Clipper Mills is in southeastern Butte and northeastern Yuba County, about eight miles east-northeast of Forbestown. Several moderate-sized deposits of Tertiary channel gravels have been mined by drifting and hydraulicking. The Pratt and Gentle Anna drift mines and the Pittsburg Hill hydraulic mines have been the principal placer-gold sources. A few narrow goldquartz veins have yielded small but rich pockets. The district is underlain by slate, serpentine, and gabbrodiorite.
lindgren, Woldemclr, 1911, Tertiary grovels of the Sierra Nevada: U.S. Geol. Survey Prof. Poper 73, pp. 99-100.
Turner, H. W., 1898, Bidwell Bar folio: U. S. Geol. Survey Geol. Atlas of the U. S., folio 43, 6 pp.