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Ecoregions of
North Dakota
and
South Dakota

43. Northwestern Great Plains


43g. Semiarid Pierre Shale Plains Level IV Ecoregion

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North Dakota Ecoregions

South Dakota Ecoregions

43a. Missouri Plateau

43b. Little Missouri Badlands

43c. River Breaks

43d. Forested Buttes

43e. Sagebrush Steppe

43f. Subhumid Pierre Shale Plains

43g. Semiarid Pierre Shale Plains

43h. White River Badlands

43i. Keya Paha Tablelands

43j. Moreau Prairie

43k. Dense Clay Prairie

  The Northwestern Great Plains ecoregion encompasses the Missouri Plateau section of the Great Plains. It is a semiarid rolling plain of shale, siltstone, and sandstone punctuated by occasional buttes and badlands. Native grasslands persist in areas of steep or broken topography, but they have been largely replaced by spring wheat and alfalfa over most of the ecoregion. Agriculture is limited by erratic precipitation patterns and limited opportunities for irrigation.

GIF - Soft shales
Overgrazing or tilling the soft shales of ecoregions 43f and 43g risks wind and water erosion

West of the Cheyenne river, the Semiarid Pierre Shale Plains take on a drier aspect. Although the precipitation is only one or two inches less per year than in ecoregion 43f, successful yields for tilled crops occur more infrequently than they do further east. In this region the mixed-greass prairie has a predominance of shortgrass species, e.g., little bluestem and buffalograss.

Physiography

Area (square miles): 3853

Elevation/Local Relief (feet): 2500-3700/100-300

Unglaciated. Undulating to rolling plains. Steep-sided, incised stream channels.

Geology

Surficial Material and Bedrock
Cretaceous Pierre shale.

Soil

Order (Great Groups)
Aridisols (Camborthids), Mollisols (Argiustolls), Entisols (Torriorthents), Inceptisols (Ustochrepts)

Common Soil Series
Pierre, Samsil, Lismas, Satanta, Nunn

Temperature/Moisture Regimes
Mesic/Aridic, Ustic

Climate

Precipitation - Mean annual (inches)
14-15

Frost Free - Mean annual (days)
125-140

Mean Temp. - Jan. min/max; July min/max, (°F)
6/29;57/87

Potential Natural Vegetation

Shortgrass prairie grasses such as western wheatgrass, green needlegrass, blue grama and buffalograss.

Land Use and Land Cover

Cattle grazing, rangeland. Dryland farming of winter wheat and alfalfa.

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