Yucca Mountain is a ridge-like volcanic mountain in southern Nevada near the California border, shaped by ancient explosive eruptions whose ash and rock fragments hardened into layers of tuff, then were tilted by faults and fractured as they cooled. Most of this volcanic activity ended about 12 million years ago, though smaller eruptions in the surrounding area continued until about 80,000 years ago. The mountain and nearby lands were central to the Western Shoshone and Southern Paiute for ceremony, resources, and gathering, and it remains sacred to Shoshone people. In modern times, it became nationally significant as the proposed site for the nation’s spent nuclear waste repository, a project still contested after federal defunding in 2010.