UNEARTHING ANCIENT HISTORY
Discovery: Dam construction project uncovers whale skulls, giant shark teeth Fossils: More than 1,500 items dating back 20 million years have been found
For the past five years, construction workers building a new 220-foot-high dam in the remote canyons east of Milpitas and Fremont have been slowly discovering a long-ago, not-quite-tropical world of buried treasures, from giant shark teeth to whale skulls to pieces of ancient palm trees. Now the huge haul of fossils beneath the Calaveras Reservoir is heading for a permanent new home at UC Berkeley.
What began with a few shells has steadily grown into one of the most significant fossil discoveries in the Bay Area in decades, scientists say, painting a picture of the region roughly 15 to 20 million years ago, when large areas were submerged under a vast, shallow inland sea that stretched to Bakersfield.
“It was warmer in the Bay Area
then. We had large palm trees,” said Cristina Robins, a paleontologist hired by UC to manage the new collection. “It would have been like San Diego or L.A., but without the smog.”
Construction crews have blasted and dug roughly 500 feet down to construct the new dam as part of an $823 million seismic upgrade project at the 1920sera reservoir, scheduled for completion next year. So far they have found more than 1,500 fossils, and they are still finding them.
The San Francisco Public Utilities Commission, which owns the reservoir that is part of its Hetch Hetchy water system, has agreed to provide $500,000 to the UC Museum of Paleontology to set up a new lab for the fossils and assemble a team to work on the collection for the next two years.
The museum, said its education and outreach director Lisa White, plans to use the fossils on its website and in classrooms at Bay Area schools and universities in the coming years to explain geology, climate change and other historic processes that have shaped the planet over millions of years. Some of the fossils will be shown to the public from 9 a.m. to 4 p.m. on Saturday in Room 1101 of the Valley Life Sciences Building at UC Berkeley as part of Cal Day, the university’s annual open house.
Workers have found six teeth from a megalodon, an extinct species of shark similar to a great white that grew up to 50 feet long. They also have found teeth from a hippopotamus-like creature called a Desmostylus that had tusks and spent most of its life in the water. And they have found ancient scallops the size of dinner plates, and parts of seals, and bony fish like halibut, clams, snails, mussels and barnacles.
One of the main finds: 20 whale skulls, each from animals about 15 to 25 feet long, including from baleen whales, toothed whales and dolphins.
In one large chunk of rock on a table in her lab recently, Robins pointed to hundreds of tiny lines. They are fossilized ship worms, she said, a type of saltwater mollusk known as the “termite of the sea” that is notorious for boring into wooden piers, docks and ships.
“Every cylinder you see is a ship worm,” she said. “We assume this is a conifer tree. It was probably driftwood or part of a landslide.”
There have been other famous fossil finds in the Bay Area. A few turned up during the construction of the Caldecott Tunnel’s new bore in 2012 to 2014. Among the most famous discoveries was at the Bell Quarry in Irvington, near Fremont, in the 1940s, when a group of boys from Hayward spent years digging in a gravel quarry. They found the bones of Ice Age creatures including mammoths, bears, dire wolves, sabertooth tigers, horses, camels, and a new species of fourpronged antelope.
The boys were featured in radio and newspaper stories and even were written up in Life magazine in 1945. The quarry, now closed, is under Interstate 680, between Washington Boulevard and Durham Road, and the fossils are in museums.
Jim Walker, a paleontologist who has been working on the Calaveras Dam site since 2011, has trained dozens of construction workers on what to look for.
“You spend a lot of your day being wrong,” he said. “You say, ‘Hey, that looks like something!’ But 97 percent of the time, it’s a rock. What you are looking for is something different.”
Dark, spongy-looking streaks through rocks can be a bone. A shiny black or dark gray patch can be the enamel on an ancient tooth.
Once fossils are located — and Walker has dug out everything from the small teeth of bat rays to the whole backbones of whales — they are taken to the UC Berkeley Museum of Paleontology.
Crews mark the locations where each was found with GPS. Then graduate students and undergraduates in the lab photograph them, wash them, set up a tracking sheet for each one, catalog it in an online database, and photograph each step of the work.
Every whale skull takes hundreds of hours to prepare. They often look to the casual observer like big rocks. Using electric chisels, metal picks, saws, grinders and other tools, even toothbrushes, Robins’ lab workers slowly and painstakingly chip away, sometimes taking weeks to unearth the fragile fossils that have been trapped for millions of years inside sandstone, shale and other geologic tombs.
“That whale skull started as a 600-pound block,” Robins said. “It now weighs about 150 pounds.”
She pointed at a shiny black tooth in another rock.
“This was probably similar to a mako shark. Maybe about a 10-footer.”
Then to a big chunk on another desk.
“This was a gigantic palm tree,” she said. “Look, it has barnacles on it.”
Crews have finished the spillway and have another 80 feet to go to finish the new dam. The old one will be largely submerged under the lake, which will remain the same size as before — 96,850 acre feet — with a broad enough dam base so that it could be raised one day. The entire project should be done by late next year.
“All of the challenges are behind us,” said construction manager Susan Hou. “In October or November, we should be ready to start filling the reservoir up. Depending on the rain, it could take one year or a few years.”
Until then, when everything will be submerged again for 100 years or more, the fossils keep coming out.
“We get one shot at it,” said Robins. “Everything in here is irreplaceable, a new scientific record.”