The Difunta Group of the Parras Basin, southern Coahuila and western Nuevo Leon, Mexico, consists of two major intertonguing lithic facies with a composite thickness of approximately 4,000 meters.

Three gray, brown, red, and green, partly variegated, fine- to coarse-grained calcareous sandstone, siltstone, and mudstone units are thickest on the south in the Saltillo-General Cepeda area; they wedge out north and east in the vicinity of the Saltillo-Paredon-Hipolito railroad.

Four units of interbedded, black, gray, brown, and green calcareous shales and siltstones and gray to brown sandstones and shales occur between the red units. East of the Saltillo-Paredon-Hipolito railroad they compose an as yet undifferentiated sequence.

The various red and gray-brown units have been mapped westward and northward from the vicinity of Saltillo for distances of approximately 100 and 50 miles, respectively, in a region of relatively complex structure. They are, therefore, mappable lithic units and are thus defined as formations in this paper, being named in descending order: Rancho Nuevo, Las Encinas (redbeds), Cerro Grande, Las lmagenes (redbeds), Canon del Tule, Cerro Huerta (redbeds), and Cerro del Pueblo Formations.

Type localities for the various formations are located along or adjacent to major roads leading south-southwest and north-northwest from Saltillo.