Natural Bridges State Beach is a 65-acre (26 ha) California state park in Santa Cruz, California in the United States. The park features a natural bridge across a section of the beach. It is also well known as a hotspot to see monarch butterfly migrations. The Monarch Butterfly Natural Preserve is home to up to 150,000 monarch butterflies from October through early February.
Natural Bridges State Beach is named for the naturally occurring mudstone bridges that were carved by the Pacific Ocean into cliffs that jutted out into the sea. The arches formed over a million years ago when a combination of silt, clay and diatoms were solidified into a mixture of stone that formed the three original arches of the beach. Wave erosion carved the arches and then cut away the cliffs leaving only islands. Of the three original arches only the middle one remains. The outermost arch fell during the early 20th century and the inner arch collapsed during a storm in 1980. The middle arch is in danger of collapsing as well due to erosion by wind and waves. Visitors were formerly permitted to climb up, walk and even drive on the bridges. Now the arch is closed to public access.
Natural Bridges State Beach is open to year-round recreation including swimming, surfing, hiking, nature walks and picnics. The beach is small and sheltered. The afternoon winds attract kite flying and wind surfing. The beach is open to surfing and is busiest during the winter when large swells wash up onto the shores of Natural Bridges State Beach. Hiking trails pass through the Moore Creek estuary and the Monarch Butterfly Nature Preserve. Guided tours of the butterfly preserve take place on weekends during the fall and winter. Tours of the tidal pools take place year-round as do nature walks.