LATE OLIGOCENE AND EARLY TO MIDDLE(?) MIOCENE LAND PLANTS, UPPER PIUMA MEMBER, SESPE FORMATION, AND FERNWOOD MEMBER, TOPANGA CANYON FORMATION, CENTRAL SANTA MONICA MOUNTAINS, LOS ANGELES COUNTY, CALIFORNIA

Land plant taxa constitute two stratigraphically superposed floral assemblages in the upper unit of the Piuma (upper) Member (PM) of the continental Sespe Formation. The upper PM overlies the Saddle Peak Tongue of the marine Vaqueros Formation, which contains the lower Vaquerosian (late early to early late Oligocene) gastropod Turritella inezana bicarina and overlies late early Arikareean (late Oligocene) land mammals (including cricetid Leidymys nematodon), which occur in the lower PM. The Lower Piuma Road Florule (PRF), 4.5 m above the base of the upper PM, includes an otherwise unidentified arborescent land plant represented by compressions of logs that approach 2 m in length and are associated with the bones and teeth of Arikareean or early Hemingfordian land mammals. The Upper PRF, 7.9 to 8.5 m above the base of the upper PM, includes the sabal palm or Washington fan palm Sabalites and underlies early Hemingfordian (late early Miocene) land mammals (including cricetid Yatkolamys), which occur at the top of the upper PM.

One or more arborescent land plant taxa, including the plane tree- or sycamore-like form genus Platanoxylon, occur as petrified wood, including logs at least 2 m in length, at numerous sites in the upper half of the continental Fernwood (middle) Member of the overlying Topanga Canyon Formation. These taxa constitute the Calabasas Peak Motorway Florule. The plant-bearing interval is mostly if not entirely above the level of late Hemingfordian (late early to early middle Miocene) land mammals, including the equid Parapliohippus carrizoensis. Rodent remains occur at a site at or very near the base of the plant-bearing interval, and a specimen of Turritella(?) occurred as float at a site higher in the interval. The overlying marine Cold Creek (upper) Member 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).