Indiana, Illinois, and Missouri
60,860 km² (23,500 mi²)

    Land use: Nearly all this area is in farms, and about 40 percent is cropland. Feed grains and hay for livestock are the principal crops, but grape vineyards and peach and apple orchards are important in some places. About 35 percent of the area is forested, which includes some national forests. Most of the remainder of the farmland is in permanent pasture and native grasses. The hazards of erosion and sedimentation are severe in urban areas near St. Louis and other cities and on the farmland.
    Elevation and topography: Elevation ranges from 100m on the main valley floors to 300m on the ridgetops. This dissected glacial till plain has rolling narrow ridgetops and hilly to steep ridge slopes and valley sides. The small streams have narrow valleys and steep gradients. The major rivers have nearly level broad flood plains. Valley floors are tens of meters below the adjoining hilltops.
    Climate: Average annual precipitation-900 to 1,150 mm. About two-thirds of the precipitation falls during the freeze-free period. The maximum is in spring and early in summer and the minimum from mid-summer through autumn. Average annual temperature-12 to 14°C. Average freeze-free period-180 to 200 days, increasing from north to south.
    Water: In most years precipitation is adequate for the crops commonly grown, but in some years yields are reduced by drought. Ground water is the source of water for domestic and livestock needs on farms. The Mississippi, Missouri, and Ohio Rivers are major transportation arteries and are also used for recreation.
    Soils: Most of the soils are Udalfs. They are deep and medium textured to moderately fine textured and have a mesic temperature regime, an udic moisture regime, and mixed mineralogy. Well drained and moderately well drained Hapludalfs (Alford, Fayette, Menfro, Muren, Weller, and Winfleld series) are in silty loess; other Hapludalfs (Gara, Hickory, Keswick, and Lindley series) are in glacial till; and still others (Bloomfield and Princeton series) are in sandy aeolian material. Well drained and moderately well drained Fragiudalfs (Grenada, Hatton, and Hosmer series) are on ridgetops in silty material. Well drained, cherty Paleudalfs (Goss series) weathered from cherty limestone. Somewhat excessively drained shallow Hapludolls (Gasconade series) are on steep slopes. Udifluvents (Eel, Genesee, Haymond, Nodaway, and Sharon series), Fluvaquents (Piopolis, Shoals, and Wakeland series), Haplaquolls (Beaucoup, Darwin, and Wabash series), and Hapludolls (Leta series) are on flood plains.
    Potential natural vegetation: This area supports a forest flora consisting mainly of oak and hickory species.

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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