Named for Browns Canyon, Poncha Springs NE quad, Chaffee Co., CO. Type locality is in secs 22, 27, and 28, T51N, R8E, in Eagle basin. Consists of seven [SIX] small masses at type locality. Composed of gray and brown to yellow-brown, locally finely ripple marked, tuffaceous siltstone interbedded with calcareous siltstone, sandy siltstone, ferruginous claystone, and lithic and crystal tuff. Rocks are moderately well consolidated, locally dense and flinty, and have a conchoidal fracture. A basal conglomeratic arkose contains angular to subrounded fragments mostly of underlying Precambrian quartz monzonite. Ranges from a few ft to about 50 ft thick. Mapped as a separate unit from Dry Union because siltstone is more consolidated, indurated, folded and faulted, and has a different lithology (locally mineralized with fluorite); the siltstone dips steeply on upthrown side of a normal fault whereas nearly horizontal Dry Union forms hanging wall. Fossils are Miocene plants rather than Pliocene vertebrates as in Dry Union.

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