Named as middle member of Tres Hermanos Formation (raised in stratigraphic rank) for town of Carthage 16 mi southeast of Socorro, Socorro Co, NM in Orogrande basin. Type section measured in SE1/4 SE1/4 sec 8 and NE1/4 NE1/4 sec 17, T5S, R2E. Consists of 116 ft (35.2 m) several sandstone beds that may be gray to buff, fine- to very fine-grained, calcareous, and dark gray shales and siltstones. The sandstones are paludal-lacustrine or crevasse-splay bay-fill types. Some of the shales are carbonaceous. Ranges from 100 to 225 ft thick. Overlies Atarque Sandstone Member (formerly assigned to Mesaverde Formation) and underlies Fite Ranch Sandstone Member (new), both of Tres Hermanos. Intertongues with Mancos Shale. Age assignment to late middle to earliest late Turonian (Late Cretaceous) based on ages of overlying and underlying members. Was deposited on a broad, very low relief coastal or delta plain.

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