Spooky season is finally here, and there is no better way to celebrate than with a ghost story. It seems even state-of-the-art construction projects like the Calaveras Dam Replacement Project aren’t without their ghostly places. 

Back in the early 1900’s, the best way engineers had to explore the rock and soil for a dam site was to excavate adits. An adit is an entrance or tunnel into a mine and engineers used them to look at the underground geology. 

While moving the rock and soil to make space for the New Calaveras Dam, workers uncovered what looked like holes dug into the area surrounding the existing dam. The holes were actually adits excavated by the builders of the first Calaveras Dam, built from 1913 to 1925, and a total of 16 adits were uncovered at the site.

The San Francisco Public Utilities Commission (SFPUC) knew about the presence of these adits before digging for the new dam foundation. However, it didn’t ease the creepy feeling workers had when they uncovered them. A few workers even claim equipment broke down and didn’t work properly while they were working around the adits, as if they were haunted. Some workers avoided working around the adits altogether.

Crews carefully mapped and filled each adit with concrete or rock to stabilize the ground prior to the construction of the new dam on top, sealing in any potential ghosts in the area.