Natural Evolution of the Carson Pass of the Sierra Nevada

Michael MoscaGeology 103

Professor Mark LawlerJuly 13, 2011

The Sierra Nevada Range was formed 150 – 200 million years ago during the Mesozoic in what is known as the Nevadan Orogeny. It

was formed when magma crystallized within the earths crust forming igneous plutons.

(Monroe, Wicander 2009)

Whats unique about the Carson Pass area is there is a transition area right

at the Sierra Crest between the igneous

Granodiorite rock which forms the bed surface for

the range and volcanic Peperite which has

flowed over the granitic bed (Skilling, Busby

2004) The erosion of this upper volcanic layer can be visually examined in

this area.

In this slide we can see the approximate 5 to 6 layers of unconformities that have taken place in the area over millions of years. These show the uplifting and

erosional forces taking place in the area beginning with the uplift and erosion of the igneous base and the building and erosion of the volcanic cap .

This slide shows the igneous granodiorite rock that makes up the bed surface of the Sierra Nevada. This rock is similar to granite but contains more minerals. Notice the speckling of the rock, these are

deposits of feldspar and micas within the rock.

Here is visual evidence of erosional forces taking place on the granodiorite surface. This erosion was caused from atmospheric and glacial forces over millions of years. The boulders sitting atop of the

formation have been placed by glacial plucking ( The glacial ice pulling the loose rock from the bed surface)

(Pidwirney, Jones 1999-2010)

These photos show the upper volcanic layer in the area known as Peperite. The Peperite was formed when the magma uplifted into the

crust layer of wet sedimentary rock. When rising it plucked pieces of the igneous layers underneath mixing them with the sedimentary layer. These

pieces of igneous stone mixed with the sediment are called clasts. (Skilling, Busby 2004)

This slide was taken in the Kirkwood area. It shows the volcanic flow or fluvial moving

downward forming a new uncomformity on the upper portion of the canyon.

This slide shows an area where the erosional process is beginning to uncover the igneous rock

underlying the volcanic.

These are slides of the sierra crest at Carson Pass. The slide on the left is Elephants Back, it is a solidified lava dome. The photo on the right is Round Top. Round Top is an ancient volcanic cone that is probably

responsible for most of the volcanic activity in the area.(Eldorado National Forest Information Site)

Evolution of Plant and Animal Species

Most plant species evolved from spores in the oceans. The flowering plants were originally gymnosperms that eventually evolved into angiosperms or pollinating plants. These pollinating flowers are

dominate in the Sierra Nevada Mtns.. The large forests are comprised of conifers, mostly pines. These are gymnosperms and are seed bearing. The seeds are usually in some type of cone until they are spread by air, water,

or animals. (Monroe, Wicander 2009, p.588, p.613)

This species of conifer is named Juniperus occidentalis. It is native to the Western United States and grows in alpine climates up to 10,000 ft.. It is a gymnosperm and begins seed production at 20 years but has no seed cones until 50 to 70 years. The seeds are dispersed by animals, water, and air. The oldest known living Juniper is 3000 yrs. Old. (Adams 2004), (Eddleman, Miller, Miller, Dyshart 1994 p.131),

Most plant and animal life increased in this area with the deglaciation and warming of the climate about 10,000 years ago. (Sierra Nevada Geotourism 2009)

This is Spreading Phlox (Phlox diffusa). It is a groundflower common to the Sierra Nevada , it prefers to grow in rocky areas. It is in a group of flowers with ultraviolet patterns. These are naked to the human eye but were developed to guide insects to the nectar for pollinization. These are angiosperms.

(Muir Laws, 2007)

This is the Yellow Bellied Marmot ( Marmota flaviventris ) also known as a Rock Chuck. They are herbivores that also eat insects and have been reported to be cannibals at times (Amitage, Johns, Andersen 1979, Fraas, Hoffman 1980).

Marmots evolved from Therapids during the Permian Period. These evolved into placental animals in the early Cretaceous Period. (Monroe, Wicander 2009, p.624 )

References

Monroe, J. S., & Wicander, R. (2009). The Changing Earth (5th ed.). Belmont, CA: Brooks/Cole.

Skilling, I. P., & Busby, C. J. (2004). Retrieved July 15, 2011, from http://www.geol.ucsb.edu/faculty/busby/VSSACFlyer.pdf

Pidwirney, i. (2006). Fundamentals of Physical Geography (2nd ed.). Retrieved July 15, 2011, from http://www.physicalgeography.net/fundamentals/10at.html

N.p.: n.p., n.d. Web. 15 July 2011. < http://www.enfia.info/natural_history/geology.html>.

Eddleman, L., Miller, P., Miller, R., & Dyshart, P. (1994). Western Juniper Woodlands (p. 131). Retrieved July 15, 2011, from http://www.fs.fed.us/database/feis/plants/tree/junocc/all.html_BOTANICAL AND ECOLOGICAL cHARACTERISTICS

(2009). Retrieved July 15, 2011, from http://(SierraNevadaGeotourism.org.2009).org/index.php

Laws, J. M. (2007). The Laws Field Guide to the Sierra Nevada (p. 158).

Amitage, K. B., Johns, D., Anderson, D., Fraas, B., & Hoffman, R. (1979). Cannibalism among yellow-bellied marmots. In Marmota flaviventis (135th ed., pp. 1-8). Baltimore, MD: John Hopkins University Press. Retrieved July 15, 2011, from http://en.wikipedia.org/wiki/Yellow-bellied-marmot