Mono Lake Field AssignmentGeology 103, LTCC Summer 2011,Professor Lawler

By Ron Sitton

• Mono Lake is a ancient lake and is anywhere from 1 to 3 million years old. It is located on the eastern side of the Sierra Nevada Mountains at an elevation of 6400 feet. The Mono Basin is a tectonic basin formed by faulting and folding. The surrounding hills are volcanic in nature with the exception of the Sierra Nevada to the west. (Mono Lake .org)

• Mono Lake has a diverse ecology and is on a main migratory path for many birds because of it’s alkali fly and brine shrimp populations. (Storer and Usinger 1963)

Animal Evolution of the California Gull

• California Gulls, Larus californicus. Mono Lake is second only to the Great Salt Lake in nesting populations of gulls. In late spring between 44,000 to 65,000 arrive to nest on Mono Lakes’ islands, mainly Negrit. Evolved from reptiles that branched off into the Archaeopteryx, about 120 million years ago the Ichthyornis species evolved which closely resembles the gull of today. (Callado, SFSU 2005)

Geologic Evolution

• The Mono Basin is still actively volcanic with the last major eruption occurring about 350 years ago forming Paoha Island. It consists of lakebed sediments deposited above volcanic domes. (mono lake.org)

• There are also many active hot springs changing the geology of the lake and frequent earthquakes.

• Limestone Tufa: Formed underwater from calcium rich springs mixed with lake water rich in carbonates creating a chemical reaction and depositing a form of limestone. (Storer and Usinger 1973)

• Obsidian Group: Igneous, Origin: Extrusive, Grain size: very fine, Crystal shape: Anhedral• Silica rich volcanic rock with glass as it’s main component, formed by the very rapid cooling of

viscous acid lava (Pellant, 1992)

• Vesicular Basalt Group: Igneous, Origin: Extrusive, Grain: Fine, Crystal shape: Anhedral, Euhedral Very similar composition of Basalt. Surface may be covered with empty gas bubble cavities. Forms from the cooling of basalt lava. (Pellant,1992)

References

• Storer, Tracy and Usinger, Robert (1973), Sierra Nevada Natural History, University of California Press

• Pellant, Chris (1992), Rocks and Minerals, DK Publishing• Hill, Mary((1975), Geology of the Sierra Nevada, University of California Press• (2011) Retrieved July 16,2011 http://www.monolake.org/ • (2005) Callado, Retrieved July 16,2011 http://bss.sfsu.edu/holzman