Oakland Geology

The skull of a Pleistocene mammoth appears on this building at Telegraph and Sycamore.

Oakland’s youngest rocks are Miocene in age, around 10 million years. Next in age come the gravels and sands of Pleistocene time, within the last 2 million years or so. (I’m vague about this number because the definition of the Pleistocene just changed, and because I don’t know any firm dates for these sediments.) Any material from the time in between either was erased by erosion or never existed.

Because the great glaciers sucked more than 200 feet of water out of the ocean, Ice Age Oakland was part of an enormous grassland that extended across today’s Bay and far west of today’s coastline. State Parks paleontologist Breck Parkman has called it a California Serengetti (sic), teeming with large herbivores and predators to match, all of them extinct today except the condor.

Remains of these animals have been found in Oakland. When the Alameda Tube was being dug, fossils of ground sloths, short-faced bears, mammoths, camels and bison were recovered. Mammoth remains have been found in the Harris Street Tunnel, Montclair Playground, and 81st Avenue. A Pleistocene horse was found at Oak Knoll Hospital. A ground sloth was found at the Coliseum. When the next large-scale excavations happen in Oakland, the diggers may find these as well as fossils of dire wolves, mastodons, deer, llamas, pronghorns and smaller ground-dwelling mammals.

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