The city had removed several cemeteries early in the 20th century, and in the process of moving the graves to Colma -- known as the "city of souls" for its large deceased population -- many of the headstones were used as fill or crushed up and used for roads, National Park Service spokeswoman Alexandra Picavet said.
At Ocean Beach, unclaimed headstones were used to armor the beach to guard against erosion -- and with the recent wind that has blown sand off the beach and onto the Great Highway, a few of the headstones have become exposed, Picavet said.
The U.S. Park Service archeologist is aware of the uncovered pieces of San Francisco history, Picavet said, but staff has decided to leave the stones in place.
Colma Historical Society volunteer Bunny Gillespie said that in March 1900, the San Francisco Board of Supervisors voted to close all but two city cemeteries and relocated many graves to Colma.
In the transfer process, which began by 1914, some of the stones were wrecked, while others found more functional purposes, such as those at Ocean Beach, Gillespie said.
In 1891, there were 27 cemeteries within San Francisco city limits, according to the historical group's records.