Tennessee is a long, narrow state that occupies parts of three North American physiographic provinces. From east to west they are the Appalachian Highlands, the Central Lowlands, and the Gulf Coastal Plain. Within the state they are officially called East, Middle, and West Tennessee.
The Appalachian Highlands section is a mountainous area running northeast-southwest through the eastern third of the state. Along the Tennessee-North Carolina border rise the heavily forested Unaka, Bald, Great Smoky, and Unicoi mountains. They lie at the southern end of the Blue Ridge and contain many of the loftiest peaks in the eastern United States. Clingmans Dome, rising 6,643 feet (2,025 m) in Great Smoky Mountains National Park, is the highest peak in the East (after Mount Mitchell in North Carolina). Fifteen other peaks in Tennessee attain heights of more than 6,000 feet (1,830 m).
Just west of the mountains lies the Ridge and Valley region. It consists of a series of more or less parallel ridges and intervening valleys, which together are known as the Great Valley. Farther west is the Cumberland Plateau. It rises along a relatively sharp escarpment to an average elevation of about 2,000 feet (610 m). Throughout the plateau, rivers have carved deep, steep-sided valleys, making the terrain rough.
The Central Lowlands, a vast interior physiographic province of the United States, juts southward into central Tennessee. Here the landforms are varied, and the surface is hilly to flat. The dominant features, however, are low plateaus, cuestas (ridges with one steep side), and a large depression known as the Nashville Basin. Bordering the basin is the so-called Highland Rim.
The Gulf Coastal Plain extends inland from the Gulf of Mexico into the western part of the state, where it is called the Jackson Plain. It is a fertile area of low, rolling terrain between the Mississippi and Tennessee rivers. Marshy bottomlands and low cliffs fringe much of the Mississippi's course. In the extreme southwest, near the Mississippi state line, is Tennessee's lowest point—182 feet (55 m) above sea level.Tennessee's state tree is the tulip-poplar.
All the water of Tennessee's streams flows eventually to the Gulf of Mexico by way of the Mississippi-Ohio river system. Well over half of the state is drained by the Tennessee River and its tributaries; the rest, by the Cumberland and Mississippi systems. The state also has areas of underground drainage, marked by caverns and subterranean rivers.
Because of their relatively rapid descents and large flows, rivers in eastern and central Tennessee have afforded excellent opportunities for damming. From development programs have come abundant hydroelectric power, flood control, improved navigation, and new recreational areas. Both public and private agencies have taken part in harnessing the rivers; however, the leader has been the TVA, a federally owned corporation.
Behind the dams are impounded long, meandering lakes, the largest of which is Kentucky Lake, shared by Tennessee and Kentucky. Other such lakes wholly or partly within the state include Barkley, Center Hill, Cherokee, Chickamauga, Dale Hollow, Douglas, Norris, Old Hickory, Tims Ford, and Watts Bar lakes. Reelfoot Lake, in the northwest, is Tennessee's only large natural lake. It was created by severe earthquakes in 1811–12.
Tennessee has a humid climate that has characteristics of both the harsh continental kind of the northern United States and the subtropical type of the South. Its chief marks are warm to hot summers, moderately cold winters, and abundant precipitation.
Summers are hottest in the valleys and lowlands, where July temperatures average 75° to 80° F. (24° to 27° C.). January temperatures in the same areas average about 40° F. (4° C.). Because of their height, the mountainous areas experience lower temperatures in summer and in winter.
Except for the Appalachian peaks, which receive as much as 80 inches (2,030 mm) of precipitation a year, the state normally gets 45 to 55 inches (1,140 to 1,400 mm), depending on the locality. Only a very small part of the total precipitation falls as snow, even in the mountains. Destructive storms are few, since the state lies outside the main areas affected by hurricanes and tornadoes.
Except in the high, remote parts of the Appalachians, the forest wilderness that once covered Tennessee vanished long ago with the settling of the land. Today, second-growth forests cover about half of the state and make up a valuable source of commercial timber. Northern and southern forest tree species are found in Tennessee; the variety is unequaled by most other states. Hardwoods—primarily oak (especially white and red oak), hickory, yellow poplar, sweetgum, maple, and beech—predominate from the Mississippi bottomlands to the Appalachians. Softwoods, mainly pines, are confined largely to the lower mountain slopes of eastern Tennessee. Cedars are widely distributed.Tennessee's state flower is the iris.