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Rock River Hills

Ecoregion in IL

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The Rock River Hills ecoregion is mostly composed of agriculturally dominated, rolling hills and undulating plains; however, more rugged, partly forested ridges, ravines, and bluffs occur in the southeast and northwest. Physiography is strongly influenced by the underlying limestone, dolomite, and sandstone; it is not significantly masked by the region’s thin mantle of glacial till. Caves occur in limestone and dolomite. Most soils were derived from loess, but other soils in major valleys typically developed from glacial outwash or alluvium, and still others were derived from till or residuum (Natural Resources Conservation Service, various dates). In the early 19th century, dry, shortgrass prairies characteristic of Ecoregion 52 were found on undulating to rolling uplands, and transitioned into mesic prairies dominated by big bluestem and Indian grass. Dry or mesic upland forests grew on ridge slopes and on fire-protected uplands, Canada yew – yellow birch forests grew on cool bluffs and in ravines, and floodplain forests occurred on bottomlands (Schwegman, 1973, p. 14). Native flora is influenced by bedrock, with several species confined to areas underlain by sandstone (Schwegman, 1973, p. 14). Today, more than half of The Rock River Hills ecoregion is used as cropland; livestock farming is also important, and forest remnants are largely confined to steep slopes and riparian areas. Main crops include corn, soybeans, and wheat. Field tiles are normally used for drainage. Cropland is more common than in Ecoregions 52 and 53, but is much less extensive than in the Illinois/Indiana Prairies (54a).

— EPA

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