The Colfax district is in southwestern Placer County in the vicinity of the town of that name. It includes the deposits in the Weimar-New England Mills area and placer-mining areas along the American and the Bear Rivers. The Colfax district also has been know as the Illinois district.
Placer mining began here soon after the beginning of the gold rush. The locality was first known as Alder Gulch and later Illinoistown. The Rising Sun mine was discovered in 1866. Colfax, which was named for U. S. Senator Schuyler Colfax who visited the place in 1865, was an important center during the construction of the Central Pacific Railroad. Considerable mining continued in the district until about 1900. Small-scale placer mining, some done by skindivers, has continued until the present time.
Slates of the Mariposa Formation (Upper Jurassic) are found in the central portion of the district, and slate of the Cape Horn Formation (Carboniferous) crops out to the east. A gabbro intrusion lies to the north and northwest, a diabase body to west, and serpentine lenses and amphibolite to the east and southeast. A fairly extensive patch of Tertiary channel gravel is exposed on the north side of Colfax Hill. The extensive quartz gravels in the Bear River are hydraulic mine tailings from the You Bet and Lowell Hill districts.
The ore bodies occur in a number of northeast-striking quartz veins that usually range from two to five feet in thickness. The ore contains free gold and often abundant sulfides. Considerable highgrade ore was found near the surface during the early days.
Lode: Annie Laurie, Big Oak Tree $100,000+, Bauer, Black Oak, Brushy Creek, Chubb, Hinchy, Last Chance, Live Oak Ravine, Rising Sun $2 million+, Victory, Whiskey Tunnel.
Placer: Bear River Ext., Bear River Tunnel, Burnt Flat, Collins, Rocky Bar.
Chandra, D. K., 1961, Geology and mineral deposits of the Colfax and Foresthill quadrangles: California Div. Mines Spec. Rept. 67, 50 pp.
Irelan, William, Jr., 1888, Rising Sun and Big Oak Tree mines: California Min. Bur. Rept. 8, pp. 462-464.
Lindgren, Waldemor, 1900, Colfox folio, California: U. S. Geol. Survey Geol. Atlas of the U. S., folio 66, 10 pp.
Logan, C. A., 1936, Gold mines of Placer County, Rising Sun mine: California Div. Mines Rept. 32, pp. 34-35.