U.S. Department of the Interior U.S. Geological Survey California Aqueduct Harper Lake Coyote Lake Troy Lake Lucerne Lake El Mirage Lake Rabbit Lake Barstow Hesperia 15 15 Mojave Desert Centro subarea Este subarea Alto subarea Baja subarea Oeste sub- area Iron Mtn San Gabriel Mts Afton Canyon Newberry Springs Lower Narrows Lower Narrows San Bernardino Co Los Angeles Co Kern Co San Bernardino Co Victorville 35° 00' 34° 00' 116°30' 117° 00' 117°30' 20 KILOMETERS 0 20 MILES 0 Mojave River Surface-Water Drainage Basin San Bernardino Mts 40 Transition zone subarea Regional aquifer Floodplain aquifer Mojave River Ground-Water Basin Mojave River Channel Los Angeles CALIFORNIA San Francisco San Diego Mojave Desert Mojave Water Agency management area The Mojave River and the associated aquifer system are important water supplies in the Mojave Desert of southern California. The river and aquifer system are in hydraulic connec- tion in many areas, and when flow conditions change in one, the other usually is affected. The river is an unpredictable source of water; therefore, residents of the basin rely almost entirely on ground water for their water supply. This reliance on ground water has resulted in overdraft conditions that have caused water-level declines, changes in the quantity and spa- tial distribution of recharge from the Mojave River, and loss of riparian habitat. The U.S. Geo- logical Survey (USGS), in cooperation with the Mojave Water Agency (MWA), has completed several studies to determine the likely effects of overdraft on the ground-water and surface- water relations along the Mojave River. This report summarizes those studies, highlighting some of the simulation results from a ground-water flow model, and describes the ground- water and surface-water conditions of the Mojave River Basin. USGS Fact Sheet 122-01 November 2001 Water Supply in the Mojave River Ground-Water Basin, 1931-99, and the Benefits of Artificial Recharge Mojave River Ground-Water Basin The Mojave River ground-water basin is in the western part of the Mojave Desert and is about 80 miles northeast of Los Angeles, California. The basin encompasses about 1,400 square miles and is divided into six management sub- areas: Oeste, Este, Alto, Transition zone of the Alto (hereinafter refer- red to as the Transition zone sub- area), Centro, and Baja (fig. 1). The major source of surface water and replenishment (recharge) to the ground-water system in the basin is the Mojave River, but the river is unreliable for direct water supply because its 100 miles of streambed is dry—except for a short reach of perennial flow and periods of flow after intense storms. Therefore, Figure 1. Location of the study area and subareas of the Mojave River ground- water basin, southern California.