The University of New Hampshire’s Center for Coastal & Ocean Mapping collected ~321,500 km2 of bathymetry and backscatter data of the U.S. Gulf of Alaska continental margin (Fig. 1a) using a 12-kHz multibeam echosounder in support of the U.S. Extended Continental Shelf (United Nations Law of the Sea Treaty) project (Gardner and Mayer, 2005). A previously unmapped small submarine fan, unofficially named Chatham fan (Figs. 1b and 1c), was identified that has buried a portion of the head of the much larger Baranof Fan (Stevenson and Embley, 1987; von Huene, 1989; LeVoir et al., 2011).