Geology 310

                                                                                                Professor Moosavi


Taylor’s Falls Field Trip


Of all the day trips that Geology students take, the trip to Taylor’s Falls has generally been found to be the most illuminating and enjoyable. Unfortunately, it takes from 2.5 to 3 hours to travel each way to get to Taylor’s Falls, on the Wisconsin border north of Stillwater. This is the closest site to Mankato where one can observe evidence for an ancient plate boundary. Students will receive a brochure on the park geology, which will assist in understanding the geology of this site. The questions below are designed to guide your investigation of this site. Remember the instructions and requirements for the Field Trip Project as you work.


Stop 1: Highway Bridge


·      Examine the shape of the valley and river flow level here. Make sure to look both up and down stream!


What is the nature of the St. Croix River?


What does its bed appear to be made of?


What color is the water and why do you believe this is so?


Does the flow you observe appear to be strong enough to account for the size of the St. Croix River Valley in this location?


Where is Taylor’s Falls?


Why is the Town of Taylor’s Falls found  in this location?


Stop 2: River-side Trail


·      Be CAREFUL not to fall into the river as we walk south along the river side trail.

·      Be sure to examine the rocks to try to determine their type.

·      Note also the type of vegetation found here.


What kind of rocks do these appear to be?


In what kind of environment did they form?


What physical evidence can you find to support this?


What does the presence of these rocks indicate about this region in the past?


Are these relatively hard or soft rocks?


What role would this play in their erodibility?


Do you see any evidence for columnar jointing and fracturing?


What role would this play in their erodibility?


Do you see any signs of erosion on these rocks?


How might this erosion have taken place?


Do you see any signs of mass wasting in this area?


What kind of vegetation is found here?


How is it similar or different to what you would find in Mankato?


What might account for any differences?


Stop 3: Pothole Trail



What formed the potholes?


Can you think of other rivers that possess potholes?


Given the size of some of these potholes, how high and fast must the river have been to make them?


Could such potholes be made in a typical flooding of the St. Croix River today?


What conditions would allow for the potholes to form?


Is the rock homogeneous?


What are the small pit-like holes found in the rock?


Why are they only found in certain layers?


Stop 4: Campground



Does the character of the river channel change in this area?


How does the flow rate change?


What effect does this have on the sediment carried within the river?


What might cause the river to change its character so abruptly?


What does the material upon which the campground sites appear to be made of?


How would this material have arrived in this location?



Stop 5: Highway 95 Underpass (Gates of Moria!)



Is this location built upon bedrock like the Stops 1 – 3 or something else?


What types of rock can be found here (at least 3 distinct types are present)?


Where did each rock type form?


How did each rock type get to be here?


What accounts for the presence of these rock types in this location?


What land-form are Stops 4 and 5 build upon?


Given what you have observed, what would you expect to encounter further upstream?


Stop 6: Curtain Falls Valley



What does the shape of the valley indicate about the age and development of this stream?


Where is most erosion occurring?


Is mass wasting occurring here and if so where?


Why have the stairs in the trail been damaged?


Can the park management expect such damage to recur? Why or why not?


What type of rock appears to be found in the floor of the stream?


In what type of rock would such rock form?


What kind of rock appears to be found on the higher walls of the valley?


In what type of environment would such rock form?


What stratigraphic feature must lie between these two rock types? Can you find it?


What does this stratigraphic feature represent?


Does it affect our ability to reconstruct the history of this location?


Stop 7: Curtain Falls



What type of rock seems to underlie Curtain Falls?


Are all the layers below this the same?


In what kind of environment did they form?


Are they similar to the rocks seen in Stops 1 – 3?


Are they similar to the rocks, which can be seen around Mankato?


Do you find any evidence for fossils in these rocks?


Are these rocks harder or softer than those seen in Stops 1 – 3?


How would this affect their erodibility?


What material appears to overlie the rocks supporting Curtain Falls?


Is it relatively harder or softer than those seen in Stops 1 – 3 and which hold up the falls?


How would this affect its erobility?


How old would expect this material to be?


What is the material found in the base of the stream below Curtain Falls evidence of?


Is this a significant force in the formation of this stream valley?


How old is Curtain Falls?


What caused it to form in this location?


If we were to return 10,000 years from now, how might this location look different?


Stop 8: St. Croix Valley Overlook


·      Examine the shape of the St. Croix Valley looking south toward the Stillwater.

·      Examine the forest that we pass through during this hike.


How is this forest the same or different than the vegetation found around Mankato and that found in Stops 1 – 3?

What does the shape of the St. Croix Valley tell you about the size of the river in the past?


Do the rock structures you have observed thus far suggest to you why this valley is broad and relatively flat rather than a steep canyon like the Grand Canyon?



Stop 9: Tributary 2


·      Look closely at the type of rock found within the stream. Make sure to look both up and down stream.

·      Note, this location corresponds roughly to where the St. Croix River Valley changes character between Stops 3 and 4.


What type of rock is found in the base of this stream?


Relative to the elevation of Curtain Falls, is this rock found at a higher or lower elevation?


Does this suggest a cause for the change in the structure of the St. Croix River valley proper?


If we, were to climb up stream from this location, what do you believe we might encounter?


·      Note, we will perform this test this hypothesis if the weather and trail conditions allow.