mole

A mole is a massive structure, usually of stone, used as a pier, breakwater, or a causeway separating two bodies of water. A mole may have a wooden structure built on top of it that resembles a wooden pier. The defining feature of a mole, however, is that water cannot freely flow underneath it, unlike a true pier. The oldest known mole is at Wadi al-Jarf, an ancient Egyptian harbor complex on the Red Sea, constructed ca. 2500 BCE. The word comes from Middle French mole, ultimately from Latin mōlēs, meaning a large mass, especially of rock; it has the same root as molecule and mole, the chemical unit of measurement. San Francisco Bay Area In the San Francisco Bay Area in California, there were several moles, combined causeways and wooden piers or trestles extending from the eastern shore and utilized by various railroads, such as the Key System, Southern Pacific Railroad (two), and Western Pacific Railroad: the Alameda Mole, the Oakland Mole, and the Western Pacific Mole. By extending the tracks the railroads could get beyond the shallow mud flats and reach the deeper waters of the Bay that could be navigated by the Bay Ferries. A train fell off the Alameda Mole through an open drawbridge in 1890 killing several people. None of the four Bay Area moles survive today, although the causeway portions of each were incorporated into the filling in of large tracts of marshland for harbor and industrial development.