The Mountain Pass rare earth mine in California sits at the start of the US rare earth supply chain. For most of its recent history, though, the ore left the country before it became anything useful. The concentrate was shipped abroad, and the separation into individual elements took place in China. How that arrangement formed and how it unravelled explains a lot about the weak points in Western rare earth supply.
What lies under Mountain Pass
According to the technical report summary that MP Materials filed with the US Securities and Exchange Commission (SEC), the deposit is a carbonatite deposit enriched in rare earth elements. Its main rare earth mineral is bastnaesite.
The US Geological Survey (USGS) reports that bastnaesite was mined as a primary product at Mountain Pass in 2025. In its Mineral Commodity Summaries 2026 chapter on rare earths, the USGS also identifies magnets as the leading global use of rare earths. That matters for Mountain Pass, because neodymium and praseodymium (NdPr) are the elements that end up in permanent magnets.
A mine with a long stop-start history
Mountain Pass has never run smoothly for long. Molybdenum Corporation of America began rare earth mining there in 1952, according to MP Materials' annual report (10-K) for 2020. Unocal bought that company in 1977 and production continued until 1998. Chemical processing was then suspended, mainly because of leaks in a wastewater pipeline.
Ownership changed again in the 2000s. ChevronTexaco acquired Unocal in 2005, and Molycorp bought the facility from Chevron Mining in 2008. Molycorp invested heavily in new processing and separation plants. Even so, operations were placed into cold idle after the company declared bankruptcy in June 2015.
MP Materials acquired the mine and processing facilities out of bankruptcy in July 2017. Mining and milling restarted between December 2017 and February 2018, and the first concentrate sales followed in the first quarter of 2018.
Why the concentrate went to China for processing
Mining bastnaesite and producing a concentrate is only the first step. The rare earths in the concentrate then have to be separated from each other, which is a long, chemically demanding stage. When Mountain Pass restarted, it had no separation of its own in operation, so processing in China became the default route for its concentrate. The arrangement mirrored China's control over rare earth processing.
The commercial structure followed the technical one. MP Materials' 10-K for 2020 states that the company sold its concentrate to an affiliate of Shenghe Resources Holding on a take-or-pay basis under an offtake agreement first signed in 2017. Shenghe sold the concentrate on to customers in China, who separated the individual elements. In the same filing, MP Materials said it expected to stop selling concentrate once its own separation project was complete.
Government support and the push for domestic processing
The US Department of Defense (DoD) has funded several steps aimed at moving separation, and later magnet production, onto US soil. The amounts and terms below are taken from MP Materials' announcements and filings:
- November 2020: a $9.6 million award under Title III of the Defense Production Act to establish domestic processing of separated light rare earth elements.
- February 2022: a $35 million contract from the DoD's Industrial Base Analysis and Sustainment programme for a commercial-scale plant at Mountain Pass to process heavy rare earth elements.
- July 2025: a public-private partnership. The DoD agreed to buy $400 million of a new series of MP Materials' convertible preferred stock, set a 10-year price floor of $110 per kilogram for the company's NdPr products, and committed that all magnets made at a planned new magnet plant (the "10X Facility") would be bought by defence and commercial customers for 10 years. MP Materials also said it expected a $150 million DoD loan for heavy rare earth separation at Mountain Pass. The price floor is a contract term, not a signal of future market prices.
The 2025 break with Chinese processing
The trade dispute between the US and China changed the arrangement in 2025. In its quarterly report (10-Q) for the period to 30 June 2025, MP Materials stated that in April 2025 it made the strategic decision to cease shipments of rare earth concentrate to China, in response to China's retaliatory tariffs and export controls. The company said it was prioritising processing concentrate into separated products or stockpiling it.
The USGS records the policy background. In April 2025 China tightened export controls on rare earth elements. In November 2025 it suspended for one year the export controls it had introduced in October.
What the US still depends on
The domestic picture has improved, but dependence on imports remains high. The USGS estimates that US net import reliance for rare earth compounds and metals was above 90% in 2021–2023. It fell to 53% in 2024 and was an estimated 67% in 2025.
China (including Hong Kong) supplied 71% of US imports of rare earth compounds and metals over 2021–2024, followed by Malaysia (13%), Japan (5%) and Estonia (5%), according to the same USGS chapter. Mountain Pass alone does not close that gap. A mine supplies concentrate, while the products that manufacturers actually buy, such as separated oxides, metals and magnets, depend on capacity further down the chain.
That downstream capacity is still being built. In the technical report summary filed with the SEC in February 2026, MP Materials describes a recommissioned separations facility at Mountain Pass designed to produce four saleable products: PrNd oxide, SEG+ precipitate, lanthanum carbonate and cerium chloride. The report states that full output from the separations facility is expected by approximately the first quarter of 2027. Until then, Mountain Pass remains a mine in transition from exporting concentrate to supplying separated materials inside the US.