The document summarizes geological features and organisms found in Joshua Tree National Park. It describes the park's location and landscape, composed of the Colorado and Mojave deserts. It then details the oldest rocks in the park, Pinto gneiss dating to 1.5 billion years ago, and younger monzogranite intrusions. Features like Joshua trees and cholla cacti, western fence lizards, and the San Andreas Fault zone are also summarized.

1. GEL 103 Field Assignment
By Abby Oswalt

2. • 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).

3. • 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).

4. 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).

5. • 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

6. • 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

7. aka Jumping Cholla

8. • 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).

9. • 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).

11. • 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).

12. • 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).

13. Above: sign posted at the San Andreas Fault Zone in Joshua Tree National Park

14. • 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).

15. • 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).

16. • 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).

18. • "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>.

19. • 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>.

20. • 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>.