The Driftless Area

No drift

Drift is everything glaciers deposit: till, outwash, moraine. The Driftless Area of southwestern Wisconsin (and neighboring Minnesota, Iowa, and Illinois) has none from the last ice sheet. “Unquestionably the oldest surfaces in Wisconsin are those in the classical Driftless Area of the southwest,” Black wrote; it “was not invaded by ice of the last two major substages, the older of which covered most of the rest of the state” ¹.

So instead of the lakes, wetlands, and rolling hummocks the ice left elsewhere ², the Driftless Area is a landscape carved by running water over a very long time: flat-topped ridges, steep, deep valleys (coulees), bluffs, springs, and cold, clear trout streams. There are almost no natural lakes.

Black also noted that geologists had long found evidence that earlier ice reached farther west than the last, so “driftless” is about the last glaciations, not all of them ¹.

The edge: the Cross Plains moraine

About 10 miles west of Madison, near Cross Plains, the last ice sheet “ground to a halt on the southwestern Wisconsin uplands, marking the east boundary of the Driftless Area with a young moraine” ¹. Stand on that terminal moraine and the contrast is plain: hummocky glacial ground to the east, deep, smooth-sided valleys to the west. Cross Plains is one of the Ice Age Trail’s reserve units ³.

Devil’s Lake

In the Baraboo Range, Devil’s Lake sits in a steep-walled, L-shaped gorge whose floor lies about 500 feet below the rolling upland near 1,400 feet ¹. The bluffs are ancient Precambrian quartzite.

What holds the lake in is glacial: the gorge is plugged at both its north and southeast ends by end moraine, part of the Johnstown Moraine that traces the front of the Green Bay Lobe ¹. Black called the pair of moraine plugs, with a well-defined end moraine running for miles from them, “certainly one of the few best such features to be found anywhere in the world” ¹. West of the moraine, on the upland, is ground the last ice never reached.

Glacial Lake Wisconsin

During the ice advances into central Wisconsin, a large meltwater lake, Glacial Lake Wisconsin, spread across the center of the state, held in by the ice front. Its flat, sandy bed is the plain of central Wisconsin today ¹.

Rising abruptly from that plain near Camp Douglas are Mill Bluff and its neighbors (Bee, Camels, Round, and others): yellowish Cambrian sandstone buttes, spires, and towers. A geologist calls them stacks: their steep sides were “carved by wave and current action in Glacial Lake Wisconsin, where they stood as isolated islands” ¹. They are outliers of the sandstone upland that continues to the south and southwest ¹. Mill Bluff is also an Ice Age Trail reserve unit ³.

Try it

Drive west from Madison on U.S. 14 past Cross Plains and watch the land change at the moraine. Then visit Devil’s Lake and find both moraine plugs from the trail map, and stop at Mill Bluff State Park on the way north to climb a stack that was once an island.

What to take from this

The Driftless Area of southwestern Wisconsin has no deposits from the last ice and the oldest surfaces in the state: ridges, deep coulees, springs, and almost no natural lakes. The Cross Plains terminal moraine, about 10 miles west of Madison, marks its eastern edge. Devil’s Lake fills an L-shaped quartzite gorge plugged at both ends by end moraine. Mill Bluff and its neighbors are sandstone stacks carved by waves when they were islands in Glacial Lake Wisconsin.