GEOLOGY OF CATHEDRAL MOUNTAIN QUADRANGLE, BREWSTER COUNTY, TEXAS

Abstract

Rocks exposed in the Cathedral Mountain quadrangle in the southeastern Davis Mountains of Trans-Pecos Texas are assigned to the Word formation and to Capitan limestone in the Permian Guadalupe series; to the Maxon sandstone, Edwards limestone, Georgetown limestone, and Grayson (Del Rio) marl in the Cretaceous Comanche series; to the Buda limestone and Boquillas limestone in the Cretaceous Gulf series; and to the Buck Hill volcanic series in the Tertiary. Volcanic rocks up to 4600 feet thick cover most of the quadrangle. The volcanic succession, similar to that in Buck Hill and other quadrangles to the south, is divided into the Pruett tuff, Crossen trachyte, Sheep Canyon basalt, Potato Hill andesite, Cottonwood Spring basalt, Duff formation, and Rawls basalt. Vertebrate fossils indicate a late Eocene (Duchesne) age for the Pruett tuff (restricted to the lowermost tuff, sandstone, and conglomerate beds). The top of the Eocene is placed at a prominent disconformity between the Crossen trachyte and the Sheep Canyon basalt; it is suggested the overlying lava and tuff layers are Oligocene and younger (?). Some of the many intrusive bodies of alkalic microsyenite which are younger than the volcanic rocks have effected much local deformation of the layered rocks. Quaternary alluvium is present along streams and over valley flats. Northward across the quadrangle, the Crossen trachyte gains appreciable quartz, the Potato Hill andesite changes from highly porphyritic to nonporphyritic, and the Duff formation changes from dominantly rhyolite tuff to lava, tuff, and conglomerate (Decie member). Effects of five crustal disturbances—mid-Mesozoic, late Cretaceous, pre-upper Eocene, and three in the late Cenozoic—are apparent. Differential erosion of the intruded, folded, and faulted volcanic succession has roughened and diversified the landscape.