The New Cornelia mine is a currently inactive open-pit copper mine in Pima County, Arizona, United States. It was the only productive mine in the Ajo mining district, and is located just outside the town of Ajo, which was built as a company town to serve the New Cornelia mines. The roughly circular pit is one and a half miles across at its widest point, and 1,100 feet deep at the center. Although not generally regarded as a 'dam', the New Cornelia Mine Tailings is often cited as the largest dam structure in the United States with a volume of 7.4 billion cubic feet.