Welcome to the next edition of Doc.’s Roadside Geology Tour: Jackson County!
"You're traveling through another dimension. A dimension not only of sight and sound, but of mind. A journey into a wondrous land whose boundaries are that of imagination. That's the sign post up ahead. Your next stop...The Driftless Zone….”
The above listed coordinates will bring you to a wide spot in the road which offers a commanding view of one of Mother Nature’s Unique and Fragile Creations ~ Table Rock and it’s little sidekick, Bear Rock, named for it’s resemblance to a bear’s head. This rock formation is on private property and we can only appreciate this from the roadside pull-off.
Many have called this rock formation a “Balanced” Rock. In actuality it is classified as a Pedestal” Rock ~ a single piece of stone which has weathered in such a fashion that its mid-section is narrower than its cap or its base. This formation is one of the larger and more elegantly formed examples of a pedestal rock east of the Rocky Mountains.
Hundreds of millions of years ago an ancient sea left sedimentation deposits here and all but the most resistant of these layers were eventually worn away by wind, water and ice. What you see here today are the last remnants of those resistant layers.
The bluff which stands before you is one of many rocky treasures spared from the bulldozing effects of the last glacier which stopped only a few miles away. This formation is what is correctly known as a mesa (Spanish for "table") as it is a large formation. Smaller formations are known as buttes and pinnacles. Located in the "Driftless" (not glaciated) area of Wisconsin, these mesas, buttes and pinnacles escaped the land scouring activity of nearby glaciers. It's likely that hundreds or even thousands of similar formations (which were located outside the Driftless area) were worn away during the last ice age.
Because the capping material on these bluffs is cemented better than the under-laying material, erosion by wind and water wears away the soft sides of these formations until the weight of the overhanging cap causes it to fall. Frost is also major cause of erosion and tends to break the formations along joints keeping the tabletop appearance intact. This formation will continue to decrease in size until it eventually blends in with the plain on which it sits; this erosion accelerates once the resistant capping material has been lost.
To claim credit for this EarthCache, please email to me:
1. Given that the elevation of the top of Table Rock 1135' above sea level, please take an elevation reading where you are parked and calculate the height of Table Rock.
2. What is the colour of the rock making up the tabletop? How thick do you think this layer is?
3. Would you classify this formation as a mesa, pinnacle or butte?
4. Honestly, do you see the Bear’s Head formation? Where is it in relation to the Table Rock?
5. Please post a photo of Jackson County’s famous Table Rock to document your visit to this site.
Buckle up for the next stop on our Roadside Geology Tour of Jackson County, WI!