town, Pima county, southwestern Arizona, U.S. Spaniards mined in the area in the 1750s, and the Ajo Copper Company (1854) was the first incorporated mining concern in the Arizona Territory. Copper and silver were the most valuable minerals mined in the area. The mines remained dormant from roughly 1860 until the 1900s when a townsite was laid out and a railroad built to Gila Bend, 40 miles (64 km) north. The community, originally named Muy Vavi (Papago: “Warm Water”), was renamed Ajo (Spanish: “Garlic”), for the wild garlic found in the surrounding hills. An alternative derivation claims the Papago word au'auho, meaning “paint,” as the origin of the town's name, for the red paint pigment found there and used by the Papago.

Ajo's economy virtually depends on the Phelps Dodge Corporation, which operates the New Cornelia Open Pit Mine (390 acres 【158 hectares】) and a smelter plant. A strike in 1985 led Phelps Dodge to suspend production, and depressed worldwide copper prices throughout the 1990s stymied efforts to reopen the mine. Nearby are the Papago Indian Reservation (east), the Cabeza Prieta National Wildlife Refuge (west), and the Organ Pipe Cactus National Monument (south). In winter the town's population swells by some 4,000 because of tourists visiting surrounding RV (recreational vehicle) parks and campgrounds. Pop. (1990) 2,919; (2000) 3,705.