Natural Evolution of the Carson Pass of the Sierra Nevada Michael Mosca Geology 103 Professor Mark Lawler July 13, 2011
The Sierra Nevada Range was formed 150 – 200 million years agoduring 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 theCarson Pass area is there is a transition area right at the Sierra Crest between the igneousGranodiorite rock whichforms the bed surface for the range and volcanic Peperite which has flowed over the granitic bed (Skilling, Busby2004) The erosion of thisupper volcanic layer can be visually examined in this area.
In this slide we can see the approximate 5 to 6 layers of unconformities thathave 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 anderosion of the igneous base and the building and erosion of the volcanic cap.
This slide shows the igneous granodiorite rock that makes up thebed 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 thegranodiorite surface. This erosion was caused from atmospheric andglacial 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 ofwet 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 movingdownward forming a new uncomformity on the upper portion of the canyon.
This slide shows an area where the erosionalprocess 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)
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 aredominate in the Sierra Nevada Mtns.. The large forests are comprised ofconifers, mostly pines. These are gymnosperms and are seed bearing. Theseeds 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 isnamed Juniperusoccidentalis. It is native tothe Western United Statesand grows in alpine climatesup to 10,000 ft.. It is agymnosperm and beginsseed production at 20 yearsbut has no seed cones until50 to 70 years. The seeds aredispersed by animals, water,and air. The oldest knownliving Juniper is 3000 yrs.Old. (Adams 2004),(Eddleman, Miller, Miller,Dyshart 1994 p.131), Most plant and animal lifeincreased in this area withthe deglaciation andwarming of the climateabout 10,000 years ago.(Sierra Nevada Geotourism2009)
This is Spreading Phlox(Phlox diffusa). It is agroundflower common tothe Sierra Nevada , itprefers to grow in rockyareas. It is in a group offlowers with ultravioletpatterns. These are nakedto the human eye butwere developed to guideinsects to the nectar forpollinization. These areangiosperms.(Muir Laws, 2007)
This is the Yellow BelliedMarmot ( Marmotaflaviventris ) also known asa Rock Chuck. They areherbivores that also eatinsects and have beenreported to be cannibals attimes (Amitage, Johns,Andersen 1979, Fraas,Hoffman 1980).Marmots evolved fromTherapids during thePermian Period. Theseevolved into placentalanimals in the earlyCretaceous 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