WATER WARS: A look at Gallatin Valley Water Controversies

Stop 5:
Day Ranch

Stop 6:
Fish Creek

Stop 7:
Other Considerations



Stop 2: The Hard Rock Quarry

At this stop we will look at the ground water capacity of crystalline rock and begin to explore why crystalline rock occurs in the area

Stop 2 topo
for Air Photo
Stop 2 topographic portion Modified from Topo II
To better orient yourself, take a look at the trip log page!

contour interval: 40 feet


Geology controls groundwater, therefore geology is important to the Day Ranch controversy. In order to make in informed decision about the development of a golf course, we must understand the geology!

Gneiss outcrop, west side of road

  • Sketch the outcrop. If you would like better view, click on the photo. Include a scale, thickness and any other relevant information to describe the outcrop.

Example of good outcrop sketch?

  • Click on the photo of the outcrop, write a geologic description of the rock . Note the mineral type (if you can), porosity, and other relevant information to describe the rock.
What is a geologic description?
  • How well do you think water flows through this rock? What does the Aquifer/Aquitard map tell us about groundwater transport through this rock?

How does groundwater move through crystalline rock?

One way to judge how much water a unit can carry is to look at the vegetation.

Looking south on River Road

  • Compare and contrast the vegetation covering the West Gallatin Alluvium and the Gneiss.
  • How might this reflect the groundwater capacity of each unit?

Water can be stored in rock in two ways. At stop 1, we saw water being stored between pores in sedimentary rocks. Here we see crystalline rock which stores water in fractures and cracks.

image modified from USGS groundwater information sheet

The Aquifer/Aquitard map suggests the gneiss is a "possible aquifer." Most likely the water in that "possible aquifer" is stored in fractures and cracks since the gneiss is virtually impermeable.

possible location of water in gneiss

  • Would you expect the gneiss to hold or yield much water?

Stratigraphy: what the heck is going on here?

At this point I hope you are beginning to realize that the gneiss could cause some water problems. A geologist would be asking themselves,

"Where else in the valley am I going to see this rock? Is it at the surface at the Day Ranch? What might be the cause of the topographically high basement rock?"

Looking south on River Road

  • What kind of rock would you expect to see on the benches to the south? Click on the image to see what kind of rock it truly is!
  • Write a hypothesis that might explain why you are standing next to gneiss at this stop but can look across the valley and see a different kind of rock at the same elevation. What kind of data would you want to support your hypothesis?
What is a hypothesis?

Move on to stop 3 to examine the Tertiary sediment in detail!

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