The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Massachusetts Office of Coastal Zone Management (MA CZM), is producing detailed geologic maps of the coastal sea floor. Imagery, originally collected by NOAA for charting purposes, provide a fundamental framework for research and management activities along this part of the Massachusetts coastline, show the composition and terrain of the seabed, and provide information on sediment transport and benthic habitat. Interpretive data layers were derived from multibeam echo-sounder and sidescan sonar data collected in Great Round Shoal Channel, a passage through the shoals at the eastern entrance to Nantucket Sound, off Cape Cod, Massachusetts. In June 2006, bottom photographs and surficial sediment data were acquired as part of a ground-truth reconnaissance survey.