The last stop of the field trip: Date shakes!

Mark Wilson March 18, 2011 9:33 pm

ZZYZX, CALIFORNIA–Apparently visiting China Ranch and having the famous date shakes is a tradition on at least a few other geology field trips. We were introduced to it by Matt James at Sonoma State, and today we met students and faculty from Columbia and the University of San Diego also spending the week in the Mojave. The high point of our encounter was when the student bodies sang to each other intricate and harmonious geology songs they had created! The date shakes were also a treat (especially with chocolate added) and a suitable way to end the 2011 Wooster Geology Mojave Desert field trip.

Thank you to the Desert Studies Center staff at Zzyzx for their excellent hosting and advice (and superb food from Chef Eric). We were also very fortunate to have on our trip this year our administrative coordinator Patrice Reeder who solved many problems, gave us several new ideas, and had enthusiastic questions that kept our game up. Our students were, of course, delightful and the reason why we enjoy these trips so well. Tomorrow we pack up and leave for the Las Vegas airport and home to Ohio.

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Trilobites! Now it’s a field trip.

Mark Wilson March 18, 2011 8:41 pm

Just kidding about the trilobite requirement for a true field trip, but we must acknowledge a certain charm that comes only from these spiny little beasts. Thanks to my buddy Matthew James, we were directed to an especially fossiliferous set of outcrops of the Carrara Formation in the Nopah Range. The trilobites we collected there are Early Cambrian, roughly 540 million years old. Nick Fedorchuk found the whole specimen photographed above. Everyone collected cephala (“heads”) and the occasional brachiopod and hyolith. It was a very good afternoon for paleontologists!

Wooster students at work in what we now call "Trilobite Valley".

Travis Louvain finding good specimens.

The trilobites here are strained by tectonism, so they look "stretched" in one direction. Shelley Judge collected a set to use in her structural geology labs.

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A favorite stop: the Resting Spring tuff exposure

Mark Wilson March 18, 2011 8:27 pm

ZZYZX, CALIFORNIA–We’ve visited this roadside outcrop on California Highway 178 in the Resting Spring Range on each of our field trips to the Mojave Desert. Meagen Pollock may explain more about this fascinating outcrop later in the blog, but for now I can report that it is a “devitrified pumice tuff, welded tuff, and vesicular vitrophyre” dated by K-Ar methods at 9.5 million years old (Hillhouse, 1987). It is an excellent place for students to put their developing petrologic, stratigraphic and structural skills to the test.

Sarah Appleton on the tuff at Resting Spring Pass showing the zones of sintering.

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A little vignette of desert ecology

Mark Wilson March 18, 2011 9:12 am


ZZYZX, CALIFORNIA–While exploring the Amboy Crater lava fields on Wednesday, we noticed these small and very active “yellow” beetles. With a little research we discovered they are Desert Spider Beetles (Cysteodemus armatus) that feed on the nectar from a variety of flowers. As you might have guessed by now, the yellow color on the heads and abdomens of the beetles is actually from the pollen of a particular yellow flower blooming in abundance the day of our visit. These beetles turn out to be important pollinators for several flower species.

Some of the many flowers near Amboy Crater. I need my flower expert Mother's help to identify them!

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Back to granite on Cima Dome

Mark Wilson March 17, 2011 11:50 pm

A granite exposure near Teutonia Peak on Cima Dome. Note our jackets and hands in pockets!

ZZYZX, CALIFORNIA–Our last stop of the rapidly-cooling day was on the huge Cima Dome east of Zzyzx in the Mojave National Preserve. The dome is so large (about 70 square miles) that it is impossible to detect when you are actually on it, but easily visible from miles away. It apparently is the eroded root of a granitic intrusion formed during subduction in the Jurassic to Cretaceous. The alkali granite exposed here is very similar to that of the Granite Mountains we saw yesterday.

Potassium feldspar crystals in the coarse alkali granite of Cima Dome.

The soil of Cima Dome is derived almost entirely from the underlying alkali granite.

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A tuff afternoon

Mark Wilson March 17, 2011 11:45 pm

Lindsey Bowman and Becky Alcorn on the Hole-In-The-Wall tuff deposits.

ZZYZX, CALIFORNIA–After lunch we took a long drive south and east to the Hole-In-The-Wall visitor center and trail. Exposed here are diverse and colorful rocks called tuffs that were formed by pyroclastic eruptions from volcanoes roughly 18.5 million years ago. These eruptions of hot gases and ash swept the surrounding countryside depositing thick masses of complex rock. Plants and animals were incorporated in the ash flows, so we occasionally find charcoal in the tuffs as well as various other volcanic products.

A piece of charcoal from a burnt tree in a tuff at Hole-In-The-Wall.

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A massive pile of sand: the Kelso Dunes

Mark Wilson March 17, 2011 11:41 pm

ZZYZX, CALIFORNIA–Later in the morning the Wooster Geologists visited a favorite location: the Kelso Dunes in the Mojave National Preserve. We arrived before noon so we could work up a hearty appetite for lunch by climbing the dunes first. The Kelso Dunes are made almost entirely of medium to fine sand grains derived from the dry bed of the Mojave River (and ultimately the San Bernardino Mountains where it originates).  The most common minerals are clear quartz and white to pink potassium feldspar, with a smaller but prominent component of black magnetite that often concentrates on dune crests (see above).  Most of the sand accumulated at the end of the last ice age and has been blowing around in place since then.  No new sand is being added to the dunes today. The highest dune rises 200 meters above the valley floor — and it is a hard slog up to the top.  (And much faster going down!)

Dune grass baffling sediment and refracting the waveforms of magnetite-rich sand.

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Deep in the heart of a lava flow

Mark Wilson March 17, 2011 9:51 pm

ZZYZX, CALIFORNIA–This morning the Wooster Geologists enjoyed an ancient lava flow from the inside. We found our way to a lava tube near the center of the Mojave National Preserve and explored the interior with flashlights and flash cameras. It helped that there were a few “windows” in the basalt roof where sunlight could stream in. As Meagen Pollock (she who lives for basalt) explained, a lava tube is formed when a flow cools on its exterior portions while the lava is still moving.  When the lava drains out at the end of the flow, the result is a long tunnel of basalt.  Lava dripped from the ceilings, making the igneous equivalent of stalactites.  As the flow receded, it left horizontal “bath tub rings” along the side of the tube. It was fun to speculate on how many lava tubes remain undiscovered beneath the many square kilometers of basalt exposed in the Mojave Desert.

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Igneous delights at Amboy Crater and in the Granite Mountains

Mark Wilson March 16, 2011 11:13 pm

Greg Wiles on the rim of Amboy Crater.

ZZYZX, CALIFORNIA–This afternoon the Wooster geologists studied two very different magma products in the southern part of our field area. After lunch we drove to Amboy on historic Route 66 and then hiked up to the rim of Amboy Crater. Here we saw the extrusive, mafic rock basalt at its finest in the cinder cone itself and the lava flows across the valley.

Desert iguana on the basalt near Amboy Crater.

After Amboy, we traveled north to the Granite Mountains and examined wonderful alkali granites weathering into rounded boulders. The feldspar crystals in these intrusive felsic rocks were extraordinarily large and numerous, and there were many xenoliths scattered throughout. The countryside here was lush with desert vegetation that made our all-too-brief stop most enjoyable.

An exposure in the Granite Mountains, California.

The feldspar-rich alkali granite in closer view.

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Structural geology and mineralogy at Calico

Mark Wilson March 16, 2011 10:58 pm

ZZYZX, CALIFORNIA–It was surprisingly cool this morning in Zzyzx as we left for our day of fieldwork, but we were not surprised by the wind at our first stop, Calico Ghost Town outside Barstow. Every time we’ve been there it has been blustery. Calico is an old silver mining site with a complex geological structure complimented by hydrothermal mineralization driven by dacite intrusions roughly 17 million years ago. Shelley Judge showed us how strike-slip faulting (ultimately a result of movement on the San Andreas Fault to the west) produced compressional folds in the Barstow Formation. Meagen Pollock talked about how the silver rich veins were formed by thermal alterations of the sedimentary rocks on the flanks of the Calico Mountains. We then spent a little time in the town itself eating our packed lunches and enjoying cold sarsparilla!

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