Geologic mapping and fracture analysis of the Lower Cretaceous Edwards aquifer strata near Georgetown and Round Rock, Texas, were performed to provide a better understanding of the geologic framework of the Balcones Fault Zone and to provide information for assessing ground-water flow characteristics. Cretaceous strata dip gently eastward and are locally overlain by terrace deposits and alluvium. Several major normal faults, downthrown to the east, strike northward across the area. Gentle flexures, possibly related to faulting, parallel the faults.

Organic petrological, organic geochemical, and chemical analyses of Tertiary (Paleocene to Eocene) coals (to a 2,000-ft [610-m] depth) from the Wilcox, Claiborne, and Jackson Groups of Texas reveal characteristic properties of these coals. Most of the Wilcox, Claiborne (one sample), and Jackson coals contain greater amounts of liptinite (especially fine-grained liptodetrinite) than do average humic coals. These liptinites can be identified only by blue-light excitation in reflected-light microscopy.

Cretaceous sedimentary rocks and Tertiary intrusive, extrusive, and volcaniclastic rocks dominate the geology of the Hen Egg Mountain and Christmas Mountains quadrangles in the Big Bend region of Texas. The Cretaceous rocks consist of limestones, shales, mudstones, and sandstones that are host rocks for the Tertiary intrusions.This report focuses on the Tertiary intrusive and extrusive rocks. The intrusions were emplaced in several distinct intervals between 47 and 20 Ma ago (Eocene to Miocene) but are dominantly 44 to 40 Ma old.

Detailed characterization of the spatial distribution of hydraulic conductivity (K) by direct measurement is usually impractical. A viable alternative is to use geologic information and geostatistics to characterize interconnectedness of critical K facies that have a dominant influence on fluid flow. Conditional simulation is introduced herein as a method for estimating aquifer interconnectedness.

The purposes of this study were (1) to quantify recent (1974 to 1982) movement of Texas shorelines and vegetation lines by analysis of aerial photographs; (2) to place this movement in historical (pre-1974) context; and (3) to examine the influence of environmental variables such as storms, sea level, subsidence, and sediment supply on the movement of coastal boundaries.