Environmental Description:  This community is found on hills formed from eroded glacial drift or on deep loess deposits. These are usually found above rivers and streams, where a river valley cuts through an end moraine creating many deep, steep-sided tributary ravines. Loess deposits are especially common along the Mississippi and Illinois rivers. The sites are typically on steep, south- or west-facing slopes with well-drained to somewhat excessively drained soil (White and Madany 1978). Soil information comes from a General Soil Map of Illinois (Fehrenbacher et al. 1982). The unconsolidated material above the bedrock may be residual or transported. Residual material occurs south of the glaciated area. On most other prairie slopes, the surface material is transported (loess or glacial drift). Hill prairie soils are high in calcium carbonate, and thus alkaline (Evers 1955). Bedrock ranges from Middle Ordovician to Upper Pennsylvanian limestone, dolomite, sandstone, shale, or combinations of these (Evers 1955). Hill prairies are predominantly droughty and excessively drained.

Since Illinois soils and climate support both prairie and forest, certain geomorphic conditions are responsible for the occurrence and maintenance of hill prairies on upper bluff slopes. Location, spatial distribution, and topography, which are primarily a result of regional geomorphic history, combine to create environmental conditions which favor prairie vegetation. The growth of grassland rather than forest can be attributable to successional processes (priority of occupation), as well as harsh environmental conditions (droughty, well-drained, or somewhat excessively drained soils, steepness, exposure to sun and wind). The hill prairie community is the result of complex environmental interactions largely determined by location and topography.