Bathymetry data from various sources, including newly released 2018 and 2019 multibeam data collected by the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS), were combined to create a composite 30-m resolution multibeam bathymetry surface of the southern Cascadia Margin offshore of Oregon and northern California. The bathymetry data are available as a 30-m resolution geoTIFF file, accompanied by a polygon shapefile describing the data sources used to create the composite bathymetry surface. This bathymetric surface was created as part of a cooperative project between the U.S. Geological Survey, Pacific Coastal and Marine Science Center and NOAA. The surface was generated to assist research projects studying offshore geohazards including mapping faults, submarine landslides, sediment transport pathways, and seafloor seeps. These data are not intended to be used for navigation.