Geological diversity: Tuffs, Sands, Limestones and Lava Flows

March 10th, 2010

ZZYZX, CALIFORNIA–One of the most attractive aspects of geology is how many materials and processes are included in the study of the Earth. Today’s field experiences show this diversity. One of the best reasons to teach in a liberal arts geology program is that we are continually in touch with topics outside of our original disciplinary training. This trip has been so much fun in part because all four of our faculty are involved at each of our stops, and we always learn from each other by having no fear about asking any questions. We seem to be successfully modeling this attitude with our students because they certainly have no hesitation in asking questions either.

Our teaching approach in the field has been to introduce students to the general framework of information about a particular site, and then let them explore the area, each bringing back questions, observations and specimens for a summary session with all the faculty. This has worked very well with this class because they are advanced and very enthusiastic students. Their curiosity has been an inspiration.

This morning was sunny, windy and cold (starting in the forties and not getting past 53°F). It hardly mattered though because we had so many interesting outcrops to study.  Our first stop was Hole-In-The-Wall in the southeastern quadrant of Mojave National Preserve. Here are magnificent tuffs from an explosive volcano eruption about 18.5 million years ago. Dr. Pollock will have more to say about the geological details.

An exposed tuff at Hole-In-The-Wall showing "tafoni", which are small cave-like erosion features.

The loop trail around the major tuff exposure involved a steep climb through a slot canyon with the help of embedded rings. It was indeed physically challenging. Dr. Shelley Judge is shown climbing out with skill; Megan Innis points out the warning.

Our second stop was to climb the Kelso Dunes in the southwestern portion of the Preserve. The pile of sand here reaches 160 meters. It is trapped against the Granite Mountains in an endless swirl of winds. The students climbed the highest and most popular dune in the complex while the faculty chose to ascend a slightly lower but untrampled dune. Oddly enough, when we stood on these dunes in the middle afternoon, for the first time the wind stopped!

The graceful top of one dune at Kelso showing the shallower stoss side, steep lee side, and a small sand avalanche.

Dr. Greg Wiles made a trace fossil in the Kelso Dunes to confound future paleontologists.

Our last two stops were relatively brief.  One was at an outcrop of the Chambless Limestone, a Cambrian unit showing oncolites and dolomite-filled burrow systems.  The other was at the tip of a lava flow from the cinder cones near the center of the Preserve.  We returned to the station in the early evening with sand-filled shoes and sun-reddened faces. Another wonderful day in the Mojave.

Micah Risacher looming dramatically over our Cambrian limestone exposure.

Dr. Pollock wanted us to find her a lava tube. We did, albeit a small one, and she seemed happy enough with it.

A most impressive volcano

March 9th, 2010

ZZYZX, CALIFORNIA–Our second and last stop of the day was Amboy Crater, which is about halfway between Barstow and Needles, California, near Route 66. Meagen Pollock, our ace petrologist, prepared us well for this visit, so we’ll wait for her to post the geological details and her expert observations. I want to prepare the ground with some photos of our hike up this remarkably recent cinder cone.

Wooster geologists walking across the lava field to Amboy Crater.

A very happy Meagen Pollock with a volcanic bomb tossed from Amboy Crater.

Wooster geologists on the rim of Amboy Crater trying very hard not to be blown down either the steep slope into the crater or the steeper slope down the outside.

Calico rocks

March 9th, 2010

ZZYZX, CALIFORNIA–The day started very cold with a stiff, persistent wind and low dark clouds moving quickly across the mountain north of Soda Lake. We are comfortable in our rooms and the dining hall, but tend to notice the cold in the shower building which is, shall we say, a tad breezy. Fortunately our first stop would be mostly in buildings and underground mines.

Calico is a reconstructed mining town east of Barstow.  It was founded in March 1881 and was soon the richest silver mining district in California. It began to decline with silver prices in 1907 and dwindled to a few shacks until Walter Knott renovated the buildings in 1951 and turned the site into a tourist attraction. Now it is a county park with numerous private businesses operated inside. We visited it today to see the old silver mines and mining techniques and to look at the mineralized Pickhandle and Barstow Formations which host the ores.

Calico Ghost Town from the scenic viewpoint to the north.

Megan Innis showing us excellent desiccation cracks (from drying mud) preserved in the Barstow Formation (Middle to Late Miocene) at Calico.

Rob Lydell, Adam Samale, Rob McConnell and Andrew Retzler relaxing outside a Calico business. Andrew is drinking, of course, a sarsaparilla.

Sure it is a bit windy out here, but look at these folds!

March 9th, 2010

Syncline in the Barstow Formation at Calico Ghost Town. Note that the ductile deformation at the base of the fold becomes brittle toward the top as the fold tightened. Shelley Judge is the one with the explaining hand.

A Windy Desert Day for the Wooster Geologists

March 8th, 2010

ZZYZX, CALIFORNIA–The skies were brilliantly clear early this morning when we left the Desert Studies Center for points west. The price for the passage of the front was a stiff wind that kept up all day and even now is whistling in the darkness past our windows. I don’t mind at all.  It reminded me of delightful spring days in the desert when as kids we flew kites so high we could barely see them.

Our first stop was a visit to the extensive sedimentary layers laid down by the Pleistocene Lake Manix in what is now the lower Mojave River Valley.  We drove several miles on Harvard Road and walked across long stretches of desert pavement with ventifacts and occasional wind-polished agates.

Bottom sediments from the pluvial Lake Manix near Harvard Road. For scale, you may notice Megan Innis and Stephanie Jarvis in the central wash.

We then traveled farther west through Barstow to Owl Canyon and Rainbow Basin a few miles northwest of the city. There we met Buzz and Phyllis Sawyer, childhood friends of mine from Barstow and superb natural historians of the desert. We all enjoyed the diverse facies of the Barstow Formation (Middle to Upper Miocene) as well as the plants and animals in this protected area.

Professor Shelley Judge explains the complicated structure of Owl Canyon to her faculty colleagues using traditional geological hand language.

Wind-blown Wooster Geology field trip participants in Rainbow Basin with the famous Barstow Syncline in the background. This photograph was kindly taken by Buzz Sawyer.

Our last stop was Afton Canyon where we completed the Lake Manix story by looking at the outlet through which it catastrophically drained into Soda and Silver Lakes to the east. The sun had set by the time we gathered back at the vans, ending another productive and thought-provoking field day.

Wooster geologists crossing the mighty Mojave River in Afton Canyon. We don't think this is quite the same river Jedidiah Smith encountered.

Death Valley Day

March 7th, 2010

ZZYZX, CALIFORNIA–Today the Wooster Geology Mojave Desert field trip team visited the southern half of Death Valley National Park.  We left Zzyzx (love that name) early in the morning and drove straight north to the Furnace Creek Visitor Center.  After our orientation we headed south to the Natural Bridge trail.  There we hiked up a narrow canyon to look at the faulting associated with a metamorphic core complex.  As a bonus we studied a beautifully-dissected fanglomerate along the way.  We next spent quality time at Badwater, a fault-dissected cinder cone, and Shoreline Butte with its evidence of the receding levels of the ancient Lake Manly.  The weather could not have been better.  The little bit of rain as we drove back to Zzyzx produced one of the most brilliant rainbows I’ve ever seen.

Fanglomerate-walled canyon near Natural Bridge, Death Valley, with metamorphic highlands of the Black Mountains in the background.

The Natural Bridge made of fanglomerate.

Adam Samale, Jesse Wiles and Rob McConnell at Badwater on a recently-flooded portion of the salt flats.

A bright rainbow near Baker, California, at the end of our field day.

A bit of the Jurassic in southern California

November 27th, 2009

Waterfall (mostly dry) over Jurassic rocks in the Los Peñasquitos Canyon Preserve in San Diego County (N32.92712°, W117.17757°).

Waterfall (mostly dry) over Jurassic rocks in the Los Peñasquitos Canyon Preserve in San Diego County (N32.92712°, W117.17757°).

SAN DIEGO, CALIFORNIA–A nice geological interlude for this Wooster geologist during a family Thanksgiving.  This afternoon we visited Los Peñasquitos (meaning little cliffs) Canyon Preserve in San Diego County.  We walked about two miles along a trail to an exposure of Jurassic metaconglomerate.  The rock is interesting for several reasons.  The clasts are either highly angular (meaning parts are a breccia) or very well rounded; the clasts are volcanic in origin; and the matrix includes recrystallized belemnites.  The composition suggests that the main sediment source (if not the only one) was a set of offshore volcanic islands.

Note the very rounded and very anglar clasts in this metaconglomerate.

Note the very rounded and very angular clasts in this metaconglomerate.

This area has connections to Old California history.  Rancho Los Peñasquitos was where General Stephen Watts Kearny and his Army of the West rested after the Battle of San Pasqual in 1846.

Wooster Geologist in California

November 25th, 2009

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CLAREMONT, CALIFORNIA–The peak above is part of the San Gabriel Mountains just north of Claremont.  Today is one of the best southern California offers: brilliant sun, temperatures in the 70s, and very clear skies.  Apparently this view of the mountains is not always available because of air pollution, but you would never know it this morning.

The San Gabriel Mountains separate the Los Angeles Basin from the Mojave Desert on the other side.  The San Andreas Fault runs through them in a very complex way.

I’m here for family reasons (Thanksgiving in San Diego — can’t beat that!), but there is always something geological about!

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