First published use in south-central Owyhee Co, ID, Snake River basin. Called tuff of Alder Creek in unpublished thesis (Bernt, 1982, Univ. Idaho MS thesis), probably for creek in Owyhee Co. Assigned as lowermost of three [unranked] units of Bieroth volcanics [rank of Bieroth not specified; not clear if formal or informal unit]. Type locality not designated. Occurs as very localized unit in southeast part of mapped area (R5E at ID-NV border). Consists of light-reddish-purple welded ash-flow tuff; moderately compacted and welded; extensively weathered and devitrified; subangular to subrounded lithic fragments, principally of basalt porphyry, are common. Has chemical composition of rhyodacite. No thickness given. Unconformably overlies Cretaceous biotite granodiorite of Cottonwood Creek pluton; probably underlies Cedar Canyon tuff (new) (field relations not clear). Geologic map. Chemical analysis. Eocene age based on correlation with similar units radiometrically dated in Jarbidge Mountains (40.9 m.y.; Coats, 1964) and in Poison Creek area of northern Owyhee Co (44.7 m.y.; Armstrong and others, 1980).

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