Data for a body of rock or soil with lateral extent that composes the geologic framework for a hydrologic system.  

This table contains data on hydrostratigraphic units.  These differ from the stratigraphic units found in the STU table in that hydrostratigraphic units are defined on the basis of how groundwater behaves and is contained rather than the material that forms the units (layers.)  Hydrostratigraphic units are layers of rock and/or soil that contain hydrologic (groundwater) systems.