Ohio covers 116,096 sq km (44,825 sq mi), including 979 sq km (378 sq mi) of inland water and 9,062 sq km (3,499 sq mi) of Lake Erie. It is the 34th largest state of the United States. The extreme dimensions of Ohio are 360 km (225 mi) east to west and 345 km (215 mi) north to south. The approximate mean elevation is 260 m (850 ft). Ohio includes parts of three major natural regions, or physiographic provinces, of the United States: the Appalachian Plateaus, the Interior Low Plateau, and the Central Lowland. Most of western Ohio has flat to rolling lands typical of the Central Lowland, while eastern Ohio is composed of much hillier glaciated and unglaciated land of the Appalachian Plateaus. Only a very small area, in the southwest, is in the Interior Low Plateau.
The Central Lowland in Ohio is composed of two sections: the Lake Plain section and the Till Plains. Most of the area is flat or gently rolling, with some rougher terrain between the major rivers and in the divide between the Great Lakes and Ohio River drainage systems. The flatness of the land is a result of several glacial advances and retreats that occurred during the Ice Age, which ended about 10,000 years ago.The Lake Plain section, along Lake Erie, varies in width from about 8 to 16 km (about 5 to 10 mi) in northeastern Ohio and from about 100 to 115 km (about 60 to 70 mi) in the northwest. The land is very flat, with slight elevation on old beach ridges, but most of it is the old bottomland of a much larger Lake Erie formed by the blocking of its outlet by glacial ice. Marshes and swamps are prevalent in undrained areas.
The Till Plains in west-central Ohio offer a greater variety of landscape than the Lake Plain. Broad valleys and rolling divides occur between the rivers. This section is covered with glacial material composed mainly of fine clay, sands, and gravels.
This material, called glacial drift, was deposited very unevenly so that in some places it is only 60 cm (24 in) deep and in others it is more than 30 m (100 ft) deep. This deposition softened the relief of the area compared to its preglacial landscape. While the valleys and their subsequent divides run north-south, a series of low east-west ridges of glacial drift, called moraines, crosses them. The moraines, seldom more than 30 m (100 ft) above the surrounding landscape, vary in width. Near the northern edge of the Till Plains is Campbell Hill, the highest point in Ohio, with an elevation of 472 m (1,549 ft). The Appalachian Plateaus, which cover the eastern part of the state, are subdivided into the glaciated Allegheny Plateau and the unglaciated Allegheny Plateau.
The landscape of the glacial plateau has been softened by repeated glacial activity, while the unglaciated plateau is hilly.
In the hilly unglaciated section there are level floodplains along the major streams, but tributary streams occupy narrow V-shaped valleys. The tops of the hills have very little flat land and most of the area slopes. The hills, increasing in elevation to the east, rise 90 to 180 m (300 to 600 ft) above the adjacent valleys. In the glaciated Allegheny Plateau the valleys are broader than those in the unglaciated section, and they are filled with glacial material. The Interior Low Plateau is found in a very small triangular area of southern Ohio. The glaciers moved through this area early, and by now much of the glacial drift has been removed. The topography is rolling and has an elevation of 270 to 300 m (900 to 1,000 ft) above sea level. The lowest point, 139 m (455 ft), lies at the Ohio-Indiana border on the Ohio River. "Ohio" © Emmanuel BUCHOT, Encarta, Wikipedia
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