The Ouachita Mountains are fold mountains like the Appalachian Mountains to the east. During the later, Pennsylvanian period of the Carboniferous, about 300 million years ago, the coastline of the Gulf of Mexico ran through the central parts of Arkansas. The oceanic crust met the continental crust in this region and was forced underneath the denser continental crust, as South America drifted closer. Geoliogists call the collision the Ouachita orogeny. The collision buckled the continental crust producing the fold mountains that we call the Ouachita. At one time the Ouachita Mountains were very similar to the Rocky Mountains, but due to their age, the craggy tops have eroded away leaving the low formations that used to be the heart of the mountains.
The Ouachita, unlike most other mountain ranges in the United States, run east and west rather than north and south. This unique formation has been known to cause confusion to pilots flying over the region.
The Ouachita Mountains contain the Ozark National Forest and Hot Springs National Park as well as numerous state parks and scenic byways.