LOS ANGELES: The future of wind farms and hybrid cars may well hinge on what happens to a 22.3-hectare hole in the ground at the edge of California's high desert.

The open-pit mine at Mountain Pass, California, holds the world's richest proven reserve of "rare earth" metals, a family of minerals vital to producing the powerful, lightweight magnets used in the engines of Toyota Motor Corp's Prius and other hybrid vehicles as well as generators in wind turbines.

Colorado-based Molycorp Minerals LLC plans to reopen its long-idled quarry to resume extracting and refining thousands of tons of rare earth ore in the next few years, seeking to become one of the leading suppliers of these scarce materials.