WhereIsAtlas · Rare earths

What Happened to the Mountain Pass Mine?

Three prospectors hunting uranium found rare earths instead — and a single Californian pit went on to supply most of the world. Then it shut for 15 years.

Mountain Pass was found in 1949 by prospectors looking for uranium, became the West's dominant rare earth source at roughly 70% of world supply, closed in 2002 under environmental pressure and Chinese competition, and was restarted by MP Materials in 2017. It is the only developed commercial rare earth source in the Western hemisphere.

A mine that was looking for something else

In 1949, three prospectors were working the Clark Mountain Range in San Bernardino County, California, searching for uranium. What they found instead was bastnaesite — an ore rich in rare earth elements, the seventeen metallic elements that would later become essential to magnets, catalysts and phosphors.

Uranium was the strategic mineral of that moment. Rare earths were a curiosity with industrial uses nobody had yet scaled. The accident at Mountain Pass turned out to be the more valuable discovery by a wide margin.

The West's rare earth engine

Commercial production began in the early 1950s under the Molybdenum Corporation of America, or Molycorp. Over the following decades the mine became the backbone of Western rare earth supply — at its peak, roughly 70 percent of world demand came out of this one deposit.

That concentration is worth pausing on. For two decades, the global supply of a strategically important group of elements ran through a single open pit in the Californian desert, operated by one company.

Why it closed

Two forces ended that era. The first was environmental. Rare earth ore at Mountain Pass is not clean: it carries thorium, which is radioactive, and the waste streams from processing became a mounting regulatory and financial liability.

The second was China. Chinese producers scaled up aggressively with state backing and priced Western production out of the market. Facing both, Molycorp halted production in 2002. The mine that had supplied most of the world went quiet.

The revival that failed

The first attempt to bring it back became a cautionary tale in its own right. In 2008, Chevron — which had inherited the site through its acquisition of Unocal — sold Mountain Pass to a revived Molycorp, which restarted mining in the 2010s on the thesis that the West needed its own rare earth supply.

It did need it. But needing something is not the same as being able to produce it profitably against a competitor with far lower costs and far more patience. Molycorp filed for bankruptcy in 2015.

MP Materials and the second revival

In 2017, MP Materials acquired the site and restarted production — and unlike its predecessor, it did not stop at digging ore out of the ground. It has since built out separation capacity and moved toward magnet manufacturing, the higher-value stages of the chain.

That shift matters because the hard part of rare earths is not mining. It is the chemical separation and the magnet-making that follow, and those steps had become overwhelmingly Chinese. Mountain Pass is the West's answer at the mining end; the company's bet is that it can be an answer further up the chain too.

Why anyone cares again

Rare earths are not rare in the earth's crust — the name is a historical accident. What is rare is economically viable, separated, processed supply outside China. Those elements are in the magnets inside electric vehicle motors, wind turbine generators, headphones, hard drives and guided missiles.

That is why a mine that was abandoned in 2002 became strategically significant again within a decade. Concern about supply dependence did not exist because rare earths ran out. It existed because almost all of the processing had moved to one country.

Where Mountain Pass is now

Mountain Pass is operating: the pit is active, ore is being processed, and its owner is expanding into the stages of the supply chain that matter most. It remains the only developed commercial rare earth source in the Western hemisphere, which is simultaneously its strategic value and its fragility.

The mine's story is a reminder that supply chains are not decided by geology alone. The rock was always there. What changed — twice — was who was willing to process it.

Frequently asked questions

These are the questions people actually search for about Mountain Pass, answered directly.

Is the Mountain Pass mine still operating?

Yes. MP Materials restarted production in 2017 and the site is operating, with the company expanding into rare earth separation and magnet manufacturing.

Why did the Mountain Pass mine close?

Production halted in 2002 because of environmental costs — the ore carries radioactive thorium — and because Chinese producers undercut Western prices.

Who owns the Mountain Pass mine now?

MP Materials, which bought the site in 2017. Before that it passed through Molycorp, Unocal, Chevron and a failed revived Molycorp.

Are rare earths actually rare?

No. Several are more common in the crust than copper or lead. The difficulty is that they occur together and are expensive and environmentally messy to separate, so usable supply is concentrated in a few places.

Why is Mountain Pass important?

It is the only developed commercial rare earth source in the Western hemisphere, giving the United States a domestic mining foothold in a supply chain otherwise dominated by China.

Entries in this story

• Mountain Pass Mine

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)