Abstract
The Malone Mountains lie within and along the northern front of the Sierra Madre orogenic belt in Trans-Pecos Texas. Folded and faulted sedimentary rocks composing the mountains and outlying hills belong to the Permian, Jurassic, and Cretaceous systems. Cenozoic basin-fill mantles older rocks in the surrounding Hueco Bolson. Since the Malone area includes the only marine Jurassic and the oldest Cretaceous rocks known in Texas, it figures critically in correlation of Mexican Mesozoic deposits with those of southern United States.
Briggs formation, name given to Permian strata of the Malone area, consists of anhydrite and gypsum with interbedded limestone and intraformational breccia. The base of the Briggs is concealed; maximum exposed thickness is 630 feet. Leonard index fossils occur in the lower part; the upper 500 feet is unfossiliferous.
The Malone formation of Upper Jurassic age rests unconformably on the Briggs. It consists of sandstone, sandy shale, limestone, and conglomerate aggregating about 1000 feet maximum thickness. Two divisions are recognized; the lower contains Idoceras and other Kimmeridgian ammonites, while the upper has species of Kossmatia characteristic of the Upper Portlandian (Tithonian). With the ammonites are pelecypods (Trigonia, Ptychomya, etc.) previously thought by some to be Cretaceous.
The Torcer formation of Lower Cretaceous (Valanginian) age includes more than 400 feet of limestone, sandstone, and shale with basal conglomeratic quartzite resting on the Malone. Younger Cretaceous strata belonging to the Las Vigas (?) and Glen Rose formations form hills south of the Malone Mountains.
