Named as second from top of five members of Tesuque Formation (revised) of Santa Fe Group (ascending): Nambe, Skull Ridge, Pojoaque, Chama-El Rito, and Ojo Caliente Sandstone. Type area of Santa Fe Group is here restricted to north of Santa Fe, in the Rio Grande Valley (includes parts of northern Santa Fe Co (Estancia basin), southeastern Rio Arriba Co (San Juan basin), and southern Taos Co (San Luis basin). In this area, Santa Fe Group is divided into Chamita Formation (top) and Tesuque Formation, with its 5 members (base). Chama-El Rito Member consists of coarse to fine, pinkish to gray soft sandstones and siltstones interbedded with beds of well-rounded pebble- to cobble-sized clasts of volcanic rock, lenticular in outline. The San Juan region of southern CO is postulated as the source area, either directly or indirectly by reworking, of most of the volcanic pebbles. Type section designated in W 1/2 sec 23, T23N, R7E, Rio Arriba Co, NM in San Juan basin; in the two easternmost rincons at the head of Canada Honda, it underlies area called Rincon del Cuervo (see USGS Mendanales Quadrangle map, 1953). South of Santa Clara Canyon, and especially east of Battleship Mountain, Chama-El Rito Member interfingers at base of, and is locally overlain by, part of the Ojo Caliente Sandstone Member--this means that only late part of the Chama-El Rito is younger than Pojoaque Member. Of Clarendonian age. Geologic map. Sections.

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

The Chama-El Rito Member of Tesuque Formation of Santa Fe Group of Galusha and Blick (1971) is shown by Galusha (1974) to range from 15.5 to 8.0 m.y. in age. A basalt flow interbedded in the Chama-El Rito and derived from a small volcanic center near El Rito Creek, Medanales quad, Rio Arriba Co, is K-Ar dated as 13.5 m.y. old (whole rock) in this report. Area of report is Espanola basin, Rio Arriba Co, NM in San Juan basin.

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