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 River (Nevada) abandoned the area in 1871. Many of the LDS people returned to the area in the 1880s and it currently has a substantial Mormon population. Muddy River (Nevada) The Muddy River, formerly known as the Moapa River, is a short river located in Clark County, in southern Nevada, United States. It is in the Mojave Desert, approximately north of Las Vegas. The Muddy River is approximately long. It begins as a series of thermal springs in the Moapa Valley before continuing on its course to Lake Mead, where it drains into the northern arm of the lake near Overton, Nevada.