Geology field assignment
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A Look at Joshua Tree National Park
A Look at Joshua Tree National ParkGEL 103 Field AssignmentBy Abby OswaltJoshua Tree National Park - Background
Joshua Tree is a beautiful national park and a gem for geological observation and appreciation. The park is located in southern California.Two large desert ecosystems comprise the landscape of the park the Colorado Desert (part of the Sonoran Desert) and the Mojave Desert (A Desert Park, 2013).The landscape we see around the park today is the result of two widely separated periods of mountain building. The most recent occurrence caused uplift and deep erosion, which was then followed by more uneven uplift near faults.
Due to erosion, we are left with the amazing rock formations that we see today in Joshua Tree National Park, the remnants of ancient mountains (Biringer, 2005).Rock IdentificationMetamorphic - Gneiss
1.5 billion-year-old Pinto gneissFormed from sedimentary and igneous rocks that were buried deep long ago and underwent a chemical change to arrive at its present state (Biringer, 2005)Oldest rocks in Joshua Tree National Park, dating from the PrecambrianPinto gneiss is primarily made up of quartz, feldspar, and biotite (Rock Types, 2011).Rock IdentificationA type of granitic rock, which is made up of quartz, mica, and feldspar (Buscher, 2011)150 million years oldMonzogranite was an intrusion of the much older gneiss in the park. At a depth of 15 miles below Earths surface, the magma cooled and began to crystalize and form into solid rock.Millions of years of erosion have weathered away much of the gneiss that these rocks once intruded, leaving the monzogranite exposed as we see it today (Biringer, 2005).Igneous - Monzogranite
Rock IdentificationThe monzogranites fractures allowed ground water to seep through, softening some of the grains. This constant moving water gave the rocks their characteristic roundness.Before Joshua Tree National Park was a desert environment, flash floods eroded away the ground surface and gneiss, exposing the monzogranite and allowing the huge rectangular boulders to settle on top of one another and leaving us with the impressive formations of the present (Geologic Formations, 2013).Igneous - Monzogranite
aka Jumping ChollaTeddy Bear Cholla
Teddy Bear ChollaGenus opuntia; family cactaceaThrives in the hot desert of the American SouthwestGrows in very dry, rocky soil (Cholla Cactus, 2013)Grows to a height of 3-5 feet (Teddy Bear Cholla, 2010)Develops in desert valleys between 100 and 2000 feet elevationAlso known as jumping cholla for the way the cactus is able to reproduce. The fruits of the teddy bear cholla are sterile, and the plant relies on fallen stems to grow new cacti. The spines of the teddy bear cholla separate easily from the cactus and catch a ride on any animal or person that is unlucky enough to get that close. The stems are said to jump onto passersby as a means to spread out and multiply (Kuchan, 2012).Teddy Bear Cholla
As plants lose a lot of water through their leaves, desert plants had to adapt to the arid environment by slowing this water loss.Leaves became smaller and smaller as the cacti evolved, eventually forming sharp points, and finally arriving at the spines that currently adorn the cacti, which are resistant to the harsh environment and allow better water retention.The spines have evolved to provide more than just water retention. The sharp spines provide protection from animals. They also are handy for catching onto animals to get a free ride to a new place to take root. The numerous spines create their own shade and deliver protection from the sun (Saunders, 2009). Great Basin Fence Lizard
Great Basin Fence LizardFamily phrynosomatidaeGrow 6 to 9 inches longFound predominantly in CaliforniaMales often have distinguishing blue marks, specifically on the throat or belly (Western Fence Lizard, 2007), while females and young lizards lack this coloration. Some are all black.Diet consists of insects and spiders.Commonly referred to as a spiny lizard due to their overlapping, pointed scales (Sceloporus Occidentalis, 2013).The lizards like to settle on rock outcroppings, rocky slopes, cliff faces, and forested areas (Western Fence Lizard, 2012).Great Basin Fence LizardReptiles and amphibians came from a group of organisms called terrestrial vertebrates.Reptiles split from amphibians into a group called Amniota about 350 million years ago. It was through the development of the amniotic egg that lizards were able to adapt to the rigors of living on land (Ivanyi, 2004).An important evolutionary development that some lizards have acquired, including the great basin fence lizard, is that of autotomy, or the ability to detach the tail. This self-amputation is done as a means of protection and the tail will slowly regenerate (Western Fence Lizard, 2012).
Above: sign posted at the San Andreas Fault Zone in Joshua Tree National ParkSan Andreas Fault
San Andreas FaultThe San Andreas Fault represents the meeting of two of earths constantly moving plates. It is the boundary between the Pacific Plate (to the west) and the North American Plate (to the east).The Pacific Plate moves in a northward direction, which is the cause of earthquakes along this fault.The fault is more than 800 miles in length and goes as deep as ten miles into the earth.Visually, the presence of the fault can be seen on the surface by a linear trough over most of its length (Schulz, 2013).San Andreas Fault
Came into existence 15-20 million years ago. Comparing the geography along the fault, scientists believe that the total accumulated displacement since its existence is at least 350 miles, with a drift rate of approximately 2 inches per year (Schulz, 2013).
San Andreas FaultThe southern segment of the San Andreas Fault is the part that can be seen from Joshua Tree National Park. It extends from the Cajon Pass to the Salton Sea, 186 miles.
This part of the fault has documented aseismic creep.
As for the future of activity along the San Andreas Fault, the southern segment is long overdue for an earthquake, as it has not ruptured since prior to 1700. It is projected that the next big earthquake will be approximately magnitude 8 (Alden, 2013). Joshua Tree National Park is full of geological marvels. I love the beauty of the rocks, the landscape, and the animals that call this park their home. There is a lot of history here, which is why I chose this location for my field assignment. I enjoyed learning about the area and have a renewed appreciation for every plant, animal, mountain, and everything else I encountered. I hope you also enjoy hearing about the life and history of Joshua Tree National Park. Works Cited"A Desert Park." U.S. Department of Interior National Park Service, 1 May 2013. Web. 19 May 2013. .Alden, Andrew. "All About the San Andreas Fault." About.com, 2013. Web. 19 May 2013. .Biringer, Brad. "A Geological History of Joshua Tree National Park." N.p., 2005. Web. 19 May 2013. .Buscher, Linda, and Dr. Dick Buscher. "Desert Green: Joshua Tree National Park." LiveScience, 3 June 2011. Web. 19 May 2013. ."Cholla Cactus." DesertUSA.com, 2013. Web. 19 May 2013. ."Geologic Formations." N.p., 1 May 2013. Web. 19 May 2013. .
Works CitedIvanyi, Craig. "Life as a Lizard Unit: An Introduction to Lizards." Tree of Life Project, 2004. Web. 19 May 2013. .Kuchan, Ryan. "Cactus Types - What is Jumping Cholla?." Cactus Facts. N.p., 9 Mar. 2012. Web. 19 May 2013. ."Rock Types." Geology of the Joshua Tree National Monument. California Division of Mines and Geology, 5 Sept. 2011. Web. 19 May 2013. .Saunders, James. "Darwin and the Cactus." Chihuahuan Desert Nature Center, 19 Feb. 2009. Web. 19 May 2013. ."Sceloporus Occidentalis." Idaho Museum of Natural History, 2013. Web. 19 May 2013. .
Works CitedSchulz, Sandra S., and Robert E. Wallace. "The San Andreas Fault." U.S. Department of the Interior, 11 Jan. 2013. Web. 19 May 2013. ."Teddy Bear Cholla, Jumping Cholla." The Living Desert, 2010. Web. 19 May 2013. ."Western Fence Lizard." eNature.com, 2007. Web. 19 May 2013. ."Western Fence Lizard." N.p., 7 Nov. 2012. Web. 19 May 2013. .