It includes about 6000 square miles of land of which 17 percent is privately owned and the remainder is under the stewardship of state, federal and tribal governments. The watershed of the Gila River and its tributaries has wide, flat valleys between narrow, rugged mountain ranges. Climate above 7000 ft. ranges from cool to subhumid, and annual precipitation is up to 20 inches. The valleys below are arid with average annual precipitation of 9.5 inches. Vegetation is primarily desert scrub or desert grassland type.
Most rain is received from summer thunderstorms resulting in heavy, localized runoff.
Winter rains are generally gentle but can result in heavy runoff after the soil becomes saturated.