This is an extensive gold-bearing region in southern Plumas County. It is contiguous with the Quincy district to the north and the Gibsonville district in Sierra County to the south. It includes the Last Chance, Sawmill Flat, Monitor Flat, Onion Valley, Harrison Flat, Blue Nose Mountain, and Nelson Point areas. The district was named in 1850 for a pit that was dug for the use of a whipsaw. The region was extensively mined during the early days and has been intermittently prospected since. In recent years there has been some placer mining at Monitor Flat. Skin divers have prospected in the Middle Fork of the Feather River.
The east portion of the district is underlain by slate, schist, and quartzite of the Calaveras Formation (Carboniferous to Permian). Also there are several limestone lenses. To the west the district is underlain by serpentine and amphibolite. The ridges are capped by Tertiary andesite and basalt.
The Tertiary gravels are largely quartz-rich, and in places, rich in gold. At Saw pit Flat the gravels are part of the Richmond Hill-Onion Hill channel, while those to the east at Bunker Hill and Blue Nose Mountain are in the northeast end of the famous La Porte channel. A number of gold-quartz veins are in the district, some of which are part of a vein system that extends along the contact zone between serpentine and schist and slate.
Placer: Boulder West, Bunker Hill, Fordham, Golden Gate, H & G, Kelly, King Solomon, Mayflower, Morning Star Cons., Nelson Creek, Red Slide, Richmond Hill, Rio Vista, Smith, Turkeytown, Union Hill, Zumwalt.
Lode: Bainbridge, Belfrin, Dean, Five Bear, Gold Point, Gold Run, Independence, Oro Fino, Oversight, Pilot, Pilot Peak, Plumas Bonanza, Rose Quartz, Sugar Pine, Wilson-Gomez.
Averill, C. V., 1937, Plumas County, gold: California Div. Mines Rept. 33, pp. 103-124.
Lindgren, Waldemar, 1911, Tertiary gravels of the Sierra Nevada: U.S. Geol. Survey Prof. Paper 73, p. 110.
MacSoyle, Errol, 1920, Plumas County, Sawpit Flat mining district: California Min. Bur. Rept. 16, pp. 42-46.
Turner, H. W., 1897, Downieville folio, California: U. S. Geol. Survey Geol. Atlas of the U.S., folio 37, 8 pp.