This field guide introduces the complex history and ecology of Illinois' largest natural landscape state park. On its west side, the 8000-acre landscape is bounded by the Illinois River near its confluence with the Mississippi. Protecting one of the state's few unglaciated regions, the resulting rugged topography exposes ancient geology and supports a diversity of forests and prairies. Founded in 1932, using local and state contributions, the park infrastructure was established by the Civilian Conservation Corps. It includes many amenities including a lodge of classic design, cabins, campgrounds, group camps, and equestrian and boating facilities. Its drives and trails invite exploration of a variety of habitats in all seasons. Checklists of organisms cover about 461 species of vascular plants, including 57 species of trees and shrubs. Animal observers have counted nearly 230 species of birds and about 59 species of amphibians and reptiles.

At least 46 species of mammals may be expected to occur in the park. Adding to the guide's utility are color maps, graphs, and 59 color photographs of the park's features.