Geo 103 lab field assignment

1. Geology of Lake Tahoe
Caleb Smith
Geo 103

2. Introduction
This assignment identifies various natural and geologic features and
characteristics of the Lake Tahoe area. I gathered the information and data in
this assignment by performing research online, and from experiences that I
have had hiking and exploring Lake Tahoe Wilderness areas.

3. Formation of Lake Tahoe
• Long believed to be formed by a volcanic crater
collapsing, Lake Tahoe was formed by the rise
and fall of the landscape due to faulting
• Lave flowing from Mt. Pluto on the north shore
created a barrier at the Truckee river when
streams and snowfall filled the lake bed to
much greater heights.
• During the Pleistocene, large glaciers formed
and carved the western slopes, leaving
distinctive U-shaped valleys and bays on the
western shore
(USDA, N.D.)

4. Facts about Lake Tahoe
• 3rd deepest lake in North America, 10th deepest lake in the world
• 22 miles long, 22 miles wide
• Approximately 72 miles of shoreline
• Greatest measured depth is 1,645 ft.
• Bottom of the lake is actually lower than Carson Valley floor.
(USDA, N.D.)

5. Mount Tallac
• Elevation of 9,735 ft.
• Situated on the boundary between the granites of the Sierra Nevada
Batholith and earlier metamorphosed sedimentary rocks
• Known for the distinctive “cross” shape that faces towards the lake.
• “Tallac” is derived from the Washoe word meaning, “big mountain.”
(Summitpost, N.D.)

6. North American Beaver
• Almost hunted into extinction by early American settlers, the North American Beaver population is
currently stable, but it very elusive.
• Largest rodent in the United States
• Known best for it’s long, flat, black tail that is used to slap the water to alert other beavers of nearby
predators, and for balance.
• They have waterproof fur, webbed feet, and teeth that continually grow. Gnawing on trees shortens
their teeth, and many layers of protective enamel give them an orange color
• Beavers are known for the ability to build dams that extend underwater and have the potential to
change the surrounding landscape.
• Beavers are monogamous and mate around 3 years of age.
• Beavers can hold their breath underwater for 15 minutes and have transparent eyelids that allow them
to see underwater.
(National Wildlife Federation, N.D.)

7. Where did beavers evolve from?
• North American Beaver (Castor
Canandensis) evolved from the
European Beaver (Castor Fiber)
when they migrated to North
America From Asia 7.5 million
years ago
• Giant beavers known as
Castoroides existed in North
America during the Pleistocene
and were about twice the size of
beavers today
(Jorgensen, 2015)

8. Snow Plant (Sarcodes Sanguineae)
• Belongs to the Monotropaceae family
• Sarcodes Sanguineae is mycotrophic (has no
clorophyll) and get their nutrition from fungus
underneath the soil.
• This plant has a “parasitic” relationship with
conifers, providing water and minerals while
taking photosynthates from the mychorrhizae
(fungus roots) of the conifers.
(Guana, N.D.)

9. Igneous Granite
• Granite is an igneous rock type
• It is an intrusive igneous rock that formed
deep under the earther’s crust from
cooling magma
• Granite is commonly found in the areas
surrounding Lake Tahoe
• Granite contains mostly feldspar, but also
contain quartz and other minerals
(Encyclopedia Britannica, 2019)

10. Igneous Basalt
• Basalt is an Extrusive Igneous rock that
is formed from lava that reaches the
surface and then cools
• These rocks were formed by magma
from erupting volcanoes during the
Pleistocene.
• Basalt is typically low in silica and rich in
iron and magnesium.
(Encyclopedia Britannica, 2019)

11. Metamorphic gneiss
• Gneiss is a Metamorphic type rock
• Gneiss has well-developed foliation and
poorly developed cleavage and schistosity
• Gneiss typically displays parallel, somewhat
irregular banding which has little tendency to
split along planes.
(Encyclopedia Britannica, 2019)

12. Unconformities
• Cave rock is an example of an
Unconformity in Lake Tahoe
• You can observe the different
layers or strata as they are
layered

13. Law of Superposition
• Eagle Lake Buttress is an
example of the Law of
Superposition.
• The law of superposition states
that in a sequence of layered
rock, the younger rocks lies on
top of the older rocks.
• This is a principle that is applied
when it comes to relative dating

14. References
• U.S. Department of Agriculture. (N.D.) Geology of the Lake Tahoe Basin. Retrieved from https://www.fs.usda.gov/detail/ltbmu/learning/?cid=stelprdb5109570
• Guana, F.J. (N.D.) Snow Plant. Retrieved from: https://www.fs.fed.us/wildflowers/plant-of-the-week/sarcodes_sanguinea.shtml
• SummitPost. (2019). Mount Tallac. Retrieved from: https://www.summitpost.org/mount-tallac/150430
• National Wildlife Federation. (N.D.) American Beaver. Retrieved from: https://www.nwf.org/Educational-Resources/Wildlife-Guide/Mammals/American-Beaver
• Jorgensen, D. (2019). On the origins of the beaver. Retrieved from: http://dolly.jorgensenweb.net/nordicnature/?p=2099
• Editors of the Encyclopedia Britannica. (2019). Granite. Retrieved from: https://www.britannica.com/science/granite
• Editors of the Encyclopedia Britannica. (2019) Basalt. Retrieved from: https://www.britannica.com/science/basalt
• Editors of the Encyclopedia Britannia. (2019) Gneiss. Retrieved from: https://www.britannica.com/science/gneiss