After a short period of extensive deformation and erosion, the Monterey Shale was deposited on top of the Upper Topanga Formation. This photo, taken on the east side of the 405 Freeway and south of the Mulholland Drive bridge, shows the pebble conglomerate that was deposited at the base of the Monterey Shale. Note that the pebbles are mostly made of black slate. The black slate comes from the Santa Monica Formation, the oldest rock unit in the Santa Monica Mountains, which will not be seen until Day 3 of the hike, but which occurs here immediately under the Monterey Shale. This occurrence proves that all the Cretaceous, Paleocene, and Miocene rock units described above were removed by erosion prior to deposition of the Monterey Shale.
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