sentences:  It is bounded by the Mississippi River on the east and the Missouri River on the west and consists of generally low-relief, flat-lying marine and stream deposits from the Mesozoic and Cenozoic Eras.Geologically, the area is tectonically stable and part of the continental core.It has been impacted by structural folding, faulting, deformation, erosion and sedimentation from the ancient, eroded mountains of the Ouachita-Ozark Highlands in the southern portion of the region.