Geologic Unit: Imnaha

Usage:

Imnaha Basalt of Columbia River Basalt Group (ID*,OR*,WA*)

[Columbia River Basalt Group adopted by the ID, OR, and WA Geol. Surveys, and the USGS (rules suspended).]

Geologic age:

late Tertiary (early Miocene)*

Type section, locality, area and/or origin of name:

Origin of name not stated by author, but probably named from Imnaha River, approx. 6 km west (as the crow flies) of Dug Bar, Wallowa Co., OR. Mapped area lies between Wallowa Mountains of northeastern OR and Seven Devils Mountains of western OR. Part of Snake River Canyon included (Vallier, 1967).
Type locality: at Dug Bar, on Snake River near the mouth of Imnaha River in extreme northeast OR (Hooper, 1974; see entry under Swanson and others, 1979).
Type [section] (base not exposed): exposures in cliffs on west side of Snake River above north end of Dug Bar, [near mouth of Imnaha River, Wallowa National Forest boundary, Lat. 45 deg. 48 min. 35 sec. N., Long. 116 deg. 41 min. 30 sec. W., BM 1005], Cactus Mountain quadrangle, Wallowa Co., OR. Base exposed at south end of Dug Bar (Swanson and others, 1979).
Reference sections: (1) near confluence of Lower Sheep Creek and Imnaha River; (2) anticline on north side of Lewiston Basin (center T. 11 N., R. 45 E.); and (3) lower Rocky Canyon, 25 km west of Grangeville, ID (Swanson and others, 1979).

AAPG geologic province:

Blue Mountains province*
Eastern Columbia basin*