Mount Diablo, an isolated peak in Contra Costa County, dominates the eastern San Francisco Bay Area with exceptional visibility and sweeping views that made it a landmark during the gold rush and early statehood. Sacred to many California Native peoples, including Ohlone and Miwok communities, it is tied to creation narratives and older Indigenous and Spanish names. Its summit became the reference point for land surveys across much of northern California and Nevada after Colonel Leander Ransom selected it in 1851. Later roads, a hotel, and a navigation beacon increased access and prominence, while park creation, Civilian Conservation Corps work, and preservation efforts led by Mary Leolin Bowerman helped protect it.