Authority (TVA) owns over 90% of the state's generating capacity. Nuclear power is Tennessee's largest source of electricity generation, producing about 43.4% of its power in 2021. The same year, 22.4% of the power was produced from coal, 17.8% from natural gas, 15.8% from hydroelectricity, and 1.3% from other renewables. About 59.7% of the electricity generated in Tennessee produces no greenhouse gas emissions. Tennessee is home to the two newest civilian nuclear power reactors in the U.S., at the Watts Bar Nuclear Plant in Rhea County. Tennessee was also an early leader in hydroelectric power, and today is the third-largest hydroelectric power-producing state east of the Rocky Mountains. Tennessee is a net consumer of electricity, receiving power from other TVA facilities in neighboring states. Tennessee has very little petroleum and natural gas reserves, but is home to one oil refinery, in Memphis. Bituminous coal is mined in small quantities in the Cumberland Plateau and Cumberland Mountains. There are sizable reserves of lignite coal in West Tennessee that remain untapped. Coal production in Tennessee peaked in 1972, and today less than 0.1% of coal in the U.S. comes from Tennessee. Tennessee is the nation's leading producer of ball clay. Other major mineral products produced in Tennessee include sand, gravel, crushed stone, Portland cement, marble, sandstone, common clay, lime, and zinc. The Copper Basin, in Tennessee's southeastern corner in Polk County, was one of the nation's most productive copper mining districts between the 1840s and 1980s, and supplied about 90% of the copper the Confederacy used during the Civil War. Mining activities in the basin resulted in a major environmental disaster, which left the surrounding landscape barren for more than a century. Iron ore was another major mineral mined in Tennessee until the early 20th century. Tennessee was also a top producer of phosphate until the early 1990s. Tourism Tennessee is the 11th-most visited state in the nation, receiving a record of 126 million tourists in 2019. Its top tourist attraction is the Great Smoky Mountains National Park, the most visited national park in the U.S., with more than 14 million visitors annually. The park anchors a large tourism industry based primarily in nearby Gatlinburg and Pigeon Forge, which includes Dollywood, the most visited ticketed attraction in Tennessee. Attractions related to Tennessee's musical heritage are spread throughout the state. Other top attractions include the Tennessee State Museum and Parthenon in Nashville; the