Here the landscape consists of level to rolling uplands interspersed with deeply cut rivers and ravines with well-developed floodplains. It is a land of deep, forested ravines with intervening flat prairie openings. The area was covered by Illinoian age glaciers. Bedrock outcroppings are common in some locations. This division has two sections—Galesburg and Carlinville—separated by the Illinois River valley.
The Galesburg Section is north of the Illinois River valley; both the Spoon and La Moine rivers drain this area. The amount of prairie here once almost equaled the amount of forest. One interesting habitat type is the dry-mesic barren, also known as an oak opening. In the spring at Argyle Hollow Barrens Nature Preserve look for the very unusual bi-colored bird’s foot violets growing among the mounds of lichens and mosses.
The Carlinville Section is southeast of the Illinois River valley. Macoupin Creek and the Illinois River are the major streams that drain this section. The original vegetation of this section was forest, with only 12% of the area in prairie. Very little prairie or forest remains today in this section.
To experience this area, visit Siloam Springs and Arglye Lake State Parks.