LATE OLIGOCENE AND EARLY MIOCENE LAND MAMMAL BIOSTRATIGRAPHY, PIUMA MEMBER, SESPE FORMATION, AND FERNWOOD MEMBER, TOPANGA CANYON FORMATION, SADDLE PEAK AREA, CENTRAL SANTA MONICA MOUNTAINS, LOS ANGELES COUNTY, CALIFORNIA

Continental vertebrate taxa constitute at least two stratigraphically superposed faunal assemblages in the Piuma (upper) Mbr. (PM) of the continental Sespe Fm. (SF) in the Santa Monica Mtns. The Lower Piuma Road (PR) Local Fauna (LF) (4.3 to 19.9 m above base, PM) includes an anuran, a didelphid (Herpetotherium?)/insectivore, and the Arikareean cricetid Leidymys nematodon. In the transitional zone between the SF and the overlying marine Vaqueros Formation (VF) of Simi Valley, L. nematodon occurs in late Oligocene Chron C9r, 1.5 to 36.3 m above the first (late early Arikareean) occurrence of archaeolagines (Archaeolagus?). In the San Emigdio Mtns., L. nematodon occurs 7.6 to ~75.0 m below the top of the lower mbr. of the Tecuya Fm. Laterally equivalent, late Oligocene strata in the marine Temblor Fm. contain the upper lower to lower middle Vaquerosian bivalve "Macrochlamis" magnolia ojaiensis and upper Zemorrian benthic foraminifers.

The 5.2-m-thick Saddle Peak Tongue of the VF (97.8 to 103.0 m above base, PM) separates the lower and upper units of the PM and contains the lower Vaquerosian (late early to early late Oligocene) gastropod Turritella inezana bicarina. The Upper PRLF (427.0 to 428.9 m above base, upper PM; 7.4 to 9.3 m below basal conglomerate, marine Saddle Peak [lower] Mbr. [SPM], Topanga Canyon Fm.), includes an ochotonid, the heteromyid Trogomys, which last occurs in late early Miocene Chron C5Er in the SF/VF transitional zone in the Santa Ana Mtns., and the early Hemingfordian (late early Miocene) cricetid Yatkolamys. The SPM contains the upper Vaquerosian (early Miocene) bivalve Vertipecten bowersi. The Stunt Road LF, which includes an insectivore, the heteromyid Proheteromys sulculus, the late Hemingfordian (late early to early middle Miocene) equid Parapliohippus carrizoensis, and a camelid, occurs near the middle of the overlying continental Fernwood (middle) Mbr. The overlying marine Cold Creek (upper) Mbr. contains the Temblorian (late early to late middle Miocene) gastropod Turritella temblorensis and is overlain by the Conejo Volcanics (16.0 to 13.4 Ma, middle Miocene).