The Coteau des Prairies: orange arrows indicate paths of the two lobes of the glacier around either side of the formation.

The Coteau des Prairies is a plateau, approximately 200 miles in length and 100 miles in width, rising from the prairie flatlands in eastern South Dakota in the United States.

The plateau was named by early French explorers from New France. Coteau means "slope" in French.

The plateau is composed of thick glacial deposits, the remnants of many repeated glaciations, reaching a composite thickness of approximately 900 feet. They are underlain by small ridge of resistant Cretaceous shale. During the last Pleistocene ice age, two lobes of the glacier probably parted around the prexisting plateau and further deepend the lowlands flanking the plateau.

The plateau has numerous small glacial lakes and is drained by the Big Sioux River. A quarry in the plateau was once the site for Native American peace pipes.

External links

• USGS Site on the Coteau des Prairies
• Glacial History of Coteau des Praries (University of South Dakota).
• Early Observations of the Coteau des Prairies