At several Alaskan North Slope localities south of the shore of the Arctic Ocean the Gubik Formation, herein regarded as latest Pliocene and Pleistocene in age, contains a marine unit at its base. Near Ocean Point and near Teshekpuk Lake this basal unit, or the lowest exposed marine unit, of the Gubik contains unusual, relatively warm-water marine mammals. Although these mammals have poorly known fossil histories, consideration of what is known suggests that the basal marine unit near Ocean Point is of latest Pliocene age, between 2.2 and 1.7 my old, and that the marine unit near Teshekpuk Lake is probably late Pleistocene, most likely correlating with the Sangamon Interglaciation and about 120,000 yr old. ?? 1983.