Geology of the Elkmont quadrangle, Alabama-Tennessee

The Elkmont quadrangle is in parts of Limestone County, Ala., and Giles County, Tenn. The town of Elkmont, in the west-central part of the quadrangle, had a population of about 250 in 1960.

Most of the fieldwork in the Elkmont quadrangle was done during an investigation of the ground-water resources of the Athens area, Alabama, of which the Elkmont quadrangle is a part. The investigation was made by the U.S. Geological Survey in cooperation with the Geological Survey of Alabama and the city of Athens. 

The northwestern one-third of the quadrangle is in the Nashville Basin section of the Interior Low Plateaus physiographic province. Here the topography is characterized by steep-sided hills, narrow stream valleys, relatively steep stream gradients, and narrow drainage divides. Drainage is generally northward into the Elk River, but Sulphur Creek, in the southwestern quarter of the quadrangle, flows westward into the Elk River. The Nashville Basin section is underlain by rocks of Ordovician age, but in places remnants of rocks of Mississippian age cap hilltops. Altitudes in the Nashville Basin of the quadrangle range from about 590 feet in the north-central part to about 850 feet in the northeastern part.

The southeastern two-thirds of the quadrangle is in the Highland Rim section of the Interior Low Plateaus province. The boundary separating the Nashville Basin and the Highland Rim is a very irregular but distinct escarpment that coincides with the contact of Mississippian rocks with older rocks. The Highland Rim in the Elkmont quadrangle is characterized by broad stream valleys, low stream gradients, and broad, low drainage divides. Drainage is southward into the Tennessee River. The Highland Rim is capped by rocks of Mississippian age, but in the southeastern part of the quadrangle along Piney Creek, and in a large sinkhole in the northeastern part, rocks of Ordovician and Devonian age are exposed. Altitudes on the Highland Rim range from about 700 feet in the southwestern part of the quadrangle to about 940 feet in the northeastern part. 

The rocks exposed in the Elkmont quadrangle consist chiefly of limestone and siliceous dolomite and range in age from Middle Ordovician to Early Mississippian. The Ordovician formations are correlated with those which crop out extensively in central Tennessee, where they have been subdivided and mapped in detail by the Tennessee Division of Geology, and also are correlated with those which crop out in the Salem quadrangle adjacent to the west (McMaster, 1964). The type areas for the Ordovician and Devonian formations referred to in this report are in central Tennessee. 

The Elkmont quadrangle is on the southern flank of the Nashville dome. The strata dip generally southwestward, but the regional dip is modified considerably by the presence of minor anticlines and synclines. 

The author is indebted to Mr. Robert Barnes of the Tennessee Division of Geology, with whom he spent 2 days in the field reviewing the Ordovician stratigraphy in the Elkmont quadrangle.