The
serpentine belt extends from central Plumas County south to Fresno
County, but is not a continuous outcrop. The larger areas shown in the
geologic folios mentioned above are located as follows:
Plumas County.—Near Whisky Diggings, Indian Hill, Goodyear Bar, Grizzly Hill, and Gravel Hill.
Butte County.—Near Big Bar, Brush Creek, and Clipper Mill.
Yuba County.—Near Nevada City and Sweet Ranch.
Sierra County.—Near Chips Plat.
Nevada County.—Near Washington.
Placer County.—Near Auburn, Towle, Sugarpine mill, and Bath.
Eldorado County.—Near Pilot Hill, Flagstaff Hill, and Mount Ararat.
Amador County.—Near Drytown and Mountain Springs.
Calaveras County.—Near Cottage Springs.
Tuolumne County.—Near Rawhide, Montezuma, and Jacksonville.
Mariposa County.—Near Benton mill and Mount Bullion.
In
Fresno County there are large masses of chromiferous serpentine at
Portersville and east of Piedra, on Kings River, but so far as known to
the Survey no placer operations have been attempted in this region.
Lindgren 1 says of this belt:
Platinum
is of widespread occurrence in the Sierra Nevada. * * * It is derived
from serpentine, peridotite, or gabbro * * *. It is safe to say that
platinum is universally present in the gravels of the Sierra Nevada
wherever these have been derived from the erosion of serpentine areas.
In
northwestern California, particularly in the Klamath Mountains,
platinum was won at several mines in 1916, the production from this
region amounting to 127 ounces, largely from Trinity, Humboldt, and
Siskiyou counties. Platinum is also known to occur in Del Norte County.
The recently published geologic map of California 2 does
not distinguish the serpentine areas, but from other sources it is
known that there are considerable bodies of serpentine in the following
general localities:
A
large area in southeastern Siskiyou and northeastern Trinity counties,
centered about Trinity Center, Minersville, Carrville, Dodge, and
Dunsmuir.
Several
small areas on Hayfork Creek of Trinity River, in central Trinity
County, and a large tongue extending southeast from Loudon to Bully
Choop in the eastern part of the county.
A large but little-known area in Western Siskiyou and eastern Del Norte counties which extends north into Oregon.
A
belt along the eastern and northern boundaries of Humboldt County
concerning which there is little detailed geologic information.
The
irregular mountain mass in southwestern California, in San Diego and
Riverside counties, is made up largely of igneous rocks, which in some
areas are very basic. Gold veins have been worked, and Calkins 3
has recently described the occurrence of nickeliferous
pyrrhotite-chalcopyrite ore in amphibole-olivine gabbro in the Julian
district, 60 miles north of San Diego, and has suggested the
possibility of these ores carrying platinum. He states that the ores
have apparently not been tested for platinum. It might be advisable to
investigate such gravels of the streams in this region as are
definitely known to have originated in areas of basic igneous rocks.
1 Lindgren, Waldemar, Tertiary gravels of the Sierra Nevada of California: U. S. Geol Survey Prof. Paper 73, p. 74,1911.
2 Smith, J. P., Geologic map of California, California State Min. Bureau, 1916.
3 Calkins,
F. C., An occurrence of nickel ore in San Diego, Cal.: U. S. Geol.
Survey Bull. 640, pp. 77-82, 1916 (Bull. 640-D).
