When one moves enough dirt to fill four Levi’s Stadiums, they just might find hidden treasures. In the case of the Calaveras Dam Replacement Project, fossils were found.

Calaveras is located 33 miles east of the Pacific Ocean. About 15 and 20 million of years ago it was next to an inland ocean. The water was deep enough for whales, Megalodon sharks, scallops and even hippopotamus-like creatures to flourish. This is evidence to the amount of fossils that were found during the replacement and reconstruction of the Calaveras Dam.

Because the site had a high potential for finding fossils, the SFPUC put a paleontological monitoring plan in place. Workers in the field received environmental training to be aware of the paleontological plan while performing their tasks at the job site. If they found something that looked like bone, they were instructed to stop work and call the paleontologist team. From there, the paleontologist team assessed, salvaged and documented their findings. One of the crew members found a four inch Megalodon shark tooth.  

Calaveras Dam Replacement Project paleontologists, Bruce Hanson and Jim Walker, were on site to help recognize and excavate the different fossils. Dirt and rocks were removed layer by layer until the fossils are revealed. Each finding was then measured and documented. Discovery of larger marine fossils like a whale skull had to be wrapped in a plaster jacket before it was removed. This consisted of strips of burlap that was soaked in an adhesive mixture and applied to the bone. The wrap protected and kept the bone in tacked when it was removed from the ground and transported to the lab for cleaning and identification. Walker’s tool kit included chisels, picks, brushes, small pick-hammer, ruler, bayonet and cleaning solutions. Occasionally a jack hammer was used to break up the rocks and get to the fossils.

It took a crew and a crane crawler operator to safely move the whale skull from the dig site to the back of the truck. The skill and experience of the operator were very important in order to safely and slowly maneuver the crawler down a narrow path way on the side of the slope. The truck then delivered the fossils to the University of California Museum of Paleontology (UCMP) lab where they were cleaned, assembled and identified.

In the end, over 5,000 fossils were found, including over 20 whale skulls and vertebrae with the possibility of discovering a new whale species.

Now that the Calaveras Dam Replacement Project is done, Jonathan “JT” Mates-Muchin, SFPUC Project Environmental Compliance Manager, shared that the excavated fossils have a home at the UCMP at the University of California, Berkeley.

“For the past two years, scientists, graduate and undergraduate students, and volunteers have been working with the fossils to clean, identify, store and catalogue the fossils,” said Mates-Muchin. “They are well above 4,000 catalogued fossils which is very exciting for the paleontological community. And you can view the cataloged specimens on the UCMP website.”

For Mates-Muchin, one of his favorite paleontological discoveries was the fossil teeth of the Megalodon and the Desmostylus. “They are, in my opinion, the most spectacular fossils in terms of look, but the number of identifiable whales, I feel, will have the largest impact on the scientific community,” he shared.

As he thinks back on the Calaveras Dam Replacement Project, Mates-Muchin reflected “As Winston Churchill said, ‘Those that fail to learn from history, are doomed to repeat it.’ Our mammalian ancestors can teach us about how our earth changed in the past and how it might change in the future. UCMP’s education program provides modules for learning about climate change, extinctions, and evolution. They bring this information to teachers and students around the Bay Area.”

The Calaveras Dam Replacement Project consisted of building a new zoned earth and rock fill dam immediately downstream of the existing dam. The replacement dam has a structural height of 220-feet high and is designed to accommodate a maximum credible earthquake on the Calaveras Fault. The dam has a crest length of 1,210 feet, a base thickness of 1,180 feet, and crest thickness of 80 feet. The total volume of the dam is approximately 3.5 million cubic yards. The replacement dam will restore the original reservoir capacity of 96,850 acre-feet, or 31 billion gallons of water. The storage is crucial to providing adequate water to the SFPUC’s 2.7 million customers in the Bay Area.