The extent of amino acid racemization in Chione, Tivela, Mytilus, and Protothaca shells has been analyzed to estimate ages of seven raised marine terrace sites in San Diego County, California. Sites at Scripps and Crown Point are correlated with the Nestor terrace (120,000 yr old). Sites at Del Mar, Tecolote Creek, and Border Park are estimated to be about 200,000 yr old. A site at Morena Boulevard is somewhat more than 300,000 yr old, and a Linda Vista terrace site is too old to be dated by this method.
The ages of terraces derived in this and previous studies demonstrate tectonic activity in the area and suggest the need for reassessment of geomorphic correlations and for comparison of fossil assemblages of similar age for paleobiogeographic interpretation. Amino acid dating is a useful method for estimating the ages of raised marine terraces a few hundred thousand years old.