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.

Located in Nueces County, 5 mi southeast of Aransas Pass in Corpus Christi Bay, Red Fish Bay field has yielded more than 19 MMbbl of liquid hydrocarbons and 103 Bcf of gas from more than 50 stacked Frio Sandstone reservoirs since field discovery in 1950. This study forcused on delineating bypasssed hydrocarbons in 19 upper Frio reservoirs. Red Fish Bay field exemplifies the tremendous bypassed hydrocarbon potential in supposedly depleted sandstone reservoirs of the Downdip Frio BarrierIStrandplain Sandstone on the San Marcos Arch play in SouthTexas.

The urban corridors associated with the Dallas, Austin, and San Antonio metropolitan areas lie on Austin Chalk outcrop. In these areas of rapid urbanization, ground-water information is needed to resolve environmental issues. The Austin Chalk also produces hydrocarbons in the deep subsurface. Fluid migration in both oil-field and ground-water environments is strongly controlled by fractures. In each geologic setting, a conceptual model of fracture intensity is required to model or predict flow. Using geologic and engineering data collected during development of the U.S.