By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
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Sacramento County ranks among the leading gold-producing counties in California.
Auriferous quartz veins have been mined intermittently since the gold-rush days, but lode production is insignificant compared to the amount of gold dredged from the gravels along the American River. From 1880 through 1959, production in the county was 5,005,700 ounces; only about 5,000 ounces was from quartz lodes.
The productive gravels are at the base of Pliocene and Pleistocene terraces or near the contact of the Pliocene Laguna Formation with the underlying Miocene Mehrten Formation (Carlson, 1955, p. 134). Bucketline and dragline dredges have been used extensively to mine these gravels. Folsom has been the center of this activity; other dredge operations were at Sloughhouse and at various localities along the Cosumnes River.
In 1952, bucketline dredging was reactivated south of the American River, and some gold was also obtained from sand and gravel preparation plants. Production for several years before and through 1959, however, was only a few ounces annually.
Quartz veins containing gold are found in green metavolcanic rocks and in the Mariposa Slate of Jurassic age but do not occur in any of the rocks of Late Cretaceous age or younger (Carlson, 1955, p. 133).
FOLSOM DISTRICT
The Folsom district is in the southeast part of T. 10 N., R. 7 E., along the American River, in the northeast corner of Sacramento County.
Lindgren (1911, p. 222) considered this district to be the largest area of Quaternary gravels in the state. In 1899 the first bucketline dredge used in Sacramento County was installed at Folsom. Before this the gravels were mined by drift and hydraulic methods. Huge electrically powered draglines and dredges were introduced in the late 1920's and 1930's, and some of these continued operating into the 1950's (Carlson, 1955, p. 136-142).The largest dredge handled about 4 million cubic yards of gravel per year. Rising cost gradually forced curtailment of these large-scale activities, but in 1958 some dredging was resumed in the district. Before 1930 some drift mines were operating, but later the dredges accounted for most of the production. The total production of the district through 1959 was at least 3 million ounces.
SLOUGHHOUSE DISTRICT
The Sloughhouse district is in T. 7 N., R. 7 E., along the Cosumnes River.
The auriferous gravels of the Tertiary lone Formation were mined by hydraulic methods in the early years, but most of this activity was curtailed by a court decree in 1884 aimed to prevent devastation of farmlands by debris-laden streams (Carlson, 1955, p. 143).
Large-scale dredging operations were conducted during the 1930's, 1940's, and early 1950's. In this district, as in the Folsom area, large deposits of late Tertiary and Quaternary gravels carried small quantities of gold. Total production through 1959 is not known but was probably about 1,700,000 ounces.