One of the most common questions asked about Devil’s Lake is, “Did the glaciers make the lake?”
It’s a great question. We all learned about glaciers in school, and we know they covered large parts of Wisconsin. Add in the mammoth imagery on park signs, and it’s easy to assume glaciers carved out the lake itself. The real story, though, is a little more complicated.
Let’s start with the bluffs surrounding the lake, part of the Baraboo Range, often called the Baraboo Hills. These rocks are incredibly ancient, about 1.6 billion years old. They’re older than the Rocky Mountains and even the Himalayas. In fact, they’re so old that you won’t find dinosaur fossils here at all. What we see today is the deeply eroded core of mountains that once stood much higher, worn down and partially buried over immense spans of time.
Long before glaciers arrived, this landscape went through many transformations. At one point, the Baraboo Hills were covered by a shallow inland sea that later receded, leaving behind ripple marks preserved in stone.
You can still see modern ripple marks forming in the shallow sands today along the shoreline of Devil’s Lake. At another point in deep time, parts of central Wisconsin were likely desert-like, shaped by wind and blowing sand.
About 500 million years ago, during another chapter of Earth’s history, the Baraboo Hills formed a chain of islands rising out of a warm, tropical sea. The gorge where Devil’s Lake sits today was then a narrow channel between those islands, roughly aligned with the present-day East and West Bluffs. Powerful storms and large waves battered those shorelines, and evidence of that energy can still be found in rock layers along the East Bluff Trail.
Fast forward to the last ice age, roughly 12,000 years ago. By then, a river flowed through the gorge. When the glaciers advanced into southern Wisconsin, they reached the edge of the Baraboo Hills and stalled. Ice flowed around the bluffs rather than over them, depositing debris at both the north and south ends of the gorge. These deposits, called terminal moraines, acted like natural dams.
Those glacial dams blocked the river, allowing water to collect in the basin between the bluffs. While glaciers played a key role in forming the lake as we know it today, the water in Devil’s Lake is not leftover glacial meltwater. That ancient meltwater is long gone, recycled through Earth’s systems many times over. Today, the lake is fed by rainfall, groundwater springs, and a small stream entering from the southwest end.
The place we call Devil’s Lake has existed in many forms for billions of years. It has traveled across the planet on moving tectonic plates, rested beneath warm tropical seas, and endured multiple ice ages. The Baraboo Hills and Devil’s Lake weren’t created in a single moment, but shaped slowly through countless upheavals. We hope this brief look at the geology behind the lake adds a little depth to what you see when you stand at the water’s edge.
** Credit goes to Charles R. Van Hise, Paul Herr, Ken Lange, Sue Johansen-Mayoleth, Keith Montgomery, Alton Dooley, and a host of other researchers, writers, bloggers, naturalists, and geologists whose concepts I’ve generalized and mangled to create this very short overview of Devil’s Lake State Park geology…
Read On!
- Wisconsin Glaciation – Wikipedia
- The Baraboo Ranges & Devil’s Lake Gorge
- Roadside Geology of Wisconsin – Robert H. Dott, Jr. and John W. Attig
- The Changing Earth – James Monroe, Reed Wicander