Dunnings Spring, Decorah, Iowa

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Dunning's (named after E.C. Dunning who originally owned the property in 1861) Spring, water originates near the base of the Galena Aquifer. The much less permeable Decorah Shale - the confining bed “floor” for the aquifer - is near the land surface, forcing the water to discharge from the wall of the Upper Iowa River Valley. The result is the picturesque falls. The groundwater issuing from the spring is flowing through an open, cavernous conduit, formed by the solutional enlargement of fractures. Number 1A1681.