San Manuel Mine, Arizona

When it shut down in 1999, this was the largest operating underground copper mine in the country. 2,200 people worked in its 356 miles of tunnels and pits, as well as at the massive smelter (the largest of its type in the industry), located six miles south at San Manuel. Australia's Broken Hill Proprietary Co. Ltd (BHP) took over operations of the mine, smelter, and rod plant from Magma Metals in the late 1990's. The smelter and rod plant were torn down in 2006.