Mel Reusche, WGNHS Communications and outreach specialist
Devil’s Lake State Park is one of many geologic marvels dotted around the oval-shaped footprint of the Baraboo Range that are explored by millions of visitors each year. The Range stretches west from Portage more than 40 miles, a stubborn island of purple quartzite bordered by the Wisconsin River. This region is adorned with gems of natural beauty and recreation: Devils Lake, Parfrey’s Glen, Ableman’s Gorge, Van Hise Rock, Point of Rocks, and two downhill ski resorts.
Released this month, Geology of the Baraboo Hills, Sauk and Columbia Counties, Wisconsin (link) includes a geologic map of this popular destination and adds to the rich history of geoscience research in this region decoding the last 1.7 billion years of Earth’s history.
“Generations of geologists in Wisconsin and the surrounding region have been educated by studying the well-trodden outcrops in Devil’s Lake State Park, Rock Springs, and surrounding areas.” says UW-Milwaukee Professor and structural geologist Dyanna Czeck. “You would think that with so many eyes on these rocks for more than a hundred years, we would know all there is to know. Not so! This new scientific bulletin and map provide critical information about the middle of the continent.”
WGNHS geologists Eric Stewart, Esther Stewart, and Billy Fitzpatrick along with several collaborators have been creating an updated map of the Baraboo Hills since 2015. Over the last decade, the authors have gathered new data from the field and the lab to answer ongoing questions about the geological history of this well-known area. As a result, this publication showcases the range in geologic time visible in the Baraboo Hills, from rocks that are over 1.7 billion years old, to sand and gravel deposited during the last ice age only 24,000 years ago.
Before the ice ages, before the Age of Dinosaurs, before the sandy beaches and coral reefs of the Paleozoic Era came the first few billion years of Wisconsin’s geologic history. These early years contain dramatic stories of volcanoes, shifting continents, and even microbial life. In this earliest eon, the Baraboo Quartzite began as sand on an ancient beach, which had eroded from volcanoes towering above what is now Sauk County. This sand solidified into sandstone, which was then squished and squeezed deep underground until the grains of sand fused together to create a new rock—quartzite—that preserved the sandy environment in stone.
WGNHS geologists have studied the sandstone features preserved in the Baraboo Quartzite to characterize distinct units within the rock that are now traced around the region in the new geologic map. Importantly, the new mapping allows the authors to better identify faults: places where the rocks have shifted so the original layers are displaced. They could reconstruct how these rock layers have been folded and faulted through time by adding these faults to the map. Dr. Dyanna Czeck: “By incorporating new detailed mapping of the internal Baraboo Quartzite stratigraphy and new structural data, this work expands our knowledge of the deposition and tectonic deformation of the Baraboo Quartzite. This contribution comes at a perfect time. Geologists are revising the Proterozoic tectonic history of North America.”
All this faulting and folding created towering, tough quartzite hills and cliffs that stood high above the landscape over a billion years ago. Since then, they have been islands in ancient seas, then buried in sediment and then uncovered again. Finally, during the last ice age the edge of the ice sheet nestled into the hills, leaving behind sediment from meltwater streams, glacial lakes, and the ice itself. Sediments from the edge of the ice plugged up the valley that now contains Devils Lake.
This map captures several extraordinary geologic stories from deep in Wisconsin’s past. Learning about this history can expand our perspective of time and space as we find our own way through this unique landscape. “It was very rewarding,” says Eric Stewart, “to work in such a fantastic area that serves as an outdoor classroom for geology students and the public.”
Explore the map today! Visit the project webpage (link) to learn more and download the map for free.
Visualizing rock deformation
More information
For more details, contact one of the following WGNHS geologists:
- Eric Stewart, eric.stewart@wisc.edu
- Esther Stewart, esther.stewart@wisc.edu
- Billy Fitzpatrick, william.fitzpatrick@wisc.edu