Most of the sandy beaches in southern California are artificially replenished. The rivers that used to carry new sand to the sea have been dammed and cemented, reducing or eliminating the natural source of sand. Beach sand is made up of fragments of shells and rocks with many exposed edges. The color and texture of the sand is dependent upon the source of sediments. Seasonal changes result in significant changes in the profile of the beach.
Winter storms wash sand off the beach and often leave a steep profile behind.
Gentle summer waves build up the beach. Much like a desert, sandy bottoms look barren, yet they host large numbers of animals. Most of these animals blend in with the sand while others burrow for protection. Plants do not live on the sandy beach since there is no stable surface for attachment. The beach wrack, made up of plants and other materials washed on shore by the tide, provides temporary refuge and food for animals along the high tide line.