Field assignment for Mark Lawler's geology class at LTCC.

1. GEOLOGY:
Geology 103
Field Assignment
Erin Yamaoka
A Study of the Tahoe Basin

2. INTRODUCTION
I did my field/lab assignment here in the Tahoe basin. A
majority of the rocks I found/pictures I took are from Fallen
Leaf Lake. I also took pictures in the meadow behind my
house, off of North Upper Truckee road, as well as in my
backyard. This assignment consists of the evolution of three
species: the black bear (Ursus americanus), the Sierra
shooting star (Primula jeffreyi), and the western fence lizard
(Sceloporus occidentalis). I also classify three types of rock:
granite, greenstone, and quartzite. Finally, I give an example of
a nonconformity and of Steno’s principle of original
horizontality.

3. Lake Tahoe Geologic
History
● The Cordilleran mobile belt
underwent multiple
mountain-building episodes during
the Jurassic (Monroe & Wicander,
2015)
○ The Nevadan orogeny in the
Late Jurassic created the
enormous granitic batholiths
that are now the Sierra Nevada
(Monroe & Wicander, 2015)
● The uplifting of Carson Range
eastern fault and Sierra Nevada
western fault 24 million years ago
created Sierra Nevada Block, which
sank, creating a valley (Geology of,
n.d.)

4. Lake Tahoe History (Cont.)
● Tahoe’s ancestral Truckee river outlet was blocked by lava, allowing
water to accumulate in a lake “several hundred feet higher than the
present lake” (Geology of, n.d., para. 3)
● A new outlet would erode from the dam to create the current Lower
Truckee River (Geology of, n.d.)
● U-shaped valleys formed as a result of glaciers moving down western
side of lake (Geology of, n.d.)
● As glaciers melted, the bays, ridges, peaks, and clear lakes, all distinct
features of the Tahoe basin, formed (Geology of, n.d.)

5. ● Long, narrow leaves at its base
● Flowers hang down from stem, with
“4-5 backwards-swept petals”
connected at stamen tube (Fretwell
& Starzomski, 2013, para. 1)
● Stamen point out below the tube
● Flowers contain pollen, but not
nectar (Shooting star, n.d.)
● Found in wetter areas, such as
meadows and near streams
(Fretwell & Starzomski, 2013)
Sierra Shooting Star
Primula jeffreyi (sometimes called Dodecatheon
jeffreyi)
A shooting star plant found in the
meadow behind my house.

6. EVOLUTION
● Angiosperms first appeared during the Early Cretaceous (Monroe
& Wicander, 2015)
● Diversification of angiosperms occurred during middle
Cretaceous along with diversification of pollinators (Evolution of,
n.d.)
○ For Primula jeffreyi, as well as other species of Shooting Star,
the shape of the flower allows for “buzz pollination”,
indicating the occurrence of coevolution (Shooting star, n.d.)
○ Also indicates convergent evolution, as other families of
flowers adopted similar shape of flower to allow for “buzz
pollination” (Shooting star, n.d.)

7. ● While they are “black bears”, they
vary in color, from black to
cinnamon to white (Black bear, n.d.)
● Shorter, narrower, and curved claws
allow for easy tree climbing
(Herrero, 1972)
● Classified as carnivores, but have an
omnivorous diet (Black bear, n.d.)
● Hibernate during winter
● Smaller territory ranges where food
is more prevalent (Black bear, n.d.)
Black Bear
Ursus americanus
A black bear I saw while at Fallen
Leaf Lake.

8. EVOLUTION
● Cynodonts mark the evolution between reptiles and mammals during the Late
Triassic (Monroe & Wicander, 2015)
● Fossils of the Ursaine line appear in fossil record by the lower Miocene (Herrero)
● The Auvergne bear, Ursus minimus, appears in fossil record in Europe, around
the upper Pliocene (Herrero, 1972)
○ Marks origin of Ursus genus
○ Small, but “anatomically it resembled the black bears” (Herrero, 1972, para.
8)
○ Adapted to forest life and was omnivorous (Herrero, 1972)
● The Auvergne bear was replaced by the Etruscian bear, Ursus etruscus, during
lower Pleistocene (Herrero, 1972)
○ The “nucleus” of Ursus genus, as rapid evolution occurred after the
Estrucian bear as a result of rapid climate changes during the Pleistocene
(Herrero, 1972)
○ Also a forest adapted type (Herrero, 1972)

9. EVOLUTION (CONT.)
● Asiatic black bear, Ursus thibetanus, was one of the evolutionary
lines from Estrucian (Herrero, 1972)
○ Similar to the Estrucian bear, unlike other evolutionary lines
from Estrucian, which adapted to the tundra and treeless
conditions of the Pleistocene (Herrero, 1972)
● During the Mindel Glacial stage, Asiatic black bears had entered
North America (Herrero, 1972)
● Ursus americanus represents the evolutionary line of bears that
stayed adapted to a forest biome, not adapting to the barren
climate as a result of the Ice Age (Herrero, 1972)

10. ● Colors range from brown to grey (James,
2014)
● They are well-known for their distinguished
blue underbellies and throats (James, 2014)
● Are considered “spiny lizards” due to their
pointy scales (James, 2014)
● Diet is primarily insects (James, 2014)
● Sharp claws allow for climbing (James, 2014)
● Live in variety of habitats, from forests to
grasslands (James, 2014)
Western Fence Lizard
Sceloporus occidentalis
A western fence lizard that lives in
my backyard.

11. EVOLUTION
● Fossil skeletons, most famously, fossil skeleton of Westlothiana (oldest
known reptile) indicates evolution of reptiles by Late Mississippian
(Monroe & Wicander, 2015)
● Megachirella wachtler is the oldest lizard fossil found, marking the origin
of lizards, dating back to around the end of the Paleozoic (Simões, 2018)
● Fossil record of N. America first shows lizards in the Mesozoic (Scarpetta,
et al., 2020)
● Fossils of Sceloporus occidentalis found in California, dating back to
Pleistocene Epoch (Bell & Price, 1996)
● Among Sceloporus occidentalis, evolution occurs in response to
environmental changes
○ For example, in Yosemite, Sceloporus occidentalis located in higher
elevations seem to be darker-colored as a response to “more
challenging thermal environments” (Leaché et al., 2010, para. 24)

12. 01
GRANITE
The image on the right
depicts granite rock found
in the lot next to my house.

13. Characteristics/Formation
● An intrusive igneous, coarse-grained rock (Granite, n.d.)
● Formed by the cooling of magma below the surface (Monroe &
Wicander, 2015)
○ For the rock in the previous slide, large amounts of granite
generated beneath the western margin of North America
resulted in the huge granitic batholiths composing Sierra
Nevada (Monroe & Wicander, 2015)
● Mainly composed of feldspar (Granite, n.d.)
○ Plagioclase feldspar and alkali feldspar are both prominent in it,
but in Tahoe, plagioclase feldspar is most prominent in granite
(Granite, n.d.)
● Over 20 percent quartz
● Less than 20 percent of granite accounts for darker minerals, such as
muscovite, biotite, amphibole, or pyroxene (Granite, n.d.)

14. 02
GREENSTONE
The image on the right depicts
what I believe is greenstone found
on the western shore of Fallen Leaf
Lake, just north of Stanford camp.

15. ● Metamorphic rock formed
by “low grade regional
metamorphism along a
convergent plate
boundary” (Greenstone,
n.d.)
● Composed of epidote and
chlorite (Greenstone, n.d.)
● Formed from basalt and
mafic igneous rocks
(Greenstone, n.d.)
● Fine-grained, non-foliated
to weakly-foliated texture
(Greenstone, n.d.)
Characteristics and
Formation
● Olive green color as well as
texture is nearly identical to
example of greenstone
provided by East Carolina
University
● The specific area where I
found the rock is one of the
only places in the Tahoe basin
to find types of metavolcanic
rock, including greenstone
(Fram & Levy, 2021)
● The same area has serpentine,
another metavolcanic rock,
which also forms at
convergent plate boundaries
(Fram & Levy, 2021)
Reasoning to my
classification

16. 03
QUARTZITE
The image on the right depicts what I
believe is quartzite found at Sawmill
Cove at Fallen Leaf Lake.

17. Characteristics/Formation
● Metamorphic rock that forms when quartz-rich sandstone is metamorphosed
(KIng, n.d.)
○ Sand grains and silica cement is recrystallized, making strong interlocked
quartz grains (King, n.d.)
● Composed almost entirely of silicon dioxide (Helmenstine, 2019)
● Has a “grainy surface with a sandpaper texture” (Helmenstine, 2019, para. 1)
○ Perfectly describes the texture of the quartzite in the image in the
previous slide
● Like greenstone and serpentinite, quartzite forms at convergent plate
boundaries
○ During mountain-building events, sandstone is deposited on a
continental plate and transformed into quartzite through metamorphic
processes (King, n.d.)
● Color is usually white or gray, but can range from a variety of colors due to
impurities or stains from iron (King, n.d.)

18. “A sequence of sedimentary
rock layers that is steeply
inclined from the horizontal
must have been tilted after
deposition and lithification”
(Monroe & Wicander, 2015, p.
419).
STENO’S PRINCIPLE OF
ORIGINAL HORIZONTALITY
This picture was also taken at the western shore of
Fallen Leaf Lake, north of Stanford Camp (same as
the greenstone).

19. NONCONFORMITY
“An erosional surface cut into metamorphic or igneous rocks is
covered by sedimentary rocks” (Monroe & Wicander, 2015, p. 427).
This picture was
also taken at the
western shore of
Fallen Leaf Lake,
north of Stanford
Camp (same as the
greenstone and
demonstration of
Steno’s principle of
original
horizontality).

20. References
Bell, E.L., & A.H. Price. (1996). Sceloporus occidentalis. Catalog of American Amphibians and Reptiles,
631.1-631.17.
https://repositories.lib.utexas.edu/bitstream/handle/2152/44822/0631_Sceloporus_occidentalis.pdf?se
quence=1&isAllowed=y
Black bear. (n.d.). Britannica School. https://school.eb.com/levels/high/article/black-bear/15468
Evolution of seed plants. (n.d.). Lumen.
https://courses.lumenlearning.com/boundless-biology/chapter/evolution-of-seed-plants/
Fram, M. S., & Levy, Z. F. (2021, May). Geologic influences on the quality of groundwater used for domestic
supply in the Northern Sierra Nevada foothills. United States Geological Survey.
https://pubs.usgs.gov/fs/2021/3013/fs20213013.pdf

21. References
Fretwell, K., & Starzomski, B. (2013). Tall mountain shootingstar, jeffrey's shootingstar, sierra shootingstar •
Dodecatheon jeffreyi, dodecatheon jeffreyi ssp. jeffreyi. Biodiversity of the Central Coast.
https://www.centralcoastbiodiversity.org/tall-mountain-shootingstar-bull-dodecatheon-jeffreyi.html
Geology of the Lake Tahoe Basin. (n.d.). United States Department of Agriculture.
https://www.fs.usda.gov/detail/ltbmu/learning/?cid=stelprdb5109570
Granite. (n.d.). Britannica School. https://school.eb.com/levels/high/article/granite/37718
Greenstone. (n.d.). East Carolina University. https://geology.ecu.edu/geol1501/metamorphic/greenstone/
Helmenstine, A. M. (2019, March 15). Quartzite rock geology and uses. ThoughtCo.
https://www.thoughtco.com/quartzite-rock-geology-and-uses-4588608

22. References
Herrero, S. (1972). Aspects of Evolution and Adaptation in American Black Bears (Ursus americanus Pallas)
and Brown and Grizzly Bears (U. arctos Linné.) of North America. Bears: Their Biology and
Management, 2, 221-231. https://www.bearbiology.org/wp-content/uploads/2017/10/Herrero.pdf
James, M. (2014). Western Fence Lizard. Friends of Edgewood.
https://friendsofedgewood.org/western-fence-lizard
King, H. M. (n.d.). Quartzite. Geology. https://geology.com/rocks/quartzite.shtml
Leaché, A. D., Helmer, D., & Moritz, C. (2010). Phenotypic evolution in high-elevation populations of western
fence lizards (Sceloporus occidentalis) in the Sierra Nevada Mountains. Biological Journal of the
Linnean Society, 100(3), 630–641. https://doi.org/10.1111/j.1095-8312.2010.01462.x

23. References
Monroe, J. S., & Wicander, R. (2015). The changing earth: Exploring geology and evolution (7th ed.). Cengage
Learning.
Scarpetta, S., Ledesma, D., Llauger, F., & White, B. (2020, December). Evolution of North American Lizards.
ResearchGate.
https://www.researchgate.net/publication/348072039_Evolution_of_North_American_Lizards
Shooting star. (n.d.). Illinois Wildflowers. https://www.illinoiswildflowers.info/prairie/plantx/shootingstarx.htm
Simões, T. R. (2018, June 1). Bridging the gap on the origin of lizards. Nature.
https://natureecoevocommunity.nature.com/posts/33764-bringing-balance-to-the-force-morpholog
y-and-molecules-along-with-fossil-data-coming-to-agreement-on-the-origin-of-lizards