Vivian Field Assignment- GEL 102

1. Historical Geology
Southern California Region: San Diego
By: Vivian Loewer
GEL 102

2. Cowels Mountain
Cowels mountain is a
popular hike in San Diego.
It is located in the San
Carlos neighborhood and is
one of my favorites!
Pictured to the right is me
and a friend after
completing a run up to the
peak for sunrise. The other
2 pictures show the view
from the top and looking
up at the mountain.

3. Cowels Mountain
Backround Info
• 1593 ft summit
• Highest peak in San Diego
• One of 5 mountains in the
Southern Peninsula range
(pictured left) called the
Laguna Mountains
• Also includes Santiago Peak, Del
Cerro, Black Mountain, and
Mount Miguel
• Made of Jurassic and early
Cretaceous metavolcanic and
shallow intrusive igneous rocks
Source: Gren, 2012

4. Why/When Cowels
Appeared…
• The mountain formed between 100 to 110 million years ago
• Caused by a collision, similar to the San Andreas Fault,
between the western arc and the Jurassic arc
• The growing westward arc moved toward the Jurassic arc
(parallel to the coast), growing larger and larger with granitic
magmas being created at depth
• The 100km thick tectonic plate carrying the western zone
ground into the old Jurassic off the coast causing a collision
• The collision compressed and deformed the Jurassic Plutons
and created the peaks that we see exposed today
Source: Gren, 2012

5. How Cowels has Evolved…
• After the collision, some of the magmas that had be forming rose to the
surface
• This formed large active volcanoes
• The remnants of these volcanoes are what compose the Laguna Mountain
range through San Diego
• Cowels is found inland from the coast, protruding from its cover of younger
sedimentary rocks

6. Modern Day Cowels
• Popular hiking spot
• Named after a 1870-80’s rancher, but was locally known as
“S” Mountain to the students at San Diego State University
• Most of the base of the mountain has been developed on,
creating the San Carlos neighborhood
• The hike is about 2 miles round trip and has an elevation of
about 1500 ft
• The Mountain opened for public use in 1972 but is protected
within Mission Trails Regional Park

7. Brittlebush
Encelia fairnosa
• Small shrub averaging 2-3ft tall, with green and white
stems and leaves, and bright yellow daisy flowers
• Typically arrives early summer in San Diego, Los
Angeles, Bakersfield, and other places throughout
southern California
• Scientific name is Encelia fairnosa
• Member of the sunflower family
• I choose this plant because it blankets Sunset Cliffs
every spring
Photo taken @ Sunset Cliffs San Diego by Vivian Loewer

8. Classification of Encelia fairosa
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Genus: Encelia
Source: Deere, 2019

9. How Brittlebush Evolved…
• Native to the unites states, not found natively in other countries
• There are seven other species of Encelia in North America and additional species in
South America
• Occurs mainly in the Mojave Desert, Sonoran Desert, Desert Mountains, and lower
elevations of the Peninsular and inner Southcoast Ranges
• It extends westward towards the coast and northward due to roadside and utility
corridor revegetation plantings
• Spreading due to coastal projects where it is being introduced by humans
Source: Deere, 2019

10. The Fox Squirell,
Sciurus niger
• First found in San Diego
in 1929
• Introduced species, not
native to San Diego but
have been here for
decades
• Bushy tail and greyish
brown with a large busy
tailPhoto taken at Balboa Park, San Diego
Source: Berger, 2019

11. Fox Squirrel Evolution…
• Native to eastern South Dakota
• They are the most widespread tree squirrel species
• Fox squirrels are easily distinguishable by a large bushy tail, rounded ears, and lack
of ear tufts
• The genus name for fox squirrel, Sciurus, comes from the Greek meaning "shade
tail.” which aligns with the dark appearance of their tails
• They are an invasive species to California but have a large population throughout
eastern San Diego
Source: Berger, 2019

12. Classification of the Fox
Squirrel
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Sciuridae
Genus: Sciurus
Subgenus: Sciurus
Species: S. niger
• Most abundant in open forest stands with tall trees and little
understory
• Fox squirrels are diurnal and spend more of their time on the
ground than most other tree squirrels
• They are non-territorial and live for an average of 18 years
• Overhunting and destruction of mature forests have caused the
species to be in decline
• Another reason for decline in population is the mite infestation
that is mortal, and severe winter weather (although not a
problem in San Diego)
Source: Berger, 2019

13. Rock Identification #1
The Igneous Rock, Granite
• This picture was taking in San Carlos, near Cowels
Mountain
• I classified it as granite because of the grainy look, as well
as the visible minerals giving it all the different colors and
patterns
• From my research, this granite is composed of quartz
(dark grey), Potassium Feldspar because of the
salmon/orange color, and biotite micas because of the
obvious brown hues and because of the dark spots giving
it a “black pepper” look towards the bottom of the photo
Photo taken by Vivian Loewer at Cowels Mountain
Source: Nace, 2016

14. More on Granite…
• Granite forms from the slow crystallization of magma below the Earth’s surface
• It is the best known igneous rock because it is the most abundant rock in the continental
crust
• It is exposed in many mountain ranges, within large areas known as batholiths, which is why
I was able to find it on Cowels Mountain
• The mineral crystals inside the granite are usually easily identifiable to the human eye and are
evidence that it cooled from molten rock at a relatively slow rate
• The minerals are what give each granite rock its color and unique characteristics
• Granite is typically made out of feldspar (10-65%), quartz (20-60%), and micas (5-15%)
Source: King, 2005

15. Rock Identification #2
The Sedimentary Rock Sandstone
• This picture was taken 3 blocks
away from my house. I choose the
cliffs as my second rock
identification because of the the
obvious layers of sediment which
make these cliffs so beautiful!
• I identified it as sandstone
because of the dark red orange
color, the fluid and irregular shape
with obvious patterns and layers,
the texture to the touch (soft and
thin), and the environment, being
right next to the ocean.Photo taken by Vivian Loewer @ Sunset Cliffs, San Diego
Source: Contributor for Science Direct, 2019

16. More on Sandstone…
• I think the sandstone at the cliffs is made up of
quarts and feldspar, but has impurities of Iron Oxide
because of the deep coloration ranging from pink to
dark red
• Sandstone can have different grain sizes depending
on the environment and location of the deposit
• It is typically very thin ranging from .1 to .2 mm and
forms when grains of sand from exsisting rocks or
crystals become cemented together
Picture of me and my dog, Dash, @ Sunset Cliffs
Source: Contributor for Science Direct, 2019

17. Rock Identification #3
The Metamorphic
Rock, Julian Schist
• I identified this rock as Julian Schist
because of larger crystals imbedded in
the rock. Also the coloration is the same
as identified schist, and this specific kind
of rock is known to be found in the
Laguna Mountain Range (where I found
this). The folding patterns and texture
also are clues because schist has this
specific distinct look.
• It may contain amphibolite because of
the dark areas of metamorphic rock
composed of hornblende and
plagioclase
• I found this rock while hiking in Eastern
San Diego
Source: Cantrell, 2017

18. More on Julian Schist…
• This metamorphic rock is composed of micaceous schist, gneiss and
quartzite
• It has been subjected to higher temperature and pressure which makes it
coarser and more distinct because of the increased crystallization of minerals
• It is typically found in the Peninsular Ranges batholith of San Diego
• According to GeoScienceWorld, these rocks were deformed and
metamorphosed during mid-to late Mesozoic, during the arc collision
Source: Cantrell, 2017

19. Steno’s Law of Original Horizontality
• The law of Original Horizontality was first proposed in the 17th century by
Nicholas Steno
• States that layers of sediment that were originally deposited in horizontal
layers, and that any tilting or faulting has been altered later by outside forces
• It is a fundamental law in geology and is important in understanding plate
tectonics and being able to learn and perform relative dating from rocks
Source: Alamo, 2016

20. Example of the Law of
Original Horizontality
• This photo was not taken by me, although I
have been to this exact place many times
• I like this photo because it is a clear example
of the Law of Original Horizontality
• You can see mostly horizontal layers that have
been deposited, with different thickness of
sediment
• Some unconformities that are present: some
areas where fault lines are present and some
evidence of tilting (angular unconformity)
• Part of the appearance of horizontal strata
come from erosion
Photo taken by Amy Cantrell at Sunset Cliffs San Diego

21. Works Cited
Alamo, T. (2016, July 2). Law of Horizontality in Sediments Sedimentary Rock Processes. Retrieved from
http://geology.isu.edu/Alamo/rocks/law_horizontality.php
Berger, J. (n.d.). Fox squirrel - Sciurus niger - NatureWorks. Retrieved June 3, 2019, from
https://nhpbs.org/natureworks/easternfoxsquirrel.htm
Cantrell, C. (2017, May 23). The early Mesozoic Julian Schist, Julian, California. Retrieved from
https://pubs.geoscienceworld.org/books/book/420/chapter/3798336/the-early-mesozoic-julian-schist-
julian-california
Contributor. (2019, March 02). How to Identify Sandstone. Retrieved from https://sciencing.com/identify-
sandstone-2155821.html

22. Continued…
Deere, J. (2019, September 31). Brittlebush Fact Sheet. Retrieved from
https://www.desertmuseum.org/kids/oz/long-fact-sheets/Brittlebush.php
King, H. (2005, October 3). Granite. Retrieved from https://geology.com/rocks/granite.shtml/
Nace, T. (2016, June 06). Why Granite Colors Range From White To Black. Retrieved from
https://www.forbes.com/sites/trevornace/2016/06/05/granite-colors-white-black-
countertops/#e31e2777b982
Wayne, G. (2012, December 18). Hiking Cowles Mountain: Tallest Mountain in San Diego City. Retrieved from
https://californiathroughmylens.com/2011/10/hiking-cowles-mountain-tallest-mountain-in-san-diego-city/