Big Muddy River Southern Illinois with "loess", fine grained, wind born deposits. At the edge of the floodplain, dunes, called "loess hills", formed. The Pine Hills are loess hills standing several hundred feet above the floodplain. Prior to the construction of Rend Lake, much of the ancient lake bed was swamp: a forested area that was covered by water through most of the winter, and during wet summers. When the Big Muddy flooded, the water covered the flat bottom of the ancient lake bed for miles either direction from the meandering channel. The upper reaches of the Big Muddy are near Dix, Illinois.
Little Wabash River counties, about southeast of New Haven. In its upper course in Shelby County, the river is dammed to form Lake Mattoon and collects the short West Branch Little Wabash River, which flows for its entire length in Shelby County. Other tributaries include the Fox River, which joins it in Edwards County; the Elm River, which joins it in Wayne County; and the Skillet Fork, which joins it in White County. Little Wabash River The Little Wabash River is a tributary of the Wabash River in east-central and southeastern Illinois in the United States. Via the Wabash and Ohio rivers, it