A catastrophic flood known as the Kankakee Torrent,[REF] which took place somewhere between 14,000[REF] and 17,000 years ago,[REF] before humans occupied the area, helped create the park's signature geology and features, which are very unusual for the central plains.
The park is on the south bank of the Illinois River, a major tributary of the Mississippi River, between the Fox and Vermilion Rivers.