This district is in northern Sierra County about 10 miles north of Downieville. It includes the Howland Flat, Table Rock, Deadwood, Mt. Fillmore, Potosi, and Rattlesnake Peak areas. It is mainly a placer-mining district.
The streams were first mined during the gold rush. The locality was extremely rich then; in one month gold valued at $700,000 was produced. Hydraulic mining was done on a major scale from the late 1850s through the 1880s. Some lode mining and drift mining continued through the early 1900s, and the area was prospected in the 1920s and 1930s. The district was made famous by Bret Harte's tale, The Outcasts of Poker Flat. This district has been highly productive, the mines at Howland Flat alone being credited with an output valued at $14 million.
The northern part of the district is underlain by amphibolite with some serpentine. To the south and east there are slates of the Blue Canyon Formation (Carboniferous). Substantial portions of the area are capped by andesite. Extensive deposits of Tertiary auriferous quartz gravels are part of the Port Wine channel, which extends west and northwest through this district and then west and southwest into the Port Wine district. The lower quartz-rich gravels were also gold-rich. Portions of the channel have been faulted. Some narrow gold-quartz veins occur in amphibolite and slate.
Placer: Caledonia, California, Clippership, Deadwood, Forest Queen, Gibraltar, Hawkeye, Herkimer and Bunker Hill, Manchester, Miners Home, Pacific, Poker Flat, Potosi, Rattlesnake, Scott, Virginia, Tennessee, Winkeye.
Lode: Alhambra, Mammoth, Mt. Fillmore Cons., New York.
Lindgren, Waldemar, 1911, Tertiary gravels of the Sierra Nevada: U.S. Geol. Survey Prof. Paper 73, pp. 108-109.
Logan, C.A., 1924, Gravel mines of Howland Flat Ridge: California Min. Bur. Rept. 20, pp. 362-367.
Logan, C.A., 1929, Sierra County, placer mines: California Div. Mines Rept. 25, pp. 184-211.
MacBoyle, Errol, 1920, Sierra County, Poker Flat district: California Min. Bur. Rept. 16, pp. 15-19.
Turner, H. W., 1897, Downieville folio: U. S. Geol. Survey Geol. Atlas of the U. S., folio 37, 8 pp.