Oahe Reservoir Archeology, Geology, History>

OAHE DAM is located in central South Dakota 1,123 miles above the mouth of the Missouri River and 6 miles northwest of Pierre, the capital of the state. The reservoir created by the Dam extends approximately 250 river miles upstream, to within a short distance of Bismarck, North Dakota.

The dam and reservoir take their name from Oahe Mission, established among the Dakota (Sioux) Indians in 1874. In the Dakota language the name is said to signify "a place to stand on." The mission chapel was built in Peoria Bottom within view of the future site of the Oahe Dam.

The Missouri River valley in South and North Dakota sustained heavy glaciation during late geological times. The river is now deeply entrenched, in some areas flowing as much as 600 feet below the uplands it drains. East of the river abundant evidence can be seen of glacial action particularly in the form of extensive, undulating deposits of boulder till. West of the river the topography is even more broken as a result of extensive erosion of the underlying bedrock. Probably the most notable of these is the Pierre shale, the source of the troublesome gumbo soil that plagues so much of North and South Dakota. The only major tributaries of the Missouri in this part of the valley enter it from the west—the Bad, Cheyenne, Moreau, Grand and Cannonball Rivers.

Oahe Reservoir Area, Missouri River, North & South Dakota. (click on image for a PDF version)

The vast uplands bordering the Missouri River support hardy, nutritious native grasses, which once provided pasture for enormous herds of buffalo and other large game, as well as food for upland birds and waterfowl. Bottomlands, often heavily wooded, provided winter shelter. Today, the region west of the river is primarily cattle-range country, while the east side is chiefly a small-grain producing region.

The climate of the region is one of great extremes, with hot summers and cold winters, often accompanied by severe winds and heavy rain or snow. Although the average annual precipitation is about 16 inches, there is wide variation from season to season.

Oahe Indian Mission in Peoria Bottom, a short distance upstream from Pierre. The chapel, built in 1877 by Rev. Thomas L. Riggs, missionary to the Sioux, has now been removed to a new location overlooking the Oahe Dam, to which it gave its name. The Riggs home (left) was built of native boulders in 1902. Photo: Courtesy of the U. S. National Park Service

The combination of soils, vegetation, and climate favored the occupation of the region by various native Indian peoples. Permanent earth-lodge villages were usually located on the lower terraces or "benches" in the immediate valley of the Missouri, though these early farmers frequently ranged far afield in pursuit of game. Along the river, timber and water were always available, as well as fertile sandy bottomlands that were suitable for gardening with simple tools.

Other less settled native peoples, who moved freely about the region following the migrating buffalo and other game, probably clung close to the Missouri and its tributaries for centuries. For both the settled villagers and the more venturesome buffalo-hunting tribes and bands, the introduction of the horse—through trade with other Indian groups to the south and west—and of the gun—through trade with Whites—were of major importance since they permitted still more extensive travel over the Plains as well as more efficient taking of game. Yet for these First Americans of the Northern Plains, as for the first Whites who followed them, the river was the chief geographic feature of the area.