Geology of Frontenac – Frontenac, MN - Minnesota Historical Markers on Waymarking.com

This marker tells about the geology of the Mississippi River valley. It is located at a scenic overlook and picnic area of Frontenac State park and reads as follows:

This site offers a magnificent view of the Mississippi River valley. The valley is carved into rock that was deposited as sediment in a warm, shallow sea that covered the area of southeastern Minnesota and much of North America about 500 million years ago. The upper parts of the bluffs are composed mostly of dolostone, a chemically altered limestone that is resistant to erosion. The lower parts are mostly weakly cemented sandstone. This layering of resistant rock over erosive rock helps keep the bluffs steep.

During the Ice Age of the last two million years, tremendous torrents of glacial meltwater repeatedly discharged from huge glacial lakes in the region of northern Minnesota and Canada. The forceful currents eroded this river valley to its present width and flushed it clean of sediment, right down to the bedrock. This colossal river was much higher than the Mississippi is today, and locally it flowed through both the main channel before you and a secondary channel, which passes just south of this bluff along Highway 61/63. The spot where you are now standing was, for thousands of years, on an island between these channels.

Today the Mississippi River is but a trickle compared to its volume when it drained meltwater from the glaciers. Its much slower current is unable to wash away all the sediment that tributary streams carry into the valley, so the valley is slowly filling. Here, the valley contains Lake Pepin, a river lake formed behind the delta of Wisconsin’s Chippewa River. The Chippewa enters the Mississippi near Wabasha, about 127 kilometers downstream. Its delta is large enough to dam the Mississippi back into this valley. Two other rivers have built deltas into the lake near here: the Rush River to the north on the Wisconsin side, and Wells Creek to the south on the Minnesota side. Visible just downstream on the right-hand shore are Willow Point and Sand Point (more distant), both parts of the Wells Creek delta.

Erected by the Geological Society of Minnesota in partnership with the Minnesota Department of Transportation, the Minnesota Geological Survey, and the Minnesota Department of Natural Resources. 2003.

Marker Type:: Other

Visit Instructions:
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