Paleozoic Formations     

During the latter part of Precambrian time and into the early Paleozoic, South Dakota’s surface was severely eroded forming a relatively flat plain interrupted by low knobs and ridges of resistant rocks. The first sea to advance over South Dakota’s Precambrian surface covered the western part of the state. For most of Paleozoic time, water lapped on and off the state repeatedly, as continental seas advanced from and retreated to the oceans. With each advance and retreat, new rock layers of sandstone, shale, and/or limestone were deposited.

Occasional periods of weathering and erosion were interspersed throughout the Paleozoic. For example, during Late Mississippian time, the Black Hills area was subjected to weathering and erosion. Sinkholes and caverns formed in the upper part of the old limestone surface, and a residual soil of red clay and gravel accumulated in low places. This red soil and gravel can be observed in the upper part of Wind Cave. The end of the Paleozoic was a time of erosion across South Dakota.