New geophysical data from Antarctica’s Ross Embayment illuminate the structure and subglacial geology of subsided continental crust beneath the Ross Ice Shelf. We use airborne magnetic data from the ROSETTA-Ice Project (2015-2019) to locate the basement-cover contact and map the extent of sedimentary basins. We delineate a broad, segmented high with thin (0-500 m) sedimentary cover which trends northward into the Ross Sea’s Central High. Before subsiding below sea level, this feature likely facilitated early glaciation in the region and subsequently acted as a pinning point and ice flow divide. Flanking the high are wide basins, up to 3700 m deep, parallel with Ross Sea basins, which likely formed during Cretaceous-Neogene intracontinental extension. NW-SE basins beneath the Siple Coast grounding zone, by contrast, are narrow, deep, and elongate. They suggest tectonic divergence upon active faults that would localize geothermal heat and/or groundwater flow, both important components of the subglacial system.