Analyses of uranium isotopes and their long-lived daughter products showed evidence of uranium migration in most of the 22 fossil mollusk shell samples from marine terrace deposits in southern California. Two samples, however, remained an ideal closed system as indicated by concordant 230Th/234U and 231Pa/235U dates. The closed-system age of the lowest exposed marine terrace deposit along part of the mainland coast of southern California is 69 000 ?? 10 000 yr, and correlation of this discontinuous deposit is afforded between the Newport Beach-Laguna Beach area and the Palos Verdes Hills. Some mollusk shell samples were dated by the open-system model; the remaining samples were found to be unsuitable for uranium-series dating. ?? 1971.