1. A Geological Study
Geology 103
Field Assignment
By Gina Niceforo

2. Lake Tahoe,
California
• The Basin was formed about 4
million years ago, during the
the Pliocene Epoch (Cenozoic
Era), caused by normal faulting.
• The mountains of the Carson
Range on the East and the
Sierra Nevada on the West
were created by uplifted
blocks.
• The basin in between the
mountains was created by
down-dropped blocks.
• The highest peaks were formed
during this process, including
Mt. Tallac, reaching 9,735ft.
(USGS).
*Mt Tallac

3. The First
Lake Tahoe
• An estimated 3 million
years ago during the
Pliocene Epoch, lava from
erupting volcanoes formed
a barrier across the basin’s
outlet (Antonucci, 2011).
• Water from rivers and
streams flowed in the
basin filling it hundreds of
feet above its present level
(Keep Tahoe)
• The ancestral Lake Tahoe
was formed, in the Middle
of the Cenozoic Era
(USGS).
*A stream in the basin that
flows into Lake Tahoe today.

4. Lake Tahoe
Today
• During the Ice Age, an
estimated 1 million years
ago in the Pleistocene
Epoch (Cenozoic Era),
glaciers formed in
surrounding mountains and
scoured the landscape.
• U-shaped valleys were
carved, especially on the
West shore, that now
occupy Emerald Bay, Fallen
Leaf Lake, and Cascade
Lake (Keep Tahoe).
• The modern day Lake
Tahoe was Beginning to
take shape (USGS).*Cascade Lake with Lake
Tahoe in the background.

5. Lake Tahoe
Today
• Tahoe today has about
66,000 residents.
• During peak periods
the number of
residents and tourists
reaches around
300,000 people at
peak times (Antonucci,
2011).
• 63 streams and rivers
presently flow into
Lake Tahoe.
• There is now one
outlet for the lake, the
Truckee River (Keep
Tahoe).
*Cave Rock on the East
shore of Lake Tahoe.

6. Igneous-Granite
• Granite is of the igneous
rock type.
• It is coarse grained or very
coarse grained.
• It is formed deep within the
Earth’s crust from cooling
magma that contains a lot of
silica.
• It’s slow cooling process
large crystals (Peck, n.d.).
• The most common rock type
in Lake Tahoe, it surfaced
when the basin was formed
around 4 million years ago
during the Pliocene Epoch
(Cenozoic Era) (USGS).
• Granite most commonly
contains such minerals as
feldspars, quartz, biotite and
muscovite (Peck, n.d.).
*Granite in Lake Tahoe containing a
large amount of pink colored
feldspar and specks of biotite mica
(Monroe & Wicander, 2009).

7. Igneous-Granite
• The most
common granite
that cover the
Lake Tahoe basin
looks similar to
these two rocks.
• The rock on the
left is granite
containing mostly
yellowish, white,
and feldspar with
specks of biotite.
The rock on the
right is granite
containing white
and gray
feldspars, glassy
looking, smoky
gray and white
quartz, and
traces of biotite
(Peck, n.d.).

8. Igneous-Basalt
• Basalt is of the
igneous rock type.
• It is fine-grained often
containing
microscopic crystals.
• This volcanic rock
formed from lava that
surfaced and cooled
quickly.
• This surfaced magma
came from erupting
volcanoes during the
Pliocene Epoch
(Cenozoic Era).
• This rock was
weathered by water,
most likely the
streams that run
along the trails at
Cascade Falls (Peck,
n.d.).
*Igneous rock Basalt,
found in Lake Tahoe.

9. Epidote Xenolith
Encased in Basalt
*Both photos are of Basalt containing a xenolith
(epidote) at Cascade Falls in Lake Tahoe (Alden, n.d.).
• Epidote is a rock
forming mineral of
secondary origin
occurring in
metamorphic rocks
beneath the Earth’s
surface (Epidote, wiki).
• The epidote became
caught in magma after
breaking off from
surrounding country
rock, maintaining its
original properties in
the form of a xenolith.
• Therefore, the epidote
is older than the basalt
it is encased in (Gore,
1998).
• The basalt is most likely
around the same age as
the previous example,
surfacing during the
Pliocene Period, and
weathered differently.
(Peck, n.d.).

10. Jeffrey Pine
Pinus Jeffreyi
• This pine species is
the most prominent
tree in Lake Tahoe.
• It is very closely
related to the
Ponderosa Pine.
• It’s characterized by
a massive trunk, long
symmetrical crown,
and beehive shaped
pinecones (McCrae,
2009).
• It occurs in North
America in Southern
Oregon, throughout
California and into
Northern Mexico
(The Gymnosperm).*Both pictures show
Jeffrey Pines flourishing
on the mountainsides of
Lake Tahoe.

11. Jeffrey Pine-Pinus jeffreyi
Evolution
• The evolution of the Jeffrey Pine began with the first appearance of seeds in
the Devonian Period, about 400 million years ago (Paleozoic Era).
• Next was the appearance of gymnosperms, or flowerless seed plants, during
the Carboniferous Period, about 325 million years ago (Paleozoic Era).
• The evolution of gymnosperms meant that unlike seedless vascular plants,
gymnosperms did not need moisture tor reproduce, in turn gymnosperms
quickly migrated and became abundant throughout the Permian Period, about
275 million years ago (Monroe & Wicander, 2009).
• The gymnosperm division Conifers, or seed-bearing plants with cones, evolved
during the 2nd half of the Carboniferous Period (Pennsylvanian), possibly from
Cordaites, a seed-bearing plant with cone-like fertile structures.
• Conifers not only survived, they benefited from the Permian-Triassic extinction
event (Conifers, wiki).
• The first Jeffrey Pine was discovered in Shasta Valley, CA in 1852, by it’s
namesake John Jeffrey, a Scottish botanical explorer (Nix, n.d.).
• The oldest Jeffrey Pine was found in 1964 in Tioga Pass, CA, containing a record
813 rings (The Gymnosperm).

12. Manzanita
Arctostaphylos
*(Manzanita, wiki)
• Manzanita are
prominent in Lake
Tahoe and
throughout
Northwest America.
• There are 106
species of Manzanita,
all known for their
twisting, tough
branches and bark
(Manzanita, wiki).
• The top picture taken
by author was most
likely the species
Pinemat Manzanita,
as this type grows at
elevations above
above 7,000ft (Graf,
1999).
*Pinemat Manzanita growing at an
elevation of about 8,000ft in Lake Tahoe.

13. Manzanita-Arctostaphylos
Evolution
• The evolution of Manzanita began with the appearance of
Angiosperms, or flowering plants in the Mesozoic Era, during the
Cretaceous Period, possibly as early as the Late Jurassic, about 150
million years ago.
• Though it is believed angiosperms are closely related to
gymnosperms, their early fossil records are sparse, so precise
ancestry is unknown.
• Angiosperms brought the evolution of enclosed seeds, adaptability
to almost any environment, the evolution of flowers allowing for
insects to pollinate (Monroe & Wicander, 2009).
• Fossil ancestors of the genus itself occurred as recently as the
Middle Miocene, about 20 million years ago (Cenozoic Era), with
the species diversification and evolution centered in the far western
part of North America (Hogan, 2010).
• Today, Manzanita occurs in British Columbia, Washington to
California, Arizona, New Mexico, and outside of the U.S. in Mexico
(Manzanita, wiki).

14. Ground Squirrel
*(Ground Squirrel, wiki)
• Ground squirrels are
part of the Rodentia
order, as part of the
Sciuridae family of
rodents (Ground
Squirrel, wiki).
• They live in dry
margins of mountain
meadows and rocky
slopes.
• They are solitary
burrow dwellers that
hibernate from late
summer to early
spring.
• They are omnivores
that will eat almost
anything
(Smithsonian).
• They are known for
rising on their hind
legs when sensing
danger (Ground
Squirrel, wiki).
*A Ground Squirrel at Cascade Falls in
Lake Tahoe.

15. Ground Squirrel
Evolution
• Fossil record of rodent-like mammals began around 65 million years
ago as early as the Paleocene Epoch at the beginning of the
Paleogene Period (Cenozoic Era).
• By the end of the next Epoch, the Eocene, relatives of squirrels
appear in the fossil record, about 35 million years ago. They
originated in Laurasia, the supercontinent of North America,
Europe, and Asia (Rodentia, wiki).
• About 30 million years ago, the beginning of the Oligocene there re
fossil records of the oldest known ground squirrel species, as
primitive marmots and chipmunks.
• “True” ground squirrel fossils begin from the Middle Miocene,
about 15 million years ago. They are located in the species present
day range of dry, mountainous regions (Ground Squirrel, wiki).
• In terms of geological time, the Ground Squirrel evolved relatively
quickly, within about 50 million years throughout the Early to
Middle Cenozoic Era.

16. References
Alden, a. (n.d.). About.com-Geology. Green minerals: The most common and significant ones.
Retrieved from: geology.about.com/od/mineral_ident/tp/Green-Minerals.htm.
Antonucci, D., (2011). The natural world of lake tahoe: Answers to the most frequently asked
questions about the lake of the sky. Incline Village, NV. UC Davis Environmental Research Center at
Sierra Nevada College.
Gore, P. (1998). Laboratory 1: Relative dating laboratory. Retrieved from: https//myetudes.org/
portal/site.
Hogan, M. (2010). The encyclopedia of earth: Arctostaphylos. Retrieved from: www.eoearth.org/
article/Arctostaphylos#gen2
McCrae, T. (2009). Beetles in the bush: Trees of lake tahoe-the pines. Retrieved from:
beetlesinthebush.wordpress.com/2009/03/28/trees-of-lake-tahoe-the-pines/

17. References
Monroe, J., & Wicander, R. (2009). The changing earth: Exploring geology and evolution. Belmont, CA:
Brooks/Cole, Cengage Learning.
Nix, S. (n.d.) About.com-forestry: Jeffrey pine, an important tree in north america. Retrieved from:
forestry.about.com/od/conifers/tp/Pinus_jeffreyi.htm
Peck, D. (n.d.) The rock identification key: Igneous rocks. Retrieved from: www.rockhounds.com/
rockshop/rockkey
Conifers. (n.d.). In wikipepia.org. Retrieved June 15, 2013 from wiki: en.wikipedia.org/wiki/Conifers
Epidote. (n.d.). In wikipepia.org. Retrieved June 14, 2013 from wiki: en.wikipedia.org/wiki/Epidote
Ground Sqirrel. (n.d.). In wikipepia.org. Retrieved June 12, 2013 from wiki: en.wikipedia.org/wiki/
Ground_Squirrel
Keep tahoe blue: League to save lake tahoe. Fun facts and history.Retrieved from: keeptahoeblue.org/
abouttahoe/history-facts/

18. References
Manzanita. (n.d.). In wikipepia.org. Retrieved June 16, 2013 from wiki: en.wikipedia.org/wiki/Manzanita
Rodentia. (n.d.). In wikipepia.org. Retrieved June 12, 2013 from wiki: en.wikipedia.org/wiki/Rodent
USGS: Science for a changing world. Facts about lake tahoe. Retrieved from: tahoe.usgs.gov/facts.html
*All photos not referenced were taken by author, Gina Niceforo*