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Santa Margarita Sandstone Reconnaissance, Santa Cruz Mountains, CA

The Santa Margarita Sandstone is of early Late Miocene age (10-12 Ma) and is exposed in a broad belt through much of central and southern California, and as far north as Point Reyes. Fossils of sand dollars, sharks, dolphins, baleen whales, walruses, fur seals, sea cows, and desmostylians are abundant in portions of this rock unit exposed in the southern Santa Cruz Mountains. While much work has already been conducted on the fossil sea cow Dusisiren jordani and the walrus Imagotaria downsi from this unit, much more work remains to be conducted with respect to the other marine mammals (especially cetaceans).

Local collector C. Pirrone on the search for Santa Margarita Sandstone fossils.

C. Pirrone (above) and A. Poust (below) prospecting for fossils.

Here is the conformable contact between the Santa Margarita Sandstone (10-12 Ma) below and the Santa Cruz Mudstone above (~10-8 Ma).

Success! C. Pirrone discovered this lovely canine of the primitive walrus Imagotaria downsi. This is likely a lower canine, as it has a large wear facet on the crown consistent with wear due to the upper 3rd incisor.

Local collecter C. Argento exploring an abandoned sand and gravel quarry in the Santa Margarita Sandstone in the Santa Cruz Mountains.

View of the quarry wall, with a 2m thick sand dollar coquina exposed in the lower part of the photograph. The lighter green trees in the center of the photo mark the floor of the abandoned quarry.
A 3-4m thick sand dollar coquina exposed in the wall of the quarry.
Sand dollars (Astrodapsis spatiosus) weathering out of an exposure of the Santa Margarita Sandstone. These were beautiful, untouched specimens, being cleaned naturally by occasional rainfall. At typical localities accessible to hordes of amateur collectors, you are extremely lucky to find any over three inches in diameter. Here you could pick up a dozen 4-5" specimens in a few minutes.

Liz Johnson (North Carolina State University) exposing a bone in a different sand and gravel quarry, lower in the Santa Margarita Sandstone.

Same as above.

Piece of a baleen whale bone exposed in the lower gravels of the Santa Margarita Sandstone by Liz Johnson.
John O'Brien ( digging nearby at the same locality as above for shark teeth.
Uncovering a pathologic sea cow (Dusisiren jordani) from the lower gravels of the Santa Margarita Sandstone.