Chicago Portage

The Chicago Portage is a water gap, and in the past, it was sometimes a wind-gap portage, connecting the Mississippi River and the Great Lakes. 
The Chicago Portage cuts through the Valparaiso Moraine, crossing the Saint Lawrence River Divide. The saddle point of the gap is within the city of Chicago, and the Chicago Portage is a reason Chicago exists and has developed to become very important city that it is.
The official flag of the city of Chicago includes four red stars which represents city history, separating two blue stripes symbolizing the waters that meet at the city.