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Ecoregions of
North Dakota
and
South Dakota

43. Northwestern Great Plains


43c. River Breaks 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.

JPG - Rolling fields and native range
Rolling fields, native range, and rural hamlets characterize the Northwestern Great Plains.

The River Breaks form broken terraces and uplands that descend to the Missouri River and its major tributaries. They have formed particularly in soft, easily erodible strata, such as Pierre shale. The dissected topography, wooded draws, and uncultivated areas provide a haven for wildlife. Riparian gallery forests of cottonwood and green ash persist along major tributaries such as the Moreau and Cheyenne rivers, but they have largely been eliminated along the Missouri River by impoundments.

Physiography

Area (square miles): 10517

Elevation/Local Relief (feet): 1300-2700/200-500

Unglaciated. Highly dissected hills and uplands bordering major rivers and associated alluvial plains.

Geology

Surficial Material and Bedrock
In North Dakota, Tertiary sandstone and shale (Fort Union Formation). In South Dakota, Cretaceous Pierre Shale, on the west side of the Missouri River; on the east side of the Missouri River, breaks eroded through glacial till to Tertiary and Cretaceous foundation.

Soil

Order (Great Groups)
Mollisols (Calciborolls, Haploborolls), Entisols (Ustorthents, Ustipsamments, Flavaquents), Aridisols (Natrargids), Vertisols (Haplusterts), Inceptisols (Ustochrepts)

Common Soil Series
Sansarc, Opal, Bullock, Cabba, Amor, Flasher, Vebar, Temvik, Mandan, Cherry, Chama, Zahl, Lallie, McKeen

Temperature/Moisture Regimes
Frigid (north), Mesic (south of Moreau River)/Ustic

Climate

Precipitation - Mean annual (inches)
16-18

Frost Free - Mean annual (days)
80-125 (north);100-130 (south)

Mean Temp. - Jan. min/max; July min/max, (°F)
-3/21;56/87 (north) 3/27;60/91 (south)

Potential Natural Vegetation

Blue grama, western wheatgrass, buffalograss, and some bluestem. Juniper and deciduous trees on northfacing slopes. Cottonwood gallery forests on the floodplain.

Land Use and Land Cover

Steep slopes restrict landuse to cattle grazing. Land cover is mostly rangeland and native grasses. Remnant woodlands in draws and on existing (unimpounded) alluvial flats.

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