The San Pedro Valley in southeastern Arizona extends from the International Boundary northward about 120 miles to the junction of the San Pedro River with the Gila River. The river basin also extends about 75 miles into Mexico. The valley varies in width from 5 to 20 miles, being widest in its middle portion, in the vicinity of Benson. The area of the portion of the basin within the United States in about 3,770 miles.
Ground-water supplies and irrigation in San Pedro Valley, Arizona