“Walking with the Ancients” was the fifth in a series of E/V Nautilus expeditions to the Channel Islands and the Southern California Continental Borderland that began in 2016. Cruise sponsors were NOAA’s Office of Ocean Exploration and Research, the Office of Naval Research, the National Geographic Society, and the Lounsbery Foundation. The primary focus of the five expeditions was to discover and investigate submerged caves carved by the sea since the Last Glacial Maximum (LGM) some 19,000 years ago. When the great continental ice sheets began to melt, sea level rose discontinuously, creating a series of paleoshorelines.