The Permian stratigraphy of southeast New Mexico and northern trans-Pecos Texas displays abrupt changes in lithology and fauna. Interpretations concerning relationships in the Sacramento, Hueco, Sierra Diablo, Guadalupe, Delaware, and Apache mountains are presented. The Sacramento and Hueco mountains reveal rocks of lowest Permian age, resting unconformably upon the Magdalena formation of upper Pennsylvanian age.

The Chupadera formation of New Mexico is separated partly from the greater part of the Guadalupian by a topographical and structural feature, called the Bone Springs arch. Reef-building agencies adjacent to and upon the arch had a profound effect upon the lithology of the upper Delaware Mountain formation and younger strata. The Capitan is, in reality, the dolomitic phase of the upper Delaware Mountain formation and the Carlsbad formation. On the surface the reef fringe extends from Guadalupe Point to Carlsbad, New Mexico; thence, by subsurface data, its presence is indicated through southeastern New Mexico and part of the West Texas Permian salt basin, defining the north, east, and south limits of the Delaware Mountain "sand" basin.

Oil pools of large size are located near the reef fringe in Winkler County, Texas, and parts of Lea and Eddy counties, New Mexico; accumulation is probably the result of exceptional conditions of sedimentation and structure.