Named for exposures at Idaho Canyon, Big Mountain. Type locality: sec. 1 T43N R26E, Idaho Canyon quad, Humboldt Co, NV; forms upper part of north-trending ridge east of Idaho Canyon and directly south of mouth of canyon. North of type locality forms cliff on eastern flank of Big Mountain. Maximum thickness of 400 ft at type; thins east, south, and southeast; pinches out in Pine Forest Range and northern part of Black Rock Range. Also crops out north and northeast of Gooch Table, northwest Humboldt Co; in NE Washoe County NV; and in OR where is stratigraphically above Steens Basalt. [Recognized in Idaho Canyon, Duffer Peak, Denio, Railroad Pt, and Big Spring Butte quads, NV and OR]. At type overlies tuff of Craine Creek. Thickens from south east and toward Virgin Valley which is approximate center of distribution. Densely welded, granophyrically crystallized. Is greenish gray or tan, weathers dark brown. Has lenticular gas cavities. Lithic fragments rare. No K-Ar ages but younger than Craine Flat and older than Summit Lake Tuff; thus about 15.5 Ma.

Source: GNU records (USGS DDS-6; Menlo GNULEX).