These giant jacks are used to protect harbors from damaging
currents. As waves hit the tetrapods, the force of the water is
dissipated by the curve of the legs. There are 1630 tetrapods on
the ocean side of the Crescent City breakwater. There are 1900
tetrapods and 768 steel reinforced dolos on the newer leg of the
This 25-ton tetrapod was on display near Front Street
and was moved nearly three feet of a pedestal by the
force of the March 28, 1964 Tsunami.