Natural Bridges State Beach is named for the naturally occurring mudstone bridges that were carved by the Pacific Ocean into cliff 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.