The Tennessee Valley and Ridge section in Alabama is the southernmost section of the Valley and Ridge province of the Appalachian Highlands Region [ see Figure 1 in Related Links ]. Hereafter called the Valley and Ridge, the section is one of Alabama's five physiographic sections, each of which is recognized by its pattern of relief features and landforms that differ significantly from those of adjacent sections. The Valley and Ridge section occupies about 9 percent of the state. It occurs as a roughly northeast-trending rectangular area in central and east-central Alabama, mainly encompassing Shelby, St. Clair, Calhoun, Cherokee and parts of Jefferson, Bibb, Talladega and Etowah counties and continues northeast into Georgia and Tennessee.
The Valley and Ridge borders the Cumberland Plateau section to the north and west, the Piedmont Upland section to the southeast, and the East Gulf Coastal Plain section to the southwest. The landscape developed on tightly folded and thrust-faulted rock layers and thus consists of numerous uniquely zigzagging ridges separated by deep steep-sided valleys. The landscape formed on Paleozoic sedimentary rocks that range in age from Cambrian to Pennsylvanian, around 540 to 290 million years before the present age. The ridges are composed of Pennsylvanian sandstone belonging to the Pottsville Formation, whereas the valleys cut through shale, limestone, and dolomite.
The Valley and Ridge is comprised of seven districts: Birmingham-Big Canoe Valley, Cahaba Ridge, Coosa Ridges, Cahaba Valley, Coosa Valley, Weisner Ridges, and Armuchee Ridges [ see Figure 2 ].
The Birmingham-Big Canoe district is the westernmost district and runs for about 90 miles from near Vance, in Tuscaloosa County, where it disappears under the East Gulf Coastal Plain, to Gadsden, in Etowah County, where it merges with the Coosa Valley. The valley itself, known as Jones Valley in the Birmingham area, is eroded into folded and thrust-faulted Lower Paleozoic limestone and dolomite [ see Figure 3 ]. Rock layers were folded into two large anticlines (upward-trending archs) and a syncline (downward-trending arch). The southern limb of the westernmost anticline is cut by a thrust fault. Red Mountain is a cuesta (a ridge with an asymmetrical profile), with the gentler southeasterly slope indicating the direction of dip or tilt of the underlying rocks. It is composed of sandstone, iron ore, and shale that dip to the southwest. Shades Valley, the southeasterly edge of the district, is underlain by softer Mississippian shale.
The Cahaba Ridge, Coosa Ridges, and Cahaba Valley districts comprise a 15-mile-wide complex of rugged ridges and deep valleys to the east of the Birmingham-Big Canoe Valley/Cahaba Ridges Boundary. The Cahaba and Coosa Ridges consist of several parallel, zigzag ridges capped with Pottsville Formation sandstone. The ridges are actually the sides of plunging folds [ see Figure 4 ]. Several ridges occur along the eastern margin of the Coosa Valley. From south to north they are the Sleeping Giants, Weisner Ridges, and Armuchee Ridges. The thrust faults that bound each ridge stand above the surrounding Knox Group dolomites because they are composed of more resistant Lower Cambrian sandstone.
The Coosa Valley is the largest of the Valley and Ridge districts. It reaches up to 23 miles wide, about 115 miles long, and runs from the Alabama-Georgia border north of Centre, in Cherokee County, to southern Shelby County, where it joins with the Cahaba Valley west of Columbiana. The western edge of the valley has formed on closely spaced thrust faults, exposing shale on the surface. The central and eastern parts of the valley formed on limestone and dolomite, predominantly of the Knox Group.
The Coosa River drains some 5,350 square miles in Alabama, most of it in the Valley and Ridge. The river enters Alabama in Cherokee County and flows southwesterly until it passes into the Piedmont physiographic section, north of Lay Lake Dam. Several main tributaries flowing from the Cumberland Plateau join the Coosa near Gadsden, including the Little River, Big Canoe Creek, Little Canoe Creek, and Big Wills Creek. The main channel ranges from 300 to 500 feet wide and is flanked in places by banks up to 25 feet in height near Gadsden. North and east of Hokes Bluff, in Etowah County, the river meanders across its own floodplain, which is about 15 miles wide. To the southwest, the valley narrows and deepens along the boundary between St. Clair and Calhoun counties, where the river cuts through the more resistant shale and sandstone of the northern edge of the Coosa Ridges district. Neeley Henry Dam is located on the Coosa at the southern edge of the ridges. To the south, the valley widens to about 20 miles across near Pell City, in St. Clair County, and the river begins to meander again. The meanders are less pronounced here because the dolomites of the Knox Group contain varying amounts of chert, and the river's meanderings are restricted by ledges of more resistant rocks along its course. Logan Martin Dam, located south of Pell City on the Coosa, was built on one of these ledges. The seven dams on the Coosa River together produce 58 percent of Alabama Power's hydroelectric power.
The Red Mountain Formation crops out on the slopes of Red Mountain in the Valley and Ridge and along the slopes of the Big Wills, Murphrees, and Sequatchie valleys of the Cumberland Plateau. The iron-ore deposits within the formation attracted both Native American artisans and European settlers, and Jones Valley became the center of Alabama's iron and steel industry during the late-nineteenth and early-twentieth centuries. The red color is the result of hematite, a red iron-oxide mineral that was the main reason for Birmingham's establishment and growth and a major part of the economy of the Birmingham area. Although hematite was mined sporadically along Red Mountain's length, extensive and long-term mining took place only in the Birmingham area in the three seams: the Big Seam, the Irondale Seam, and the Ida Hickory Nut Seam.
Red Mountain iron ore was used sporadically during the Civil War, notably in the Oxmoor and Irondale furnaces but its use didn't take off until the late nineteenth century, when coke (a gray, hard, and porous material formed when coal is baked so that all the gases and volatile materials are removed) replaced charcoal as the main source of energy. In 1876 Levin Goodrich succeeded in producing pig iron using the Red Mountain Formation and coke made from local coal. Numerous coal seams, most notably the Pratt seam in the nearby Warrior basin, guaranteed a constant source of coke. Limestone and dolomite, used in iron manufacturing, were also extremely abundant in the Birmingham-Big Canoe Valley. Mining of the Red Mountain ore continued until the early 1970s, and a total of about 375 million tons of ore was removed in all.
Kidd, J. T., and Shannon, S. "Stratigraphy and Structure of the Birmingham Area, Jefferson County, Alabama." Geological Society of Alabama Guidebook 16. Tuscaloosa: Geological Society of Alabama, 1978.
White, M. L. The Birmingham District . Birmingham: Birmingham Historical Society, 1981.
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