Histories: Trempealeau Co. Historical Accounts:
"History of Trempealeau County Wisconsin, 1917":
The Trempealeau Bluffs
(By George H. Squier)-As transcribed from pages 23 - 24
It remains before bringing this article to a close, to notice that feature, which, because it is so conspicuous and distinctive, has attracted the attention of all who have entered the region, Indians apparently as well as whites, the Trempealeau bluffs.
It is, perhaps, generally recognized that these were at one time a part of the west (Minnesota) shore, but the process through which they became separated is not well understood.
In one of the recent publications of our State Geological Survey, Mr. Martin, who, I understood, had not personally studied the situation, gives an explanation which is quite incorrect -- impossible, indeed.2 His explanations and diagrams assume that the notch at Trempealeau Bay was the continuation of one of the valleys on the Minnesota side. But the valley in question is very much wider than the notch, and no explanation is offered of an adequate agency for the removal of the divide at the place where it is assumed to have been removed.
To correctly understand the process, it must be remembered that when the streams were "young," they were flowing in narrow, gorge-like valleys, and that in the case of the Mississippi, this was probably much nearer the Wisconsin than the Minnesota side of the present valley. On the Minnesota side several of the small streams united in one which partly paralleled the Mississippi, but which, in its meandering, approached it more closely for a stretch of its upper course than it did below. As the streams, having cut down to grade, proceeded to widen their valleys, the narrow divide between this parallel stream and the Mississippi was gradually cut away.
It must be borne in mind that so long as the streams were running on the rock bottoms, this divide might be wholly removed for some distance above our present Trempealeau bluffs without causing the diversion of the Mississippi into the smaller body, because, not only would the steeper grade of the smaller valley have carried its bottom above that of the larger stream, but the greater depth of the channel required by the larger stream would be sufficient to control its flow even though their surfaces had been at the same level. When, however, the conditions had changed so that the Mississippi did not keep its channel cleared out, but instead became gradually filled, its newer course was left unobstructed. Some other attendant circumstances, also, would have made that its most easy and natural course.
Naturally, when the large stream invaded the valley of the small one, there began a rapid process of erosion whereby the salient points and minor flexures were reduced into an adjustment to its own requirements.
The accompanying diagramatic map is supposed to show the conditions while the valleys were still narrower; the consequences of the widening of the valleys will be readily apparent.
The point where the Trempealeau chain of bluffs connected with the Minnesota shore is a matter of some interest. The projecting headland on the Minnesota shore which may be supposed to have marked the point of junction has, of course, been worn away, but it is believed that the long line of cliffs near Homer has resulted from such rapid wearing back of the shore line and marks the probable line of junction, as it is also the point toward which the present trend of the Trempealeau bluffs points.
The conspicuous isolation and insular position of Trempealeau Mountain proper may call for a few remarks.
It is obvious that not only the larger streams, but the smaller ones, and the torrent courses were everywhere dissecting the region. Small valleys similar to those now extending into our bluffs would also have existed in the portions now wholly removed. One who is familiar with the present condition of our bluffs will realize how little erosion along their north side would serve to remove the low connectipg ridges and leave, instead of a connected chain, three or four disconnected hills. The little valley between Trempealeau Mountain and Brady's Bluff had been cut so low that the flooded Mississippi was able to pass through and further rapid deepening was the result.
Resources for the above information:
2 - Martin, Physical Geography of Wisconsin, 136-197.
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