Falcon Reservoir, a dammed lake on the Rio Grande operated jointly by Mexico and the United States, is used for irrigation, electric power, and recreation. Barely discernible are Laredo and its Mexican counterpart, Nuevo Laredo (lower right corner). Because it receives less than 20 inches (8 centimeters) of rainfall annually, this semiarid area is identified as the Arid Plains. Visible (top of photograph) are the darker outliers of the more massive Sierra Madre Oriental range of northeast Mexico.