This is an Earthcache, which does not have a container, but rather brings you to a significant geological feature. Click here for more information.
Under the Glacier--The Wilkie Gorge
This earthcache highlights several features of the Cross Plains unit of the Ice Age National Scientific Reserve. This area was selected as a unit of the Ice Age National Scientific Reserve because of the fascinating and complex geologic history that the area experienced. However, the Cross Plains unit of the reserve is still in development. To date there are no public facilities. The Reserve is managed by a number of State and Federal agencies. The area immediately south of Old Sauk Pass is managed by the National Park Service, the area further south, around Shoveler's Pond, is managed by the US Fish and Wildlife Service, and the area north of Old Sauk Pass is part of the new Cross Plains State Park (again undeveloped). As you walk through the reserve please use care and remain on established trails, especially near the gorge as this area is especially sensitive. The Wisconsin DNR and the National Park Service request that you do not enter the gorge itself. To complete this earthcache you will need to walk just over 1 mile.
Overview of the Ice Age National Scientific Reserve
While this earthcache focuses on the Wilkie Gorge, it is necessary to understand a little of the geologic history of the reserve as a whole. The focus of the Cross Plains unit is on the area at the glacier’s edge and just beyond. In fact most of the unit, with the exception of the far northern section, was not covered by the glacier at all. The glacier’s edge paralleled what is today Timber Lane. It stopped roughly 100 yards to the east of Timber Lane. In the northern section of the reserve the glacier bent west, now roughly paralleling Old Sauk Pass, again stopping short of the road by about 100 yards. Along this edge a chain of small glacial lakes were formed. Modern day Shoveler's Pond and Coyle's Pond are the only surviving members of this chain of lakes. Melt water from the glacier flowed north through this chain of lakes, finally descending to the Black Earth Creek valley along the edge of the glacier.
Formation of the Wilkie Gorge
The Standard Theory: The flow of water through this chain of lakes and into the valley crossed what will become the Wilkie Gorge. It is unclear exactly how, but at some point, melt water found its’ way under the glacier creating a tunnel at the point where the Wilkie Gorge exists today. It is possible that there was a pre-glacial ravine at this point or some other weakness that the melt water exploited as the glacier began to warm and melt. This new opening caused a rapid drainage of the lowest lake, which in turn caused deep scouring of this new tunnel, creating Wilkie Gorge. There is a difference in elevation of about 200 feet from the top of the gorge to the Black Earth Creek valley below. The pressure generated by this drop in elevation resulted in such intense flow of water through the gorge, that it actually began to cut into the underlying limestone and dolomite bedrock. Such tunnels of flowing water under glaciers are a well-known phenomenon. However, what makes the Wilkie Gorge different is that the melt water flowed toward the glacier, went under, and then re-emerged at a lower elevation. This type of tunnel is known as a submarginal chute. Such chutes are not typical, but similar examples exist in modern glaciers.
Alternative Theories: While the above explanation is the most generally accepted explanation for the formation of the Wilkie Gorge, there are several alternative theories. First, it is possible that as the melting glacier retreated, the edge of the glacier moved to what is now the east side of the gorge. The melt water stream simply change course to follow the new edge of the glacier. This melt water stream over time, carves the Wilkie Gorge. Second, it is possible that a deep crevasse opened perpendicular to the edge of the glacier. The melt water stream then moved between opposing walls of the glacier and scoured out the gorge.
To log this cache you will need to think a little like a geologist. A geologist must make careful observations of the existing physical features and then try to imagine the forces and processes that created these features. Often more than one story can be told. However, it is the explanation that best accounts for these features that will gain the most support. Visit each of the four stops described below. As you visit the stops, think about the three theories for the formation of the Wilkie Gorge. At each stop I will ask you a series of questions or ask you to observe a feature visible at that stop. If you like, you may send me your answers to these questions and your observations of these features. However, this is not a requirement for logging this earthcache. After you have visited the four stops decide for yourself which of the explanations makes the most sense.
To log this cache email me your conclusions on which of the three theories best explains the formation of the Wilke Gorge. Include in your answer any feature that appeared especially significant to you. However, your answer must address the questions of how the melt water stream could have breached the moraine, which would have created a dam or dike in the area that crossed what is now the gorge. Your answer must also explain how the erratics, visible from stops 2 and four came to rest on the floor of the gorge (remember that there was a torrent of water coming down the gorge so strong that it cut through bedrock).
The posted coordinates will take you to a small parking lot. From this parking lot take the path leading north. As you walk on the trail to the coordinates for stop one, enjoy the restored prairie that surrounds you. At stop one turn to the east. As you look east the terminal moraine will be on your left. Directly in front of you, you will observe the curved bed of the original melt water stream that led down from the melt water lakes. Now turn to the west. The melt water stream would have descended down through the ravine in front of you. Based on your observations of the cutting done by the melt water stream, in relative terms, for how long of a time period do you think the stream flowed before being diverted by Wilkie Gorge?
Continue north a short distance on the trail from stop one. Before you reach the edge of the terminal moraine you will see a path on the right. Take this path which parallels the moraine and generally follows the old channel of the melt water stream. As you near the trees on the east side of the prairie the path will begin to divide.
At this point you may need to leave the path and carefully make your way through the woods towards the coordinates for stop two. As you approach the gorge you will find a well-established trail following the edge of the gorge. Take this trail to stop two. Please be careful along the edge of the gorge as there are some steep drop offs. Stop two is the approximate location of where the moraine would have crossed the area that is now the gorge. Stop two also offers great views of the gorge. First look across the gorge slightly to the south east. Can you see the moraine on the opposite side? Now look around on the west side of the gorge. How prominent is the moraine on the west side? Observe the course of the gorge from this location.
Follow the trail south all the way back to Old Sauk Pass. Please avoid climbing the walls of the gorge. It is both dangerous and damaging to the fragile environment of the gorge. Carefully follow Old Sauk Pass east to stop three located in an alternative parking lot. The north shoreline of a melt water lake would have been approximately where you are standing. The lake would have covered much of the area to the south. It was the catastrophic draining of this lake that is responsible for scouring out most of the Wilkie Gorge.
There are two trails leading north from the parking lot you are standing in. Take the trail to the right. As you head north you will begin to see the terminal moraine. As you continue north the path will ascend the moraine and continue to stop four. Again as you approach the gorge please be careful near the edge as the drop offs are especially steep on the eastern side. Look across the gorge to where you stood at stop two. Observe any differences between the two sides of the gorge. If the season allows for observation, what is the terrain like to the northeast? How would this affect the runoff of melt water? Also notice the presence of erratics laying on the floor of the gorge. Erratics are rocks carried by the glacier from their normal range to an area where they otherwise would not be found. Considering the massive amount of bedrock carried away by the torrent of water flowing through the gorge, how did these erratics come to rest where they are?
Robert F. Black, Geology of the Ice Age National Scientific Reserve of Wisconsin. NPS Scientific Monograph no. 2, 1974.
Lee Clayton and John W. Attig, Pleistocene Geology of Dane County, Wisconsin. Wisconsin Geological and Natural History Survey, Bulletin 95. Madison: University of Wisconsin, Extension, 1997.
Robert H. Dott and John W. Attig, Roadside Geology of Wisconsin. Missoula, Montana: Missoula Press Publishing Company, 2004.
David M. Mickelson, Landscapes of Dane County, Wisconsin. Wisconsin Geological and Natural History Survey, Educational Series 43. Madison: University of Wisconsin, Extension, 2007.
David M. Mickelson, Louis J. Maher Jr., and Susan L. Simpson. Geology of the Ice Age National Scenic Trail. Madison: The University of Wisconsin Press, 2011.
The Geocache Notification Form has been submitted to and approved by Dana White Quam, District Park Specialist of the Wisconsin DNR. Geocaches placed on Wisconsin Department of Natural Resource managed lands require permission by means of a notification form. Please print out a paper copy of the notification form, fill in all required information, then submit it to the land manager. The DNR Notification form and land manager information can be obtained at: http://www.wi-geocaching.com/hiding