Mountain Pass rare earth mine. This large open pit mine is located in the Clark Mountain Range, California, USA. Operated by Molycorp, it is the only rare earth oxide (REO) mine in the Western hemisphere and the world's largest such mine outside of China. Dominating world trade from the 1960s to the 1980s, it was closed in 2002, with active mining resuming in 2010. It is expected that the renewed mining will enlarge the pit from a depth of 150 metres to 300 metres in a couple of years. The minerals are part of a 1.4-billion-year-old Precambrian carbonatite intrusion into gneiss rock. Photographed in October 2011.