The hydrogeologic framework of basin-fill aquifers and associated ground-water-flow systems in southwestern New Mexico-An overview
— John F. Kennedy, John W. Hawley, and Molly M. Johnson

Ongoing cooperation between the governments of the United States and the Republic of Mexico, particularly projects involving the U.S. Environmental Protection Agency, requires that major aquifer systems with transboundary components be adequately characterized in terms of their hydrogeologic framework, groundwater- flow regimes and water-quality conditions. As part of this program, the New Mexico Water Resources Research Institute and cooperating institutions have developed Geographic Information System (GIS) coverages (ARC/INFO® format) that integrate large amounts of available surface and subsurface information on basin-fill aquifers in the International Boundary region between Trans-Pecos Texas and southeastern Arizona. Emphasis of this overview is on major GIS elements relating to aquifer composition and general ground-water-flow regimes in four intermontane basin systems of southwestern New Mexico and northwestern Chihuahua: Mimbres, Hachita-Moscos, Playas, and Animas. The ARC/INFO® format allows 3-D presentation of hydrogeological information and related interpretations that can be used in numerical ground-water-flow models. The hydrogeologic framework and hydraulic properties of basin and valley fills are categorized on the basis of (1) hydrostratigraphic unit (HSU) and lithofacies assemblage (LEA) composition and (2) the nature of basin-boundary and intra-basin bedrock and structural controls. Major aquifers arc formed by medium– coarse-grained fluvial- facies assemblages deposited by the ancestral Mimbres and Animas fluvial systems. These poorly consolidated HSUs and LFAs are informal subdivisions of the (Pliocene Quaternary) upper Gila Group and overlying basin-floor deposits. Typical horizontal hydraulic conductivities range from 1 to 10 m/day, and unit thicknesses are as much as 150 m, Laterally equivalent piedmont-slope facies and underlying middle and lower Gila Group HSUs have much lower aquifer potential because of finer matrix texture and greater degree of consolidation and cementation. Whereas all of the basin systems in the study area have surface-flow components that discharge to subbasins with topographic closure and ephemeral lakes (playas), the ground-water-flow regime in most subbasins has an underflow-discharge component that drains to terminal sinks in lower contiguous basins or river-valley areas. Historically, transboundary ground-water flow from the United States to Mexico has been documented in a few areas, but at a very low rate (<10.5 x 10⁶ m³/yr).