The Amundsen Sea sector of West Antarctica Ice Sheet is losing mass at a rate that has more than doubled in the past four decades, and continues to increase. Pine Island Glacier (PIG), the second largest drainage basins in this sector, experienced the fastest grounding-line retreat and its ice-mass loss increased more rapidly than any others in the last two decades. The large mass imbalance of PIG is attributed to the increased sub-ice-shelf melting by the incursion of relatively warm Circumpolar Deep Water (CDW) beneath the PIG ice shelf (PIGIS), although the lack of precise bathymetry data have restricted thorough understanding of the ice-ocean interactions. Here we present updated bathymetry and sediment distribution beneath PIGIS, modeled by inversion of aerogravity data with constraints from active-source seismic and autonomous underwater vehicle data, and the regional gravity anomaly derived from satellite gravity observations. Modeled bathymetry shows that the submarine ridge beneath the middle of PIGIS appears to continue across the width of the ice shelf, with no major deep troughs crossing it, consistent with previously predicted sub-ice-shelf ocean circulation. However, the relatively low resolution of the aerogravity data and limitations in our inversion method leave a slight possibility that there is an undetected, few kilometer-scale narrow trough that may alter this predicted sub-ice-shelf ocean circulation. Modeled sediment distribution indicates that the submarine ridge marks the transition from a thick sedimentary basin (soft, smooth bed for ice flow) around the current grounding zone of the main PIG trunk to a region of thin-to-no sediment with some exposed crystalline basement (rough, resistant bed for ice flow) that extends seaward into Pine Island Bay. We hypothesize that this transition in basal conditions caused the post-Last Glacial Maximum retreat of PIG to stabilized near this geological boundary.