In 2016, funding from NOAA OER supported systematic mapping of portions of Channel Islands National Marine Sanctuary (CINMS) by E/V Nautilus. One focus of that effort was to locate and explore submerged paleoshorelines formed over the last 22,000 years when sea level stopped rising for 2,000 to 3,000 years at a time. These lulls in sea level rise permitted pounding waves, typical of the high-energy coast of today’s Southern California shoreline,to excavate caves, as they continue to now. The goal of our 2017 expedition in the Channel Islands area of the Southern California Continental Borderland was to search for submerged sea caves. Areas initially selected for investigation were the islands of Santa Cruz, Catalina, and Santa Barbara, where numerous sea caves are known to exist above present sea level, as well as where divers have already located them at the base of rock scarps resting at the 8 m to 10 m and 33 m paleo-shorelines.