In the summer of 1954 the University of Illinois undertook an extensive archaeological village site survey of the Illinois River valley. The Illinois River, more than 250 miles long, is located in the heart of the great Central Plains, an essentially uneroded region of drift covered uplands, with a billowy surface and less than 1000 feet altitude above sea level. The river is the largest, except for the Ohio, draining into the Mississippi from the east. It gathers rainfall from about 25,000 square miles, almost half the total area of the state of Illinois, and flows into the Mississippi about midway between its head and mouth. It is located centrally on a venation of waterways stretching from the foothills of the Rockies to the Appalachians, and from the Great Lakes to the Gulf.