Time and water: A lesson in St. Croix River geology

A rock slide in Osceola, Wis. provides an example of the forces which have shaped the region’s creeks, rivers and bluffs.




2 minute read

Cross-posted at the Heritage Initiative, a St. Croix 360 partner.

Cascade Falls, Osceola, WI
Photo by Philip Bock, Osceola Sun

Many participants in the Heritage Initiative have identified the St. Croix River region’s geology as one of its important defining characteristics.

The combination of shallow seas covering the area 500 million years ago, and the glaciers which receded about 14,000 years ago, have crafted a unique region of sandstone and limestone bluffs, all of it shaped by flowing water.

Philip Bock, of the Osceola Sun, was recently inspired by a minor rock slide at Oscela’s Cascade Falls, and talked to Professor Kerry Keen, a geology professor from the University of Wisconsin – River Falls, about what it reveals:

According to geologists, much of the sandstone around Osceola dates back to the Cambrian period, roughly 500 million years ago. At that time, much of the area was covered by shallow seas, Keen said, which deposited sand and sediment that, over millions of years, compressed into the sandstone we see today.

Glaciers during the last ice age, too, shaped the valley and deposited silt and sand that eventually developed into the rock formations in the St. Croix Valley. Rivers, such as the St. Croix, carved through the soft sandstone over thousands of years, creating the valleys.

“All materials have a hardness,” Keen said, explaining that harder rocks take longer to erode. “Cascade Falls is falling over mostly sandstone of various resistances.”

The St. Croix originally flowed at a higher altitude, Keen said, and, as it carved deeper into the bedrock, a falls was likely created on what is now Osceola Creek. Over the last 14,000 years, the falls have been eroding further into the valley — one small rockslide at a time.

Continue reading…

The little rock slide in Osceola was just one small chapter in the long story of how our region’s landscape has been shaped by nature.


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Time and water: A lesson in St. Croix River geology