The Amnicon Falls area is the result of many geological forces; vulcanism, sedimentation, faulting and glaciation to name just a few. A short hike on the Geology Walk Trail brings you close to many of these. To enhance your visit, pick up the guidebook for this walk at the Park Office before you set off. This guide has numbered informational stops that correspond to numbered signs on the trail, and will give you a fuller understanding of the area's geological history.
The posted coordinates will bring you close to the trailhead. Take a moment to read the sign, then stop at the signs numbered 1 and 2. At this point, you are viewing two different geological eras. The Upper Falls plunges over dark basalt rock, formed by ancient lava flows. The fine texture of this rock suggests that the lava was very fluid and cooled rapidly enough to prevent the formation of crystals. Heading about 50 feet downstream brings you to a nice view of the Lower Falls, which flows over sandstone. This sandstone is known as "Lake Superior Sandstone," having been deposited here by an ancient sea even larger than Lake Superior. You can see the horizontal bedding planes of the sandstone looking across the river at this point.
Cross the charming covered bridge across the river at this point. You have now crossed the Douglas Fault Line. The Douglas Fault runs from east of Ashland Wisconsin to the Twin Cities area. What you are seeing to the left of the falls near the stairway is Kewauneean basalt, which has been exposed due to an interesting geological occurence. The bedrock, which at one time was basalt overlain with sandstone, gradually was forced upward at a 50-60 degree angle in what is called a "thrust fault." Water, wind, and ice have worked to erode away that sandstone layer, exposing the basalt above the falls. North of the fault, the sandstone was protected from these forces to some degree by the adjacent basalt. Take some time to appreciate this study in contrasts.
Proceed along the river's edge to the next footbridge. Here you will discover that the river splits as a result of the fault. Look for signs of glacial action here, such as occurence of other rock types and glacial striations, deep scratches that indicate the direction of glacial flow.
Enjoy following the trail around the island, being sure to stop at the impressive Snake Pit Falls. When you cross back over the covered bridge, head for the final waypoint located behind the restrooms. This location *may* display another waterfall, called "Now and Then Falls." If the river flow is low, this channel becomes dry. During heavy flow, you can enjoy this little falls away from its bigger siblings.
In order to claim a find for this EarthCache, please answer these questions in an email to the cache owners.
1) At the location of the Upper Falls and Lower Falls (near trail markers 1/2), take note of the huge undercut in the riverbank. Explain what geological process or processes you think is responsible for creating this feature.
2) At the location of the Douglas Fault (near trail marker 3), describe the texture, color and any striking features of the basalt and the sandstone exposed here.
3) At the location of the footbridge (near trail marker 4), please take an elevation reading. Also make note of any signs of glaciation you observe here.
4) At the location of Now and Then Falls (near trail marker 9), estimate the height of the falls. Share whether or not there *were* falls here on the date of your visit.
Though not required, this is a "wow" location that invites photography. We would love to see photos of you and your team exploring the area. If you're willing to share, please upload these photos with your "found it" log.
Any logs by finders who do not send us the answers to the above questions within one week will be deleted.