Prepared in conjunction with the 2022 GSA Cordilleran/Rocky Mountain Sections Joint Meeting, this Field Guide showcases trips to geologically interesting areas in Arizona, Nevada, and California. Enjoy a three-day trip to the Buckskin-Rawhide and northern Plomosa Mountains metamorphic core complexes in Arizona. In Nevada, learn about the geology of Frenchman Mountain and Rainbow Gardens and landslide deposits and mechanisms in the eastern Spring Mountains. Or learn about microbialites in Miocene and modern lakes near Las Vegas. When weather permits, unravel the geological history of southern Death Valley, and explore vertebrate paleontology and Cenozoic depositional environments in Death Valley, California.

ABSTRACT Large-scale landslide deposits (covering >1 km 2 ) are prevalent throughout the Basin and Range province. However, their presence and importance in the evolution of the Basin and Range remain poorly recognized. On this field trip, we will visit four landslide deposits along the eastern flank of the Spring Mountains on the western margin of Las Vegas Valley. The first half of the day will be spent looking at vertical and lateral textures within the Blue Diamond landslide deposit, which mostly caps hills and ridges between the southern ends of the Wilson Cliffs and Blue Diamond Hill. We interpret this deposit as having a two-phase emplacement, with an initial rock avalanche emplacement onto Blue Diamond Hill, followed by failure as a rock compound landslide along weak gypsum layers in the Kaibab Formation. During the second half of the day, we will visit a smaller rock avalanche deposit (La Madre), a large rock compound slide that resulted from failure of the northern flank of Blue Diamond Hill (Red Rock Wash), and a large block of Paleozoic rock that likely was emplaced as either a rock compound slide or a rock planar slide (Lone Mountain).

ABSTRACT This field guide synthesizes more than a half century of research by many geologists and paleontologists on Frenchman Mountain and Rainbow Gardens, southern Nevada, USA. The field-trip consists of seven stops to be visited in one day. The guide was written not only for field-trip participants on the occasion of the 2022 ­Cordilleran/Rocky Mountain Geological Society of America Joint Section Meeting in Las Vegas, but also with future users in mind. The Frenchman Mountain/Rainbow Gardens block of crust exposes an extraordinary sample of Earth history. The geologic features include (1) Proterozoic crystalline rocks, (2) the Great Unconformity, (2) a Paleozoic interval that is essentially a ­tilted section of the western Grand Canyon, (3) a Mesozoic interval that preserves strata that were eroded off the southern Colorado Plateau during the Miocene “Great Denudation” episode, and (4) a Cenozoic section that records a wealth of paleo­climatic, paleontological, and tectonic data. Among the many stories that are recorded in the rocks of the Frenchman Mountain/Rainbow Gardens block, I have chosen three to emphasize in this field guide: (1) the history recorded in the Proterozoic Vishnu Basement Complex and the Great Unconformity; (2) the stratigraphy, sedimentology, paleontology, and geochronology of the Cambrian Tonto Group [with a focus on (a) trilobite biostratigraphy in the Bright Angel Formation, (b) the significance of the abundance of glauconite in the Tonto Group, and (c) the Frenchman Mountain Dolostone]; and (3) the tectonic story recorded in the Thumb Member of the Horse Spring Formation. The basement rocks record events and processes associated with the assembly of supercontinents Nuna and Rodinia. The Great Unconformity records the breakup of Rodinia and the associated denudation interval that played a role in triggering the Cambrian explosion. The Tonto Group, which was recently expanded to include the Frenchman Mountain Dolostone, records the Sauk Transgression. And the Thumb Member of the Horse Spring Formation contains rock avalanche deposits that have played a key role in sorting out the tectonic history of the southern Nevada region and the translational history of the Frenchman Mountain/Rainbow Gardens block.

ABSTRACT This field trip is designed to highlight recent findings in regard to the tectonic history of the southern Death Valley region. During the first day, stops will take place in the Ibex Hills and adjacent Ibex Pass area. These stops were chosen to emphasize recent work that supports multiple phases of extension in the region, and is recorded by the interactions of complexly overprinted normal faults. Mapping of the Ibex Hills revealed an older set of normal faults that have a down-to-the-SW sense of movement and are cross-cut by down-to-the-NW style normal faults. Additionally, the Ibex Pass basin poses a number of questions regarding its stratigraphy and how it relates to the timing and kinematics of the region. Multiple stops within the basin will show the variation of volcanic and sedimentary units across Ibex Pass. The second day of the field trip is focused more so on the more recent transtensional and strike-slip history of southern Death Valley. In particular, recent mapping has correlated features in the Avawatz and Owlshead Mountains that indicate ~40k m of offset along the Southern Death Valley Fault Zone (SDVFZ). Stops will take place along traces of the SDVFZ in the Avawatz Mountains and the Noble Hills. The final stop of the trip is in the Mormon Point turtleback, where the implications of the SDVFZ offset are discussed, alongside the metamorphic rocks at the stop, suggesting the restoration of the Panamint Range partially atop the Black Mountains.

ABSTRACT The vertebrate paleontology, lithostratigraphies, and depositional environments of the Cenozoic continental Titus Canyon and Furnace Creek Formations have been the subjects of several recent investigations. The two units are exposed in the Amargosa Range in northeastern Death Valley National Park, Inyo County, southeastern California, USA. Fossil tracks and trackways are preserved in playa mudflat deposits of the Pliocene Furnace Creek Formation at the Cow Creek tracksite on the western slope of the central Funeral Mountains. The tracksite includes footprints of birds and land mammals, as well as associated sedimentary structures. The lower red beds of the Titus Canyon Formation have produced numerous fossilized bones and teeth at Titus and upper Titanothere Canyons in the southeastern half of the Grapevine Mountains. The fossil remains represent 17 extinct genera and species of land mammals and one genus and species of pond turtle. The taxa constitute the Titus Canyon Fauna. The rodents Quadratomus ? gigans and Dolocylindrodon texanus , the bear dog Daphoenictis n. sp. (small), and the tapir Colodon stovalli are associated elsewhere only in the correlative, late early late Duchesnean Upper Porvenir Local Fauna of Trans-Pecos or Far West Texas. The local fauna occurs in the Blue Cliff Horizon (i.e., above lower marker bed) in the lower part of the Chambers Tuff Formation. The two assemblages share 12 species. The age of the latter unit is constrained by corrected single-crystal laser-fusion 40 Ar/ 39 Ar dates of 37.83 ± 0.09 Ma for the underlying Buckshot Ignimbrite and 37.14 ± 0.08 Ma for the overlying Bracks Rhyolite. However, both determinations should be considered tentative and subject to change with further investigation. The first green conglomerate unit of the Titus Canyon Formation overlies the lower red beds, underlies the Monarch Canyon Tuff Bed, and has produced the first records of land mammal footprints and a land plant (petrified palm wood) from the formation. The Monarch Canyon Tuff Bed and the Unit 38 Tuff Bed, which lies at the mutual tops of the upper “red beds” and the Titus Canyon Formation, are 34.7 ± 0.7 m.y. old and 30.4 ± 0.6 m.y. old, respectively, based on recalculated 40 Ar/ 39 Ar dates. Consequently, the Titus Canyon Formation is latest middle Eocene to earliest Oligocene in age, according to the 2020 Paleogene time scale.

ABSTRACT On this field trip, we will examine a modern lake in central Nevada, the Lower Pahranagat Lake, and lacustrine carbonate outcrops of the late Miocene, upper Horse Spring Formation. Both of the modern and ancient systems hold significant microbialite populations and we interpret that the Lower Pahranagat Lake is a possible analog for the ancient unit. Both systems are or were spring-fed from a similar Paleozoic carbonate aquifer. Both have evidence of microbially influenced sedimentation, probably related to spring activity. Both are dominated by the deposition of carbonate to the exclusion of nearly all siliciclastic material. In the Lower Pahranagat Lake, we will focus on the Holocene depositional record of the lake and the microbialites that are found therein. Molecular genetic data from three sites near the Lower Pahranagat Lake suggest that carbonate deposition could be strongly mediated by varying and complex microbial communities, and that simple interpretations of carbonate geochemistry probably neglect this influence. In the Lake Mead area, we will examine both the vertical (stratigraphic) and lateral relationships between a wide diversity of microbial macro- and mesostructures, to critically evaluate the relative effects of climate change, variable lake chemistry, and the role of microbial mat metabolisms on microbialite geochemistry.

ABSTRACT This guide begins with an overview of the internal structure and petrology of the Catalina Schist terrane as exposed on Santa Catalina Island, California, followed by a discussion of the tectonic setting and exhumational history of the terrane, and the Cenozoic tectonic and geological evolution of the Inner Borderland, within which it lies. The guide then presents an itinerary for a three-day field trip from 9–11 May 2020. Next, we present a tectonic model for the formation of the Catalina Schist, followed by a discussion of its relationship to the Pelona, Orocopia, Rand, and related schists in southern California. This field trip generally follows the GSA guide published in GSA Field Guide 59 (available at https://pubs.geoscienceworld.org/gsa ): Platt, J.P., Grove, M., Kimbrough, D.L., and Jacobson, C.E., 2020, Structure, metamorphism, and geodynamic significance of the Catalina Schist terrane, in Heermance, R.V., and Schwartz, J.J., eds., From the Islands to the Mountains: A 2020 View of Geologic Excursions in Southern California: Geological Society of America Field Guide 59, p. 165–195, https://doi.org/10.1130/2020.0059(05) .

ABSTRACT The Buckskin-Rawhide and northern Plomosa Mountains in west-central Arizona are metamorphic core complexes that record NE-directed, large-magnitude extension in the early to middle Miocene. Both core complexes consist of mylonites exposed in the footwall of corrugated, low-angle detachment faults. The Late Cretaceous Orocopia Schist and early Miocene intrusions dominate the mylonitic footwall of the northern Plomosa Mountains. The Orocopia Schist was emplaced during low-angle subduction of the Farallon plate and exhibits the hallmarks of the underplated Laramide subduction complexes, including blocks of metasomatized peridotite encased in quartzofeldspathic schist. In the Buckskin-Rawhide Mountains, carbonate-rich metasedimentary rocks that were buried to midcrustal depths by Mesozoic thrust faults preferentially absorbed Miocene footwall strain and localized the Buckskin detachment fault. A correlation between distinct granodiorite in the footwall of the Buckskin detachment fault in the eastern Bouse Hills and a hanging-wall conglomerate sourced from this granodiorite provides constraints on middle Miocene displacement across the detachment fault and indicates that displacement increased northeastward in the slip direction. The termination of slip on the Buckskin detachment fault also younged northeastward, largely ending by ca. 19 Ma in the western Bouse Hills and ca. 17 Ma in the westernmost Buckskin Mountains, but continuing to <16 Ma in the southern Buckskin Mountains and to ca. 12 Ma in the eastern Buckskin Mountains. Late stages of slip on the detachment fault record minor NW-SE shortening during amplification of corrugation folds. Postdetachment faulting across the region was dominated by dextral and oblique-dextral slip on NW-striking faults influenced by the Pacific–North America plate boundary. Locations visited on this three-day field trip highlight the structural evolution of these metamorphic core complexes.

Abstract The Ruyang (Mesoproterozoic; Pt 2 ) and Luoyu (Neoproterozoic; Pt 3 ) groups in the southern North China Platform are dominated by peritidal siliciclastic rocks and contain abundant microbially induced sedimentary structures (MISS), including multidirected and mat-protected ripple marks, mat chips, mat-smoothed ripple marks, various sand cracks, and irregular growth ridges. These MISS can be grouped into four MISS associations, each of which has distinctive MISS morphology resulting from changes in depositional environments. The upper subtidal to lower intertidal zone commonly lacks in situ MISS but contains redeposited mat chips. The upper intertidal zone is characterized by mat-protected ripple marks and mat chips. The lower supratidal zone is rich in various MISS, especially the large and morphologically complex sand cracks indicative of growth of thick mats in microenvironments with low hydrodynamics, sufficient moisture level, and frequently exposed substrates. The upper supratidal zone abounds with small sand cracks formed from relatively thin microbial mats. The morphological associations from tidal-flat deposits of the Ruyang and Luoyu groups are similar to those found in modern siliciclastic coastal environments. Similarities in MISS between modern and Proterozoic tidal flats suggest that the MISS morphological associations can be used for paleogeographical and paleoenvironmental reconstructions, especially in Precambrian siliciclastic successions.