GEOLOGIC MAPPING OF URBAN CORRIDORS AND IMPORTANT AQUIFER AREAS FOR THE TEXAS STATEMAP PROGRAM

Geologic mapping for the Texas STATEMAP Program has focused on studying the geology of urban growth corridors and critical aquifers and their recharge areas. Recently published maps, scale 1:100,000, of a critical part of the Edwards aquifer near San Antonio, central Texas, and of the El Paso–Hueco Bolson region of west Texas will be presented with an overview of completed and current mapping. These maps were constructed through reviewing existing maps, field mapping, interpreting aerial photographs, constructing 1:24,000-scale open-file maps, and digitizing and compiling the open-file maps for a geographic information system. Recent and planned maps are intended for a diverse audience and have a variety of applied uses, including identifying aquifer recharge boundaries, recognizing attributes and variations within aquifer strata, making water-management decisions related to ground-water flow and aquifer response for pumpage and recharge, providing information necessary for land-use activities such as planning and permitting construction projects, designing foundations, and locating landfills and other waste-disposal sites, and meeting demands for local construction materials. Central Texas mapping is being conducted in urban growth corridors of San Antonio and Austin that coincide with the Edwards (Cretaceous limestone), Hill Country Trinity (Cretaceous limestone, sandstone, conglomerate), and Carrizo-Wilcox (Paleocene-Eocene sandstone) aquifers. Bedrock stratigraphy includes Cretaceous shallow-marine shelf deposits onlapped by chalk and calcareous, clastic-slope sediments. Eastward are Paleocene and Eocene marine, deltaic, and fluvial deposits. Normal faults of the Balcones Fault Zone provide structural control on Edwards aquifer strata. West Texas mapping was conducted in the El Paso–Hueco Bolson region along the border of Texas and Mexico. Stratigraphy includes Precambrian through Tertiary bedrock in the mountain areas and late Tertiary to Quaternary basin-fill and surficial deposits of the mountain flanks, Hueco Bolson, and Rio Grande Valley. Quaternary faults cut basin-fill and surficial deposits along the mountain flanks and within the basin.