Friday, February 29, 2008

Geology of the San Andreas Fault - A Class at Coconino Community College

I just completed teaching a class in the Geology of the San Andreas Fault (GLG 298 at Coconino Community College). Fifteen lucky students and myself traveled for five days to the southern segment of the fault adjacent to Anza-Borrego Desert State Park and Joshua Tree National Park. Here are some pictures of the things we saw and learned about.

Palm tree oases are rather abundant in this desert land and their occurrence is related to faulting, whereby water is forced to the surface when encountering a fault trend. These palms are in Borrego Canyon just 1.5 miles from our campsite.

Inside the palm oasis in Borrego Canyon.

We hiked to the top of Borrego Mountain, known locally as the West Butte. Mesozoic age granite greeted us here and was a nice lookout for lunch.

On the way down we discovered something called The Slot and it was narrow beyond belief.

Here are two of my students, George and Bruce, admiring the narrow slot.

After exiting The Slot, we drove into Split Mountain along Fish Creek. This is a shot of the famous anticline along the drive into the mountain. Incredibly, this deformation happened when an earthquake along the San Andreas Fault displaced 300,000,000 cubic yards of earth on Fish Creek Island within the ancestral Gulf of California. This happened about 5 million years ago. The resulting slide (7 miles long) crumpled the deposits that were accumulating on the gulf floor. Wow!

Here is Rex Stephens admiring some tilted but otherwise undeformed layers of the Imperial Formation (ancestral Gulf of California deposits).

After exiting Split Mountain the Elephant Knees came into view. This is also an outcrop of the Imperial Formation and this section is full of fossils. We found many oyster shells and gypsum crystals (selenite) laying around here in the late afternoon light.

Traveling around the southeast side of Anza-Borrego, we came across an old Indian village where morteros had been ground into the hard granite.

Here's Mary Gavan taking notes while visiting the morteros.

At Font's View, one gets a sweeping view of the Borrego Badlands. Many of these deposits were laid down by the advancing delta of the Colorado River.

Driving towards Joshua Tree, we traversed the southern shore of the Salton Sea and visited the Salton Buttes. These are six small volcanic plugs that are quite young. Here a flow of pure obsidian is preserved on the shore of the inland sea.

Just a few miles away are the mud volcanoes - which are constantly erupting mud.

Everyone enjoyed seeing these amazing structures. Water from the Salton Sea seeps into hot rocks below where it becomes heated and rises to form these volcanoes.

A gaseous and hot mud pool. It spattered everyones shoes.

Next we drove to Painted Canyon near Mecca and in the Mecca Hills. These sediments belong to the Palm Springs Formation and were derived from alluvial fans than entered the Salton Trough about 2 million years ago. The San Andreas Fault has lifted these sediments to their present height.

We entered Ladder Canyon by a series of well placed ladders in a slot canyon.

I never expected to find so many wonderful slot canyons in California! But desert runoff will create these features.

In Ladder Canyon in the Mecca Hills.

Sunrise in Joshua Tree National Park

We got up before dawn on our last day and watched the sun rise on Mt. San Jacinto and the San Andreas Fault below it.

We finished up the trip taking a short hike within the White Tank monzogranite, at 85 million years old, it has weathered into fantastic shapes. Waht a trip!


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