WhereIsAtlas · Mining

Mountain Pass Mine

The Californian mine that accidentally became the West's rare earth backbone — found by prospectors hunting uranium

Active — Mountain Pass was found in 1949 by prospectors looking for uranium, became the world's dominant rare earth source, shut in 2002 under environmental pressure and Chinese competition, and was restarted by MP Materials in 2017. It is operating again and is the only developed commercial rare earth source in the Western hemisphere.

Mountain Pass sits in the Clark Mountain Range of San Bernardino County, California, and it was not looking for rare earths at all. In 1949 three prospectors were hunting uranium, a mineral the Cold War wanted badly, when they instead found bastnaesite — a rare earth-bearing ore. That accident turned out to matter far more than the uranium would have.

Commercial production began in the early 1950s under the Molybdenum Corporation of America, known as Molycorp. Through the 1960s and into the early 1980s the mine was the West's rare earth engine, at its height supplying roughly 70 percent of world demand. A single pit in the Californian desert effectively underwrote the supply of the elements used in magnets, catalysts, polishing powders and phosphors.

The decline was slow and then abrupt. Environmental problems mounted — rare earth ore at Mountain Pass comes with radioactive thorium, and waste handling became a legal and financial problem — while Chinese producers scaled up with state support and undercut prices decisively. Production halted in 2002, and the site sat idle while concerns about dependence on Chinese rare earths quietly grew.

The revival came in two stages. Molycorp Minerals bought the property in 2008 and restarted mining in the 2010s, but the company collapsed into bankruptcy in 2015 — a spectacular failure of the "bring rare earths home" thesis. In 2017 MP Materials acquired the site and restarted production, and it has since moved beyond mining into separation and magnet manufacturing. Mounting demand for electric vehicles, wind turbines and defence applications has made Mountain Pass strategically important again in a way it had not been since the 1980s.

Quick facts

Location
Mountain Pass, San Bernardino County, California
Discovered
1949, by prospectors hunting uranium
What they found instead
bastnaesite, a rare earth ore
Peak
about 70% of world rare earth supply, 1960s to early 1980s
Production halted
2002
First revival attempt
Molycorp Minerals, 2008 (bankrupt 2015)
Restarted
2017, by MP Materials
Significance
the only developed commercial rare earth source in the Western hemisphere
Complication
the ore carries radioactive thorium

Lineage — where the name went

Mountain Pass is a place, not a company, so this tree follows the mine itself — who found it, and the four sets of owners it has passed through since.

  1. 1949 — Three uranium prospectors created Mountain Pass (discovered bastnaesite while hunting uranium)
  2. 1952 — Mountain Pass acquired by Molybdenum Corporation of America (commercial production begins)
  3. 1977 — Molybdenum Corporation of America acquired by Unocal (Unocal buys Molycorp)
  4. 2005 — Unocal acquired by Chevron (Chevron absorbs Unocal)
  5. 2008 — Mountain Pass acquired by Molycorp Minerals (Chevron sells the idle mine to a revived Molycorp)
  6. 2017 — Mountain Pass acquired by MP Materials (MP Materials restarts the mine)

Entities in this tree: Three uranium prospectors (person, 1949); Mountain Pass (place, 1949); Molybdenum Corporation of America (company, 1952); Unocal (company, 1977); Chevron (company); Molycorp Minerals (company, 2008); MP Materials (company, 2017)

Sources

  1. Mountain Pass history and timeline — MP Materials (2026-09-15)
  2. Molycorp prospectus: Mountain Pass is the only developed commercial rare earth source in the Western hemisphere — U.S. Securities and Exchange Commission (2026-09-15)
  3. Mountain Pass rare earth mine, San Bernardino County — NS Energy (2026-09-15)
  4. Rare earth mining may be key to our renewable energy future — but at what cost? — Ames National Laboratory (Science News) (2026-09-15)

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