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Geology of the Ouachitas

GENERAL OUACHITA NATIONAL FOREST GEOLOGY :

From the Ouachita National Forest USDA Forest Service Web Site.

The Ouachita National Forest is located in the heart of the Ouachita Mountains through the west central portion of Arkansas and the southeastern portion of Oklahoma. The Forest is principally within the physiographic province referred to as the "Ouachita Province". In Arkansas, the northern portions of the Poteau, Cold Springs, and Fourche Ranger Districts are within the "Arkansas Valley Province."

The Ouachita Province is a mountainous, geologically complex area located between the Gulf Coastal Plain to the south and the Arkansas Valley to the north. These other physiographic provinces are also known for their oil and gas production and potential. The physiographic "Ouachita Province" is subdivided into the Fourche Mountains in the northern half of the Forest, and the Novaculite uplift in the southern half of the Forest.

The Ti Valley / Winding Stair / Choctaw fault system is projected through the northern portion of the Forest in eastern Oklahoma and western Arkansas. Major structural and stratigraphic changes caused by this significant fault system occur between the Arkoma Basin to the north of the Forest and the Ouachita Mountains (Caplan, 1963). Geologically, the area between the Choctaw and Winding Stair faults is referred to as the "frontal" part of the Ouachita Mountains and represents the geologic transition zone between the Ouachitas and the Arkoma Basin. The rock sequence south of the Ti Valley fault is referred to as the "Ouachita Mountain facies" and may reflect a north-northwest thrust of approximately 20 miles. The "Broken Bow - Benton uplift" extending through the southern third of the Forest from Benton, Arkansas south-southwest to Broken Bow, Oklahoma, is the principal anticlinal fold of the Ouachita Mountains (Miser, 1963).

The relief within the main division of the Ouachita National Forest in the Ouachita Mountains is 2,381 feet. Elevations range from the 300 foot elevation along the Fourche-LeFave River at the north eastern boundary of the Forest in Arkansas, to 2,681 foot elevation at Rich Mountain along the Talimena Drive in the west central portion of the Forest near the Oklahoma border. Rich Mountain is also the second highest point in Arkansas surpassed only by Magazine Mountain at the 2,823 foot elevation in the northern part of the state.

The rocks in the Ouachitas consist primarily of Paleozoic sandstones, shales, novaculites and cherts that have been intensely folded and deformed during the late Paleozoic age mountain building process into anticlinal and synclinal forms that trend almost due east and west (Engel, 1951). Typically, the novaculites -- the most resistant of the rock types -- form the prominant ridge tops in the southern portion of the Forest, while the Bigfork Chert and Jackfork Sandstone are the dominant ridge formers in the northern portion of the Forest. The oldest rocks at the surface in Arkansas are found in the Ouachitas in the Cambrian/Ordovician age Collier Shale Formation.

The most prominent hardrock mineral commodity in the Ouachitas at this time is quartz crystal produced from quartz veins in the Paleozoic formations of the Forest and adjacent lands, and building stones and aggregate material produced from many of the formations. A belt or zone of quartz crystal bearing veins extends 30 to 40 miles wide for 170 miles from Little Rock, Arkansas to Broken Bow in eastern Oklahoma. Major production of quartz crystal occurs within the heart of this belt in a zone about 70 to 90 miles through the eastern and southern portions of the Ouachita Mountains on Ouachita National Forest and adjacent lands.

For More Information about the Minerals and Geology of the Ouachita Mountains, please visit:

From the Ouachita National Forest USDA Forest Service Web Site.

 


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