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.[3] Wave erosion carved the arches and then cut away the cliffs leaving only islands. Of the three original arches only the middle one remains.