTertiary contact at the base of andesitic and basaltic volcanic rocks. At both localities one can see smooth, well rounded clasts in float of white bull quartz and light gray quartzite. At the Section 12 locality, some cobbles have an iron-oxide coating. The Section 12 (PB42) locality is in the area that MacBoyle (1920a, p. 79) reported that the Morning Star Consolidated Placer Mines Company drift workings produced gold from an old channel below andesite; the gravel was said to consist of quartz and andesite tuff. Both the Section 11 and 12 areas are actually about 1200 ft and 900 ft lower, respectively, in elevation than my estimate of the elevation of the channel at Bunker Hill Mine. Turkeytown Diggings is apparently named for placer workings near the modern stream. Some bedrock workings in the Shoo Fly are also present there; but no smooth gravel clasts were found.
In addition to the above two localities, Turner (1897) reported white quartz gravel at the Blue Lead gravel mine located on a ridge 2.5 mi northeast of Pilot Peak on the ridge above Poorman Creek. This location was not visited, but would plot in the area of SW¼ Section 35, T23N, R10E, about 2.5 km northeast of the above described and visited areas. MacBoyle (1920a, p. 172) described the Bonnie Mine (Eclipse) in Section 3, T22N, R10E, as being formerly worked as a hydraulic and drift mine. Except for the fact that this property is only 1.2 mi (2 km) northeast of Pilot Peak, it could be the property described by Turner (1897). An adit is shown in Section 3 on the Blue Nose Mountain 7.5-minute Quadrangle. MacBoyle (1920a, p. 172) reported the gold to be found in Pleistocene gravels (including glacial gravels), and probably to have been derived from quartz veins on the eastern slope of Pilot Peak. This information came at least in part from Turner (1897, Economic Geology section).
It is difficult to be certain if these areas of gravels represent nearby subcrops of Auriferous Gravel or clasts reworked into basal beds of the considerably younger andesitic volcanic rocks. Probably the Blue Lead Mine is in Quaternary gravels. The iron-oxide coating on some cobbles, if it represents original cement in the Auriferous Gravels, suggests that those cobbles did not move far. However, MacBoyle's (1920a, p. 80) report of andesite tuff in the gravel at the Morningstar Consolidated Placer Mine suggests that the channel may be intervolcanic (interandesitic). The areas of gravel lie along a northeast line from the Bunker Hill Mine toward Cromberg, a logical continuation of this paleochannel. This line crosses the Plumas trench, a graben in which the Tertiary-preTertiary contact is dropped down about 3000 ft in the central area, while the contact is at approximately the same elevation on either side (Durrell, 1987, Fig. 129). For example, the base of the Auriferous Gravels at Cromberg/Prugh Mine are at an elevation of about 5400 ft, very close to that of the Blue Nose Mountain area. There is no clear evidence of faulting between Bunker Hill Mine and Blue Nose Mountain (for example, see map by Saucedo and Wagner, 1992). Either there are unrecognized faults that set the Blue Nose gravels down in this area or the gravels are reworked into channels at the base of the andesites. The base of the andesite unit rises at least 300 ft between the northeast slope [P37] and the northern nose [P34] of Blue Nose Mountain, a possible indication of a Miocene channel.
Photos
P35b.JPG Andesite neck, 1.5 km south of Turkeytown Diggings, Blue Nose Mountain area.
The abandoned camp of Buckeye [P174] is located in NW¼ NW¼ Section 3, T22N, R6E, essentially on the section line with adjacent Section 4. The place name is shown on the Soapstone Hill 7.5-minute quadrangle just west of the Oroville-Quincy Highway (Forest Highway 119) at Walker Plains. The site was a stop on the Beckwourth Emigrant Trail. According to Trails West Trail Marker B40 at the site, “Buckeye Dry Diggings established here 1850. A way stop for Emigrants of 1851 and later.” The mining area has been included in the more inclusive Granite Basin District (Clark, 1970). Turner's (1898) map shows a drift mine at the site, but no indications of underground workings were observed in 2003. MacBoyle (1920a, p. 21) also described the drift, but that may be based only on Turner (1898).
Near the Trails West marker arkose and quartz-pebble conglomerate lie on hornblende quartz diorite (Merrimac pluton of Hietanen, 1973). The sands and conglomerates are overlain by Lovejoy Basalt (Durrell, 1959; Hietanen, 1973), which lies directly on the quartz diorite in many places. Apparently, these Auriferous Gravels were locally cut out by later, pre Lovejoy, erosion or were not deposited. The Lovejoy is well exposed in a quarry along the highway about 1 km to the northwest [P172]; Durrell (1959) reported a thickness of about 60 m for the Lovejoy at Walker Plain[s]. The outcrop of Lovejoy appears to be a remnant of channel-filling flows; the most likely direction of this channel was west or southwest. Probable cross bedding and cut-and fill features in underlying Eocene(?) sandstone suggest a southerly direction of transport. Lovejoy basalt (ca. 16 Ma; Page and others, 1995) that flowed down this paleovalley may have once continued to the Oroville area where Lovejoy caps Table Mountain.
The Auriferous Gravels at Buckeye consist of nearly horizontal beds of clean arkosic sandstone, pebbly sandstone, and quartz-pebble conglomerate. Feldspar grains in the sand were probably derived from underlying granitic rock. Pebbles are well rounded to subrounded. About 300 m west of the Buckeye site marker [near P173], smooth, rounded 1-6 cm (rarely 12 cm pebbles and cobbles of quartzite, and gray chert, were observed in float below Lovejoy. Chert cobbles have crescentic percussion marks related to high-energy stream transport. No Tertiary volcanic clasts were noted.
Turner (1898) shows two hydraulic sites, one located about 2 km east of Buckeye, and one about 2 km southeast of Buckeye. No evidence of Auriferous Gravel or hydraulicking could be found these areas [P175, P176] during a 2003 visit.
Photos
P172a.JPG Columnar jointed Lovejoy basalt 2 km south of Four Trees (Buckeye area).
P174a.JPG Trails West emigrant trail marker at Buckeye Dry Diggings.
P174b_70.JPG Pebbly arkose at Buckeye.
P174e_69x.JPG Quartz cobbles at Buckeye. Hammer head is 18 cm.
Turner (1897) described the Bunker Hill tunnel as being on a probable upstream continuation of the main paleochannel from La Porte through Gibsonville to Hepsidam. The Bunker Hill Mine is located in NW¼ NW¼ SE¼ Section 15 (PB45), T22N, R10E (Blue Nose Mountain 7.5-minute Quadrangle). Lindgren (1911, p. 106) reported that the channel had been mined between Hepsidam and Bunker Hill, a distance of about a mile, by drifting operations between 1875 and 1895. Hepsidam is located in the area of Whiskey and Slate Creeks, to the southwest of the Bunker Hill Mine, across Bunker Hill Ridge.
At the Bunker Hill Mine [P36] a dump and caved probable drift portal are seen near the road. The dump material is mainly yellowish deeply weathered(?) Shoo Fly schist, but a few smooth, rounded bull-quartz clasts up to 30 cm in diameter were seen. Some clasts have attached limonite-cemented sand matrix, indicating that they are probably not reworked. About 100 m up the creek from the mine fragments of original Auriferous Gravel can be seen in mining debris. In these, about 80% of the pebbles (mostly 1-6 cm) are quartz, with the remainder gray phyllite (probably from the Shoo Fly). Based on the drift orientation and the bedrock outcrops, it appears that the lowest part of the channel may have at least a local north trend.
Photos
P36a.JPG Quartz cobble with attached limonitic sandy matrix, Bunker Hill Mine.
P36b.JPG Quartz- and phyllite-pebble conglomerate, Bunker Hill Mine. Marking pen is 13.5 cm.
Burlington Mine (not examined during this study)
The Burlington Mine is shown on the Portola 30x60-minute topographic map in NW¼ Section 11, T19N, R11E. This follows the usage on the Sierra City 15-minute quadrangle (1955), where a mine/quarry symbol (crossed pick and hammer) is labeled the Burlington Mine. MacBoyle (1920b, p. 68) reported a hydraulic mine by this name in Section 2 just to the north. The Burlington Mine name could have been misapplied on the Sierra City 15-minute quadrangle. Two mine/quarry symbols (crossed pick and hammer) are shown on the Chico 1x2-degree topographic map along Negro Canyon (name from the Sierra City 7.5-minute quadrangle) near the canyon bottom at its junction with side canyons. One of these is in Section 2, T19N, R11E and the other is near the boundary of Sections 11 and 14 of T19N, R11E. One of these is labeled the Banner Mine on the Sierra City 15-minute quadrangle; also shown on that map is a prospect symbol in a side canyon to Negro Creek about 300 m up a side canyon from the other Negro Creek symbol shown on the Chico map. The Burlington as plotted on the Sierra City 7.5-minute quadrangle is more than 100 ft above Negro Creek. No Tertiary rocks were shown in this area by Saucedo and Wagner (1992); however, the source of the geologic mapping in that area was unpublished mapping by Schweickert and others, which did not have an emphasis on Tertiary rock units. Turner (1897) showed a quartz vein near the Burlington Mine location as shown on the Sierra City 15-minute map, with the label Mercer and Salinas nearby. The Mercer and Salinas is a quartz mine (Preston, 1890, p. 649). MacBoyle (1920b, p. 116) reported the Salinas and Mercer claims to be a lode mine in Section 35, T20N, R11E. Workings shown in that section on the Sierra City 7.5-minute quadrangle are called the Cleveland Mine, which MacBoyle (1920b, p. 81) also describes as a lode mine. So, it is unlikely the Salinas and Mercer is another name for the Cleveland. The Banner Mine is reportedly located in the upper reaches of Black Jack Ravine (center, Section 15, T19N, R11E), about 1.7 km southwest of its location as shown on the Sierra City 15-minute quadrangle (R. Hess, oral commun., 2005). Lode gold deposits are found near the Banner Mine, and placer gold (some with attached vein quartz) is found in the modern stream (R. Hess, oral commun., 2005). Smooth, well rounded boulders in the creek may have been derived from eroded Tertiary channel gravels. The best guess, without visiting the properties on the ground, is that the Burlington Mine name as shown on the Portola 30x60-minute map (and the Sierra City 15-minute map)is a lode mine, reported by Turner and later workers as the Salinas and Mercer. The Burlington Mine was probably a hydraulic mine in Negro Canyon about 1.5 km to the north, in Section 2. Because it is in the canyon bottom, it probably was not on Tertiary Auriferous Gravels. Thus, evidence for the extension of a Tertiary paleochannel northeast from American Hill is minimal in this area. See the Ladies Canyon Mine.
Grose (2000c) showed an area of altered silicic tuff over an area of nearly 2.5 km2 along Grizzly Road (County Road 175) about 5 km north of its junction with State highway 70 east of Portola. The area is predominantly in sections 7, 8, and 17, T23N, R14E of the Portola 7.5-minute Quadrangle. I was unable to find any outcrops that were tuff, either along the highway or along a side road near Big Grizzly Creek. Most light colored outcrops in this area are hydrothermally altered (sericite and clays) granitic rock. Based on the probable absence of Oligocene tuffs in this area, the possible presence of a paleovalley in the area is low.
Ash-flow tuff and granodiorite clasts are found along with a variety of andesite clasts near the base of an andesite lahar exposed in road cuts along the Portola McLears Road (County Road 114) about 300 m northwest of Calfpasture Creek (SW¼ SE¼ SE¼ Section 19, T22N, R13E, Clio 7.5-minute Quadrangle). Granodiorite clasts are up to 2 m in length. The tuff clasts contain wormy (vermiculated) quartz phenocrysts, and were probably derived from nearby(?) outcrops of the tuff of Campbell Creek. The presence of these tuff clasts is probably related to a zone of Oligocene ash-flow tuff outcrops in a probable paleovalley from Graeagle to Beckwourth. A K-Ar age determination on an andesite clast from the lahar about 500 m to the north along the highway yielded an age of 19.7±2.3 Ma (unpubl. data of C. Durrell, reported in Saucedo, 1992, no. 69; also see Grose, 2000a). This age determination is significant because it dates andesitic rocks in the Blairsden area as older than the ~16 Ma Lovejoy Basalt. Except for some equivocal outcrops in the Red Clover Creek area (see Wagner and others, 2000), this is nearly the only evidence for such older rocks. However, Durrell (1959, p. 170) reported that there are cobbles of hornblende andesite between flows of the Lovejoy Basalt west of Lovejoy Creek (Sections 8 and 17, T24N, R12E, Mount Ingalls 7.5-minute Quadrangle). Because of the heterolithic nature of the lahar near Calfpasture Creek, and the rather poor precision of the determination, the evidence for pre-Lovejoy andesites in the Blairsden area is not strong. The dated clast could have been transported some distance; for example, ca. 21 Ma andesite lahars are known from the Reno, Nevada area (Garside and others, 2003).
Approximately 1.2 km to the northwest, across the Middle Fork of the Feather River (1.5 km northeast of Clio, SE¼ NW¼ SW¼ Section 19, T22N, R13E; [P128]), blocks of rhyolitic ash-flow tuff are observed in a road cut, apparently in the lower part of a fluvial section (see Yount, 1995, p. 12) of the Quaternary Mohawk beds. The presence of these blocks also suggests the presence of nearby, concealed Oligocene ash-flow tuffs.
An area of outcrop of Oligocene ash-flow tuffs was shown by Saucedo and Wagner (1992) about 0.5 km to the south of the above described occurrence of tuff clasts in lahar. Based on that geologic map, the tuffs should crop out along or near Calfpasture Creek and the adjacent Portola McLears Road (County Road 114 or A15) near the intersection of that road with State Route 89. No evidence of ash-flow tuff could be found in this area in 2004. Quaternary “Mohawk beds” lie directly on Mesozoic metasedimentary and granitic rocks as well as on Miocene andesitic lahars along the Portola McLears Road and Calfpasture Creek in E½ Section 30, T22N, R13E.
Photos
P128a.JPG Probable large block of rhyolitic ash-flow tuff in Mohawk Lake Beds, 1.5 km northeast of Clio.
P29a_21.JPG Heterolithic andesite lahar with clasts of granodiorite and tuff of Campbell Creek; exposed in road cut near Calfpasture Creek.
MacBoyle (1920a, p. 90) included the Cascade Mine in the Quincy Mining District, although it is at least 16 km east of the town of Quincy. Clark (1970, p. 111) apparently followed this designation.
Crawford (1896, p. 290) reported of the Cascade Mine (Hydraulic) that:
It is 10 miles S. from Genessee, at 5900′ elevation, and contains 160 acres. The bank is 120′ high, and all gravel; the pit is 250′ across the face and carries fine gold throughout; it is said that, as the work has progressed up the channel, the value per cubic yard has gradually increased from 13 cents to 20 cents. A hand-derrick, with 90′ mast and 50′ boom, is used. Water is obtained from Clear Creek through ditches 3½′ wide; the north ditch has a grade of 2½″ per rod and the south ditch 1½″ per rod, the combined capacity being 800 miners inches. The water season is about 90 days, but a reservoir under construction at Lovejoy's ranch will extend it to eight months. Two No. 3 giants, with 4″ and 4½″ nozzles under 250′ pressure, are employed. T. R. Wash, of Vallejo, Solano County, owner.
MacBoyle(1920a, p. 90) reported that hydraulicking was done at the site, leaving a bank of gravel 100-200 ft (20-60 m) high. The hydraulicking was stopped by the debris law (the Sawyer Decision of 1884). A 200 ft (60 m) tunnel was reported to have not struck pay gravel. Based on a projection of the possible original extent of the gravel, the mining operation could not have been a large one. No indication of the reported drift was found in 2003.
The workings of the Cascade Mine are located near the mine symbol shown on the Mount Ingalls 7.5-minute Quadrangle in SW¼ SE¼ SE¼ Section 11, T24N, R11E. The previously worked gravel face is still easily discerned [P51b], and piles of gravel can be observed near the stream (Cascade Creek). The Auriferous Gravels appear to lie on Cretaceous biotite hornblende granodiorite, which is exposed just upstream from the mine. The approximate elevation of the base of the gravels is 5760 ft. based on the topographic map. The gravel clasts consist of a considerable variety of metavolcanic and metasedimentary rocks as well as light-colored biotite hornblende granodiorite. One metavolcanic type observed was meta-igneous porphyry, which could have been derived from the Permian Reeve Formation (E.R. Brooks, oral commun., 2004) which is exposed nearby, both to the northeast and southwest. A few smooth clasts of black chert were seen, as well as one fine-grained tourmaline(?)-bearing clast. Notably absent are white vein quartz clasts, although a single quartz pebble was collected along the logging road about 100 m above the mine. The clasts are commonly well-rounded, and range in size from 1 cm to over 60 cm; some clasts that were apparently hydraulicked have local patches of limonite-cemented sand matrix still attached. Sand lenses in the Auriferous Gravel consist of locally derived quartz, feldspar, biotite, and hornblende (arkose). The Auriferous Gravels are overlain here by andesite lahars and flows; however, about 2 km to the southeast Lovejoy basalt flows are found in a channel cut on and into the Auriferous Gravels channel (Grose, 2000a; Durrell, 1987).
Lindgren (1911, p. 112) reported that large granite boulders in the gravel were probably derived from an area of granite immediately to the south, bolstering his belief that the paleo-river (the Jura River) flowed north. The proposal that the boulders suggest a northerly flowing river originally came from Turner (1897; see Diller, 1908, p. 63). However, granitic rock underlies at least a small area of the Auriferous Gravel at the Cascade Mine and nearly all of the gravels in the main part of the paleochannel 1-3 km to the southeast (see geologic map by Grose, 2000a). Also, granitic rocks crop out a short distance east of the Cascade Mine, and these outcrops could have been the source of the large granitic boulders. Thus, the presence of the granitic boulders does not confirm a northerly direction of transport.
Bedding in the gravels and sands is nearly horizontal when observed in the face left by hydraulicking. Lindgren (1897) reported that the Auriferous Gravel is 825 ft (about 250 m) thick; nearly 200 m of thickness can be seen in the area of the mine face today (2003). The historic mine face is seen in a photograph in Lindgren (1911, Plate XVII after page 104). Tangential foreset beds of trough(?) cross-bedding in a sand lens examined in 2003 suggests a downstream direction of S45°W to S90°W. Durrell (1987, p. 183) also reported that cross-bedding indicated a southwest paleo-downstream direction, and he noted as well that the clasts at the Cascade Mine came from the north in the Taylorsville district and possibly farther away in northwestern Nevada. The Mesozoic metavolcanic rocks exposed on Mt. Jura and elsewhere near Taylorsville are much more likely sources for the metavolcanic clasts at the Cascade Mine than are the mostly Paleozoic bedrock units to the south. The one black-tourmaline-bearing clast seen probably also has a source to the north in areas of Jurassic porphyry mineralization (i.e., the vicinity of the Walker Mine only 2.5 km to the northeast or the Lights Creek stock farther to the north-see the Taylor Diggings description for a more complete discussion).
At the exposed gravel face of the Cascade Mine, a few (probably <1%) disk-shaped cobbles appear to have their long or intermediate-length axes inclined in the same general direction as the dip of cross bedding foreset beds (southwest). Except for one observed case, these cobbles are not definitively shingled against similarly inclined clasts. Most of the clasts in the gravels are not imbricated and have their long axes nearly parallel to the plane of deposition (photos). If the inclined clasts truly represented imbrication (shingling) or preferential inclination of single platy cobbles in a finer matrix, they should dip upstream (unless they represent cobbles deposited flat on foreset beds). The origin of the inclination of the few inclined clasts in not clear; they could suggest a northeast paleostream direction, they could represent random orientations, or they could indicate that some coarse conglomerate units include indistinct, unrecognized foreset beds. Because paleocurrent directions determined from the dip of plane cross beds seem to be subject to fewer ambiguities, the probable conclusion is that at the Cascade Mine ,the paleostream flowed southwesterly. This is in agreement with the southwesterly direction of the apparently coincident 16 Ma Lovejoy Basalt channel (Wagner and others, 2000).
Photos
P51c_clast.JPG Boulder at Cascade Mine. Ruler is 15 cm.
P51j_clasts.JPG Limonite coated cobbles, Cascade Mine. Hammer is 32 cm long.
P51k_Cascade.JPG Worked face at Cascade Mine; note inclined disk-shaped cobbles, probably on indistinct foreset beds.
P51p_Cascade.JPG Cross bedded sandstone underlying gravel at the Cascade Mine.
CascadeMine_adj.JPG View of working face at Cascade Mine during operation; stiff-leg derrick in foreground. From Lindgren (1911).
Nine Hill Tuff crops out in Castle Valley, surrounded by morainal material, slightly more than 1 km north of the Boreal Ridge–Castle Peak interchange on Interstate 80, in NE¼ SE¼ SW¼ Section 12, T17N, R14E [P132]; Norden 7.5-minute Quadrangle. The tuff is flat-lying, strongly welded, and vapor-phase altered. Because granitic rocks are mapped nearby, it appears that the tuff outcrop is near the base of the Tertiary section, having an elevation of about 7400 ft.
Photos
P132b_64.JPG Andesite flows and lahars, Castle Peak.
Cedarville area (not examined during this study)
Haley (1923, p. 100) reported that:
Beyond Alturas, on the east side of the Warner Range, is a channel near Cedarville which has been prospected slightly but without satisfactory results. This, also, is volcanic wash. It is reported that a deep blue channel under the shoulder of Eagle Peak in this range contains some Auriferous Gravel.
This gravel is in a section of andesitic volcaniclastic and lesser pyroclastic rocks of Oligocene age (Duffield and McKee, 1986) exposed at the eastern base of the Warner Range for a distance of nearly 50 km (Russell, 1928). There do not appear to be any other reports of gold-bearing gravels in this part of the Warner Range, no indications of placer workings are known, and no gold was detected in stream sediments from the area (Duffield and Weldin, 1976).
Andesitic ash near the base of the exposed section was dated at about 32 Ma by K-Ar methods (Duffield and McKee, 1986). The oldest rhyolitic (quartz-biotite-feldspar, trace hornblende) ash-flow tuffs in an overlying section of tuffs and interlayered andesite flows were dated at about 26 Ma. A younger rhyolitic (quartz-biotite-feldspar) ash-flow tuff was dated at 17.3 Ma. It is not clear which regional ash-flow tuffs from northern Nevada calderas may correlate with these tuffs. There are a number of ca. 16 Ma calderas in northern Nevada (for example, Idaho Canyon or Highrock/Soldier Meadows). A possible correlative for the 26 Ma tuff would be the Ashdown Tuff. This tuff was reported to be 25 Ma according to Noble (1988); however, a more accurate age may be 26.3 (as presented in a talk by Colgan and Dumitru, 2003).
Russell (1928) reported that fossil leaves were found in the sedimentary rocks that make up the base of the lower Cedarville section. These leaves were found 2 mi (3.2 km) north of Cedarville and in Steamboat Canyon (about 11 km south of Cedarville). A lignitic zone toward the base of the lower Cedarville was prospected for coal, particularly in Cedar Canyon west of Cedarville. An andesitic tuff was reported at the base of the lignitic zone (Russell, 1928). This tuff could be the ca. 32 Ma tuff dated by Duffield and McKee (1986); possibly the same tuff was dated by Myers (1998) at 31.56 Ma.
Axelrod (1966, p. 500 and Table 1) briefly summarized the geology and paleobotanically estimated later Oligocene age (e.g., MacGintie, 1941) of a large and well preserved flora exposed in the lower part of the lower Cedarville Formation on a ridge about 6 km north of Cedarville (center Section 19, T43N, R16E). He also reported (Axelrod, 1966, Table 1) a K-Ar age on feldspar (plagioclase) from a hornblende andesite flow about 100 ft (30 m) stratigraphically below the flora. The reported age of 40.0±3.0 Ma is based on decay and abundance constants not in use today. Recalculation using modern constants (Steiger and Jager, 1977) indicate a range of ages from 37 Ma to nearly 41 Ma (from two separate radiogenic 40Ar analyses). The calculated age from averaged analytical data of Axelrod (1966, Table 1) is 39±3.0 Ma.
Myers (1998, 2003), in a re-examination of the lower Cedarville flora, estimated the Badger's Nose and Steamboat Canyon floral assemblages to be 34-35 Ma (late Eocene); the younger Granger Canyon assemblage, which overlies the latest Eocene assemblages, is dated by 40Ar/39Ar methods at 31.56±0.46 Ma (Myers 1998). The dated unit is a minimally reworked tuff with associated fossil leaves exposed in Granger Canyon; the tuff is evidently andesitic or dacitic, as the horizon was reported to contain plagioclase and hornblende suitable for dating (Myers, 1998, p. 289). A hornblende-phyric dacitic tuff which overlies the lower Oligocene floral assemblages was reported to be 30.15±0.41 Ma based on analyses from two(?) samples (Myers, 1998; p. 105, 116). The Late Eocene Plant fossils in Steamboat Canyon are found in sandstone and mudstone that grade laterally to gravel; these clastic rocks are in a southwest–northeast paleochannel cut in the underlying ca. 39 Ma andesite (Myers, 1998, p. 118). The paleo direction of stream flow was not reported. Myers (2003) estimated the elevation of northeastern California to be about 1500 m in the late Eocene; the present elevation of the flora locality is about 1700 m.
The andesitic rocks near Cedarville, ranging in age from ca. 39 Ma to less than 26 Ma are part of a southern extension of the Clarno Arc (Walker and Robinson, 1990; Myers, 1998, p. 11). Because all the older dated tuffs appear to represent local intermediate-composition stratovolcano sources, the first indication of ash-flows from remote sources is the 26 Ma ash-flow tuff dated by Duffield and McKee, 1986). The Oligocene andesitic rocks of the Clarno Arc near Cedarville may extend to the southwest to the area of the andesitic rocks of the Susanville flora southwest of Susanville.
Rhyolitic ash-flow tuffs crops out on a ridge about 2 km northeast of the community of Chilcoot (Section 31, T23N, R17E; about 2 km northwest of Beckwourth Pass). The area of outcrop is shown by Saucedo and Wagner (1992) as bounded on the southeast by a northeast-striking fault and cut off at the northeast end by a northwest-striking fault. The northeast-striking fault is eliminated in the later map by Grose and Merger (2000). Two ash-flow tuffs make up the exposed section on the ridge. They lie nonconformably on Cretaceous granodiorite. No fault along the southeast side of outcrop is required or observed, although a knob of granodiorite near the northeast end must have been a small topographic high when the tuffs were laid down. If the tuffs were laid down in a paleovalley, this small topographic high may have been along the southeast edge of a northeast-trending canyon. That potential paleocanyon can be projected northeast to cross the crest of the range at about the same elevation. Saucedo and Wagner (1992) and Grose and Merger (2000) show a fault between the tuff outcrop and the range crest; however, if the northeast projection of the paleovalley is correct, no displacement on this fault is required.
The ash flow tuffs are nearly horizontal; measured attitudes range from horizontal to N30°E, 10°SE. Some original dip is possible because of compaction against canyon walls or other topographic relief. Two cooling units are recognized. Both contain sanidine and plagioclase phenocrysts, with sanidine predominate; biotite is a trace constituent. Cobbles and boulders of granodiorite are observed in float near the base of the lower tuff. Some of these may be corestones from the weathered granodiorite surface rather than fluvial clasts. The lower tuff is about 30 m thick, having a basal unwelded zone and vitrophyre. The upper tuff may be as thick as 70 m. It has a gravel at the base, which includes boulders of granodiorite and cobbles to pebbles of the following: granodiorite, granodiorite porphyry, foliated and epidotized granodiorite, white quartz, white quartz with black tourmaline (schorl) veining, and black schorlite. The vitrophyre of the upper tuff contains fragments of charcoal up to 1 cm or more. Based on present knowledge, these tuffs may be the tuff of Rattlesnake Canyon and the somewhat younger tuff of Cove Spring of the Dogskin Mountain area (Henry and others, 2003a).
Photos
P233a.JPG Layered basal vitrophyre of upper ash-flow tuff northeast of Chilcoot.
P233b_70.JPG Dark gray granodiorite boulders from gravel at base of upper ash-flow tuff northeast of Chilcoot.
P233e_68.JPG Schorl-veined quartz clast from gravel at base of upper ash-flow tuff northeast of Chilcoot.
P235b_65.JPG Two cooling units (left) lying on granodiorite (right) northeast of Chilcoot.
Lindgren (1897, Economic Geology Map) showed an area of “Neocene” rhyolite near the head of Coldstream Valley. Such rhyolite is almost always found today to be Oligocene ash-flow tuff. Nine Hill Tuff crops out along a road in SE¼ SE¼ SE¼ Section 27, T17N, R15E [P189]; the tuff of Campbell Creek crops out about 200 m to the south, in NE¼ NE¼¼ Section 34, T17N, R15E [P190] of the Norden 7.5-minute Quadrangle. The Nine Hill has an attitude of N85°W, 25°NW. The elevation of the tuff outcrops is about 6600 ft, which is about 480 ft (150 m) lower than the base of subhorizontal ash-flow tuffs near Donner Pass. The tilt and elevation difference is probably due to displacement on the Donner Lake fault (see Henry and Perkins, 2001) located just to the west. Some of the tilt may be original dip, as the south side of a paleovalley may be represented by considerably higher granite outcrops to the south on the flank of Anderson Peak. Probably both of these outcrop areas as well as similar outcrops in Castle Valley represent deposition in a west-trending paleocanyon that connects with a thick ash-flow tuff section south of Soda Springs and then southwest to the Forest Divide area.
Photos
P189b_61.JPG Close up of fiamme in Nine Hill Tuff, Coldstream Valley.
The Commodore Mine is shown as a prospect symbol on the Sierra City 15-minute quadrangle in NE¼ SE¼ Section 8, T19N, R12E along with a symbol for building ruins. No mine is shown on the Sierra City 7.5-minute quadrangle. Averill (1942, p. 23-24) reported that the Commodore Placer claims, in Sections 2, 3, 4, 5, 8, 9, 10, 11, T19N, R12E, covered 3.5 mi of an ancient river channel capped with lava. The Cornish Cabin claim (160 acres) was the only patented claim; it's location is not reported but might be available from the Sierra County recorder. Based on the geologic map of Saucedo and Wagner (1992), the area of the Commodore mine appears to be near the base of Tertiary andesitic pyroclastic rocks, and thus, could be at the site of a paleochannel under Tertiary andesitic rocks. However, field examination of an area just to the east indicates that the area of the mine is in preTertiary bedrock, and probably a lode mine.
The Klondyke Mine is shown as prospect and shaft symbols in SW¼ Section 4, T19N, R12E, about 1.8 km north-northeast of the Commodore Mine. No workings are shown on the Sierra City 7.5-minute quadrangle, but a mine symbol is shown on the Chico 1x2-degree map. According to MacBoyle (1920b, p. 45), the workings of this mine were made in search of a ancient channel. A mine examined during this stuty, probably the Klondyke Mine (NW¼ NE¼ SW¼ Section 4, T19N, R12E [P236]) explores a quartz vein in olive slate of the Shoo Fly Complex. No evidence of older, pre-andesite gravels was seen at the Tertiary-preTertiary contact in this area. If an Eocene paleochannel existed here, connecting the Hilda Mine area to the northeast with a channel at Graniteville to the southwest, most or all of it has been removed by erosion before the andesitic rocks were laid down.
Continental Ravine/Queen Group (not examined during this study)
MacBoyle (1920a, p. 83) described placer claims and workings in Sections 19, 20, 29, and 30, T22N, R11E. The property was reported to be under bond to the Continental Mining Company at one time. One ditch was called the Porter Ravine Ditch. Mine workings are shown on the Blue Nose Mountain 7.5-minute Quadrangle in Continental Ravine, just south of Porter Ravine, on the east side of Mc Rae Ridge, near the center of the S½ Section 19, T22N, R11E.
According to MacBoyle (1920a, p. 83):
The deposit is supposed to be on the old “Blue Lead River Channel.” It is made up of free quartz gravel with medium-sized boulders on slate bedrock. The channel courses south and is capped with 600' [feet] of lava. A good-sized flow of water was encountered. The pay gravel is 1000' [feet] wide and has a depth of 90' which it would pay to hydraulic.
Saucedo and Wagner (1992) show the area as a landslide on Shoo Fly Complex from a higher elevation area of Tertiary andesite above. Their data source is a thesis by Strand (1972).
T.L.T. Grose (oral commun., 2003) reported smooth, rounded pebbles of preTertiary rocks in float near the old railroad siding of Crest. The area was described to him by M.C. Reheis (USGS) and R.Bowers (Humboldt State). The clasts are smooth to somewhat pitted, rounded pebbles of resistant rock types (chert, vein quartz, quartzite) that occur as a small percentage of the pebbles and cobbles on the surface of a dry lake or reservoir (Crest Reservoir) in NW¼ NE¼ NW¼ Section 14, T33N, R14E [P169]in the Snowstorm Mountain 7.5-minute Quadrangle. Most of the pebbles and cobbles that litter the surface of the dry lake are subrounded to rounded vesicular basalt. Some of the smooth preTertiary pebbles display half-moon percussion marks. Because of the differences in maturity, the smooth pebbles are almost certainly multicycle with respect to the basalt clasts. Although the source conglomerate for the float clasts on the playa was not observed, it is apparently a unit or units within the Miocene and Pliocene mafic flows and interbedded tuffs and gravels (see Grose and Abrams, 1991). There are no known outcrops of pre Miocene Tertiary rocks in the vicinity. The nearest outcrop of older Tertiary conglomerate is 70 km to the northeast near Eagleville and Cedarville and 35 km to the southwest near Eagle Lake (Deans Ridge, see below). The presence of the smooth rounded pebbles here suggests that an Eocene paleochannel may have existed somewhere in this area before being at least partly eroded in the Miocene.
Photos
P169d_77.JPG Sparse smooth resistant pebbles and common basalt pebbles in float on surface of Crest Lake Reservoir dry lake.
Grose and others (1992) showed two small outcrops of siliceous pebble-cobble conglomerate near the pass between Black Mountain and Deans Ridge, 1-2 km east of Eagles Nest and Eagle Lake (Sections 3 and 4, T31N, R11E; Gallatin Peak 7.5-minute quadrangle). The conglomerate or float from it was observed along a road from Willow Creek Valley to Eagles Nest at two localities: SW¼ NE¼ Section 3 [P170] and SW¼ NW¼ NW¼ Section 3 [P171], T31N, R11E. At locality P170, the clasts seen in float are subrounded to subangular cobbles and pebbles of metaigneous rock, probably mainly meta-andesite. The clasts consist of schist, gneiss, flaser gneiss, and amphibolite. At P171 about 1 km to the west, the conglomerate consists of well rounded pebbles, up to about 5 cm in diameter, of light gray quartzite, black chert, and less aplite in a matrix of granite wash and dark metamorphic sand. The light gray quartzite pebbles resemble those from the Crest Reservoir area, suggesting a possible source to the east or northeast, in northern Nevada.
White, rhyolitic, welded and nonwelded ash-flow tuffs crop out in road cuts along the north side of California State Highway 70 between Delleker and Portola (S½ S½ Section 35, T23N, R13E and N½ NE¼ NE¼ Section 2, T12N, R23E; [P13] and [P147], respectively; on the Portola 7.5-minute Quadrangle). The area of outcrop is shown on a geologic map of the Portola 15-minute Quadrangle (Grose, 2000c). One sample contains phenocrysts of plagioclase, sanidine, biotite, and possibly quartz, as well as lithic fragments of granitic rock. This tuff can not be easily correlated with the known tuffs to the east in northwestern Nevada, although it may be related to the tuff of Axehandle Canyon or the somewhat younger tuff of Sutcliff of the Dogskin Mountain (Henry and others, 2003) and Tule Peak areas north of Reno, Nevada. The tuff is overlain by Miocene gravel and andesite lahars. The gravels directly above the ash-flow tuffs contain rounded clasts of aplite, and granitic clasts to 30 cm in diameter were observed (2003) upward in the andesitic unit. Dalrymple (1964) and Durrell (1984, personal commun. in Saucedo, 1992) report K-Ar ages on ash-flow tuff from this area of 26.8 Ma and 23.4 Ma, respectively. It is uncertain if these determinations are close to the true age of the tuff; probably they are too young.
Lawler (1995) showed an area of placer workings on a ridge top about 3 km east of Omega Diggings (NE¼ NW¼ SE¼ Section 15, T17N, R11E, Blue Canyon 7.5-minute quadrangle; [P195X]). The area has some recent bulldozer workings as well as indications of previous hydraulic and drift(?) mining. Boulder piles contain only resistant clasts of quartz-pebble metaconglomerate (75%), quartzite and related rock types (15%), granite and diorite (9%), and schorlite? (black tourmaline)+quartz (1%). The quartzite and metaconglomerate were probably derived from the Paleozoic Shoo Fly Complex; the schorlite(?)+quartz clasts are probably from schorlite-bearing quartz veins of the Meadow Lake mining district 20 km to the east-northeast. Based on backhoe-cuts exposures, unmined gravel consists of the resistant clasts described above plus rotted granite(?) clasts in a clay-rich matrix. The gravels do not contain clasts of Tertiary volcanic rocks and lie on vertically foliated slate of the Shoo Fly Complex. Boulders up to 1 m in diameter are present in the pit; some quartzite boulders have crescentic percussion marks (photo).
About 1.3 km south-southeast of the placer workings white ash-flow tuff (sanidine-plagioclase-quartz-biotite) is exposed near the road to Omega (SW¼ NW¼ NW¼ Section 23, T17N, R11E; [P196a]). Although exposures are poor and there are areas of glacial gravels, it appears the white ash-flow tuff lies on the Auriferous Gravels. The quartz is not vermicular; one possibility for a correlative of this tuff is the nonwormy-quartz-bearing tuff which lies under the tuff of Campbell Creek at Haskell Peak (Tuff E of Brooks and others, 2003).
Photos
P195Xb.JPG Boulder of quartz-pebble metaconglomerate at Diamond Creek Placer. Hammer is 32 cm.
P195Xd.JPG Smooth, rounded quartzite boulder with crescentic percussion marks, Diamond Creek Placer.
P195Xe_54.JPG Crescentic percussion marks on quartzite boulder, Diamond Creek Placer. Hammer head is 18 cm.
P195Xf.JPG Coarse-reject boulder piles at Diamond Creek Placer. Large metaconglomerate boulder is approximately 3 m in diameter.
P195Xg.JPG Black cobble of tourmalinized rock, Diamond Creek Placer. 15 cm scale.
P195Xj.JPG Boulders of black tourmaline, white quartz, and gray metaconglomerate at the Diamond Creek Placer.
P195Xl_46.JPG Mining face of clay-rich gravel in place; clasts include rotten granitic rock. Diamond Creek Placer.
P196a.JPG Block of ash-flow tuff that is exposed 1.2 km southeast of Diamond Creek Placer. Pen is 13 cm.
P196_Omega_ditch.JPG Ditch for Omega(?) Diggings, 1.2 km south of Diamond Creek Placer.
P196a.JPG Block of ash-flow tuff that is exposed 1.2 km southeast of Diamond Creek Placer. Pen is 13 cm.
Rhyolitic ash-flow tuffs and underlying granite-clast conglomerate, and arkosic and tuffaceous sedimentary rocks underlie the ski-lift hill for Donner Ski Ranch located about 1 km west of Donner Pass and just north of old US Highway 40 between Donner Lake and Soda springs (Section 17, T17N, R15E; Norden 7.5-minute Quadrangle). The lower part of the section may include nonwelded ash-flow tuffs equivalent to pre-Nine Hill Tuff units in the area north of Reno (Garside and others, 2003; Henry and others, 2003a), possibly the tuff of Sutcliff. The Nine Hill Tuff lies above this nonwelded and sedimentary section [P188]; it has an attitude of about N85°W, 5°S. A smoky quartz-bearing tuff (tuff of Chimney Spring?) crops out just above the Nine Hill. The tuffs are capped by Miocene andesite lahars. The base of the Tertiary section has an elevation of about 7080 ft.
Photos
P187b.JPG White ash-flow tuffs (tuff of Sutcliff?) lying on a grey hill of granodiorite, 1 km west of Donner Pass.
P188a_70.JPG Nine Hill tuff with paleomag drill hole, hammer is 32 cm long. Donner Pass area.
P188d.JPG Arkosic sediments with clasts of granitic rock, Donner Pass area.
P188e.JPG Arkosic grit with cobbles of granitic rock, Donner Pass area.
Doyle Crossing/Last Chance Creek (not examined during this study)
Wagner and Saucedo (1990b) showed a very small outcrop of rhyolitic ash-flow tuff south of Last Chance Creek about 1 km east of Doyle Crossing (NW¼ Section 13, T26N, R13E) The ash-flow tuff appears to underlie 9.6 Ma andesitic pyroclastic rocks and is adjacent to outcrops of Lovejoy Basalt. Cretaceous granitic rocks crop out farther east. The Lovejoy flows were apparently deposited in a paleovalley here as they flowed south from their probable source on Thompson Peak (Wagner and others, 2000, p. 159) and then southwest toward Red Clover Creek and Lee Summit The turn southwestward probably followed an older Oligocene paleovalley that was partly filled with ash-flow tuffs. Nick Hinz (oral commun., 2003) reported that no actual outcrops of tuff can be found at this site; he believes the tuff (tuff of Campbell Creek) observed is a clast or clasts in andesitic lahars. If the tuff is present only as a clast, actual tuff outcrop may have been several kilometers away; however, there are probably concealed Oligocene ash-flow tuffs somewhere in this area that mark an Oligocene paleovalley.
Diller (1895, p. 1) noted that “Auriferous Gravels of ancient streams” had been mined at Dutch Hill, where the gravels were said to have been rich. Diller also commented (1895, p. 1) that the gravels were about 1000 ft (300 m) above the present level of the North Fork of the Feather River. Diller's map shows the Neocene Auriferous Gravels under Neocene basalt. Clark (1970, p. 32) reported that the mine produced over $575,000 in gold. The Dutch Hill Mine is shown on the Twain 7.5-minute Quadrangle in SW¼ SE¼ SE¼ Section 8, T26N, R8E, about 2 km northeast of Seneca. Adits (“tunnels”) shown to the west about 1 km are along quartz veins in the Shoo Fly, not drifts in (to) gravel. The area was apparently worked by ground sluicing, as diversion ditches can be seen on the ridge above the workings. Ireland (1888, p.482-483) described an extensive system of ditches, tunnels, and flumes that brought water to the mines. Additionally, drift mines (Crawford, 1894, p. 215) are described. At the Dutch Hill Mine, piles of 15-30 cm subangular to rounded boulders are seen where they were left following placer operations. The boulders include rounded clasts of basalt with fresh olivine. Most clasts are not smooth, and many are subrounded to subangular. About 1% of clasts have the well-rounded shape and smooth surface commonly seen in Eocene Auriferous Gravels; these could have been recycled from Eocene gravels. The bedrock which directly underlies the gravels, where not stripped by placer mining, is deeply weathered, yellowish to reddish phyllite of the Paleozoic Shoo Fly Formation. The gravels appear to have collected in a relatively steep alluvial canyon. Crawford (1894, p. 215) reported that the gravel clasts included greenstone, red jasper, quartz, and some lava (presumably Tertiary).
Basalt flows were not observed in the area of the mine, but were noted at a lower elevation about 1 km to the southwest and at a higher elevation about 2 km to the northeast. According to Wakayabashi and others (1994b), basalt flows of this area are ~1.1 and ~0.6 Ma, and are found along the canyon of the North Fork of the Feather River as terrace-like remnants, with older flow remnants found at higher elevations than younger ones (a result of renewed down cutting of the river following deposition of the older flow in the channel). Wakabayashi and Sawyer (2000, p. 208) report that high cuts above the road near the community of Seneca expose river gravels below the basalt of Warner Valley (0.6 Ma) These are either the Dutch Hill Mine gravels or are related to them. Thus, the placered gravels at the Dutch Hill Mine are apparently younger than at least some of the basalt flows, and thus probably Quaternary. Probably they are part of or related to a Quaternary alluvium and colluvium unit shown several kilometers to the south and southwest on a map by Wakabayashi and others (1994, Fig. 2). The only possible evidence of Eocene paleovalley deposits is the very few well polished and rounded clasts (one of which had iron-oxide cemented sand attached). If any Eocene gravels were deposited in this area, they were apparently eroded later.
Photos
P104c.JPG Piles of subrounded to subangular boulders, remnants of placer mining, lying on yellowish deeply weathered Shoo Fly phyllite at the Dutch Hill Mine.
P104d_32.JPG Diversion ditches that were probably used for ground sluicing at the Dutch Hill Mine.
East Branch Lights Creek-Head of Lights Creek
According to Lindgren (1911, p. 116), in the east branch of Lights Canyon, Auriferous Gravels have been prospected and found to have good values in bore holes which penetrate the overlying andesite to a depth of 200-300 ft (60-90 m). This description could refer to an area of Eocene Auriferous Gravels shown in this area by Grose and others (1990).
Along a ridge between Fant Creek and East Fork Lights Creek (Kettle Rock 7.5-minute quadrangle), in SW¼ SW¼ Section 2 and N½ NW¼ Section 11, T27N, R11E, yellowish clay-rich arkosic sandstone and sandy siltstone are found in sparse road-cut exposures along an old logging road [P159]. The remains of an old ditch, possibly used for placer mining, was seen near here (photo).These arkosic sedimentary rocks resemble those of the Moonlight Valley area about 5 km to the northwest. About 200 m southwest of locality [P159], in SE¼ SE¼ SE¼ Section 3, T27N, R11E, one can see well rounded cobbles of resistant, nongranitic rock types in an arkosic matrix. Cretaceous intermediate-composition granitic rock underlies the arkosic sedimentary unit nearby and presumably supplied the sand-sized material to the arkose. Smooth, well rounded pebbles and cobbles are found as lag on the arkose and Quaternary surficial material. Some have crescentic percussion marks. Presumably, these 2-15 cm clasts were eroded from pebble and cobble sandstones like the one observed with an arkose matrix. The well rounded float clasts consist of: reddish and gray chert pebble conglomerate, light gray quartzite, meta-andesite(?), smooth black tourmalinized rock, and rare white vein quartz.
Approximately 1.5 km east of the above area, in SW¼ SW¼ SW¼ Section 1, T27N, R11E, along a 400 m section of road centered on location [P161], clasts similar to those described above can be seen. Poor outcrops near Fruit Growers Boulevard, about 1 km to the north, appear to contain only preTertiary clasts, but similar exposures in the area of P161 contain a mix of preTertiary clasts (including white granitic rock) and Tertiary hornblende andesite and basalt. One clast in float near(?) gravel outcrop consists of a white, wormy-quartz ash-flow tuff like the tuff of Campbell Creek. Apparently, as one goes up section in the conglomerates of this area, the basal material does not include Tertiary andesitic clasts, while beds higher in the section do. If the lowest conglomerate beds are Eocene, there may be a considerable hiatus between them and the beds with Tertiary andesite clasts. Alternatively, at least some of the andesitic volcanic rocks are Eocene, like those at the Susanville Flora locality.
Photos
P159a_61.JPG Percussion marks on polished cobble, East Branch Lights Creek. Ruler is 15-cm.
P159b_60.JPG Some clasts (chert, quartzite, schorl) from float near an outcrop of arkosic sandstone, East Branch Lights Creek.
P159c_59.JPG Old water diversion ditch, possibly used for placer mining in the vicinity of East Branch Lights Creek.
P159e_58.JPG Rounded resistant clasts in arkosic sand matrix, East Branch Lights Creek. Hammer is 32 cm.
P161a_56.JPG Rounded clast of tuff of Campbell Creek(?) collected from float, east of Fant Creek (East Branch of Lights Creek area). Ruler is 15-cm.
P161c.JPG Float (near outcrop) of cobbles of Tertiary andesite, basalt, and rare rhyolitic ash-flow tuff. East Branch of Lights Creek area.
East Fork Canyon Creek/ Rattlesnake/Red Oak (not examined during this study)
Turner (1897, Economic Geology map) showed an area of “Neocene“ rhyolite in the vicinity of the North Fork of Canyon Creek in about Sections 1 and 12, T21N, R10E, Mt Fillmore 7.5-minute Quadrangle. This is in the area of a possible paleochannel shown by Lawler (1995) through the Rattlesnake hydraulic mine and the Red Oak drift as shown by Turner (1897, Economic Geology map). However, these mines are somewhat difficult to plot on modern topographic maps. A more recent geologic map (Bergquist and others, 1986) does not show Tertiary volcanic rocks in that area, and no rhyolitic rocks are mentioned in the Tertiary rock descriptions. Turner (1897) reported that there was a volcanic tuff with many well rounded particles under the gravel at Rattlesnake Diggings. The gravel is also reported to be subangular. These features suggest the gravel is interandesitic, which Turner (1897) also suggested when he included with his description of later gravels. Logan (1929, p. 197) offered a somewhat different suggestion, that the gravel in the channel was pushed aside by lava and then covered by another layer of mud. The legal location of the mine associated with this latter description is Section 7 and 18, T20N, R11E. However, the use of the canyon name and the reported distance by trail from Downieville indicate it is the probably the same mine as described by Turner. It appears that Lawler's (1995) continuation of the Rattlesnake-Red Oak channel to the north is based on a projection through a drift mine shown by Turner northeast of Rattlesnake Peak (in area of present day Cowell Mine on the Mt Fillmore 7.5-minute topographic map). Based on the above discussion, it appears that gravels of this area are probably interandesitic. So, much of this channel could be interandesitic.
Crawford (1896, p. 295) reported the Gladiator (Sunnyside, Franklin, etc.) drift mines at the south end of McRae Ridge 9 miles west of Johnsville. The Cowell Mine is shown on the Mt. Fillmore 7.5-minute quadrangle at the south end of McRae Ridge on Sunnyside Creek and near Sunnyside Meadows. This is in the same area that Turner (1897, Economic Geology map) showed a drift mine on granite near the contact with Tertiary volcanic rocks. It is not clear that the Cowell Mine is the drift mine referred to by Turner and Crawford. Although Crawford (1896, p. 295) describes a southwest-coursing channel on bedrock below lava, indications of glacial gravel are also reported. MacBoyle (1920b, p. 138) reported the location of the Sunnyside Claim to be in Sections 5 and 8, T21N, R11E; this is the area of the Cowell Mine.
Rhyolitic ash-flow tuff crops out in road cuts along California State Highway 70 about 1.5 km southeast of Blairsden or 2 km northeast of Graeagle (N½ NE¼ SE¼ Section 14, T22N, R12E, Blairsden 7.5-minute Quadrangle; [P10], [P146]). The tuff is white, moderately welded, and contains phenocrysts of large, platy-fracturing sanidine, plagioclase, and biotite. The rock contains sparse lithic fragments, and large, black, glass shards and appears to have a basal vitrophyre, although the underlying unit is not exposed. This tuff could be the tuff of Rattlesnake Canyon (Henry and others, 2004)of the Dogskin Mountain area, Nevada. To the north of the road cuts, the tuff has an attitude of approximately N50°E, 20°SE. Wagner and Saucedo (1992) reported a 13.6 Ma K-Ar age determination for intrusive andesite near this site.
Photos
P10a.JPG White rhyolitic ash-flow tuff (tuff of Sutcliff?) overlain by Pliocene Mohawk beds along Highway 70 east of Blairsden.
Grose and others (1990b) showed a small area of their unit Ts (Eocene clastic rocks equivalent to Auriferous Gravels) in the SW¼ NW¼ NE¼ Section 10, T27N, R10E (Moonlight Peak 7.5-minute quadrangle), on the north flank of a hill east of Cooks Creek and about 3 km southwest of Moonlight Valley. In this area [P78] a probable flow of biotite-plagioclase andesite crops out. The biotite is sericitized and the rock contains rare quartz. This dacite(?) could be a part of unit Tsd of Grose and others (1990b) which was mapped about 1.5 km to the north. A few rounded clasts seen in float here consist of both preTertiary rocks and Tertiary(?) andesite. I speculate that any gravel here would be interandesitic, that is, younger than at least some of the Tertiary andesitic volcanism in the area. This would suggest a correlation with unit Tvg of Grose and others (1990), a Miocene(?) conglomerate unit containing both preTertiary and Tertiary volcanic clasts. However, at least some andesitic rocks of the Mountain Meadows and Cheney Creek areas may be Eocene, and andesites there are also hydrothermally altered.
Diller (1908, Plate III) showed two small areas of Auriferous Gravels about 3 km northwest of Taylor Lake. These areas lie south of Eisenheimer and Rattlesnake Peaks, in the S½ of Section 27, T27N, R11E, Kettle Rock 7.5-minute Quadrangle. Christe (1987, included the rocks of this area in his unit Tu, andesitic mudflows and andesitic basalt flows.
The rock exposures that Diller (1908, Plate III) thought were part of the Auriferous Gravels consist of andesitic lahars, block and ash flows, and minor fluvial(?) gravels and sands. The clasts in these rocks are mainly fresh pyroxene andesite but also include rounded cobbles to boulders of Mesozoic granodiorite and metavolcanic and metavolcaniclastic rocks ([P151]; photos). The rocks are part of a regional unit that is considered Miocene (Grose and others, 1990b) and underlie Pliocene and(or) Miocene andesite of Eisenheimer Peak (Grose and others, 1990b).
About 600 m south of the exposures described above, in NW¼ NW¼ NE¼ Section 34, T27N, R11E [P152], the andesitic lahar unit lies on a distinctive dark-colored basalt flow which lies directly on Cretaceous granodiorite. The basalt contains poker chip-like phenocrysts of plagioclase, commonly 1 cm by 1 mm, and rounded pyroxene phenocrysts up to 3 mm.
Photos
P151e_72.JPG Andesite clast lahar which underlies the andesite of Eisenheimer Peak.
P151f_71.JPG Granite boulder and smaller clasts of Tertiary basalt and Mesozoic metavolcanic rocks from the from the lahar which underlies the andesite of Eisenheimer Peak.
P151g_70.JPG Andesite of Eisenheimer Peak on Eisneheimer Peak.
P152.JPG Basalt flow containing “poker chip” plagioclase phenocrysts. Underlies andesite of Eisenheimer Peak.
Turner (1898) briefly mentioned old river gravel at Fales Hill. Gudde (1975), based on earlier sources, reported that the placer and hydraulic mining area was located about four and a half miles north of Spanish Peak and that the gravels were nearly exhausted before 1875. This mining area is located on a ridge above Fales Basin, in E½ NE¼ NW¼ Section 25, T25N, R7E [P96], Caribou and Bucks Lakes 7.5-minute quadrangles.
The area of gravels is shown by Hietanen (1973, Plate 2), lying on Jurassic ultramafic rocks. The gravels consist mainly of clasts of white quartz and quartzite. One rare but distinctive clast type is red jasper containing patches of white quartz (photo). The clasts can only be observed in piles left from hydraulic mining (photos), and can not be observed in place. The associated red soil probably developed as a result of weathering of the ultramafic rocks. A very few clasts in the mining debris are of Tertiary basalt and hornblende andesite. It is not clear if these were in the original mined gravels or if they came from younger, overlying deposits. Andesite-clast lahar or conglomerate [P97] is poorly exposed along the east arm of a hairpin bend road about 300 m east of the placer workings, and such rock could have supplied the fresh volcanic clasts to the mining debris during hydraulicking. If the placered gravel at Fales Hills is Miocene (that is, interandesitic) and reworked from prevolcanic Eocene gravels) it had very few Tertiary volcanic clasts. It seems somewhat more likely that the gravels are the remnants of an Eocene channel that was later covered by Miocene lahars and volcaniclastic rocks. The distinctive jasper clasts are similar to clasts and source rock material observed to the north and northeast (e.g., Taylor Diggings and southeast of Canyon Dam areas). Such clasts may also be recycled clasts from the Jurassic Kettle Formation of the Mt. Jura area (see the Taylor Diggings description).
Photos
P96c.JPG Piles of gravel on weathered, iron-stained bedrock; Fales Hill mining area.
P96d_49.JPG Red jasper clast from Fales Hill area; hammer head is 18 cm.
The Feather Fork Mine is located near the South Fork Feather River, just west of County Highway 511, in the W½ Section 14, T22N, R9E (Onion Valley 7.5-minute Quadrangle). The name is presumably for the adjacent river. The property should not be confused with other properties that the company apparently operated on the La Porte—Hepsidam channel to the east, in particular the Thistle Shaft, about 4 km to the south. That shaft was operated by the Feather Fork Gold Gravel Co. (Lindgren, 1911, p. 107) and has been referred to as the Feather Fork (Thistle) Mine (Crawford, 1894, p. 265; Clark, 1970, p. 52). Because the name seems to apply to the mine on the South Fork, that mine could be where the company began.
The oldest workings at the Feather Fork Mine are probably adits (drifts) that are shown (Onion Valley 7.5-minute Quadrangle) heading in a southeast direction from near the east side of the South Fork Feather River. Little remains of these workings; however, based on material in dumps, the workings are apparently rim drifts that began in Tertiary andesitic rocks (Hietanen, 1981, Plate 1) and penetrated the underlying preTertiary bedrock (in part, serpentinite) in an effort to intersect the Auriferous Gravels concealed under the Lovejoy Basalt. This was apparently successful, because some Auriferous Gravel is seen in dumps from the drifts. There are apparently no significant outcrops of Auriferous Gravel in the area of the Feather Fork Mine (Hietanen, 1981, Plate 1), although there probably were some indications of concealed gravel that inspired the early underground drifts. The considerably younger Lovejoy Basalt apparently lies directly on preTertiary bedrock in a channel that cuts out much of the gravel in this part of the north branch of the La Porte Fork (see the section on Richmond Hill, Sawpit, Union Hill) of the Tertiary Yuba River.
A 250 ft (76 m) shaft [P66] was sunk in the 1970s by Sunshine Mining Co. (Trinity Plumas Capital Corporation, 2003) about 200 m east of the drift portals. The shaft is collared in dense, black Lovejoy Basalt and reportedly reached the bottom of the channel. The gravel was reported to be 140 ft (43 m) thick in the modern workings, with large boulders on 1 ft (30 cm) of weathered bedrock. The channel was reported to be up to 1500 ft (450 m) wide and 1.5 mi (2.4 km) long; values were reported to be 0.12 oz per cubic yard in the lower 10 ft (3 m) of gravel (Trinity Plumas Capital Corporation, 2003). Gravel in the vicinity of the shaft that was presumably taken from the channel through the shaft consists almost entirely of quartz clasts; the quartz in these is either milky white or light gray and vitreous. This latter variant is also common at workings in the Richmond Hill area (described elsewhere) 4.5 km to the northeast. The Eocene paleochannel at the Feather Fork Mine almost certainly continues to the northeast, below the Lovejoy, toward Richmond Hill and Sawpit (see a more complete description of the channel there).
Photos
P66c_building.JPG Old mine building at the Feather Fork Mine.
Grose and Mergner (2000) showed silicic ash-flow tuffs in an area near the Spring Creek arm of Frenchman Lake. An area of the tuffs near the Spring Creek Campground and below the highway was visited in 2003 (NE¼ NE¼ NW¼ Section 34, T24N, R16E; [P18]). The ash-flow tuffs apparently rest on Jurassic metavolcanic rocks, although the contact can not be observed. The tuffs present include the tuff of Campbell Creek and the Nine Hill Tuff; they appear to be in a north-northwest-trending paleovalley. About 2 km to the southwest, along Frenchman Lake Road (State Route 284) in the canyon below Frenchman Dam (SW¼ NW¼ NE¼ Section 4, T23N, R16E; [P19]) Miocene andesite lahars have an apparent buttress unconformity against Cretaceous granitic rock. A 1.5 m diameter block of the tuff of Chimney Spring was observed in the lahars, and an approximately 50 m long block of the same tuff also appears to be included in lahars. The southwest continuation of the Oligocene paleovalley observed near the Spring Creek Campground may be nearby, as this large block probably did not travel far.
Gopher Hill/Spanish Creek Mines
Tuner (1898) reported that gold-bearing gravels worked by hydraulic methods in the vicinity of Gopher Hill (SW¼ Section 7, T24N, R9E) near the Oroville Quincy Highway were the deposits of a Pleistocene Lake. He also reported beds of volcanic ash in the deposits, which he speculated may have come from the Mount Lassen area. Hietanen (1973, p. 60 and Plate 2 also attributes these extensive deposits in Meadow Valley and the Gopher Hill area to the Pleistocene. Turner (1898) reported that although most pebbles were of preCretaceous rocks, a few decomposed lava pebbles were noted.
A 2003 visit to an area of hydraulic mining about 500 m east of Gopher Hill confirmed the presence of a few rotten clasts of hornblende andesite in hydraulicked material. Also, the exposed beds at the limit of hydraulicking [P127a] consist of yellowish pebbly mudstone, containing sub rounded to subangular pebbles of schist. A bed of white, reworked tuff, containing phenocrysts of biotite and quartz(?) is exposed in one face that is visible from the highway. The deposits are clearly not related to Eocene gravels; their exact age is unknown. They may be similar to gold-bearing Quaternary colluvium and related material in the Greenville and Canyondam areas (see Dutch Hill Mine, Canyondam area, etc.).
Photos
P86.JPG Plaque near site of Spanish Creek Mines.
P127a.JPG Riveted steel pipe elbow lying on phyllite, Gopher Hill area.
P127b.JPG White ash in yellowish Quaternary(?) pebbly mudstone, Gopher Hill area.
P127f_38.JPG Piles of coarse reject boulders from hydraulic mining at Gopher Hill, sitting on bedrock.
P127i_36.JPG Yellowish hydraulicked face of Quaternary(?) colluvium and alluvium, Gopher Hill area.
P127r_27.JPG Clasts of quartz and preTertiary rocks hydraulicked from Quaternary (?) pebbly mudstone, Gopher Hill area.
Diller (1908, Plate III) showed Tertiary rhyolite just south of the town of Greenville lying on Paleozoic metarhyolite. Diller's Tertiary rhyolite is exposed (2003 visit) in a road cut lying over yellowish colluvium in SW¼ SE¼ SE¼ Section 3, T26N, R9E [P164] on the Greenville 7.5-minute Quadrangle. The rock unit exposed there is light-gray, welded, rhyolitic ash-flow tuff with a basal unwelded unit above the colluvium. It is very similar to and herein correlated with ash-flow tuff seen just north of Paxton and along the Union Pacific Railroad cut, 3 km east of Canyondam (see description elsewhere in this report). That tuff is believed (Wakabayashi and Sawyer, 2000, p. 204-205) to have a source in the 3-2.5 Ma Yana volcanic center located in the vicinity of Butt Mountain (Mt. Butte of the Susanville 1x2-degree sheet), 20 km east of Lake Almanor (Page and others, 1994, p. 4-19). The ash-flow tuff and underlying colluvium are thus not likely to represent remnants of an Eocene-Oligocene paleovalley.
Photos
P164a.JPG Welded ash-flow tuff (from the Yana volcanic center?) exposed in road cut just south of Greenville.
P164c.JPG Ash-flow tuff from the Yana volcanic center(?) lying on yellow colluvium just south of Greenville.
Grizzly Ridge (Cromberg, Little Long Valley Creek, Prugh Mine)
Auriferous Gravels cap the noses of three ridges on the southwest side of Grizzly Ridge, northeast and north of Cromberg (Grose, 2000a). The gravels lie on Devonian and Mississippian marine rocks and the base of the channel is at about the 5420 ft elevation. Durrell (1959, p. 187) illustrated gravels with cross-laminated arkose in a photograph at the Prugh Mine in Section 1, T23N, R11E as well as in a very similar photograph in Durrell (1987, p. 154). Turner (1897) showed two hydraulic sites at this area on the spur north of Long Valley Creek. Crawford (1896, p. 307) also described the Tefft & Co. Lone Star and Concordia hydraulic mine in this area.
The smooth, well rounded clasts in the Grizzly Ridge exposures consist of light purplish and yellowish gray metavolcanic rocks, including flow-banded metarhyolite and meta-andesite. A few clasts of dark metasedimentary rock, including metaconglomerate, as well as aplite and granite were also seen. Commonly, pebbles are 1-4 cm, but they range up to 10-25 cm long by 6 cm thick. Durrell (1987, fig. 84) reported that cross-bedding indicated a southwesterly flow of the streams that deposited the gravels at the Prugh Mine. He also reported that the cobbles are easily recognized as being derived from the Taylorsville District not less than 8 km to the northeast. This is consistent with similar data at the Cascade Mine, described elsewhere in this report.
South of Long Valley Creek and the Tomba Road to Happy Valley (SW¼ SE¼ SE¼ Section 8, T23N, R12E) [P22] fragments of white ash-flow tuff were noted in float. They are either from a concealed tuff outcrop or are clasts from within a volcaniclastic sandstone at the base of the Miocene andesite lahars and flows. The ash-flow tuff contains biotite, feldspars, and smoky, vermiculated quartz phenocrysts. The tuff is probably the tuff of Campbell Creek (e.g., Garside and others, 2003). The Lovejoy Basalt lies on Auriferous Gravels and under Miocene andesites nearby. Thus, in this area, Auriferous Gravels, Oligocene ash-flow tuffs, and Lovejoy Basalt were deposited in a broad southwest-trending paleovalley from the Eocene until at least 16 Ma, the presently accepted age of the Lovejoy Basalt (Page and others, 1995). The downstream continuation of this channel is probably either the Gibsonville-Bunker Hill Mine channel or the Sawpit Flat-Union Hill Mine channel that have been displaced downward across the Mohawk Valley fault.
Photos
P21b.JPG Four pebbles from gravels in Cogswell Ravine along Tomba Road (Grizzly Ridge area); largest is flow-banded metarhyolite. Notebook is 19 cm long.
A thick stack of Oligocene ash-flow tuffs and inter-tuff conglomerates is exposed on and around Haskell Peak, located about 13 km northeast of Sierra City (Brooks and others2003). The Peak is in SW¼ Section 19, T21N, R13E on the Clio 7.5-minute quadrangle. The tuffs exposed represent a section similar to that at Black Mountain to the north and in the seven Lakes Mountain-Dogskin Mountain area to the east in Nevada (see Henry and others, 2003), including the tuff of Chimney Spring, Nine Hill Tuff, tuff of Campbell Creek, and several older tuffs ranging downward to 31 Ma. The conglomerate of Locke Mine, which underlies the lowest ash-flow tuff, may have a lower part that is prevolcanic, and thus possibly Eocene. It lies locally on red soil developed on preTertiary rocks (Brooks and others, 2003). At Locke Mine (NE¼ SW¼ NE¼ Section 13, T21N, R13E) the conglomerate appears to lie directly on Jurassic granodiorite, although recent reclamation of hydraulic mining workings has obscured most relationships. Brooks and others (2003, p. 4) reported that the conglomerate of Locke Mine occupies a broad northwest-southeast paleovalley. However, based on the pattern of thinning and eroded-out tuffs and their underlying gravels, it appears equally likely that the Eocene(?) and Oligocene paleovalley is oriented north-south. This orientation would allow the Haskell Peak channel to be projected south about 6 km to the Pride Mine, which is on a channel (containing gold-bearing gravels and overlying Oligocene ash-flow tuffs) that continues even farther south to the 1001 and Hida Mines (all in the Haypress Valley 7.5-minute Quadrangle).
Photos
P46b_cabin.JPG Log cabin near Hayes Mine, Haskell Peak.
P46d_cabin.JPG Log cabin near Hayes Mine, Haskell Peak.
P46e_cabin.JPG Log cabin near Hayes Mine, Haskell Peak.
P46f_cabin.JPG Log cabin near Hayes Mine, Haskell Peak.
P47a_LockeMine.JPG Reclaimed Locke Mine, Haskell Peak.
Saucedo and Wagner (1992) showed Auriferous Gravels in the vicinity of the Hayden Mine, in NE¼ NE¼ Section 32, 22N, R13E about 2 km east of the mouth of Calfpasture Creek (see the Calfpasture Creek area description). The Hayden Mine [P213b] consist of an inclined shaft and nearby trench along copper mineralization in Mesozoic metasedimentary rocks. A very few rounded clasts of preTertiary rocks were seen near the mine, but the rest of the mapped area of Auriferous Gravels appears to be either Quaternary Mohawk beds or Miocene andesite lahars (or float from them) which lie directly on metasedimentary rocks and adjacent granitic rocks. Thus, based on a 2004 visit, the presence of significant Auriferous Gravel in this area is not confirmed..
Head of Cheney Creek (Susanville Flora)
Diller (1878, p. 417) reported fossil leaves from a thin, lenticular shale in conglomerate a short distance north of the summit on the Lights Canyon—Susanville Road. The complete description is:
about three fourths of a mile north of the point where the Light Canon and Susanville road crosses the summit. The surest way to reach the exposure is to start from the first small bridge, one-fourth of a mile below the summit on the Susanville side, and go up the gulch almost directly west for a few hundred yards to the summit of a partially bare ridge. Cliffs of conglomerate appear on the left (south side) as the summit is approached. The ridge or rather spur extends northerly and upon its sides soon appear two deep, precipitous, rocky gulches which unite about a quarter of a mile below. More than half way down the spur on its northwesterly slope, in a open space about fifty feet above the bottom of the gulch, the very limited exposures may be found.
The above location is apparently the same one referred to by Diller (1908, p. 74) as being “three-fourths of a mile north of the road summit between Taylorsville and Susanville, at an elevation of 6000 feet on the slope of Gold Run, and about 7½ miles southwest of Susanville.” Diller (1908, p. 76) reported that “The small lens of shale collected in 1886 was exhausted , but another shaly lens near by in the same conglomerate furnished the material collected by James Storrs in 1904.” Storrs was a field assistant to Diller. Diller (1908, p. 77) reported that “The lenses differ lithologically and the floras are different, but they are reported by Storrs to be in the same mass of conglomerate and therefore essentially the same age.” The 1878 Diller location is very close to a site location given to me by Howard Schorn (written commun., 2003), which was examined in September 2003. This site [P123] is along a ridge which follows the Section 32-33 boundary, in SW¼ NW¼ SW¼ Section 33, T29N, R11E (Fredonyer Pass 7.5-minute quadrangle). This is certainly very close to the sites described by Diller (1878, 1908), although Diller's 1878 description may refer to an area slightly closer to the gulch east of the ridge. It may be that the site I visited [P123] is Storrs' later site (Diller, 1908, p. 68). The gravels at the Stors site are reported to be cut by dike-like bodies of hornblende andesite (Diller,1908, p. 68), which I did not observe during a 2003 visit. However, Diller (1893. p.399) does mention that the area where the gravels are cut by dikes is at the head of Cheney Creek, essentially the area examined by me.
Lindgren (1911, p. 115) described what is apparently this same site as being “7½ miles southwest of Susanville near the head of Willard Creek.” Although the head of Willard Creek is 5 or 6 km southwest of this locality on Cheney Creek, the description otherwise appears similar. Knowlton (in Lindgren, 1911, p. 60, describes the earlier collected flora locality as being in a deep ravine and the later collected flora as being “apparently at a higher horizon.” I conclude that the site on the ridge, where leaf fossils can still be found, is the later collected site discovered by Storrs.
The fossil leaves are found as impressions and darker films on bedding planes of light grayish green, fine-grained sandstone to siltstone. The leaf-bearing sandstone is underlain by a dark greenish to purplish gray conglomerate containing pebbles and cobbles of andesite and granodiorite in a sandy matrix consisting of small rock grains, and granodiorite- and andesite(?)-derived feldspathic sand. The andesite is somewhat altered, containing cloudy plagioclase and chloritized mafic minerals (including biotite). The beds are subhorizontal. To the south up the ridge approximately 400 m (approximately 120 m vertically up section), a hornblende andesite flow is interbedded with conglomerate containing clasts of hornblende andesite, gray quartzite, meta-conglomerate, and white granitic rock. The conglomerate beds exposed along the ridge are all somewhat similar, and there does not appear to be any significant stratigraphic change or break between the flora beds and the hornblende andesite flow higher in the section. Knowlton (1911, p. 63) regarded the Susanville flora as clearly Eocene and older than the other known flora from the Auriferous Gravels of California. Wolf (1978, p. 698) reported that the physical characteristics of the fossil leaves suggested a tropical rain forest with a mean annual temperature of ca. 27şC; this is consistent with other Eocene flora of the western U.S. This flora age determination poses somewhat of a problem, because no Eocene volcanism has been dated from this area. Grose (1993) mapped the gravels in the vicinity of Cheney Creek in his unit Tvg (Miocene?), and he reported that the gravels intertongue and are transitional with overlying andesite flows (Grose, 1990b). Based on available K-Ar dating in the Susanville area, the overlying andesite flows are only ca. 11 Ma (Grose and others, 1990, Table 1). Thus, based on present knowledge, it does not seem reasonable that the leaf-bearing beds are Eocene while somewhat stratigraphically higher beds are 25-30 m.y. younger.
About 3.5 km to the southeast, along the Diamond Mountain Road, in W½ SW¼ Section 10, T26N, R11E, [P126] near the base of Tertiary gravel on Cretaceous granodiorite (Grose and Porro,1989b), andesite clasts apparently from their map unit Tvg contain glassy plagioclase phenocrysts and must be Tertiary (probably Miocene). At least here, it does not seem likely that the clasts in the lower part of unit Tvg are Mesozoic, which could be proposed for the somewhat altered ones at the fossil leaf locality.
Gravels of probable Miocene age (unit Tvg of Grose, 1993) are widespread in the area southwest of Susanville. They were considered by Diller (1906) to be evidence for an Eocene delta at the mouth of the Tertiary Jura River. Much of the gravel contains clasts of probable Miocene andesite, and is, thus, considerably younger than the Auriferous Gravels. Probably some Auriferous Gravels were reworked in the Miocene, with consequent destruction of evidence for Eocene paleovalleys.
If the andesitic flows and conglomerates of the Cheney Creek area are Eocene, they may represent a southern extension of the Clarno Arc (Walker and Robinson, 1990) of central Oregon. Andesitic rocks of this arc are as old as about 39 Ma in the vicinity of Cedarville (Myers, 1998, p. 11), 150 km to the northeast (Fig. 1). Any evidence of Eocene(?) gravels between Cedarville and Susanville is limited to two areas: Deans Ridge, just east of Eagle Lake (19 km northwest of Susanville), and Crest Lake Reservoir (42 km northeast of Susanville).
Photos
P122a.JPG Rounded boulder of Cretaceous granitic rock in conglomerate near the Susanville Flora locality at the head of Cheney Creek. Hammer is 32 cm long.
P122b.JPG Rounded pebbles of andesite in conglomerate near the Susanville Flora locality at the head of Cheney Creek. Hammer head is 18 cm.
P123f.JPG Fossil leaf from Susanville Flora at head of Cheney Creek. Centimeter scale.
P123k_46.JPG Purplish gray outcrops of andesite clast conglomerate at the site of the Susanville Flora, head of Cheney Creek.
P124.JPG Outcrop of hornblende andesite flow which crops out stratigraphically above the Susanville Flora at the head of Cheney Creek.
Hungarian Placer Mine/Claremont (Clermont Hill)
The Hungarian Placer Mine is shown on the Quincy 7.5-minute Quadrangle about 4 km west of Quincy, at the end of a 7 km-long northwest ridge from the peak of Claremont (SW¼ Section 17, T24N, R9E). This is close to a hydraulic mine site shown by Turner (1897, Economic Geology map). Turner’s map refers to the peak as Clermont Hill. The hydraulic workings were also described by Crawford (1896, p. 303). There is some evidence of placer workings in the area, mainly the remains of small water retention reservoirs, water diversion ditches, a piece of ~22 in. riveted pipe, square nails, etc. In a few places, a few scattered cobbles are seen in float; these consist of smooth, rounded quartz or preTertiary metamorphic rocks. I found no evidence of significant amounts of gravel; however, the Shoo Fly bedrock is deeply weathered in some areas. The scattered cobbles could represent recycled Eocene gravel cobbles. The only other description of gold-bearing gravels on Claremont is that of Turner (1897), who reported that gravel of quartz and siliceous rocks at the mouth of a tunnel at the 6,400-foot elevation was mainly subangular and indicative of a small watercourse. Equally as likely is that it represented basal interandesitic gravel. Turner (1911, p. 111) included it with a group of gravels that he believed probably belonged to the epoch of intervolcanic gravels. Thus, there is little evidence for an Eocene channel in this area, although its existence can not be completely discounted, as it could have been almost completely eroded away by Miocene or later streams.
Photos
P83a.JPG Flattened riveted pipe in vicinity of the Hungarian Placer Mine. Hammer is 32 cm long.
Keystone Gap area (Roman and St. Louis Mines)
The Sierra City 15-minute quadrangle shows two mines in SW¼ Section 5, T19N, R12E near Keystone Gap on the Henness Pass Road (St. Louis Mine and Roman Mine). No information can be found on these workings in the California State Mineralogist's Reports. The Keystone Mine, about 2 km to the northwest, is reported to be a lode mine (Preston, 1890, p. 653). The mines may be in the vicinity of the contact of Tertiary andesitic rocks with preTertiary basement, and thus could represent workings in “Auriferous Gravels.” However, a 2004 visit found that the St. Louis Mine (NW¼ SW¼ SW¼ Section 5, T19N, R12E [P237]) explored quartz veins in metarhyolite? (Sierra Buttes Formation?). The nearby Tertiary andesitic rocks appear to lie in a paleovalley developed on the preTertiary basement in this area. No evidence of older, pre-andesite gravels was seen at this contact in the area. If an Eocene paleochannel existed here, connecting the Hilda Mine area to the northeast with a channel at Graniteville to the southwest, most or all of it has been removed by erosion before the andesitic rocks were laid down.
The tuff of Campbell Creek crops out along the Meadow Lake Road, about 8 km south of its intersection with Fiberboard Road, near the head of Lacy Creek (Weber Peak 7.5-minute quadrangle). This area is about 5 km northeast of Meadow Lake, in SW¼ NE¼ NW¼ Section 7, T18N, R14E [P194]. As with other areas of ash-flow tuff in the vicinity (Weber Lake area, Meadow Lake Hill), this is near an outcrop shown by Lindgren (1897, Economic Geology Map).
Ladies Canyon Mine (not examined during this study)
MacBoyle (1920b, p. 71) reported that the Ladies Canyon Mine was patented ground covering a length along the channel of 1 mile in Section 13, T20N, R11E. The best match for this mine on the Sierra City 7.5-minute quadrangle is a mine symbol (crossed hammer and pick) about 20 ft vertically above Ladies Canyon. Mines in the hills to the southeast and northwest (Monarch Mine, Primrose Mine) are quartz mines (MacBoyle, 1920b). Except for a Tertiary andesite intrusive about 1 km to the northwest (Saucedo and Wagner, 1992), no Tertiary rocks have been mapped in the area. It seems likely that the channel referred to by MacBoyle was in the active stream, and that there is no evidence from the literature of any Auriferous Gravels in this area.
Turner (1897) showed a small outcrop of Auriferous Gravel about 700 m west of Lee Summit (Spring Garden 7.5-minute Quadrangle) and under what is now called Lovejoy Basalt. The Lovejoy is exposed in a small road-metal pit just west of California State Highway 70 (see Stop 1 of Wakabayashi and Sawyer, 200, p. 203; Durrell, 1987, p. 172). The Lovejoy here has been dated at 15.51 ±0.15 Ma (Page and others, 1995, Table 3). Scattered smooth rounded cobbles of resistant preTertiary rocks (including vein quartz) are found as float about 300 m west and 300 m southeast of the roadside Lovejoy outcrop. These clasts may be originally from Auriferous Gravel, but there is no clear evidence of Auriferous Gravel outcrop; the clasts could have been recycled into Miocene or later gravels. In fact, Sheeks (1977) showed the gravels in the area south of Lee Summit as Quaternary “sediments of extinct Long Valley,” presumably equivalent to the Quaternary Mohawk Valley lakebeds.
Gianella (1956) did find thin, platy flakes of gold by panning samples collected from a ravine about 600 m south of the Lovejoy pit ([P50]; S½ NE¼ NW¼ Section 8, T23N, R11E; Blue Nose Mountain 7.5-minute quadrangle). He reported that these gravels were within the Miocene andesitic lavas and lahars, rather than the Auriferous Gravels, and he estimated that the andesitic rocks were at least 120 m thick below the sampled gravels. Some old bulldozer cuts are present in the area he described, but there is no evidence of actual mining. Smooth, rounded clasts of resistant preTertiary rocks and at least one rounded clast of Miocene(?) andesite were seen in float during a 2003 visit. However, because Auriferous Gravel, Lovejoy, and younger andesite may all be found in channels that place younger units topographically lower than older units, it is not certain if Auriferous Gravels are present in the Lee Summit area in outcrop or subcrop. As described above, Sheeks (1977) mapped the gravels in this area as Quaternary. Gold-bearing Auriferous Gravels do underlie Lovejoy about 10 km to the northeast at the Cascade Mine. Gianella (1956) also reported a rumor that the Spring Garden Railroad Tunnel cut older gold-bearing gravel that could have been pre-volcanic and rest on the Paleozoic Shoo Fly Complex. Gravel clasts were rumored to make up railroad grade fill west of the northwestern portal of the tunnel. The source of this information may have been Lindgren (1911, p. 111) who mentioned a channel cut in the Western Pacific Railroad tunnel near Spring Garden. No clasts were seen in fill along the railroad grade during a 2003 visit, although a few smooth, rounded clasts were observed in railroad cuts in predominantly andesite-clast lahars of the post-Lovejoy andesite units.
Thus, it is possible that prevolcanic Auriferous Gravels are present in the subsurface near Lee Summit and Spring Garden (see the description of Spring Garden), or that they were previously present and eroded by streams that cut a channel for the Lovejoy Basalt or younger Miocene andesitic units.
Hietanen (1973, Plate 2) showed a small area of Eocene Auriferous stream deposits on a hill above Little Schneider Creek, in NW¼ NW¼ Section 36, T24N, R8E [P108], about 5 km south of Spanish Ranch (Meadow Valley 7.5-minute Quadrangle). The exposures are poor, but float and a red soil suggest Tertiary gravels subcrop below alluvium. The subrounded pebbles and cobbles consist of preTertiary rock types, vein quartz, and about 10% Tertiary andesite and basalt. None of the clasts have polished surfaces. Based on these data, the gravel at the site is post-Eocene and possibly of similar age to the gravels at Monte Cristo Mine.
Nine Hill Tuff and the underlying tuff of Campbell Creek crop out in a canyon about 1.8 km northeast of the top of Meadow Lake Hill, in SW¼ SW¼ SE¼ Section 13, T18N, R14E (Weber Peak 7.5-minute quadrangle, [P195a]). The Nine Hill has an approximately 2 m vitrophyre and about 3 m of overlying vapor-phase rock is also exposed. The tuff is essentially horizontal.
Photos
P195.JPG Nine Hill vitrophyre, Meadow Lake Hill.
Turner (1898) described gravel, capped by andesite breccia, cropping out at the south end of a ridge that projects south from Spanish Peak in SW¼ Section 30, T24N, R8E. He also reported that the deposit was mined by a tunnel (adit), reported to be at least 3000 ft (914 m) long (Diller, 1878, p. 418). No indication of the adit was found in a 2003 visit, but in the area of gravel float, a ditch was seen that may have been used for ground sluicing. Also, about 1 km to the north, a very shallow shaft was seen, an apparent attempt to penetrate the overlying Miocene andesite lahars.
The gravels do not crop out, but the clasts observed in float near the probable contact with underlying granodiorite [P116] consist of both preTertiary and Tertiary rocks. The clasts of preTertiary rock are well rounded and polished, 1-15 cm long, consisting of: light brown and reddish quartzite, black chert, dark gray to black chert-pebble conglomerate, white vein quartz, light gray pebbly quartzite, and quartz-veined dark gray silicified schist. The clasts of Tertiary rocks are well rounded but not polished; they include light gray pyroxene-plagioclase andesite and finely crystalline, black, magnetic basalt (Lovejoy Basalt?). Turner (1898) also reported pebbles of pyroxene andesite in the gravels, as well as fossil leaves of upper Miocene age. Miocene pollen is reported from the gravels and sands (Howard Schorn, written commun., 2003). Deposits of gravel in a similar stratigraphic position to those of the Monte Cristo Mine site are reported to the north on Spanish Peak and about 1.5 km to the northeast of the peak (Hietanen, 1973).
Because the gravel deposits in the Spanish Peak area are apparently Miocene, and apparently represent an interandesitic channel or channels, geologic information from the area is not as useful for projection of Eocene-Oligocene channels as older gravel deposits. However, the presence of cobbles of possible Lovejoy Basalt in the gravels suggests that the channel below the andesite lahars on Spanish Peak is younger than ca. 16 Ma. The clasts of preTertiary rock probably were eroded from older Eocene(?) gravels, possibly those which crop out northeast of Spanish Ranch (Bean Hill, Fales Hill, Mulligan Slide), if those are truly Eocene.
Moonlight Valley-West Branch Lights Creek
Diller (1908, p. 66) reported that Tertiary sandstone and conglomerate crop out in the vicinity of Moonlight. McFarlane (1981, p. 42-43) reported that the Tertiary sedimentary rocks of Moonlight Valley consist mainly of arkose and less conglomerate, with coal seams that locally contain leaf fossils. Diller (1908, p. 66, 92) also reported that collections of the fossil leaves were made, from an area “near the eastern end of Moonlight on the slope toward the west fork of Lights Creek at an elevation of about 6000 feet.” Elsewhere in Diller (1908, p. 66), Moonlight is described as being 12 miles north of Taylorsville at the head of Surprise Creek. It appears from the usage in Diller (e.g., 1908, p. 118), that Moonlight is a peak, probably Moonlight Peak of the Moonlight Peak 7.5-minute Quadrangle. According to Durrell (1959, p. 215), Diller's flora locality is near the center of Section 36, T28N, R10E. The sedimentary rocks crop out for a distance of about 4.5 km along Moonlight Valley and the West Branch Lights Creek (Grose and others, 1990). According to Diller (1908, 117) Auriferous Gravels were mined “near the border of Moonlight.” The exact location of these placer workings is unknown.
During visits in 2003, the sedimentary rocks of the area were examined at several areas along the West Fork Lights Creek in the eastern part of the area of mapped Tertiary sedimentary rocks. The rocks exposed near the Moonlight Valley Road in NW¼ NE¼ NW¼ Section 32, T28N, R11E [P156] consist of yellowish weathering arkosic sandstone, granite wash, pebbly sandstone (with pebbles of rotten granite), and interbedded, reddish weathering, light gray pebbly siltstone (with at least one pebble of tourmalinized? rock). Underlying diorite of the Lights Creek stock was observed in outcrop about 500 m to the north. The arkose and granite wash appear to be derived from rock more silicic than the Lights Creek stock, probably from light-colored Cretaceous granodiorite exposed about 1 km to the east (Grose and others, 1990). Well rounded pebbles and cobbles of resistant preTertiary rocks are seen as float or lag on the sandstone beds; these clasts may have been derived from nearby beds of coarser conglomerate. However, McFarlane (1981, Plate 1 and p. 43) showed Pleistocene(?) gravels having rounded to well rounded clasts exposed just to the south. The cobbles that litter the surface are all of preTertiary rocks, and consist of black tourmaline-bearing diorite, tourmalinized and pyritic rock and breccia (both presumably from the Lights Creek stock), light-gray chert, light-gray quartzite, and reddish chert pebble conglomerate (from a Mesozoic metasedimentary unit).
About 1.5 km to the southwest along the West Branch Lights Creek (NW¼ SE¼ Section 31, T28N, R10E; [P157]) arkose beds have an attitude of N75°E. 15°NW. Cross bedding in the arkose is inclined to the southwest (S20°-50°W) while some channel-like features have a northeast-southwest trend. Probably the best indication of stream direction is the northeast-southwest trend of the outcrop of the sedimentary rocks in an apparent channel down the West Branch Lights Creek toward Moonlight Valley (see McFarlane, 1981, Plate 1; Grose and others, 1990).
Lindgren (1911, p. 63) reported that the fossils from the lower beds south of Susanville (presumably Moonlight) and a locality “7.5 mi southwest of Susanville”(see the description of the Cheney Creek area), are clearly Eocene. Axelrod (personal commun., in Durrell, 1959) also confirmed the Eocene age based on a later collection from the same locality.
Photos
P156a_68.JPG Yellowish Eocene sandstone and pebbly siltstone, Moonlight Valley Road.
P156b_67.JPG Reddish pebbly siltstone, Moonlight Valley Road.
P156c_66.JPG Pebbly arkosic sandstone, Moonlight Valley Road.
P156d_64.JPG Cobbles in float, recycled(?) from Eocene gravel. Black clasts are tourmalinized rock, probably from the Lights Creek Stock. Moonlight Valley Road.
P157a_63.JPG Bedded Eocene sandstone, Moonlight Valley.
P157c_62x.JPG Cross bedded Eocene sandstone, Moonlight Valley.
Diller (1908, p. 67) reported a body of well rounded gravel exposed at the southeastern head of Mountain Meadows and Cooks Canyon. Diller's map (Diller, 1908, Plate II) shows an area of Auriferous Gravels totaling about 2 mi2 (5 km2) in the low hills between Mountain Meadows and Fredonyer Pass (Greenville and Fredonyer Pass 7.5-minute Quadrangles). An outcrop area of “Auriferous Gravels” of very similar shape and size is shown by Grose and others (1990b), apparently based on unpublished mapping by McMath in 1959-1960 (Grose and others, 1990b, p. 4). Diller (1908, p. 67) reported the gravel, underlain by sand, to be no more than 20 ft (6 m) thick where mined. Lindgren (1911, p. 116) reported that gravels were mined for gold in the present gulches, where eroded from the Auriferous Gravels.
Gravels in the area southeast of Mountain Meadows are poorly exposed; clasts are commonly seen only in float. These areas of poorly exposed gravels appear to be capped by a Tertiary(?) plagioclase-phyric andesite flow(?) that can be seen just west of the top of a hill (elevation 5686) in S½ Section 32, T28N, R10E.This andesite contains sparse biotite, and may correlate with unit Tsd of Grose and others (1990b) mapped a few kilometers to the east. The lithologic types of pebbles observed in float near the corner of Sections 31 and 32, T28N, R10E and Sections 5 and 6, T27N, R10E [P75] include epidotized basalt (Tertiary?), plagioclase-phyric andesite (Tertiary?), white vein quartz (only one seen), black pebbles with clear quartz (quartz-tourmaline breccia?), and red jasper with white quartz veining (very similar to jasper pebbles at Taylor Diggings and Wards Diggings). About 1.4 km to the north [P76], similar gravel containing smooth clasts of preTertiary rocks as well as clasts of Tertiary (?) andesite appears to lie on Jurassic (?) maroon meta-andesite and metavolcaniclastic sandstone. The andesite clasts in the gravel do not resemble the underlying meta-andesite.
The gravels in the Mountain Meadows area either represent Eocene gravels containing clasts of older or contemporary intermediate volcanic rocks or they represent reworking of Eocene gravels in the Miocene. I am unaware of any isotopic age determinations from preMiocene Tertiary volcanic rocks of this area; to the south, in the Quincy and Portola area, Tertiary andesitic rocks are apparently entirely Miocene. The source andesite and basalt units must have been propylitically altered in the source area of the clasts; this is similar to the gravels and interbedded flows at the head of Cheney Creek (Susanville Flora area) which is about 14 km to the northeast. As at the Susanville Flora site, a reasonable explanation for an Eocene age of the andesitic flows and conglomerates is that they represent a southern extension of the Clarno Arc (Walker and Robinson, 1990) which contains andesitic rocks as old as about 39 Ma in the vicinity of Cedarville, 150 km to the northeast (Myers, 1998, p. 11).
Fossil leaves (from two species according to the list in Diller, 1878; one species according to Knowlton, 1911, p. 63) were found at “the northeastern corner of Mountain Meadows” according to Diller (1878, p. 416 and 420; 1908, p. 75); Lindgren (1911, p. 61) reported this locality as north of Mountain Meadows. Diller's (1878) description states that the locality is at the “northwestern corner of Mountain Meadows by main road, 1 mile southwest of where it crosses summit towards Susanville ...; elevation 5,000 feet.” This is probably in the general vicinity of Section 35, T29N, R9E, 10 to 12 km northwest of the area described here. Lindgren (1916, p.61) reported a single species, which had also been found in both Eocene and Miocene rocks elsewhere (however, some of these Miocene rocks would be today considered Oligocene or Eocene.
Mt Jura Divide/Hull Diggings/ Lucky S Road
Diller (1908, p. 61, Plate III) described Hull Diggings as being at the head of the north Fork of Hosselkus Creek along the Lucky S road, and described exposures of Auriferous Gravels along that road. The Hull Diggings area of gravels would be located in N½ NW¼ Section 14, and SE¼ SW¼ Section 11, T26N, R11E [P155X](Genessee Valley 7.5-minute Quadrangle) along a well-traveled road from Indian Valley to Taylor Lake. A narrow (<0.5 km) northeast-trending band of Auriferous Gravel has been mapped along this road, from a ridge top just east of the North Arm of Indian Valley, traveling between Kettle Rock to the north and Kessler and Wheeler Peaks to the south (e.g., Grose and others, 1990b). Diller (1908, p. 61) has referred to this as the Mt Jura Divide. The eastern end of this band connects with a more extensive mapped area (about 2 km2) of gravel east of Taylor Lake mainly in Section 36, T27N, R11E (Christe, 1987, Plate 2).
Diller (1908, p. 61) reported that the workings at Hull Diggings exposed over 100 ft (30 m) of gravel, including 15 ft (4.5 m) of fine sand and gravel in the upper part. Clasts were reported to be mostly smaller than a man's head (say 25 cm), but some near the base were up to 5 ft (1.5 m). Diller (1908, p. 61) also reported that the boulders were hornblende meta-andesite porphyry, and that although many pebbles consist of igneous rocks, none were derived from Tertiary units.
Gravels are poorly exposed along most of mapped band as described above. I found no evidence of placer mining in the area of the Hull Diggings, although there are remnants of a ditch along this zone that transferred water from Taylor Lake to Taylor Diggings (photo; see description of Taylor Diggings). Almost all of the subrounded to rounded clasts seen in float (and presumed to be from the Auriferous Gravels) are of hydrothermally altered or metamorphosed andesite or basalt. They are a few to 25 cm in diameter, and some contain phenocrysts of biotite (sericitized) and rare quartz. Their age is uncertain; they could be either metamorphosed Mesozoic rocks or propylitized Tertiary rocks. In the area east of Taylor Lake, similar altered or metamorphosed volcanic rock clasts are subangular to subrounded, and in poor exposures along a road (SE¼ SE¼ NE¼ Section 35, T27N, R11E; Kettle Rock 7.5-minute Quadrangle, [P154]), vesicular andesite pebbles in a conglomerate are almost certainly Tertiary, as they are unaltered and vesicles are unfilled. Larger clasts there are rotted granitic rock and altered or metamorphosed andesite of undetermined age. Also, a Tertiary andesite lahar is exposed about 3.5 km to the south-southeast, along the road in Center, NW¼ SE¼ Section12, T26N, R11E ([P155], Franks Valley). This is in an area mapped as Eocene gravel by Christe (1987, Plate 2). At the west end of the band of gravel, near the top of Beardsley Grade (NW¼ NW¼ NE¼ Section 20, T26N, R11E, Taylorsville 7.5-minute Quadrangle, [P148]) the matrix to the gravels is clay-rich and arkosic.
The evidence for the gravels of the Jura Divide to be Eocene and a part of Eocene paleochannel deposits is equivocal. One possibility is that most of the gravel along the elongate band from Beardsley Grade nearly to Franks Valley is Eocene, but most gravel mapped east of Taylor Lake is younger. The elongate band along the road from Beardsley Grade to Franks Valley may represent the actual course of the stream that deposited the gravels, no matter their age. The ridge-capping nature of the gravels at the west end of the band suggests they are nearly horizontal, and their base appears to gain elevation to the east. Both Diller (1908, p. 61) and McMath (1958, p. 162) reported that there are no Tertiary clasts in the Auriferous Gravels of this area.. However, McMath (1958) did not map the gravels east of Taylor Lake. McMath (1958, p. 162) also reported that in the elongate band, “the progressive appearance of rock types derived from the subjacent Kettle Formation indicates the gravel was carried in a westerly direction. Mc Math (1958, p. 162) also suggested that “the rather continuous east-west trending channel-like segment of gravel on the south side of Kettle Rock is almost certainly bounded on the north by a significant fault.” His evidence for this was that this gravel is almost 1000 ft lower than Auriferous Gravel mapped north of Kettle Rock by Diller (1908, Plate III). However, that gravel is clearly andesite lahar units of probable Miocene age (see the section on Eisenheimer/Rattlesnake Peaks) and thus not related to the channel-like segment. Additionally, more recent mapping by Christe (1987, Plate 2) does not confirm an east-west fault in this area.
The evidence available suggests a west-flowing Eocene stream channel in this area; at the west end, it may turn south to include probable Eocene gravels in the vicinity of Taylor Diggings.
Photos
P148b.JPG Andesite-clast gravel exposed near the top of Beardsley Grade along the Lucky S Mine road.
An area of hydraulicked gravels is present in the area of Mulligan Slide in the W½ Section 32 and the SE¼ SE¼ Section 30, T25N, R8E [P92 to P95]. As at the adjacent Bean Hill area, the historic name of the mine is not known.
The well rounded clasts seen in the hydraulicking debris are similar to those at Bean Hill to the southeast, consisting mainly of white vein quartz and quartzite, with a few meta-igneous clasts and some large (30-50 cm) boulders of ultramafic rock. The underlying bedrock is serpentinized ultramafic rock; the surface is commonly deeply stained by iron-oxide minerals. A speculative upstream course for the lower part of the paleochannel here over a distance of about 1 km is northerly, with a bend to the northwest in the vicinity of Mulligan Slide.
Photos
P92b.JPG Iron-stained serpentinite in stream course overlain by quartz-pebble gravel that was disturbed by hydraulicking. Mulligan Slide area.
Lindgren (1911, p. 111) reported that:
On the north side of the Middle Fork of Feather River, about half a mile west of Nelson Point, is a gravel deposit that was formerly mined by the hydraulic method. Andesitic breccia occurs on the slope to the north and presumably at one time covered the deposit. The occurrence is remarkable as being only about 200 feet above the present Feather River, at an elevation of about 4,000 feet.
Lindgren (1911, p. 111) also stated that Turner (1897) believed this gravel to belong to the epoch of intervolcanic channels.
Sheeks (1977) showed a gravel unit of the Bonta Formation (which is predominantly Miocene andesitic rocks) on preTertiary basement due north of the prominent Feather River meander loop at Nelson Point (NE¼ NW¼ NW¼ Section 15, T23N, R10E) on the Blue Nose Mountain 7.5-minute quadrangle. The gravel is exposed at the level of the North Fork Feather River [P224a], in an apparent channel cut into the Shoo Fly complex. The conglomerate consists of hornblende andesite clasts in an andesite-derived sandy matrix. The beds are nearly flat lying. One or two smooth, rounded clasts of quartzite and pyroxene diorite porphyry were seen in the conglomerate exposed at the river level, and a few clasts from float, apparently derived from somewhat higher in the section, include granodiorite and one clast of the tuff of Campbell Creek. The basal conglomerate is also present, lying on Shoo Fly, about 500 m to the northeast, in road cuts along the La Porte Quincy Highway [P224c]. These two conglomerate outcrop areas apparently lie along a narrow northeast trending channel that marks the south margin of a considerably wider (two km or more) channel to the north that is filled with Lovejoy Basalt and younger andesitic rocks (also see the Spring Garden description).
Except for the trace of an old road across the gravel exposures, I found no indication of hydraulicking; however, because the gravel exposures are near the river level, evidence of mining could have been washed away.
Photos
P224c.JPG Outcrop of andesite-clast conglomerate at level of North Fork Feather River, near Nelson Point.
P224d.JPG Gravel exposed above the level of the North Fork Feather River, near Nelson Point.
P224e.JPG Basal andesite-clast gravel on Shoo Fly along the La Porte Quincy Highway, 1 km north of Nelson Point and the North Fork Feather River.
P224f.JPG Basal andesite-clast gravels at river level in mid distance overlain by darker lahars to upper left; Shoo Fly to near right. North Fork Feather River, Nelson Point.
Lindgren (1911, p. 111) reported that:
The New Nelson placer mine is situated 3 miles northeast of Nelson Point, on the slope of the high ridge overlooking Feather River, the tunnel having an elevation of about 4,500 feet. The channel opened by this tunnel has been followed under the volcanic cover for some distance in a northeasterly direction, and it is believed that it may connect with the gravels at Spring Garden, 3 miles farther to the northeast, or with the channel found in the tunnel of the Western Pacific Railroad near by.
It is difficult to locate this area exactly on modern maps. The distance between Nelson Point and Spring Garden is only about 4.5 mi (on either the modern 7.5-minute topographic maps or those of the Downieville Folio (Turner, 1897). To be on the Feather River side of the ridge, the distance northeast to the New Nelson Mine from Nelson Point would have to be about 2.5 mi. One possible location for the Nelson Point Mine would be in Sections 1 or 2, T23N, R10E. On the Spring Garden 7.5-minute quadrangle, the Johnson Mine is shown as a shaft in Section 2, with an adit to the southwest. The Johnson Mine, located 3.3 km west of Spring Garden (SE¼ NE¼ NE¼ Section 2, T23N, R10E; [P223]) could have been an attempt to explore for gold-bearing gravels at the base of the Miocene andesite sequence. However, a small dump from a caved shaft at the Johnson Mine contains only Tertiary andesite clasts from probable lahars, and there is no evidence that any mined material was processed. An adit shown 600 m to the southwest could not be located in 2004. Old cans and other material at the Johnson Mine are probably from the 1940s or 1950s, although the workings themselves may be older.
Photos
P223b.JPG Pipe and logs in caved shaft(?) at the Johnson Mine (New Nelson Mine area?).
Newton Flat/Emigrant Hill Workings
A number of placer gold deposits were worked by hydraulic and drift methods in canyons 3-5 km north of the town of Quincy. Although no capping volcanic units are mentioned in the literature, it is not possible to determine from the references (MacBoyle,1920a; Clark, 1970) if the age of the gravels is Eocene, Quaternary, or somewhere between. The area that has been worked includes Elizabethtown Flat and Newton Flat, mostly in Section 3, T24N, R9E (Quincy 7.5-minute quadrangle). Apparently Newton is a contraction of Newtown (see Newtown Flat Mine and Newtown Consolidated Placer Mines listed in MacBoyle (1920a, p. 80-81).
Remains of placer workings and water diversion ditches were seen in the vicinity of an Emigrant Trail marker installed by Trails West in NE¼ SE¼ SW¼ Section 3, T24N, R9E [P84]. The marker reads:
Beckwourth Trail-Water erosion. The deep depression above this marker was created when water from a miner's ditch flowed down the emigrant road. The broken ditch may still be seen farther up the [road].
Based on the name, this could be near the Emigrant Hill hydraulic workings or Emigrant Drift Mine mentioned by MacBoyle (1920a, p. 81) and Crawford (1894, p. 215, 219). A few smooth rounded quartz and quartzite pebbles were seen as float in this area.
The Newton Mine [P85] is shown on the topographic map about 1 km to the north of the Beckwourth Trail Marker (SE¼ NE¼ NW¼ Section 3). It is at the site of a very shallow, water filled shaft and trench in Quaternary alluvium. Sparse fragments of vein quartz as well as other rock fragments in the area are subangular.
Based on the sites visited, there is little evidence of Tertiary paleochannels in this area north of Quincy.
Photos
P84a.JPG Beckwourth Trail marker near Emigrant Hill workings.
P84c.JPG Ditch formed by break in water diversion ditch near Beckwourth Trail Marker, Emigrant Hill workings.
Diller's (1908, Plate III) geologic map shows one small outcrop of Auriferous Gravels and several outcrops of Tertiary rhyolite and overlying basalt on a ridge 1-3 km north of Paxton (approx. Sections 4, 8, and 9, T25N, R9E; Crescent Mills 7.5-minute quadrangle). These are shown as Tertiary colluvium on a map by Wakabayashi and others (1994, Appendix 3-2). Only a few, poorly rounded clasts of slate were seen during a 2003 visit, but rhyolitic welded ash-flow tuff (Diller's rhyolite) was observed lying on Paleozoic marine rocks (Lyndon and others, 1960) on the ridge crest (SW¼ SW¼ SW¼ Section 4, T25N, R9E; [P167]). This ash-flow tuff is very similar to a tuff which overlies colluvium east of Lake Almanor along Highway 89 (see the description of the Union Pacific Railroad cut, 3 km east of Canyondam elsewhere in this report; Wakabayashi and Sawyer, 2000, p. 204-205). That tuff is correlated with the ~2.8 Ma volcanic rocks of the Yana volcanic center located in the vicinity of Butt Mountain (Mt. Butte of the Susanville 1x2-degree sheet), 20 km east of Lake Almanor. Thus, clastic (?) and volcanic rocks north of Paxton are probably Pliocene, and not Eocene Auriferous Gravels or Oligocene ash-flow tuffs.
Turner (1897, Economic Geology map) showed a small area of Auriferous Gravel on a ridge northeast of Haskins Valley and about 4 km south of the Monte Cristo Mine. The area as shown on the map is surrounded by Turner's younger, “Neocene” andesite. The area is projected to be in Center NE¼ SE¼ Section 1, T23N, R7E, Haskins Valley Quadrangle. Examination on the ground along a U.S. Forest Service road [P177] found exposures of rounded cobbles of Tertiary basalt and andesite (and one of granitic rock) in an andesite mud matrix. Thus, there is no indication here of Eocene gravels or even reworked clasts from such gravels, and thus no suggestion of an Eocene paleochannel nearby.
Grose (2000a) showed a small area of outcrop of ash-flow tuff about 300 m north of the Portola McLears Road (County Road 114) in SE¼ NE¼ NE¼ Section 16, T22N, R13E; Blairsden 7.5-minute Quadrangle. The ash-flow tuff here is only observed in float, but the amount of float and the angular fragments suggest that in-place tuff underlies the float (locality [P130]). The tuff contains phenocrysts of feldspar, quartz, and biotite. It is not readily correlated with tuffs of the Reno, Nevada area, although it could be tuff E of the Haskell Peak area (Brooks and others, 2003). The tuff lies on Cretaceous granodiorite and is overlain by Miocene andesitic lahars. See also the description of the Calfpasture Creek area.
The name Pride Mine is applied to an adit symbol (drift?) on the Haypress Valley 7.5-minute quadrangle in NW¼ SW¼ NW¼ Section 13, T20N, R12E. The working is one of several for 1-1.5 km along Williams Creek, about 6 km northeast of Sierra City. The Pride Mine was reported (Averill, 1942) to have worked morainal material and gravel derived from the erosion of a northern continuation of an Auriferous Gravel channel that was mined at the Hilda and 1001 Mines to the south. Averill (1942) also reported that boulders as much as 5 tons were found in the ground.
At the head of Williams Creek, a probable hydraulic mine site in Auriferous Gravels was visited in 2004 [P228]. The gravels, which underlie Oligocene rhyolitic ash-flow tuffs exposed nearby, consist of poorly sorted, sub-rounded to rounded pebbles, cobbles, and sand of metavolcanic and granitic rocks, and minor gray and black chert, dark quartzite(?), and one granite with black tourmaline. About 0.8 km to the south, along the road, rhyolite ash-flow tuff crops out. At least two tuffs are exposed; they resemble tuffs from the lower part of the Oligocene ash-flow tuff section, possibly the tuffs of Axehandle Canyon and Rattlesnake Canyon (see Henry and others, 2003a, for descriptions). .These two tuffs, referred to as tuff A and tuff B, respectively, are present at Haskell Peak about 8 km to the north-northeast (Brooks and others, 2003). Additionally, the gravels below the tuffs at Haskell Peak contain clasts that are similar to those observed at the head of Williams Creek. The presence of similar tuffs and gravels support the projection of a paleochannel northward from the Hilda Mine, through the 1001 Mine and the Pride Mine, to Haskell Peak.
Photos
P228d.JPG Auriferous Gravel exposed at the head of Williams Creek above the Pride Mine.
The area of Red Clover Creek has been a site of considerable interest to geologists because rhyolitic ash-flow tuffs, Lovejoy Basalt, and Miocene andesitic lahars, breccias, and flows all crop out in an aerially restricted site where stratigraphic relations can be observed. Unfortunately, the area is geologically complex because volcanic units were deposited as canyon fill rather than as sheets (Wagner and others, 2000). Younger units can be found deposited in canyons, topographically below older units. It is now clear from geochronologic and field studies elsewhere that the Tertiary stratigraphic sequence in the Plumas county area is, from bottom to top: Auriferous Gravels (Eocene), rhyolitic ash-flow tuffs (probably entirely Oligocene), Lovejoy Basalt (16 Ma), and Miocene andesitic rocks. There is evidence for some andesitic rocks older than the Lovejoy (e.g., Wagner and others, 2000), but it seems likely that such rocks are of limited extent.
Rhyolitic ash-flow tuff is exposed, apparently in place, just west of the intersection of the Beckwourth-Genesee Road with the road to Thompson Valley (near the south quarter corner of Section 4, T24N, R13E, Grizzly Valley 7.5-minute Quadrangle; [P16]). This tuff resembles the sanidine-plagioclase-biotite tuffs from Black Mountain to the northeast and adjacent Nevada (Garside and others, 2003) that are known to be older than about 28.8 Ma.
Areas of poor exposure that include float fragments of ash-flow tuff similar to the above can be seen at a number of sites in Sections 28, 29, 32, and 33, T25N, R13E, on a ridge 1-2 km north of Red Clover Valley ([P109, P110, P111, P112]). In addition, clasts of ash-flow tuff and granite in andesite lahars can be see locally. The exact stratigraphic relationships are not clear in this area (see Wagner and others, 2000); it is possible that all ash-flow tuff is present as small to large clasts in andesite lahars. However, even in that case, subcrops of ash-flow tuff are probably nearby below the lahars. The area is certainly one where ash-flow tuffs, Lovejoy, and andesite lahars are deposited in a paleovalley, probably the northeast continuation of a paleovalley containing Auriferous Gravels on Grizzly Ridge about 12 km to the southwest.
Richmond Hill, Sawpit (Sawpit Flat), Union Hill
Turner (1897) described Auriferous Gravels and mines in the area northwest of Onion Valley. He speculated that the area was on a channel that connected from the Union Hill Mine southwest to Sawpit, to Richmond Hill, and then (through the Feather Fork Mine area) to quartz gravels under the alluvium of Little Grass Valley (now covered by Little Grass Valley Reservoir). This proposed northeast-trending channel is parallel to but about 4 km north of the better-known La Porte-Hepsidam channel. Hietanen (1981, p. 30) makes a similar suggestion for this north branch of the La Porte fork, which probably connects to the main La Porte channel near La Porte (e.g., Lawler, 1995). This northerly channel is also shown connecting to Sawpit by Clark (1965).
Turner's (1897, Economic Geology map) map shows the Richmond Hill hydraulic mine near Onion Valley Creek, in approximate NW¼ SW¼ Section 6, T22N, R10E, Onion Valley 7,5-minute Quadrangle. This area may have been placered, but most of the Auriferous Gravels crop out and were worked in the NW¼ Section 6 (see Hietanen, 1981, Plate 1). The area of most extensive hydraulicking is at and to the southwest of the Mine symbol [P62] on Bird Creek in NW¼ Section 6 near the border with Section 31 of T23N to the north. The paleochannel thalweg appears to go southwest from this point about 200 m and then turn south for about 300 m. The pregravel surface is red, deeply weathered phyllite. Tertiary white claystone with layers of lignitic material (photos) is exposed along the east wall of the mined area. The claystone lies on the red, weathered phyllite. No leaves were observed in the lignitic material, just pieces of carbonized wood and stems. The claystone beds dip about 3° or 4° to the west. Most of the gravel was apparently hydraulicked, leaving only piles of cobbles and a few remnant areas of limonite cemented quartz pebble conglomerate and pebbly sandstone. Most of the clasts are white quartz.
Turner (1897, Economic Geology map) showed a drift near Sawpit and reported that “at Sawpit there is said to be white quartz gravel under the black basalt.” The drift could not be located in 2003; it probably should be in NW¼ SE¼ Section 31, T23N, R10E on Monitor Flat about 0.5 km northwest of Sawpit Flat. MacBoyle (1920a, p. 78) reported an 800 ft (about 250 m) drift in the area. No gravels are found in this area on Sawpit Flat; most of the area is underlain by Lovejoy Basalt. The Lovejoy apparently lies in a channel in which the Auriferous Gravels were cut out before Lovejoy deposition. There certainly could be gravels entirely concealed by the Lovejoy. Hill (1972, p. 50) reported that two diamonds have been found in gravel at Sawpit Flat.
MacBoyle (1920a, p. 74) described the possibility of two paleochannels in the Sawpit area. One of these was said to cross Onion Valley Creek about one-fourth mile west of the mouth of Bird Creek. If these features are correctly named on the present Onion Valley 7.5-minute map, this would be in the area of the east half of Section 2, T23N, R9E; the Williams and Dorf Mine is shown in the center of that section, near the base of the andesitic rocks (Hietanen, 1981). That mine was not visited during this study.
The Union Hill Mine is a hydraulic mine located near the center of NW¼ NE¼ Section 5, T22N, R10E, at the Gravel Pit symbol [P39] just east of County Road 511 (the Quincy La Porte Road) about 1 km north of Onion Valley. Gravel has been mined there more recently. Over 50 m of white gravel with clay-rich lenses is exposed in the west pit wall. The gravel is overlain at about the elevation of the highway by Miocene andesite lahars; no Lovejoy Basalt is present. The bedrock underlying the channel is light gray phyllite of the Silurian Shoo Fly Formation. The gravel clasts are mostly 1-15 cm in diameter, but rarely up to 1 m long. They consist of 60-70% white quartz, with the remainder phyllite and quartzite of the Shoo Fly. One clast with quartz eyes could be silicic metavolcanic rock. The matrix of at least some conglomerates is limonitic. Based on nearby Shoo Fly outcrops and the gravel exposures, the channel appears to trend northeast and be no more that 200-300 m wide in its lower part. This channel could be the continuation of the Richmond Hill-Sawpit channel to the west, or more likely, a side channel to a main channel 2 km to the north (under Finger Board hill) where Auriferous Gravel has been cut out by postgravel, preLovejoy erosion in the same channel.
Auriferous Gravels in this area lie beneath the 16 Ma Lovejoy Basalt. The stream channel that the Lovejoy flowed down appears to project northeast (upstream) from the La Port area to Sawpit Flat and then across the Plumas Trench (Durrell, 1987) to the Cascade Mine or Grizzly Ridge and then to Red Clover Creek (also see Durrell, 1987, Fig. 80). It appears likely that the channel Lovejoy flows followed was cut along one or more Eocene Auriferous Gravel channels. Drainage was apparently to the southwest from the Eocene to at least 16 Ma (Lovejoy).
Photos
P39a.JPG Conglomerate at Union Hill Mine (Sawpit Flat area). Hammer is 32 cm long.
P39c.JPG Gravel quarry face at Union Hill Mine.
P39d.JPG Boulder at Union Hill Mine. Hammer is 32 cm long.
P62d.JPG Block of quartz-pebble conglomerate of the Auriferous Gravel, Richmond Hill workings. Ruler is 15-cm.
P62f_12.JPG White pipe-clay beds lying on weathered phyllite, Richmond Hill workings.
P62h_pipe.JPG Flattened 18-in. riveted steel pipe at Richmond Hill workings; white pipe-clay beds in background. Hammer is 32-cm.
P62i_15wood.JPG Black fragment of wood in Auriferous Gravel at Richmond Hill workings. Ruler is 15-cm.
P62j_18pipeclay.JPG Pipe clay exposed in worked face at Richmond Hill workings.
P62l_19clast.JPG Rounded boulder with attached limonite-cemented sand matrix, Richmond Hill workings. Hammer is 32 cm long.
P62n_21Lovejoy.JPG Outcrops of Lovejoy Basalt, which overlies Auriferous Gravel east of Richmond Hill workings.
P62o_22distance.JPG White outcrops of Richmond Hill workings viewed from the Quincy-La Porte Highway.
Grose (2000c) showed rhyolitic ash-flow tuff capping a granodiorite hill northwest of Ross Ranch Meadow (NW¼ SW¼ SE¼ Section 28, T23N, R18E, Portola 7.5-minute quadrangle; [P68]). This area is just south of the Middle Fork Feather River about 4.5 km east of Portola. The ash-flow tuff appears, based on a 2003 visit, to be the tuff of Campbell Creek, although it is hydrothermally altered to clays. About 30 m of tuff lies on biotite granodiorite, which is weathered and red colored below the tuff. The tuff is sub-horizontal, based on the orientation of its lower contact.
Grose (2000c) also showed an area of ash-flow tuff in the vicinity of the Ramelli Ranch, about 5 km east of Portola on State Highway 70 and 1.5 km north of the area described above. Strongly hydrothermally altered rock that is exposed in a road cut north of the highway from the Davis Rest Stop and about 300 m southwest of the Ramelli Ranch (NE¼ NW¼ NE¼ Section 28, T23N, R18E; [P17]) could be ash-flow tuff, but original textures and minerals have been almost entirely destroyed. No outcrops of ash-flow tuff could be found in the vicinity of the altered road cut exposure.
MacBoyle (1920a, p. 5) reported that Auriferous Gravels of an ancient stream had been mined one-third of a mile northwest of Round Valley Reservoir. There is some indication of land disturbance by placer mining about 1 km northwest of Round Valley Reservoir [P165] in NE¼ NE¼ NW¼ Section 16, T26N, R9E (Crescent Mills 7.5-minute Quadrangle). All the cobbles observed in alluvium were subrounded and included Tertiary volcanic rocks. This area is reported to be the area of the placer mine of G.H. Wolters in glacial gravels along Long Valley Creek (Edman, 1905). Apparently gold values are found under the Reservoir as well (Edman, 1905; Bumsted, 1916). No indications of older Tertiary gravel were found in the area.
Photos
P165a.JPG Round Valley Reservoir.
P165b.JPG Dam at Round Valley Reservoir.
Rhyolitic ash-flow tuff (the tuff of Sattley; Grose, 2000d) crops out in a road cut on California State Highway 49 about 2 km NW of Sattley (SW¼ NE¼ SW¼ Section 32, T21N, R14E; Calpine 7.5-minute quadrangle; [P179]). The ash-flow tuff contains phenocrysts of sanidine, plagioclase, pink to slightly smoky, vermiculated quartz, and biotite. The tuff is nearly horizontal, only slightly welded, and lies on Cretaceous granodiorite. The tuff does not appear to be as extensive in the Sattley area as shown by Grose (2000d) on his Sierraville 15-minute quadrangle geologic map. The tuff is also present in a road cut about 2 km farther northwest along Highway 49 [P180]. A similar, although highly altered, tuff is exposed below andesite flows about 11 km to the east, in Antelope Valley (approx. center Section 33T21N, R15E) (this study, Young and Cluer, 1992).
This tuff probably correlates with the tuff of Campbell Creek (e.g., Garside and others, 2003; Henry and others, 2003), which is present in several northern California Eocene-Oligocene paleovalleys from the Diamond Mountains to Interstate 80. The tuff of Campbell Creek is 28.67 Ma on Dogskin Mountain north of Reno, Nevada (Henry and others, 2003). The tuff of Sattley was previously dated (Dalrymple, 1964) at the road cut [P179] by K-Ar methods on plagioclase (28.8 Ma) and sanidine (16.5 Ma); ages were converted to new constants using the table of Dalrymple (1979). Dalrymple (1964) considered the plagioclase age to be too old and the sanidine age more likely; however, it now appears that the plagioclase age is probably correct while the sanidine age is clearly too young.
A thick ash-flow tuff section crops out south and southwest of the community of Soda Springs. About 4 km south of Soda Springs, along Serena Creek, the Nine Hill Tuff, Mickey Pass Tuff (ca. 27 Ma), and older 28-31 Ma tuffs crop out (C.D. Henry, oral commun, 2003) in a probable south trending paleovalley (also see Deino, 1994). The tuff of Campbell Creek crops out [P198] south of Kilborn Lake, about 3 km southwest of Soda Springs, near Emigrant Trail Marker T-43 of the Trails West organization. Fossil leaves of probable Eocene age have been found about 1.6 km south of Soda Springs (Howard Schorn, written commun., 2001).
Photos
P198a.JPG Trails West emigrant trail marker for trail through boulder field, 3.3 km southwest of Soda Springs. Glacial erratics sit on flat surface of the tuff of Campbell Creek.
Saucedo and Wagner (1992) showed an area of Oligocene rhyolite (commonly ash-flow tuff) south of Donner Lake along and below the railroad tracks. In a 2003 visit, I could find no outcrops of silicic volcanic rocks. The Miocene andesitic lahars directly overlie Cretaceous granitic rock or crop out near the lake shore along most of the south side of the lake.
Photos
P186b_Donner_L.JPG Donner Lake, looking east.
Grose (2000c) showed an area of altered silicic tuff over an area of about 2.5 km2 located 0.5-1.5 km south of the south end of Lake Davis. The area is in Sections 11 and 12 of T23N, R13E, mainly on the Portola 7.5-minute Quadrangle. I could find no outcrops of silicic tuffs in the area; all of the light colored rocks examined were clay-altered Miocene andesite. Thus, no early Tertiary paleovalley is projected through this area.
Diller (1895) shows “Neocene” rhyolite capping a ridge about 4 km south of Prattville. I project this as the ridge on either side of the boundary between Section 23 and 26, T27N, R7E. A field examination (2003) found that the high area of the Section 23 part of the ridge [P100] is capped by dark gray, locally vesicular, pyroxene andesite. However, light gray rhyolitic welded ash-flow tuff does crop out at a lower elevation (about 5080 and 5180 ft) on either side of the ridge (NW¼ SW¼ SW¼ and SW¼ NW¼ SE¼ Section 23, T27N, R7E; [P98, P99]). This ash-flow tuff is probably the ~2.7 Ma tuff from the Yana volcanic center (see the section on the Union Pacific Railroad cut and elsewhere). If so, the tuff was probably deposited in paleovalleys more than 800 ft (250 m) above the present drainages. The ash-flow tuff is not similar to Oligocene ash-flow tuffs that are found in early Tertiary paleovalleys; thus there is no evidence of such tuffs in this area. The andesite could be considerably older, possibly Miocene, and similar to rocks to the south of the North Fork of the Feather River near Spanish Ranch (e.g., Hietanen, 1971).
Photos
P98a.JPG Sample of light gray rhyolitic ash-flow tuff (from the Yana volcanic center?) from area south of Prattville; pen is 13 cm.
Diller (1895) showed small areas of “Auriferous Gravels of ancient streams,” termed “Necoene ” gravels, approximately 1-3 km southeast of the present site of the community of Canyondam (in the vicinity of Sections 26 and 35, T27N, R8E; Canyondam 7.5-minute Quadrangle). His map also shows areas of “Neocene” rhyolite somewhat higher in the hills to the south. Locally, in this area, one can see (2003 visit) yellowish colluvium lying on Paleozoic marine rocks and Mesozoic granitic rocks. Some of this colluvium consists mostly of clasts of slate with fewer of unaltered basalt; in some outcrops, the clasts are subangular. Rhyolitic ash-flow tuff was seen along a U.S. Forest service road in SW¼ Section 26, T27N, R8E. That tuff was similar to tuffs at other sites in the Greenville-Canyondam area that have been related to the ~2.7 Ma Yana volcanic center. Thus, areas of Neocene gravel shown by Diller (1895) in this area are probably Pliocene.
In an area of reclaimed mine workings in SW¼ Section 26, T27N, R8E [P102] I noted several large blocks of distinctive jasper with white quartz veining. This material probably was mined nearby. It closely resembles the jasper seen in outcrop at Taylor Diggings and in clasts at several other sites.
Photos
P102a.JPG Yellowish Pliocene colluvium with basalt clasts exposed near pond southeast of Canyondam.
P102d.JPG Red jasper and specular hematite veined with white quartz in a block of rock from the area southeast of Canyondam.
Turner's (1897) map of the Downieville Quadrangle shows Auriferous Gravel and hydraulic sites at the end of a ridge about 2.5 km northwest of the present site of Spring Garden (Center, E½ SE¼ Section 25, T24N, R10E; Spring Garden 7.5-minute quadrangle). MacBoyle (1920a, p. 37) reported that hydraulic mining had been carried on in late Tertiary gravel three-fourths of a mile northwest of Spring Garden Ranch. This was probably based, at least in part, on Turner's (1897) description that a mass of volcanic gravel had been mined by the hydraulic method there. Gravels are exposed in a road cut [P27] along California State Highway 70 near Williams Loop, essentially at the site of Turner's locality. These gravels consist of about 90% andesite clasts, predominantly hornblende andesite. They are, therefore, considered to be a part of the Miocene andesitic sequence, thus a fluvial sand and gravel unit of Grose's (2000a) map unit Thp, and not Auriferous Gravel. The gravels and associated andesitic rocks are similarly mapped as either Penman Formation or Penman and Bonta Formations undivided by D'Allura (1977) and Sheeks (1977), respectively. Clark (1970, p. 124) reported recent prospecting (presumably somewhat before 1968). No evidence of hydraulicking or other prospecting was observed during a 2003 visit. However, placer gold may be locally present in the gravels, possibly derived from erosion of nearby Auriferous Gravels.
The road-cut gravel exposure appears to be near the north edge of an east-west trending paleochannel that was in existence at least as long ago as the time of Lovejoy Basalt deposition (ca. 16 Ma). Lovejoy basalt may have flowed across a low divide between two channels in this area, allowing Lovejoy flows to travel southwest toward La Porte as well as west toward Bucks Lake and Walker Plains. This scenario requires a reinterpretation of many of the Tertiary-preTertiary fault contacts of Sheeks (1977) as buttress unconformities. An outcrop of Shoo Fly Formation nearly 2 km west of Fells Flat (NW¼ Section 10, T23N, R10E) may be a hill where the two Lovejoy channels divided. The Nelson Point Mine (see description elsewhere in this report) is located along the south side of the postulated paleochannel.
A potato-shaped approximately 7 Troy(?) pound nugget was found along the edge of a tributary to Squirrel Creek (which joins Greenhorn Creek just west of the area of gravel exposed in the road cut) in 1933 (newspaper clipping in display case at Plumas-Eureka State Park). The nugget contained rose quartz as well as gold, and was reported to be at the Smithsonian National Museum. The discovery area is probably 1 to a few km northeast of the highway road cut. Based on the contained quartz, it may not have traveled far.
The Squirrel Creek Mine is shown in SE¼ SW¼ SW¼ Section 3, T22N, R11E, on the Johnsville 7.5-minute Quadrangle. Turner (1897, Economic Geology map) shows the Squirrel Creek hydraulic site in approximately the same area. The mine is apparently the same or near the Garfield Flat Mine and Grizzly Bear Mine of Crawford (1896, p. 294, 297). No Auriferous Gravels are shown in the area on a map by Grose (2000a); however, Quaternary alluvium is shown by Saucedo and Wagner (1992).
The area of the mine appears to have been placer mined. Piles (photo) of mostly subrounded boulders and large cobbles (10 to >30 cm) were seen at the edges of and between drainages [P30]. A few percent of the clasts are white bull quartz, but most are phyllite. Wooden stave pipe (photo) and a small pond with eroded dam are probably related to hydraulicking as described by Crawford (1896, p. 294). There is no indication of well rounded, highly polished clasts, and the area is over 400 m below the base of the overlying Tertiary andesite. These gravels are almost certainly Quaternary.
Photos
P30a.JPG Coarse reject piles of subrounded boulders and cobbles at the Squirrel Creek Mine.
P30b.JPG Spiral-bound, 12 in wooden stave pipe, Squirrel Creek Mine.
P30c.JPG Spiral-bound, 12 in wooden stave pipe, Squirrel Creek Mine.
P30d.JPG Dry stone facing on old dam, Squirrel Creek Mine.
Turner (1898) described the Sweet Oil Diggings as being at the head of Dogwood Creek, where he reported some gravel capped by “the older black basalt.” The gravel clasts seen in a shaft that penetrated the basalt were said to include mostly white quartz, but also quartzite ,siliceous argillite, and variegated breccia. Lindgren (1911, p. 100) reported that:
The gravels of the Sweetoil diggings, at the head of Dogwood Creek, were probably in some way connected with those of Little Grass Valley and La Porte. The bedrock elevation is about 4,600 feet, and the narrow trough filled with gravel is covered by some basalt, and above this several hundred feet of andesitic breccia.
Hietanen (1973, Plate 2) showed a small area of Ts, auriferous stream deposits, in this general area, under the Lovejoy Basalt. This area of outcrop is at the nose of a ridge in N½ S½ SW¼ Section 18, T22N, R9E, Dogwood Peak 7.5-minute Quadrangle. Based on an interpretation of the location of Sweet Oil shown by Turner (1898), it should be located about 800 m northeast of the Hietanen outcrop.
I was unable to find any gravel deposits in the area of the Hietanen's (1973, Plate 2) Ts. The Lovejoy Basalt appears to sit directly on the preTertiary rocks [P114], although one highly polished pebble of black chert was observed in float. In the area of the projected site of Sweet Oil (SE¼ NW¼ Section 18, T22N, R9E) no indication of mining was seen; however, near the base of the Lovejoy [P115] on granodiorite and diorite, I observed smooth white quartz pebbles and some red metasandstone pebbles in float along an abandoned road. One quartz pebble had a patch of attached iron-oxide-cemented sand matrix, suggesting that it did not travel far from its source conglomerate. Nearby, I found several cobbles (up to about 15 cm long) of light greenish gray to white ash-flow tuff. The ash-flow tuff clasts contain phenocrysts of plagioclase, sanidine, biotite, and quartz; at least some of the quartz phenocrysts are distinctly wormy (vermiculated). Some cobbles of Lovejoy Basalt are also seen in float along the road.
There is only indirect evidence for an Eocene paleochannel at Sweet Oil Diggings. The ash-flow tuff cobbles are soft and could not have traveled far or been recycled. They are, it would seem, evidence of erosion from nearby tuff outcrops some time after deposition. If these cobbles are from the tuff of Campbell Creek (ca. 28.6 Ma), then erosion would postdate that. By analogy with other areas, the tuff probably was deposited in a paleocanyon somewhere in this area. The quartz pebble with attached matrix is similar to pebbles seen in areas of eroded or hydraulicked Auriferous Gravels. The Lovejoy clasts in float were derived either from interflow erosion or have been transported downhill from gravels in the overlying andesite lahars. The above reasoning, when combined with Turner's (1898) description of gravel clearly below the Lovejoy, suggests that the most likely interpretation is that the gravel float seen at Sweet Oil Diggings represents a pre Lovejoy (ca. 16 Ma) and post 28.6 Ma paleovalley that Lovejoy Basalt later flowed down (from Thompson Peak in the Diamond Mountains south and southwest through the Red Clover Creek area and past La Porte and Little Grass Valley Reservoir. Sweet Oil is, speculatively, the western-most area of Oligocene ash-flow tuffs in Plumas County. It is along the north margin of a southwest striking band of Lovejoy and the presence of clasts of probable Auriferous Gravels, ash-flow tuffs and Lovejoy in the same area suggests that the channels remained in the same area for a considerable period. If the gravels at Sweet Oil represent deposits in an Eocene paleovalley, its connection with nearby channels is speculative. Possibly the channel connected to the south with the La Porte–Hepsidam channel.
Photos
P115a.JPG Rounded and polished quartz clasts found in float near possible site of Sweet Oil Diggings. One clast has attached, iron-oxide cemented matrix. Hammer head is 18 cm.
P115c.JPG Rounded cobbles of tuff of Campbell Creek(?) found in float near possible site of Sweet Oil Diggings; pen is 13 cm.
Turner (1898, Economic Geology map) showed “Neocene” gravel along a stream drainage just south of an area now called Tamarak Flat (name applied in the Meadow Valley Quadrangle 7.5-minute Quadrangle). The area is the approximate NE¼ Section 11 and NW¼ Section 12, T23N, R8E (Dogwood Peak 7.5-minute Quadrangle). Hietanen (1973, Plate 2) showed only Lovejoy and Miocene andesitic lahars in this area. Although smooth, well rounded clasts of preTertiary rock are seen as float in this area (vicinity of [P121]), clasts of Tertiary basalt (Lovejoy?) and andesite are just as common. All the cobbles appear to be concentrated along the present drainage; probably the gravel is Quaternary and the smooth preTertiary clasts have been recycled from older (Miocene or Eocene) units. Thus, there is little firm evidence of an Eocene paleovalley in this area.
Diller (1908, p. 61) described Taylor Diggings as being located “a mile northeast of the summit of Mount Jura.” On Diller's (1908) Plate III, the diggings are shown in a creek bottom just downstream from an outcrop of Auriferous Gravel. If this location is plotted on the modern Taylorsville 7.5-minute quadrangle, it is located in approximately NE¼ SW¼ NE¼ Section 31, T26N, R11E. This is approximately 1 mile northeast of Mount Jura, and in Hinchman Ravine as shown on the Taylorsville 7.5-minute quadrangle. However, Diller (1908, Plate III) applied that name to a canyon about 0.8 km to the east. The Taylorsville 7.5-minute topographic map labels an adit in Section 29, T26N, R11E as Taylor Diggings; this is obviously in error, as the workings there are on hematite mineralization in Paleozoic rocks (see below for a description of the geology at that site). Diller's description of the Auriferous Gravel and placer workings at Taylor Diggings are quoted below:
Taylor Diggings, a mile northeast of the summit of mount Jura, were operated years ago by a ditch from Taylor Lake, near Kettle Rock, and expose about 100 feet of gravel, at the bottom of which lies a bed of impure lignitic coal about 5 feet in thickness. Prospect tunnels have been run into this bed for a short distance to the west and south and about a ton of coaly material removed and tried for blacksmithing. The coaly material lies on Jurassic bed rock and is overlain by gravel, varying in size, but through a thickness of 100 feet rarely as much as 6 inches in diameter. The pebbles are chiefly metarhyolite, like the rock so well exposed along the eastern slope of Grizzly Mountains. The remaining pebbles are for the most part granite and basic igneous rocks, some of which are rich in pyroxene.
Remnants of the 45 km-long ditch used to transport water from Taylor Lake (photo) to the diggings can be seen at a number of places along the “road to Lucky S Mine” as identified on Diller's (1908, Plate III) map. Ditches were reported to be under construction in ca. 1896 (Crawford, 1896. p. 289). The gravels at Taylor Diggings were reported to be four 4-60 ft thick and to carry fine gold throughout (Crawford, 1896. p. 289).
The Auriferous Gravels can be examined in float on a ridge above the probable location of Taylor Diggings, along a road on the flank of Mount Jura in NE¼ NW¼ NE¼ Section 31, T26N, R11E [P149]. The mostly well-rounded clasts observed in float range from a few to about 20 cm in diameter. Except for fine-grained, resistant rock types, they are not highly polished. The lithologic types of the clasts include: light-gray biotite meta(?)-andesite, pyroxene meta(?)-andesite, aphyric meta-basalt(?), light- and dark-gray chert, aplite, granite, and quartz-eye porphyry. The more rare clast lithologic types include pyritic black-tourmaline breccia, black-tourmaline-veined granitic rock, white vein quartz, and white-quartz-veined red jasper. The Auriferous Gravels lie nearby on Jurassic (McMath, 1958, Plate 2) slightly foliated meta-andesite. The probable source of the tourmaline-bearing clasts is porphyry- and vein-type mineralization associated with the Lights Creek stock about 15 km to the north (e.g., McFarlane, 1981; Putman, 1975). The jasper clasts were probably derived from an area of bedrock outcrop of hematite and jasper nearly 2 km to the northeast (see below). The coal mentioned by Diller (1908; see above) is in a similar stratigraphic position to coal reported from Lights Canyon (McFarlane, 1981; see description elsewhere in this report).
The short adit that is incorrectly labeled Taylor Diggings on the Taylorsville 7.5-minute quadrangle in NW¼ NW¼ SE¼ Section 29, T26N, R11E [P72] explores a N20°W, 70°SW zone of banded red jasper and specular hematite in pods 0.5 to 1 m thick. The wall rock is red siltstone. The jasper zone appears to be parallel to compositional layering in the wall rocks, which include probable subaqueous intermediate pyroclastic volcanic rocks; these rocks are in the Carboniferous Peale Formation (Grose and others, 1990b). The jasper and specular hematite probably represent metamorphosed submarine exhalative deposits. Diller (1908, p. 85) reported that pebbles of red jasper are found in conglomerate of the Jurassic Kettle tuffaceous meta-andesite and that the jasper may come from Carboniferous rocks; this comment suggests that the jasper pebbles found at Taylor Diggings and Wards Diggings could be recycled from pebbles in Jurassic clastic units as well as derived directly from the Peale Formation. About 200 m to the east of the adit, along the road and near the remains of an old cabin [P72a,b] (photo), cobbles observed in float consist of volcanic-pebble conglomerate, feldspar porphyry, and jasper. These cobbles apparently represent float from poorly exposed Auriferous Gravel on the ridge immediately to the east.
Photos
P72f_jasper.JPG Jasper from bedrock mineralization near Taylor Diggings.
P149c.JPG Clasts from Auriferous Gravel in the vicinity of Taylor Diggings, including red jasper and black tourmaline-veined granitic rock.
P150.JPG Remains of ditch from Taylor Lake that provided water for hydraulicking at Taylor Diggings.
P151a.JPG Taylor Lake, water supply for placer mining at Taylor Diggings.
P151c_69.JPG Dam on Taylor Lake, constructed to provide water for placer mining at Taylor Diggings.
Union Pacific Railroad cut, 3 km east of Canyondam
Wakabayashi and Sawyer (2000, p. 204-205) describe exposures in railroad cuts of the Union Pacific Railroad just north of California State Highway 89 about 3 km east of the community of Canyondam (N½ NW¼ Section 25, T27N, R8E, Canyondam 7.5-minute Quadrangle). They reported that yellowish, iron-stained colluvium is capped by light gray, welded ash-flow tuff. This relationship can be observed (2003) for at least 0.5 km along the tracks (particularly at [P101_16]. This ash-flow tuff is correlated with the ~2.7 Ma Yana volcanic center about 25 km to the east at Butt Mountain (also see the Greenville and north of Paxton descriptions). Wakabayashi and others (1994b, Figure 1) show an extensive area of Tertiary colluvium north of Highway 89 between Greenville and Canyondam. Presumably this entire area of colluvium is also Pliocene, and thus does not represent deposits in an Eocene paleovalley.
Photos
P101b.JPG Light gray ash-flow tuff (from the Yana volcanic center?) lying on yellowish Pliocene(?) colluvium exposed in a Union Pacific Railroad cut, 3 km east of Canyondam.
Upper Dutch Diggings (La Porte)
Upper Dutch Diggings is an area of extensive hydraulic mining along Rabbit Creek about 1 km northwest of the town of La Porte (La Porte 7.5-minute quadrangle). Although placered gravel material is seen for over 1 km along the creek, the area of outcrop of the unmined sediments is in SE¼ NE¼ Section 8 and SW¼ NW¼ Section 9, T21N, R9E (Hietanen, 1981, Plate 1). The area examined in this study was the face exposed by hydraulic mining in NE¼ SE¼ NE¼ Section 8 [P113]. This exposure is the site of a collection of Eocene fossil leaves (Chaney, 1932, p 300-301; Millar, 1996) as well as an area of considerable interest regarding the stratigraphic position of the Lovejoy Basalt and the age of a tuff at the top of the exposed section. The sediments exposed in Upper Dutch Diggings have been described by numerous workers.
Durrell (1959, p. 166) described well rounded pebbles and cobbles of white and black weakly metamorphosed chert at La Porte that he believed had their source in the Paleozoic rocks of central or northern Nevada. He also (Durrell, 1959a, p.167) thought that the Lovejoy Basalt was older than the fossiliferous tuff at La Port because “large numbers of slightly rounded fragments of Lovejoy basalt, two of which are about 25 feet in diameter, are embedded in the lacustrine clays that overlie the Auriferous Gravels and are overlain by the fossiliferous tuff.” However, Dalrymple (1964, p. 15) reported that the basalt fragments were float on the steep surface exposures.. The Lovejoy is now known to be ca. 16 Ma, so Dalrymple's assessment of the evidence at Dutch Diggings appears correct. I did not see any basalt blocks in or on the exposed sediments.
Plagioclase from the La Porte leaf-bearing tuff was dated using K-Ar methods by Dalrymple (1964, p. 14) at 32.5 Ma (33.3 Ma using new constants). He reported that the hypersthene dacite vitric tuff unconformably underlies andesite mudflow and appears to fill a small channel cut in carbonaceous lacustrine clay and arkose which overlie the Auriferous Gravels (Dalrymple, 1964, p. 13). MacGinitie (1941, p. 85) reported that the La Porte flora is found in a dacite tuff, and that there is an erosional break between the sedimentary formation containing the fossiliferous tuff and the underlying white quartz gravels of the Ione Formation (the Auriferous Gravels).
The light gray lignitic siltstones exposed at the head of Upper Dutch Diggings [P113] are nearly flat lying. They appear to overlie coarse white-quartz gravel near the base (see MacGinitie, 1941, Fig. 1). Where incompletely disaggregated pieces of gravel are seen in placer debris, chert and quartz pebbles and sand are cemented by iron-oxide minerals. The beds are overlain by younger Tertiary andesitic laharic rocks (see Hietanen, 1981, Plate 1). The underlying gravels must be part of the La Port channel, which trends upstream to the northeast from here toward the Thistle Shaft and Gibsonville. The lignitic siltstones resemble rocks exposed at the limit of hydraulicking in the Richmond Hill deposit about 12 km to the north on a separate paleochannel. Additionally, thick beds of clay are reported from the paleochannel above La Porte at the Thistle Shaft and Whiskey Diggings as well as at Hepsidam in the Port Wine channel (Lindgren, 1911; Durrell, 1987, p. 153). Such silt- and clay-rich rocks may be stream overbank deposits, and may actually represent a facies somewhat more distal to the main stream channel gravels, possibly related to the confluence of at least three Eocene stream channels in the La Porte area. The bedrock under the gravels at Dutch Diggings is light greenish gray, steeply dipping slate-like rock (metatuff according to Hietanen, 1981, Plate 1).
About 4 m of light gray, massive to indistinctly bedded tuff is exposed near the top of the approximately 35 m high cliff face. The tuff does not appear to be mixed with other sedimentary material, although it has been somewhat reworked. These features suggest that it was deposited in shallow water. The main constituents of the tuff appear to be ash and small plagioclase crystals.
Photos
P113a.JPG White La Porte Tuff over Eocene Auriferous Gravel at the head of Upper Dutch Diggings near La Porte.
P113c.JPG Bedding in a block of La Porte Tuff from Upper Dutch Diggings. Hammer is 32 cm long.
P113e_76.JPG Carbonaceous claystones exposed below La Porte tuff at Upper Dutch Diggings near La Porte.
P113j_71.JPG White La Porte Tuff exposed above carbonaceous claystones, Upper Dutch Diggings near La Porte.
P131l. JPG Flattened riveted steel pipe, Upper Dutch Diggings near La Porte.
P113m_68.JPG Piece of quartz- and chert-pebble conglomerate cemented with iron-oxide minerals, Eocene Auriferous Gravel at Upper Dutch Diggings near La Porte.
P113o_66.JPG Vertical, preTertiary slates which underlie the Auriferous Gravel at Upper Dutch Diggings near La Porte.
Turner (1897) described and showed on his Economic Geology map an area of Auriferous Gravels and hydraulicking “two and a half miles northwest of Onion Valley.” This area should be in SW¼ Section 30, T23N, R10E (Onion Valley 7.5-minute Quadrangle). Hietanen (1981, Plate 1) does not show any gravels in this area, only Lovejoy Basalt lying directly on serpentine and peridotite. I was unable to find any gravel in this area [P63], only Lovejoy on basement, confirming the relationships shown by Hietanen (1981, Plate 2). The absence of older gravels in this area does not prove they were not originally present and then eroded before Lovejoy deposition; however, it does tend to support the interpretation that the main Auriferous Gravel channel continued to the northeast, toward Cromberg (see the section on Richmond Hill, Sawpit and Union Hill).
Auriferous Gravel caps the higher parts of Peale (Peel on the Genessee Valley 7.5-minute Quadrangle) Ridge, in Sections 21, 22, 26, and 27, T25N, R11E (Diller, 1908, p. 62; McMath, 1958, p. 74, Plate 2). Peal(e) Ridge is a northwest trending ridge located south of Genessee in Genessee Valley; it lies between Ward Creek on the northeast and Little Grizzly Creek on the southwest. McMath (1958, p. 74) reported that the ridge was known as Peale Ridge at the time of that writing. Diller (1908, p. 62) appears to associate the name Peale Diggings with much of the Auriferous Gravels that cap the ridge. Lindgren (1911, p. 116) uses essentially the same language to describe the location and geology of Wards Diggings. There is little evidence today of any placer workings, although small ponds near the center of the west edge of Section 26, T25N, R11E [P71] could be from that era. Hydraulicking is unlikely because there was no more elevated area as a source of pressurized water.
The placer workings are reported to have exposed about 100 feet (30 m) of gravels; clasts of meta-rhyolite and quartzite were reported to be the most common, with some of dark igneous rock and a few of granite (Diller, 1908, p. 62). Diller reported clasts from 6-10 in. (15-25 cm) with rare ones as large as 2 ft (60 cm). No exposures of the gravels were seen during a 2003 visit to Peale Ridge, but smooth, rounded to well rounded clasts of preTertiary rock types were seen as float in several areas along the ridge. The clasts include the following observed rock types: greenschist (epidote, chlorite) facies meta-andesite; glomeroporphyritic meta-andesite; dark metabasalt(?); spherulitic and flow-banded meta-rhyolite; red slate; quartz-veined, black chert; distinctive red jasper; sparse vein quartz; rare light gray chert, and rare black tourmaline(?) breccia. Most of the clasts are in the 15 cm size range, but dark meta-basalt boulders up to 1.5 m long were seen. The gravels are apparently near horizontal and less than 20 m thick on the ridge top.
Diller (1908, p. 62) reported that imbrication (shingling) of clasts at Peal Diggings indicated a northerly direction of current flow. He also suggested that quartz porphyry clasts were more likely to be from the Grizzly Mountains to the south. This was considered evidence for a northerly flowing Jura River, from near Meadow Lake north of Soda Springs on Interstate 80 to the vicinity of Susanville (Lindgren, 1911, p. 33). However, more recent studies have discounted the northerly flowing Jura River that Diller (1908) described (McMath, 1958, p. 162; Durrell, 1987, p. 153). Most of the clasts described above are more likely to have been derived locally in the Mount Jura area or from the north near Kettle Rock and Lights Creek. In particular, the tourmaline(?) breccia cobble probably had a source in the area of the Lights Creek stock (see the description of the Moonlight area), and the red jasper may well have been derived from outcrops near Taylor Diggings. Because no exposures of gravel were seen, it was not possible to check for pebble imbrication; however, imbrication-like features seen at the Cascade Mine are probably related to pebble inclination on indistinct foreset beds, an indication of south current direction.
Photos
P70_clasts.JPG Clasts of metabasalt, quartz, jasper, and quartz-tourmaline vein material, Peale Ridge.
Rhyolitic ash-flow tuffs crop out to the east and west of Weber Lake (Weber Peak 7.5-minute quadrangle). Two of these areas are along Fiberboard Road between Perazzo Meadows and Weber Lake [P191, P199], respectively NW¼ NW¼ NW¼ Section 27 and SW¼ SW¼ SE¼ Section 23, T19N, R14E. The Nine Hill Tuff crops out at P199 and the tuff of Campbell Creek crops out at P191. Nine Hill Tuff also crops out along the Meadow Lake Road about 13 km south of its junction with the Fiberboard Road ([P193]; NW¼ NE¼ NW¼ Section 32, T19N, R14E). The tuffs appear to be essentially horizontal. These tuffs probably were laid down in a paleovalley that continues to the southwest to the Meadow Lake Hill area and then to placer workings on probable Eocene gravels at the Snowflower Mine (Loyd and Clinkerbeard, 1990, p. 33). From there, the channel can be projected to the Diamond Valley placer workings, Omega, and Alpha Diggings. Lindgren (1897) mentioned the “especially fine” rhyolite outcrops in the vicinity of Weber Lake. He suggested the rhyolite outcrops in this area and extending northwest toward Jackson Meadow Reservoir outlined a paleovalley; this description was probably the basis for a northwest flowing channel in this area shown by Jenkins (1932). I suggest that it is more likely the ash-flow tuffs filled two parallel southwest-flowing drainages and a low area between them; the tuff outcrop area is nearly 20 km long, from Meadow Lake to southeast of Sierra City.
Photos
P191.JPG Road cut exposure of tuff of Campbell Creek between Perazzo Meadows and Weber Lake.
Willards Creek (not examined during this study)
Diller (1908, p. 92) reported that rhyolite tuffs occur in his Auriferous Gravels near the head of Willards Creek 10 miles southwest of Susanville. Based on that distance and direction, this locality would plot in approximately Section 36, T29N, R10E, along the main branch of Willard Creek as shown on the Fredonyer Pass 7.5-minute Quadrangle. Diller (1908, p. 92) reported that because the tuff outcrop was too small to represent on his Plate II, he mapped it with the Auriferous Gravels. He also reported that the gravels contained “numerous pebbles of fresh lava with those of black chert, sandstone, and other siliceous material , which appear to have been derived from earlier gravels by erosion.” He described a stratigraphic section with tuff 1.5 miles southeast of the road summit. It is not clear today where this section is located, if different from the Section 36 projected location. Diller (1908, p. 73) considered these to be intervolcanic gravels. He also reported (1908, p. 68) that the tuff contained “light-brown amorphous dust, splinters of clear glass with fragments of clear glass pumice, and angular grains of quartz, feldspar, augite, and hornblende.” He reported that the tuff was decidedly cross-bedded and had a silica content of 70% (p. 92). He suggested that, based on previous work to the south of the Fortieth Parallel by Lindgren and Turner, the rhyolite tuff may lie on the Auriferous Gravels, although he could find no satisfactory exposure of underlying rocks. Grose and others (1990b) showed this area as unit Tvg, a Miocene(?) boulder to pebble conglomerate found at the base of the Tertiary section in the Susanville 30- x 60-minute Quadrangle but containing clasts of both preTertiary and Tertiary rocks.
This locality was not visited during this study, but most recent evidence suggests that the gravels and tuff in Willard Canyon are younger than the Auriferous Gravels and probably Miocene. Tertiary andesitic rocks of the Susanville 30 x 60-minute sheet (Grose and others, 1990, Table 1) that have been dated by K-Ar methods are younger than about 14 Ma. The mafic phenocrysts reported by Diller (1908, p. 68) from the tuff are much more likely to be found in the somewhat more silicic pyroclastic rocks of the Miocene andesites than in the Oligocene ash-flow tuffs from sources in central Nevada that overlie the Eocene Auriferous Gravels elsewhere in the Sierra Nevada (e.g., Henry and others, 2003; Garside and others, 2002; Davis and others, 2000).
Diller (1908) mapped a small area of “Neocene” gravel at the base of a ridge at the southwest corner of Indian Valley about 2 km northeast of Greenville (SW¼ SE¼ Section 35, T27N, R9E, Greenville 7.5-minute Quadrangle). McMath (1958, p. 163) also mentioned it briefly. The material was examined in 2003 at a road cut [P163] exposure along the North Valley Road (County Road 112). It consists of andesite lahar and possibly block-and-ash-flow; some clasts contain fresh hornblende. A very few smooth, rounded clasts of preTertiary rock were seen. The material is clearly a part of the Miocene andesite unit, and not Auriferous Gravel.
Rhyolitic ash-flow tuff crops out near the center of Section 32, T23N, R13E, Blairsden 7.5-minute Quadrangle [P12]. The tuff contains sanidine, plagioclase, and biotite (<1%); no phenocrysitc quartz was observed. Small lithics include volcanic, granitic, and metamorphic(?) rock types. The tuff appears to be essentially horizontal and lies on Jurassic (Grose, 2000a) granodiorite to the east; no gravel was observed at the tuff-granodiorite contact. Miocene andesitic lahars overlie the tuff to the south, possibly in a paleovalley. Durrell (1987, p. 170) also described the tuff (part of his Delleker Formation) at this site, which he reported to be near Willow Creek Road. The tuff was dated by K-Ar methods (Dalrymple, 1964) at 21.0 Ma on sanidine, and 30.7 Ma on biotite (ages modified by Wagner and Saucedo, 1992, based on new constants). The tuff is most likely correlated with quartz-deficient, sanidine-plagioclase-biotite tuffs to the east in the Reno, Nevada area. These tuffs there are older than 28.7 Ma and as old as about 31 Ma (Garside and others, 2003). Thus, the biotite age may be nearly correct.