After hearing recent discussions speculating the height of Dunning’s Spring, Fort Atkinson resident Paul Herold decided to find the answers for himself.
Because he is a professional land surveyor, he has access to equipment and the ability to determine the facts.
Utilizing a Trimble Global Positioning System (GPS), he calibrated to the Winneshiek County GPS Control System and established control points and then performed a survey of the site with a Trimble Robotic Total Station.
The results of the survey listed the streambed elevations below the source to the nearest half foot due to the irregularity of a stream bed in general. They are:
• Elevation of the streambed in the cave at the source = 950.2 feet
• Elevation of the streambed where the springs enters the Upper Iowa River = 850 feet 
• Elevation drop from the cave (950.2 feet) to the Upper Iowa River (850.0 feet) = 100.2 feet
• Length from the cave at the source to the edge of the Upper Iowa River = 1,280 feet (more or less)
• Falls – Top, 932 feet; base, 903 feet; height of the falls, 29 feet 
Related information
• The top of the large rock at the top of the waterfall is 934.1 feet
• The concrete pad of the bench near the bridge is 897.1 feet
• The parking lot at the southerly end of the stone wall is 896.5 feet
• The wooden walkway bridge over the stream is 896 feet
• The highest point of the wooden walkway to the top is 963.4 feet
• The lookout platform at the top is 958.8 feet
• The centerline of Quarry Street at the entrance to the springs is 866 feet