Ajo was first located on the ground that later became the open pit mine. The modern city was founded in its present location in 1917 coincident with the beginning of large scale mining of the copper deposits. Ajo is the home of the New Cornelia Mine of the Phelps Dodge Corporation, one of the great copper mines of the world. The open pit mine is located one mile south of the city, and the concentrator, smelter, and shops are adjacent to the town site on the east. In 1917 the leaching plant started in operation, in 1924 the concentrator started in operation, and in 1950 the smelter started in operation.