View Ajo’s open-pit copper mine, more than a mile wide, from the Mine Lookout. The town of Ajo was established to mine the large deposit of copper and gold here, and the mine ran for many years until its closure in 1985. At one point, it was the fourth- largest copper-producing mine in the United States; its plant had a capacity of treating more than 31,000 tons of ore daily. Much of the processing infrastructure has been removed, but there is still ample evidence of the huge industrial operation carried out here, including the pit and gigantic piles of rocks and tailings. The Visitor Center is open from October through May and by special appointment in the offseason.