Located on U.S. highway 61, at Reads Landing Overlook, about 3 miles northwest of Wabasha
Turn out on Hwy 61, North of Reads Landing, South of Lake City
Text On Markers:
GEOLOGY OF LAKE PEPIN
Lake Pepin, a widening of the Mississippi River, occupies the river valley north of here for a distance of 35 kilometers. The lake was created by the delta of Wisconsin's Chippewa River, which enters the Mississippi directly east of this site. The Chippewa, a relatively small river, has a much steeper gradient, or slope, than the Mississippi. This steeper slope causes a faster flow, which transports more sand and coarser gravel than the Mississippi can remove. Consequently, the sediments brought in by the Chippewa dam the Mississippi back in this gorge, thus forming Lake Pepin.
But this scene was not always so tranquil. About 10,000 years ago, near the end of the last glacial period, this site was submerged by a colossal river that spanned the gorge. The immense volume of water came from the combined discharge of Glacial River Warren draining Glacial Lake Agassiz, Glacial River St. Croix draining Glacial Lake Duluth, and many smaller tributaries. That tremendous current eroded this gorge to its present width and flushed it clean of sediment, right down to the bedrock. After the glacial meltwaters were gone and the Mississippi dwindled, sediment from the Chippewa dammed the main channel. At that time Lake Pepin extended for 100 kilometers—all the way back to where St. Paul is today. Where the Mississippi first entered the lake, its sediments deposited to form a delta. The delta has since advanced downstream by progressively filling in the head of the lake and thus reducing its length. The top of the bluffs that line the shores of Lake Pepin are about 140 meters above the surface of the lake. The walls of the gorge are composed of sandstone, shale, and dolostone. These rocks were 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 rock-walled gorge ex-tends 46 meters below the lake surface. It has been filled to the present lake bottom mostly with clays that have settled out of the still waters of the lake.
Erected by the Geological Society of Minnesota in partnership with the Minnesota Department of Transportation and the Minnesota Geological Survey. 2003
Marker Current Status:
Found. Site visited.The plate is aluminum,MnDot indicate 1950
Planned for 2003 with updated text. Probably not done, 1950 marker still present.
- Marker Images