Tessa De Oca conducted a field assignment in La Cañada, California, focusing on the evolutionary histories of oak trees, desert cottontails, and coyotes. She also identified three rock samples as diorite, basalt, and granite. Additionally, she observed examples of disconformity and the principle of original horizontality in the local geology.

1. LAB/FIELD
ASSIGNMENT
GEOLOGY 103
By: Tessa De Oca

2. Introduction
My Field Assignment was based in
Southern California, particularly the city of La
Cañada. My area is very mountainous and has
a variety of native plants and animals. I decided
to focus on the evolutionary history of oak trees,
desert cottontails, and coyotes. I also found and
identified 3 rock samples. Lastly, I observed both
an example of disconformity and the Principle of
Original Horizontality.

3. Geological Background: La
Cañada, CA
 Small town in LA County of Southern California
 Surrounded by San Gabriel Mountains, San Rafael Hills, and
Angeles National Forest
 Located in Crescenta Valley and San Gabriel Valley
Photos taken by me
of the field I’m
working in

4. Although the landscape of La Cañada has many trees, the
most prevalent is the native oak.
PART 1 Evolutionary History: Oak Tree
Oak tree in
neighborhood

5. Evolutionary History: Oak Trees
 “The oaks (Family Fagaceae, genus Quercus)
belong to an old lineage of trees and shrubs
that dates back to at least the Late
Cretaceous, about 85 million years ago”(
Jensen, )
 Old oak fossils suggest evolutionary
connections with beech trees
 Fossils of the major groups of oak trees have
existed since about 23 million years ago

6. Oak Trees Today
 Major groups in Southern California: Coast
Live Oak, Interior Live Oak, California Black
Oak, Canyon Live Oak, California Scrub Oak
 Based on observing the trees’ features
(leaves, bark, general shape etc.) , La Cañada
has mainly Coast Live Oak trees
 Each type has adapted to their local habitat’s
conditions
 Ex. Leaf structure

7. Rabbits are a common site in La Cañada, even in our own backyards!
PART 1 Evolutionary History: Desert Cottontail
Rabbit
[Desert Cottontail Rabbit]. (n.d.). Retrieved from
http://greglasley.com/images/Mammals/Desert%20Cottontail%2
00054.jpg

8. PART 1 Evolutionary History:
Desert Cottontail Rabbit
 Mammalian order: Lagomorpha (includes
rabbits, hares, and Pikas)
 Family name: Leporidae
 “Fossil records suggest that Lagomorpha
evolved in Asia at least 40 million years ago,
during the Eocene period” (History of Rabbits)
 When the continents split up, the different
species of Lagamorpha spread around the
world
 Earliest rabbit relative: Gomphos elkema

9. Early Rabbits vs Modern
Cottontail
Desert
Cottontail
BOTH Gomphos
elkema
Medium/tall
ears
Hindlimb
longer than
forelimb
Short/small
ears
Small in size Hopped around Small/medium
in size
Short cotton
ball-like tail
Same general
skeletal
structure
Medium length
tail
http://www.amnh.org/our-
research/science-news/2006/earliest-
rabbit-fossil-found-suggests-modern-
mammal-group-emerged-as-
dinosaurs-faced-extinction/
Gomphos elkema drawing
based on fossil finds

10. A lot of coyotes live in the nearby hills and mountains and we often hear
them howling at night
PART 1 Evolutionary History: Coyotes
coyote
https://en.wikipedia.org/wiki/Coyo
te#Evolution
https://3.bp.blogspot.com/-
gcRsAPabQzM/V2YTqXsxDZI/AAAAAAAAHeU/G
efVsl2qFuQkebxkRHhUBbY28QQSm96bgCLcB/s
1600/Screen-Shot-2015-07-28-at-4.20.55-PM.png

11. Evolutionary History: Coyotes
 Order/genus: Canis (including
wolves, coyotes, jackals, and
domestic dogs)
 Name: Canis Latrans
 “The evolution of the genus is
a complex topic involving at
least five continents”
 Genus Canis evolved from
Eucyon davisi
 Coyotes derived from a North
American lineage called C.
leophagus
Fossil remains of Eucyon
davisi (Late Miocene- Late
Pilocene)
https://en.wikipedia.org/wiki/Eucyon#/media/File:Eu
cyon_davisi.JPG

12. Evolutionary History: Coyotes
Canis latrans
Canis lepophagus
Canis edwardii
Eucyon davisi
Simplified evolutionary lineage of modern coyotes

13. Part 2 Rock Classification:
Diorite
Location found: My backyard (La Cañada, CA)
Colors: White, Black, Gray
Size: 3’ by 3’ by 2.5’
Other characteristics/observations:
 Visible grains that are both fine and course
 Relatively smooth surface; partially rough
 Relatively light in color
 Not shiny
 Salt and pepper appearance
Based on observations, believed to be Diorite
(igneous)

14. Part 2 Rock Classification:
Basalt
Location found: Hillside (La Cañada,
CA)
Colors: Mainly dark gray; some light
gray
Size: 6’ by 5’ by 7’
Other Characteristics/ Observations:
 Irregular shape
 Fine grained
 Dark in color
 Dense
 Hard
Based on observations, believed
to be Basalt (igneous)

15. Part 2 Rock Classification:
Granite
Location found: Hill along neighborhood
(La Cañada, CA)
Colors: Light tan with some clear, gray,
and white specs
Size: about 1’ all around
Other Characteristics/ Observations:
 Mainly coarsely grained
 Light in color
 Dense
 Hard
 Small
 Speckled
Based on observations, believed to be
Granite (igneous)

16. Part 3: Principle of Original
Horizontality
“sediment is deposited in essentially horizontal layers”
(Monroe, 2012 p.418).
 One of Steno’s fundamental principles of Relative Dating
https://s-media-cache-
ak0.pinimg.com/originals/ec/fd/13/ecfd13180327bbfe11

17. Example of Principle: Hillside
behind house
The different rock layers (denoted by the change in colors) is more or less
horizontal
The sloping occurred due to geological changes after the rock layers were
formed, according to the principle

18. Part 3: Disconformity
“surface of erosion or nondeposition separating younger
from older rocks, both of which are parallel with one
another”( Monroe, 2012, p. 420)
 One of the three types of unconformity
https://s3.amazonaws.com/classconnection/135/flashcards/3647135/jpg/typ
es-of-unconformities-img-1511380F2E440712164.jpg

19. Example of Disconformity: Hillside
behind house
You can see the separation of older and younger rocks
There is a middle horizontal strip that is darker in color than the above and
below layers, suggesting the layers are different ages
Layers run parallel

20. Works Cited
Plumb, T. R., & Gomez, A. P. (n.d.). Five Southern California Oaks. Retrieved June 20, 2017.
Jensen, R. About > The Origins of Oaks. Retrieved June 20, 2017, from
http://www.oaksofchevithornebarton.com/about-history-of-garden.cfm
Coyote. (2017, June 26). Retrieved June 20, 2017, from https://en.wikipedia.org/wiki/Coyote#Evolution
Wolves, Coyotes, and Dogs (Genus Canis). Retrieved June 20, 2017, from
http://exhibits.museum.state.il.us/exhibits/larson/canis.html
Smith, A. T. (2017, April 24). Rabbit. Retrieved June 20, 2017, from
https://www.britannica.com/animal/rabbit
B. History of rabbits. Retrieved June 20, 2017, from http://www.bunnyhugga.com/a-to-z/general/history-
rabbits.html
Earliest Rabbit Fossil Found, Suggests Modern Mammal Group Emerged As Dinosaurs Faced
Extinction. Retrieved June 20, 2017, from http://www.amnh.org/our-research/science-
news/2006/earliest-rabbit-fossil-found-suggests-modern-mammal-group-emerged-as-dinosaurs-faced-
extinction/
Monroe, J. S., & Wicander, R. (2012). The changing earth: exploring geology and evolution (6th ed.).
Stamford, CT: Cengage Learning.
** Photos not cited within presentation were taken by author (Tessa De Oca)**