This active mine is the likely the second biggest open pit copper mine in the world, slightly smaller than the Chuquicamata pit in Chile. Digging started in 1904, and the hole is now half a mile deep and more than two miles wide. Overseen and operated by Kennecott Copper Company, which is itself owned by Rio Tinto Group, the operation employs around 2,400 people at the site and the nearby smelter. On the National Register of Historic Places. In April 2013, a 165-million-ton landslide occurred inside the mine, one of the largest earth movements in American history. It was expected (though not expected to be so large), so the mine was evacuated at the time, though several giant haul trucks were buried, and some buildings collapsed into the pit. Operations resumed 48 hours later.