Big Muddy River The Big Muddy was not covered by the Wisconsin Glacier, about 70,000 to 10,000 years before present. However, during the melting of that glacier, the level of the Mississippi River was much higher. Water backed up into the Big Muddy Basin, forming a lake much like the artificial Rend Lake but covering a larger area. The ancient lake silted in, forming a flat bottom. After the melting of the Wisconsinan glacier, the level of the Mississippi dropped, allowing the lake to drain. A new channel formed within the old lake bed. This channel meandered in the flat bottom of the
Muddy River (Nevada) to the Colorado River and followed it westward. In 1844, the expedition of John C. Frémont discovered a cutoff route that avoided the Colorado River, following a route between Resting Springs in California, and the Virgin River Valley that passed through Las Vegas Springs and crossed the Muddy River near modern Glendale. Mormon pioneers blazed a wagon road from Salt Lake City to Los Angeles along this pack trail in 1847, followed by Forty-niners attempting avoid the winter snows of the Sierra Nevada Mountains, and wagon trains of Mormon colonists on their way to settle in San Bernardino in 1852.