During the Paleozoic period, the land now known as Arkansas was overlaid by ocean waters. Centuries of continental drift and plate collisions shaped the landscape. The Encyclopedia of Arkansas separates the state into six regions based upon natural landforms.
The Boston Mountains in northwestern Arkansas are part of the southern Appalachian Plateau. The Ouachita Mountains chain runs from east to west through central Arkansas south of the Boston Mountains.
Over half of the state geography is plains. The Mississippi Alluvial Plain covers the eastern third while the West Gulf Coastal Plain is in southwestern Arkansas.
The Arkansas Valley separates the Appalachian Plateau from the Oachita Mountain range. Mount Magazine rises 2,753 feet above the surrounding valley and is the highest point in the state.
Crowley's Ridge descends from north to south in northeastern Arkansas. The three- to twelve-mile wide ridge runs through the Mississippi Alluvial Plain. Its height is 300 feet in places.
The state's two major rivers are the Arkansas River, which cuts through the Arkansas Valley, and the Mississippi River, which borders Arkansas on the east. Secondary rivers include the Ouachita, White and St. Francis.
