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Cretaceous Hills

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About the Cretaceous Hills

The Cretaceous Hills is a small, hilly region, oriented east-west, located near the southernmost tip of Illinois.

This region consists of rolling hills, steep in places, underlain by unconsolidated sediments, including sand, gravel, and clay. Atop this are layers of loess, fine-textured wind-blown sediments. Most of the soils here are formed on loess, but in places the underlying sediments are exposed and soils are instead formed on these other substrates.

The original forest cover here is not well-known. In the mid-19th century, this area was largely forested, with dominant trees including various upland oaks, tupelo (Nyssa sylvatica), various hickories, and tuliptree (Liriodendron tulipifera). This region contains some acidic seeps, unique communities supporting rare orchids, mosses, and ferns. The climate is humid and subtropical, with four seasons and a weak bimodal precipitation pattern, wet springs peaking in late April to Early May, and wet falls peaking in late November; summers are drier with rainfall lowest in August.

Nowadays, forest here is mostly limited to the steeper slopes. The rest of the land is heavily farmed, with livestock farms, general farming, and cropland producing corn, wheat, hay, and soybeans. There is some public, protected land here, in Cretaceous Hills Nature Preserve and adjacent State Natural Area. The State Natural Area is open to hunting and the Nature Preserve is not. The forest cover here varies considerably based on slope and aspect, with white oak (Quercus alba), hickories, and other upland oaks found on the drier uplands, and northern red oak (Quercus rubra) and tuliptree found in the cooler ravines.

This area is mostly sparsely populated, but there are a few very small towns. The largest communities include Olmsted, Grain Chain, and Round Knob.

This region is mostly surrounded to the north, south, and west by the Wabash-Ohio Bottomlands. At the east, it is bordered by a small, isolated piece of the Southern Shawnee Hills. The westernmost end of this region is bordered to the south by the Northern Holocene Meander Belts of the Mississippi Alluvial Plain.

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.