At the end of the Wisconsin glacial period about 8,000 years ago, the continental glacier that covered the Great Lakes region of North Amerca melted suddenly, releasing a torrent of water that followed the route of the present day Kankakee river, but was many miles wide. When the flood waters abated, a huge deposit of outwash sand--gigantic sandbars up to one hundred feet in depth--was left behind on the southern side of the Kankakee valley.
The effect was to create a beach-like environment of rolling sand dunes, similar to the nearby Lake Michigan dunes as well some areas of New Jersey and Nebraska. Over the ensuing millenia, a dry or 'xeric' sand prairie developed on some of the highest elevations of these small dunes. A sand prairie is dominated by perennial grasses, especially little bluestem and forbs such as blazing star, western sunflower, prickly pear cactus and blue lupine.