Field trips and optional excursions

Thanks to its tectonic setting within an active rift and developing transform boundary, Nevada has a long history of Cenozoic hydrothermal activity.

On this trip, we will witness first-hand an active geothermal system, whose power is harnessed for geothermal energy, and then visit the 14 Ma Comstock Lode in Virginia City, the first large, bonanza grade epithermal deposit mined in the United States. Discovered in 1859, the Comstock Lode helped finance the Civil War for the Union, leading to Nevada’s statehood in 1864. Production from the Comstock was approximately 8.4 Moz of gold and 193 Moz of silver. The spectacular Big Bonanza ore body at the Consolidated Virginia mine alone produced 1.24 million tons of ore with average grades of 2.5 ounces per ton gold and 53 ounces per ton Ag. The Steamboat geothermal power plant produces ~78 MWe and was the location of Nevada’s first significant geothermal development.

Field trip stops at Steamboat will include the extensive sinter deposit, from which geysers once emanated, a geothermal power plant, and evidence for recent volcanism. Stops at Virginia City will focus on the styles and formation of hydrothermal alteration and mineralization, while also touching upon the Miocene volcanic setting of the Comstock district. In addition, anecdotes and other historical information on Virginia City and the Comstock will be shared. We will end the day with the icebreaker and welcoming dinner at the Ridge at Tahoe. 

The focus of this trip is the scenic Carson Valley, with a mix of human and geological history. The valley is exemplary of the basin and range, with dramatic topography, faulting, and the Carson River terminating in the Great Basin.

Dramatic earthquake fault scarps and hot springs frame the approach to Genoa, home to Nevada’s oldest bar, and Mormon Station, site of Nevada’s first permanent, non-native settlement. Ranches with historical barns abound in the valley, whose crops and livestock fed a hungry populace dating back to the 49ers heading to the California Mother Lode and to early Virginia City-Comstock Lode days. We’ll also visit the Stewart Indian School’s recently completed cultural center and museum and have a scavenger hunt for local rocks used in constructing buildings on the school campus.

This field trip will focus on the earthquake geology and hazards along the eastern range front of the Sierra Nevada and will provide the opportunity to view active geologic processes from picturesque viewpoints.

We will discuss the long-term history of the Carson Range-Kings Canyon fault system that has generated the spectacular faceted eastern Sierra topography, the timing and recurrence of earthquakes, glacial stratigraphy and chronology, debris flow and flooding hazards, and recent quadrangle mapping. Late Pleistocene and Holocene fault scarps extend along much of the trip’s route and will provide context to review seismic hazard assessment methodologies being employed by NBMG to better understand the seismic potential of this active fault system.

Field trip stops will include (1) a paleoseismic trench site along the Genoa strand of the fault at Fay Canyon which provides information on the timing of the most recent event; (2) a slicken-sided exposure of the Genoa strand of the fault at a quarry; (3) the location of several massive debris flow deposits and the devastating 1983 debris flow in Washoe Valley; and (4) an overview of the recently published Washoe Valley and Mount Rose quadrangle maps (STATEMAP) from atop Mount Rose. The trip will circle back to Lake Tahoe and finish at Sand Harbor, where we will gather for a beachside barbeque.

The Truckee River begins its 121 mile journey as the sole outlet of Lake Tahoe in the Sierra Nevada at an elevation of 6,233 feet.

From here, it flows north to the town of Truckee and then northeast and east into the Truckee Meadows (where Reno and Sparks are located). It continues east, carving its way through the mountains before turning north and terminating into Pyramid Lake at an elevation of 3,793 feet. The river provides water for residential and agricultural purposes in the greater Reno area and is regulated by a series of dams east of Truckee. The majority of the water in the river is sourced from snow pack in the Sierra Nevada. As a result, the river is susceptible to flooding. On this trip we will discuss the geology, geologic hazards, and water resource infrastructure along the Truckee River.

We will make our way upstream from Reno to Lake Tahoe and visit localities to view and discuss historic floods and pre-historic mega floods, volcanic activity, alluvial terrace formation, and glacial outwash and moraine deposits. These geologic processes have all contributed to the formation of the Truckee River Canyon. We will also visit Lake Tahoe and the outlet of the Truckee River via a short State Park trail.  Additionally, we may have the opportunity for a tram ride to the top of Palisades Tahoe Resort along the Pacific Crest Trail, which affords fantastic views of the Sierra Batholith and Lake Tahoe.

For the past 30 million years, western North America has been evolving from a convergent plate margin marked by subduction and magmatic arcs to a major transform plate boundary characterized by strike-slip faulting and regional extension.

The San Andreas fault currently accommodates about 75-80% of the right-lateral motion between the Pacific and North American plates.  The other 20-25% of this motion is accommodated well inland on a system of faults known as the Walker Lane and eastern California shear zone that cuts across western Nevada and eastern California. The evolution of the plate boundary over the past 30 million years suggests that the Walker Lane is the heir apparent to the San Andreas and may one day accommodate most or all (?) of the plate motion.

On this field trip, we will examine this dynamic tectonic setting and traverse across the incipient plate boundary in western Nevada. Our traverse will take us across the steep eastern and largely extensional front of the uplifted Sierra Nevada, through major right-lateral faults in the Walker Lane, and into a classic extensional part of the Basin and Range province. Along the way, we will discuss the evolving landscapes, geologic hazards, and mineral and geothermal resources. We will end the day with a great dinner at a local brew pub in Reno prior to returning to the Ridge at Tahoe.