Every two years, the Geophysical Applications class ventures to the Mojave Desert between Las Vegas, Nevada, and Death Valley, Calif. for a one-week geophysical field camp. At left you see a graduate and undergraduate student cooperating on a shallow ground-conductivity survey in Stewart Valley on the Calif.-Nevada state line. The 3 m long horizontal pole has a radio-frequency inductive transmitter coil at one end, and a receiver at the other.
At left left is a view north up a branch of the Pahrump Valley fault zone, showing soil-color and vegetation contrasts. Here in southern Stewart Valley the fault has almost purely dextral strike-slip motion and lacks the scarps seen to the south.
The 1996 class completed a 3-d shallow seismic survey across this fault, employing a new Bison Galileo-21 48-channel seismic reflection recorder purchased for the Mackay School of Mines by the Keck Foundation. Click at left to see a QuickTime movie of some examples of the more than 4500 16-lb sledgehammer blows the class had to make to complete a 3-d survey with 480 source locations, or here for an MPEG version.
While both the ground-conductivity and seismic surveys were designed to characterize the fault within several meters of the surface, total-field magnetic measurements can locate discontinuities at both shallow and deeper depths, up to 1000 m or more. A kerosene-filled cylinder atop the pole provides hydrogen nuclei that precess at a frequency proportional to the local magnetic field strength. The cable connects the receiver coil around the cylinder with the data logger carried at left.
Previous work by the 1994 Geophysical Applications class on branches of the fault in southern Pahrump Valley suggested that hot-spring mineralization along the fault caused condutivity and magentic anomalies. At left is an attempt to use time-domain electromagnetic methods to test the fault zone for conductivity anomalies deeper than a few meters. At left a graduate student is unreeling the 40 m wide transmitter loop, which will incite telluric currents at increasing depths after transmitter cutoff. A 5 m receiver loop measures the telluric currents.
The class bunked in and around the ``Flower Building,'' a community hall in Shoshone, Calif. owned by the Shoshone Development Co. It functions each year as an art exhibition venue, and so fortunately contains many large tables. The class needed every one for maps, equipment setup, and computers. Any comprehensive geophysical expedition requires many specialized and costly instruments. It is likely the contents of the Flower Building during the trip were not more than $50,000 underinsured.

This page's background is a desaturated version of a close-up photo of deformed gypsum veins in this fault prepared as a texture.
Across the Amargosa River near Saratoga Springs, Bennie showed the class a diamictite more than one billion years old, with angular and faceted clasts suspended in a muddy and poorly-sorted matrix.
Other pre-Cambrian diamctites are known from cratons around the world, and also from many eras. Given the matrix-supported, poorly-sorted fabric of diamictites, together with their angular clasts, many geologists have proposed that they are glacial in origin. As extensive as this diamictite is in the Death Valley region, if it is glacial it would record an ancient and substantial climatic fluctuation.
Another odd formation within the Amagosa complex is this varved distal marine shale that somehow includes erratic blocks a meter or more in size, exposed near where the Amargosa River emerges on the floor of southern Death Valley. Although possibly ice-rafted dropstones, a glacial origin is still not consistent with the very continuous mantling of the blocks with the varve layers both above and below them.
Just north, near China Ranch where the California Valley drainage drops into Amargosa Gorge, the Miocene China Ranch beds expose a more recent poorly sorted and matrix supported sequence. Consisting of alluvial fan, slump, and megabreccia deposits, it records a period of intense tectonism probably beginning 11 million years ago. Previous work by Geophysical Applications classes in 1991 and 1992 showed that the slowly deposited Tecopa Lake beds that depositionally overlie the China Ranch beds belie the cessation of this tectonism before 7 million years ago.