But not all of it - some of it is built right on the beach. You get a sense of this looking at the south end of Seacoast Drive. The homes are practically in the ocean. Or they would be if SANDAG didn't pump large amounts of sand onto this beach now and then.
It's a good thing storm surges and tsunami aren't too common here or these places would all be a marker layer of coarse sediment in Oneonta Slough - the northern arm of the Tijuana Estuary that lies right behind them.