Named for the Donkey Hills, Custer Co, ID in Idaho Mountains province. Extends north into Lemhi Co, ID. Also mapped on east side of Rock Creek, T9N, R22E, and west of Grouse Creek, T13N, R22E, Custer Co, No type locality designated. "Principal exposure" is west of Donkey Creek in western part of T11N, R24E. Composed almost exclusively of rounded to subangular pebbles, sand, and dirt in a mixture of quartz and calcite. Porous calcareous material is predominant in cement at some localities, especially near limestone and dolomite outcrops such as along the Pahsimeroi River near where Brazer limestone, Three Forks limestone, Grand View and Jefferson dolomites, and Saturday Mountain formation occur. In the eastern part of the quad, gravel is mostly derived from Lemhi, Swauger, and Kinnikinic quartzites; some is derived from Lemhi, Swauger, and Kinnikinic quartzites; and some is derived from Challis volcanics. Rests on Challis and older rocks. No known fossils except for fossil wood. Is trenched by modern streams. Locally covered by Pleistocene glacial deposits. Thickness not given. Probably correlated with Salt Lake formation. Assigned to the Tertiary. Geologic map and cross sections.

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