The mountain area of trans-Pecos Texas is divisible into a northern part, which has been more or less stable, and a southern part, which has shown considerable mobility from Paleozoic down to Cenozoic time. Strong folds and overthrusts of late Pennsylvanian age, raised from a geosyncline, are found in the Marathon and Solitario uplifts in the southern part of the province. Northwest of them, in the stable area, Permian rocks later than the deformation lie unconformably on broadly folded older Paleozoic foreland rocks, and were deposited in broad basins.

In some mountain ranges of western trans-Pecos Texas, and extending southward into Mexico, are close folds and overthrusts raised from a Mesozoic geosynclinal area. East of them are broad folds, domes, and basins of marginal type. These structural features were produced during two movements, one older and the other younger than the extensive Tertiary lavas of central trans-Pecos Texas. These may be classed as the northern ends of the Sierra Madre Oriental of Mexico. After the last folding, trans-Pecos Texas was extensively broken by normal faults, some of the movements being of late Tertiary age, and some of relatively recent date. In the northern stable part of the province, features of Basin and Range type were produced. Here, thick intermontane deposits were laid down in the areas epressed by faulting. The present surface features of trans-Pecos Texas result in part directly from the various later tectonic movements, and to a greater degree from the modification of the structural features by stream erosion.