Coteau des Prairies
The Coteau des Prairies is a plateau in the flat prairie in eastern South Dakota, which extends into southwestern Minnesota and northwestern Iowa. The plateau is 320 kilometers long and 160 kilometers wide and has the form of an iron. The name comes from French explorers from New France. Coteau means in the French slope.
The plateau consists of thick glacial deposits, the residues of many repeated glaciations, with a total thickness of 275 meters. Below is a ridge of resistant shale from the Cretaceous period. During the last Ice Age ( Pleistocene ), the glacier has split into two halves and pushed to the pre-existing plateau and so deepens the lowlands to the plateau.
The plateau has many small glacial lakes and is drained by the Big Sioux River in South Dakota and the Cottonwood River in Minnesota. A quarry in the plateau was once the source of traditional stones, which was used for the production of Indian peace pipes. This Pipestone ( Catlinit ), a fine-grained, easy to be processed mineral, was recovered near the present-day town of Pipestone (Minnesota) and in the adjacent Minnehaha County ( South Dakota).