Geology 310

                                                                                                Professor Moosavi


Minnesota Valley – Mankato, Rapidan Field Trip




Our goal for today’s field trip is to pose some big questions to provide a framework for the course. Contained below is an itinerary with activities and questions for the locations we will visit. Your observations and thoughts should be recorded within your classroom journal. Remember to leave some blank space to add to your answers later on.


The BIG QUESTIONS! (Like those your students may ask!)


What was Minnesota like, long, long ago?


What makes life possible here on the earth?


What determines the ecosystem found in a place?


How will the land change in the future?


What role do humans play in that future?


Stop 1 MSU – Mankato

            Trafton Lawn


            What can we learn about the geology of Minnesota in this spot?




·      Brief discussion.


            Where could we go to learn more about Minnesota’s geologic past?


·      EN ROUTE:  Note the landscape features we traverse.

(Gage Hill, Stoltzmann Road Wetlands, Mt. Kato)


            What could account for the landscape features we see?





Stop 2 Blue Earth River

MN Rte. 66 and Blue Earth County Road 90, Park in small roadside lot.


·      Hike along trail at woodland, field boundary.

·      Upon entering the woods, look for features of the valley present.

·      Note the small lake along the trail and stop.


            What material appears to underlie this site?


·      Feel free to use the spade to dig a small sample.


            What can you conclude about the underlying material?


·      Continue walking until you come to the river.

·      Look into the river.

·      Describe the quality of the river water in terms of its color and turbidity.

·      One student should take a sample of river water for return to the lab.  (We’ll compare this with another sample after it has settled to look at turbidity.)


            Is there life within the river?  What kind?


            What is the bottom of the river like?


            Does erosion or deposition appear to be occurring here? How do you know?


      What do you notice about the forest floor? (Is something missing? Does it look like a typical forest floor or has something happened to it?)


      What process could account for the state of the forest floor?


·      Examine the raised structure along the riverbank.


      What could account for this structure?


      How might it form?


·      Draw a quick side profile of the valley from the river into the forest. Focus on elevation, structure and location of vegetation.


What type of vegetation is present here?


What characteristics must this vegetation have to survive here?


How would this site change if the vegetation were removed in terms of its stability?


·      Continue walking along the river trail until it plunges into the water.


What is occurring with the river in this location?


What evidence might you find elsewhere nearby to support your contention?


·      Brief discussion before walking back to the van.       


What do you call the landscape we just visited?


Stop 3 Red Jacket Bridge

            MN Rte 66


·      At this site we will look at the stream gauging station below the bridge before ascending the steps to the Red Jacket Trail.


            What is the importance of measuring stream discharge?


·      Make a sketch on how you think a stream gauge might work.


·      After climbing to the bridge, take a good look up and down the valley of the Le Seuer River.


            What is the shape of the river valley here?


·      Make a quick sketch of the river valley’s shape.


            What do you observe is occurring downstream from this site (think of Stop 2!)?


            What features that you have observed so far today might this explain? How?


            What 3 major economic activities have you observed in this valley?


            How does the geology present dictate these economic opportunities in each place?


            What do they tell us about the geology in turn?


·      Brief discussion before returning to the van.








Stop 4 Road Cut

            MN Rte. 66 near hilltop.


·      Look at the material exposed by the road cut.

·      Describe the texture and composition of the material.

·      Note the large boulder seen at the upper right.

·      Consider our elevation near the top of the river valley.


            What is this material?


            How did it get to be in this location?


            How old do you believe it is?


            What role does this material play in soil formation?


            What role does it play in aiding/impeding our ability to examine the underlying geology?


·      Look at the shape of the side valley across the road from the road cut.

·      Draw its shape.


What does this tell us about the age of this small valley?


What stage in stream development are we seeing?




Stop 5 Agricultural Land

            Along Blue Earth County Road 9, East of Rapidan


·      Look to the south of County Road 9. Describe the nature of the landscape that you see.


            What do you believe created this landscape?


            When would it have formed?


            If you were to dig down 3 meters in that area, what would you expect to encounter?







Stop 6 Rapidan Dam

            Blue Earth County Road 9, 2 miles West of Rapidan


·      As we approach Rapidan Dam note the shape of the Blue Earth River Valley we are entering.

·      Next, examine the dam itself.


What does the dam appear to be used for?


·      On the dam, first look downstream.

·      Describe the shape of this part of the valley.


How is this valley’s shape the same or different from the part of the valley above?




What is exposed below the eastern end of the dam?


Is this material the same or different from that at Site 4?  How?


What type of rock do you believe this is? Why?  Be as specific as you can.


Where might we go to examine these rocks close up?


·      Describe the bed of the river below the dam.


Is this bed similar to that seen at Stop 2? How or how not?


·      Next look upstream of the dam (south).

·      Describe the environment you find there.  Note the vegetation and foam in the water especially.


Where does the river water appear to be moving more energetically, above or below the dam?


What effect might this have on the river’s sediment load?


What is the cause of the foam?


What effect might this have on chemical contaminants contained in the water?


How has the presence of the dam altered the river valley in terms of its geology?


Where are erosion and deposition occurring?


How has the presence of the dam altered the river water in terms of its turbidity?

How has the dam altered the conditions for life in the river (temperature, nutrient status, oxygen level, migration routes for fish, etc.)?


What is the ultimate fate of this system?


Once this occurs, what would you predict would happen if the dam were removed?  Think in terms of erosion, deposition, and water quality.


In light of all you have said, is the presence of this dam benign, i.e. does it produce the benefits it is intended to without negative impacts?


What does this tell us about this form of meeting this societal need?


·      More extensive discussion before leaving by van.





Stop 7 Mills Lake

            Off US 169 South of Blue Earth County Road 9.


·      Examine the shoreline and water of Mills Lake.

·      One student should collect a water sample for return to the lab.

·      Another student should measure water clarity using the Secchi disk from the end of the dock.


            Where does water for this lake come from?


            Where does it go? (Describe 3 possible exits.)


            How did this lake form?


            How is it likely to evolve in the future?


What makes the water of Mills Lake so turbid?


            What does that tell us about the water quality?


            What role does the farmland around the lake play in its water quality?


            What role do the trees along the shore play?


            How is this lake likely to evolve over the next few thousand years?




Stop 8 Tributary Stream

Judson Bottom Road


·      Begin by examining the pinkish/purple rocks along the road embankment.  These rocks are not native to this site, but were brought in from an hour to the West.

·      Use the rock hammer, HCl acid, your knowledge of rock identification to classify the rock in terms of general and specific type.


            What general and specific type of rock is this?


            How does the acid test help you to distinguish this rock type?


            What mineral does this suggest is found in this rock?


            What would give the rock this interesting color? (Is it a Vikings tribute?)


            What environment would this rock have formed in originally?


            Why would MN DOT spend so much money to bring in this rock for road stabilization instead of using local rock?


·      Next, enter the small stream valley from the opposite side of the bridge.

·      Describe the shape of the valley.

·      Look at the rocks in the outcrop across the stream above you.


            What do these rocks appear to be made of?


            What general and specific types of rock are they?


            Are they strong or weak?


            What geologic process are they undergoing?


·      Look at the rocks in the streambed and in places along the bank. Look at how they break.


            Are these rocks of the same type as the others?


            What do they appear to be made of?


·      Use the rock hammer, acid, and your knowledge of geology to identify these rocks.


            What mineral are they made of?


            In what environment would they have been deposited?

            Does the presence of these rocks play a role in determining the shape of the valley?  If so, what?


            What would happen if the stream were to erode through this layer of rock?


            How old is this small valley?


            How did it come to be?


            How old are the rocks in this small valley?


·      Before leaving the valley, look around the base for any rock that does not match the 3 types we have just looked at.  Bring it to the attention of the class.


What does the rock appear to be made of?


What does its shape tell you about it?


Does it appear to belong here?


If not, where did it come from?


How did it get here?


·      Discussion before returning to the van.


EN ROUTE:   Note the rock beds exposed along the highway.

Focus on their levelness and structure.



















Stop 9 Minnewaukon Falls

Judson Bottom Road


·      Be careful at this site as we are along the road.  Examine the stream from the highway bridge.  Look both up and down stream. This is the same rock bed that supported the stream at stop 9.  Here however, the rock bed has been breached by the stream.  Look at the results.


            What happens to the stream as it heads toward the Minnesota River?


            What feature do you expect to see there?


·      Walk around to the fence and look back at the stream.

·      Draw a quick sketch of what you see.


What is the shape of this stream valley in profile?


What is happening at this location?


What role do the rock beds exposed play in creation of this feature?


Is this feature stable? If not, how has it and will it evolve over time?


How old is this feature?


·      Brief discussion before returning to the van.





















Stop 10 Road Cut

Judson Bottom Road


·      Begin by looking at the bed of the small stream along the road.


            What is the shape of this stream valley?


            Why is it different?


            What effect is this having on the course of the stream?


·      Look closely at the bends in the stream.


            What are they called and how do they form?


·      Sketch one of the bends.  Indicate where you think the water is moving fastest and where it is moving slowest.


What effect should variable speeds have on the stream’s ability to do work?


How will this manifest itself in the development of the stream channel?


·      Indicate on your sketch areas of erosion and deposition which result.


            How is this small stream likely to evolve in the future?


Would you build your house across this stream from the road?  Why or why not?


·      Move on to the rock outcrop to the right. Look closely at the layers in the rock.


What 2 types of rock are we seeing?


·      Use the acid test on samples that have fallen from the cliff to verify your identification.


Why does the darker layer overhang the lower layers?


What would this form in a wetter setting?


·      Test the hardness on a sample of the white rock.


How strong does the white rock appear to be?


·      Look at the layers within the white rock. They layers cross back and forth.


·      Speculate as to the cause of these cross beds.

What do they suggest about the environment in which they formed?


·      Brief discussion before returning to van.


En Route:  Look at the structure of the Minnesota River and its valley to our right. 

Look for its resemblance to other features seen on this field trip.

Look also at the rock outcrops on our left.  See any parallels?


Stop 11 Look Out Drive Overlook

            Look Out Drive, North Mankato


·      Look up and down the Minnesota River Valley.

·      Describe its shape.

·      Look at the industries and towns present.

·      Look at the notches in the opposite valley wall.


Why is the Minnesota River valley so big compared to the river?


Did the Minnesota River form this valley? If no, how did it form?


How did the notches in the valley wall form?


What would you expect to find in each case?


How old is the Minnesota River valley?


Why is the valley not deeper than it is?


Why does the river valley make such a sudden sharp bend north of Mankato?


What does the river appear to be doing when it bends back in forth?


Why does this happen?


What does this tell us about the scalability of geologic processes like stream channel evolution?


What materials would you expect to find underneath the river?


How would you expect this river valley to evolve over time?


What would happen if very heavy rains and snowmelt were to occur upstream?


How has the presence of the river valley affected human occupation of this area?


·      Final Discussion before returning to MSU.