Alabama is divided into four major physiographic regions: the Gulf Coastal Plain, Piedmont Plateau, Ridge and Valley section, and Appalachian (or Cumberland) Plateau. The physical characteristics of each province have significantly affected settlement and industrial development patterns within the state.
The coastal plain, comprising the southern half of Alabama, consists primarily of lowlands and low ridges. Included within the coastal plain is the Black Belt—historically, the center of cotton production and plantation slavery in Alabama—an area of rich, chalky soil that stretches across the entire width of central Alabama. Just to the north, the piedmont of east-central Alabama contains rolling hills and valleys. Alabama's highest elevation, Cheaha Mountain, 2,405 ft (733 m) above sea level, is located at the northern edge of this region. North and west of the piedmont is a series of parallel ridges and valleys running in a northeast-southwest direction. Mountain ranges in this area include the Red, Shades, Oak, Lookout, and other noteworthy southern extensions of the Appalachian chain; elevations of 1,200 ft (366 m) are found as far south as Birmingham. The Appalachian Plateau covers most of northwestern Alabama, with a portion of the Highland Rim in the extreme north near the Tennessee border. The floodplain of the Tennessee River cuts a wide swath across both these northern regions.
The largest lake wholly within Alabama is Guntersville Lake, covering about 108 sq mi (280 sq km) and formed during the development of the Tennessee River region by the Tennessee Valley Authority (TVA). The TVA lakes—also including Wheeler, Pickwick, and Wilson—are all long and narrow, fanning outward along a line that runs from the northeast corner of the state westward to Florence.
The longest rivers are the Alabama, extending from the mid-central region to the Mobile River for a distance of about 160 mi (260 km); the Tennessee, which flows across northern Alabama for about the same distance; and the Tombigbee, which flows south from north-central Alabama for some 150 mi (240 km). The Alabama and Tombigbee rivers, which come together to form the Mobile River, and the Tensaw River flow into Mobile Bay, an arm of the Gulf of Mexico.
About 450 million years ago, Alabama was covered by a warm, shallow sea. Over millions of years, heavy rains washed gravel, sand, and clay from higher elevations onto the rock floor of the sea to help form the foundation of modern Alabama. The skeletons and shells of sea animals, composed of limy material from rocks that had been worn away by water, settled into great thicknesses of limestone and dolomite. Numerous caves and sinkholes formed as water slowly eroded the limestone subsurface of northern Alabama. Archaeologists believe that Russell Cave, in northeastern Alabama, was the earliest site of human habitation in the southeastern US. Other major caves in northern Alabama are Manitou and Sequoyah; near Childersburg is DeSoto Caverns, a huge onyx cave once considered a sacred place by Creek Indians.
Wheeler Dam on the Tennessee River is now a national historic monument. Other major dams include Guntersville, Martin, Millers Ferry, Jordan, Mitchell, and Holt.