We are down in the deep caves and tunnels of Mammoth Cave National Park in Kentucky. They have many tours guided by nice National Park Rangers every day (and night) and this one shows not only the spectacular rock arrangements, but some history. Here you can see the walls are methodically scratched. These and many other areas were “mined” by the Native Americans hundreds of years ago. The marks were made when a mineral or chemical was scratched off of the walls up to as high as they could reach. What the material they took was used for is not known.