The Copper Basin, located in the extreme southeastern corner of Tennessee in Polk County, was the center of a major copper-mining district from 1847 into the 1970s. The district also produced iron, sulfur and zinc as byproducts. The copper was discovered in 1843 by a prospector, presumably panning for gold, who found nuggets of native copper. The first shipment of copper ore was taken out on muleback in made in 1847. More than 30 mining companies were incorporated between 1852 and 1855 to mine copper at Ducktown. Development was speeded by a road built in 1853 connecting the area with Cleveland, Tennessee. The first smelter was built in the Ducktown district in 1854. Mining ceased when Union troops destroyed the copper refinery and mill at Cleveland, Tennessee in 1863. Mining resumed in 1866, and continued until 1878, when the mines had exhausted the shallow high-grade copper ores.