MLRA 108
Illinois and Iowa Deep Loess and Drift

Illinois, Iowa, and Missouri
79,790 km2 (30,800 mi2)

    Land use: Nearly all this area is in farms, and about 80 percent is cropland. Corn, soybeans, and other feed grains grown extensively on the less sloping soils are sold as cash crops. In areas where slopes are strong, more of the land is used for hay and pasture and more of the grain is fed to livestock on farms where it is grown. About 10 percent of the area is in introduced and native grasses. Making up about 5 percent are narrow bands of forest on steep valley sides and wet bottom land. About 5 percent is used for urban development and other purposes. Conservation practices are used to reduce erosion, flooding, and sedimentation.
    Elevation and topography: Elevation ranges from 200m on the lowest valley floors to 300m on the highest uplands, increasing gradually from east to west. Much of this dissected loess-mantled glacial plain is rolling to hilly, but some of the broad uplands far from the large streams are level to undulating. The smaller streams have narrow valley floors, but the large streams have broad flood plains. Local relief is mainly several meters to 25 or 50m, but the upland flats have relief of only 1 or 2m.
    Climate: Average annual precipitation-750 to 900 mm. Two-thirds or more of the precipitation falls during the freeze-free period. The low precipitation in winter is mostly snow. Average annual temperature-8 to 12°C. Average freeze-free period-160 to 180 days.
    Water: The favorably distributed moderate precipitation and the many perennial streams are important water sources. Ground water is abundant in the glacial drift that underlies much of the area. The Mississippi River and a few large tributaries are transportation arteries and are used for recreation.
    Soils: Most of the soils are Udolls. They are deep, medium textured soils that formed mainly in loess. These soils have a mesic temperature regime, an udic moisture regime, and montmorillonitic or mixed mineralogy. Somewhat poorly drained, nearly level Argiudolls (Flanagan, Ipava, and Mahaska series) and Hapludolls (Muscatine series) and poorly drained nearly level Haplaquolls (Drummer and Sable series), and Argiaquolls (Taintor and Virden series) are on uplands. Well drained and moderately well drained Argiudolls (Sharpsburg, Shelby, and Tama series) are gently sloping to strongly sloping. Well drained Hapludalfs (Fayette, Seaton, Clinton, and Hickory series) on the steep slopes of valley sides make up only 10 to 15 percent, of the total area. Somewhat poorly drained Hapludolls (Lawson series), well drained Hapludolls (Huntsville series), and moderately well drained Udifluvents (Nodaway series) are in silty alluvium on the flood plains. Poorly drained and very poorly drained Haplaquolls (Colo and Zook series) are in clayey alluvium on the flood plains.
    Potential natural vegetation: When this area was settled, it supported tall grass prairie vegetation. The present potential for natural vegetation is unclear. Forest vegetation consisting of black oak, white oak, bur oak, shagbark hickory, and some walnut grows on the steep slopes of valley sides. Silver maple, elm, and ash grow on flood plains.

Data Source:
U. S. Department of Agriculture, Soil Conservation Service. 1981.
       Land Resource Regions and Major Land Resource Areas of the United States.
       Agriculture Handbook 296.U. S. Government Printing Office, Washington, D. C.

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