The Granite Basin district straddles the Butte-Plumas County line about 30 miles northeast of Oroville and 30 miles west southwest of Quincy. It includes the Buckeye, Gold Lake, Milsap Bar, Soapstone Hill, and Merrimac areas. The area was placer-mined during and after the gold rush. There was some lode mining here in the 1930s, and there has been minor prospecting since.
Several granitic stocks are intrusive into slate, quartzite and limestone of the Calaveras Formation (Carboniferous to Permian) and amphibolite. Exfoliation has formed several round granitic domes, of which Bald Rock is the most prominent. Serpentine, some Tertiary basalt and a few patches of Tertiary auriferous gravel are present. The quartz veins usually occur in the granite. The veins are narrow, but the ore bodies often are rich. Pyrite and galena are abundant.
Lode: Hardquartz, Hose, Reynolds. Placer: Buckeye drift, Coquette, Horseshoe, Milsap Bar, Robinson.
Averill, C. V., 1937, Plumas County, Granite Basin Mining Company: California Div. Mines Rept. 33, pp. 108-109.
Heitanen, A. M., 1951, Metamorphic and igneous rocks of the Merrimac area. Geol. Soc. America Bull. Vol. 62, pp. 565-607.
Lydon, P. A., 1959, Geological section and petrography along the Poe tunnel, Butte County: California Div. Mines Spec. Rept. 61, 18 pp.
MacBoyle, Errol, 1920, Plumas County, Granite Basin mining district: California Min. Bur. Rept. 16, pp. 18-21.
Turner, H. W., 1898, Bidwell Bar folio: U. S. Geol. Survey Geol. Atlas of the U. S., folio 43, 6 pp.