Rocks of Permian age have been known in West Texas for over a century, and in the last 40 years the drilling of numerous test holes has made subsurface information available concerning these rocks. These data have enabled geologists to correlate beds of late Paleozoic age across the basin, a distance of more than 200 mi. Results of these correlations are presented in a series of eight paleogeographic maps.

In early Paleozoic time this region formed a broad, generally shallow basin. In the middle Paleozoic the basin slowly filled with carbonate and siliceous rocks. In Mississippian time a positive median belt developed in a north-south direction, separating the larger basin into the eastern or Midland basin and the western or Delaware basin. In Pennsylvanian time wide carbonate shelves developed around these basins, especially the eastern one. At the south end of the basins tectonic activity increased and foredeeps developed and were filled with flysch material.

In the Early Permian, seas spread over much of the basin region, depositing shale in the low parts of the sea floor while limestones accumulated on the higher parts. However, by Middle Permian (Leonardian) time, marine circulation was restricted and evaporites began to form. This restriction became increasingly severe during the remainder of the period. Thus carbonate reefs and banks formed on the margins of the Delaware and Midland basins, as well as on the Central Basin carbonate platform, overlying the old median mountain range.

In the latter part of this period, high limestone reefs were formed on the basin edges, separating basinal sediments from evaporitic and clastic lagoonal strata. The Capitan reef surrounding the Delaware basin is a notable example. All these formations show traces of cyclical deposition which may be attributed to eustatic changes in sea level, perhaps glacial in origin.

During the closing epoch of the period, thick sequences of anhydrite, halite, and potash salts accumulated in the basin areas. After a final marine transgression, continental redbeds covered the region and Permian sedimentation ended.