During major glacial-pluvial intervals of the Late Quaternary, a complexly linked system of intermontane basin lakes and through-going streams dominated the geohydrologic setting the Paso del Norte region of southern New Mexico, Trans-Pecos Texas, and Chihuahua, Mexico. Hydrogeologic setting and fluctuating paleoclimatic conditions were the major controls on size and permanence of lakes and streams in this now arid to semiarid Chihuahuan Desert region of the Basin and Range—Mexican Highland section. Bolson complexes of the region have both open and closed topographic components, but many closed subbasins are partly drained hydrologic systems with groundwater inflow and outflow links with adjacent areas. The entrenched Rio Grande/Bravo fluvial system formed the regional discharge zone or sink for large amounts of surface and subsurface flow during much of the Middle and Late Quaternary.

The Mesilla and El Paso/Juárez Valleys of the Rio Grande/Bravo (1090-1175m) bisect the floors of the Los Muertos-Guzman-Santa Maria and Tularosa-Hueco bolson complexes (1175-1210m), which are the sites of the region’s two largest pluvial lakes, Palomas (Chihuahua) and Otero (NM). At highest (Wisconsinan) stages, Lakes Palomas and Otero had areas of at least 7500 and 2000 km², respectively. Linked closed basins with smaller pluvial lakes include the Playas-Basilio and Hachita-Moscos basins that drain to the Rio Casas Grandes Valley of northwestern Chihuahua. Watersheds (~3000m max elev, 63,700 km² area) contributing to Lake Palomas include highlands bordering the northern Sierra Madre Occidental (Rios Casas Grandes, Santa Maria and Carmen headwaters) and southeastern ranges of the Datil-Mogollon—Transition Zone province (Mimbres River source). The Sacramento-Sierra Blanca and Organ-San Andres-Oscura ranges form the major highlands of the Lake Otero watershed (~2750m max elev, 17,500 km² area). In many places, major shoreline features with good age control are visible on LANDSAT imagery; and advanced GIS technology enables basin-scale paleohydrologic and hydrogeologic reconstructions.