Named for exposures (the type locality) in Pack Rat Canyon, lat 37 deg 32' 39" N, long 116 deg 56' 29" W, near southeast margin of Stonewall Flat in Nye Co, NV, Great Basin province. These exposures were previously mapped as Spearhead and Trail Ridge Members of Thirsty Canyon Tuff. Distribution, facies relations, trace element abundances, and paleomagnetic signatures show that two ash-flow sheets near Stonewall Mountain were not derived from the same center as the Thirsty Canyon Tuff. They were derived from the Stonewall Mountain volcanic center. Is well exposed between Cuprite and Goldfield, and near Stonewall Mountain. Is divided into Spearhead Member, at base which is reassigned from the Thirsty Canyon Tuff, and the Civet Cat Canyon Member (new) at top. Both members are ash-flow sheets composed of a number of ash-flows and associated air-fall tuffs, and are distributed symmetrically around Black and Stonewall Mountains. Topographic highs--Mount Helen, Obsidian Butte, and vicinity of Pahute triangulation station--probably acted as barriers restricting movement of Stonewall Flat ash flows to the south, southeast, and east. Except for Spearhead Member, the Stonewall Flat and the Thirsty Canyon Tuff of the Black Mountain volcanic center are not in contact. Is of late Miocene age--6.3 +/-0.2 Ma--on basis of two K-Ar ages on sanidine from the Spearhead.

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