The dry hilltop prairies found within the Severson Dells Forest Preserve can be labeled as Dolomite Prairies. The sedimentary rock known as dolomite occurs at a shallow depth from the surface and hosts a rare and delicate ecosystem. Dolomite has a high magnesium content, which means the soil is alkaline and rich in that mineral. For this reason, dolomite prairies boast a unique species composition with very few trees. The shallow bedrock prevents the prairie soil from draining so the plants in this community are adapted survive in saturated soil in the spring and dry soil in the summer. A 1992 survey found that only 140 acres of this habitat type remain in Illinois.
The dry hilltop prairie habitats are in need of consistent management. Efforts are being made to clear invasive species as well as late-successional species (black cherry, hackberry) from shading the hilltop prairies.