The valleys of the Illinois River (center) and the Mississippi River (west of the Illinois River) are apparent in this near-vertical photograph. Agricultural field patterns dot both river valleys, depicting a recovery from the devastating floods of the spring and summer of 1993. More than 20 000 years ago, this part of the Illinois River was the main course of the Mississippi River. The continental glacier that covered most of Illinois to the east shifted the Mississippi River westward to its present course. North of the rivers’ confluence is hilly, forested Pere Marquette State Park, the largest state park in Illinois.