Three cut-and-fill terraces of the Missouri River are present in the Big Bend Reservoir. The upper terrace (Mt-2), tentatively correlated with the Cary moraine, consists of outwash sands and gravels. It stands at heights of 80-100 feet above the river. Its surface is capped by a deposit of as much as 30 feet of aeolian sand and silt. The intermediate terrace (Mt-1) consists of gravel, sand, and silt, and stands at heights of 35-45 feet above the river. It, too, is capped with aeolian sand and silt. This terrace is tentatively dated as Mankato, but may be younger. The lower terrace (Mt-0) stands 10-15 feet above the average river level and is the flood plain of the present Missouri River. The upper part of the terrace fill consists of sand and silt of Recent age. The lower part of the fill is gravel, sand, and silt and is probably post-Altithermal but may be late Pleistocene in age. Several humic horizons are present in the silt covering both Mt-1 and Mt-2, and a well-defined paleosol is buried in the silt on Mt-2. Study of these horizons indicates the possibilities of correlating them with geological events and of finding a stratigraphic separation of archeological remains dating from Pleistocene to late prehistoric times.
Proceedings of the Iowa Academy of Science
©1959 Iowa Academy of Science, Inc.
Coogan, Alan H. and Irving, William N.
"Late Pleistocene and Recent Missouri River Terraces in the Big Bend Reservoir, South Dakota,"
Proceedings of the Iowa Academy of Science, 66(1), 317-327.
Available at: https://scholarworks.uni.edu/pias/vol66/iss1/44