Welcome to Caltrans District 4

The History and Archaeology of Yerba Buena Island - Underwater Archaeology

Knowing that constructing the New East Span and dismantling the old span would cause disturbance to the Bay floor and any shipwrecks or other cultural materials along the route, Caltrans embarked on archaeological studies that were rather unique for a transportation agency-underwater archeology.

The studies began in 1999 with archival research to identify shipwrecks or other cultural remains that might lie submerged within the project area. Early local newspapers and historic photo collections were examined, as were ships records from the War and Commerce Departments and the National Archives, the National Oceanographic and Atmospheric Administrations sea floor maps, and other records in the Library of Congress, the Naval History Center, and local libraries. This research indicated that four shipwrecks might be in or near the project. Two wrecks were known to be near Yerba Buena Island, one was somewhere near the Berkeley shore, and the fourth location was uncertain.

A combination of robotic cameras, archaeologist/divers, and sonar equipment was used to conduct the underwater search. The robotic cameras proved ineffective because of the murky Bay waters, so a side-scan sonar system was used and divers visited the sonar targets that were difficult to define. These dives were made treacherous by the strong tides within the Bay and the extremely poor visibility.

underwater sonar

After several weeks of fieldwork and a dozen dives, no shipwrecks or other important resources were found in the project area, but the Bay floor is far from empty of cultural debris. Among the items discovered were several large train wheels with axles, a large basket-like carrier-perhaps used for bridge maintenance-cables, an irregularly shaped concrete block, wood pilings, and pieces of fused metal. Much of this material was associated with the Key System Ferry, which was the main mode of transportation between San Francisco and the East Bay before the Bay Bridge was built. A causeway and pier with ferry terminal extended 16,000 feet into the Bay from the west end of Yerba Buena Avenue in Oakland. In 1939, the ferry service was replaced by Key System trains that ran on the lower deck of the newly opened bridge.