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.
Muddy, Illinois Muddy, Illinois Muddy is a small incorporated village located in the Harrisburg Township in Saline County, Illinois, United States. The population was 78 at the 2000 census. During the 19th century, the site of Muddy was home to a small settlement known as Robinson's Ford, which was among the communities considered for the seat of Saline County after the county's creation in the 1840s. The modern village of Muddy had its start as a mining settlement established by the Harrisburg Big Muddy Coal Company, for which it was named, in 1903. The mine was sold to the larger O'Gara Coal