INDIANA, thirty-seventh in size of the forty-eight States, is almost an exact parallelogram in shape, bounded on the north by Michigan, on the east by Ohio, on the south by Kentucky, and on the west by Illinois. The entire southern boundary is formed by the Ohio River, and the Wabash becomes the western boundary just south of Terre Haute. Except for these irregular river courses and the arc of Lake Michigan shore that forms part of its northwestern border, the boundary lines are straight. The length of the State from north to south is approximately 265 miles; its breadth is 160 miles. Of the total area of 36,354 square miles, 309 square miles are water surface -exclusive of that portion of Lake Michigan over which Indiana has jurisdiction. This lake area, defined by extensions of the west and north boundary lines, fills out the northwest corner of the rectangle.
Indiana lies in the heart of the east central section of the United States. The parallel of latitude approximately halfway between its northern and southern extremities passes through Indianapolis; and the north-south line bisecting the eastern half of the Nation passes just east of that city.
About two-thirds of Indiana is prevailingly level or rolling, while a smaller portion, largely in the south, is hilly. The average altitude is 700 feet above sea level. The greatest height, 1,285 feet, is in Randolph County, near the eastern border; the lowest point, 313 feet, is in Vanderburgh County on the Ohio River.
The State is divided into three great regions: the northern lake country; the central agricultural plain; and the more varied southern section, containing both hills and lowlands. The boundary of the northern region is the upper Wabash, which flows southwestward across the State to Terre Haute. This northern area consists of low plains, little modified by stream action and broken by marshes and many lakes. The northeastern section, in particular, has hundreds of small bodies of water, and is characterized by low morainal hills left by retreating glaciers. Farther west, in Kosciusko County, lies Lake Wawasee, the largest lake in Indiana.
Within the lake country rises the almost imperceptible watershed separating the systems of the St. Lawrence and the Mississippi. Across the marshy area in the northwest flow the Kankakee and Iroquois Rivers, to empty into the Illinois. The Tippecanoe, long and meandering, empties into the Wabash near LaFayette; Eel River rises north of Fort Wayne and reaches the Wabash at Logansport. But the tiny tributaries of these Mississippi-seeking streams have their sources often only a few hundred feet from those that flow ultimately into the St. Lawrence. The St. Joseph of Michigan dips across northern Indiana through South Bend, flowing northward again into the lake and draining a considerable area. The St. Mary's rises in Ohio and flows northwest to Fort Wayne, there uniting with another stream, also called the St. Joseph, to form the Maumee, which flows northeastward into the St. Lawrence system. Thus, intricately winding between the sources of tiny streamlets, the watershed runs through Adams and Allen Counties, curves around Fort Wayne, passes northwest through the lake country, and skirts Lake Michigan. Only a faint ground swell in a marshy plain, it divides two great river systems, the Mississippi and St. Lawrence. In northwestern Indiana, where Lake Michigan cuts into the corner of the State, is the famous dunes region.
The central portion of Indiana is a great till plain, which owes its remarkable levelness to deep glacial deposits of soil and gravel. Next to the Wabash the most important stream is White River, the west fork of which has its source in Randolph County and wanders sluggishly southwestward across the State to reach the Wabash in Gibson County. Other important tributaries of the Wabash are the Mississinewa and the Salamonie, flowing northward through the upper part of the plain. In eastern Indiana the twin forks of the Whitewater meet and flow southward into the Ohio. In the southernmost part of this region some stream erosion has taken place and there is more topographical variety.
The southern third of Indiana consists of an east-to-west succession of seven lowlands and uplands, bounded sometimes by steep escarpments of outcropping rocks. The first three of these divisions are usually (except in highly technical descriptions) grouped together as southeastern Indiana; the next three form south central Indiana (the unglaciated, or 'driftless,' area); while the seventh is known as southwestern Indiana, or the Wabash lowland. Topographically the most interesting division is south central Indiana, which is decidedly rugged and drained by scores of little rivers meandering toward the Ohio. The Crawford Upland in this area is the most beautiful and the most inaccessible part of the State; stretching from Parke and Putnam Counties to the Ohio, it contains hills, sharp ridges, and rounded knolls, valleys and wall-like bluffs, canyon-like gorges, natural bridges, caves and waterfalls. Its best-known formations are the Wyandotte and Marengo caves in eastern Crawford County, and 'Jug Rock' and 'The Pinnacle,' remarkable pillars of rock near Shoals in Martin County. In marked contrast to this region the Wabash lowland is an alluvial plain through which the Wabash, fed now by hundreds of lesser streams, moves majestically toward the Ohio.