The Moore's Flat district is in north-central Nevada County about 15 miles northeast of Nevada City. It is both a lode and placer district and includes the "diggings" at Moore's Flat, Oreleans Flat, Woolsey Flat, Snow Point, and Snow Tent. The Alleghany district adjoins the Moore's Flat district on the northeast. Moore's Flat was named for H. M. Moore who built a store there in 185!.
A number of gravel deposits were accumulated in a west-southwest-trending Tertiary channel of the Yuba River that continues west and southwest into the North Bloomfield district. At Moore's Flat, Lindgren (1911, p. 141) estimated, 26 million cubic yards were removed and 15 million remained. The gravels are quartz-rich and in places more than 100 feet thick. Hydraulic mining here during the 1880s had reported gold recoveries of 11 to 15 cents per yard. The gravels are capped by andesite on the south side of the district. Bedrock consists of amphibolite, slate, and serpentine. The gold-quartz veins usually are narrow and contain small but often rich pockets.
Lindgren, Waldemar, 1911, Tertiary gravels of the Sierra Nevada: U.S. Geol. Survey Prof. Poper 73, p. 141.
Lindgren, Waldemar, 1911, Colfax folio: U. S. Geol. Survey Geol. Atlas of the U.S., folio 66, 10 pp.