Paleontology and geology
There are two exposures of Precambrian rocks in South Dakota. The Sioux Arch in the eastern part of the state consists of metamorphosed sandstone and claystone deposited in a shallow sea. A particular type of claystone from this area, catlinite, is mined by Native Americans and used to make ceremonial pipes and figurines. The second exposure, the Black Hills in western South Dakota, is an uplifted geological dome consisting of metamorphic rocks up to 2.5 billion years old that formed in the deep past from even older rocks. Due to the metamorphic nature of these Precambrian rocks, no fossils have been found in them.