The Great Smoky Mountains are a mountain range rising along theTennessee–North Carolina border in the southeastern United States. The range is sometimes called the Smoky Mountains and the name is commonly shortened to theSmokies.The Great Smokies are part of an International Biosphere Reserve. Along with the Biosphere reserve, the GreatSmokies have been designated a UNESCO World Heritage Site. The name "Smoky" comes from the natural fog that often hangs over the range and presents as large smoke plumes from a distance. This fog is caused by the vegetation exhaling volatile organic compounds.