The Ouachita Mountains are a physiographic section of the larger Ouachita province (which includes both the Ouachita Mountains and the Arkansas Valley), which in turn is part of the larger Interior Highlands physiographic division.[3]
The Ouachita Mountains are fold mountains like the Appalachian Mountains to the east, and were originally part of that range. During the Pennsylvanian part of the Carboniferous period, about 300 million years ago, the coastline of the Gulf of Mexico ran through the central parts of Arkansas. As the South American platedrifted northward, a subduction zone was created in this region. The South American oceanic crust was forced underneath the less-dense North American continental crust. Geologists call this collision the Ouachita orogeny. The collision buckled the continental crust, producing the fold mountains we call the Ouachitas. At one time the Ouachita Mountains were very similar in height to the current elevations of the Rocky Mountains. Due to the Ouachitas' age, the craggy tops have eroded away leaving the low formations that used to be the heart of the mountains.
Unlike most other mountain ranges in the United States, the Ouachitas run east and west rather than north and south. Also, Ouachitas are distinctive in that volcanism, metamorphism, and intrusions are notably absent throughout most of the system.
The Ouachita Mountains contain the Ouachita National Forest and Hot Springs National Park as well as numerous state parks and scenic byways. They also contain the Ouachita National Recreation Trail, a 223 mile long hiking trail through the heart of the mountains. The trail runs from Talimena State Park in Oklahoma to Pinnacle Mountain State Park, near Little Rock, Arkansas. It is a well maintained, premier trail for hikers, backpackers, and mountain bikers (for only selected parts of the trail).
