High Quality Content by WIKIPEDIA articles! The Mountain Pass rare earth mine is an open-pit mine of rare earth elements (REEs) on the south flank of the Clark Mountain Range and just north of the unincorporated community of Mountain Pass, California, United States. The mine, owned by Molycorp Inc., once supplied most of the world`s rare earth elements. The facility is currently undergoing expansion and modernization, and expected to return to full production in 2012.