Geology 103 Lab/Field Assignment

2. Introduction
The following is a brief presentation about Lake
Tahoe, the evolution of three modern species of flora
and fauna found there, the identification of three
different rock types, and the observation of some
geologic principles used in relative dating.
I conducted my study in the Lake Tahoe Basin by
hiking around different areas and making
observations using the knowledge from our
readings.

3. Formation of Lake
Tahoe
• Sierra Nevada's were formed 24 mya by
uplifting
• Mt. Pluto a volcano on the North Shore
helped dam the lake off and form the
northern border
• Lake filled to hundreds of feet higher
than present day
• The water eroded away an opening to
the only outlet the Truckee River
• During the ice ages, glacier activity
helped to form the rest of the lake
carving out areas like Emerald Bay,
leaving behind jagged peaks and crystal
clear lakes
(“Frequently Asked Questions”)
Photo by Me of Harper at Emerald Bay Lookout

4. Tahoe Basin Quick Facts
Tenth deepest lake in the world
22 miles long, 12 miles across
Fallen leaf lake was also formed by
glaciers
The lake could cover California with 14 in
of water
The lake is at 6225ft above sea level
The Highest point in the basin is Freel
Peak at 10886ft above sea level
(“Frequently Asked Questions”).
Today there are 3 main fault lines
throughout the basin
Up thrown Fault blocks created the high
peaks like the Eastern Margin Fault that
created the Carson range where as the
Westen Margin Fault created Crystal
mountain Range
Down thrown Fault blocks sank and
created the valley between the two ranges
which we now know as Lake Tahoe
(Henry).

5. Geological Makeup
North shore primarily
volcanic rock
East shore was primarily
granite rock
West shore granite Rock/
Glacier sediment
South Shore Glacial/
Lacustrine Deposits
(Geology and Glacial History of the Lake Tahoe
Basin 2008)

6. Rock #1: Igneous (Granite)
I found this rock up near Heavenly
It is usually found at convergent plate
boundaries where uplift occurred like
the Sierra Nevada’s
It makes up a large portion of the
mountains that surround the basin (as
they were formed this way)
It is usually light colored with a
phaneritic texture (course grained) like
the sample
(Monroe 2015) (photo by me)

7. Rock #2: Metamorphic
(Hornfel)
These rocks have been metamorphosed by
contact with extreme heat.
Identified by layers of light and dark, caused
by separation of minerals. Fine grained, hard
and dense. They have a non-foliated texture
meaning the mineral grains are
equidimensional.
This rock was cuboidal in shape and felt
heavier than the granite rock of a similar size.
Both are characteristics of Hornfels. The
texture was similar to a horn also.
Found out on the trail between Fallen Leaf
Lake and the campground
(Monroe 2015) (Photo by Me)

8. Rock #3: Sedimentary
(Siltstone)
Compacted silt, which is finer than
sandstone but more coarse than clay.
The particles are slowly deposited by
calm waters. Although the water was
rushing when I went, it is not always.
Reddish brown color
Not shale because the pieces break off
in thicker non parallel chunks.
This was from the Glen Alpine Falls
Area just south of Fallen Leaf Lake,
(Monroe 2015) (Photo by Me)

9. Steno’s Principle of
Cross-Cutting
Relationships
• The principle states that an
“igneous intrusion or a fault must be
younger than the rocks it intrudes or
displaces” (Monroe 2015).
• By this principle we can deduce that
the lighter band that extends up
through the darker granite would be
younger.
• By Steno’s Principle of Inclusions
we could also deduce that the dark
circular rock inclusion is older than
the large boulder.

10. Unconformity
• Location: Glen Alpine Falls
• Definition: times of non-deposition,
erosion or both making a
unconforming surface amongst the
strata (Monroe 2015).
• You can see times of erosion and
times of deposition here.
• This makes sense with the location
of the water fall as changing water
levels and long periods of drought
or flood would cause missing pages
in the geologic history book.
(Photo be Me)

11. Common Name: Forget Me Not’s
Found: Along hiking trail near Fallen Leaf Lake
Left Picture: Taken by Me, Forget Me Not’s in Bottom left corner
Right Picture: flowermeaning.com
Myosotis scorpioides

12. Myosotisscorpioides
Little flowers with a yellow center and outer leaves that resemble that of a
mouse ear. This is where they get their Greek based name which literally
translates over to “Mouse’s ear” (dictionary.com)
Also called Forget Me Not’s found along hiking trails in Lake Tahoe
Boraginaceous family
From Eurasia and New Zeeland they managed to migrate across to the
America’s most likely by boat as a decorative plant that then were able to
survive because of there ability to self-seed
Prefer to inhabit marshes, wooded areas, meadows, and fields (Myosotis
stricta).
Boraginaceae family is made up of more that 148 genera and 2,700 different
species Some members of this group are flowers used for medicinal practices
in Asia, others are used for their distinct colors and transformed into ink,
however forget me not’s don’t seem to serve much purpose for any of these
reasons and are descendants from these plants that have become more of a
garden flower used for looks/ decorations (Boraginaceae).
Angiosperms (flowering plants) appeared on the planet 80-90 mil years ago.
They are now the most abundant and diverse plants. Early plants were
generated from spores not seeds so they could reproduce them selves. The
newer seed producing plants require an outside locomotive to bring together
male and female parts safely. Flowers evolved to be colorful and showy in
order to attract pollinators like birds and insects (History of Wild Flowers).

13. Common Name: Lupines
Location: Hiking Trail by Fallen Leaf Lake
Picture: Taken by me, Lupines are the more dense stalks with purple
flowers
Lupinus polyphyllus

14. Lupinus polyphyllus
Large leafed lupines
Member of the Fabaceae family which is actually the legume family that’s part of the angiosperm
order Fabales (Beuthin 2012).
flowers have a seed which is very bitter in tastes and must be thoroughly rinsed off before being
cooked due to the high level of Alkaline within the seed, for this reason they are generally boiled and or
roasted to help and reduce the nasty taste. These seeds however are commonly used as a
replacement for soybeans, however the Lupin seed is higher in protein lower in fat and “superior” to
soybeans for their prebiotic qualities (Lupinus polyphyllus).
Attract bees, help fertilize and improve the soil quality where ever they are introduced
The more dense flowering spikes are a result of selective breeding as well as larger and more colorful
variations. The ones pictured are more indicative of original L. polyphyllus (Beuthin 2012).
Can survive extreme temperatures, but do best in areas with reasonable sun (think of the lupine fields)
and light soil (Lupinus polyphyllus).
Seeding plant just like the Myosotis scorpioides that evolved from spore producing flora

15. Common Name: Black Bear (despite brown coloring)
Location: Side of the road driving home from Fallen Leaf, breaking apart a log
Right Picture: Taken by me
Left Picture: bbc.com
Ursus americanus

16. Ursusamericanus
These bears are large omnivorous mammals, they can take down large prey but their
teeth are similar to humans and pigs
They are the widest distributed member of the Ursidae family
The fossil record shows only two bears of the genus Ursus in our region the brown
(grizzly) bear that was mostly killed off by humans and the smaller still prominent black
bear, U. americanus (Ursus 2015).
The bears used to be similar in size during the Wisconson but the black bears evolved
into a smaller animal during the Holocene
Usually live in large forested areas but leave for food. Attracted to human communities
due to availability of food.
Black bears split from a common ancestor of brown bears about 5 million years ago
The black bears were not as specialized or specific allowing them to survive the
changes that came from several ice ages that killed off their ancestral relatives
They can swim and climb well like their ancestors and other arboreal bear species,
they hibernate and can be active during day or night depending on environment
(Herrero).

17. References
Herrero, Stephen. "Aspects of Evolution and Adaptation in American Black Bears (Ursus americanus Pallas) and Brown and
Grizzly Bears (U. arctos Linne.) of North America" (PDF). Environmental Sciences Centre (Kananaskis)
Ursus. (2015, April 22). Retrieved June 25, 2017, from http://www.utep.edu/leb/Pleistnm/taxaMamm/Ursus.htm
Monroe, J. S., & Wicander, R. (2015). The Changing Earth: Exploring Geology and Evolution. Stamford, CT: Cengage Learning.
Boraginaceae-The Borage Family .The Seed Site. Retrieved June 26, 2017, from
http://theseedsite.co.uk/boraginaceae.html
The History of Wildflowers. (n.d.). Retrieved June 26, 2017, from http://www.americanmeadows.com/history-of-wildflowers
Lupinus polyphyllus Lindl. (n.d.). Retrieved June 26, 2017, from
https://gobotany.newenglandwild.org/species/lupinus/polyphyllus/
Myosotis stricta Link ex Roemer & J.A. Schultes. (n.d.). Retrieved June 26, 2017, from
https://gobotany.newenglandwild.org/species/myosotis/stricta/
Dictionary.com:Myosotis scorpioides. (n.d.). Retrieved June 26, 2017, from http://www.dictionary.com/
Beuthin, M. 2012. Plant guide for bigleaf lupine (Lupinus polyphyllus). USDA-Natural Resources Conservation Service, Plant
Materials Center, Corvallis, OR.
"Frequently Asked Questions about Lake Tahoe and the Basin". Lake Tahoe Basin Management Unit. Forest Service, U.S.
Department of Agriculture. Archived from the original on May 10, 2009. Retrieved June 20, 2007.
Geology and Glacial History of the Lake Tahoe Basin. UCTV Seminars (2013, January 08).
Henry, C. D. Uplift of the Sierra Nevada, California. Retrieved June 24, 2017, from
http://geology.gsapubs.org/content/37/6/575.full