Lake TahoeA Geological Study

Geology 103Field AssignmentBy Gina Niceforo

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

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.

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.

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.

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).

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.).

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.

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.).

Jeffrey PinePinus 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.

Jeffrey Pine-Pinus jeffreyiEvolution

• 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).

ManzanitaArctostaphylos

*(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.

Manzanita-ArctostaphylosEvolution

• 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).

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.

Ground SquirrelEvolution

• 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.

ReferencesAlden, 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/

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/

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*