Geology topics

Research about Nevada

Source-linked reports with geographic coverage including Nevada.

At least 55 records · Page 3Linked to original sources

USGS2024

Temperature-driven convergence and divergence of ecohydrological dynamics in the ecosystems of a sky island mountain range

Forest and woodland decline is predicted to be increasingly influenced by meteorological variation and climate change in the future. By determining how meteorological variation leads to similar versus differing ecohydrological dynamics of forest and woodland ecosystems, we can gain insight on how future climate-driven declines may be realized. We characterized 23 mixed conifer forest (MC), ponderosa pine forest (PP) and piñon pine–juniper woodland (PJ) sites with different canopy covers in southern Nevada, USA. We compared meteorological variation between these sites and employed water balance modelling and information theory to estimate similarity in the density distributions of soil temperature (Ts), soil water potential (SWP) and transpiration partitioning into total evapotranspiration (T/ET) within and across ecosystems in wetter and drier seasons and in cooler and warmer decades. From 1941 to 2020, this location experienced declines in meteorological water deficit due to higher precipitation, although temperatures increased over more recent time periods (1981–2020). From 1981 to 2020, we generally found greater similarity in SWP and T/ET distributions within MC sites and PP sites in the cool season and in the warm season generally found greater similarity in Ts and T/ET distributions within and between PP and PJ sites (excepting T/ET between PJ sites and higher canopy cover PP sites). Recent warm decades promoted convergence in warm and cool season Ts dynamics, such that Ts dynamics generally became more similar between higher elevation MC sites and lower elevation PP–PJ sites. At the same time, warmer decades initiated divergence of SWP and T/ET dynamics within groups of MC–PP and PP–PJ sites that were formerly more similar to each other (excepting SWP in wet seasons). Although their dynamics will remain strongly coupled to precipitation, warming temperatures have the potential to promote divergence in the ecohydrological dynamics of ecosystems at lower and higher elevations in this sky island system and may also promote novel within-ecosystem divergence associated with variation in vegetation structural attributes.

Nevada↗

USGS2024

Assessment of water levels, nitrate, and arsenic in the Carson Valley Alluvial Aquifer and the development of a data visualization tool for the Carson River Basin, Nevada

Residents of Carson Valley, Douglas County, Nevada, rely on the basin-fill alluvial aquifer underlying the valley for drinking water. Since the 1980s, groundwater levels and water-quality data have been collected to monitor the status of the aquifer system and to assist in planning efforts to address current (2024) and future demand. The U.S. Geological Survey (USGS), in cooperation with Douglas County, Nevada, evaluated trends in water levels, nitrate, and arsenic concentrations from a network of monitoring and domestic wells in Carson Valley. This work also assessed the monitoring well network to determine the suitability of wells for characterizing the occurrence of arsenic in the groundwater. Monitoring of constituents, such as nitrate and arsenic concentrations, is needed to assess changes in contaminant distribution and to evaluate the effect that changing land use and groundwater pumping has on their occurrence and transport. Results of the trend analysis indicate water levels are declining ( p <0.05) in 17 of 26 selected monitoring wells (65 percent). Areas with the largest change in water levels, with more than 20 feet of declines, were within the community areas of Johnson Lane, Ruhenstroth, South Agricultural, East Valley, and Fish Springs. Variations in water levels measured in wells from the Central Agricultural, Minden, Foothill, Alpine County (one well), and Gardnerville Ranchos areas show periods of increase and decrease over time, but they also maintain long-term declining trends ( p <0.05). Increases in nitrate concentrations in groundwater samples collected from 9 out of 14 selected monitoring wells (64 percent) are statistically significant ( p <0.05) within the Ruhenstroth, Gardnerville Ranchos, East Valley, Genoa, and Johnson Lane community areas. Samples collected from a well in Indian Hills/Jacks Valley indicated a decreasing trend in nitrate concentration over time. Nitrate concentrations in samples collected from wells in East Valley, Genoa, Johnson Lane, and Indian Hills/Jack Valley were consistently low (less than 3 milligrams per liter [mg/L]) and stable. Nitrate concentrations from selected wells in Johnson Lane and Garnerville Ranchos exceeded the U.S. Environmental Protection Agency (EPA) maximum contaminant level (MCL) of 10 mg/L (as nitrogen) and have trends that are increasing over time. In 2022, a sample collected from Johnson Lane had a concentration (7.3 mg/L) below the MCL with an increasing trend over time. Temporal trend analyses for groundwater arsenic concentrations in Carson Valley could not be done because of a lack of temporal data. However, using available historical data, arsenic concentrations seem to be greater in groundwater from wells located on the eastern and northern areas of the valley than in wells located on the western or southern areas. Groundwater arsenic concentrations exceed 5 micrograms per liter (μg/L) in most samples collected from wells in Johnson Lane, Airport, Central Agricultural, and East Valley areas and in many cases exceed the U.S. Environmental Protection Agency (EPA) MCL of 10 μg/L. Data indicate that groundwater from domestic wells screened at deeper intervals are likely more vulnerable to elevated arsenic concentrations than shallower wells. A groundwater network evaluation for Carson Valley identified potential modifications in the sampling locations and frequency to better understand the effect of groundwater pumping in communities where municipal and domestic demand are greatest, potentially enhancing understanding of contaminant transport in these areas. Potential modifications to the active well network include reducing the frequency of sample collection from existing network wells (6 out of 11) that have consistently shown low and stable nitrate concentrations, adding wells in areas where data are sparse, and increasing the number of wells in areas with elevated groundwater nitrate concentrations. Including the analysis of arsenic in samples from the active groundwater monitoring well network will provide more detail on the temporal and spatial variability of arsenic concentrations. A visualization tool for the Carson River Basin was developed to provide access to discrete and near real-time hydrologic and water-quality data. The Carson River Basin Hydro Mapper (CBH; U.S. Geological Survey, 2023b) shows active and historical discrete water levels measured by the USGS and the State of Nevada Division of Water Resources, discrete groundwater nitrate and arsenic concentration data collected by the USGS, near real-time streamflow, and surface water levels for select waterbodies. The hydrologic data in the CBH provides resource managers, the public, and the scientific community with an easily accessible tool to present and communicate the most up-to-date information available about local and basin-wide water resources.

Nevada↗

USGS2024

Evaluating mountain lion diet before and after a removal of feral horses in a semiarid environment

Non-native species can affect ecosystems by influencing native predator-prey dynamics. Therefore, management interventions designed to remove non-natives may inadvertently lead to increased predation on native species. Feral horses are widely distributed throughout the arid parts of western North America. A growing body of research indicates that horses can be an important prey species to mountain lions in ecosystems where they overlap. In December 2020, the Bureau of Land Management removed 455 horses from the Delamar Mountains, Nevada, USA. We leveraged this management intervention to implement a before–after–control–impact study to test hypotheses about predation on horses and native ungulates. We predicted (1) that horses would comprise an important part of the diet in this mixed-prey community, (2) following removal, the proportion of horses in the diet would decrease and native ungulates would increase, and (3) mountain lion home ranges overlapping the treatment areas would increase in response to decreased prey availability. From 2018 to 2022, we investigated 1360 clusters from 29 GPS-collared lions and identified 1056 prey items. To model the probability of a predation event (a kill), we fit a mixed-effects logistic regression model for ungulate prey as a function of lion sex, treatment area (in/out), and treatment period (pre-/post-removal). We used a log-linear regression model to evaluate changes in home range size. The most common prey were mule deer (55%), feral horses (32%), and coyotes (4%). Twenty-two of 29 lions consumed horses, although the rate of horse consumption was highly variable across individuals. Horses of both sexes and all age classes were predated. In contrast to predictions, our models detected no effect of removals on diet composition (β interaction = 0.30 ± 1.1), nor did the removal influence home range size (β interaction = 0.02 ± 0.02). Despite a 46% reduction in horse abundance, we found no evidence for prey-switching following the horse removal treatment. Removal magnitude, rapid horse immigration, and/or behavioral specialization of individual mountain lions may help explain these results. Our findings have important implications for mountain lion and feral horse management in arid environments characterized by high prey diversity, but low prey abundance.

Nevada↗

USGS2024

Modeling the potential habitat gained by planting sagebrush in burned landscapes

Many revegetation projects are intended to benefit wildlife species. Yet, there are few a priori evaluations that assess the potential efficiency of restoration actions in recovering wildlife habitats. We developed a spatial vegetation–habitat recovery model to gauge the degree to which field planting strategies could be expected to recover multi-factor habitat conditions for wildlife following wildfires. We simulated a wildfire footprint, multiple sagebrush ( Artemisia spp.) planting scenarios, and tracked projected vegetation growth for 15 years post-fire. We used a vegetation transition framework to track and estimate the degree to which revegetation could accelerate habitat restoration for a Greater sage-grouse ( Centrocercus ) population within the Great Basin, western United States. We assessed the amount of habitat 15 years post-fire to estimate the degree to which revegetation could be expected to accelerate habitat restoration. Our results highlight a potential disconnect between the expansive areas required by wide-ranging wildlife such as sage-grouse and the relatively small areas that planting treatments have created. Habitat restorations and planting strategies that are intended to benefit sage-grouse may only speed up localized habitat restoration. This study provides an example of how linked revegetation–habitat modeling approaches can scope the expected return on restoration investment for habitat improvements and support the strategic use of limited restoration resources.

Nevada↗

USGS2024

Argillization by descending acid at Steamboat Springs, Nevada

Steamboat Springs, Nevada, an area of present-day hot springs, clearly illustrates the genetic dependence of some kaolin deposits on hot-spring activity. Andesite, granodiorite and arkosic sediments are locally altered at the land surface to siliceous residues consisting of primary quartz and anatase, plus opal from primary silicates. These siliceous residues commonly exhibit the textural and structural features of their unaltered equivalents. Beneath the siliceous residues, kaolin and alunite replace primary silicates and fill open spaces, forming a blanketlike deposit. Beneath the kaolin-alunite zone, montmorillonite, commonly accompanied by pyrite, replaces the primary silicates. On the ground surface, the same alteration mineral zones can be traced outward from the siliceous residue; however, hematite rather than pyrite accompanies montmorillonite. Chemical analysis indicates that sulfuric acid is the active altering agent. The acid forms from hydrogen sulfide that exsolves from deep thermal water, rises above the water table and is oxidized by sulfur-oxidizing bacteria living near the ground surface. This acid dissolves in precipitation or condensed water vapor and percolates downward destroying most of the primary minerals producing a siliceous residue. Coincidence of the water table with the downward transition from siliceous residue to kaolin-alunite signifies decreasing hydrogen metasomatism because of dilution of descending acid by ground water. In hot-spring areas, beds of siliceous sinter deposited at the surface by hypogene thermal water look, superficially, like areas of surficial acid alteration. Features diagnostic of a surficial alteration are the relict rock structures of a siliceous residue and a kaolin-alunite zone immediately beneath.

Nevada↗

USGS2024

Late Triassic paleogeography of southern Laurentia and its fringing arcs: Insights from detrital zircon U-Pb geochronology and Hf isotope geochemistry, Auld Lang Syne basin (Nevada, USA)

Fluvial strata of the Upper Triassic Chinle Formation and Dockum Group, exposed across the Western Interior of North America, have long been interpreted to record a transcontinental river system that connected the ancestral Ouachita orogen of Texas and Oklahoma, USA, to the Auld Lang Syne basin of northwestern Nevada, USA, its inferred marine terminus. Fluvial strata are well-characterized by existing detrital zircon data, but the provenance of the Auld Lang Syne basin is poorly constrained. We present new detrital zircon U-Pb and Hf isotopic data that characterize the provenance of Norian siliciclastic strata that dominate the Auld Lang Syne basin. Mixture modeling of Auld Lang Syne basin data identifies the Alleghany−Ouachita−Marathon belt of eastern Laurentia as a dominant source of sediment, but the presence of Triassic detrital zircon grains in Auld Lang Syne basin strata indicates that at least one peri-Laurentian arc segment had to have also contributed sediment. A comparison of new Hf isotopic data with those characterizing various peri-Laurentian volcanic arcs demonstrates that although multiple arc segments may have simultaneously contributed zircons to the Auld Lang Syne basin, the west Pangean arc of northern Mexico stands out as a unique source of highly evolved Permian to Triassic detrital zircon grains in samples from the Auld Lang Syne basin. Altogether, our data and analyses demonstrate source-to-sink connectivity between the Late Triassic (Norian) Cordilleran margin and remnant late Paleozoic highlands of southern to eastern Laurentia, which ultimately framed a Mississippi River−scale, transcontinental watershed that traversed the topographically subdued Laurentian continental interior.

Nevada↗

USGS2024

Paleogene sedimentary basin development in southern Nevada, USA

The cause of the transition from Mesozoic and early Cenozoic crustal shortening to later extension in the western United States is debated. In many parts of the extant Sevier hinterland, now the Basin and Range Province, the sedimentary sections that provide the most direct record of that transition remain poorly studied and lack meaningful age control. In this paper, we present field characterization supported by U-Pb detrital zircon and 40 Ar/ 39 Ar feldspar ages for ten sections across southern Nevada. We describe a newly identified basin, here named the Fallout Hills basin, which preserves >1.0 km of sedimentary deposits as old as middle Eocene, ca. 48 Ma. Deposition occurred during the 20 m.y. (million years) before the 27.60 ± 0.03 Ma Monotony Tuff blanketed much of south-central Nevada, based on 47.6 Ma and younger detrital zircon maximum depositional ages (MDAs) from near the Pintwater and Spotted Ranges. Elsewhere in southern Nevada, prevolcanic Cenozoic strata commonly form thinner (~100 m), isolated exposures that yield detrital zircon MDAs ≤10 m.y. older than (and in some cases essentially the same age as) the ca. 27–28 Ma ignimbrites that cap the sections. A variable but overall upward-fining facies pattern is observed in both the Fallout Hills basin and the thinner sections. These localized patterns imply topographic changes that are unlikely to reflect plate-scale processes and are not consistent with large-magnitude extension. Instead, variable uplift due to magmatism combined with antecedent topographic relief from thrust faulting and subsequent erosion likely provided accommodation for these deposits.

Nevada↗

USGS2024

Paleogene mid-crustal intrusions in the Ruby Mountains–East Humboldt Range metamorphic core complex, northeastern Nevada, USA

Middle Eocene to early Oligocene intrusions, widespread in the Ruby Mountains–East Humboldt Range metamorphic core complex, Nevada, USA, provide insights into a major Paleogene magmatic episode and its relation to tectonism in the northeastern Great Basin. These intrusions, well-exposed in upper Lamoille Canyon, range in composition from gabbro to leucomonzogranite. They form small plutons, sheets, and dikes that intrude the metamorphic and granitic infrastructure of the core complex. Two types of Paleogene monzogranite were recognized. The first is exemplified by two of the larger intrusive bodies, the Snow Lake Peak and Castle Lake intrusions, which occur as sheet-like bodies near and at the structural base of metamorphosed Neoproterozoic and Cambrian Prospect Mountain Quartzite where it is inverted above Cambrian and Ordovician marble of Verdi Peak in the Lamoille Canyon nappe. Swarms of dikes are associated with these intrusions. U-Pb (zircon) ages range ca. 40–33 Ma and typically display relatively simple and minor inheritance. The rocks have the lowest ε Hf (zircon) and ε Nd (whole rock) of any of the middle Cenozoic granites. The second type of monzogranite, Overlook type, typically occurs as thin, isolated dikes and leucosome-like bodies in Late Cretaceous granites of the infrastructure, with no obvious relationship to the large monzogranite bodies. Overlook-type monzogranite displays complex zircon inheritance, yields igneous ages ca. 37–32 Ma, and has ε Hf (zircon) and ε Nd (whole rock) identical to those of Late Cretaceous granites in the core complex. These isotopic and field data indicate that Overlook-type monzogranite formed in situ through anatexis of host Cretaceous granites. A pervasive thermal event was required to stimulate this crustal melting.

Nevada↗

USGS2024

Variable climate-growth relationships of quaking aspen (Populus tremuloides) among Sky Island mountain ranges in the Great Basin, Nevada, USA

The Great Basin is an arid province located in the interior western United States. The region encompasses millions of hectares and quaking aspen ( Populus tremuloides Michx.) forests comprise a minor portion of the total area. However, montane aspen forests play a disproportionately large role in providing ecosystem services in the region, including water retention, biodiversity, wildlife habitat, livestock forage, and recreational uses. With warming temperatures, increasing evaporative demand, and heightened precipitation variability, the future of aspen has become a critical concern. Using dendroecological approaches, we assessed growth patterns of 20 aspen stands across three geographically isolated “sky island” mountain ranges spanning portions of the north-central Great Basin. We anticipated that the growth of Great Basin aspen would be strongly influenced by regional climatic patterns and largely in synchrony. Results revealed a more complex growth dynamic that varied among mountain ranges and across environmental gradients. In particular, aspen climate-growth relationships in the slightly dryer Ruby Mountains were strongly and positively correlated (r > 0.5) with previous fall to winter moisture availability. The Jarbidge Mountains had a positive but modest relationship with previous fall to winter moisture availability (r > 0.3). Climate-growth response in the Santa Rosa Mountains, the wettest range, showed no significant response to moisture availability during any time period examined but had greater tree-ring growth with warmer May temperatures. Although tree-ring centennial (1910 – 2010) growth trends were positive for all three mountain ranges, only the Santa Rosa Mountains maintained a positive recent growth trend (1970 – 2010). Moreover, distinct temporal shifts in tree growth-climate relationships in each mountain range suggest potentially unique aspen population adaptations to climate variability. For instance, in two of the mountain ranges, there was a shift from positive/neutral to negative growth relationships with temperature starting around the 1963 – 1987 time period, while tree growth also began simultaneously responding more positively to moisture availability. These growth shifts and observed enhanced sensitivities to monthly and seasonal climate variables over time may reflect dynamic tree growth responses caused by ongoing global climate change, but that may be tempered by local or regional factors, such as the relative availability and timing of soil moisture provided by spring snowmelt. A better understanding of biogeographic variation and causality in aspen growth could provide multiple management pathways governed by resilience characteristics in the face of future anthropogenic and climatic threats.

Nevada↗

USGS2024

Hyperspectral mapping of magmatic-hydrothermal sericite, Battle Mountain mining district, Nevada

We demonstrate the utility of multi-scale imaging spectroscopy data (hyperspectral data) to differentiate magmatic-hydrothermal sericite from other white micas based on grain size, in a case study of the Battle Mountain mining district in Humboldt and Lander Counties, Nevada. The Battle Mountain mining district contains porphyry, skarn, and distal disseminated deposits that formed in magmatic-hydrothermal systems, as well as sedimentary-rock hosted gold deposits of less certain origin. We generated spectral-based mineral maps of the Battle Mountain mining district to examine the spatial distribution of spectrally dominant minerals such as kaolinite, montmorillonite , and white micas (muscovite, sericite, and illite). We then used spectral-based mineral mapping to characterize the grain size and composition of white micas, enabling us to differentiate igneous muscovite from magmatic-hydrothermal sericite. By integrating our spectral-based maps with geologic mapping, airborne aeromagnetic data, and prior studies on mines and deposits in Battle Mountain, we determined that finer grained, higher Al sericite spatially correlated with the footprints of known magmatic-hydrothermal systems and is interpreted as forming from magmatic-hydrothermal alteration. Larger grained, lower Al muscovites are distal from known magmatic-hydrothermal systems and are interpreted as being igneous derived siliciclastic sediments that became constituents of the host sedimentary rocks. Techniques described in this contribution can be applied to any appropriate hyperspectral data, regardless of sensor type used to collect the data.

Nevada↗

USGS2024

An accuracy assessment of the surface reflectance product from the EMIT imaging spectrometer

The Earth surface Mineral dust source InvesTigation (EMIT) is an imaging spectrometer launched to the International Space Station in July 2022 to measure the mineral composition of Earth’s dust-producing regions. We present a systematic accuracy assessment of the EMIT surface reflectance product in two parts. First, we characterize the surface reflectance product’s overall performance using multiple independent vicarious calibration field experiments with hand-held and automated field spectrometers. We find that the EMIT surface reflectance product has a standard error of ±1.0 % in absolute reflectance units for temporally coincident observations. Discrepancies rise to ±2.7 % for spectra acquired at different dates and times of day, which we attribute mainly to changes in solar geometry. Second, we develop an error budget that explains the differences between EMIT and in-situ field spectrometer data. We find that uncertainties in spatial footprints, field spectroscopy, and the EMIT-reported measurement were sufficient to explain discrepancies in most cases. Our approach did not detect any systematic calibration or reflectance errors in the timespan considered. Together, these findings demonstrate that a space-based imaging spectrometer can acquire high-quality spectra across a wide range of observational and atmospheric conditions.

Nevada↗

USGS2024

Surficial geology and Quaternary fault map of the Las Vegas Valley, Clark County, Nevada

The Surficial Geology and Quaternary Fault Map of the Las Vegas Valley, Clark County, Nevada is a 1:50,000-scale compilation of published 1:24,000-scale geologic maps integrated with new field and desktop mapping. This geologic map compilation and GIS database are part of a broader study on the Quaternary faults in the Las Vegas Valley, the results of which are summarized in this report. The map compilation utilized a variety of digital base maps to evaluate the characteristics of surficial deposits and Quaternary fault scarps including lidar data in undeveloped parts of the valley and orthorectified historical aerial photos in the urbanized center of the valley. The map distinguishes twenty surficial map units including alluvial-fan and ephemeral-wash deposits, groundwater discharge deposits of the Las Vegas Formation, and alluvium deposits of Las Vegas Wash. Quaternary faults include the Quaternary Las Vegas Valley fault system in the center of the valley and the Frenchman Mountain fault system along the eastern margin. All Quaternary fault traces in the valley were evaluated, and the previously published fault mapping was modified as needed. The new mapping and uniform correlation of surficial deposits displaced by Quaternary faults yields a consistent valley-wide characterization of the recency of fault activity. The map and GIS database include a Quaternary geochronology compilation of 119 previously published surficial deposit ages of various types, 35 new luminescence ages, and 3 new radiocarbon ages. The new age data further bracket the ages of the Las Vegas basin Quaternary stratigraphy and provide new constraints on the timing of Quaternary fault activity.

Nevada↗

USGS2024

Models no not provide proof: An example of model ambiguity and application of isotopic data in a mine pit lake

Geochemical and hydrologic models of pit lakes are commonly used in environmental regulatory decisions to predict future water quality and hydrologic conditions and to understand existing pit lakes. Models may be used to quantify sulfide oxidation, predict thermal/chemical stratification and mixing, and better understand connections between pit lakes and aquifers. One concern related to the hydrologic character of pit lakes is if they are terminal (a groundwater sink with no outflow) or flowthrough (both receiving groundwater inflow and discharging to groundwater). This question was pertinent to the Liberty pit lake, a small acidic pit lake formed in a former Cu deposit in south-central Nevada where potentiometric and geochemical data potentially indicate pit-lake outflow. Potential discharge to groundwater from the pit lake was evaluated using a water-balance model, but uncertainty in hydraulic parameters led to ambiguity in the hydrologic character. Stable isotopes of water were then sampled from the pit lake and adjacent groundwater wells, which unambiguously indicated the lack of an evaporative signature in downgradient groundwater because the groundwater did not plot on a hypothetical mixing line between evaporated pit lake water and observed meteoric recharge. This methodology provided a more effective and more data-driven approach for understanding pit-lake hydrology. Although predictive models are required to quantify reasonable bounds on future conditions, many models contain substantial uncertainty and are not well suited in some environments. Datasets that provide more clear lines of evidence could be collected from existing pit lakes whenever possible to inform water-rock interaction, limnological behavior, and connectivity to adjacent groundwater.

Nevada↗

USGS2024

Geophysical modeling of a possible blind geothermal system near Battle Mountain, NV

The northeastern portion of the Reese River basin in north-central Nevada is the focus of detailed geophysical and geological studies as part of the INGENIOUS project, which aims to identify new, commercially viable hidden geothermal systems in the Great Basin region of the western U.S. This location, herein referred to as Argenta Rise, occupies a broad (~15km wide) left-step between major range-front fault systems along the northwestern edge of the Shoshone Range and Argenta Rim, with numerous ENE-striking intra-basin faults presumably accommodating sinistral-normal oblique slip across the step-over. Four discrete regions have been identified within the study area that have favorable structural settings for hosting a blind hydrothermal system. However, with no definitive or extensive surface manifestations of an active hydrothermal system (e.g., geysers, steam vents, sinter, etc.), detailed geophysical studies are necessary to resolve subsurface geology and structure, and identify zones of enhanced structural complexity that may promote hydrothermal fluid flow. Hence, we collected high-resolution gravity, MT, and rock property data (density, magnetic susceptibility), and analyzed the recently acquired GeoDAWN aeromagnetic data to characterize potential geothermal resources in this region. Using the new geophysical datasets, we jointly modeled gravity and magnetic data along a series of intersecting 2D profiles that integrated information from recent, local-scale fault mapping. Rock property measurements performed on outcrops and hand samples throughout the study area constrained the models. The MT data were used to construct a 3D resistivity model that highlights the location of inferred alteration and fluids in the subsurface. Combined MT and potential field results reveal which structures may be most important for controlling hydrothermal fluid migration, as well as which geologic units may host hydrothermal fluids. Our gravity derived depth to basement surface coincides well with the base of shallow conductive anomalies, suggesting hydrothermal fluids may be confined to basin fill sediments and volcanics. This work supports our development of 3D geophysical and geologic models that are focused along the western flank of the northern Shoshone Range and aids the process of selecting sites for temperature gradient drilling.

Nevada↗

USGS2023

Evaluation of stream capture related to groundwater pumping, Lower Humboldt River Basin, Nevada

The Humboldt River Basin is the only river basin that is contained entirely within the State of Nevada. The effect of groundwater pumping on the Humboldt River is not well understood. Tools are needed to determine stream capture and manage groundwater pumping in the Humboldt River Basin. The objective of this study is to estimate capture and storage change caused by groundwater withdrawals in the lower Humboldt River Basin that can provide the Nevada State Engineer with data and information needed to manage groundwater and surface-water resources. A numerical groundwater flow model was developed for the purpose of estimating stream capture from pre-2016 and future pumping as well as for any location of potential future pumping within the lower Humboldt River Basin. This model was developed using MODFLOW-NWT to represent the lower Humboldt River Basin hydrologic system, including Humboldt River; Rye Patch Reservoir; groundwater evapotranspiration; pumping from municipal, agricultural, mining, and domestic wells; and agricultural drains. Aquifer properties were calibrated using results from numerous single- and multi-well aquifer tests (Nadler, 2020) and through the process of model calibration. Historical capture was estimated for 1960–2016 and predictive capture for the system was projected 100 years into the future (2017–2116) based on historical pumping patterns. Stream capture and drain capture are relatively low for the historical and predictive periods. During the historical period, increased pumping during dry years caused increased connections with capture sources and less water sourced to wells from aquifer storage. Storage and groundwater levels generally recovered during subsequent wet years. Overall, storage change has been the main source of water to wells in the lower Humboldt River Basin, followed by groundwater evapotranspiration capture. During the predictive period, pumping is projected to remain constant and capture 9 percent of stream water after 100 years. Capture and storage change maps were created to visualize spatial variability in potential capture and storage change through time and to provide a database of results that can be used to manage groundwater and surface-water resources. These maps show that potential stream capture would be a minor source of water to wells located across most of the simulated area, except for locations close to the Humboldt River and Rye Patch Reservoir. Drains also would be a minor potential source of water to wells except for those directly adjacent to the drains. In general, the potential supply of water to wells is storage-dominated and over time groundwater evapotranspiration-dominated in the agricultural area. Capture difference maps were generated to visualize where potential capture results might have greater limitations associated with nonlinear flow processes, such as head-dependent boundary conditions. Higher capture differences indicate larger capture map bias and therefore greater capture map uncertainty due to the inability of capture maps to account for nonlinear flow processes. Stream capture differences are highest directly adjacent to the river but are otherwise minimal. Drain capture differences are highest in the region of the agricultural drain network but are otherwise minimal. The Humboldt River, Rye Patch Reservoir, and drains introduce very little nonlinearity to the model, and their associated capture map bias is minimal. Potential groundwater evapotranspiration capture introduces a fair amount of nonlinearity to the model and has the potential to result in significant, localized groundwater evapotranspiration capture map bias over time. Groundwater evapotranspiration capture differences are the result of higher pumping rates lowering the water table below the root zone faster than lower pumping rates and essentially removing groundwater evapotranspiration as a potential source of capture faster than lower pumping rates. Wells that can no longer source their supply through groundwater evapotranspiration capture then generally source more of their water from storage. Thus, storage change bias increases over time as well. Capture prediction uncertainty due to parameter estimation was evaluated using a covariance matrix adaptation-evolution strategy. One hundred Monte Carlo realizations of model parameters were applied to the model to assess capture uncertainty at 13 grid cell locations within the model domain. In general, results indicated that greater capture uncertainty for a given source (river, drains, or evapotranspiration) is associated with proximity of a pumping well to that source. The magnitude of maximum capture fraction uncertainties after 100 years of pumping for stream capture, drain capture, groundwater evapotranspiration capture, and storage change were plus or minus (±) 0.17, ±0.10, ±0.20, and ±0.22, respectively.

Nevada↗

USGS2023

The enigmatic Rattlesnake Knoll, Spring Valley, east-central Nevada—A geophysical perspective

Rattlesnake Knoll is a small, 30-meter-high mound of igneous breccia in the center of Spring Valley, east-central Nevada. In the past, researchers have disagreed as to whether the unusual-looking outcrop is intrusive or volcanic. The breccia possesses a normal magnetic polarity, but this is not apparent in aeromagnetic survey data. These data instead show that the knoll lies within a small aeromagnetic low that partially overlaps the extent of a small gravity high. The small gravity anomaly associated with the knoll, combined with an initial, limited ground magnetic survey taken at the knoll, indicates that the knoll rocks extend northward in the subsurface. A second, more extensive ground magnetic traverse was also done north of the knoll. Taking into consideration these new survey data and preexisting data, a two and one-half dimensional modeling program based on Webring (1985) was used to produce a geophysical model that accounts for gravity and magnetic properties, satisfies available geologic information, and conforms to current estimates of basin thickness. This model and the field observations support the interpretation that the knoll consists of gently west-dipping beds of Tertiary volcanic flow breccia, mudflow breccia, and conglomerate.

Nevada↗

USGS2023

A spatially explicit modeling framework to guide management of subsidized avian predator densities

Anthropogenic resource subsidization across western ecosystems has contributed to widespread increases in generalist avian predators, including common ravens ( Corvus corax ; hereafter, raven). Ravens are adept nest predators and can negatively impact species of conservation concern. Predation effects from ravens are especially concerning for greater sage-grouse ( Centrocercus urophasianus ; hereafter, sage-grouse), which have experienced prolonged population decline. Our objectives were to quantify spatiotemporal patterns in raven density, evaluate sage-grouse nest success concurrent with fluctuating raven densities, and demonstrate a spatially explicit decision support tool to guide management applications to appropriate conflict areas. We combined ~28,000 raven point count surveys with data from more than 900 sage-grouse nests between 2009 and 2019 within the Great Basin, USA. We modeled variation in raven density using a Bayesian hierarchical distance sampling approach with environmental covariates on detection and abundance. Concurrently, we modeled sage-grouse nest survival using a hierarchical frailty model as a function of raven density and other environmental covariates that influence the risk of nest failure. Raven density commonly exceeded 0.5 ravens km −2 and increased at low elevations with more anthropogenic development and/or agriculture. Reduced sage-grouse nest survival was strongly associated with elevated raven density (e.g., >0.5 ravens km −2 ) and varied with topographic ruggedness, shrub cover, and burned areas. For conservation application, we developed a spatially explicit planning tool that predicts nest survival under current and reduced raven numbers within the Great Basin to help direct management actions to localized areas where sage-grouse nests are at highest risk of failure. Our modeling framework can be generalized to multiple species where spatially registered abundance and demographic data are available.

Nevada↗

USGS2023

Flood-inundation maps for the Muddy River, near Moapa, Nevada

The Muddy River provides habitat for several wildlife and endemic aquatic species protected under the Endangered Species Act. Near Moapa, Nevada, in the Bureau of Land Management’s Muddy River Floodplain Restoration Project Area, a previously constructed levee on the east side of the river alters the natural hydrology and decreases connectivity between the river and its floodplain. The Bureau of Land Management is interested in restoring the project area to a more natural state and proposed removing the existing levee (at the time of this study in 2019) on the east bank of the river and replacing it with a new levee farther away from the river. The 50-, 20-, 10-, 4-, 2-, and 1-percent annual exceedance probability flood streamflows were estimated based on a flood-frequency analysis of a streamgage in the study area. River cross-sections were surveyed and combined with a digital elevation model of the floodplains to create a coupled one- and two-dimensional hydraulic model of the study area. The estimated flood streamflows were used as inputs in the hydraulic model to simulate how flood-inundation extents would change with the proposed restoration. Simulated inundation extents expand with increasing flood magnitudes, with nearly the entire valley inundated by the 2-percent flood streamflow. Within the project area, inundation extents with restoration increased on the east floodplain and decreased on the west floodplain for the 20-, 10-, 4-, 2-, and 1-percent flood streamflows. Outside the Muddy River Floodplain Restoration Project Area, inundation extents decreased with restoration east of the project area for the 20- and 10-percent flood streamflows, but changes in extent for larger streamflows were minor because most of the streamflow leaves the main river channel upstream of the restoration area.

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