[3] The Ouachitas continue in the subsurface to the northeast, where they make a poorly understood connection with the Appalachians and to the southwest, where they join with the Marathon uplift area of West Texas.

[2][5] The Ouachita Mountains is a Level III ecoregion designated by the Environmental Protection Agency (EPA).

[9] The shortleaf pine (Pinus echinata) and post oak (Quercus stellata) thrive in dry, nutrient-poor soil and are common in upland areas.

[9] Some native tree species, such as the eastern red-cedar (Juniperus virginiana), are colonizers of human-disturbed sites.

[10] It is one of the largest and oldest national forests in the Southern U.S., created through an executive order by President Theodore Roosevelt on December 18, 1907.

pubifolium, Houstonia ouachitana, Hydrophyllum brownei, Liatris compacta, Quercus acerifolia, Polymnia cossatotensis, Solidago ouachitensis, Spiranthes niklasii (near endemic, also found on Crowley's Ridge), Streptanthus maculatus subsp.

Today, there are large populations of white-tailed deer, coyote, and other common temperate forest animals.

The ecoregion's low ridges and hills are widely underlain by Mississippian Stanley Shale in contrast to other parts of the Ouachitas.

The highest natural point is Rich Mountain at 2,681 feet (817 m), which intersects the Arkansas-Oklahoma border near Mena, Arkansas.

Ridges are longer, habitat continuity is greater, the lithologic mosaic is different, and the topographic orientation is more consistent than in other parts of the Ouachitas.

Differences in moisture and temperature between north- and south-facing slopes significantly influence native plant communities; they are products of the prevailing topographic trend.

The Frontal Ouachita Mountains are located in the Arkansas River Valley and feature a number of isolated landforms.

[3] In a general sense, the Ouachitas are considered an anticlinorium because the oldest known rocks are located towards the center of the outcrop area.

[14] The Ouachitas continue in the subsurface to the Black Warrior Basin of Alabama and Mississippi where they plunge towards the Appalachian Mountains.

Due to the high degree of folding and faulting, the Ouachitas are clustered into distinct subranges, with ridges separated by relatively broad valleys.

[16] The quartz formed after the Ouachita Orogeny when fractures in rocks filled with silica-saturated fluids and, over millions of years, precipitated crystals up to several feet in length.

The Ouachitas are also known for novaculite, a variety of chert that has undergone low-grade metamorphism; particular grades found only in Arkansas are used for making whetstones.

[19] Compressional forces caused the crust to buckle, producing complex folds at all scale levels and several overturned sequences.

The Collier Shale, located at the core of the Benton-Broken Bow Uplift, is the oldest exposed formation of the Ouachitas.

The Talimena Scenic Drive begins at Mena, and traverses 54 miles (87 km) of Winding Stair and Rich Mountains, long narrow east-west ridges which extend into Oklahoma.

The two lane winding road is similar in routing, construction, and scenery to the Blue Ridge Parkway of the Appalachian Mountains.