Putnam County was the site of several saltpeter mines. Saltpeter is the main ingredient of gunpowder and was obtained by leaching the earth from several local caves. Calfkiller Saltpeter Cave, located in the Calfkiller Valley, was a major mining operation, as was Johnson Cave, also located in the Calfkiller Valley. Both caves still contain significant remnants of the mining activity. Several other caves in the county were the site of smaller operations. Most saltpeter mining in Middle Tennessee occurred during the War of 1812 and the Civil War.