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Collection: Books and Periodicals
The Tertiary Gravels of the Sierra Nevada of California by Waldemar Lindgren (1911) (301 pages)
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Page: of 301
CHAPTER 12. THE COLFAX QUADRANGLE
GENERAL GEOLOGY.
The ‘‘Bedrock series” in the Colfax quadrangle is represented chiefly by the Calaveras
formation (Carboniferous) in its several subdivisions.’ A strip of the Mariposa formation
(Jurassic) lies along the southern part of the western margin, and a strip of the Sailor Canyon
formation (mainly Triassic) along the east side. Intrusive in these altered sediments are
amphibolites of many kinds along the west side and a large central dike of peridotites, serpentines, and gabbros, which traverses the whole quadrangle from north to south. A part of the
granodiorite batholith of the high Sierra enters the quadrangle at the eastern margin, and along
the west side lie several smaller intrusive masses of granodiorite and diorite. The list of
important intrusive igneous masses closes with the body of soda granite that reaches up into the
Downieville quadrangle from a point near Emigrant Gap, where only a narrow strip of contactmetamorphic slate separates it from the main granitic mass of the Sierra.
GOLD-BEARING AREAS AND PRODUCTION
The largest and richest masses of Tertiary gravel known in the Sierra Nevada are found in
this quadrangle and derived their contents from a great number of gold-quartz veins. Few of
these veins are continuous for a great distance, and the bulk of the gold was evidently derived
from small veinlets and seams. Almost the whole area is gold bearing to a greater or less extent.
The most barren parts are in the granitic rocks northwest of Cisco and in the clay slates of the
southeast corner. The western margin of the quadrangle is followed by an irregular belt of
gold-quartz veins from the Alaska and Delhi on the north to the great complex of veins around
the south end of the granodiorite of Nevada City and to the veins in the vicinity of Colfax.
From north to south in this quadrangle the great Serpentine belt is followed by an
enormous number of auriferous veins, few of which are continuous enough to warrant extensive
mining, but which seem to have enriched, in an extraordinary degree, the gravels of the streams
which flowed over them. East of the Serpentine belt, chiefly in slates of the Calaveras formation,
but partly also in the soda granite, lies another strongly auriferous zone marked by continuous
and longer quartz veins. This extends from Johnsville, in Plumas County, by American Hill,
Graniteville, Eagle Bird, Blue Canyon, and Humbug Bar, and leaves the quadrangle south of
Michigan Bluff. This zone is second only to the Serpentine belt in its enriching power. Some
of its veins are continuous for several miles. The rocks are comparatively barren from this zone
to the eastern boundary of the quadrangle, except at two places, one at Meadow Lake in the
granodiorite, the other at Duncan Peak in the slates. The veins in the Duncan Peak auriferous
area have enriched the surrounding gravels, which, however, are not extensive.
It is impossible to obtain exact data regarding the total amount of gold produced in this
quadrangle. That part of Nevada County which is contained in it has certainly produced
$60,000,000. The part of Placer County which is contained in it has surely produced, at the
very least, thesame amount. To this must be added the production from Minnesota, Alleghany,
and Forest, in Sierra County, which is large. It is thought that $150,000,000 is a very conservative estimate of the total. Of this amount probably not more than $10,000,000 has been
contributed by the quartz mines. The yield of the Nevada City and Grass Valley districts, just
outside the quadrangle, is estimated at $123,000,000; of this amount about $75,000,000 may
have been derived from the quartz mines in those districts. These figures are only the rudest
approximations, but they serve to convey an idea of the astounding richness of the region.
1 See Colfax folio (No. 66), Geol. Atlas U. 8., U.S. Geol. Survey, 1900. 133