The city takes its name from a dry lake, a unique dryland plains geographic feature situated atop the divide between the Rio Grande and Colorado River watersheds, located less than two miles south of the city, through which St Hwy 137 passes. The dry lake, with no outlet, is over two sections in size, making it the largest in Texas; it holds water temporarily and only after high-runoff rain events, being used for grazing the remainder of the time. Though seasonal and temporal, the "big playa lake", in wet periods, is significant in a semiarid, drought-frequented environment and has been utilized regularly as a food and water resource by man and animal, alike, since prehistoric times.