The Guadalupe-Nipomo Dunes form an eighteen-mile coastal dune system on California’s Central Coast and remain the largest dunes south of San Francisco. Built over thousands of years by windblown sand and Santa Maria River sediment, they include the highest dunes on the western U.S. coast and the rare freshwater Oso Flaco Lake. Protected for their ecological importance, the dunes support many endangered plants and hundreds of bird species, while conservation since the 1970s has worked to restore habitat and control invasive species. The area also preserves a deep human history, from Chumash habitation and the Portolà expedition to the Dunites, Cecil B. DeMille’s 1923 film set, and later oil contamination followed by long-term cleanup.