Lake Pepin occupies the Mississippi Valley above this point for a distance of 22 miles. The lake is formed by the delta of the Chippewa River which enters the Mississippi directly east of this site.
The Chippewa, a relatively small river, has a much steeper gradient than that of the Mississippi. I t was therefore able to transport more sand and coarser gravel than the master stream could remove. In consequence the Mississippi was dammed back in the gorge to form Lake Pepin.
The surface of the lake is 664 feet above sea level and 450 feet below the top of the bluffs which line its shores.
The sand and limestone walls of the gorge are composed of material deposited in Cambrian and Ordovician seas when the continent was submerged some 400 million years ago.
The bottom of the gorge is 150 feet below the lake surface having been filled to its present elevation as the carrying power of the river decreased. 

There is another plaque below stating that this was constructed by National Youth Administration 1939.