St. Croix River (Wisconsin–Minnesota) (Wikipedia)

About 500 million years ago, a shallow sea covered the area, laying down layers of sand and minerals that make up much of the sandstone bluffs now seen along the river.
The presence of older glacial deposits within the St. Croix River basin proves that the Laurentide Ice Sheet has repeatedly glaciated this region during the Pleistocene Epoch.
St. Croix Boom Site (Wikipedia) The St. Croix Boom Site is a historic and scenic wayside on the St. Croix River in Stillwater Township, Minnesota, United States. It commemorates the location of a critical log boom where, from 1856 to 1914, timber from upriver was sorted and stored before being dispatched to sawmills downstream. The site was developed as a roadside park along Minnesota State Highway 95 in the 1930s. In 1966 it was designated a National Historic Landmark for its national significance in the theme of industry. It was nominated for being the earliest, most important, and longest serving of the log storage and handling operations that supported Minnesota’s major logging industry. Virtually no traces remain of the site’s original buildings and structures.

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The St. Croix River (/ˈseɪnt ˈkrɔɪ/ SAYNT KROY; literally “holy cross” in French) is a tributary of the Mississippi River, approximately 169 miles (272 km) long, in the U.S. states of Wisconsin and Minnesota. The lower 125 miles (201 km) of the river form the border between Wisconsin and Minnesota. The river is a National Scenic Riverway under the protection of the National Park Service. A hydroelectric plant at the Saint Croix Falls Dam supplies power to the Minneapolis–St. Paul metropolitan area.