Built three-quarters of a mile west in 1845 by Charles and John Stacker, Mammoth Furnace was a steam-powered, charcoal-fueled stone stack 31 and a half feet high and 9 feet across inside at its widest. It made white, unusually hard pig iron from ore deposits near the furnace and produced 1514 tons in 48 weeks in 1857. Iron spikes made here were used by the Confederate States Army to obstruct the Tennessee River at Fort Henry. Its last blast was in 1874. Kentucky had been a major iron producer since 1791, ranking third in the United States in the 1830s and eleventh in 1965. Charcoal timber, native ore, and limestone supplied numerous furnaces in the Hanging Rock, Red River, Between Rivers, Rolling Fork, and Green River regions, where pig iron, utensils, and munitions were made. The charcoal-furnace era ended in the 1880s with depletion of ore and timber and the use of modern methods.