HYDROGEOLOGIC FRAMEWORK OF THE WESTERN HUECO BOLSON AREA OF THE RIO GRANDE RIFT, TEXAS, NEW MEXICO, AND CHIHUAHUA: PROGRESS REPORT ON DEGITAL MODEL DEVELOPMENT
Late Cenozoic extensional-tectonic features that characterize the entire RGr region have had a profound influence on both basin-fill composition, and groundwater flow and chemistry in the Hueco Bolson area. Primary tectonic components are half-graben basins and flanking ranges that are linked across zones of structural accommodation. Major aquifer systems are formed by fluvial basin-floor LFAs deposited by Pliocene ancestral-river distributaries, and inset-channel deposits in the inner valley of the Late Quaternary Rio Grande. These poorly consolidated sediments are grouped into upper to middle Santa Fe and river-valley HSUs. Horizontal hydraulic conductivities commonly range from 3-30 m/day, and basin-fill fluvial sequences are as much as 300 m thick and 30 km wide. In marked contrast, the inner river-valley fill is less that 30m thick and 9 km wide. Except for deeply buried eolian-sand facies, subjacent middle to lower Santa Fe basin-floor deposits (Miocene) and intertonguing piedmont-slope LFAs have much lower aquifer potential because of finer matrix, and greater consolidation and cementation.