How a prehistoric catastrophe created the Fox River Valley

In 1837, Swiss geologist Louis Agassiz announced his theory that an ice age had enveloped the Earth’s northern hemisphere, creating the landforms then in existence. His studies were done in his native area, Switzerland’s Jura Mountains, and, oddly enough, he was a friend, classmate, and associate of one of my distant cousins—the Matiles had lived in Switzerland’s Jura Mountain region since the 1300s.

After Agassiz, scientists began to better understand how, after the vast ice sheets melted, modern landforms were created. But until relatively recently, it was thought that geological features like our own Fox River Valley were created over eons as water and wind erosion did their work. Now, however, it’s looking more and more like many river and stream valleys were created in the blink of a geologic eye.

Midwestern waterways have always been mixed blessings, including those here in northern Illinois. While they were barriers to travel for both the Native People that lived here as well as for the pioneers who later displaced them, they were also sources of food and—for the pioneers—water power that ran the mills that were so vital to the region’s growth.

In 1867, the first iron bridge was built across the Fox River at Oswego, replacing the old 1848 timber bridge. A King’s Patent tied-arch (also called a bowstring arch) truss iron bridge, it was built by Oswego Township at a cost of $17,000. (Little White School Museum collection)

Virtually all the region’s early towns were established on some waterway or another. Sometimes those settlements grew where the region’s roads and trails crossed streams, because the pauses in traffic they caused offered an opportunity to serve—or exploit—travelers with inns, stores, blacksmith shops and the like. Many of those crossings also offered sites for the dams that provided water power to run saw mills that produced lumber for homes and other buildings, grist mills that ground flour from grain, carding and filling mills that processed raw wool, and for other useful and necessary activities.

In addition, streams provided relatively clean sources of drinking water (at least for the first settlers, until pollution made them questionable sources at best), as well as sources of food. Before the settlement era, the area’s Native American inhabitants had intensively utilized local streams for food production. It is rare but not unheard-of in Kendall County to find carefully crafted stone plummets ancient fishermen used to weight their nets, along with bone fishing hooks and fishing spearheads. Village sites are invariably on the bank of a creek or the Fox River itself—or on the shorelines of ancient lakes that dried up hundreds or thousands of years ago. In virtually all of those villages are found mussel shells, fish bones, scales, and other evidence that Native People relied on streams to produce important parts of their diets.

Like our pioneer ancestors, however, we tend to pretty much take the landscape, including the geological features of the Fox River Valley, including all its tributary creeks, for granted, as if the landscape has always looked this way. And, certainly for the past several thousand years it has, as it provided a relatively rich natural area where people ranging from paleo Indian hunters and gatherers to modern anglers, canoeists, and kayakers have found food and natural beauty.

Native Americans made extensive use of the Fox River and its tributaries. Fish and a variety of invertebrates were regularly harvested while the river’s floodplain provided rich land where various wild plants could be cultivated.

But like everything else, the current geography of the Fox Valley had a starting point. In our case the familiar lay of our land was created by titanic forces unleashed when the last glacial advance into northern Illinois began to retreat.

Sometime around 19,000 or so years ago, the Lake Michigan Lobe of the Wisconsin Glacier had begun to melt and retreat as the Earth warmed. During the previous tens of thousands of years, glacial advances had covered almost all of northern Illinois except a small iceless island in what eventually became the far northwest corner of our state. Called the Driftless Region, that fragment of northern Illinois and southern Wisconsin is today a scenic area of rocky hills, valleys, and lakes.

Geologists don’t really know what triggered these various ice ages, but the global cooling that caused them resulted in heavy snowfalls far to the north that never completely melted during the summer months. That, in turn, caused the snow cover to build up, its own weight gradually compacting it into ice. As the ice became thicker and thicker—and we’re talking hundreds and thousands of feet here, nothing like a modern Illinois or Michigan winter snowdrift—its own weight began squeezing the lowest regions out like toothpaste from a tube, causing glacial advances.

The Wisconsin Glacier was the last of these advances, and as it slowly advanced, it bulldozed and abraded the landscape right down to the bedrock, then briefly retreating before moving forward again, leaving a variety of glacial landforms behind from kames (irregularly shaped sand, gravel and till hills or mounds that accumulates in a glacial depression) to eskers (long, winding ridges of stratified sand and gravel) to moraines (an accumulation of debris ranging in size from silt-sized glacial flour to large boulders created by glacial action).

During its last advance, the glacier had built a high moraine of gravel, rocks, and ground up organic materials along its leading southern edge. Glaciers act more like a conveyor belt than a bulldozer, with the pressure of the ice above forcing material from under the glacier out under the front, creating the moraine along its foot. And as the giant ice sheet melted and retreated, water filled the area between the foot of the glacier and the moraine. It must have been a spectacular sight as the ice cold water deepened year after year, creating a huge impoundment.

The rampaging Fox River Torrent carved the sandstone bluffs along the Lower Fox River that are enjoyed so much by canoeists.

And then one day, the natural dam gave way, and a catastrophic flood rushed southwestward washing and grinding everything before it. The unprecedented flood may have created a cataract nearly 100 feet high as it crashed along its course, carrying huge boulders and giant chunks of ice with it, gouging and washing its way through the till previous glaciers had laid atop the primordial bedrock.

The end result of this catastrophe was the Fox River Valley we see today, which was created, geologically speaking, in a relatively short period of time by that single astonishingly destructive event geologists have named the Fox River Torrent. From the wide valley in the river’s northern reaches to the narrow stream bound by towering white sandstone bluffs in its southern course, the Fox Valley had been created in virtually a blink of a geologic eye.

This image, from a vintage postcard, shows Starved Rock at it’s summer best. The white sandstone rock, carved by the Kankakee Torrent, soars high above the Illinois River, which washes its base.

Just as the unimaginable force freed by the break in the moraine created the Fox Valley, just to the east, the similar, although much larger, Kankakee Torrent gouged out the modern Illinois River Valley. When the Kankakee Torrent rampaged westerly from the Saginaw Lobe of the Wisconsin ice sheet, the leading wave was some 180 feet high, carving the valley and the river’s main channel, leaving behind the spectacular sandstone bluffs at Starved Rock State Park.

It must have been quite a sight, had anyone been around to see it. WAS there anyone here at the time? Perhaps.

The January 2015 issue of National Geographic Magazine included a fascinating article concerning the latest thinking about the arrival of the first people in North America, and it seems that it’s not impossible that some advance party of paleo hunters following the giant Ice Age mammals they relied on for food might have been on hand to witness either or both of the Fox River or Kankakee torrents. If they were around for those titanic geological events, they would have had ringside seats for some of the most catastrophic episodes of landscape formation in recent geologic history.

 

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