Geology Lab/Field by Stephanie Rosas

1. Historical Geology:
Western Nevada Region
By Stephanie Rosas

2. Introduction
The following presentation consists of a historical
geological analysis and observations of the
common life forms found in the Western Nevada
Region. In order to collect the data I hiked
various trails located in Nevada, such as the
Moffat Open Space Property in Carson City,
Skunk Harbor in Incline Village, and I drove on
U.S. Highway 50. The life forms presented in this
document is composed of geological formations,
encountered plants and animals that inhabit
these areas, and common rocks found in these
areas. Additionally, an incite of their evolutionary
change will be provided, and identification of
three specific rocks found in the Western Nevada
Region. Lastly, documentation of one of the three
unconformities will be provided, and the
application of one of Steno's Laws and Principles
will be used for relative dating.
Photo taken at Moffat Open Space
Property in Carson City, NV.

3. Geological Background of the Western
Nevada Region
• Granodiorite, granite, and rocks
similar make up the largest group
of granitic intrusions in Nevada,
and are abundant in Western
Nevada. During the Cretaceous
Period, felsic phaneritic intrusive
rocks covered 21% of the surface
of the Western Nevada area
(Crafford 2007).
• The Nevadan orogeny occurred
in the late Jurassic to Cretaceous
phase of the Cordilleran
orogeny, as large volumes of
granitic magma were generated
at depth beneath the western
margin of North America
(Monroe & Wicander 2015:
584).
Photo taken on Highway 50, NV.

4. Conditions and Climate
• Nevada is the third most seismically
active state in the nation. Within the
previous 150 years, about once every
30 years a magnitude 7 earthquake
has occurred along the normal and
strike slip faults in Nevada (Price
2004: 2).
• The ecological regions of Nevada are
directly linked to the climate,
elevations of the mountains, and
rocks. Although Nevada already
possess a dry climate, geologic
evidence, such as fossils, display the
changing climate to even dryer
conditions within the last 10,000
years (Price 2004: 4).
• Some of the volcanic rocks in
western Nevada represent the
precursor of the Cascade Range, and
significant intrusions about 40,100,
and 160 million years ago caused by
plate tectonics (Price 2004: 5).
Photo taken at Moffat Open Space
Property in Carson City, NV.

5. Geologic
Fortunes
• Gold, silver, gypsum, barite, lithium, and mercury are commonly
produced in the state of Nevada. The metals are mainly related to
igneous activity, including major pulses of magma during the Jurassic,
Cretaceous, and Tertiary. Gympsum occurs in sedimentary beds of
Permian, Triassic, Jurassic, and Tertiary age, while barite is uncovered
from sedimentary rocks from the Paleozoic Era (Price 2004).
Photo taken at Skunk Harbor in Incline Village, NV.

6. Basalt Volcanic Igneous Rock
Photos taken at Moffat Open Space
Property in Carson City, NV.
From above.Frontal view

7. Basalt Volcanic Igneous Rock
• Volcanic rocks are a type of igneous rock.
• Volcanic rocks form when lava cools and
solidifies on the Earth's surface (Monroe &
Wicander 2015: 89).
• Overall, the rocks are very dark in color
containing mainly black, gray, and dark
reddish brown shades.
• Basalt is mainly composed of plagopclase
and pyroxene (Monroe & Wicander 2015:
97).
• Based on the small size of the infused
mineral grains, the rate at which the
mineral nuclei formed was produced at a
fast pace, thus resulting in a fine-grained or
aphanitic texture (Monroe & Wicander
2015: 95).

8. Granite Rock with Lichen and
Iron Deposits (Igneous)
Photo taken at Skunk Harbor in
Incline Village, NV.
Zoomed in image

9. Granite Rock with Lichen and Iron Deposits
(Igneous)
• Granite is an igneous rock that is mainly composed of quartz, potassium feldspar, and
plagioclase feldspar; however, small quantities of biotite, muscovite, and hornblende can
also be found (Monroe & Wicander 2015: 62).
• Granite is rich in silica because it is developed within the Earth's crust and crystallizes
from felsic magma. (Monroe & Wicander 2015: 99).
• The image displays a very coarse-grained rock, which is a common texture for
granite rocks. On the bottom and a bit on the side of the rock you can see a pink color
(almost a light salmon color) and very little white. In granite rocks, higher quantities of
potassium feldspar gives the rock a pinkish color. You can also see specks of biotite
infused with the potassium feldspar.
• Covering the rock is a grayish green crust, which is lichen. Lichen grows on exposed,
well lit, and stable surfaces. It is formed from a combination of a fungal partner and an
algal partner, which allow it to grow algal cells and create the lichen's shape (Volk 2006).
• Lastly, on the right corner you can see the formation of iron deposits, which gives the rock
a rusty reddish brown color

10. Volcanic Basalt Rocks Containing
Iron Metal (Igneous)
Photo taken at Moffat Open Space Property in Carson City, NV.
• The rocks are mainly covered in what is
believed to be red iron, which gives them a
rusty appearance.
• Due to the high quantities of visible iron and the
dark color, I believe these igneous rocks are
mafic.
• Additionally, these rocks are more likely to
possess more calcium and magnesium, and
have a lower silica content, which correspond to
its color composition. Basalt is an aphanitic rock
that crystallizes from mafic magma. Igneous
rocks are formed from magma under very high
temperatures (Monroe & Wicander 2015: 89).

11. Volcanic Basalt Rocks
Containing Iron Metal
(Igneous)
Photo taken at Moffat Open Space Property in
Carson City, NV.
• You can see that the dark parts of
the volcanic rock are fine-grained,
so during its development the
mineral nuclei form exceeded the
rate of growth (enduring a rapid
lava flow cooling pace) and
creating an aphanitic texture
(Monroe & Wicander 2015: 96).

12. Artemisia Tridentata-
Sagebrush
Photo taken at Moffat
Open Space Property in
Carson City, NV.
• Sagebrush is so abundant in Nevada
that one of Nevada's nicknames is
“The Sagebrush State.” In fact, the
sagebrush was designated as the
official state flower of Nevada in
1917 (Lavin).
• Sagebrush commonly grows in the
desert and in dry climates, such as
the Western Nevada Region.
• In the image to the right, the
sagebrush is very coarse and
contains greenish-gray and silver
colors.

13. Evolution of Artemisia Tridentata- Sagebrush
• There are about a dozen species of sagebrush whose height can vary from 12 feet to only
a few inches, but the average height reaches up to 3-6 feet (Lavin).
• The ancestors of today's sagebrush species arrived during the Pleistocene in Asia about
2.5 million years ago (Clarke 2016).
• Sagebrush is wind-pollinated meaning that they contain small seed that get dispersed,
which prevents isolated sagebrush populations dying out (Clarke 2016).
• Sagebrush has a surprising amount of biodiversity and is still evolving as the Western
landscape changes. The three subspecies of Artemisia tridentat are Wyomingensis
(Wyoming big sagebrush), Vaseyana (Mountain big sagebrush), and Tridentata (Basin big
sagebrush). Each subspecies has adapted to the environmental conditions in which they
inhabit. Wyomingensis has adapted to the low and arid elevations in the valleys and
mountains, but mainly in dry sites is where they are commonly found. Vaseyana is more
adapted to higher elevations in moist climates, such as on mountain slopes. Tridentata is
the tallest of all and is found on deep, well-drained soils in cool air valleys throughout
western North America. (Clarke 2016).

14. Tamias striatus- Eastern Chipmunk
• Chipmunks belong in the squirrel family,
and split off from mice and rats about 70
million years ago during the Late
Cretaceous Period (Briggs 2016).
• The chipmunk depicted in the images to
the right has a pattern of two dark-light-
dark stripes on its back. In the photo
above you can see that the chipmunk has
light brown fur on the lower part of its
body, a reddish brown head, and a gray-
brown body.
• The stripes located on the chipmunk's
back may have been used as a defense
mechanism to camouflages from
predators, such as birds.
Photos taken at Skunk Harbor in
Incline Village, NV.

15. Evolution of Tamias striatus- Eastern
Chipmunk
• Researchers from the University of Illinois used mitochondrial DNA to trace the genetic
lineage of chipmunk, and discovery show that the majority of the 244 analyzed chipmunks
descended from ancestors who survived the last North American ice age. Over time, these
chipmunks migrated out of the colder region to the south and ended up merging with
chipmunks that migrated into the region from the warmer east and south (Barlow 2004).
• Scientists believe chipmunks evolved their stripes independently. Research shows an
evolutionary change in the chipmunk's genes that caused the skin cells melanocytes to stop
making the dark pigment in a specific area on the chipmunk's back, which instead created a
white stripe. Usually, this gene makes the underside of the chipmunk light in color (Briggs
2016).

16. Sceloporus occidentalis-
Western Fence Lizard
• The reptile depicted in the image is
relatively small estimating a length of 12
cm from the tip of the snout to the end of
the tail. The tail is black in color, the
back is a greenish-gray color, and the
head and limbs are more of a dark gray
color.
• The western fence lizard inhabits a
variety of areas in Washington, Oregon,
Idaho, Utah, California, Arizona, and
nearly all of Nevada (Sceloporus
occidentalis 2007).
• Has adapted to diverse climates and
habitats, such as rocky canyons,
grasslands, forests, woodlands, and
deserts.
Photo taken at Moffat
Open Space Property in
Carson City, NV.

17. Evolution
The earliest amphibians have inherited many characteristics
from the ancestral group of the rhipidistian crossopterygians
(a lobe-finned fish), such as elongated bodies and powerful
fins that many scientist thought could be used for moving on
land during the Late Paleozoic, which allowed amphibians
to evolve (Monroe & Wicander 2015: 558). Amphibians
were the first vertebrates to live on the land, so their
transition from the water to terrestrial indicates that they had
to adapt to a drier atmosphere. The oldest amphibians were
found in the Upper Devonian Old Red Sandstone of eastern
Greenland. Many of these findings possessed four legs, a
rib cage, long tails, fins along their back, and pelvic and
pectoral girdles (Monroe & Wicander 2015: 560). These
characteristics are structural adaptations for walking on
land. Fortunately, the evolution of the amniotic egg allowed
vertebrates to transition from aquatic to terrestrial
inhabitants, which permitted reptiles to evolve. The
diversification of reptiles began during the Permian Period.
Reptiles produced a tougher skin and scales which
prevented desiccation and extended their time in terrestrial
areas (Monroe & Wicander 2015: 562).
Photo taken at Moffat Open Space Property in
Carson City, NV.

18. Disconformity
Photo taken by
DronePromotions at
US 50 Glenbrook, NV.
• The image of Cave
Rock illustrates the
separation of younger
rocks from older rocks
that are parallel from
one another.
• Disconformity often
resembles an ordinary
bedding plane (Monroe
& Wicander 2015:
424).

19. Steno's Laws and Principles
• The principle of cross-cutting
relationships can be applied to the
image due to the fault cutting
across the sequence of rock.
According to the cross-cutting
principle, faults can be used for
relative dating, in fact the fault is
younger than the rocks it cuts
(Monroe Wicander 2015: 419).
• The image also displays an
example of angular unconformiy.
The rocks are tilting at an angle to
the right as they continue
developing in an upward direction.
• You can also locate the key bed
which has been offset by the fault.
The hanging wall has moved
downward making this a normal
fault, which is why you can see the
fault scarp. Normal faults occur in
response to tensional stress and
tend to occur at or near divergent
tectonic plate boundaries (Monroe
& Wicander 2015: 244- 245).
Photo taken at Moffat Open
Space Property in Carson
City, NV.

20. Angular
Unconformity
Fault scarp

21. References
Barlow, J. (2004, July 12). Chipmunks descended from ancestors that survived last ice age,
scientists say. Retrieved June 10, 2018, from https://news.illinois.edu/view/6367/207561
Briggs, H. (2016, November 02). DNA clues to how chipmunk earned its stripes. Retrieved June 10,
2018, from https://www.bbc.com/news/science-environment-37828673
Clarke, C. (2016, March 28). An Introduction to Desert Sagebrush and its Evolution. Retrieved June
10, 2018, from https://www.kcet.org/redefine/an-introduction-to-desert-sagebrush-and-its-
evolution
Crafford, E. J. (2007). Geologic units in Carson City county, Nevada. Retrieved June 8, 2018, from
https://mrdata.usgs.gov/geology/state/fips-unit.php?code=f32510
DronePromotions (2015, July 16). Cave Rock, Zephyr Cove, Nevada. Retrieved June 21, 2018,
from http://www.dronestagr.am/cave-rock-zephyr-cove-nevada/
Lavin, M. (n.d.). Sagebrush. Retrieved June 10, 2018, from https://statesymbolsusa.org/symbol-
official-item/nevada/state-flower/sagebrush

22. References
Monroe, J. S., & Wicander, R. (2015). The Changing Earth: Exploring Geology and
Evolution. Stamford, CT: Cengage Learning.
Price, J. G. (2004). Nevada Bureau of Mines and Geology. Retrieved June 8,
2018,from www.nbmg.unr.edu/_docs/GeologyOfNevada.pdf
Sceloporus occidentalis . (2007). Retrieved June 14, 2018, from
http://bioweb.uwlax.edu/bio203/f2013/hopkins_cien/habitat.htm
Volk, T. (2006). Lichens: Life History & Ecology. Retrieved June 8, 2018, from
http://www.ucmp.berkeley.edu/fungi/lichens/lichenlh.html
*All photos taken by the author, Stephanie Rosas, except for the image of Cave Rock.*