Ozark Division

The 12th Natural Division is the Ozark Division in southwestern Illinois. (map)

A narrow band from northern Monroe County to Alexander County makes up the Ozark Uplift, a domelike geologic structure of exposed, ancient bedrock centered in the Ozark Mountains of Missouri. Great limestone bluffs mark the edge of the Mississippi Valley. Sandstone ravines in Randolph County and the sinkhole region of Monroe County, with its caves and springs, make this landscape unique in Illinois. This division is divided into three sections. The Northern Section was glaciated during the Illinoian glacial episode and is underlain with relatively pure limestone. The Central Section, which was also glaciated during the same period, is underlain with sandstone. The Southern Section is unglaciated and underlain with cherty limestone. Prior to settlement most of this division was forested and a rich assemblage of tree species can still be found here. This is the only division where shortleaf pine occurs naturally. Hill prairies occurred on the river bluffs of the Northern Section. Unique organisms include the eastern coachwhip snake and the plains scorpion. Visit Pine Hills in Union County and Fults Hill Prairie Nature Preserve in Monroe County to experience this division.

Wabash Border Division

The 11th Natural Division is the Wabash Border Division, stretching from Vermilion County south to Gallatin County.(map)

The eastern border of Illinois contained the great trees that made up the last stronghold of the eastern deciduous forest. Traces of this magnificent forest still remain in the landscape surrounding theWabash and Vermilion rivers. This division is divided into three sections: Bottomlands, Southern Uplands, and Vermilion River. The Wisconsin glacial-episode impacted the Vermilion River Section, while all three sections were influenced by the earlier Illinoian glacial episode. This division is a transition zone between forest and prairie, but lowland and upland forests dominate the landscape, containing a great diversity of trees: beech, tulip poplar, cottonwood and several species of oak—pin, overcup, cherrybark, bur, Shumard, and swamp white. The understory is a garden of spring ephemerals with a nearly continuous cover of forest vegetation. In addition to a large number of tree species, the state’s only National Wild and Scenic River is found here with several species of fish found nowhere else in the state, including the bluebreast and harlequin darters. To experience this division visit the Russell Duffen Nature Preserve in Vermillion County and Beall Woods State Park in Wabash County.

Southern Till Plain Division

The 10th Natural Division is the Southern Till Plain Division is the second largest division in Illinois. (map)

This division encompasses the area south of the Shelbyville Moraine, the Sangamon River, and Macoupin Creek. The Illinoian glacial episode reached its southernmost limit just beyond this division. The bedrock consists of sandstone, limestone, coal, and shale. A layer of thin soil with poor internal drainage, usually loess or till, covers the bedrock. Many of the soils have a high clay content leading to “claypan” subsoil. From north to south the glacial till becomes thinner.

This division is divided into two sections. The Effingham Plain Section which is a relatively flat plain drained by the Kaskaskia River, contained mostly prairie, while the Mt. Vernon Hill Country Section has rolling, hilly topography and was mostly forested. Found in both sections are post oak flatwoods which occur on the hardpan, clay soil. Trees do not live excessively long in a flatwood forest. They undergo a regular cycle of 150 to 200 years, and when they reach a certain size, the trees are inevitably blown down because of their shallow root penetration in the clay soil. Post Oak Rest Area along I-57 is a good example of this community type.

Lower Mississippi River Bottomlands Division

The 9th Natural Division on the map is the Lower Mississippi River Bottomlands Division stretches along the Mississippi River, from Madison County south to the northern part of Alexander County. (map)

This division includes the Mississippi River and its floodplain from Alton to the Thebes Gorge. The Mississippi River is muddy here due to the silt load brought in by the Missouri River. The soils have developed from this alluvium and are either finely textured and well-drained with areas of sand, or clayey with poor drainage. The division is divided into two sections—the Northern, which originally contained prairies, marshes, and forest, and the Southern, which was densely forested. The Northern Section contains the American Bottoms, a montage of swales, backwater lakes, ridges, and river terraces. When Charles Dickens visited the area in 1842 all he could hear was the loud chirping of frogs and all he could see on the “unwholesome, steaming earth” was mud, mire, brake (overgrown marshland) and brush. Horseshoe Lake, which is a U-shaped ox-bow, is now a state park. The Southern Section’s forests have not only pin, overcup, and cherrybark oaks, but also species associated with bottomland swamps. Look for pumpkin ash, swamp cottonwood, and bald cypress in La Rue Swamp and listen for the calls of green treefrogs.

Middle Mississippi River Border Division

The 8th Natural Division on the map is the Middle Mississippi River Border Division.(map)

The narrow band of river bluffs and rugged terrain along the Mississippi River floodplain from Rock Island County to St. Clair County and the lower Illinois River valleys make up this division. Bedrock cliffs and outcrops of limestone and sandstone are common along the river bluffs. Hill prairies occur atop south and west-facing bluffs, while oak-hickory forests predominate in the ravines and on cooler, north- and east-facing slopes. Deep deposits of loess (windblown silt) form high bluffs. Two peaks in Pere Marquette State Park are examples of loess deposits—McAdams Peak and Lovers Leap. The division is divided into two sections— Glaciated and Driftless. The topography of the Glaciated Section is a result of the Pleistocene glaciers—the Illinoian and pre-Illinoian stages. Unusual habitats found here include limestone glades, loess hill prairies, and glacial-drift hill prairies. The topography of the Driftless Section is rougher because the area escaped the glaciers. Limestone and sandstone outcrops frequently occur. Unusual habitats found here include limestone glades and loess hill prairies. Pere Marquette State Park is found in this section.

Upper Mississippi River and Illinois River Bottomlands Division

The 7th division is the Upper Mississippi River and Illinois River Bottomlands Division. (map)

This division encompasses the rivers and floodplains of the Mississippi River from Wisconsin to where it meets the Missouri River in Calhoun County. It also stretches along the Illinois River and its major tributaries south of LaSalle. This division is divided into two sections—Illinois River and Mississippi River. Broad floodplains and gravel terraces formed by glacial floodwaters characterize the terrain. Both big rivers have oxbow lakes, but backwater lakes are found only in the Illinois River and its major tributaries south of LaSalle. The Sportsman’s and General Guide described this area in 1877: “The most noted sporting grounds in Central Illinois, if not in the whole State, lie upon the Illinois River . . . The game here is of great variety and abundance . . .” Much of this land was originally forested and forests still occur along the broad floodplains. Prairies, marshes, and moist savannas also occurred. One unique habitat in this division was originally classified as a springfed bog or a “hanging fen.” This rare natural community is characterized by sloping peat at the edge of a moraine.

Illinois River and Mississippi River Sand Areas Division

The 6th Natural Division is the Illinois River and Mississippi River Sand Areas, encompassing much of Mason County as well as parts of Whiteside, Henderson, Woodford, Peoria, Putnam, Tazewell, Cass and Scott Counties.(map)

The sand areas and dunes in the bottomlands of the Illinois and Mississippi rivers comprise this division. Dry sand prairie and scrub oak forest, dominated by black and blackjack oak, are the natural vegetation. The division is divided into two parts—Illinois River and Mississippi River sections. The meltwaters of the Wisconsin glacial episode greatly affected the formation of both the Havana sand deposit (Illinois River) and the Hanover-Oquawka sand deposit (Mississippi River). The Havana sand was formed as meltwater cascaded down the prehistoric course of the Illinois River. The Hanover-Oquawka deposit occupies an expanse between the bluffs on the east and the Mississippi River on the west. In both of these areas, tremendous floods carried a huge volume of sand and gravel downstream at breakneck speed, depositing material when the water slowed. Look for prickly-pear cactus, three-awn grass, little bluestem, and Indian grass in Sand Ridge State Forest or Thomson-Fulton Sand Prairie Nature Preserve.