Clifton, town, seat (1909) of Greenlee county, southeastern Arizona, U.S. It lies near the New Mexico border. Copper was discovered in 1865 at nearby Morenci (unincorporated) and was first mined there in 1872. In 1937 the Phelps Dodge Corporation began excavating an open-pit mine, now one of the largest in the United States (7,920 feet [2,414 metres] across and more than 1,320 feet [402 metres] deep). Clifton lies 2 miles (3.2 km) east of Morenci along the San Francisco River and is one of the oldest continuously producing copper-mining camps in the Southwest. Gems (agates, azurite, turquoise) are also found in the area. Much of the historic town was destroyed by flooding in 1983 and 1993, and only a few buildings have been restored. Clifton is notable as the southernmost point of the scenic Coronado Trail. It is also one of the towns that claims to be the birthplace of Geronimo, although historians do not support this claim. Inc. 1909. Pop. (2000) 2,596; (2010) 3,311.