 Reddish sandstone, known as the Amsden, laid down in the Pennsylvanian age was uplifted to current heights during the Laramide Orogeny around 70 million years ago.This uplift constructed joints in the Madison Limestone that would later become caves, such as the Lewis and Clark Caverns.Most of the cave was probably excavated during the ice ages, a time of much greater water supply than today.