"A mole is a massive structure, usually of stone, used as a pier, breakwater, or a causeway between places separated by water."
The Oakland Long Wharf, later known as the Oakland Pier or the Mole was a large railroad wharf and ferry pier at the foot of Seventh Street in Oakland. Below is an aerial view from the 1930s.
Pre-1868 it was used as a long pier for the San Francisco ferry. In 1868 it was acquired by Central Pacific Railroad who extended it and renamed it the Oakland Long Wharf. It transported freight and passengers to San Francisco (both local commuters and beginning in 1876 transcontinental railroad passengers). After passengers (or freight) got off their trains in the Mole, they hopped on the ferry to head to San Francisco.
The mole closed in 1958 and was demolished in the 1960s due to the growing Port of Oakland.
I was down at the Middle Harbor Shoreline Park the other day and came across a sign I’d previously ignored:
I should have taken a picture of the sign’s surrounding location, but oh well.