The Valparaiso moraine to the south of the Chicago Outlet is drained on its inner border by short streams tributary to the Little Calumet River. Valparaiso and Laporte, Indiana, are in the Kankakee Basin, while Chicago Heights, Illinois, Ham mond, Gary, and Michigan City, Indiana, are in the Lake Michigan Basin.
Rock River Riverrises in Fond du Lac County, about 20 miles south of Oshkosh, Wisconsin. It flows south westward and empties into the Mississippi 6 miles below Rock island, Illinois. The length of the river is 285 miles, and the length of the basin 175 miles. The total area of the basin, 10,S00 square miles, is almost equally divided between Wiscon sin and Illinois, The stream has an elevation of 1,000 feet at its source and 540 feet at its mouth. The width of the basin on the state line is 75 miles, about one-half the width of the state along the northern boundary. The basin lies mainly in the Iowan and pre-Iowan glacial deposits.
The Pecatonica River flows through Freeport and joins the Rock River at the village of Rockton, near the state line. Kishwaukee Creek, on which Belvidere is located, is an eastern tributary which joins the Rock a few miles below Rockford.
Green River, the most important tributary of the Rock, flows from DeKalb County to Rock Island County, and drains the southern portion of the Rock River Basin in Illinois.
The course of Rock River has determined the location of several important cities. On its banks are found Janesville and Beloit in Wisconsin; Rockford, the fifth city of Illinois in population; and the smaller but important cities of Oregon, Dixon, Sterling, and Rock Falls. Rock Island and Moline are large cities on the Mississippi just above the mouth of Rock River.
Glaciation produced profound changes in preglacial drain age. Rock River Basin furnishes evidence of great changes in drainage lines. From Janesville, Wisconsin, to the mouth of Kishwaukee Creek, Rock River flows in a broad preglacial valley which continues southward, joining the Illinois Valley at Great Bend near Hennepin. Rock River, however, turns southwestward at the junction of Kishwaukee Creek and flows through a narrow post-glacial valley to Sterling, where it enters the broad plains occupied also by Green River. In
its course from Kishwaukee Creek to Sterling the river has cut across stretches of solid rock and thereby produced much picturesque scenery.
Between Rock River and the Driftless Area of Jo Daviess County, the glacial drift is so thin that many small streams have deepened their valleys into the underlying bedrock, carving out numerous rock gorges. The greater part of the basin consists of undulating prairie lands with woodlands along the streams. Few of the hilltops arc more than 100 feet above the intervening valleys.
The moraines of the Iowan glaciation are low and incon spicuous in the general surface, but a more rugged morainic topography occurs where the Rock River Basin occupies the outer margins of the Valparaiso and Bloomington moraines of the Wisconsin glaciation. A number of eskers are found in the Rock River Basin. The largest and best-defined is the Leaf River or Adeline esker in northern Ogle County. It is found in the valley of Leaf River, a western tributary of the Rock, and the village of Adeline is located on the esker near its eastern end. This esker is 12 miles in length; from 100 to 1,000 feet wide; and it rises from 20 feet to 100 feet above the level land on either side. The Hazelhurst esker is on the border between Ogle and Carroll counties. The Garden Plain esker is in Whiteside County, and numerous esker-like ridges are found in Stephenson County.
The flat land of the basin is found along the lower course of Rock River and in most of the Green River Basin. These flat lands were originally extensive swamps which have been largely reclaimed by expensive drainage systems.
Illinois River Illinois River is the most impor tant tributary of the Mississippi above the Missouri, and the Ohio is the only eastern tributary of greater importance. The Illinois River lies wholly within the state, but the Des Plaines and Kankakee rivers which unite at the eastern edge of Grundy County to form the Illinois have their sources in Wisconsin and Indiana respectively.