Geology: The fossiliferous layers are part of an unnamed Pleistocene formation. Once you park, walk down to the beach and look for the sedimentary rocks on the beach cliff. However, the geology of the area should be similar to the Monterey formation which contains both Gaviota Beach, and Jalama Beach.
Fossils: The layers of sandstone contain marine assemblages from the Pleistocene epoch.
Geology:
The Sespe Wilderness lies within the Transverse Mountain Ranges. The USGS has information on the geological setting of the mountain range province here. More specifically, the Sespe Wilderness and Sespe Condor Sanctuary are mostly within the Topatopa Mountains and foothills. The Topatopa Range is composed of Oligocene-Eocene age sandstones of the Juncal, Matilija, Cozy Dell, and Coldwater Formations. The uplifting of the Topatopa Mountains was chiefly caused by the San Cayetano fault, which was initiated at 1.9 Ma.
The fossils in the Sespe Wilderness are incredibly common and can be found on the trail and in the abundant boulders nearby. Marine shells can be seen exposed on the outside of eroded and smooth boulders, and on the surface of the rotated strata of the foothills.
Paleontology:
A variety of marine invertebrates are common in the area, including mussels, oysters, cephalopods, and other shelled organisms.
Works Cited:
MCKAY, HANNAH. QUATERNARY STRATIGRAPHY AND GEOLOGIC EVOLUTION OF OJAI AND UPPER OJAI VALLEYS, WESTERN TRANSVERSE RANGES, CALIFORNIA. P.2011
These oysters were found on the Huntington trail about 1.0 miles from the Thacher School. They are part of the Topatopa strata, which is dominantly marine in origin. The Topatopa Range is composed of Oligocene-Eocene age sandstones of the Juncal, Matilija, Cozy Dell, and Coldwater Formations. The uplifting of the Topatopa Mountains was chiefly caused by the San Cayetano fault, which was initiated at 1.9 Ma. The fossils were found in slightly consolidated, matrix- and clast- supported, pebble-boulder conglomerate ground from the Topatopa Mountains.
Chunk of mussel-dense rock
Example of Mussel Extracted
The Cenozoic bivalves were likely to have become extinct in the Pliocene mollusc extinction in California and particularly in the Etchegoin Group that occurred due to falling sea levels and the subsequent cooling of California waters. The mussels are dark blue and have a black sheen when wet. The specimens were hypothesized to be composed of calcium carbonate, which was reinforced by a Hydrochloric Acid test which dissolved it. The fossil have the appearance of regular oysters, and are shaped by concave contours.They were found in clusters, each facing random directions. There appears to be no pattern in their orientation or size.
