The 2003 GPS Postdoc Field Trip

By Division of Geological and Planetary Sciences

For their annual field trip, the GPS postdocs went to Baja California, Mexico and the Salton Sea in southern California, on January 31 – February 3rd, 2003. Participants were (from left to right in the group photo below): top row: Joanna Smith, David Noone, Paula Smith, Juliette Artru, Nadine McQuarrie, Hiroto Kimura, Laurent Bollinger, Luc Margot, Norbert Shorghofer. bottom row: Eric Cowgill, Kari Cooper, Karena McKinney, Tara and Chad Trujillo, Chad Hall, Chris Walker.

Photo taken north of San Felipe with the Gulf of California in the background.

The purpose of this field trip was to give an overview of the boundary between the Pacific and North American plates and the opening of the Gulf of California. We also took advantage of other stops of scientific interest along the way.

Day 1

Cretaceous-Tertiary boundary is near the top of the darker layers attracting the geologists.

San Onofre Breccia: The provenance of this breccia is from the NW (now offshore), and the breccia includes clasts of high-pressure metamorphic rocks (blueschist). We debated whether the source was the Channel Islands or the Transverse ranges. After crossing the border at San Diego, we stopped to see the Cretaceous-Tertiary boundary near Colonet and then camped on the beach near Colonia Guerrero.

Day 2

Identifying microbial mats in Laguna Figueroa.

The first stop was at Laguna Figueroa to observe microbial mats. We then crossed the Baja Peninsula from west to east with stops to look at rocks of the Alisitos arc and the suture between arc rocks and continental North America. This transect was made possible by the 4WD Division vans which performed admirably as we were traversing spectacular canyons in the Sierra San Felipe.

Suture zone: debate about a possible plate between Farallon and NA plates; pictured are Nadine McQuarrie (left) and Eric Cowgill.

Day 3

We drove north from San Felipe to Laguna Salada through el Sierra Mayor where we saw a low-angle normal fault exposure and then a high-angle fault scarp at the western range front, which may be structurally linked to the low-angle fault system at depth within the basin. We crossed the border at Mexicali and drove north to Ocotillo Wells in Anza Borrego State Park for the night.

Possible low-angle normal fault along the western range front of the Sierra Mayor (Laguna Salada).

Day 4

Our first stop was Fish Canyon, within Anza Borrego, to see a sequence of sedimentary rocks that represent the terrestrial to marine transition and possible sturtzstrom deposits. We then drove east to the southern edge of the Salton Sea to look at Obsidian Dome, one of several recent (~16 ka) silicic eruptions resulting from extension related to the opening of the Gulf of California. Over lunch, Chad Trujillo set up a Questar telescope, loaned to us from the Astronomy Department, so that wee could observe sunspots. As we drove back towards Caltech, we couldn’t resist the temptation to stop at an exposure of the San Andreas fault zone in the Mecca Hills.

Fish Canyon sturtzstrom deposits; Chad Trujillo in foreground.

Obsidian domes at the south end of the Salton Sea.

Geoscientists drawn to the San Andreas fault.

The postdoc fieldtrip is an annual event sponsored by the Division of Geological and Planetary Sciences. The first year's group traveled to Owens Valley, the Sierra Nevada and the White Mountains, the second visited the metamorphic core complex of the Whipple Mountains in Southeastern California, and the third explored the rugged beauty of Death Valley. All of the participants agreed that the field trip was a valuable addition to the postdoc experience, and provided an opportunity to get to know each other more as well as to learn about some spectacular geology, microbiology, and planetary science. We would like to thank Ed Stolper and Marcia Hudson for making this trip possible, and the GPS division for financial support.

Last updated: Tue Oct 09 10:45:08 -0700 2007

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