Arid land ecosystems along the border region of the United States and Mexico are being rapidly developed. Two of the most important natural resources of this region are water and soil. Hydrogeological characteristics (such as the size and quality of aquifers) combined with geomorphic units (such as alluvial fans and floodplains), provide important information that can help prevent poorly planned development. Making these maps involves 1) delineating geomorphic features based on aerial photographs and satellite images, 2) ground-truthing the features, and 3) combining geomorphic maps with groundwater maps using GIS (Geographic Information System). These hydro-geomorphic maps help to locate high producing wells, as along faults, and identify groundwater recharge zones, as along mountain arroyos. Moreover, these hydro-geomorphic maps identify areas unsuitable for development. For example, housing development should not take place in arroyo and river floodplains, which are subject to flooding. Instead, housing sh ould occur on higher, geomorpho logically stable fan-piedmont surfaces. Building on stable surfaces not only will protect houses from flooding and erosion, but also will preserve the topographically lower and texturally finer floodplains for agriculture, wildlife, and recreation.