1. Field Assignment
At the Bighorn Mountains
Wyoming
Stephanie Wrenn
Geo. 103
Prof. Lawler
26 July, 2012

2. Table of Contents
Map of area traveled
Shell Falls: Big Horn Mountains, Wyoming. Visited July 7th, 2012
Amsden Formation, Dayton, Wyoming. Visited July 14th, 2012
Syncline Fault, Dayton, Wyoming. Visited July 14th, 2012
Goose Egg Formation, Dayton, Wyoming. Visited July 14th, 2012
Leopardite Rock, Big Horn Mountains, Wyoming. Visited July 21st, 2012
Pink Flower, Big Horn Mountains, Wyoming. Visited July 21st, 2012
Elk, Big Horn Mountains, Wyoming. Seen July 22nd, 2012
How the area changed over time
Works cited

3. Map of area traveled

4. Shell Falls
The rock shown is a 2.9 Billion year old
Mesoarchean granite (James, 479).
It has been cut out over the years to form
a natural water fall.
The Shell Falls are an example of a very
rare pre-cambrian crust that has not been
overlayed by other sediment. Most rocks
this old have been covered deep below the
rising marine layer. With these rocks still
uncovered, it shows that either the mountain
range could have started to rise before many
others, or that their was an early cut that
diverted the water away from them (Wyckoff,
113).

5. Amsden Formation
This formation was discovered after a road cut was made.
The exposed rock is from the Pennsylvanian Period, 280-325 Million years old
The formation originated from carbonate-shale-sandstone that was carried over
when the sea encroached through Northeastern Wyoming during that period.
(Sandro, A1, A2)

6. Syncline Fault
The Syncline Fault is apart of the Amsden
Formation, it resides at the tail end of the road
cut.
The fault is shown as a Syncline Fault by the way
it curves down in a U shape. (James, 237)
The fold on this Syncline Fault was from a
compression where two plate boundaries met.
(James, 238)

7. Goose Egg Formation
This formation was formed in the Triassic- Permian
Period, 205- 290 Million years ago.
The primary rock type is red sandstone and
siltstone, and it also has: white gypsum, halite,
dolmite and limestone. (Schweitzer, no page
number)
The formation came into the area from a large
evaporite basin when a thin marine layer came in
through Idaho and Utah during that period. (Miller,
11)
The Goose Egg Formation's age was easily
distinguished because of the abundance of fauna.
Also, it is a very noticeable and uncommon
occurrence in the area. Basically, the area did not
see much water during that period when the marine
layer rose. (Miller, 4)

8. Leopard Rock
The Leopard Rock was found
in an old quarry that used them
for decorative fireplaces. They
are a very remote rock. Many
other rocks are nicknamed
Leopard rocks for their spots.
However this is an actually
Leopardite rock which is rare in
these mountain ranges. They
are Diabase, porphyritic, or
porphyritic dolerite with a white
subhedral plagioclase
phenocrysts. This means they
have quartz dolerite inside an
igneous rock or landmass
( Leopardite, no page number).

9. Pink Flower
This Western Germander with beautiful purplish
rose petals is caught in bloom at 9000 feet
elevation. The genus it belongs to is Teucrium
candense and the species is Lupinus argenteus.
(Jensen, 142)
This high elevation plant can not simply choose
where to grow, the strict habitat is primarily made up
of debris and rocks, and have to contend with other
species for their spot. (Huxley, 14)
These plants can be described as very strong in
order to have germenated so high up and to have
been able to survive underneath heavy snow
loads. (Huxley, 15)

10. Elk

11. Elk Continued
While camping at the Tie Flume campground I overheard a low growl
which sounded like a moose. As I started up towards the sound with my
party the woods became thick so we retreated back and I almost gave
up on the task of finding an animal for my project. However, as luck
would have it, a elk cow with her calf walked right behind our campsite.
I also saw the beautiful six point bull in the distant laying down, but was
unable to gather enough nerve to venture for a photo.
This majestic creature is of the Cervidae family, and one of the largest
in the deer family, just under the moose. Their fossil records indicate
they have survived since the Miocene period, 25 million years ago.
They first originated on the continent Eurasia, but were able to cross
into North America when the Baltic was frozen over. (Lapinski, 123)
They have survived for so long by keeping a yearly rutting season in the
same area where bulls compete to breed with the cows. They also are
very adaptable, but prefer to be away from humans. (Clark, 250)

12. How the area changed over time
Sedimentary rocks have been making their way into the folded mountains of the
Big Horns by marine intrusions as previously mentioned in the first few
formations. That is how the Big Horns have gained an exciting array of rocks.
These mountain ranges are proven to have rock formations from the Archean
period, like Shell Falls, which constitutes them as being from the Laurasia super
continent (Monroe, 236). The Big Horns are a folded Mountain range which
means a part of the crust folded down which plunged the Lithosphere deep into
the Asthenosphere causing steep mountain ranges (Wyckoff, 197). Also, they
have contained a water gap which allowed water to come in through a cut
(Wyckoff, 113). When the marine layer hightened it would settle on what used to
be a foothill, but what was soon folding to become a mountain range. It is
interesting to see that during different periods, a different sedimentary rock would
settle making a unique formation. This settling came during the time when the
mountain range was beginning to grow, so you can see that the older formations,
500 million years old, are now at the top of the mountain, and the younger
formations, 200 million years old, are at the base.

13. Works Cited
Clark, Tim W., and Mark R. Stromberg. Mammals in Wyoming. Lawrence,Ks: University Press of Kansas,
1987. 250. Print.
Huxley, Anthony. Mountain Flowers in color. New York: The Macmillian Co, 1968. 14-15. Print.
Lane, Donald W. The Phosphora and Goose Egg Formations in Wyoming. Laramie, Wy: State of Wyoming
Geological Survey, 1973. 4-11. WYGS. Web. 21 July 2012. <http://www.wsgs.uwyo.edu/public-
info/onlinepubs/docs/PR-12.pdf>.
Lapinski, Mike. The Elk Mystique. Stevensville, Mo: Stoneydale Press, 1998. 123. Print.
Leopardite and Leopard Rock. Ed. R V. Dietrich. Central Michigan University, 24 June 2005. Web. 18 July
2012. <http://stoneplus.cst.cmich.edu/leopardite.htm>.
Jensen, Earl R. Flowers of Wyoming's Big Horn Mountains. First ed. Basin, Wy: Basin Republican Rustler
Printing, 1987. 147. Print.
Monroe, James S., and Reed Wicander. Historical Geology: Evolution of the Earth and Life through time. San
Francisco: West Publishing, 1989. 236. Print.
Monroe, James S., and Reed Wicander. The Changing Earth: Exploring Geology and Evolution. sixth ed.
Belmont, Ca: Brooks/Cole, 2012, 2009. 237, 238, 479, Print.
Sandro, William J., Mackenzie Gordon, and Thomas J. Dutro. Stratigraphy and geologic history of the
Amsden Formation (Mississippian and Pennsylvanian) of Wyoming. N.p.: U.S. Department of the interior,
1975. A1-A2. Geological Survey Professional Paper. Web. 19 July 2012.
http://books.google.com/books?id=VVNCAAAAIAAJ&printsec=frontcover#v=onepage&q&f=false.
Schweitzer, Peter. Mineral Resources, Chugwater and Goose Egg Formations. USGS, 2012, 2009. Web. 19
July 2012. <http://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=WYTRPcg;0>.
Wyckoff, Jerome. Reading the Earth: Landforms in the Making. New Jersey: World Color Press, 1999. 113-
97. Print.