||New Mexico Water Resources Research Inst., Las Cruces.; New Mexico State Univ., Las Cruces.; Department of the Interior, Washington, DC.; National Science Foundation, Washington, DC.; Environmental Protection Agency, Washington, DC.
The binational western Hueco Bolson-Paso del Norte area of the southern Rio Grande rift (RGr) tectonic province occupies parts of Trans-Pecos Texas and south-central New Mexico, USA, and north-central Chihuahua, MX. It includes a long reach of the Rio Grande Valley, adjacent parts of the southern Mesilla and Tularosa Basins, and the El Paso-Ciudad Juarez metro-area with a population of about two million. This overview and progress report emphasizes recent development of hydrogeologic-framework models and GIS datasets that integrate large amounts of geologic and geochemical information on Neogene RGr basin-fill (Santa Fe Group) and river-valley aquifer systems. The digital GIS format (ESRI ArcGIS(Trade Name)) allows 3-D integration of surface and subsurface information that can be used in numerical groundwater-flow modeling and hydrogeochemical interpretations. Provisional hydrogeologic maps and cross sections completed to date include a surficial map, 11 sections (to mean sea level), and a structure-contour map of the base of the basin-fill aquifer system in the Paso del Norte area. The hydrogeologic framework of basin-fill aquifers is defined in terms of (1) dominant lithofacies-assemblages (LFAs) that are grouped as informal hydrostratigraphic units (HSUs); and (2) basin-boundary and intra-basin structural controls.