Geology 310
Professor Moosavi
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?
· 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?
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?
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?
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?
· 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?
· 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.