All Black Hills caves have formed in this layer 300 to 600 feet thick. Originally it was laid down on a shallow seabottom about 300 million years ago. Its name derives from the Lakota word meaning "Black Hills".
The Civilian Conservation Corps established a camp here during the Great Depression of the 1930s to make improvements to the park. This camp employed 200 men at a time and provided much needed jobs and training. Over an eight-year period, the youn…