The Bofecillos Mountains and Big Bend Ranch State Park contain a complex sequence of volcanic, volcaniclastic, and intrusive rocks that erupted from sources both within and outside the area. Detailed geologic mapping and stratigraphic, petrographic, geochemical, and 40Ar/39Ar and K-Ar studies justify substantial revision of previously recognized relationships. Magmatism occurred in several distinct episodes between 47 and 18 Ma ago, spanning the complete range of activity in Trans-Pecos Texas.

Fluvial-deltaic reservoirs contain large volumes of oil and gas. These reservoirsandstones may have complex stacking patterns, and shales or very fine grained sandstone may form baffles or barriers to flow. As a result, significant compartmentalization or baffling may occur in fluvial-deltaic reservoirs. Because of their close analogy with reservoirs in the Gulf of Mexico region, outcrops of Ferron Sandstone in central Utah have been used to investigate the heterogeneity and possible recovery behavior of high-accommodation fluvial-deltaic reservoirs.