During the Calaveras Dam Replacement Project in Fremont California, workers at the construction site uncovered over 500 marine fossil specimens that are believed to be about 20 million years old, dating back to the Miocene Epoch.
The replacement project at the Calaveras Dam is expected to be completed by 2018. Construction began in August of 2011 and will cost the state of California $718 million, but the project is essential in order to continue supplying Bay Area residents with an adequate water supply. The major excavation work that is currently taking place has yielded the tremendous discovery on Monday, and now paleontologists will work with construction crews over the next few years to obtain the fossils.
However, this is not the first fossil discovery in the Calaveras Dam. Paleontologist Jim Walker told the San Jose Mercury News that marine fossils were previously discovered at the dam before the construction even began. Those in charge of the dam project work to "protect the environment, to preserve the pristine watershed lands, and the natural habitats surrounding the project," according to the project's web page. Perhaps the discovery of the fossil trove was a result of the "unexpected geological features" that were identified back in June 2012, forcing the crews to move and dig through additional land.
But even before then, in 2011, construction crews found nine whale skulls and fossils of scallops. On Monday, the crews inventoried a total of 529 types of fossils: 168 vertebrates, 267 invertebrates, 39 plants, and 55 other 'ancient items.' The fossils are likely from the Miocene Epoch, when it was believed the oceans extended as far inland as Bakersfield, CA, which is slightly northwest of Los Angeles. The Miocene era lasted from 24 million years ago until 5.3 million years ago.
The discovery of the fossils only occurred because of earthquake threats that would jeopardize the water supply for hundreds of thousands Californians. Studies have shown, the Calaveras Dam - the tallest Earth-filled dam in the world - could collapse in the event of a large earthquake, which would then release a wall of water as high as 30 feet into the city of Fremont. The Division of Safety of Dams declared it seismically unsafe in 2001, thus beginning a plan to fix the issue.
As construction is expected to continue (they've already moved five million cubic yards of Earth), Walker and fellow paleontologist, Bruce Hanson, and others will work with the crews to ensure the safe excavation of the fossils. Walker and Hanson will spend the next few months digging out the backbone of a 40-foot baleen whale they found on a hillside.
You can read more about the fossil discovery at the Calaveras Dam in this San Jose Mercury News article.
