The coast of Lake Michigan, stretching from North Chicago to Winnetka, is referred to as a bluff coast. The bluffs are part of the Lake Border Morainic System formed by sand, silt, and clay carried in the glaciers. As the Wisconsin Episode’s glacial ice retreated 14,000 years ago, it paused in this area, allowing this sediment to accumulate at its margin, forming the moraines we see today. Deep ravines with intermittent streams cut through the wooded bluffs. Historically, bluff erosion provided sediment for the beaches, but measures have been undertaken to reduce bluff erosion.
Where the lake intersects the moraine, there are bluffs, some up to 90 feet high. As you head south along the shore, the elevation drops and you enter the Chicago Lake Plain, an area that was the floor of Glacial Lake Chicago at the end of the last ice age.
