This week we look at the fourth natural division, the Grand Prairie Division. This area encompasses much of Illinois, from as far north as Ogle County, south to Shelby County, west to Henry County and east to the Indiana border (map).
This area, the largest natural division of the state, is a vast plain formerly occupied by tall-grass prairie. The grassland landscape was so unusual that early travelers had to turn to the sea for analogies, evoking “a sea of grass” or “a vast ocean of meadow-land.” In time this landscape came to be known as “prairie.” The fertile soils are young and high in organic content. They were developed from deposited loess, lakebed sediments, and glacial drift. Natural drainage was poor resulting in many marshes and prairie potholes. The prairies were a veritable wildflower garden containing several hundred species of grasses and forbs.
Forests interrupted the landscape on floodplains, on slopes bordering streams, along river bends, and in isolated prairie groves. Like their prairie counterparts, prairie groves have a remarkable number of plant species, especially spring-blooming herbs.In addition to the more common moist forest and prairie communities, dolomite, loess hill, and shrub prairies are found here, as well as barrens, sandstone cliffs, eroding bluffs, sand savannas, and sand ponds. This division has five sections— Grand Prairie, Springfield, Western, Green River Lowland and Kankakee Sand Area.
While much of the prairie has been lost, there are remnants and restorations including Goose Lake Prairie State Park, Midewin National Tallgrass Prairie, Allerton Park, and Kennekuk Cove County Park. Spitler Woods State Natural Area shows a prairie grove habitat and is one of the largest stands of old growth woods in Central Illinois.