Examining an undercut portion of the Platteville carbonate that was created by erosion of the less resistant Glenwood Shale. Anytime a stream cuts through the Platteville Formation it can rapidly erode the underlying soft St. Peter Sandstone and Glenwood Shale to create similar undercuts. As the undercut deepens, it will eventually intersect a fault plane and the overlying Platteville will fall.

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