WIWisconsin Geography

The last ice sheet covered nearly all of Wisconsin and then went around one corner of it. The southwest, across Grant, Crawford, Vernon, Richland and their neighbours, was never overridden, and it is called the Driftless Area because it carries no glacial drift. About 24,000 square miles of driftless country spill into Minnesota, Iowa and Illinois, and Wisconsin holds the largest share. It looks nothing like the rest of the upper Midwest: sharp ridges, deep valleys with springs and trout in them, sandstone bluffs above the Mississippi, and almost no natural lakes.

The most recent ice age is named after this state

Geologists everywhere call the latest North American glaciation the Wisconsin Glaciation. The name stuck because Thomas Chamberlin worked out the sequence of moraines here in the 1870s and 1880s, and the evidence was easier to read on this ground than anywhere else.

Lobes of ice pressed in from several directions, and where two of them ground against each other they piled debris into a ridge instead of spreading it flat. That ridge is the Kettle Moraine, an interlobate moraine running roughly 120 miles from Walworth County northeast toward Kewaunee County, littered with kames, eskers and the steep-sided pits that gave it its name, each one the hole left by a stranded block of ice. The Ice Age National Scenic Trail follows the terminal moraine for about 1,200 miles across the state and exists for the sole reason that the ice stopped along that line.

Between two Great Lakes and one great river

Wisconsin touches Lake Superior in the north and Lake Michigan in the east, one of the few states on two Great Lakes. The Mississippi makes the western border with Iowa and the lower half of Minnesota. Above Prescott the St. Croix takes over, one of the eight rivers named in the original Wild and Scenic Rivers Act of 1968.

In the east the Door Peninsula reaches about 70 miles northeast into Lake Michigan and walls Green Bay off from the open lake. The strait at its tip is Porte des Morts, Death's Door, named for what happened to sailing ships in it, and Door County counts eleven lighthouses, more than any other county in the United States. Off the north shore, the 21 Apostle Islands in Lake Superior are sandstone with wave-cut sea caves that freeze into ice caves in a cold enough winter.

None of these lines came easily. Wisconsin Territory once included what is now Michigan's Upper Peninsula and lost it in 1836. Congress had already pushed the northern edge of Illinois about 61 miles above the bottom of Lake Michigan in 1818, which is the reason Chicago is an Illinois city. The water boundary with Michigan out in Lake Michigan stayed unsettled until the Supreme Court fixed it in 1926.

A mile and a half of portage that decided a continent

North of Madison the land divides between two of the world's larger drainage systems. The Fox River runs northeast into Green Bay, Lake Michigan and eventually the St. Lawrence. The Wisconsin River runs south and west into the Mississippi and the Gulf of Mexico. At Portage the two come within about a mile and a half of each other across flat marsh, and for two centuries that gap was the shortest carry between the Great Lakes and the Mississippi basin. Marquette and Jolliet used it in 1673. The city standing there is named after the act of picking up a canoe.

A vertical range of 1,372 feet

Timms Hill in Price County tops out at 1,951 feet, and the Lake Michigan shoreline at 579 feet is the floor. The entire state fits inside 1,372 feet of relief, which is less than the depth of a single West Virginia gorge.

The interesting rock here is old rather than tall. The Baraboo Range south of Wisconsin Dells is quartzite roughly 1.6 billion years old, once a genuine mountain range, worn down, buried under Cambrian beach sand, and dug out again by later erosion. Devil's Lake fills a gorge through it that glaciers plugged at both ends, leaving a lake with no inlet and no outlet under purple cliffs about 500 feet high.

The Dells were cut in a hurry. Glacial Lake Wisconsin, held back by an ice dam, drained catastrophically around 14,000 years ago and the escaping water sliced a narrow gorge through soft Cambrian sandstone that the river has been widening ever since.

Fifteen thousand lakes and a record from 1936

Wisconsin counts roughly 15,000 inland lakes. The densest cluster sits on the Northern Highland in Vilas and Oneida counties, where meltwater outwash sand is pitted with water-filled hollows. Lake Winnebago, about 137,700 acres, is the largest lake wholly inside the state and shallow for its size, which is why it freezes hard enough every February for the sturgeon spearing season.

The record high is 114 degrees at Wisconsin Dells on July 13, 1936. The record low is 55 below zero at Couderay in Sawyer County, reached on February 2 and again on February 4, 1996. Lake Michigan holds the eastern shore back in spring, so Milwaukee stays cool for weeks after Madison, 80 miles inland, has warmed up. All of Wisconsin keeps Central Time.

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