Ecoregions of
North Dakota
and
South Dakota

48. Lake Agassiz Plain

48b. Sand Deltas and Beach Ridges

Level IV Ecoregion

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48a. Glacial Lake Agassiz Basin

48b. Sand Deltas and Beach Ridges

48c. Saline Area

Glacial Lake Agassiz was the last in a series of proglacial lakes to fill the Red River Valley since the beginning of the Pleistocene. The Lake agassiz Plain is composed of thick lacustrine sediments underlain by glacial till. It is extrememly flat and has fewer lakes and pothole wetlands than neighboring ecoregions. The historic tallgrass prairie has been replaced by intensive agriculture. The preferred crops in the northern half of the region are potatoes, beans and wheat; soybeans and corn predominate in the south. Sugar beets are grown throughout the region.

A rectangular agricultural patchwork covers the level Lake Agassiz Plain.

The varying relief of the Sand Deltas and Beach Ridges ecoregion interrupts the extremely flat and intensively farmed land of the Lake Agassiz Plain (48). The beach ridges appear as parallel lines of sand and gravel formed by wave action on the varying shoreline levels of glacial Lake Agassiz. Three sand deltas, the largest being the Sheyenne River delta in the south, occur where major rivers entered glacial Lake Agassiz and dropped their sediment load. A high erosion risk exists in the sand dune areas.

Physiography

Area (square miles): 1616
Elevation/Local Relief (feet): 900-1200/40-250
Parallel ridges up to several miles wide composed of medium sand to medium gravel. Deltas comprised of lenses of fine to coarse sands. Thickest sand deposits windblown into dunes. Stream substrates, sand or gravelriffles, contrast with clay and silt-bottom streams elsewhere in Red River Valley.

Geology

Surficial Material and Bedrock
Stratified sand and gravel beach and strand line deposits sorted from lacustrine silts. Sandy deltaic deposits.

Soil

Order (Great Groups)
Mollisols(Haploborolls, Calciaquolls, Endoaquolls), Entisols (Udipsamments, Psammaquents)
Common Soil Series
Embden, Inkster, Hamar, Wyndmere, Arvilla, Hecla, Searden, Renshaw, Vang, Arveson, Bantry
Temperature/Moisture Regimes
Frigid/Udic

Climate

Precipitation - Mean annual (inches)
18-21
Frost Free - Mean annual (days)
95-125
Mean Temp. - Jan. min/max; July min/max, (°F)
-7/12;56/82

Potential Natural Vegetation

Tallgrass prairie with patches of oak savannah in delta areas.

Land Use and Land Cover

Sunflowers, potatoes, small grains on beach ridges. Mainly grazing on delta sands. Corn on sandy loams. Some irrigation.

Ecoregions of North Dakota and South Dakota

Ecoregions of
North Dakota
and
South Dakota