Long, narrow, and rhomboidal, Tennessee is divided topographically into six major physical regions: the Unaka Mountains, the Great Valley of East Tennessee, the Cumberland Plateau, the Highland Rim, the Central Basin, and the Gulf Coastal Plain. In addition, there are two minor physical regions: the Western Valley of the Tennessee River and the Mississippi Flood Plains.
The easternmost region is the Unaka Mountains, part of the Appalachian chain. The Unakas actually include several ranges, the most notable of which is the Great Smoky Mountains. The region constitutes the highest and most rugged surface in the state and covers an area of about 2,600 sq mi (6,700 sq km). Several peaks reach a height of 6,000 ft (1,800 m) or more: the tallest is Clingmans Dome in the Great Smokies, which rises to 6,643 ft (2,026 m) and is the highest point in the state.
Lying due west of the Unakas is the Great Valley of East Tennessee. Extending from southwestern Virginia into northern Georgia, the Great Valley is a segment of the Ridge and Valley province of the Appalachian Highlands, which reach from New York into Alabama. This region, consisting of long, narrow ridges with broad valleys between them, covers more than 9,000 sq mi (23,000 sq km) of Tennessee. Since the coming of the Tennessee Valley Authority (TVA) in 1933, the area has been dotted with artificial lakes and dams, which supply electric power and aid in flood control.
The Cumberland Plateau, which extends in its entirety from southern Kentucky into central Alabama, has an area of about 5,400 sq mi (14,000 sq km) in Middle Tennessee. The plateau is a region of contrasts, including both the Cumberland Mountains, which rise to a height of 3,500 ft (1,100 m), and the Sequatchie Valley, the floor of which lies about 1,000 ft (300 m) below the surface of the adjoining plateau.
The Highland Rim, also in Middle Tennessee, is the state's largest natural region, consisting of more than 12,500 sq mi (32,400 sq km) and encircling the Central Basin. The eastern section is a gently rolling plain some 1,000 ft (300 m) lower than the Cumberland Plateau. The western part has an even lower elevation and sinks gently toward the Tennessee River.
The Central Basin, an oval depression with a gently rolling surface, has been compared to the bottom of an oval dish, of which the Highland Rim forms the broad, flat brim. With its rich soil, the region has attracted people from the earliest days of European settlement and is more densely populated than any other area in the state.
The westernmost of the major regions is the Gulf Coastal Plain. It embraces practically all of West Tennessee and covers an area of 9,000 sq mi (23,000 sq km). It is a broad plain, sloping gradually westward until it ends abruptly at the bluffs overlooking the Mississippi Flood Plains. In the northwest corner is Reelfoot Lake, the only natural lake of significance in the state, formed by a series of earthquakes in 1811 and 1812. The state's lowest point, 178 ft (54 m) above sea level, is on the banks of the Mississippi in the southwest.
Most of the state is drained by the Mississippi River system. Waters from the two longest rivers—the Tennessee, with a total length of 652 mi (1,049 km), and the Cumberland, which is 687 mi (1,106 km) long—flow into the Ohio River in Kentucky and join the Mississippi at Cairo, Illinois. Formed a few miles north of Knoxville by the confluence of the Holston and French Broad rivers, the Tennessee flows southwestward through the Great Valley into northern Alabama, then curves back into the state and flows northward into Kentucky. Other tributaries of the Tennessee are the Clinch, Duck, Elk, Hiwassee, and Sequatchie rivers. The Cumberland River rises in southeastern Kentucky, flows across central Tennessee, and then turns northward back into Kentucky; its principal tributaries are the Harpeth, Red, Obey, Caney Fork, and Stones rivers and Yellow Creek. In the western part of the state, the Forked Deer and Wolf rivers are among those flowing into the Mississippi, which forms the western border with Missouri and Arkansas.