Named for exposures on South Crosby Peak in eastern Crosby Mountains, Catron Co, NM, Basin-and-Range province. Type section located approximately 4.3 mi southwest of Datil and 1.8 mi northeast of South Crosby Peak, NE1/4 sec 19, T2S, R10W. Occurs also in Datil Mountains, and as thin deposits as far east as northern Jornada del Muerto. Composed of volcaniclastic sandstone, volcaniclastic conglomerate, and ash-flow tuff. Sandstone and conglomerate are tuffaceous, grayish pink, medium to coarse, some layers containing granules and pebbles up to 8 in, some clasts angular to subround. Ash-flow tuff is pale pink, unwelded to poorly welded, crystal poor with abundant lithic fragments of red, brown, purple, and green, aphanitic intermediate to felsic volcanic rocks. Is 595 ft thick at type. Is 0-200 ft in Datil and western Gallinas Mountains. Overlies Hells Mesa Tuff (revised). Underlies La Jencia Tuff (new). Its source is unknown. Formerly called tuff of Crosby Mountain and volcaniclastic rocks of South Crosby Peak. Is Oligocene age.

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