here - State of Arizona Department of Mines and Mineral Resources

70 PRINCIPAL GOLD-PRODUCING DISTRICTS OF THE UNITED STATES
lite tuff of Tertiary and Quaternary age. Granitic NEVADA COUNTY
stocks of Cretaceous (?) age form the White Moun- The gold-quartz mines of the Grass ,.,alleytains,
at the southeast boundary of the county, and Nevada City district in Nevada County have been
Blind Springs Hill, east of Benton. the most productive in the State, and the Empire
BODIE DISTRICT
The Bodie district is in northeast Mono County,
in T. 4 N., R. 27 E. Mining was started in 1860,
and the district was active until 1955. Total gold
production was 1,456,300 ounces, most of which
came from the Standard mine.
Country rock in the district consists of a "complex
of igneous rocks and breccias" overlain (perhaps
along a fault) by Tertiary hornblende andesite
(Brown, 1908, p. 343-344). Ore bodies occur in
three sets of auriferous quartz veins in the andesite
(Brown, 1908,p.345-346).
MASONIC DISTRICT
The Masonic district is in northeast Mono
County, in T. 6 N., R. 26 E. Gold occurs in quartz
veins in metamorphic rocks and granite. The Pittsburg-Liberty
mine, with a record of $470,000 in
gold (about 34,000 ounces), has been the important
producer (Sampson and Tucker, 1940, p. 121). The
district was active on a small scale in 1959. No detailed
descriptions of the geology were found.
NAPA COUNTY
Total recorded gold production for Napa County
is 23,225 ounces, all from the Calistoga district in
the northwest corner of the county. The first gold
production recorded was in 1875 when $93,000 in
combined gold and silver was listed (Davis, 1948,
p. 165). Intermittent production continued to 1941.
Gold has been a byproduct from the Palisade and
Silverado silver mines (Davis, 1948, p. 183). No
other information on this district could be found.
Along the eastern border of the county is a
4-mile-wide belt of folded siltstones, sandstones,
and a few limestones composing the Shasta Series,
of Cretaceous age (Davis, 1948, p. 162). These
rocks are flanked on the west by a 1Y2-mile-wide
strip of the Jurassic Knoxville Formation, which is
the lower, conglomeratic unit of the Shasta Series
(Weaver, 1949, p. 21-22). The remainder of the
northern half of the county is underlain by metamorphic
and cherty sedimentary rocks and associated
basic intrusive rocks of the Franciscan Group,
of Jurassic age. In the western part of the county,
the east side of the Napa Valley is covered by a
thick section of Pliocene volcanic rocks, and on the
west side of the valley, the Shasta Series is overlain
locally by Pliocene volcanic rocks.
mine in the same district was in continuous operation
from 1850 to 1940, which at that time was the
longest period of operation for any gold mine in
the country (Logan, 1941, p. 375). Placer production
has also been significant, especially in the early
days; however, no consistent records have been
kept. Tertiary gravels on San Juan Ridge, North
Columbia, Sailor Flat, Blue Tent, Scotts Flat,
Quaker Hill, and Red Dog-You Bet still c'lntain
tremendous reserves, but these are for the most
part undeveloped because of the curtailment of hydraulic
mining.
The total gold production of the county from
1849 through 1959 was 17,016,000 ounces, including
Lindgren's (1896, p. 26) estimate of $133,800,000
in gold. Since 1903, when placer and lode production
have been reported separately by the U.f', Geological
Survey (1904-24) and U.S. Bureau of Mines
(1925-34, 1933-66), 286,655 ounces of placer and
7,119,353 ounces of lode gold have been mined in
the county.
GRASS VALLEY·NEVADA CITY DISTRICT
Because the towns of Grass Valley and loTevada
City, which form the center of the Grass '-'alley­
Nevada City district, are only 4 miles apart and
because of their similarity in geology, distribution
and mineralogy of veins, and common history and
development, they are discussed together.
The initial rush to this area took place in 1850
after rich gravels were discovered near the r··esent
site of Nevada City. In October of the same year.
the first lode discovery was made at Gold Ifill on
the outskirts of Grass Valley (Johnston, 1940,
p. 19). Almost immediately the towns of Grass
Valley and Nevada City were founded; ther grew
rapidly, prospered, and became permanent communities.
By 1851 quartz mines had been developed at
Nevada City, but these early ventures failed. The
miners turned to working the rich Tertiary rravels
on a large scale by introducing hydraulic methods
(Lindgren, 1896, p. 19). The discovery at Gold Hill
was followed by discoveries of veins at Ophir Hill,
Rich Hill, and Massachusetts Hill, and by 1867
most of the major mines of the district had been
located. Grass Valley, where 1,600 men were working
and 284 stamps were crushing the ore, WNl then
one of the leading camps in California (Jol'nston,