Eaton Canyon and the San Gabriel MountainsBy Aaron Chiang

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

What types of rocks are present? (Eaton Canyon)• Diorite (right picture)• Granidiorite (right picture)• Granite Pegmatite (left picture)

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)

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).

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:

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.

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)

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.

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)

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 bouldersright before the waterfall

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.

Ecosystems (cont.)• The picture listed below shows how the mountains block the

heat from the Mojave desert

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, 2013From http://kimandgeoff.com/wp-content/gallery/san-gabriel-skiing/p4123190.jpg • [San Gabriel Mountain Wind Patterns]. Retrieved August 1st, 2013From http://latimesblogs.latimes.com/.a/6a00d8341c630a53ef0153929a1b65970b-pi• [Sage Brush]. Retrieved August 2nd, 2013From http://www.ecnca.org/plants/Images/SageBrush1.jpg• [Coyote] Retrieved August 2nd, 2013From http://www.tpwd.state.tx.us/huntwild/wild/images/mammals/coyote2.jpg