ABSTRACT This field trip explores the geology and mining history of the Bodie Hills with a focus on the Bodie and Aurora mining districts. The field trip starts and ends in Bridgeport, California. Our first geologic stop is at Travertine Hot Springs, which provides an analogy for the style of mineralization observed in the Bodie and Aurora districts. We then proceed south on Highway 395 to the Bodie exit at Highway 270. At this location on Highway 395 is the placer camp of Dogtown with outcrops of till from the Sherwin glaciation. A side trip up Cinnabar Canyon exposes rocks with veinlets of cinnabar and silicic alteration. From here, we travel through several different components of different stratovolcanoes and arrive at the preserved ghost town of Bodie. Bodie Bluff and Standard Hill contain most of the mine workings for the Bodie district. At Bodie we discuss different interpretations of volcanic history and stratigraphy and learn about the U.S. Bureau of Land Management’s 1997 economic appraisal of the mineralization there: 69.8 million tons of ore averaging 0.4 oz/ton Au. Leaving Bodie, we pass through a placer field where William Bodie made his discovery of the mine and the district that bears his name. And then we move through the Bodie volcanics to those volcanic rocks associated with Aurora. On the way to Aurora, we will see the stage stop site of Del Monte. At Aurora, we view the active open pit mining operation and compare this district with Bodie and others in the Bodie Hills. Both Bodie and Aurora were classified as principal gold deposits of the United States.

Integrated mapping, fault-kinematic, paleomagnetic, and gravity analyses around the Rhodes Salt Marsh extensional basin, located within the east-west–trending Mina deflection of the central Walker Lane, reveal that from 8.0 to 9.0 km of late Cenozoic displacement was accommodated on a curved array of faults. The dominant slip on the faults systematically varies from left-oblique, to normal, and to right-oblique as fault strike changes from east, to north-northeast, and to north-northwest, respectively. Kinematic consistency of fault slickenline rakes, preservation of displacement budget, and paleomagnetic data from a pluton and volcanic rocks in the fault-system hanging wall indicate that the curved fault geometry is primary and not due to superposition of two fault systems nor to later vertical-axis rotation. Large-magnitude extension was localized at the apex of the curved faults and resulted in the formation of an ~3.0-km-deep prismatic basin beneath Rhodes Salt Marsh. The offset geologic structures and geophysical basin models indicate that hanging-wall displacement diverged around the curved fault array and resulted in finite flattening, with primary and secondary extensional axes oriented west-northwest and north-northeast, respectively. Fault-slip inversion yields two directions of extension consistent with the finite strain axes, and slickenlines with mutually crosscutting relations indicate formation during incremental flattening. Although broadly contemporaneous, extension parallel to the primary and secondary extension axes alternated at periods ranging from months to as much as several hundred thousand years. Large through-going structures sustained extension directions recorded geodetically and seismologically through multiple seismic cycles. In contrast, the alternation between primary and secondary extension directions recorded by a strainmeter suggests that, on small structures contained within fault-bounded blocks, the two extension directions alternated over time scales of as little as 2 yr.

Paleomagnetic data from three regionally extensive Oligocene ignimbrite sheets, two sequences of Miocene andesite flows, and ten sequences of Upper Miocene to Pliocene basaltic andesite flows in the Candelaria Hills and adjacent areas, west-central Nevada, provide further evidence that, since the late Miocene, and possibly between latest Miocene and earliest Pliocene time, the broad region that initially facilitated Neogene displacement transfer between the Furnace Creek and central Walker Lane fault systems experienced some 20° to 30° of clockwise vertical-axis rotation. The observed sense and magnitude of rotation are similar to those previously inferred from paleo-magnetic data from different parts of the Silver Peak Range to the south. We propose that clockwise rotation within the transfer zone formed in response to horizontal components of simple and pure shear distributed between early-formed, northwest-striking right-lateral structures that initiated in mid- to late Miocene time. Notably, the spatial distribution of the early-formed transfer zone is larger and centered south of the presently active stepover, which initiated in the late Pliocene and is characterized by a trans-tensional deformation field and slip on east-northeast–oriented left-oblique structures that define the Mina deflection. The sense and magnitude of rotation during this phase of deformation, which we infer to be of pre–latest Pliocene age, are inconsistent with the geodetically determined regional velocity field and seismologically determined strain field for this area. As a consequence, the longer-term kinematic evolution of the stepover system, and the adjoining parts of the Furnace Creek and Walker Lane fault systems, cannot be considered as a steady-state process through the Neogene.