This district is in east-central Nevada County in the vicinity of the old mining town of Washington, 18 miles northeast of Nevada City. It is in the south end of the Goodyear's Bar-Alleghany belt and includes the "diggings" at Alpha and Omega.
The Washington district was first mined during the gold rush, and the placers of the Middle Yuba River were highly productive. The Omega and Alpha hydraulic mines were opened in the middle 18505 and worked on a major scale through the 1880s. Later, Chinese miners reworked the tailings. Lode mining also began in the 1850s and continued steadily until about 1915. There was activity in the district again during the 1930s, and the Red Ledge mine has been worked in recent years. Barite, chromite, and asbestos also have been mined here.
The district is underlain chiefly by slate, schist and quartzite of the Blue Canyon Formation (Carboniferous). A serpentine body one to two miles wide crops out in the central portion. The Relief Quartzite (Carboniferous) and amphibolite lie to the west and granodiorite to the east. The serpentine is a south extension of a belt that passes north-northwest through Alleghany and Goodyear's Bar in Sierra County. Tertiary andesite overlies the main ridges to the north and south.
The auriferous Tertiary channel gravels at Alpha and Omega are part of the main channel that extends west and north to Relief and North Bloomfield. Jarmin (1927) estimated that, at Omega, 13 million yards were mined and yielded 13.5 cents in gold per yard. Lindgren (1911) estimated that 40 million yards remained. The quartz veins contain small but rich ore bodies, similar to those of the Alleghany district to the north, but are not as plentiful. Except for arsenopyrite, sulfides are not usually abundant. A number of beautiful specimens of crystallized gold have been found in the Red Ledge mine. The Spanish mine also has yielded large amounts of barite.
Lode: Giant King, Mexican Cons., Mount Hope, Red Ledge, Red Paint, St. Patrick, Spanish, Treasure Box.
Placer: Alpha $2 million+, Centennial, Omega, Phelps, Yuba River.
Averill, C. V., 1946, Placer mining for gold in California, Omega mine: California Div. Mines Bull. 136, pp. 265--266.
Hobson, J.B., 1890, Washington mining district: California Min. Bur. Rept. 10, pp. 389-392.
Irelan, William, Jr., 1888, Washington mining district: California Min. Bur. Rept. 8, pp. 435-444.
Jarmon, Arthur, 1927, Washington and Omega hydraulic mines: California Min. Bur. Rept. 23, pp. 112-115.
Lindgren, Waldemar, 1900, Colfax folio, California: U. S. Geol. Survey Geal. Atlas of the U.S., folio 66, 10 pp.
Lindgren, Waldemar, 1911, Tertiary gravels of the Sierra Nevada: U.S. Geal. Survey Prof. Paper 73, pp. 139-141.
MacBoyle, Errol, 1919, Nevada County, Washington mining district: California Min. Bur. Rept. 16, pp. 59-63.