THE TOPOCKAl'IIY AND HYDROGRAPHY OF ILLINOIS JlX 



immediate bluffs stand at the general level of the bordering 

 uplands. 



Big Muddy River System 



Big Muddy River system drains an area of 2,390 square 

 miles lying in an elliptical shape, with a major axis about 70 

 miles long running almost north and south, and a minor axis 

 about 50 miles long. This drainage basin includes the greater 

 part of Williamson, Franklin, Jefferson, Perry, and Jackson 

 counties, the southeastern portion of Washington county, and 

 the southern part of Marion county, which forms the extreme 

 southwestern part of the district covered by the Illinoisan drift 

 sheet, lying in the low section just north of the Ozark ridge. 

 The lower 20 miles of the river flows through the Mississippi 

 bottoms. With the exception of the ridge on the southern bor- 

 der, which stands 600 to 800 feet above tide, the basin has few 

 points rising above 550 feet, the average level being 400 to 500 

 feet. The immediate borders of the main valley fall below 400 

 feet and the mouth of the stream at low water in the Mississippi 

 is but 320 feet. The country is made up of gray prairies inter- 

 sected by rivers whose bottom-lands are below the general level. 

 These rivers are skirted by timber belts, so that a large portion 

 of the basin is wooded. The bottom-lands also were formerly 

 timbered, but parts have been cleared and put under cultiva- 

 tion. Over the greater portion of the area the drift is very thin, 

 and rock divides separating the preglacial drainage areas are 

 plainly discernible. The basin of the Big Muddy has been 

 subject to long erosion, and consequently the soils are largely 

 made of clays containing little humus and giving acid reactions. 



Big Muddy River has the characteristics of an old stream, 

 in a land long exposed to erosion. It has cut its bed down to 

 drainage level, and it runs its crooked course over a broad flood- 

 plain. It rises in northern Jefferson county, and flows south 

 and then west and south, emptjdng into the Mississippi about 5 

 miles below Grand Tower, Jackson county. It is about 94 

 miles long. Beaucoup creek enters from the north 25 to 30 

 miles from the mouth, and Little Muddy River enters from the 

 same side about 10 miles farther up. These two streams together 

 drain about the same area as the main stream above the junction, 

 and Beaucoup creek drains about one half more area than the 

 Little Muddy. An eastern tributary, Crab Orchard creek, drains 

 about 250 square miles of the district bordering the Ozark ridge. 



