Lake Tahoe

Mollie Whittingham Professor Lawler

GEL 103 June 2016

Index● Overview ● Lake Tahoe● Granite● Limestone● Quartz● American Black Bear ● Snow Plant ● Pale Swallowtail Butterfly● Relative Dating● Unconformity

OverviewLocated in the Western United States just East of the Sierra Nevada Mountains lies the Lake Tahoe Basin.

This area has an incredibly rich geologic history, which has resulted in the creation of the “...highest lake of its size in the United States”(Gould, 2012), with an average elevation of 6,225 feet above sea level.Here we will discuss a few aspects of Tahoe’s geology, including the lakes formation, rock identifications, and different flora and fauna.

Formation of Lake Tahoe ● 2 to 3 million years ago three major geologic faults

resulted in land masses rising and falling in different areas, creating a large valley surrounded by mountains.

○ “The Tahoe landscape was formed, and continues to

be formed, by powerful tectonic forces”(UC Davis,

2011).

● A volcanic eruption from Mt. Pluto led to a large lava flow that eventually closed off the remaining outlet in the basin.

● Snow and rain run-off from the ring of mountains surrounding the basin began to fill the area with water.

○ “The enclosed basin has contained a lake for the last

2 million years”(UC Davis, 2011).Figure 1 Lake Tahoe Faults

Formation of Lake Tahoe ● Eventually a new outlet for water flow,

the Truckee River, was formed. However, areas such as Cave Rock are proof that the lake was once drastically deeper.

● The Tahoe Basin later entered an Ice Age resulting in the creation of massive glaciers, which would later cut through the mountain regions, creating many of the canyons, moraines and lakes that exist in the region today.

Granite ● Rock Type : Igneous

○ “Igneous rocks result when magma or lava crystallizes, or

when volcanic ejecta...accumulate and consolidate”

(Monroe & Wicander, 2016, p.18).

● Texture: Phaneritic○ Visibly coarse, granulated

● Composition: Variation of multiple minerals○ Most common:

■ Quartz (Milky, Grey, Shiny)

■ Feldspar (Most commonly: White, Pink)

■ Biotate (Black, Shiny)

Limestone● Rock Type: Sedimentary

○ “Any rock composed of sediment that forms at

or near Earth’s surface” (Monroe & Wicander,

2016, p.686)

● Texture: Non-Clastic (Varies)○ “[Not] composed of particles or fragments”

(Monroe & Wicander, 2016, p.162)

● Composition: Primarily composed of Calcium Carbonate (CaCO3)

● “Most limestones form in shallow, calm, warm marine waters” (King, 2016)

QuartzQuartz

● Type: Mineral● Luster: Nonmetallic● Silicate: Nonferromagnesian Silicate

○ “White, cream, colorless and shades of pink

and pale green are typical” (Monroe &

Wicander, 2016, p.162)

● Hardness: 7○ Based on Mohs Hardness Scale

● Quartz is a common rock-forming mineral which can be found in all rock types.

American Black Bear● The American Black Bear can be traced back to ancestors living over 20 million

years ago, however, it has seen very little evolution in its anatomical makeup.○ 20 million years ago - Dawn Bear (Ursavus Elmensis)

■ Small, size of a “Fox Terrier” (Black Bears, 2007)

■ Spent majority of life in trees

■ Ate vegetation and insects

■ Became extinct due to climate change and loss of forest habitat

○ 5.3-1.8 million years ago - Auvergne Bear (Ursus Minimus)

■ Began small, grew in size throughout existence

■ “..anatomically the same as today’s black bears” (Black Bears, 2007)

■ Teeth evolved to incorporate a more carnivorous diet

American Black Bear○ 5 million-11,000 years ago - Etruscan Bear (Ursus Etruscus)

■ Lived forrest adapted lifestyle, however, the Ice Age and glaciation led

to need for evolution

■ “..gave rise to three evolutionary lines” (Herrero, 2007)

● Asia: Black Bear, Brown Bear

● Europe: Cave Bear

■ Bering Land Bridge allowed Black Bears to migrate from Asia into N.

America

○ 500,000 years ago-Present - American Black Bear (Ursus Americanus)

■ Adaptive to multiple environments, still prefer forest habitat

■ Capable of climbing trees (for finding food and escaping predators)

■ Strong sense of smell (for finding food)

■ Omnivorous (can survive off vegetation and meat)

■ Average Size between 100-300 lbs

Snow Plant● Latin Name: Sarcodes sanguinea

○ Meaning: “the bloody flesh-like thing” (USDA, 2016)

● First recorded in the early 19th century● Mycotrophic Plant - fungus eating● Native to California, Washington and Nevada● Snow Plants are actually “...parasites on soil fungi” (Muir, 2007, p.106)

○ These “parasites” adapted and evolved to “freeload” off of other

plants that contain chlorophyll and are capable of photosynthesis,

which allows the snow plant to receive nutrients that it did not have to

create itself.

● “It will be found growing out of pine needles and other forest litter on the surface of the ground, near a conifer.” (USDA, 2016)

Pale Swallowtail Butterfly ● Latin Name: Papilio Eurymedon

● “Butterflies and moths originated when flowering plants were beginning to proliferate and have developed in close association with them” (Butterfly Garden)

○ Fossil records date back approximately 40 million years

○ Due to their fragility, fossils are rare

● Developed defense mechanisms throughout each stage of their metamorphosis:

○ Egg - Resembles “bird droppings” (Butterfly Garden)

○ Larva - Pattern resembles large eyes, emits bad smell if threatened

○ Chrysalis - Camouflaged to resemble leaves or twigs

○ Adult - Long, colorful tail which distracts predators from the more vital parts,

also poisonous to the majority of birds

Pale Swallowtail Butterfly● Male Swallowtails have developed the ability to extract

sap from plants which allows them to produce pheromones that attract females and assist in reproduction

● Butterflies have developed their own methods of hibernation and migration to increase survival

○ Life span typically between several weeks to several

months

● Biggest threats to existence today: humans, habitat loss, insecticides/herbicides

Relative Dating ● Principle of Intrusive Relationships

○ “..when an igneous intrusion cuts across a formation of

sedimentary rock, it can be determined that the igneous

intrusion is younger than the sedimentary rock” (Geology,

2013)

● In other words, the sedimentary rock had to exist before the intrusion was able to cut across it.

● Here we can see a large boulder covered in moss and lichen

○ Cutting diagonally across the rock is an igneous intrusion,

known as a dike, possibly comprised of the igneous rock

basalt or the igneous rock gabbro

Unconformity● Unconformities “...represent times of

nondeposition, erosion, or both” (Monroe & WIcander, 2016, p. 422)

● There are three types of unconformities:○ Disconformity○ Angular unconformity○ Nonconformity

● Here we can see the beginning of a nonconformity, where the erosion of an igneous rock is being covered by sedimentary rock.

ResourcesBlack Bears. (2007). Retrieved June, 2016, from http://www.bearsoftheworld.net/american_black_bears.asp

Butterfly Garden. (2016). Association of Zoos & Aquariums. Retrieved June, 2016, from http://www.tnaqua.org/images/uploads/subpages/Butterfly_Garden.pdf

Cazarez, S. (2012). Lake Tahoe Faults [Digital image]. Retrieved June, 2016, from http://skywalker.cochise.edu/wellerr/students/lake-tahoe/project.htm

Gauna, F. J. (n.d.). Plant of the Week:Snow Plant. Retrieved June, 2016, from http://www.fs.fed.us/wildflowers/plant-of-the-week/sarcodes_sanguinea.shtml

Geology. (2013, December 10). Retrieved June, 2016, from http://www.newworldencyclopedia.org/entry/Geology

Gould, M. (2012, December 13).Geography and History Overview. Retrieved June, 2016, from http://tahoe.usgs.gov/geography.html

Resources

Herrero, S. (2007). Aspects of Evolution and Adaptation in American Black Bears. Retrieved June, 2016, from http://www.bearbiology.com/fileadmin/tpl/Downloads/URSUS/Vol_2/Herrero.pdf

King, H. (2016). Limestone, What is limestone? Retrieved June, 2016, from http://geology.com/rocks/limestone.shtml

Monroe, J.S., & Wicander, R. (2001) The changing earth: Exploring geology and evolution (7th ed.) Pacific Grove, CA: Brooks/Cole

Muir, J. (2007). The Laws Field Guide to the Sierra Nevada. San Francisco, CA: California Academy of Sciences.

UC Davis Tahoe Environmental Research Center. [Steven McQ]. (2011, December 11). Lake Tahoe In Depth 2D. [Video File]. Retrieved from https://www.youtube.com/watch?v=q_mzGm-g9LI