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Research about Nevada

Source-linked reports with geographic coverage including Nevada.

At least 163 records · Page 9Linked to original sources
USGS2018

Groundwater contributions to excessive algal growth in the East Fork Carson River, Carson Valley, west-central Nevada, 2010 and 2012

Excessive algal growth and low dissolved oxygen concentrations were observed during low streamflow conditions during summer months along a 5,800-foot reach of the East Fork Carson River in Carson Valley, west-central Nevada. Algal growth from nutrient enrichment of a stream reduces aquatic diversity, threatens fish ecology and stream health, and can be a recreational nuisance. In response to concerns that groundwater discharging to the 5,800-foot reach of the East Fork Carson River may be a source of nutrients to the stream, the U.S. Geological Survey, in cooperation with the Carson Water Subconservancy District and the Nevada Division of Environmental Protection, conducted studies during the summers of 2010 and 2012 to gain an improved understanding of the contributions of nutrients to the stream from groundwater, characterize algal conditions and algal effects on water quality, assess potential sources of nitrate in groundwater discharging to the stream, and evaluate nitrate reduction in groundwater from denitrification. A reconnaissance study in the summer of 2010 along the 5,800-foot study reach located a subreach with clear evidence of nutrient-rich groundwater discharging to the stream. At the subreach, nitrate plus nitrite (referred to hereafter as nitrate) concentrations in groundwater discharging to the stream were high (average 2.75 milligrams per liter as nitrogen) along the right bank. The stream at this location had the highest stream nitrate concentrations (average 0.056 milligrams per liter as nitrogen) compared to other locations upstream and downstream of the subreach. As a result, the 2012 study focused on a 405-foot subreach of the East Fork Carson River centered where results from the 2010 study found the highest stream and groundwater concentrations of nitrate, as well as the greatest observed contributions of groundwater discharge to the stream. Groundwater nutrient concentrations were much higher than stream nutrient concentrations during the summer of 2012 during low streamflow conditions at the 405-foot subreach of the East Fork Carson River. Average groundwater nitrate and orthophosphate concentrations along the right bank of the 405‑foot subreach were 9 and 12 times higher, respectively, than in the stream at this subreach. Groundwater discharge rates to the study reach based on different methods varied from 0.09 to 1.2 cubic feet per second per mile. Estimated groundwater discharge rates to the right bank of the study subreach were used to calculate groundwater nutrient load estimates to the subreach right bank, which were found to be low when compared to stream nutrient loads. Elevated algal biomass levels above nuisance thresholds were observed during the summers of 2010 and 2012. The study reach was characterized as mesotrophic-eutrophic during the 2010 study and eutrophic during the 2012 study. The presence of algae caused daily dissolved oxygen and pH fluctuations in the stream, resulting in exceedances of the State of Nevada water-quality standards owing to low dissolved oxygen concentrations and high pH concentrations, although the standards might not have been applicable during 2012 because of extremely low streamflow. The addition of nutrients to the stream from the constant supply in groundwater discharge sustains the growth of algae during low streamflow conditions. In the summer when streamflow is low or very low, nutrient-rich groundwater discharge enters the stream through the sediment-water interface at the streambed. Because the attached algae is thick and stream velocity is low, the nutrient-rich water pools at the sediment-water interface. Higher nutrient concentrations at the streambed create a favorable microenvironment for algae attached to the substrate to consume available nutrients from the groundwater before the groundwater mixes with overlying stream water. The source of nitrate in groundwater in this subreach is anthropogenic because nitrate concentrations are greater than background groundwater nitrate concentrations in Douglas County, high groundwater nitrate concentrations are only found at the right bank of the stream near a housing development, and organic wastewater compounds indicative of human-derived sources were also detected in groundwater wells on the right bank of the stream. Nitrogen and oxygen isotope concentrations of nitrate in shallow groundwater were used to determine the specific source of the nitrate, but the isotopic values indicated denitrification was occurring. Further investigation is needed to determine the specific anthropogenic source of the nitrate in the groundwater because the denitrification present in all samples obscures the original source of nitrogen.

Nevada↗
USGS2018

Documentation of single-well aquifer tests and integrated borehole analyses, Pahute Mesa and Vicinity, Nevada

Single-well aquifer testing has been carried out at Pahute Mesa in southern Nevada since 1962. These tests include single-well pumping and slug tests to estimate geologic formation hydraulic properties. Initially, aquifer tests focused on identifying low-permeability rocks suitable for testing large-yield nuclear devices, whereas later hydrologic investigations focused on potential subsurface transport of radionuclides away from Pahute Mesa. The number of single-well aquifer tests analyzed for Pahute Mesa and vicinity was much greater than the number of actual tests because each response to a water-level displacement was interpreted multiple times using different analytical models by different investigators, which were reported as distinct, individual aquifer tests. Some aquifer tests also were reinterpreted multiple times because the wells had not been defined uniquely. Previous databases and reports identified wells by different borehole names, reported various depths to top and bottom of open intervals, and used inconsistent wetted-aquifer thicknesses, which were coupled with inappropriate analytical methods to interpret aquifer-test data. This work standardized the reporting of single-well aquifer-test results at Pahute Mesa and vicinity. A hydraulic-parameter database was created that uniquely identifies tested wells, reports all replicated aquifer tests in each well, and identifies the best transmissivity estimate for each well. Datasets, interpreted models, and results from 1,459 analyses are presented and evaluated for 360 unique wells. Integrated borehole analyses were used to estimate hydraulic conductivity by depth in Pahute Mesa because vertical variations in hydraulic conductivity greatly affect groundwater velocities, which directly affect subsurface transport rates and directions. The integrated analyses reconciled differences between transmissivity estimated from pumping tests and the summed transmissivity from straddle-packer slug tests done at different depth intervals in a borehole. An integration borehole database was created that presents integrated aquifer-test results from 17 boreholes.

Nevada↗
USGS2018

Major element and oxygen isotope geochemistry of vapour-phase garnet from the Topopah Spring Tuff at Yucca Mountain, Nevada, USA

Twenty vapour-phase garnets were studied in two samples of the Topopah Spring Tuff of the Paintbrush Group from Yucca Mountain, in southern Nevada. The Miocene-age Topopah Spring Tuff is a 350 m thick, devitrified, moderately to densely welded ash-flow tuff that is zoned compositionally from high-silica rhyolite to latite. During cooling of the tuff, escaping vapour produced lithophysae (former gas cavities) lined with an assemblage of tridymite (commonly inverted to cristobalite or quartz), sanidine and locally, hematite and/or garnet. Vapour-phase topaz and economic deposits associated commonly with topaz-bearing rhyolites (characteristically enriched in F) were not found in the Topopah Spring Tuff at Yucca Mountain. Based on their occurrence only in lithophysae, the garnets are not primary igneous phenocrysts, but rather crystals that grew from a F-poor magma-derived vapour trapped during and after emplacement of the tuff. The garnets are euhedral, vitreous, reddish brown, trapezohedral, as large as 2 mm in diameter and fractured. The garnets also contain inclusions of tridymite. Electron microprobe analyses of the garnets reveal that they are almandine-spessartine (48.0 and 47.9 mol.%, respectively), have an average composition of (Fe 1.46 Mn 1.45 Mg 0.03 Ca 0.10 )(Al 1.93 Ti 0.02 )Si 3.01 O 12 and are comparatively homogeneous in Fe and Mn concentrations from core to rim. Composited garnets from each sample site have δ18O values of 7.2 and 7.4‰. The associated quartz (after tridymite) has δ 18 O values of 17.4 and 17.6‰, values indicative of reaction with later, low-temperature water. Unaltered tridymite from higher in the stratigraphic section has a δ 18 O of 11.1‰ which, when coupled with the garnet δ 18 O values in a quartz-garnet fractionation equation, indicates isotopic equilibration (vapour-phase crystallization) at temperatures of ~600°C. This high-temperature mineralization, formed during cooling of the tuffs, is distinct from the later and commonly recognized low-temperature stage (generally 50–70°C) of calcite, quartz and opal secondary mineralization, formed from downward-percolating meteoric water, that locally coats fracture footwalls and lithophysal floors.

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USGS2018

Unsaturated zone CO2, CH4, and δ13C-CO2 at an arid region low-level radioactive waste disposal site

Elevated tritium, radiocarbon, Hg, and volatile organic compounds associated with low-level radioactive waste (LLRW) at the USGS Amargosa Desert Research Site (ADRS) have stimulated research on factors and processes that affect contaminant gas distribution and transport. Consequently, we examined the sources, mixing, and biogeochemistry of CO 2 and CH 4 , two additional important species in the unsaturated zone at ADRS. In spring 2015 and 2016, shallow unsaturated zone gas samples were collected from the 1.5-m depth both inside and outside the LLRW disposal area. Samples also were collected from two 110-m-deep multilevel gas-sampling boreholes and a distant background site. These samples were analyzed for CO 2 mole fraction ( x CO 2 ) and C isotopic composition (δ 13 C-CO 2 ) and CH 4 mole fraction ( x CH 4 ). Graphical analysis of the results indicates mixing of CO 2 characteristic of the root zone (δ 13 C −18 to −19‰), deep soil gas of the capillary fringe (−13 to −15‰), and CO 2 produced by microbial respiration of organic matter disposed in the LLRW trenches (−22 to −25‰). Distribution of CH 4 overall reflects atmospheric sources and production in anaerobic microzones in the LLRW area and methanotrophy in the undisturbed shallow subsurface outside the LLRW area. Although x CH 4 reflecting lateral transport from the LLRW area is decreasing with time in the deep profiles, deep unsaturated zone x CO 2 has changed little in recent decades. The results imply that CH 4 and δ 13 C-CO 2 may serve as good tracers of anthropogenic effects in the unsaturated zone even when CO 2 primarily reflects natural processes.

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USGS2018

Conceptual framework and trend analysis of water-level responses to hydrologic stresses, Pahute Mesa–Oasis Valley groundwater basin, Nevada, 1966-2016

This report identifies water-level trends in wells and provides a conceptual framework that explains the hydrologic stresses and factors causing the trends in the Pahute Mesa–Oasis Valley (PMOV) groundwater basin, southern Nevada. Water levels in 79 wells were analyzed for trends between 1966 and 2016. The magnitude and duration of water-level responses to hydrologic stresses were analyzed graphically, statistically, and with water-level models. The conceptual framework consists of multiple stress-specific conceptual models to explain water-level responses to the following hydrologic stresses: recharge, evapotranspiration, pumping, nuclear testing, and wellbore equilibration. Dominant hydrologic stresses affecting water-level trends in each well were used to categorize trends as nonstatic, transient, or steady state. The conceptual framework of water-level responses to hydrologic stresses and trend analyses provide a comprehensive understanding of the PMOV basin and vicinity. The trend analysis links water-level fluctuations in wells to hydrologic stresses and potential factors causing the trends. Transient and steady-state trend categorizations can be used to determine the appropriate water-level data for groundwater studies.

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USGS2018

Discharge, sediment, and water chemistry in Clear Creek, western Nevada, water years 2013–16

Clear Creek is a small stream that drains the eastern Carson Range near Lake Tahoe, flows roughly parallel to the Highway 50 corridor, and discharges to the Carson River near Carson City, Nevada. Historical and ongoing development in the drainage basin is thought to be affecting Clear Creek and its sediment-transport characteristics. Previous studies from water years (WYs) 2004 to 2007 and from 2010 to 2012 evaluated discharge, selected water-quality parameters, and suspended-sediment concentrations, loads, and yields at three Clear Creek sampling sites. This report serves as a continuation of the data collection and analyses of the Clear Creek discharge regime and associated water-chemistry and sediment concentrations and loads during WYs 2013–16. Total annual sediment loads ranged from 870 to 5,300 tons during WYs 2004–07, from 320 to 1,770 tons during WYs 2010–12, and from 50 to 200 tons during WYs 2013–16. Ranges in annual loads during the three study periods were not significantly different; however, total loads were greater during 2004–07 than they were during 2013–16. Annual suspended-sediment loads in WYs 2013–16 showed no significant change since WYs 2010–12 at sites 1 (U.S. Geological Survey reference site 10310485; Clear Creek above Highway 50, near Spooner Summit, Nevada) or 2 (U.S. Geological Survey streamgage 10310500; Clear Creek above Highway 50, near Spooner Summit, Nevada), but significantly lower loads at site 3 (U.S. Geological Survey site 10310518; Clear Creek at Fuji Park, at Carson City, Nevada), supporting the theory of sediment deposition between sites 2 and 3 where the stream gradient becomes more gradual. Currently, a threshold discharge of about 3.3 cubic feet per second is required to mobilize streambed sediment (bedload) from site 2 in Clear Creek. Mean daily discharge was significantly lower in 2010–12 than in 2004–07 and also significantly lower in 2013–16 than in 2010–12. During this study, lower bedload, and therefore lower total sediment load in Clear Creek was primarily due to significantly lower discharge and cannot be directly attributed to sediment mitigation work in the basin. Water chemistry in Clear Creek shows that the general water type of the creek under base-flow conditions in autumn is a dilute calcium bicarbonate. During winter and spring, the chemistry shifts toward a slightly more sodium and chloride character. Though the chemical characteristics show seasonal change, the water chemistries examined as part of this investigation remain within ecological criteria as adopted by the Nevada Division of Environmental Protection. There was no evidence of aqueous polynuclear aromatic hydrocarbons (PAHs) present in Clear Creek water during this study. Concentrations of PAHs, as determined in one bed-sediment sample and multiple semi-permeable membrane device extracts, were either less than quantifiable limits of analysis or were found at similar concentrations as blank samples. In July 2014, a 250–300-acre fire burned in the Clear Creek drainage basin. One day after the fire was extinguished, a thunderstorm washed sediment into the creek. A water chemistry sample collected as part of the post-fire storm event showed that the stormwater entering the creek had increased the concentrations of ammonium and organic nitrogen, phosphorus, manganese, and potassium; a similar finding of many other studies evaluating the effects of fires in small drainage basins. Subsequent chemical analyses of Clear Creek water in August 2014 (one month later) showed that these constituents had returned to pre-fire concentrations.

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USGS2018

Hydrogeologic applications for historical records and images from rock samples collected at the Nevada National Security Site and vicinity, Nye County, Nevada - A supplement to Data Series 297

Rock samples have been collected, analyzed, and interpreted from drilling and mining operations at the Nevada National Security Site for over one-half of a century. Records containing geologic and hydrologic analyses and interpretations have been compiled into a series of databases. Rock samples have been photographed and thin sections scanned. Records and images are preserved and available for public viewing and downloading at the U.S. Geological Survey ScienceBase, Mercury Core Library and Data Center Web site at https://www.sciencebase.gov/mercury/ and documented in U.S. Geological Survey Data Series 297. Example applications of these data and images are provided in this report.

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USGS2018

Insights into the emplacement of upper-crustal plutons and their relationship to large silicic calderas, from field relationships, geochronology, and zircon trace element geochemistry in the Stillwater – Clan Alpine caldera complex, western Nevada, USA

Geologic mapping, new U-Pb zircon ages, and new and published 40 Ar/ 39 Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed at least six nested silicic calderas and underlying granitic plutons to crustal depths locally ≥ 9 km. Both caldera-forming rhyolitic tuffs and underlying plutons were emplaced in two episodes, one from about 30.4–28.2 Ma that included the Deep Canyon, Job Canyon, and Campbell Creek calderas and underlying plutons, and one from about 25.3–24.8 Ma that included the Louderback Mountains, Poco Canyon, and Elevenmile Canyon calderas and underlying plutons. In these two 1–2 m.y. periods, almost the entire Mesozoic upper crust was replaced by Oligocene intrusive and extrusive rocks to depths ≥ 9 km over an estimated total area of ~ 1500 km 2 (pre-extension). Zircon trace element geochemistry indicates that some plutonic rock can be solidified residual magma from the tuff eruptions. Most plutons are not solidified residual magma, although they directly underlie calderas and were emplaced along the same structures shortly after to as much as one million years after caldera formation. Magma chambers and plutons grew by floor subsidence accommodated by downward transfer of country rocks. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada is underlain by a complexly zoned mid-Cenozoic batholith assembled in discrete pulses that coincided with formation of large silicic calderas up to 2500–5000 km 3 .

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USGS2018

Examining the relationship between portable luminescence reader measurements and depositional ages of paleowetland sediments, Las Vegas Valley, Nevada

Portable luminescence readers are exciting new tools that have the potential to rapidly determine the age structure of late Quaternary stratigraphic columns. This is important because high-resolution age profiling can reveal details about the temporal dynamics of climate cause and ecosystem effect, often while researchers are still in the field. In this paper, we compare new portable luminescence reader measurements of total photon counts with a suite of robust, highly resolved ages from middle to late Pleistocene-age paleowetland deposits in the Las Vegas Valley of southern Nevada. Our results show that total photon counts correlate with age, with a quadratic equation providing the best fit to the data. Significant scatter is present in the data, which is likely the result of dose rate variations, multiple sediment sources, and transport mechanisms that include both eolian and fluvial processes. The observed scatter can be reduced significantly using a simple pretreatment procedure involving a 250 μm sieve and neodymium hand magnet to normalize particle sizes and remove magnetic grains. Following this treatment, age estimates based on the reader measurements have an average error of 30 ± 18% when compared against known ages. These findings confirm that portable reader measurements scale with age in paleowetland deposits, allowing its use in establishing rapid, albeit approximate, chronologies for these deposits throughout the American Southwest.

Nevada↗
USGS2018

Diatom floras in lakes in the Ruby Mountains and East Humboldt Range, Nevada, USA: A tool for assessing high-elevation climatic variability

Local conditions, including lake size, depth, bathymetric profile, watershed characteristics, and timing and extent of ice cover determine the characteristics of diatom floras, and how those assemblages respond to short and long-term changes in climate. The diatom assemblages from fourteen sediment samples collected from marginal and profundal zones of seven lakes in the Ruby Mountains and East Humboldt Range of northeastern Nevada are characterized in order to identify the factors affecting controlling species diversity, equitability, and assemblage structure. Principle component analysis delineates three depth-controlled diatom assemblages: shallow (~1), medium (~11 m), and deep (>12 m). The shallowest samples are characterized by a diverse benthic assemblage, the medium depth sample is dominated by small fragilarioid taxa, and, the deepest samples, while not dominated by planktonic species, show an increase in their abundance. In general, diatom assemblages in shallower samples exhibit higher diversity and greater equitability.

Nevada↗
USGS2018

Propagation of endangered moapa dace

We report successful captive spawning and rearing of the highly endangered Moapa Dace, Moapa coriacea (approximately 650 individual fish in existence at time of this study). We simulated conditions under which this stream-dwelling southern Nevada cyprinid and similar species spawned and reared in the wild by varying temperature, photoperiod, flow, and substrate in 14 different spawning and rearing treatments in a propagation facility. Successful spawning occurred in artificial streams with the following characteristics: water flow directed both across the bottom gravel substrate into a cobble bed and across the upper water column; 12–14 fish/stream (0.016–0.026 fish/L depending on water level); static water temperature of 30–32°C; photoperiod of 12 h light and 12 h dark; gradual replacement of water from their natal stream with on-site well water; a combination of pelleted, frozen and live food; and minimal disturbance of fish. Nevada Department of Wildlife now uses these techniques successfully to produce fish in a culture setting. Identification of the effective combination of factors to trigger spawning in exceptionally rare fishes can be difficult and time consuming, and limiting factors can be subtle. Sufficient numbers of available test fish, close study and replication of wild spawning conditions, careful documentation, and patience to identify subtle limiting factors are often required to effectively rear and spawn fishes not previously propagated.

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USGS2017

Chemical quality of water and bottom sediment, Stillwater National Wildlife Refuge, Lahontan Valley, Nevada

The U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service collected data on water and bottom-sediment chemistry to be used to evaluate a new water rights acquisition program designed to enhance wetland habitat in Stillwater National Wildlife Refuge and in Lahontan Valley, Churchill County, Nevada. The area supports habitat critical to the feeding and resting of migratory birds travelling the Pacific Flyway. Information about how water rights acquisitions may affect the quality of water delivered to the wetlands is needed by stakeholders and Stillwater National Wildlife Refuge managers in order to evaluate the effectiveness of this approach to wetlands management. A network of six sites on waterways that deliver the majority of water to Refuge wetlands was established to monitor the quality of streamflow and bottom sediment. Each site was visited every 4 to 6 weeks and selected water-quality field parameters were measured when flowing water was present. Water samples were collected at varying frequencies and analyzed for major ions, silica, and organic carbon, and for selected species of nitrogen and phosphorus, trace elements, pharmaceuticals, and other trace organic compounds. Bottom-sediment samples were collected for analysis of selected trace elements. Dissolved-solids concentrations exceeded the recommended criterion for protection of aquatic life (500 milligrams per liter) in 33 of 62 filtered water samples. The maximum arsenic criterion (340 micrograms per liter) was exceeded twice and the continuous criterion was exceeded seven times. Criteria protecting aquatic life from continuous exposure to aluminum, cadmium, lead, and mercury (87, 0.72, 2.5, and 0.77 micrograms per liter, respectively) were exceeded only once in filtered samples (27, 40, 32, and 36 samples, respectively). Mercury was the only trace element analyzed in bottom-sediment samples to exceed the published probable effect concentration (1,060 micrograms per kilogram).

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USGS2017

Biological and ecological science for Nevada—The Silver State

Nevada is rich in minerals, energy, rangelands, mountains, deserts, lakes, fish, and wildlife. Many enterprises critical to Nevada's economy are based on natural resources including solar energy, livestock production, hunting, fishing, and other outdoor recreation. Nevada is a national leader in both geothermal and solar utility-scale energy production, and invested more than $ 1.2 million in 2016 in solar development alone. Agriculture, primarily livestock production, generates more than half a billion dollars annually, and wildlife watching, hunting, and fishing contribute more than $1 billion to Nevada's economy annually.

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USGS2017

A process to estimate net infiltration using a site-scale water-budget approach, Rainier Mesa, Nevada National Security Site, Nevada, 2002–05

This report documents a process used to estimate net infiltration from precipitation, evapotranspiration (ET), and soil data acquired at two sites on Rainier Mesa. Rainier Mesa is a groundwater recharge area within the Nevada National Security Site where recharged water flows through bedrock fractures to a deep (450 meters) water table. The U.S. Geological Survey operated two ET stations on Rainier Mesa from 2002 to 2005 at sites characterized by pinyon-juniper and scrub-brush vegetative cover. Precipitation and ET data were corrected to remove measurement biases and gap-filled to develop continuous datasets. Net infiltration (percolation below the root zone) and changes in root-zone water storage were estimated using a monthly water-balance model. Site-scale water-budget results indicate that the heavily-fractured welded-tuff bedrock underlying thin (<40 centimeters) topsoil is a critical water source for vegetation during dry periods. Annual precipitation during the study period ranged from fourth lowest (182 millimeters [mm]) to second highest (708 mm) on record (record = 55 years). Annual ET exceeded precipitation during dry years, indicating that the fractured-bedrock reservoir capacity is sufficient to meet atmospheric-evaporative demands and to sustain vegetation through extended dry periods. Net infiltration (82 mm) was simulated during the wet year after the reservoir was rapidly filled to capacity. These results support previous conclusions that preferential fracture flow was induced, resulting in an episodic recharge pulse that was detected in nearby monitoring wells. The occurrence of net infiltration only during the wet year is consistent with detections of water-level rises in nearby monitoring wells that occur only following wet years.

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USGS2017

Groundwater discharge by evapotranspiration, flow of water in unsaturated soil, and stable isotope water sourcing in areas of sparse vegetation, Amargosa Desert, Nye County, Nevada

This report documents methodology and results of a study to evaluate groundwater discharge by evapotranspiration (GWET) in sparsely vegetated areas of Amargosa Desert and improve understanding of hydrologic-continuum processes controlling groundwater discharge. Evapotranspiration and GWET rates were computed and characterized at three sites over 2 years using a combination of micrometeorological, unsaturated zone, and stable-isotope measurements. One site (Amargosa Flat Shallow [AFS]) was in a sparse and isolated area of saltgrass ( Distichlis spicata ) where the depth to groundwater was 3.8 meters (m). The second site (Amargosa Flat Deep [AFD]) was in a sparse cover of predominantly shadscale ( Atriplex confertifolia ) where the depth to groundwater was 5.3 m. The third site (Amargosa Desert Research Site [ADRS]), selected as a control site where GWET is assumed to be zero, was located in sparse vegetation dominated by creosote bush ( Larrea tridentata ) where the depth to groundwater was 110 m. Results indicated that capillary rise brought groundwater to within 0.9 m (at AFS) and 3 m (at AFD) of land surface, and that GWET rates were largely controlled by the slow but relatively persistent upward flow of water through the unsaturated zone in response to atmospheric-evaporative demands. Greater GWET at AFS (50 ± 20 millimeters per year [mm/yr]) than at AFD (16 ± 15 mm/yr) corresponded with its shallower depth to the capillary fringe and constantly higher soil-water content. The stable-isotope dataset for hydrogen (δ 2 H) and oxygen (δ 18 O) illustrated a broad range of plant-water-uptake scenarios. The AFS saltgrass and AFD shadscale responded to changing environmental conditions and their opportunistic water use included the time- and depth-variable uptake of unsaturated-zone water derived from a combination of groundwater and precipitation. These results can be used to estimate GWET in other areas of Amargosa Desert where hydrologic conditions are similar.

Nevada↗
USGS2017

Devils Hole, Nevada—A photographic story of a restricted subaqueous environment

This report presents selected photographic images taken by the author during U.S. Geological Survey (USGS) research into paleoclimatology and geochemistry in Devils Hole cavern during 1984 to 1993 in cooperation with the National Park Service. The unaltered suite of photographs was prepared by the USGS dive team as an aid to assist nondiving scientists with a visual perspective of the environment where earth-science samples were collected and subsequently analyzed for chemical and isotopic composition.

Nevada↗
USGS2017

A cosmopolitan late Ediacaran biotic assemblage: new fossils from Nevada and Namibia support a global biostratigraphic link

Owing to the lack of temporally well-constrained Ediacaran fossil localities containing overlapping biotic assemblages, it has remained uncertain if the latest Ediacaran ( ca 550–541 Ma) assemblages reflect systematic biological turnover or environmental, taphonomic or biogeographic biases. Here, we report new latest Ediacaran fossil discoveries from the lower member of the Wood Canyon Formation in Nye County, Nevada, including the first figured reports of erniettomorphs, Gaojiashania , Conotubus and other problematic fossils. The fossils are spectacularly preserved in three taphonomic windows and occur in greater than 11 stratigraphic horizons, all of which are below the first appearance of Treptichnus pedum and the nadir of a large negative δ 13 C excursion that is a chemostratigraphic marker of the Ediacaran–Cambrian boundary. The co-occurrence of morphologically diverse tubular fossils and erniettomorphs in Nevada provides a biostratigraphic link among latest Ediacaran fossil localities globally. Integrated with a new report of Gaojiashania from Namibia, previous fossil reports and existing age constraints, these finds demonstrate a distinctive late Ediacaran fossil assemblage comprising at least two groups of macroscopic organisms with dissimilar body plans that ecologically and temporally overlapped for at least 6 Myr at the close of the Ediacaran Period. This cosmopolitan biotic assemblage disappeared from the fossil record at the end of the Ediacaran Period, prior to the Cambrian radiation.

Nevada↗
USGS2017

The Valmy thrust sheet: A regional structure formed during the protracted assembly of the Roberts Mountains allochthon, Nevada, USA

A synthesis of field, biostratigraphic, detrital zircon geochronologic, and remote sensing data across north-central Nevada, United States, defines a thick, regionally extensive sheet of Middle–Upper Ordovician Valmy Formation quartzite that structurally overlies deformed early Paleozoic units of the Roberts Mountains allochthon. Late Paleozoic regional unconformities that record tectonic disruptions have been recognized in the foreland of central and eastern Nevada and locally within the Roberts Mountains allochthon; these identify multiple, regional tectonic events between the Devonian–Mississippian initiation of the Antler orogeny and the Permian–Triassic Sonoma orogeny. However, few studies have documented the regional kinematic history of the Robert Mountains allochthon sensu stricto. In the Independence Mountains of northern Nevada, emplacement of the Roberts Mountains allochthon is restricted to the Mississippian. In the Tuscarora Mountains, the range west and southwest of the Independence Mountains, several deformation events have been identified, and emplacement of the thrust sheet containing the Valmy Formation is restricted to the Late Pennsylvanian–Early Permian. These structural and temporal relations, reflected in the Antler foreland basin adjacent to the Roberts Mountains allochthon and overlap sequences, suggest that the Roberts Mountains allochthon is a composite stratigraphic terrane assembled along the Cordilleran margin during two or more late Paleozoic contractional events. Valmy Formation deposits likely represent the development of coalescing submarine fans below or within bypass channels in a deep slope or rise environment. Petrographic characteristics, biostratigraphy, and detrital zircon U-Pb age populations of the Valmy Formation link it to coeval slope and rise turbidites of the Vinini Formation and shelfal Eureka Quartzite; Valmy Formation detrital zircon age populations are dissimilar to the rift-to-drift facies of the Neoproterozoic–Cambrian Prospect Mountain Quartzite. Throughout north-central Nevada, the Valmy Formation is in fault contact with units of the Roberts Mountains allochthon, including the Devonian–Mississippian Slaven Chert, Silurian–Devonian Elder Sandstone, and Cambrian(?)–Ordovician Vinini Formation, which were deformed prior to, or during, emplacement of the thrust sheet containing Valmy Formation quartzite. Our mapping and data synthesis, guided by regional quartz maps based on remote sensing (Advanced Spaceborne Thermal Emission and Reflection Radiometer [ASTER]) data, delineate similar structural relationships discontinuously for >200 km along strike of the Roberts Mountains allochthon. Exploration for concealed gold deposits within reach of drilling requires knowledge of the relative thicknesses of the Roberts Mountains allochthon and the Valmy Formation. Overall thicknesses of deformed Roberts Mountains allochthon units between the Valmy Formation and underlying carbonate rocks, which host large, world-class Carlin-type gold deposits, vary by hundreds of meters, but are generally less than 700 m in three of the areas studied here. Recognition of windows through and klippen of the Roberts Mountains allochthon is essential for identification of areas where deposits may be at or near the surface. Correspondingly, most ongoing exploration for Carlin-type gold deposits subjacent to the Roberts Mountains allochthon targets concealed deposits. The model proposed in this study is applicable to determining depth to rocks prospective for undiscovered deposits.

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