Playas are the dry, level beds of ancient lakes which are found in desert country throughout the southern Southwest. Normally dry, playas occasionally fill with water, sometimes no more than a few inches deep over many square miles, after a heavy summer rain or during spring snowmelt. These shallow lakes usually last no more than a few days or weeks, evaporating to leave behind a large expanse of mudflats drying in the sun. Playas were named by Spanish explorers for their resemblance to beaches.
Playas are characteristic of desert areas and are maintained by climates that are drier than they are wet, where the combination of relentless sun, wind and aridity can evaporate more water from the land than falls in a year. Most of the Southwest’s playas formed thousands of years ago during the Pleistocene period when the climate in the Southwest was cooler and wetter. Precipitation eroded mountains and streams carried sediments to low level basins between mountain ranges which filled lakes with fine sand and silt. As the climate warmed and dried 10,000-12,000 years ago, the streams dried up and the lakes evaporated, leaving their flat beds to dry and harden.