The Black River is a 114-mile-long (183 km) river in the White Mountains of the U.S. state of Arizona. It forms south of the town of Greer and west of the towns of Nutrioso and Alpine. The river flows southwest then northwest to meet the White River west of Fort Apache. The merged streams form the Salt River, a major tributary of the Gila River. Both the Salt and Gila rivers supply water to the Phoenix metro area as well as provides water for farmland and crops around the valley. James Ohio Pattie named the river in 1826 as he explored this area in Arizona's White Mountains.