Conversion of temperature facies into depth facies appears to offer the most satisfactory interpretation of the marine Pleistocene faunas of California.
On that basis the fossils of the early Pleistocene formations, which are found in the mobile Los Angeles and Ventura basins, represent a wide range of neritic environments, from a minimum depth of 10 fathoms or less to a maximum of about 100 fathoms.
Late Pleistocene marine deposits, consisting of deposits on marine coastal terraces, generally have a littoral tide-pool and rock-cliff association, more or less diluted by an admixture of species that live below low-tide line and presumably represent debris carried shoreward by storm waves. Some localities, however, are characterized by a shallow-neritic protected-bay association.
Despite the presence of cool-water species in some associations and warm-water species in others, recognition of glacial and interglacial faunas is doubtful.
No matter how these Pleistocene faunas are interpreted, there remain some irreconcilable features in terms of present distribution and environment. Perhaps some species have evolved in physiological characters since Pleistocene time without any apparent evolution in morphological characters available to paleontologists.