Geology 103 Lab/Field Assignment 2020

1. Lake Tahoe Basin
Field Assignment
Presentation by Patricia Frega
Geology 103-01
Lab/Field Assignment

2. IntroductionThis presentation is broken down into three parts. In the
first section, the evolutionary and geologic history of flora
and fauna found in the Tahoe Basin will be examined.
Although there are a plethora of geologic formations, as well
as plant and animal species that are found in the Lake Tahoe
region, those that will be focused on include Glen Alpine
Falls, the coyote, and the Jeffrey Pine Tree. Part two will
include the examination and explanation of three different
rock types that were found either at Glen Alpine Falls or the
South Upper Truckee River. The final section will look to
identify a possible unconformity found in the basin, as well
as an explanation of the given unconformity and reasoning
for why assigning relative dating principles to formations in
the Tahoe basin is challenging. All areas discussed in this
presentation were personally documented in various
locations around South Lake Tahoe during the summer of
2020.
Geologic Map of Lake Tahoe and Surrounding Terrain
(Lake Tahoe 3-D, n.d.)

3. Background Information: The Formation of the Tahoe Basin
➢ The Sierra Nevadas are composed of tectonically
accreted terranes from both the Paleozoic and
Mesozoic Eras.
➢ During the Jurassic and early Cretaceous the
volcanic arc produced much of the granitic
batholiths common in the area.
➢ The Laramide Orogeny is responsible for the uplift
of the Sierra Nevadas in Northern California
○ This lifting caused higher elevation than is seen today.
○ (UCMP Faculty, n.d.)
➢ The Tahoe Basin was formed due to faulting which
resulted from the rise and fall of the landscape.
➢ Lava excreted from Mt. Pluto created a barrier for
the Truckee River
➢ Snowfall and steams allowed for water build up
○ Resulted in a lake that was hundreds of feet higher
than the present (Geology of the Tahoe Basin, n.d).
➢ During the Ice Age, glaciers carved parts of the
basin, creating a U-shaped valley
○ The result was the formation of Emerald Bay, Cascade
Lake, Fallen Leaf Lake, and Echo Lake. (Lake Tahoe,
n.d.)
The Sierra Nevada Mountain Range The Tahoe Basin
(Sunrise Sunset, n.d.)
Aerial View of
Tahoe Basin from
Carson City:

4. Part 1: Evolutionary and Geologic History of
Tahoe’s Flora and Fauna

5. Geologic Formation: Glen Alpine Falls
➢ General Description
○ 73 foot tall cascade
○ Classified as a steep tiered cascade
○ Drainage into Fallen Leaf Lake
○ Due to lack of soil, watershed is dependent of snow
accumulation and precipitation
■ (Glen Alpine Falls, 2019)
➢ Formation
○ Glen Alpine Falls was formed by the same geologic
event that formed Fallen Leaf Lake below.
■ Fallen Leaf Lake was formed by glacial moraines
during the Pleistocene.
■ Thick icefields covered the terrain from Fallen
Leaf Lake through Desolation Wilderness
● These icefields resulted in glaciers flowing
down the valley creating numerous smaller
lakes and falls, including Glen Alpine Falls
○ (Konigsmark, n.d.)
Glen Alpine Falls
(Frega,2020)

6. Animal: North American Coyote
➢ General Description
○ Diet: carnivorous
■ feeds on rabbits, rodents, birds, amphibians, reptiles,
fish, and carrion
○ Habitat: open grassland, but are known to travel with food source
○ Size: Males average a weight of 9-23 kilograms, a length of
120-150 centimeters, and a height of 58-66 centimeters;
females average approximately ¼ of the size of males
➢ Evolution
○ The North American coyote, also known as Canis Latrans, is a
member of the genus Canis that makes up the taxonomic family
of Canidae
○ Evolved approximately 40 million years ago from Miacis during
the Eocene-Oligocene transition
■ From the Miacis, the Daphaenus and the Cynodictis
evolved
● From these two groups evolved the Tomarctus
○ From the Tomarctus evolved the
Canidae, and therefore, the North
American coyote (Kim, 2001)
Evolution of the Coyote
Miacis:
Daphaenus Cynodictis
Tomarctus
North American Coyote
(Silver, 2013)
(Library, n.d.)
(Daphoenodon, 2019)
(Strauss, n.d.)
(Breeding Business et al., 2020)

7. Plant: Jeffrey Pine
➢ General Description
○ Also known as Pinus jeffreyi
○ Approximate lifespan of 400-500 years
○ Grow 4-6 ft in diameter and 170-200 feet tall
○ Characterized by their needles, which bundle in
threes, and their cones, which are oval and lack
spines
○ Primarily found in California
■ (Moore, 2006)
➢ Evolution
○ The earliest signs of pine evolution can be traced
back to the Laurasian supercontinent
■ The success of pine spread is due to
limited concentration of angiosperms
○ This thick bark associated with this genus is
thought to be associated with fire adaptation
during the Cretaceous
○ During the Eocene, tropical angiosperms
displaced pines due to warmer climate
○ By the Oligocene, arid conditions caused the loss
of angiosperm, and in turn led to the
reemergence of pine.
■ (Kelly, 1998)
Jeffrey Pines Found Near Tahoe Valley
Area
Jeffrey Pines Located Near South
Upper Truckee River
(Frega,2020)
(Frega,2020)

8. Part 2: Rock Identification
Igneous-Basalt Igneous-Granite Sedimentary-Conglomerate
*all photos taken by Patricia Frega

9. Igneous Rock: Basalt
➢ Basalt was found at Glen Alpine Falls
➢ What is Basalt?
○ Basalt is a igneous rock that is dark in color
○ Rich in iron and magnesium
○ Two classification groups:
■ Tholeiitic Basalts
● Contain 45-65% silica
● Found among lava of mountain belts
○ Common in the northwestern United States
○ This is likely to be the basalt found at Glen
Alpine Falls
■ Alkali Basalts
● Contain olivine and a diopsidic or titanidous augite
● Found among lava of ocean basin
○ (The Editors of Encyclopedia Britannica,
2015).
➢ Why is this sample Basalt?
○ In a continental environment, basalt forms through volcanic eruptions
from both vents and fissures (King, n.d).
○ Conditions such as these took place during the formation of the Tahoe
Basin
Basalt Located at Glen Alpine Falls
(Frega, 2020)

10. Igneous Rock: Granite
➢ Granite was found at Glen Alpine Falls
➢ What is Granite?
○ Granite is an igneous rock that is light in color
○ Contains large grains
○ It is formed from the slow crystallization of magma
○ Granite is made of mainly quartz, feldspar, and mica
○ It is the most common igneous rock to be found on
Earth’s surface
■ (King, n.d.)
➢ Why is this sample Granite?
○ Most of the granite displaced in the Sierra Nevadas
occurred during the Jurassic and Cretaceous Periods
(Granite, n.d).
■ This is also the time when volcanic activity in
the Tahoe Basin produced granitic batholiths
(UCMP Faculty, n.d.).
Granite Located Near Glen Alpine Falls
(Frega, 2020)

11. Sedimentary Rock:
Conglomerate
➢ Conglomerate was found near the South Upper Truckee River
➢ What is a Conglomerate?
○ A conglomerate is a clastic sedimentary rock with a
concrete appearance with multiple sized clasts imbedded
in it.
■ Clasts can be any rock that had been washed
downstream
■ The clasts are bound together by a combination
of sand, mud, and chemical cement
➢ Why is this sample a Conglomerate?
○ Conglomerates are commonly formed where strong water
current exists
○ They are normally present “at the base of sequences laid
down during marine transgressions”
○ Given that this conglomerate was found on the river bed
of the South Upper Truckee River, it indicates that the
river used to have a higher shoreline.
■ (Geology Science, 2019).
Conglomerate Located Near South Upper Truckee River
(Frega, 2020)

12. Part 3: Relative Dating
Steno’s Laws and Principles
Unconformities
1) Principle of Superposition
a) holds that the relative dating of sedimentary rock layers is a succession from oldest nearing the bottom and youngest on
top of a given strata.
2) Principle of Inclusion
a) Holds that fragments of rock in a given unit are older than the unit itself
3) Principle of Lateral Continuity
a) Holds that sediment expands laterally, thinning in all directions
4) Principle of Cross-Cutting Relationships
a) Holds that an igneous intrusion is younger than the unit that it intrudes on
5) Principle of Original Horizontality
a) Sediment is deposited in horizontal layers
6) Principle of Fossil Succession
a) Fossils found nearer the bottom of a strata are older than those nearing the top
1) Disconformity
a) A surface of erosion or nondeposition dividing older and younger rock units
2) Angular Unconformity
a) An erosional surface on tilted or folded strata where younger rock units are deposited above.
3) Nonconformity
a) An erosional surface that cuts into metamorphic or igneous rock which is then covered by sedimentary rock
(Monroe & Wicander, 2015)

13. Angular Unconformity:
Echo Summit➢ What is an Angular Unconformity?
○ An angular unconformity occurs when an
erosional surface occurs on folded or tilted strata.
Erosion is then covered with younger stata
(Monroe & Wicander, 2015).
➢ Why does Echo Summit contain this unconformity?
○ In this location on Echo Summit, tilted strata is
apparent.
○ Erosion takes place water, wind, and ice (National
Geographic Society, 2012).
■ Given the way in which the Tahoe Basin
was formed, glaciers, and the weathering
that occurs in this region, it is not unlikely
that an erosional surface is present.
○ It should be noted that I was unable to identify if
younger strata was present above the erosional
surface. (Frega, 2020)
Angular Unconformity Diagram
Angular Unconformity
on Echo Summit(Unconformities, n.d.)

14. Difficulty Identifying A Relative Dating Principle
Due to much of the Sierra Nevada’s, including the Tahoe Basin, being composed of primarily granitic rocks, the following
principles would be difficult to identify as they rely on sedimentary rocks
Steno’s Laws That Are Unlikely To Be Found in the Tahoe Basin
Steno’s Laws That Would be Difficult to Identify
I. Principle of Superposition
II. Principle of Lateral Continuity
III. Principle of Original Horizontality
The remaining 3 principles that have a greater likelihood of being located around the basin also have reasons for why they may
be difficult to locate.
I. Principle of Inclusion
A. This principle holds that fragments of rock in a given strata are older than the strata itself (Monroe & Wicander,
2015). I was able to find this principle on a small scale with the conglomerate that I encountered at the South
Upper Truckee River. With this being said, this was the only place that I encountered this principle.
II. Principle of Cross-Cutting Relationships
A. Since this principle relies on igneous rocks, which the Tahoe Basin has an abundance of, intruding on older strata,
this principle is more likely to be found in the Basin. With this being said, through my observations, most of the
rock units that I encountered were uniform and no intrusions were visible.
III. Principle of Fossil Succession
A. Although there is the possibility of one coming across a fossil in the Tahoe Basin, this occurrence is extremely
rare. In fact, less that 1/10 of 1% of all species that have ever existed have fossilized (Pickrell, 2018). Also, through
only making observations around the Tahoe Basin, I did not have the resources to provide evidence of this
principle in the environment.

15. References
Breeding Business, Khalil, Viena, Says:, D., Says:, R., Jay, & Leonardo. (2020, June 12). Origins & Evolution Of The Dog (Generation After
Generation). Retrieved August 06, 2020, from https://breedingbusiness.com/origin-and-evolution-of-the-domestic-dog/
Daphoenodon. (2019, July 10). Retrieved August 06, 2020, from https://en.wikipedia.org/wiki/Daphoenodon
Geology of the Lake Tahoe Basin. (n.d.). Retrieved August 05, 2020, from
https://www.fs.usda.gov/detail/ltbmu/learning/?cid=stelprdb5109570
Geology Science. (2019, May 21). Conglomerate: Properties, Composition, Classification, Formation, Uses. Retrieved August 05, 2020,
from https://geologyscience.com/rocks/sedimantery-rocks/conglomerate/
Glen Alpine Falls, California, United States - World Waterfall Database. (2019). Retrieved August 06, 2020, from
https://www.worldwaterfalldatabase.com/waterfall/Glen-Alpine-Falls-6683
Granite. (n.d.). Retrieved August 05, 2020, from https://www.nps.gov/yose/learn/nature/granite.htm
Kelly, J. (1998, January 01). Ecology and evolution of pine life histories. Retrieved August 07, 2020, from
https://link.springer.com/article/10.1007/s13595-012-0201-8
Kim, E. (2001). The Biogeography of The North American Coyote (Canis latrans). Retrieved August 06, 2020, from
http://online.sfsu.edu/bholzman/courses/Fall01%20projects/coyote.htm

16. References Continued...
King, H. (n.d.). Basalt. Retrieved August 05, 2020, from https://geology.com/rocks/basalt.shtml
King, H. (n.d.). Granite. Retrieved August 05, 2020, from https://geology.com/rocks/granite.shtml
Konigsmark, T. (n.d.). Geologic Trips, Sierra Nevada. Retrieved August 06, 2020, from http://www.geologictrips.com/sn/snttlt.pdf
Lake Tahoe 3-D shaded relief [POSTER AND 3-D GLASSES]. (n.d.). Retrieved August 05, 2020, from
https://pubs.nbmg.unr.edu/Lake-Tahoe-3-D-shaded-relief-p/sp028.htm
LAKE TAHOE INFO and FACTS: Lake Tahoe Basin Geology. (n.d.). Retrieved August 05, 2020, from
http://www.tahoecam.com/tahoefacts.html
Library, M. (n.d.). Miacis, illustration - Stock Image - C037/5120. Retrieved August 06, 2020, from
https://www.sciencephoto.com/media/888490/view/miacis-illustration
Monroe, J. S., & Wicander, R. (2015). Geologic Time: Concepts and Principles. In The changing earth: Exploring geology and evolution.
Stamford, CT: Cengage Learning.
Moore, L. M. (2006, June 22). Jeffrey Pine. Retrieved August 04, 2020, from https://plants.usda.gov/plantguide/pdf/pg_pije.pdf

17. References Continued...
National Geographic Society. (2012, October 09). Erosion. Retrieved August 07, 2020, from
https://www.nationalgeographic.org/encyclopedia/erosion/
Pickrell, J. (2018, February 15). How can I become a fossil? Retrieved August 08, 2020, from
https://www.bbc.com/future/article/20180215-how-does-fossilisation-happen
Silver, D. (2013, August 20). Officials warn of coyotes' danger to pets. Retrieved August 06, 2020, from
https://www.tahoedailytribune.com/news/local/officials-warn-of-coyotes-danger-to-pets/
Strauss, B. (n.d.). Cynodictis Facts. Retrieved August 06, 2020, from https://www.thoughtco.com/cynodictis-in-between-dog-1093069
Sunrise Sunset Times of Mount Siegel, Mt Siegel, Nevada, USA. (n.d.). Retrieved August 05, 2020, from
https://sunrise.maplogs.com/mount_siegel_mt_siegel_nevada_usa.3289.html
The Editors of Encyclopaedia Britannica. (2015, July 05). Basalt. Retrieved August 05, 2020, from https://www.britannica.com/science/andesite
UCMP Faculty (n.d.). A supplement to Paleobotany field trip to the Sierra Nevada. Retrieved August 05, 2020, from
https://ucmp.berkeley.edu/science/profiles/erwin_0609geology.php
Unconformities. (n.d.). Retrieved August 07, 2020, from https://geol105b.sitehost.iu.edu/images/gaia_chapter_6/unconformities.htm