The document summarizes Kate Albrecht's 2012 geology field assignment to the south shore of Lake Tahoe. It describes the geologic history of how the Lake Tahoe basin was formed by faulting over millions of years. It discusses specific locations like Cave Rock, an eroded former volcano, and the Upper Truckee River. It also examines rock samples like granite and clay found in the area. Finally, it profiles plants and animals that inhabit the region, including manzanita bushes, American robins, Steller's jays, and their biological classifications.

1. South Shore of the
Lake Tahoe Basin
2012 Geology Field Assignment
By: Kate Albrecht
July 10, 2012

2. Table of Contents
• Background information
• Geologic History
• Cave Rock
• Upper Truckee River
• Rock samples
• Plants and animals
• Resources

3. Basin Formation
• Although many people believe that it was volcanoes, the Lake Tahoe Basin was actually originally
formed by faulting.
(Hunt, 1998)
• Fractures in the crust caused chunks of land to rise and sink.
• Over a span of over several million years, this created the Sierra Nevada mountains.
• The highest peaks in the Basin, Freel Peak, Monument Peak, Pyramid Peak, and Mount Tallac all formed
on fault blocks around a large basin.
• Over time snow, rain, creeks, and rivers all began to fill the basin to form a lake.
• For a while, there was no outlet, so the lake kept getting deeper and deeper until it eventually found
one, near the present-day town of Truckee. This is when the volcanoes come in.
• A few volcanoes began putting lava into the basin, which eventually dammed the outlet, and the lake
rose to a few hundred feet above today’s level, until it cut another outlet near present day Tahoe City
• After that, many of the volcanoes went dormant, and the lake level slowly receded to the level we
know today
(Hunt, 1998)

4. Locations
Upper Truckee
River
Cave Rock
*Images attained using Google Earth.

5. Cave Rock
• On the east shore of Lake Tahoe, with
Highway 50 running right through it, is
what looks like one massive eroded rock
called Cave Rock.
(Hunt, 1998)
• Cave Rock was once an active volcano
that poured lava into the Lake Tahoe
Basin thousands of years ago.
• After it went dormant, however, the lake
level was hundreds of feet higher than it
is now, which caused some serious
erosion.
• Over time, the waves slowly eroded not
only the outside, but they left a
catacomb of tunnels on the inside also,
until they finally receded, leaving behind
what we see, and drive through, today.
(Hunt, 1998)

6. Upper Truckee River
• This is a bank of clay that I found on the
Upper Truckee River near the airport.
• You can easily see where the river
eroded away the bank when it flowed
at higher levels, leaving behind the dirt
overhang.
• You can also see, just under the erosion
overhang, the lines in the clay that show
the level that the river has flowed at
over the years.
• For a long time, not far below this spot
the river had been re-routed into a
straight, unnatural line. However, a
recent project this fall has re-routed the
river again in a natural, meandering
course.

7. Rock Sample: Granite
• This is a specimen of what appears to be white
granite.
(Pellant, 2002)
• White granite is an igneous rock that occurs in
plutonic environments.
• This rock is classified as an acid rock due to its
high silica content, over 65 percent.
• It is embedded with euhedral crystals of
feldspar, mica, and usually quartz as well.
(Pellant, 2002)
• Because volcanic activity was one of the main Group Igneous
factors in the creation of the Lake Tahoe
basin, this rock is quite common in the area
Origin Intrusive
today. Classification Acid
(Hunt, 1998) Occurrence Plutonic Environment

8. Rock Sample: Clay
• This is a specimen of what appears to
be clay.
(Pellant, 2002)
• Clay is a sedimentary rock that
occurs in both marine and freshwater
environments.
• Fossils are often well-preserved in clay
due to its very fine grain size.
(Pellant, 2002)
• This specific sample is a dried piece
from a small, maybe 10 foot-long clay
bed on part of the Upper Truckee Group Sedimentary
River. Origin Mainly Marine & Freshwater
Classification Detrital

9. Manzanita Bush
• The manzanita bush is mainly
found in the mountains of the
Sierra Nevada and northern Coast
Ranges.
(Wilson, 2012)
• Their scientific name, and genus in
their scientific classification, is
Arctostaphylos.
• I believe this particular specimen to
be a Mama Bear manzanita.

10. Manzanita Bush cont.
• They mostly thrive in drier areas
without a lot of water, and can
die from too much of it,
especially as they get older.
(Wilson, 2012)
• However in the correct
conditions these plants can
grow to be over 100 years old.

11. American Robin
• The scientific name of this bird is Turdus
migratorius.
(“Mid-week reptilian #15: American
Robin,” 2010)
• They belong to the order Passeriformes
the “perching birds” order.
• However they also are related to the
order of songbirds, oscines, which,
combined with the Passeriformes,
places them in the suborder Passeri.
(“Mid-week reptilian #15: American
Robin,” 2010)

12. American Robin cont.
• These birds are common all
across North America and in
most of Canada and Alaska.
(“American Robin,” 2011)
• Their diet consists of insects; they
can often be seen pulling worms
and other bugs out of damp soil
in the morning and evening
hours of the day.

13. Steller’s Jay
• Scientific classification:
Class: Aves
Order: Passeriformes
Family: Corvidae
Genus: Cyanocitta
Species: Cyanocitta Steller
(Andrijev, n.d.)
• The steller’s jay belongs to the Cordivae
family in the order Passeriformes, which is
the order of perching birds.
• They are commonly found in the evergreen
forests of the western mountains of the U.S.
and Canada.
(“Steller’s jay,” 2011)
• They are omnivores, with their diet
consisting mainly of the insects and other
things that they forage off of the ground.

14. Resources
American robin. (2011). In The cornell lab of ornithology: All about birds. Retrieved July 13, 2012
Andrijev, I. (n.d.). Steller’s jay. In Canisius ambassadors for conservation. Retrieved July 13, 2012
Hunt, J. (1998). Lake tahoe facts and info: The geological history of the lake tahoe basin. In Lake tahoe cam.
Retrieved July 13, 2012
Mid-week reptilian #15: American robin. (2010, March 30). In The obligate scientist. Retrieved July 13, 2012
Pellant, C. (2002). Rocks and minerals (2nd ed.). New York, NY: Dorling Kindersley, INC.
Steller’s jay. (2011). In The cornell lab of ornithology: All about birds. Retrieved July 13, 2012
Wilson, B. (2012, April 12). Manzanitas of california. In Las pilitas nursery. Retrieved July 13, 2012