The population of the San Luis Basin region of northern New Mexico is growing. Water shortfalls in this low rainfall region could have serious consequences. Decisions for future growth and land management in the region depend on an accurate assessment and protection of the region's groundwater resources. An important aspect of managing the groundwater resources is a better understanding of the hydrogeology of the Santa Fe Group and the nature of the sedimentary deposits that fill the Rio Grande Rift, which contain the principal groundwater aquifers. The shallow unconfined aquifer and the deeper confined Santa Fe Group aquifer in the San Luis Basin are the main sources of municipal water for the region.