OHOhio Geography

A line across the state where the ice stopped

Draw a line from the Ohio River just west of Cincinnati, northeast past Chillicothe and Zanesville, to the Pennsylvania border near East Liverpool. That line splits Ohio into its two real halves. North and west of it the Laurentide ice sheet ground the country flat and left hundreds of feet of till that weathered into some of the deepest farm soil in the United States. South and east of it the ice never came, and the Allegheny Plateau survives as a tangle of steep hollows, sandstone cliffs and narrow ridges.

The glaciated two thirds became corn, soybeans and factory cities. The unglaciated southeast became coal, timber and hill farms, and it is still the poorer and emptier part of the state.

Campbell Hill, and 1,094 feet of relief in total

The highest ground in Ohio is Campbell Hill at 1,549 feet, inside the city of Bellefontaine. It is not a peak. It is a broad rise on the campus of the Ohio Hi-Point Career Center, a vocational school on the site of Bellefontaine Air Force Station, a Cold War radar post placed there because nothing in the state stood higher.

The lowest point is 455 feet, where the Ohio River leaves the state at the Indiana line in Hamilton County. The 1,094 foot spread between the two is among the smallest of any state, less than the roof height of the Willis Tower. In the unglaciated southeast, though, the gap between a ridge top and the creek below regularly runs 400 to 500 feet, which is why the Blackhand sandstone gorges of the Hocking Hills feel like mountain country in a state with no mountains.

The buried river under the cornfields

Before the ice, the great river of this part of the continent was not the Ohio. It was the Teays, which rose in what is now North Carolina and ran northwest across West Virginia, Ohio and Indiana toward the Mississippi. The advancing ice sheet dammed it. Water backed up into Lake Tight, a glacial lake of roughly 7,000 square miles across southern Ohio, West Virginia and Kentucky, which stood for thousands of years before it overtopped a divide and cut a new outlet. That outlet is the modern Ohio River, which is why it hugs the southern edge of the glaciated country instead of crossing it: the river is tracing the outline of the ice.

The Teays did not disappear, it got buried. Its valley lies under as much as 500 feet of glacial fill, and the sand and gravel in it forms one of the state's most productive aquifers. Towns in western Ohio pump their drinking water out of a river that stopped flowing around two million years ago.

The state that owns none of its own river

Ohio's southern boundary is not the middle of the Ohio River. It is the low water mark on the northern side of the river as that mark stood in 1792, the year Kentucky entered the union carrying Virginia's old claim to the entire channel. Dams have since raised the pool, so the legal state line now sits underwater along long stretches. The Supreme Court confirmed the 1792 mark as the boundary in Ohio v. Kentucky in 1980. Ohio owns not one drop of the river it is named after.

The northern boundary took militia to settle. The Northwest Ordinance and Ohio's 1803 constitution described the Michigan line differently, and the gap left a wedge of 468 square miles, five to eight miles wide, containing the mouth of the Maumee and the future site of Toledo. Both sides sent armed men in 1835. Nobody was killed, and Congress ended it in 1836 by awarding Ohio the strip and giving Michigan the western Upper Peninsula plus statehood as compensation, a swap Michigan regarded at the time as a swindle.

A shallow lake and the swamp that delayed the northwest

Lake Erie averages 62 feet deep, the shallowest of the Great Lakes and consequently the warmest, the most biologically productive, and the only one that regularly freezes across. Ohio's shoreline and islands sit on its shallowest part, the western basin. Kelleys Island holds the largest exposed glacial grooves anywhere, channels up to 400 feet long and 15 feet deep that the ice sheet carved into 400 million year old Devonian limestone.

Behind that shoreline lay the Great Black Swamp, roughly 1,500 square miles of forested wetland on the flat clay floor of glacial Lake Maumee. It was close to impassable, and it kept northwest Ohio empty for decades after the rest of the state had filled in. Ditching and buried clay tile from the 1850s onward drained it into the flattest and richest farmland in Ohio, and that same tile drainage now carries the phosphorus that feeds Lake Erie's summer algal blooms.

Two watersheds, one clock, and a crater

A low divide runs across the northern third of the state. Roughly two thirds of Ohio drains south through the Scioto, Muskingum, Great Miami and Hocking to the Ohio River and the Gulf of Mexico. The northern third drains through the Maumee, Sandusky and Cuyahoga into Lake Erie and leaves by the St. Lawrence. The divide is so subdued that the Miami and Erie Canal crossed it with a feeder reservoir rather than a tunnel.

The whole state keeps Eastern Time while sitting at the zone's western edge, which is why the sun stays up past nine o'clock in Toledo in late June. The temperature records are 113 °F near Gallipolis on 21 July 1934 and,39 °F at Milligan on 10 February 1899.

One last oddity sits in Adams County. The Serpent Mound effigy was built along the rim of a circular structure about five miles across, where the bedrock is shattered and tilted in ways only a violent impact accounts for. It is read as a deeply eroded meteorite crater roughly 300 million years old, the only impact structure exposed at the surface in Ohio.

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