Eastern Great Basin Research Articles

Using Empirical Performance Data to Source Bluebunch and Snake River Wheatgrass Plant Materials to Restoration Sites in the Eastern Great Basin, USA.

To infer adaptation of plant material, restoration practitioners often consider only surrogate geographic or climatic information. However, empirical biomass data could assist in deciding what material to use where. To test this approach, we transplanted seven bluebunch wheatgrass (BBWG; Pseudoroegneria spicata) and five Snake River wheatgrass (SRWG; Elymus wawawaiensis) populations to three sites ranging from low to high precipitation (LPPT, MPPT, and HPPT). We measured establishment-year (2011) biomass at all sites and 2012-16 biomass at MPPT and HPPT. When data were standardized by site, P-7 and Anatone produced the mostBBWG biomass across sites and Wahluke the least in both 2011 and 2012-16, while E-58X produced the most SRWG biomass and Secar and E-49X the least in 2011 and 2012-16, respectively. Among BBWG populations in 2011, relative performance of P-7 (G6 generation) and Goldar increased and Whitmar decreased at wetter sites, while Columbia was stable (high) and Wahluke was stable (low) over sites. Among SRWG populations in 2011, Secar, Secar78, and E-58X increased at drier sites and Discovery at wetter sites. However, once established, populations of both species were much more similar for trend. In 2012-16, trend somewhat increased for five BBWG populations from MPPT to HPPT, was stable for Wahluke, but declined for Columbia, while all five SRWG populations declined at HPPT. These results suggest that, once established, BBWG is mostly stable across sites, while SRWG is less adapted to wetter sites. In 2012-16, BBWG populations originating at drier (or wetter) sites mostly performed relatively better at MPPT (or HPPT), suggesting adaptation to site. However, in the establishment year (2011), this relationship did not hold, suggesting seedling vigor and immature growth rate play a stronger role than precipitation at the site of origin.

The Fremont Frontier: Living at the Margins of Maize Farming

Abstract The Fremont provide an important case study to examine the resilience of ancient farmers to climatic downturns, because they lived at the far northern margin of intensive maize agriculture in the American West, where the constraints on maize production are made abundantly clear. Using a tree-ring and simulation-based reconstruction of average annual precipitation and maize growing degree days, along with cost-distance to perennial streams, we model spatial variability in Fremont site density in the eastern Great Basin. The results of our analysis have implications for defining the ecological envelope in which farming is a viable strategy across this arid region and can be used to predict where and why maize farming strategies might evolve and eventually collapse as climate changes over time.

Maxent Predictive Species Distribution Models and Model Accuracy Assessment for Two Species of Psilochalcis Kieffer (Hymenoptera: Chalcididae) Occurring in the Eastern Great Basin of Utah, USA

Two species of Psilochalcis wasps (P. minuta and P. quadratis) were recently described from Utah’s eastern Great Basin. The extent of their known distributions is extremely limited, based on few data points. We developed species distribution models (SDMs) using Maxent modeling software for each Psilochalcis species to identify areas of probable suitable habitat for targeted collecting to improve our knowledge of their distributions. We used six occurrence data points for P. minuta and eight occurrence data points for P. quadratis, along with ten environmental variables as inputs into the Maxent modeling software. Model-predicted areas with a potential suitable habitat value greater than 0.69 were mapped using ArcGIS Pro to help select locations for model accuracy assessment. Employing Malaise traps, eighteen sites were sampled to evaluate each SDM’s ability to predict the occurrence of Psilochalcis species. Psilochalcis minuta occurred at eight of nine juniper-dominated sample sites that were predicted as having high suitability by the model for this species. Likewise, P. quadratis occurred at two of four cheatgrass-dominated sample sites predicted by the model. Psilochalcis minuta occurred at three of nine sampled sites that were not predicted by the model, and P. quadratis occurred at seven of fourteen non-predicted sites. The Maxent SDM results yielded an AUC value of 0.70 and p-value of 0.02 for P. minuta and 0.68 and 0.02. for P. quadratis. These results were reflected in our model accuracy assessment. Of the selected environmental variables, aspect, historic fire disturbance, and elevation yielded the greatest percent contributions to both species’ models. Sympatric distributions were observed for P. minuta and P. quadratis. Elevation, vegetation type, NDVI, and soil type are the most important environmental variables in differentiating areas of optimal suitable habitat for the two species.

Snowfall Replenishes Groundwater Loss in the Great Basin of the Western United States, but Cannot Compensate for Increasing Aridification

AbstractThere has been an acceleration of groundwater loss in the Great Basin (GB) of the western U.S. as determined from total water storage (TWS) measurements from the GRACE/FO satellite missions. From 2002 to 2023, there was a loss of TWS in the GB of ∼68.7 km3 which is more than six times the current volume of the Lake Mead Reservoir. In this arid/semi‐arid region, groundwater is the primary factor contributing to the decade‐scale decline in TWS. Stronger declining trends are found in the western versus the eastern GB. Snow loading is the major cause of seasonal fluctuations of TWS in the GB. Despite annual replenishment of groundwater by snow, the downward trend persists even in notable snow years. Likely causes include declining snow mass, upstream water diversions and increased evaporation/sublimation due to increasing temperatures. Dire consequences for humans and wildlife are associated with this large loss of groundwater.

Decoupled Oligocene mylonitic shearing and Miocene detachment faulting in the East Humboldt Range metamorphic core complex, northeast Nevada, USA

Abstract The relationships between brittle detachment faulting and ductile shear zones in metamorphic core complexes are often ambiguous. Although it is commonly assumed that these two structures are kinematically linked and genetically related, direct observations of this coupling are rare. Here, we conducted a detailed field investigation to probe the connection between a detachment fault and mylonitic shear zone in the Ruby Mountain–East Humboldt Range metamorphic core complex, northeast Nevada. Field observations, along with new and published geochronology, demonstrate that Oligocene top-to-the-west mylonitic shear zones are crosscut by ca. 17 Ma subvertical basalt dikes, and these dikes are in turn truncated by middle Miocene detachment faults. The detachment faults appear to focus in preexisting weak zones in shaley strata and Mesozoic thrust faults. We interpret that the Oligocene mylonitic shear zones were generated in response to domal upwelling during voluminous plutonism and partial melting, which significantly predated the middle Miocene onset of regional extension and detachment slip. Our model simplifies mechanical issues with low-angle detachment faulting because there was an initial dip to the weak zones exploited by the future detachment-fault zone. This mechanism may be important for many apparent low-angle normal faults in the eastern Great Basin. We suggest that the temporal decoupling of mylonitic shearing and detachment faulting may be significant and underappreciated for many of the metamorphic core complexes in the North American Cordillera. In this case, earlier Eocene–Oligocene buoyant doming may have preconditioned the crust to be reactivated by Miocene extension, thus explaining the spatial relationship between structures.

Quantifying climate change impacts on low flows of small high mountain watersheds: A nonstationary approach

Study regionThe Utah Wasatch Mountains along the eastern Great Basin and the western Rocky Mountains. Study focusChanges in seasonal precipitation patterns and summer evaporation rates due to increases in temperatures will have severe impacts on low flows of the mountainous watersheds affecting downstream water availability and thus impacting ecosystems and drinking water supplies under future climate change. Reliable prediction of climate change impacts on future low flows needs to consider both the extremity of climatic variables and the physical characteristics of the watersheds. This study analyzes low flows of small mountainous watersheds addressing nonstationarity of climatic parameters and estimates the impact of climate change on low flow, combining nonstationarity and outcome of a physically distributed hydrologic model. MACA statistically downscaled climate data have been used as inputs to the DHSVM model to estimate future low flows for both near term (2036–2044) and distant future (2091–2099) under RCP4.5 and 8.5 scenarios.New Hydrological Insights for the Region: Nonstationary models with time (5 watersheds) or temperature (2 watersheds) as the covariate in the location-scale provided the best performance. This study demonstrated that RCP4.5 has more severe impact on the low flow frequency and volume in the near future than RCP8.5. In contrast, the effect of RCP8.5 is more dominant on the low flow regimes in the distant future than RCP4.5.

Quaternary lacustrine carbonate deposits of the Great Basin, USA: Impact of climate, tectonics and substrate

ABSTRACTThe Great Basin included several lacustrine systems that accommodated extensive carbonate buildups: the Lahontan on the western side (dating back to 48 kyr cal bp), and the Bonneville (from 30 to 11.5 kyr cal bp) and Great Salt Lake (starting 11.5 kyr cal bp) on the eastern side of the basin. The eastern lakes show a transition from freshwater to hypersaline conditions. In contrast, the western lakes do not show any significant change from the originally prevailing freshwater conditions. Mapping of the carbonate buildups in the different lakes settings enables a comparison of a biotic versus an abiotic composition of the carbonate buildups, their morphologies and their specific spatial distributions. The morphology, size and distribution of the carbonate deposits are predominantly governed by seasonal to long‐term water level fluctuations, particular geomorphological heritage, fault‐induced processes, groundwater seepage and substrates. All of the lakes show a palaeoshoreline distribution with some buildups containing crusts, hemispheroid domes, and parts of complex domes resulting from climate‐induced lake level variations. However, the presence of columns and complex domes made up of mixed biotic/abiotic carbonates in the western Great Basin is related to the influx of groundwater. Winnemucca Lake and Pyramid Lake contain bigger buildups than the ones observed in the eastern Great Basin lakes. The presence of these large size buildups and thinolites in the Lahontan lacustrine system are a consequence of local hydrological processes associated with influenced groundwater flows through specific sedimentary structures (for example, from springs and delta fronts) and faults. This contrast in the distribution, composition and size of the buildups between the two sides of the Great Basin suggests local changes in water chemistry (for example, [Ca2+]) and groundwater influxes. This work provides a novel conceptual model for the formation of abiotic and/or biotic carbonate buildups in lacustrine settings.

Metallogeny and exploration strategy for volcanic rocks hosting world class Be-U-F mineralization at Spor Mountain, Utah, U.S.A.

We report new geochemical data (major-elements, trace-elements, and Nd-Pb isotopes) for the Spor Mountain Formation (SMF), a volcanic sequence that hosts the largest deposit of beryllium in the world. Understanding the genesis of the deposit is critical for improved recognition of regional exploration targets containing additional volcanic-hosted beryllium resources. The deposit occurs in an area of extensive alkalic rhyolitic ash flow tuffs and calderas underlain by Paleozoic and older limestone, dolomite, shale, and quartzite. The lower fluorite and bertrandite-rich tuff and upper topaz-rich rhyolite of the SMF have overlapping zircon crystallization ages (25.59 + 0.29/−0.45 Ma). Enrichment of Be, U, and F is a key attribute of the SMF inherited from melting heterogeneous source materials and magma hybridization in the continental lithosphere. Two mineralization stages are implicated: magmatic, and hydrothermal/metasomatic. The magmatic stage occurred early, as indicated by the high beryllium content in early-crystallizing zircon. The post-magmatic/hydrothermal stage involved F-rich fluids that reacted with glass and carbonate nodules in the tuff to form bertrandite (and U-rich fluorite and opal) and high-grade mineralization. The rhyolite best displays the magmatic stage of enrichment. The SMF is alkaline. Chondrite-normalized REE patterns for tuff and rhyolite are regular, stacked subparallel, and imply a shared source derivation and evolution. The tuff and rhyolite plot along a sub-vertical array for Pb isotopes and suggest they are cogenetic; both have negative values of εNd. Pb isotopic ratios for SMF do not match the slopes, initial isotopic values, or estimated basement ages of precious and base metal mining districts in Utah; thus, they do not share a source region or evolution. Crustal ages from Nd isotopes (average TDM ~ 2.29 Ga) are older than basement ages obtained by Pb isotopes. The deposit occurs in a transitional area of thinned crust near the boundary between two basement domains, the eastern Great Basin and Colorado Plateau, which have contrasting ages. Many geochemical attributes are shared between SMF and the Ermakovka deposit in Russia: they represent the world's major commercial Be deposits. Rare-metal indices of granite-related mineralization show that SMF resembles other global beryllium-bearing granitic deposits. Despite this coincidence, none of these examples matches the mineralogy, geologic setting, or type of rare metal mineralization at Spor Mountain.

A Latest-Paleoindian-Aged Pronghorn Trap in the Goshute Valley, Eastern Great Basin, USA

ABSTRACT We report the discovery of a large-scale artificial pronghorn (Antilocapra americana) trap located near Silver Zone Pass in the northern Goshute Valley, eastern Elko County, Nevada. Evidence comes from three closely related and closely spaced surface scatters of lithic artifacts called the Silver Zone Pass Complex. Two of the scatters represent a single kill zone, or corral, while the third represents an associated campsite. The assemblage of 282 bifacial points and fragments from the three scatters is characterized by short-stemmed Windust and Pinto forms, elsewhere dated to the early-mid Holocene, about 8500–7500 calendar years ago. With this discovery, we can firmly conclude that large-scale communal trapping of artiodactyls began in the eastern Great Basin 2000–3000 years earlier than previously thought, and is coincident with other significant changes in human technology, subsistence, and settlement documented for the Paleoindian-Archaic transition in the region.

Sources and concentrations of methane, ethane, and CO2 in deep aquifers of the Surat Basin, Great Artesian Basin

Understanding the occurrence and sources of methane in aquifers is an international issue, especially in regions that host oil and gas reservoirs. Multi-isotopic studies are important to understand sources and concentrations of dissolved gases in aquifers of basins that host oil and gas extraction; or future CO2, natural gas, hydrogen storage, or compressed air energy storage. The largest artesian basin in the world, the Great Artesian Basin, extends across more than one fifth of Australia providing a fresh water source from various aquifers. The Precipice and Hutton sandstones, aquifers of the Surat Basin in the eastern Great Artesian Basin, are important water resources for town water supply, agriculture, mines, feedlots, and private landholders in Queensland. Overlying and underlying formations host gas extraction. The southern part of the basin in Queensland additionally hosts an oil field, and potential CO2 storage sites, therefore understanding the aquifer gas concentrations, processes and sources is important for fluid management. The dissolved concentrations of methane and ethane in the Hutton Sandstone were up to 96 mg/L and 1 mg/L respectively, and in the Precipice Sandstone methane ranged up to 2100 mg/L and ethane 6.5 mg/L in the southern Surat Basin. Dissolved gas concentrations were measured by an open and closed sampling method, with the concentrations lower from open sampling, and the gas wetness parameter systematically slightly lower. The Hutton Sandstone aquifer dissolved gas isotopic signatures are mainly consistent with primary microbial CO2 reduction generating methane in situ, with fractionation factors indicating acetate fermentation in a few cases. The Hutton Sandstone δ13C-DIC, δ13C-CO2, and δ13C-CH4 have an enrichment trend with increasing depth that indicate a microbial substrate depletion effect. Moonie Oil Field Precipice Sandstone and Evergreen Formation samples plot in the thermogenic region, with enriched δ13C-CO2 indicating microbial biodegradation is also occurring. The Precipice Sandstone aquifer samples have a mixed microbial CO2 reduction and early mature thermogenic gas signature in both isotope cross plots and gas wetness diagrams, with a subset of sampled δ13C-C2H6 and isotope factors consistent with early mature thermogenic gas. A potential historic source of thermogenic gas is the underlying gas reservoir of the Bowen Basin. Large volumes of water are abstracted from these aquifers, hence dissolved gases may contribute to greenhouse gas emissions.

Basketry, cordage, and perishable artifact manufacture at Bonneville Estates Rockshelter: Diachronic technological variation

As a technologically-complex material class, perishable artifacts have the potential to address a multitude of socio-economic activities and behaviors; however, their application to these subjects are limited by poor preservation and small sample sizes. This study presents a novel approach to analysis that incorporates the chaîne opératoire of basketry and cordage, demonstrating the efficacy of applying statistics to characterize technological organization. To illustrate the utility of this approach, this study provides a diachronic analysis of basketry, cordage, and related manufacturing waste from Bonneville Estates Rockshelter (BER), a multi-layered “dry cave” archaeological site in the eastern Great Basin dating from the late Pleistocene through the Holocene. The relationship between people and the environment as well as social interaction among hunter-gatherers are addressed by considering the timing, changes, and seasonality of perishables at BER. Changes in basketry manufacture and the importance of net hunting throughout the Holocene emphasize temporal variation in community participation in subsistence activities. Debris from textile production demonstrates that BER also functioned as a multi-seasonal manufacturing and repair site. By comparing functional and technological-stylistic attributes, this study characterizes the complex ways gender influenced the manufacture and use of a material class traditionally associated with feminine work in hunter-gatherer communities.

Strain and Velocity Across the Great Basin Derived From 15‐ka Fault Slip Rates: Implications for Continuous Deformation and Seismic Hazard in the Walker Lane, California‐Nevada, USA

AbstractAverage strain across the Great Basin over the past 15 Kyr derived from slip rates on individual faults shows a concentration of both right‐lateral shear and extension in the western Great Basin (Walker Lane). Straining is modest across the central Great Basin, with a zone of higher strain in the eastern Great Basin including the Wasatch Front. The horizontal velocity field derived from 15‐ka fault slip rates is similar to the pattern of GPS velocities, suggesting that regional strain release patterns have been constant over the past 15 Kyr. The magnitudes of velocities inferred from fault slip rates, relative to North America, are lower than those from GPS in the Walker Lane, suggesting that the geologic record is missing evidence of strike slip on faults, and seismic hazard may be higher than suggested by fault slip rates alone. The observed strain concentration in the western Great Basin is consistent with a Sierra Nevada block that is more rigid than the surrounding lithosphere of nonlinear rheology, which concentrates strain east of and adjacent to the rigid block. Treating the western U.S. as a thin viscous sheet with the Sierra Nevada block as a rigid boundary provides a consistent history of continuous deformation in the Walker Lane over decadal, millennial, and Neogene timescales.

Maize Dependence among the Sevier Puebloans

Some archaeologists have argued that the Formative-era villagers of the Sevier River region in the eastern Great Basin were primarily foragers whose economy was dependent upon marsh resources, especially cattails. This paper compiles multiple lines of evidence from Backhoe Village and other Sevier villages to show that subsistence was based on maize agriculture, not foraging for wild resources.

‘Dust in the wind’ from source-to-sink: Analysis of the 14–15 April 2015 storm in Utah

Abstract On 14–15 April 2015, an intense intermountain cyclone in the western USA caused high winds and a dust storm that degraded air quality in the eastern Great Basin, and deposited dust-on-snow (DOS) in the Wasatch Range near Salt Lake City, Utah. We analyzed the storm and documented its “source-to-sink” development to relate the frontal passage with dust mobilization, air quality changes, and dust deposition on montane snowpack near Alta, Utah. This case study is first to track a dust storm and measure the elemental composition and radiative properties of the resulting DOS as a single specific event layer in Wasatch montane snowpack; prior studies have assessed seasonally aggregated DOS deposits. Dust plumes on MODIS imagery indicate mobilization from known regional “hotspots” for aeolian activity, including clay- and silt-rich alluvium, modern playas, and disturbed areas within the Pleistocene Paleolake Bonneville Basin. This 2015 single event dust layer was 1–3 cm thick with a median dust size of 10.81–12.55 µm; its measured radiative properties are similar to aggregated dusts previously assessed in Wasatch snowpack. Dust from the 2015 DOS event is enriched in the elements As, Cd, Cu, and Mo by a 10× factor relative to average elemental concentrations in the upper continental crust; its heavy metals (Cu, Pb, As, Cd, Mo, Zn) are probably derived from regional mine operations. Tracking elemental fluxes from source-to-sink is important for resolving environmental impacts, and informing future analysis of single storm dust loading, ecosystem impacts, and quantity and quality of meltwater-fed drinking water.

Mississippian mud rocks of the eastern Great Basin: Stratigraphy, tectonic significance, and hydrocarbon potential

A thick succession of Mississippian mud rocks in the eastern Great Basin has historically been identified as the Chainman Shale and interpreted as a foreland basin deposit associated with the Antler orogeny. Our work shows that this section is two distinct mud-rock units separated by a Late Mississippian unconformity. The Gap Wash Formation is identified as the mud rock below the unconformity, and Chainman Shale is restricted to mud rock above the unconformity. Poor exposure, sparse age control, and limited lithologic contrast have hampered identification and correlation of the mud-rock units. New research identifies subtle differences in rock type, and mineralogical and source-rock analyses show that the two formations have contrasting characteristics. These are associated with petrophysical properties that can be correlated across the region. The data show that the Gap Wash Formation has significantly more organic carbon and better pyrolysis results than the Chainman Shale. The Gap Wash also has mineralogy that could make it more suitable for treatment as a shale reservoir. The new understanding of Mississippian mud rocks in the Great Basin can focus future hydrocarbon exploration. The mud-rock units record regional Mississippian paleogeographic evolution. The Gap Wash Formation was deposited into accommodation space created by the loading of the continental margin during the Antler orogeny. The Chainman Shale was deposited in a successor basin that formed in response to resumed continental margin contraction in the late Meramecian to early Chesterian and is not clearly associated with the Antler orogeny.

Phylogenetic revision of the psammophilic Trogloderus LeConte (Coleoptera: Tenebrionidae), with biogeographic implications for the Intermountain Region.

The genus Trogloderus LeConte, 1879, which is restricted to dunes and sandy habitats in the western United States, is revised using morphological and molecular information. Six new species are described from desert regions: Trogloderus arcanus New Species (Lahontan Trough); Trogloderus kandai New Species (Owens Valley); Trogloderus major New Species (Mohave Desert); Trogloderus skillmani New Species (eastern Great Basin and Mohave Desert); Trogloderus verpus New Species (eastern Colorado Plateau); and Trogloderus warneri New Species (western Colorado Plateau). A molecular phylogeny is presented for the genus and used to infer its historical biogeography. The most recent common ancestor of Trogloderus is dated to 5.2 mya and is inferred to have inhabited the Colorado Plateau. Current species most likely arose during the mid-Pleistocene where the geographic features of the Lahontan Trough, Bouse Embayment and Kaibab Plateau were significant factors driving speciation.

Climate and dispersal influence the structure of leaf fungal endophyte communities of Quercus gambelii in the eastern Great Basin, USA

Abstract Endophytic fungi form communities within living plant tissues. Their functions vary tremendously so the structures of their communities influence plant and ecosystem functions. We determined the separate effects of neutral and deterministic processes structuring communities of Quercus gambelii leaf endophytes by sampling north- and south-facing flanks of four canyons so local climate varied independently from spatial separation. We found that both deterministic (response to climate) and neutral (dispersal limitation) processes significantly influenced community structure. These findings, if applicable to other systems, may have consequences in both agricultural and natural ecosystems. Endophyte dispersal could limit agricultural production, ecosystem restoration or natural plant establishment. Thus deliberate inoculation may prove useful in some situations. Moreover, the influence of climate on fungal endophyte communities indicates that climate change may not only impact plant distributions directly, but may also do so indirectly via the effect of endophytes on plant tolerance to temperature and moisture extremes.

SINGLE-GRAIN OPTICALLY STIMULATED LUMINESCENCE AGES OF BROWNWARE POTTERY IN THE MIDDLE ROCKY MOUNTAINS AND THE SPREAD OF NUMIC CERAMIC TECHNOLOGY

This study presents the results of a single-grain optically stimulated luminescence (SG-OSL) analysis of brownware pottery from four Late Prehistoric-period sites in the Middle Rocky Mountains, Wyoming, USA. SG-OSL of quartz ceramic temper provides improved age control for sites where radiocarbon dating has proven problematic due to old wood, recent wildfires, and calibration uncertainties. SG-OSL results are compared to fine-grain infrared stimulated luminescence (FG-IRSL) results from the same sherds and associated radiocarbon ages. We find that the single-grain technique applied to quartz sand temper provides improved accuracy and precision over both FG-IRSL and radiocarbon. We compare our results to directly dated brownwares from the southern and eastern Great Basin based largely on thermoluminescence analysis. While brownware ceramics appear earliest in the southwestern Great Basin, our data show that the technology spread quickly to the northeastern margin of the Numic homelands. We suggest that knowledge of ceramic technology in Formative (i.e., Ancestral Pueblo and Fremont) societies was important in the adoption of pottery by Numic hunter-gatherers and that, like in the southwestern Great Basin, this technological adaptation in the Middle Rocky Mountains may have occurred within a context of resource intensification during the last 800 years.

Variation in Sagebrush Communities Historically Seeded with Crested Wheatgrass in the Eastern Great Basin

Although crested wheatgrass (Agropyron cristatum [L.] Gaertn. &A. desertorum [Fisch. ex Link] Schult.) has been one of the most commonly seeded exotic species in the western United States, long-term successional trajectories of seeded sites are poorly characterized, especially for big sagebrush (Artemisia tridentata Nutt.) ecosystems in the Great Basin. Interpreting successional trajectories is particularly difficult because many seeded sites were actively managed with subsequent treatments to kill sagebrush and sustain high forage productivity of crested wheatgrass plants. In addition, inherent differences in climate, topography, soils, and disturbance regimes may lead to variable vegetation structure and species composition among seeded sites. To clarify variation in successional trajectories, we measured vegetation composition, plant species diversity, ground cover, and soil properties in 38 historical crested wheatgrass seedings distributed across 146 sampling sites that lacked subsequent sagebrush treatments. The multivariate dataset was analyzed using principal components analysis to identify “defining factors” that best explained variation among sites. Variation was primarily attributed to an inverse relationship between crested wheatgrass and sagebrush abundance (R2 = 0.69; P < 0.0001) and their affinity for either silty or sandy soil textures, respectively, as well as a negative association between crested wheatgrass abundance and species diversity (R2 = 0.67; P < 0.0001). These results do not support the assumption that crested wheatgrass seedings uniformly remain in vegetation states with low diversity and poor sagebrush reestablishment over the long term (i.e., 43−63 yr). We suggest that a broader interpretation of plant community dynamics is needed while avoiding generalizations of how historically seeded Wyoming big sagebrush sites will respond over time.

Revisiting the deformed high shoreline of Lake Bonneville

Since G. K. Gilbert's foundational work in the eastern Great Basin during the late 1800s, the late Pleistocene Lake Bonneville (30–10 ka) has been recognized as a natural laboratory for various Quaternary studies, including lithospheric deformation due to surface loading and climate-forced water balance changes. Such studies rely on knowledge of the elevations of Lake Bonneville's paleoshoreline features and depositional landforms, which record a complex history of lake level variations induced by deglacial climate change. In this paper, we present (1) a new compilation of 178 elevation measurements of shoreline features marking Lake Bonneville's greatest areal extent measured using high-precision differential GPS (dGPS), and (2) a reconstructed outline of the highest shoreline based on dGPS measurements, submeter-resolution aerial imagery, topographic digital elevation models (DEMs), and field observations. We also (3) devise a simplified classification scheme and method for standardizing shoreline elevation measurement for different shoreline morphologies that includes constraints on the position of the still water level (SWL) relative to each feature type. The deformation pattern described by these shoreline features can help resolve the relative effects of local hydro-isostasy due to the lake load and regional solid earth deflection due to the Laurentide ice sheet, with potential implications for Earth rheology, glacial isostatic adjustment, and eustatic sea level change.