Thornton State Beach is a protected beach in the state park system of California, USA, but is officially closed to the public. It is located on the Pacific coast of Daly City in the San Francisco Bay Area. The park was closed due to damage and continued danger from landslides, though locals still access the site for hiking, horseback riding, and beach activities. The 58-acre (23 ha) park was established in 1955.
The Mediterranean climate tends toward cold and wind, with fog common in summer.
The beach was named for the first white settler of the area, one Robert S. Thornton of Rhode Island, a blacksmith who had arrived in the San Francisco area in 1851.