East Tennessee is a name given to approximately the eastern third of the U.S. state of Tennessee, one of the three Grand Divisions of Tennessee defined in state law. East Tennessee consists of 33 counties, 30 located within the Eastern Time Zone and three counties in the Central Time Zone, namely Bledsoe, Cumberland, and Marion. East Tennessee is entirely located within the Appalachian Mountains, although the landforms range from densely forested 6,000-foot (1,800 m) mountains to broad river valleys.
East Tennessee is both geographically and culturally part of Appalachia, and has been included— along with Western North Carolina, North Georgia, Eastern Kentucky, West Virginia, and Southwest Virginia— in every major definition of the Appalachian region since the early 20th century. East Tennessee is home to the nation's most visited national park— the Great Smoky Mountains National Park— and hundreds of smaller recreational areas. East Tennessee is often called the birthplace of country music, due largely to the 1927 Victor recording sessions in Bristol, and throughout the 20th and 21st centuries has produced a steady stream of musicians of national and international fame. Oak Ridge was the site of the world's first successful uranium enrichment operations which paved the way for the atomic age. The Tennessee Valley Authority is headquartered in Knoxville.