Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin
SUB-SUBSECTION III.1.2. Blue Hills
DISCUSSION: The Blue Hills consists of a small area of pitted outwash and ground moraine that occupies the east boundary of the Upper Minnesota River Country subsection. The vegetation of the sub-subsection consists largely of prairie or brush prairie surrounding numerous wetland depressions on pitted outwash.
ELEVATION: 1,150 to 1,428 feet (350 to 435 m).
AREA: 901 square miles (2,336 sq km).
STATES: Minnesota.
CLIMATE: See subsection.
BEDROCK GEOLOGY: Bedrock is covered with 100 to 300 feet of glacial drift (Olsen and Mossler 1982). Underlying bedrock is Cretaceous shale, sandstone, and clay; lower Precambrian granitic rocks, including metasedimentary and metaigneous gneiss, schist, and migmatite; and upper amphibolite to lower granulite facies (Morey 1976).
LANDFORMS: Pitted outwash of the Belgrade-Glenwood outwash plain and ground moraine of the Osakis till plain (University of Minnesota et al. 1979, Hobbs and Goebel 1982).
LAKES AND STREAMS: Kettle lakes and potholes are common, making up approximately 5 percent of the land surface (University of Minnesota et al. 1979). There are 53 lakes larger than 160 acres, but no large streams.
SOILS: Soils are derived both from loamy tills and sandy or gravelly outwash (University of Minnesota et al. 1979). Soils of the area are shown largely as grassland soils, primarily Aquolls, but also include Udolls, Ustolls, and Psamments (Cummins and Grigal 1981).
PRESETTLEMENT VEGETATION: Marschner (1974) shows the vegetation as predominantly tallgrass prairie, with many potholes dominated by wet prairie and surrounded by oak openings or savanna. The combination of sandy soils and level topography was probably responsible for prairie vegetation. The western boundary of the sub-subsection, made up of steep, irregular ice-contact ridges, consisted of a narrow band of oak openings.
NATURAL DISTURBANCE: Fire probably originated both in the tallgrass prairie to the west and within the sub-subsection itself. Fire carried well because of the relatively flat topography combined with sandy soils.
PRESENT VEGETATION AND LAND USE: Descriptions of the vegetation presently found on nature preserves within the sub-subsection indicate that the vegetation forms a complex mosaic of plant communities, the result of local differences in drainage conditions, soil texture, rockiness, slope, and aspect. Gravel prairie and tallgrass prairie are found on the uplands; wet prairie, marshes, and shrub swamps are found in the potholes (The Nature Conservancy 1988).
Approximately 80 percent of the land is used for crops, 5 to 10 percent is used for pasture, and 5 to 10 percent is used for forest. The remaining 5 to 10 percent of the land remains as marshes or other wetlands (University of Minnesota et al. 1979).
RARE PLANT COMMUNITIES: Gravel prairie and a few dry oak savannas.
RARE PLANTS: Astragalus neglectus (Cooper's milk-vetch), Cirsium hillii (Hill's thistle), Cypripedium candidum (white lady's-slipper).
RARE ANIMALS: Haliaeetus leucocephalus (bald eagle), Emydoidea blandingii (Blanding's turtle).
NATURAL AREAS: The Nature Conservancy Preserves: Roscoe Prairie, Regal Meadow.
PUBLIC LAND MANAGERS: See subsection.
CONSERVATION CONCERNS: Conversion of the prairies and wetlands to cropland.
BOUNDARIES: The relatively flat outwash and ground moraine of the sub-subsection is surrounded by steeper stagnation moraine and end moraines of the Alexandria moraine complex.
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