"The Drain". Spring rainfall and runoff from the Panamint Mountains (to west/left) and Black Mountains (east/right) creates vernal pools that evaporate, leaving behind patterns of salt and an alkalai flat on the underlying mud. Average annual precipitation is only 1.58 inches (40 mm). Death Valley National Monument Est. February 11, 1933; Death Valley National Park in 1994. 5,270 square miles (13,649 km2). Inyo County, CA.