Named as the basal member (of 4) of Supai Formation for Amos Wash. No type locality designated. Section 330 ft thick measured west of Whiteriver-San Carlos road 3 mi south of Amos Wash road junction, sec 10, T4 1/2N, R21E, Gila Co, AZ, Basin-and-Range province, where member overlies Naco Formation and underlies Big A Butte Member (named) of Supai. Lower contact placed at base of a gray, thin-bedded, highly calcareous, slope-forming claystone. Upper contact placed at base of 2 ft thick gray argillaceous limestone. Second section 131+ ft thick measured on ridge, 1 1/2 mi southwest of Amos Road junction, sec 29, T5N, R21E. Above the basal gray claystone, member consists of mostly red-brown, thin-bedded mudstone that is interbedded with gray and red-brown, thin-bedded, slope-forming claystone, and very minor amounts of red-brown, thin-bedded siltstone and sandstone. Of continental origin. Correlation chart. Of Early Permian, Wolfcampian age.

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