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The Keweenaw Boulder Garden

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Hidden : 10/26/2011
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Geocache Description:

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Connection to the Earth Science Curriculum

Essential Lessons:

1. Sandstone is classified as which basic type of rock?   Igneous, sedimentary or metamorphic?  Explain your answer.

2.  What is the name of the rock type that copper is found in? Explain how it formed. 

3.  What does a fined grained igneous rock tells us about how it formed?


Earth Science Literacy Principles-

Big Idea 2: Earth is 4.6 billion years old.

2.1 Earth’s rock and other materials provide a record of its history.
2.4 Earth’s crust has two distinct types, continental and oceanic.
2.7 Over Earth’s vast history, both gradual and catastrophic processes have produced enormous changes.

Big Idea 7: Humans depend on Earth for resources
7.3 Natural resources are limited
7.6 Soil, rocks and minerals provide essential metals and other materials for agriculture, manufacturing and building.

Common misconceptions 

All rocks and planets were formed at the some time.

Rocks have very little practical use.

All rocks are more or less the same (a rock is a rock!)

 Michigan State Science Content Expectations Addressed:

High School »ES4.A Explain the relationship between the rock cycle and plate tectonics and describe the processes that change one kind of rock into another.


Igneous- Rocks that form from the cooling and hardening of lava or magma.

Sedimentary- Rocks that form from preexisting rocks that have been broken down into sediments.

Metamorphic- Rocks that form from existing rocks that have undergone heat and pressure.

Rift- An area in the Earth’s crust that is spreading apart. Magma or lava erupts from the opening.

Vesicles- Small rounded holes in volcanic rocks caused by bubbles trapped as lava cools.

Weathering-The disintegration and breaking down of rock at or near Earth’s surface.

Erosion- The transportation of Earth’s materials by water, wind or ice.

Shale-A fine grained sedimentary rock of clay or mud sized particles compressed together.

Faulting-A fracture or break in a rock due to movement.

Amygdaloids- A gas bubble in volcanic rock that has been filled in with minerals.

Limestone-A fine grained chemical sedimentary rock formed from sediment made of shells and organisms that settle to the bottom of the ocean floor.

Erratic-A rock that has been transported from its place of origin and is different than the surrounding bedrock.

Access Information:

Dr. William Rose
Michigan Tech University
1400 Townsend Dr.
Houghton, MI 49931

Date Visited:
Friday, July 15th, 2011

The Keweenaw Boulder Garden


When you visit the Keweenaw Boulder Garden, you get the opportunity to go back in time and experience the geological history of Michigan. The inspiration of the garden came from Dr. William Rose, Volcanologist, Professor of Geological Engineering and Sciences at Michigan Tech University.  He set up the garden for both educational and aesthetic purposes. He created this garden so that it could be used to tell the geological story of these native Michigan rocks.  He also hopes that everyone walking by will enjoy and appreciate their beauty. The three basic rock groups are represented here, igneous, sedimentary and metamorphic. The rocks found here are approximately one billion years old! Every rock has its story to tell and the rocks in this garden are waiting for you to come and learn their story

Dr. Rose explains that the rocks found here were broken apart by the glaciers and then deposited out of glacial rivers when the ice melted.  The Michigan Tech campus is a flat terrace formed from outwash that had boulders on top of it before the university was built.  During the construction of the University, many of the boulders were moved out of the way. So now, the boulders have been put back where they belong, creating a glacial terrace with a variety of boulders for you to explore and study.

Figure 1. Keweenaw Boulder Garden. MiTEP students identifying boulders.

    Coordinates:  47°07.110’N  88°32.725’W

    Michigan Tech University
    1400 Townsend Dr.
    Houghton, MI 49931


Figure 2.  Campus Map.  Michigan Tech University.

A brief history lesson of Keweenaw rocks

About one billion years ago there was a giant rift which caused major volcanic eruptions in this area.  The lava cooled into basalt. Gases bubbled up to the top layers of the basalts forming vesicles.

There were alternating periods of rift eruptions which formed the basalts. These were accompanied and followed by periods of weathering and erosion of the rift walls and the formation of conglomerates.

The weight of these alternating layers caused the whole area to sink in the center forming a large “U-shaped” depression.

When the eruptions stopped, erosion continued and conglomerates, sandstones and shale’s were deposited. 

Next, these basalts and conglomerates went through a period of movement.  The rock formations underwent faulting, fracturing and tilting.  Heat caused the hot water within the rock to rise up through these fractures carrying minerals including copper. Theses minerals accumulated in vesicles forming amygdaloids. This is how the Upper Peninsula of Michigan developed its great copper deposits. Much of the copper was found in the amygdaloidal basalts.

Next there was a period where the entire area was covered by a sea for several hundred million years.  During this time, marine sediments of limestone were put down. After the sea retreated, weathering took place and eroded some of these deposits away.

More recently (geologically speaking) there was a gradual climate change and ice started to cover this area.  The massive weight of the ice as it gradually flowed toward the south eroded most of the limestone away exposing the underlying basalts and layers rich in copper.

Today much of the landscape and deposits we see on the surface of Michigan is the result of the strong erosional force of glaciers that have since left over 10, 000 years ago. It was this force that broke apart, and transported this large variety of boulders to the Mohawk Sand and Gravel quarry where Dr. Bill Rose got the idea to create a Boulder Garden in the middle of Michigan Techs campus. Landscape architect Lynn Watson along with Ashok Agarwal designed the layout and placement of these magnificent boulders.  You can learn more about them by clicking on the Michigan Tech Boulder Garden link.


Figure 3. Diagram of Boulder Garden.

Some of the boulders found in the garden:


Basalt-A dark colored fine grained igneous rock. Erupted at Earth’s surface and cooled quickly.
Vesicular basalt-
Basalt that is full of little holes that is evidence of gas bubbles when it was lava.
Amygdaloid basalt- Vesicular basalt, but the holes are filled with minerals.
Ophitic basalt- Basalt that contains light colored crystals of feldspar (looks like a snow flake)  
Fine grained volcanic rock, cooled quickly,  usually reddish or pinkish in color, high silica content.
Conglomerate- A sedimentary rock consisting of rounded gravel sized or larger pebbles cemented together by finer particles.
Sandstone- A sedimentary rock of sand sized particles of quartz cemented together.
Gneiss-A metamorphic rock that has undergone heat and pressure causing its minerals to realign and form banding (stripe) of the different minerals.
Granite- Coarse grained igneous rock, cooled slowly underground, can see individual crystals of quartz feldspar and mica, speckled pink, white, grey and black

Figure 4. Basalt containing vesicles and veins.


 Notice the shape and size of the sediment that makes this rock.

Figure 5. Close-up of conglomerate.


Notice the grain size of this rock as compared to a conglomerate.

Figure 6. Sandstone. 

How did this rock get its stripes (banding)?     

Figure 7. Gneiss.


Logging Question 1

Find the rhyolite. Rhyolite is an igneous rock. Igneous rocks are classified by their composition and texture. Observe the rock and answer the following questions:


Composition is defined as the minerals that make up the igneous rock

a. Is the rhyolite light or dark in color?

If it is light, it is Felsic: made of feldspar and quartz.

If it is dark, it is Mafic:  made of magnesium and iron.

b. What is the composition of rhyolite?



Texture of an igneous rock is determined by the size of its individual crystals.

Small- individual crystals are hard to see with the unaided eye.

Large- individual crystals can be seen easily.

c. What is the crystal size of the rhyolite?      small     or       large

If the crystal size is small, it cooled quickly from lava and the texture is fine-grained.

If the crystal size is large, it cooled slowly from magma and the texture is coarse-grained.

d. What is the texture of the rhyolite?

e. Did the rhyolite from lava or magma?

f. Did the rhyolite cool quickly or slowly?


For more information:

To learn much more about the Boulder Garden visit the Michigan Tech University link below:

You Tube Video of Earth Day celebration in the Boulder Garden


 Guth, Alex. Diagram of Boulder Garden, figure 3. Retrieved July 25th, 2011 from URL:

 Map of Michigan Tech Campus, figure 2. Retrieved July 25th, 2011 from URL: originally from Google Earth.

 Robinson, S. (2001). Is this an Agate?  An illustrated Guide to Lake Superiors Beach Stones Michigan, Hancock, Michigan: Book Concern Printers.

 Rose, W. (2010, November 15). Michigan Tech Boulder Garden. Retrieved July 25th, 2011 from URL:

 Rose, W. Photograph of Sandstone, figure 6. Retrieved August 23rd, 2011.

 Tarbuck and Lutgens. (2006) Earth Science, Prentice Hall, Pearson Education Inc.

 Young, Julie.  Photographs of various boulders, figure 1, 4, 5, 7.  Taken July, 2011.






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