The Permian series of North America attains its greatest development in trans-Pecos Texas. Strata of this age have an important influence on the geography of the region. Permian limestones, sandstones, and shales constitute many of the mountain ranges and plateaus, and the more resistant rocks crop out in bold cliffs and ledges on numerous escarpments. The highest peak in Texas, El Capitan (8750 feet), is the summit of a cliff of Permian limestone at the crest of the Guadalupe Mountains (Fig. 13 A). In New Mexico, not far northeast of this peak, is the great Carlsbad Cavern, which is carved from limestones of the same age. Permian strata beneath the plains east of the mountains have produced vast quantities of oil, and contain large deposits of valuable potash salts.
Strata of the Permian series in trans-Pecos Texas reach a thickness of about 7000 . . .