Ohio has three major geographic regions: the Appalachian Plateau in the foothills of the Allegheny Mountains in the eastern half of the state; the Lake Plains along the Erie lakeshore, extending for nearly three-fourths of the northern boundary; and the Central (or Till) Plains in the western half of the state.
The Appalachian Plateau in is made up of rugged hills and steep valleys that become lower as they sweep westward toward the central plains. The highest point in the state is Campbell Hill (1,549ft/472m), located near Bellefontaine. The Erie lakeshore is an area of flat lowland that runs across the state to the Michigan border, and includes sandy beaches. The Central Plains are made up of undulating hills which decrease in height as they reach the Ohio River, which forms the state’s southern boundary with Kentucky and West Virginia. The state’s lowest point (433ft/132m) is in this region, at the confluence of the Miami and Ohio rivers, near Cincinnati.
About two million years ago, glaciers covering two-thirds of the state leveled the western region into plains and deposited fertile limestone topsoil. As the glaciers retreated, the melting ice formed a vast lake, which overflowed southward into the channels that became the Ohio River. Perhaps 15,000 years ago, during the last Ice Age, the glacial waters ran off and reduced Lake Erie to its present size. Limestone rocks in Glacier Grooves State Park on Kelley’s Island bear the marks of the glaciers' movements.
Lake Erie, with an average depth of only 62ft (19m), is the shallowest of the Great Lakes. Its shallowness, combined with the large population, farms, and industrial plants along the lake’s watersheds, caused severe pollution by the mid-20th century. Since then, there have been attempts to clean up the lake. Fish have returned to the lake and recreational activity such as boating and swimming is again popular.
The Maumee, Portage, Sandusky, Cuyahoga, and Grand rivers empty into Lake Erie, while the Muskingum, Hocking, Raccoon, Scioto, Mississippi, Little Miami, and Miami rivers into the Ohio River, which winds for about 450mi (725km) along the eastern and southern borders. Canals and channels run along the entire length of the Ohio River, and along the Muskingum River from Zanesville to Marietta. This means that both these rivers can be navigated easily by ships.
Ohio has around 2,500 lakes, which are located mostly in the east. Most of these are reservoirs created behind river dams. The largest, Pymatuning Reservoir, on the Pennsylvania border, has an area of 14,650ac (5,929ha). Grand Lake (St. Mary’s), located near the western border, covering 12,500ac (5,059ha), is the largest lake completely within Ohio.
Ohio has a generally temperate climate, with cold winters and mild summers. Summer high temperatures rarely reach 100°F (38°C), and winter lows rarely drop below -20°F (-29°C). On a typical July day the temperature will vary from the mid-60s°F (upper 10s°C) to the mid-80s °F (about 30°C), while in January it will vary from a high in the mid-30s °F (about 2°C) to a low of about 20 °F (about −7 °C). Most of the state averages around 40 inches (1,000 mm) of rain each year, including an average yearly snowfall of 28in (700mm). In the northeastern section of the state, however, snowfall averages over 100in (2,500mm) per year. The record low temperature for the state is -39°F (-39°C), set at Milligan on 10 February 1899. The record high is 113°F (45°C), registered near Gallipolis on 21 July 1934.
