Field Trip: Death Valley
Spring Break 2008
While Wisconsin was still in the clutches of winter, the St. Norbert College geology department gave a visit to California’s Death Valley National Park. In summer, Death Valley is one of the hottest places on Earth. In early spring, Death Valley felt pleasantly summerish. Death Valley is a beautiful study of the tectonics of the American southwest. The desert southwest is a series of such valleys. Death Valley also sports textbook examples of desert erosional features. As an added plus, in deserts there is little vegetation to obscure the geology!
This photograph shows well the bleakness and ruggedness of the desert landscape. Reds, browns, and grays intermingle, dotted with a few plants which have adapted to the heat and dryness. In the background is a hill (a “range”), with an alluvial fan coming off it. An alluvial fan is a deposit of sediment (alluvium) that accumulates where a river leaves a mountain. The deposit is fan-shaped, hence the term. Though deserts do not get much precipitation, flash floods are not infrequent when it does rain, and these floods build alluvial fans.
These two hills were once connected as a single cindercone volcano. A cindercone volcano is a small, short-lived volcano which ejects hot rock called “cinders,” but does not eject much lava. These “cinders” are composed of a rock called scoria. Scoria full of tiny holes, similar to pumice. The hills show above are made of this scoria. After this hill was formed, it was torn in half by a fault and the two halves have been moving away from each other ever since.
Of course, no desert would be complete without sand dunes. We learned here how sand dunes form and grow and move. Depending on wind patterns, dunes can take a variety of shapes. There are many different kinds of sand dunes. Far from being simple mounds of sand, sand dunes reflect complex interactions between sand input, sand output, and wind strength and direction.
The town of Rhyolite was a mining town in the early 1900’s. Long ago the town was abandoned and left to crumble into the desert, including this railcar. It has since been preserved as a historic site. It is an example of human interaction with the desert. Death Valley has been the site of various mining operations since the 1800s, many of them failures. Many minerals have been sought in the valley, including gold, copper, and borax. These minerals were mined and processed, braving the searing summer temperatures and scarcity of water. Now that it is a national park, no mining takes place in the valley, but reminders of the desert's human past are scattered throughout the southwest.
The intrepid St. Norbert geology crew climbs a canyon. During flash floods, raging water gushes down these canyons, scouring sediment.
The sediment scoured from the canyons are depositing in “alluvial fans,” as seen above. This is a very common sedimentary feature, and is very prevalent in Death Valley. Death Valley’s alluvial fans are exquisitely formed and appear in a great many textbooks.
“The Mushroom,” a rock which has an unusual shape due to erosion during sandstorms. The base of the rock has been sand-blasted off. Large sand grains typically do not bounce higher than four feet, even in very strong winds. This causes the unusual shape seen above.
Farewell, Death Valley! The view from Dante’s Peak as the sun sets over the valley. The salt flats (playas) of the valley floor gleam in the waning light.