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Karstic Northern Ozarkian River Bluffs

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About the Karstic Northern Ozarkian River Bluffs

The Karstic Northern Ozarkian River Bluffs are a region of bluffs and ravines in southwestern Illinois, along the Mississippi River.

This region is underlain by limestone that is easily dissolved or eroded, and atop the limestone are layers of thick loess. This area was close to the border of the (older) Illinoian glacial period, and as such there are small amounts of highly-leached glacial till in areas. The region has extensive karst topography, with the highest density of caves and sinkholes, including sinkhole ponds, of anywhere in the broader surroundings. There is relatively little surface drainage, as many of the streams run underground. Soils on the flatter areas are mostly formed on loess, except on the steepest slopes where they are a mix of thin loess, colluvium, and limestone-derived residuum. There are bedrock outcroppings along some of the steepest slopes. The most common soils throughout the region are fine-textured but well-drained, and leached of calcium, and are well-suited to Western agriculture.

The original forest cover here is not well-known, but has been mapped as mostly oak-hickory forest on the drier uplands. There were also loess hill prairies on the loess-covered uplands and also on some of the steep slopes, as well as some areas of limestone glades. The original forests here were mostly cleared.

Presently, the flatter portions of this area is heavily farmed, although the steep slopes remain mostly forested. The region includes both pastureland and cropland, and primarily produces corn, wheat, soybeans, and hay. There are also some apple and peach orchards. The steep, forested portions of this region, which are mostly contiguous, represent an important forested corridor along the Mississippi river, where most of the forests in the Alluvial plain have been cleared. There is a small amount of protected land here, including Piney Creek Ravine Nature Preserve and Randolph County State Recreation Area. Piney Creek Ravine Nature Preserve is atypical of this region in having a population of shortleaf pine (Pinus echinata) close to its northern range limit.

This region is mostly sparsely populated, but it contains the small cities of Columbia and Chester, and the smaller towns of Valmeyer and Ellis Grove.

This region is bordered to the east and northeast by the flatter, higher-elevation Southern Illinoian Till Plain, and to the south and southwest by the low, flat Middle Mississippi Alluvial Plain. To the north, it borders the River Hills, a similar region with a mix of sandstone and limestone and a history of glaciation. To the south it is bordered by the Southern Ozarkian River Bluffs, another similar region that is underlain by slightly more erosion-resistant cherty limestone, and that thus has less karst and somewhat steeper topography.

References

1. Woods, A.J., Omernik, J.M., Pederson, C.L., Moran, B.C. "Level III and Level IV Ecoregions of Illinois", U.S. Environmental Protection Agency, Washington, DC (2006) Web.