Natural History & Geology

The Openlands Lakeshore Preserve, at Fort Sheridan, Illinois, lies on part of the Highland Park moraine, which formed as the final glacier retreated from northern Illinois about 10,000 years ago. Geologists characterize Fort Sheridan as being within the Lake Border Moraines Bluff Coast, a hilly area that extends from the town of North Chicago at the north end to Winnetka at the south, where the land flattens out again and remains relatively even through Wilmette, Evanston, and on into Chicago.

The glacial action resulted in a pleasing topography in this area, characterized by steep ravines and high bluffs along the lakefront. Part of the attractiveness of the North Shore suburbs comes from the relief provided by the hills and valleys, all products of geological forces. “Ravines are among the Bluff Coast’s most characteristic features,” writes geologist Raymond Wiggers in Geology Underfoot in Illinois. “Their precipitous gullies have been carved by youthful streams that are doing their best to cut through the high ground.”

According to Wiggers, more than thirty such ravines are located along the Illinois lakeshore—six within Fort Sheridan. The three main ravines at the Openlands Lakeshore Preserve are named Bartlett, Van Horne, and Schenck.

Because lake bluff terrain was unusual in Illinois, so were the natural communities that developed there—the land was forested with oaks on the ridges and sugar maples and basswood in the ravines. “[The ravines] cut the bluff perpendicular to the lake and provide a microclimate suitable for certain northern plants not otherwise found here,” writes Joel Greenberg in A Natural History of the Chicago Region. Paper birch and juniper are among the plants found at Fort Sheridan that tend to be more typical of Wisconsin and northern Michigan.