In 1949, prospectors looking for uranium detected unusual radioactivity in the Clark Mountain Range and identified bastnäsite, a mineral rich in rare earth elements. This discovery set the stage for Mountain Pass to become a major U.S. source of rare earths used in electronics and other technologies.
In 1950–1951, the Molybdenum Corporation of America (MCA) purchased major mining claims that included the Birthday claims and the Sulfide Queen property. This consolidated control of the deposit and enabled MCA to build a long-term mining and processing operation.
MCA began producing rare-earth concentrate at Mountain Pass in 1952, initially using existing equipment and a modest processing setup. Early production focused on concentrates (partially processed ore), while broader commercial markets for rare earth products were still developing.
In the mid-1960s, demand for europium (used in red phosphors for color televisions) triggered large expansions at Mountain Pass. MCA built specialized processing capacity and increased output sharply, moving the site into a period of global importance for rare earth supply.
In 1974, MCA changed its name to Molycorp. Through the following decades, Mountain Pass supplied a large share of global rare earth demand, especially for “light” rare earths like cerium, lanthanum, neodymium, and praseodymium.
In 1977, Union Oil of California (Unocal) purchased Molycorp and operated it as a wholly owned subsidiary. This ownership shift placed Mountain Pass within a larger energy company, shaping later decisions about operations and environmental compliance.
After major pipeline releases in 1996 affected federal lands near Ivanpah Dry Lake, the Lahontan Regional Water Quality Control Board issued Cleanup and Abatement Order 6-97-66 to Molycorp in April 1997. The spills drew in federal agencies because of impacts to sensitive desert habitat, including threatened desert tortoise areas.
In March 1998, regulators prohibited Molycorp from using the wastewater pipeline and the New Ivanpah evaporation ponds, citing repeated spills and groundwater contamination concerns. This forced a shift toward alternative waste handling, including off-site disposal and planning for on-site treatment.
In April 2000, the San Bernardino County Planning Commission granted a Conditional Use Permit for a proposed on-site wastewater treatment project. The permit supported a move away from the long pipeline disposal approach toward lined ponds and treated wastewater disposal methods intended to meet water-quality requirements.
Molycorp stopped using the P-16 tailings impoundment in 2002, marking a major change in site waste management. The impoundment was later permanently closed in 2006, reflecting increased emphasis on long-term containment and reclamation.
In 2007, Chevron Mining reactivated part of the separation plant using stockpiled rare earth concentrates as feedstock. This partial restart produced certain rare earth products while broader mining activity remained limited compared with earlier decades.
On September 30, 2008, Chevron sold the Mountain Pass facility and rare earth business to a private investor group (via Rare Earth Acquisitions LLC, later renamed Molycorp Minerals LLC). The buyers planned to modernize and expand operations after years of limited activity.
In July 2010, the reorganized Molycorp completed an initial public offering, raising capital tied closely to rebuilding Mountain Pass. The IPO period marked a renewed push to restore U.S. rare earth production capacity amid concern about global supply dependence.
By January 2012, the last section of the formerly used wastewater pipeline corridor to the Ivanpah ponds was removed, after a multi-year effort. The work included removal of about 14.8 miles of pipeline and remediation of contaminated soil linked to past releases during maintenance activities.
In June 2015, Molycorp filed for Chapter 11 bankruptcy protection after struggling with high costs, operational challenges, and weak rare-earth prices. Mining and processing operations were halted, and the site entered another transition period as ownership and assets were restructured.
In July 2017, MP Mine Operations (MPMO) acquired Mountain Pass and its processing facilities out of bankruptcy. The new owner focused first on stabilizing basic mining and concentration steps to restore reliable output before moving to more advanced refining.
After restarting operations in late 2017, MP began producing bastnäsite concentrate and made its first concentrate sales in early 2018. This marked the practical return of Mountain Pass as a steady producer, even though much downstream refining still occurred outside the U.S. at that time.
In 2023, MP completed construction and initial commissioning of its “Stage II” optimization to restore the capability to produce separated rare earth products on-site. After commissioning, MP began producing separated products in 2023 and started selling separated rare earth products, including NdPr oxide, in the fourth quarter of 2023.
In July 2025, Apple announced a $500 million multiyear commitment tied to buying U.S.-made rare earth magnets from MP and collaborating on an all-new recycling line at Mountain Pass. The plan links Mountain Pass not only to mining and separation, but also to end-of-life recovery of rare earths from used electronics and manufacturing scrap.
In July 2025, MP announced a major public-private partnership with the U.S. Department of Defense (DoD), including a planned $400 million preferred-stock investment and a $110/kg price floor commitment for NdPr products. In August 2025, DoD announced a $150 million direct loan to support adding heavy rare earth separation capabilities at Mountain Pass, linking the mine more directly to U.S. national security supply goals.
Mountain Pass mine, California — production, ownership, and remediation timeline (1950–present)