MLRA 108 Illinois and Iowa Deep Loess Hills

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 700 feet (200 meters) on the lowest valley floors to 1000 feet (300 meters) 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 feet to 100 or 200 feet, but the upland flats have relief of only 3 to 7 feet.

Climate

Average annual precipitation,-30 to 35 inches (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-39 to 54° F (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.

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