GEL 103 Field Assignment

By Abby Oswalt

• 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).

Metamorphic - Gneiss• 1.5 billion-year-old Pinto

gneiss

• Formed 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

Precambrian

• Pinto gneiss is primarily made

up of quartz, feldspar, and

biotite (“Rock Types”, 2011).

• A type of granitic rock, which is made up of quartz, mica, and feldspar (Buscher, 2011)

• 150 million years old

• Monzogranite was an intrusion of the much older gneiss in the park. At a depth of 15 miles below Earth’s 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

• The monzogranite’s 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 Cholla

• Genus opuntia; family cactacea

• Thrives in the hot desert of the American Southwest

• Grows 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

elevation

• Also 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).

• 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).

• Family phrynosomatidae

• Grow 6 to 9 ¼ inches long

• Found predominantly in California

• Males 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).

• Reptiles 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 Park

• The San Andreas Fault represents the meeting of two of

earth’s 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).

• 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).

• The 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).

• "A Desert Park." U.S. Department of Interior National Park Service, 1 May

2013. Web. 19 May 2013.

<http://www.nps.gov/jotr/planyourvisit/desertpark.htm>.

• Alden, Andrew. "All About the San Andreas Fault." About.com, 2013. Web.

19 May 2013. <http://geology.about.com/od/geology-

ca/tp/aboutsaf.htm>.

• Biringer, Brad. "A Geological History of Joshua Tree National Park." N.p.,

2005. Web. 19 May 2013.

<http://joshuatreenationalpark.net/history.htm>.

• Buscher, Linda, and Dr. Dick Buscher. "Desert Green: Joshua Tree National

Park." LiveScience, 3 June 2011. Web. 19 May 2013.

<http://www.livescience.com/30488-joshua-tree-national-park-

images.html>.

• "Cholla Cactus." DesertUSA.com, 2013. Web. 19 May 2013.

<http://www.desertusa.com/mag99/may/papr/chollas.html>.

• "Geologic Formations." N.p., 1 May 2013. Web. 19 May 2013.

<http://www.nps.gov/jotr/naturescience/geologicformations.htm>.

• Ivanyi, Craig. "Life as a Lizard Unit: An Introduction to Lizards." Tree of Life

Project, 2004. Web. 19 May 2013.

<http://tolweb.org/treehouses/?treehouse_id=3686>.

• Kuchan, Ryan. "Cactus Types - What is Jumping Cholla?." Cactus Facts.

N.p., 9 Mar. 2012. Web. 19 May 2013.

<http://cactusfacts.com/cactus/cactus-types-what-is-jumping-cholla>.

• "Rock Types." Geology of the Joshua Tree National Monument. California

Division of Mines and Geology, 5 Sept. 2011. Web. 19 May 2013.

<http://www.nps.gov/history/history/online_books/geology/publications

/state/ca/cdmg-cg-37-4/sec2.htm>.

• Saunders, James. "Darwin and the Cactus." Chihuahuan Desert Nature

Center, 19 Feb. 2009. Web. 19 May 2013.

<http://cdri.org/publications/nature-notes/evolution-ecology/darwin-

and-the-cactus/>.

• "Sceloporus Occidentalis." Idaho Museum of Natural History, 2013. Web. 19

May 2013.

<http://imnh.isu.edu/digitalatlas/bio/reptile/lacer/scoc/scocfram.htm>.

• Schulz, Sandra S., and Robert E. Wallace. "The San Andreas Fault." U.S.

Department of the Interior, 11 Jan. 2013. Web. 19 May 2013.

<http://pubs.usgs.gov/gip/earthq3/safaultgip.html>.

• "Teddy Bear Cholla, Jumping Cholla." The Living Desert, 2010. Web. 19 May

2013.

<http://www.livingdesert.org/desert_plants_page.html?name=Teddy+B

ear+Cholla%2C+jumping+cholla>.

• "Western Fence Lizard." eNature.com, 2007. Web. 19 May 2013.

<http://www.enature.com/fieldguides/detail.asp?recnum=AR0076>.

• "Western Fence Lizard." N.p., 7 Nov. 2012. Web. 19 May 2013.

<http://blm.gov.id/st/en/environmental_education/BLM-

Idaho_nature/wildlife/reptiles/turtles_and_lizards/western_fence_lizard

.html>.