Ouachita Mountains

The Ouachitas are dominated by pine, oak, and hickory.[9] The shortleaf pine (Pinus echinata) and post oak (Quercus stellata) thrive in dry, nutrient-poor soil and are common in upland areas. The maple-leaf oak (Quercus acerifolia) is found at only four sites worldwide, all of which are in the Ouachitas.[9] Some native tree species, such as the eastern red-cedar (Juniperus virginiana), are colonizers of human-disturbed sites.[9]

The Ouachita National Forest covers approximately 1.8 million acres of the Ouachitas.[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.[10] There are six wilderness areas within the Ouachita National Forest, which are protected areas designed to minimize the impacts of human activities.[11]

Several plants are endemic to the Ouachitas, including: Agalinis nuttallii, Cardamine angustata var. ouachitana, Carex latebracteata, Galium arkansanum var. 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. obtusifolius, Streptanthus squamiformis, Valerianella palmerii, and Vernonia lettermanii.[12]

Bison and elk once found habitat in the Ouachita Mountains, but have since been extirpated. Today, there are large populations of white-tailed deer, coyote, and other common temperate forest animals. Though elusive, hundreds of black bear roam the Ouachitas. Several cryptic species of salamander are endemic to the Ouachitas and have traits that vary from one locale to another.[13]

The Athens Plateau or Athens Piedmont (EPA Level IV ecoregion 36a) consists of a series of low relief ridges, none exceeding 1,000 feet. It is located south of the Ouachitas and extends from to the Arkansas-Oklahoma border. The Athens Piedmont runs from Arkadelphia, Arkansas into Oklahoma through Clark, Howard, Pike, and Sevier counties in Arkansas and McCurtain County in Oklahoma. The ecoregion's low ridges and hills are widely underlain by Mississippian Stanley Shale in contrast to other parts of the Ouachitas.[7] Today, pine plantations are widespread; they are far more extensive than in the more rugged parts of the Arkansas Ouachitas. Pastureland and hayland also occur. Cattle and broiler chickens are important farm products.[6]

The Caddo, Cossatot, and Missouri mountains are a high, compact group of mountains composed of the weather-resistant Arkansas Novaculite. They are located primarily in Montgomery and Polk counties, Arkansas. The highest natural point is Raspberry Mountain at 2,358 feet. The headwaters of multiple rivers are found in this area, including the Caddo, Cossatot, and Little Missouri rivers.

The Cross Mountains are located in Polk and Sevier counties, Arkansas and McCurtain County, Oklahoma. The highest natural point is Whiskey Peak at 1,670 feet.

The Crystal Mountains are located primarily in Montgomery County, Arkansas. They are so named because of the occurrence of some of the world's finest quartz. The Crystal Mountains are generally taller than the nearby Zig Zag Mountains, achieving elevations over 1,800 feet.

The Fourche Mountains (EPA Level IV ecoregion 36d) are a long, continuous chain of east-west mountains composed of the weather-resistant Jackfork Sandstone. They extend from Pulaski County, Arkansas to Atoka County, Oklahoma and are home to several popular sites of interest, including Pinnacle Mountain State Park near Little Rock, Arkansas. The highest natural point is Rich Mountain at 2,681 feet, which intersects the Arkansas-Oklahoma border near Mena, Arkansas.

Fourche Mountain salamander

The Fourche Mountains are the archetypal Ouachita Mountains. Forested ridges are heavily forested with oak–hickory–pine forest; intervening valleys are cut into shale. 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.[6] Forests on steep, north-facing slopes are more mesic than on southern aspects; the steepest, south-facing slopes contain shallow, moisture deficient soils supporting shrubs and rocky glades or grassy woodlands.[7] Pastureland and hayland are restricted to a few broad valleys. Logging is not nearly as intensive as in the commercial pine plantations of the less rugged Athens Plateau. Nutrient, mineral, and biochemical water quality parameter concentrations are low in the surface waters of the Fourche range, but turbidity can be higher than in other mountainous parts of the Ouachitas.[6] Although most streams stop flowing during the driest part of the summer, enduring deep pools, high quality habitat, and good water quality allow sensitive aquatic species to survive through the summer.[7] They are the only home and namesake of the Fourche Mountain salamander.

The Fourche Mountains form a major watershed divide between the Arkansas River Basin to the north and the Red River Basin to the south.

The Frontal Ouachita Mountains are located in the Arkansas River Valley and feature a number of isolated landforms. The highest natural point is Mount Magazine at 2,753 feet, which is also the highest natural point of the Ouachitas and U.S. Interior Highlands. The Frontal Ouachita Mountains are structurally quite different from the rest of the Ouachitas and are sometimes considered a separate range.

The Trap Mountains are located primarily in Garland and Hot Spring counties, Arkansas. The highest natural point is Trap Mountain at 1,310 feet.

The Zig Zag Mountains are located in Garland County, Arkansas and are home to the thermal springs of Hot Springs National Park. They are so named because of their unique chevron shape when viewed from above, the result of plunging anticlines and synclines. The Zig Zag Mountains are not exceptionally tall, but do reach heights over 1,400 feet.

Cambrian through Mississippian strata of the Ouachitas were deposited in a narrow, two-sided basin called the Ouachita Trough, which formed as part of a Cambrian failed rift system.[3][17] Succeeding Pennsylvanian strata of the Ouachitas were deposited in a foreland basin during the early stages of the Ouachita Orogeny.[18] Subduction of the South American Plate beneath the North American Plate resulted in this mountain-building event.[19] Compressional forces caused the crust to buckle, producing complex folds at all scale levels and several overturned sequences.[14] The area of greatest deformation occurred in the Benton-Broken Bow Uplift, which extends from Benton, Arkansas to Broken Bow, Oklahoma.[3] The total height of the Ouachitas is not known, though they may have exceeded 10,000 feet (based loosely on geologic cross-sections).[14] The terrain has been deeply eroded since the late Paleozoic.[3]

The Ouachitas are composed of Cambrian through Pennsylvanian sedimentary rocks. The Collier Shale, located at the core of the Benton-Broken Bow Uplift, is the oldest exposed formation of the Ouachitas. The Atoka Formation, which was deposited much later during the Pennsylvanian, has the largest areal extent of any of the Paleozoic formations in Arkansas.[14] The geologic formations of the Ouachitas are as follows (in order of ascending age).

The South Fourche La Fave River, Ouachita Mountains, Arkansas

• Beavers Bend State Park
• Black Fork Mountain Wilderness
• Caney Creek Wilderness
• Cossatot River State Park-Natural Area
• Flatside Wilderness
• Hot Springs National Park
• Jack Creek Recreation Area
• Lake Catherine
• Lake Hamilton
• Lake Maumelle
• Lake Ouachita
• Mount Magazine State Park
• Pinnacle Mountain State Park
• Queen Wilhelmina State Park
• Mount Nebo State Park