The rich geological history of this area encompasses some of the most significant tectonic events that have shaped the North American continent. Note air-fall debris from erupting volcanoes. Weakened crust allowed magma from mantle to move upward through weak zones. The largest known igneous intrusive body emplaced at this time is the nepheline syenite batholith underlying Saline and Pulaski Counties. Most of the batholith is still deeply buried.
Sediments indicate shoreline and near-shore of shallow seas.
Bauxite developed on Cretaceous alkalic intrusions. The highlands were eroding. Dinosaur extinction at end of this period. Ozark highlands eroded and filled Mississippi Embayment. Ancestral Mississippi and Ohio rivers deliver Pleistocene glacial outwash to eastern Arkansas.