2. Background information
• Eaton canyon is the main emphasize, but the canyon itself is a
small part of the San Gabriel Mountains
• Eaton Canyon itself doesn’t have specific history, but is just
part of San Gabriel Mountain’s history
3. What types of rocks are
present? (Eaton Canyon)
• Diorite (right picture)
• Granidiorite (right picture)
• Granite Pegmatite (left picture)
4. Rocks: How they formed
• Oldest rock: Pelona Schist (not seen on the trip there)
(Nourse, 2002)
• Thought to have formed from the subduction of the now
destroyed Farallon plate underneath the North American plate
during the Paleocene. (Nourse, 2002)
• The San Gabriel Mountains contain mainly igneous and
metamorphic rocks that were disrupted and broken by faults
that delineate the boundary between the North American and
Pacific plate. (Nourse, 2002)
• The boundary between these two plates started forming in
the late Cenozoic, particularly the Miocene. This fault is the
famous San Andreas fault (Nourse, 2002)
5. Rocks: How they formed
(cont.)
• San Gabriel Mountains are bounded by the San Andreas fault
(right-lateral) to the north and the Sierra Madre-Cucamonga
fault system (thrust) to the south (Nourse, 2002)
• The San Gabriel Mountains were formed because the San
Andreas fault 'jogs' to the east along this area, creating
tension between the southern block wanting to move
northward and the north block moving south. In addition to
this, the Sierra Madre-Cucamonga thrust fault exerts a
compressional force against the rocks. The mountains are
"currently experiencing a state of transpression" (Nourse,
2002, p. 175).
6. Rocks: How they formed
(cont.)
• Through palinspastic reconstructions done by multiple
geologists, it seems that the rocks in the San Gabriel
Mountains were once connected to the rocks found in
Orocopia and Chocolate Mountains in the south. When right-
lateral movement was initiated through the birth of the San
Andreas fault, it moved some of these rocks northward.
(Nourse, 2002)
• San Gabriel Mountains:
7. Plants & Animals
• The prickly-pear cactus is "most common in disturbed areas
such as … land once cleared by man" (Vaughan, 1954). It
serves as food for many animals like rats, mice, and rabbits.
• The coyote is the most dominant predator in Eaton Canyon,
though it was not seen on the time of the visit (Vaughan,
1954)
• Sage Brush is a native shrub, it has a strong, sagelike aroma
but is a member of the sunflower family.
8. Prickly Cactus: (1)
• Prickly Cactus is the most widespread species from a hybrid
origin. (Pensoft Publishers, 2012)
• The hybrid origins are from Western and Southeastern North
America. (Pensoft Publishers, 2012)
• Studies show that the prickly cactus came about throught
genome duplication (Pensoft Publishers, 2012)
• Genome duplication is “a result of the genetic separation of
closely related parent species through habitat fragmentation
during different times of the Pleistocene.” (Pensoft Publisers,
2012)
9. Sagebrush, California (2)
• It's thought these days that the ancestors of today's sagebrush
species arrived from Asia at some point during the
Pleistocene-- or less than 2.5 million years ago
• Armed with adaptations to cold that would have proved handy
against drought, with small seed that could be quickly
dispersed by wind, water, and animals, the paleo-sagebrushes
would have exploded across the west, finding new habitats to
shape their descendants' evolution.
10. Coyote (3)
• “Pleistocene coyotes were larger and more robust than
Holocene populations” (Meachen and Samuels, 2012)
• “However, within 1,000 years of the mega faunal extinctions,
coyotes are morphologically indistinguishable from modern
populations.” (Meachen and Samuels, 2012)
11. Ecosystems: Waterfall (4)
• Eaton Canyon is known for a waterfall at the end of its “short”
trail. We can assume that animals go there for a drink of
water or to cool off in the summer heat.
• Picture on the left are boulders
right before the waterfall
12. Ecosystem: Dry River Bed (5)
• The mountains prevent cold ocean air from leaving the coastal
basins, keeping them cool. In comparison, the Mojave desert,
which is on the other side of the Mountains, receives the
brunt of the heat and mostly stays dry. (Vaughan, 1954)
• During the summer, because of the lack of rain and the heat of
the desert, river beds tend to dry up
• The picture is part of a dry river bed along the Eaton Canyon
path.
13. Ecosystems (cont.)
• The picture listed below shows how the mountains block the
heat from the Mojave desert
14. Bibliography
• Nourse, J.A. (2002). Middle Miocene reconstruction of the central and eastern San Gabriel Mountains, southern California,
with implications for evolution of the San Gabriel fault and Los Angeles basin, in Barth, A., ed., Contributions to
Crustal Evolution of the Southwestern United States: Boulder, Colorado, Geological Society of America Special
Paper 365, p. 161–185.
• Vaughan, T.A. (1954, November 15). Mammals of the San Gabriel Mountains of California. Naturespace, 7. Retrieved from
http://www.naturespeace.org/sangabrielmammals1954.b.htm
• Pensoft Publishers (2012, February 14). Chromosome analyses of prickly pear cacti reveal southern glacial
refugia. ScienceDaily.
• Clarke, C. (2012, Feb. 28). An Introduction to Desert Sagebrush and its Evolution. KCET. Retrieved from
http://www.kcet.org/news/the_back_forty/botany/evolution-at-work-in-a-sea-of-sagebrush.html
• Meachen, J.A. and Samuels, J. X. (2012) Evolution in coyotes (Canis latrans) in response to the megafaunal extinctions. PNAS.
Retrieved from http://www.pnas.org/content/109/11/4191.long
• [San Gabriel Mountains]. Retrieved August 1st, 2013
From http://kimandgeoff.com/wp-content/gallery/san-gabriel-skiing/p4123190.jpg
• [San Gabriel Mountain Wind Patterns]. Retrieved August 1st, 2013
From http://latimesblogs.latimes.com/.a/6a00d8341c630a53ef0153929a1b65970b-pi
• [Sage Brush]. Retrieved August 2nd, 2013
From http://www.ecnca.org/plants/Images/SageBrush1.jpg
• [Coyote] Retrieved August 2nd, 2013
From http://www.tpwd.state.tx.us/huntwild/wild/images/mammals/coyote2.jpg
