Bolson

A bolson is a desert valley or depression that drains into a playa or salt pan and is entirely surrounded by recently uplifted hills or mountains, a closed drainage basin typical of basin and range topography in arid regions. Water rarely escapes a bolson; instead it collects on the enclosed valley floor, allowing sediment to build up over time through aggradation. The term entered English usage during the exploration of western North America in the 1830s and 1840s, borrowed from the Spanish bolson, meaning large purse. Notable examples include the Hueco Bolson in western Texas and the Mesilla Bolson, which spans southern New Mexico and northeastern Chihuahua, Mexico. Over long periods, water accumulating within a bolson deep sediments can form a bolson aquifer, and several such aquifers have been developed as sources of water for human use.