Summer 1999

Preserve features wetland wildlife — tiger salamander, chorus frogs and spring peepers

Cook County, Illinois

Cranberry Slough, named for its unique peat bog community populated by cranberry and other plant survivors from post-glacial times, was dedicated as the fifth nature preserve of Illinois in January, 1965. Secluded in southwestern Cook County, its 372 acres are nestled within the larger 14,000-acre Palos Preserves, which are laced together by 35 miles of meandering multi-use trails made of packed earth and crushed limestone.

When the Wisconsin glacier retreated north 12,000 years ago, it fragmented and sloughed off big blocks of ice, some as large as barns or even stadiums, mixed with the detritus of the Valparaiso and Tinley Moraines. Where these gigantic ice cubes slowly melted, they transformed the land into peat bogs, potholes, and swamps with little, if any, outlet for water. As glacial detritus deposited around these ice blocks, the hilly, rolling topography of the Valparaiso Moraine was formed.

During the Great Depression of the 1930s, the Forest Preserve District, in conjunction with the Civilian Conservation Corps and other work-relief forces, artificially blocked and dammed many of these glacially created wetlands to create the Palos Preserve's current lakes, ponds, and sloughs. European settlers coming to this area saw a rich mosaic of oak savanna and prairie. Now, young upland forests and remnants of degraded prairie can be found on its steep slopes. And its kettle hole conditions — the remnant glacial wetlands — support vernal pond, marsh, and sedge meadow communities. Here, visitors can observe herons, egrets, ducks, gulls, pied-billed grebes, common gallinules, and swallows, as well as beaver, tiger salamanders, chorus frogs, spring peepers, and other wetland wildlife. Birders will find this an especially rewarding site for spring and fall migratory sightings.

Observant visitors can detect the signs of glacial and post-glacial forces at work here. This area was once part of the Mount Forest Island, one of the first dry areas where plants could colonize when the water level of ancient Lake Chicago fell and left these wetlands puddled within the freshly exposed rolling landscape. On the higher ground, which tends to be more dry, hikers can enjoy solitary walks through the savanna, prairie, and oak-hickory woodlands that surround Cranberry Slough.

Wetland enthusiasts can visit a slew of other sloughs nearby: Hidden Pond Slough, Belly Deep Slough, Pollywog Slough, Hogwash Slough, and Katydid Slough, among others. For further information contact the Forest Preserve District of Cook County at: (708) 366-9420.

— Eugene Bender