The Drift less Area of northwestern Illinois, which includes nearly all of Jo Davicss County and small areas of Stephenson and Carroll counties, is equaled in ruggedness of topography only by the Ozarks of the southern part of the state. The land surface presents a mature topography. Slopes of con siderable steepness occur throughout the unglaciated region. Galena, Apple, and Plum rivers are the principal streams of Jo Daviess and Carroll counties. Galena is the principal city. Lead and zinc mining is carried on in the Driftless Area.
In Whiteside County, and in Rock Island County to the mouth of Rock River, the Rock River Basin approaches very near to the Mississippi bluffs. Fulton, East Moline, Moline, and Rock Island are located on small upland areas with lower lands on all sides. Edwards River, Pope Creek, and Hender son River, which enter the Mississippi in Mercer and Henderson counties, are the longest streams of the minor basins of the Mississippi. Edwards River drains land more than 50 miles from the Mississippi.
Hamilton, in Hancock County, is at the Illinois end of the great Keokuk darn. Warsaw is located on the Mississippi a few miles below Hamilton. Quincy, for many years the largest city of Illinois on the Mississippi, has recently been outstripped by East St. Louis.
The unglaciated region of Pike and Calhoun counties forms a narrow, rugged, elevated ridge which separates the Missis sippi and Illinois rivers. This line of upheaval extends east of the Illinois through southern Jersey County into Madison County.
A narrow limestone ridge extends from St. Clair County through Monroe and Randolph counties to Jackson County, where it joins the main ridge of the Illinois Ozarks. This ridge is from 5 to 10 miles wide and stands 100 to 200 feet above the level plains of the Kaskaskia and Big Muddy basins. The region has numerous caves. The surface is thickly dotted with sink holes characteristic of limestone regions with under ground drainage. This long, narrow ridge is broken only at two places where the Kaskaskia and Big Muddy flow across it in water gaps less than 2 miles in width. As the traveler journeys southward from East St. Louis on the St. Louis, Iron Mountain, and Southern Railroad, he may observe this precipitous ridge which rises to the cast as an object of beauty and grandeur. The river gaps arc also clearly noticeable.
The term "American Bottoms" is applied to that part of the Mississippi flood plain in Illinois extending southward from the bluffs at Alton. It is commonly applied to the exception ally wide portion extending from Alton to Prairie du Pont Creek in St. Clair County. In this region the average width is about 7 miles. The name is also applied to all the Mississippi flood plain in Illinois from Alton to Cairo at the mouth of the Ohio. On this broad valley floor in Madison and St. Clair counties are Granite City, Madison, Venice, and East St. Louis. This populous district is protected by an elaborate system of levees.
The flood plain of the Mississippi is noted in the pioneer history of Illinois. Cahokia, one of the first permanent settlements, now a small village, is located about 4 miles south of East St. Louis. Old Fort Chartres, now a state park, is in northwestern Randolph County near Prairie du Rochcr. Old Kaskaskia, the first permanent settlement in Illinois, and once the metropolis of the Mississippi Valley, occupied a site which now lies in the bed of the present main channel of the Mississippi River.
Wabash River Basin.—The Wabash River rises in the western part of Ohio, flows west and southwest across Indiana, and from a point 15 miles below Terre Haute, Indiana, to its junction with the Ohio River, forms the Illinois-Indiana boundary line. Of the 33,000 square miles of the Wabash River Basin, 8,770 square miles are in Illinois. There are several important Illinois tributaries. The Vermilion, on which Dan ville is located, flows across a portion of Indiana to reach the Wabash. The Embarras is one of a group of streams which have their sources in the vicinity of Champaign and Urbana, and radiate in various directions to widely separated regions of the state. The Embarras flows southward through Cham paign, Douglas, Coles, Cumberland, and Jasper counties, then southeastward, touching Richland County and crossing Crawford and Lawrence counties. Along its course are Newton and Lawrenceville; within its basin are Tuscola, Charleston, and Bridgeport. Bonpas Creek enters the Wabash at Grayville.