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The Mountain Pass Mine, located in the Mojave Desert of southeastern California, is the largest and currently the only producing rare earth element (REE) mine in the United States. Its history dates back to the 1940s, when prospectors exploring the Clark Mountain Range sought uranium deposits amid the Cold War-driven demand for nuclear materials. In 1949, rather than uranium, the prospectors discovered bastnaesite, a mineral rich in rare earth elements crucial to modern technologies.
Rare earth elements, a group of 17 chemical elements, are widely distributed throughout Earth's crust but are rarely concentrated enough to make extraction economically viable. REEs are critical to manufacturing magnets, speakers, smartphones, microphones, vibration monitors, and advanced communication devices.
The Mountain Pass open-pit mine spans approximately 800 meters (2,600 feet) across and plunges to depths of more than 180 meters. Beneath the surface lies a 1.7-billion-year-old carbonatite terrane dating from the Paleoproterozoic era. This carbonatite formation, intruded later by alkaline magmas, became a prime site for REE mineralization. Despite extensive study, the precise geological processes that formed the exceptionally rich REE deposit at Mountain Pass remain not fully understood.
Mountain Pass supplied a major portion of the world’s rare earths from the 1960s through the 1990s, playing a pivotal role in global technology development. Today, it is owned and operated by MP Materials (NYSE: MP) and represents a strategic asset for U.S. national security and technological independence.
On April 8, 2025, the U.S. Department of the Interior (DOI) officially approved development activities at the Colosseum rare earths project, located within the Mojave National Preserve in San Bernardino County, California. This project, owned by the Australian company Dateline Resources (ASX: DTR), marks a significant milestone: it will potentially become America’s second rare earth mine after Mountain Pass.
For years, the project was delayed due to its sensitive location within federally protected desert lands. However, the DOI’s recent communication confirms that Dateline Resources’ rights under both the Mining Act and the California Desert Protection Act remain valid, paving the way for active exploration and development.
The federal government's decision aligns with national efforts to boost domestic production of critical minerals, an initiative intensified under President Donald Trump’s executive orders focused on enhancing the United States’ critical mineral supply chains, particularly to reduce reliance on Chinese imports.Dateline’s Managing Director Stephen Baghdadi stated that the DOI’s support "provides a strong foundation" for accelerating the Colosseum project's development.
Upon review, Dateline concluded that the Colosseum Project shares critical geological features with the neighboring Mountain Pass deposit. Both sites are situated along the Colosseum–Mountain Pass corridor, an area distinguished by its unique carbonatite-related geology. Radiometric surveys conducted by the USGS have indicated strong REE-associated radiometric anomalies within this corridor. The Colosseum's geological setting, characterized by carbonatite intrusions and surrounding alkaline rocks, is highly favorable for rare earth mineralization.
At present, Colosseum does not yet have a rare earth resource estimate, but Dateline’s technical assessments suggest considerable potential for REE-bearing ore within its claims.Additionally, Dateline has defined a JORC-2012-compliant gold resource at Colosseum totaling 1.1 million ounces, with about two-thirds classified as measured and indicated. An internal scoping study completed in August 2024 outlined a projected mine life of more than eight years, targeting an average production of 75,000 ounces of gold per year.
The development of the Colosseum Project carries broad strategic significance. At present, Mountain Pass remains the only active REE production facility in the U.S., while China dominates over 60% of global rare earth mining and nearly 90% of refining capacity.
Adding a second U.S. rare earth operation could greatly improve national security, especially for industries such as renewable energy, electric vehicles (EVs), aerospace, defense systems, and advanced electronics, all of which depend heavily on rare earth materials.
Moreover, Colosseum's proximity to Mountain Pass could create valuable synergies, allowing shared infrastructure, technical expertise, and supply chain efficiencies. Together, these operations could reestablish southern California as a vital hub for rare earth production and processing, significantly strengthening the domestic supply of critical minerals.