The Scenic St. Croix EarthCache

In Douglas County, WI there is a large spring-fed swamp whose waters flow out to the northeast marking the origins of the Brule River and to the southwest into Upper St. Croix Lake out of which emerges the St. Croix River. These headwaters of the St. Croix River are located near Solon Springs, WI, twenty miles south of Lake Superior. From this area, the St. Croix River flows west and south over 160 miles until it joins the Mississippi River at Prescott, Wisconsin. Approximately 80% (129 miles) of the St. Croix River forms part of the boundary between Wisconsin and Minnesota. The upper 20% of the river is entirely within Wisconsin. The watershed covers approximately 7,760 square miles and extends from near Mille Lacs Lake in Minnesota on the west to near Cable, Wisconsin, on the east. Approximately 46% of the watershed is located in Minnesota.

Major tributaries of the St. Croix River consist of the Namekagon River, were the river considerably widens, the Kettle River, Snake River and Sunrise River, joining from the west, and the Apple River, Willow River and Kinnickinnic River joining from the east, as well as numerous springs emerging from the river bluffs spanning the route to the Mississippi.

The surficial bedrock exposed in this immediate vicinity is Ordovician sandstones of the Trempealeau Group, Jordan and St. Lawrence Formations. Just south of this point, and angling northeast lies the eastern arm of the Mid continental Rift fault line and the exposed bedrock east of this fault is older Cambrian limestones and dolostones of the Praire du Chien formations. The bedrock geology is very different further upstream.

The St. Croix River was carved over 11,000 years ago as a result of a glacial lake outburst flood as the ice and terminal moraine dams burst, releasing torrents of water from proglacial Lake Duluth. Steep sided gorges were carved through resistant basalt, and the soft Cambrian sediments eroded into a wide valley, where you stand today. Further downstream, dramatic limestone and dolostone bluffs continue to withstand the ongoing erosive forces of wind and water as it joins the Mississippi River.

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**As an interesting mathematical side note, and something to consider as you look at this beautiful river valley, please ponder this amazing lesson in physics and fluvial dynamics:

“A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. According to Brahm's law, the mass of objects that may be flown away by a river is proportional to the sixth power of the river flow speed. Thus, when the speed of flow increases two times, it can transport 64 times larger (i.e., more massive) objects. In mountainous torrential zones this can be seen as erosion channels through hard rocks and the creation of sands and gravels from the destruction of larger rocks. In U-shaped glaciated valleys, the subsequent river valley can often easily be identified by the V-shaped channel that it has carved.”

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Please forward in an e-mail the following:

1. The width of the St. Croix River at this spot along the river, and reference your unit of measurement;

2. The elevation reading of the bluff; and

3. Posting a photograph of yourself or GPS at this site is now an optional requirement. Posting interesting photographs of this geological anomaly to educate other visitors to this EarthCache and to document your experience here are appreciated.