Massive East Bay dam project moves 7 million yards of dirt, unearths fossils and dynamite

One of the largest state reservoir projects in decades has forced crews to shovel enough soil to cover Treasure Island in 7.5 feet of dirt, digging up long buried treasures in the process.

During the excavation phase of the Calaveras Dam Replacement Project east of Milpitas, crews turned up old train rails, donkey shoes and 100-year-old dynamite which had been submerged for years. But that's not all they found.

"The most remarkable things we've come across are fossils, actually...20 million year old marine fossils," said Betsy Lauppe Rhodes of the Hetch Hetchy Regional Water System.

Several miles inland from the San Francisco Bay, diggers turned up whale bones, shark teeth and other sea life. Here's a look at what the found and some photos of how the new spillway looks compared to the previous version:

Sea Scallop fossils found during the construction of the Calaveras Dam. Sea Scallop fossils found during the construction of the Calaveras Dam. Photo: Photo Courtesy Of San Francisco Public Utilities Commission Photo: Photo Courtesy Of San Francisco Public Utilities Commission Image 1 of / 12 Caption Close Massive East Bay dam project moves 7 million yards of dirt, unearths fossils and dynamite 1 / 12 Back to Gallery

The massive project that led to these discoveries can be seen in the timelapse above. Rhodes says there are still about 3 million cubic yards of soil yet to be moved.

The project recently hit a major milestone: the completion of the new spillway, a key step in building up the modernized dam. Many Bay Area residents have only seen the body of water on approach to local airports, but the reservoir actually serves 2.5 million homes, many of them in Southern Alameda and Northern Santa Clara counties. The current project, which has been underway since 2011, will make the dam safe enough to be completely filled.

"The goal is to return the Calaveras Reservoir to its historic capacity of 31 billion gallons. In 2001 we lowered the levels of Calaveras Reservoir to 40% out of seismic safety concerns for the existing 91-year-old dam," said Rhodes. "Restoring it to its historic capacity with a new dam is crucial in times of drought and also when Hetch Hetchy supplies are unavailable for any reason."

Construction of the embankment and dam itself are expected to being this summer. Full completion of the $810 million project is expected in 2019.

"Building a new earth and rock fill dam is a lot like painting your house. Most of the work is in the preparation," said Rhodes. "We have been injecting grout into the ground (up to 150 feet deep) to seal up the ground around the future foundation of the dam. The completion of the spillway is a huge accomplishment."