On top are the Pleistocene San Pedro and Pleistocene-upper Pliocene Santa Barbara formations; under that the Pico Sands, of Pliocene age, which contain areas of tar sands; under that, separated by an unconformity, the Monterey Formation, of Miocene age, which also contains tar sands (the Vaca Tar Sand); under that, again separated by an unconformity, the relatively impermeable Conejo-Topanga Formation, which caps the faulted anticlinal structure containing medium-grade oil about 6500 feet below ground surface.