Central Rocky Research Articles

The frequency and typology of ceramic sites in western Wyoming

Native ceramics are rare in the northwestern High Plains and Central Rocky Mountains where prehistory is dominated by mobile foraging societies and pottery appears late in the archaeological record. Our survey of the Wyoming Cultural Resource Information System for 11 western Wyoming counties and the Yellowstone National Park found 209 sites with sherd frequencies ranging from less than 10 to more than 1,000 yielding an estimate of 6175 total sherds. Ceramic sites are most common in southwest Wyoming, due in part to intense energy development and associated archaeological inventories but also to the overlap of multi-regional ceramic traditions. Ceramic typologies for western Wyoming are poorly standardized with variable grey wares attributed to Fremont, Shoshone, and Crow ceramic traditions. In this study, we summarize the frequency and typology of Wyoming ceramic traditions and outline a protocol for further research of an understudied but potentially informative component of the regional archaeological record.

Late-Holocene paleoclimate and treeline fluctuation in Wyoming’s Wind River Range, USA

This study presents evidence for treeline advance in the central Rocky Mountains, United States, between 1800 and 800 cal. yr BP. This evidence was generated by systematic survey, sampling, and accelerator-mass spectrometer (AMS) dating of remnant Pinus albicaulis above the modern treeline ecotone of Union Peak, in the Wind River Range of western Wyoming. The survey identified 257 tree remnants, of which AMS dates were generated on 15 samples. Based on AMS results, it appears that treeline was approximately 100 m higher in elevation and covered an additional 1 km of horizontal distance for approximately a millennium, 1800–800 cal. yr BP. These findings are surprising given the tendency of remnant forests across the region to date to the middle Holocene but are consistent with regional evidence for increases in effective moisture that are contemporaneous with the Union Peak treeline advance. The age of death for most of the sampled trees occurred, however, near 800 cal. yr BP, 200 or more years prior to the onset of the type of regional and hemispheric temperature decreases that might be expected to result in treeline decline. Given the contemporaneity of the Union Peak treeline decline with a substantial regional megadrought 820–780 cal. yr BP, it is hypothesized that declining moisture availability played a fundamental role in this phenomenon. If true, the late-Holocene advance and subsequent decline of treeline on Union Peak would emphasize the role effective moisture plays in the complex interactions between temperature, precipitation, and local-scale factors conditioning treeline elevation across the central Rocky Mountain region.

Managing Downy Brome (Bromus tectorum) in the Central Rockies: Land Manager Perspectives

AbstractSuccessful management of downy brome (also known as cheatgrass) requires understanding land managers' perceptions and decisions about whether to invest in its control. We investigated ranchers' and natural resource professionals' (NRPs) perceptions and knowledge about downy brome ecology and its impacts, their current downy brome management practices and satisfaction with those practices, and their information and technical needs using focus groups and a mail survey of ranchers and NRPs in Colorado and Wyoming. Both groups thought downy brome was a problem, and perception of the severity of downy brome corresponded to the level of infestation in the respondent's region. NRPs identified downy brome as a bigger problem than did ranchers from the same area in all but one region. Ranchers were most likely to use early spring grazing to control downy brome, and NRPs were most likely to use seeding, imazapic herbicide, or a combination of methods. Both groups reported that the primary constraint to controlling downy brome was that other weeds were a higher priority. Ranchers and NRPs wanted more information about the control methods they were already likely to use as well as other downy brome control methods. Our findings suggest that (1) listing a species as a noxious weed may provide an important incentive to control it, but trade-offs among control efforts for different species must be carefully considered; (2) managers need to know more about low-cost, low-labor strategies for managing downy brome; and (3) some managers need to be informed about how to identify downy brome, its potential negative effects, and how to prevent its spread. Better quantification of the economic and ecological impacts of downy brome in the Central Rocky Mountains, continued development of effective and economically viable management methods, and improvement in the dissemination of that information to land managers are necessary for successful control of downy brome.

Regionalization of fire regimes in the Central Rocky Mountains, USA

Fire is one of the most important natural disturbances in the coniferous forests of the US Rocky Mountains. The Rocky Mountains are separated by a climatic boundary between 40° and 45° N, which we refer to as the central Rocky Mountains (CRM). To determine whether the fire regime from the CRM was more similar to the northern Rocky Mountains (NRM) or southern Rocky Mountains (SRM) during the Holocene, a 12,539-yr-old sediment core from Long Lake, Wyoming, located in the CRM was analyzed for charcoal and pollen. These data were then compared to charcoal records from the CRM, NRM and SRM. During the Younger Dryas chronozone, the fire regime was characterized as frequent at Long Lake. The early and middle Holocene fire regime was characterized as infrequent. A brief interval from 4000 to 3000calyr BP, termed the Populus period, had a frequent fire regime and remained frequent through the late Holocene at Long Lake. In comparison to sites from the NRM and SRM, the fire regime at Long Lake was most similar to the SRM during the past 12,539calyr BP. These results suggest the disturbance regime in the CRM has a greater affinity with those of the SRM.

Nutrient Availability Assessment Method in Semiarid Ecosystems in the Central Rocky Mountains, Utah

We tested the performance of Plant Root Simulator (PRS) probes as a tool to determine plant nutrient availability across the semiarid environments of the central Rocky Mountains. We used PRS probes in a lab‐field comparison representing the climatic and physiographic complexity in a high‐elevation watershed in the Wasatch Range, northern Utah. We determined soil nutrient supply rates for 10 selected soils in the lab at two soil temperatures (5 and 25°C) and three moisture levels (10, 30, and 50% volumetric soil moisture content), and compared them to nutrient pools and field nutrient supply rates. Using two independent techniques, simple regressions and principal component analysis (PCA) ordination, we concluded that soil moisture content was the most important driver of nutrient supply, while incubation temperature had no influence, and nutrient pool sizes were generally poor predictors of nutrient supply rates. Lab supply rates correlated well with field PRS results. Therefore, lab PRS assays can serve as a reasonable substitute for the field use and can be beneficial for large‐scale comparison of nutrient supply rates among semiarid wildland ecosystems of the western United States.

Summer Roadside use by White-Tailed Deer and Mule Deer in the Rocky Mountains, Alberta

Deer-vehicle collisions are on the rise in North America, requiring a better understanding of road use patterns by deer. We examined summer use of roadside areas by White-tailed Deer (Odocoileus virginianus) and Mule Deer (Odocoileus hemionus) in the central Rocky Mountains, Alberta. Deer surveys were conducted along the main highway at dawn and dusk for 6 summers. We observed more White-tailed Deer than Mule Deer along the highway during the study. White-tailed Deer were also involved in collisions with vehicles more often than Mule Deer, and may pose a higher risk for collisions because they tend to flee when approached. Time of day did not affect Mule Deer sightings during the study period, but White-tailed Deer were observed more frequently in the morning than evening. Both species were observed more frequently in May than other months. While little association was observed between deer species, large-scale spatial segregation along the highway did not occur. Our data suggest that drivers were likely to encounter deer in single-species pairs, and based on deer roadside use, we suggest that the potential for deer-vehicle collisions was highest in May, close to dawn, and along the northern sections of the highway. Deer-vehicle collision data indicated that the predominant locations of collisions reflected the spatial patterns of roadside usage by deer, but temporal patterns of collisions are also affected by visibility and traffic patterns. Collision-mitigation strategies incorporating deer behavior and driver-education are discussed.

Dynamically downscaled winter precipitation over complex terrain of the Central Rockies of Western Montana, USA

[1] We evaluate the results of dynamically downscaled winter precipitation over Western Montana using the weather research and forecasting (WRF) model through comparison with estimates from the observationally based parameter-elevation regressions on independent slopes model (PRISM). Seven years (six winters) from 2000 to 2006 are simulated at 4 km resolution to assess the similarities and differences between the two models as well as the implications for hydrologic modeling. Inherent biases in both approaches are apparent, highlighting the difficulty in climate model validation. Results show general agreement between the two models in the spatial distribution of winter precipitation. A principal component analysis shows similar spatial patterns between models in the leading six components suggesting that the main processes that drive the spatial distribution of precipitation were properly captured. The first component explains almost 70% of total variance, and the first three components explain more than 85% in both data sets. The largest differences between the two data sets exist in areas at high elevation and upstream of the continental divide where observations are sparse. In these areas, WRF consistently predicts higher amounts of precipitation and larger interannual variability than PRISM. We suggest that these results are realistic for impingement of moist air masses on topography and, if correct, could have significant implications in flood forecasting, water resource management, and climate change studies.

Dynamically downscaled winter precipitation over complex terrain of the Central Rockies of Western Montana, USA

Key Points NCEP GFS‐WRF winter precipitation downscale is compared to PRISM Largest differences seen at high elevations and west of continental divide WRF predicts higher amounts of precipitation than PRISM at high elevations

Area change of glaciers in the Canadian Rocky Mountains, 1919 to 2006

Abstract. Glaciers in the Canadian Rocky Mountains constitute an important freshwater resource. To enhance our understanding of the influence climate and local topography have on glacier area, large numbers of glaciers of different sizes and attributes need to be monitored over periods of many decades. We used Interprovincial Boundary Commission Survey (IBCS) maps of the Alberta–British Columbia (BC) border (1903–1924), BC Terrain Resource Information Management (TRIM) data (1982–1987), and Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) imagery (2000–2002 and 2006) to document planimetric changes in glacier cover in the central and southern Canadian Rocky Mountains between 1919 and 2006. Over this period, glacier cover in the study area decreased by 590 ± 70 km2 (40 ± 5%), 17 of 523 glaciers disappeared and 124 glaciers fragmented into multiple ice masses. Glaciers smaller than 1.0 km2 experienced the greatest relative area loss (64 ± 8%), and relative area loss is more variable with small glaciers, suggesting that the local topographic setting controls the response of these glaciers to climate change. Small glaciers with low slopes, low mean/median elevations, south to west aspects, and high insolation experienced the largest reduction in area. Similar rates of area change characterize the periods 1919–1985 and 1985–2001; −6.3 ± 0.6 km2 yr−1 (−0.4 ± 0.1% yr−1) and −5.0 ± 0.5 km2 yr−1 (−0.5 ± 0.1% yr−1), respectively. The rate of area loss, however, increased over the period 2001–2006; −19.3 ± 2.4 km2 yr−1 (−2.0 ± 0.2% yr−1). Applying size class-specific scaling factors, we estimate a total reduction in glacier cover in the central and southern Canadian Rocky Mountains for the period 1919–2006 of 750 km2 (30%).

Multiscale observations of snow accumulation and peak snowpack following widespread, insect‐induced lodgepole pine mortality

ABSTRACTSeasonal snowpack in forested lands is the primary source of fresh water in western North America, where mountain pine beetle (MPB) infestation has resulted in rapid and extensive tree die‐off. Forests significantly influence the amount and spatial distribution of peak seasonal snowpack, but the impacts of large‐scale tree mortality on the processes controlling peak snowpack are not well understood. We evaluate the effects of widespread tree mortality on winter snow accumulation and peak seasonal snowpack across multiple spatial scales and several levels of MPB impact in the Central Rocky Mountains. Observations for winters 2010 and 2011 include continuous snow depths in 20 plots, distributed snow surveys at peak accumulation and climate observations above and below canopy including precipitation, temperature, humidity, wind and shortwave radiation. Stable water isotopes were observed for fresh snowfall and for snowpack. Plot‐scale snowfall observations showed 20% lower interception (p < 0.05) in grey‐phase stands (needles lost) than in unimpacted stands. However, distributed snow surveys found no differences in peak seasonal snow water equivalent between unimpacted and grey‐phase stands. Water isotopes of snowpack from MPB‐killed stands indicated kinetic fractionation; enriched values demonstrated higher winter snowpack sublimation in MPB‐killed forest. Following MPB infestation, reduced canopy sublimation of intercepted snow appeared to be compensated by increased snowpack sublimation, consistent with observations of higher snowpack insolation. Consequently, the effects of widespread tree mortality on peak seasonal snowpack, which is crucial for downstream water resources, will be influenced by compensation for lower interception by higher snowpack sublimation. Copyright © 2012 John Wiley & Sons, Ltd.

Abrupt landscape change post–6 Ma on the central Great Plains, USA

The principal control on landscape evolution in the central Great Plains of the United States over the past 10 m.y. is a contentious subject. New sedimentary data collected from Late Miocene Ogallala Group and Pliocene Broadwater Formation of the Nebraskan Great Plains demonstrates a twofold increase in the median grain size (from 20 mm to >40 mm) exported from the Rocky Mountains across the Miocene-Pliocene boundary. Paleoslope reconstructions derived from these data support the tilting of the Miocene Ogallala Group after 6 Ma, but demonstrate that the transport slope of the lower part of the unconformably overlying Pliocene succession is identical to the present-day slope. These data allow us to constrain the timing of differential uplift in the Great Plains to between 6 and 3.7 m.y.; the wavelength and short duration of this tilting are best explained by the initiation of localized dynamic topography. Our results also suggest a threefold to fourfold increase in specific stream power at this time, meaning that Pliocene rivers draining the central Rockies were considerably more competent than their Miocene predecessors. Incision during this period was not continuous. A significant episode of aggradation from 3.7 to 2.5 Ma is best explained by high rates of sediment supply relating to the warm, wet mid-Pliocene climate optimum. The modern pattern of incision on the Great Plains occurred from 2.5 Ma, and not from the end of the Miocene as is sometimes supposed, reflecting the onset of major Northern Hemisphere glaciation.

Twenty-first century central Rocky Mountain river discharge scenarios under greenhouse forcing

The present-day hydroclimatology of the central Rocky Mountains is heavily influenced by recurring large-scale climate patterns: the Pacific Decadal Oscillation (PDO), the El Niño-Southern Oscillation (ENSO), and the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). Hence, low frequency central Rocky Mountain river discharge variability can be successfully modeled by regression techniques using these climate indices as predictors. Generalized Least Squares (GLS) regression equations captured a large portion of streamflow variability at the hydrological apex of North America. Using archived runs from global climate models from the IPCC Fourth Assessment Report (AR4) (Phase 3 of the Coupled Model Intercomparison Project – CMIP3), the PDO, ENSO and the NAO were projected for the 21st century for the B1, A1B and A2 Special Report on Emission Scenarios (SRES). These projected climate indices were used as inputs into the GLS regression equations, giving projected central Rocky Mountains river discharges. These projections showed generally declining trends in central Rocky Mountains surface water availability for 2006–2050 and 2006–2096. This study's novel result is that projection distribution functions show a shift in the variance of the flows, from a relatively symmetric equal probability of low versus high flows about the mode and mean in 2006, to a broader, left-skewed flow pattern with a higher probability of low flows in general, and extreme low flows in particular, by 2096.

Whitebark Pine Stand Condition, Tree Abundance, and Cone Production as Predictors of Visitation by Clark's Nutcracker

BackgroundAccurately quantifying key interactions between species is important for developing effective recovery strategies for threatened and endangered species. Whitebark pine (Pinus albicaulis), a candidate species for listing under the Endangered Species Act, depends on Clark's nutcracker (Nucifraga columbiana) for seed dispersal. As whitebark pine succumbs to exotic disease and mountain pine beetles (Dendroctonus ponderosae), cone production declines, and nutcrackers visit stands less frequently, reducing the probability of seed dispersal.Methodology/Principal FindingsWe quantified whitebark pine forest structure, health metrics, and the frequency of nutcracker occurrence in national parks within the Northern and Central Rocky Mountains in 2008 and 2009. Forest health characteristics varied between the two regions, with the northern region in overall poorer health. Using these data, we show that a previously published model consistently under-predicts the proportion of survey hours resulting in nutcracker observations at all cone density levels. We present a new statistical model of the relationship between whitebark pine cone production and the probability of Clark's nutcracker occurrence based on combining data from this study and the previous study.Conclusions/SignificanceOur model clarified earlier findings and suggested a lower cone production threshold value for predicting likely visitation by nutcrackers: Although nutcrackers do visit whitebark pine stands with few cones, the probability of visitation increases with increased cone production. We use information theoretics to show that beta regression is a more appropriate statistical framework for modeling the relationship between cone density and proportion of survey time resulting in nutcracker observations. We illustrate how resource managers may apply this model in the process of prioritizing areas for whitebark pine restoration.

A caveat regarding diatom-inferred nitrogen concentrations in oligotrophic lakes

Atmospheric deposition of reactive nitrogen (Nr) has enriched oligotrophic lakes with nitrogen (N) in many regions of the world and elicited dramatic changes in diatom community structure. The lakewater concentrations of nitrate that cause these community changes remain unclear, raising interest in the development of diatom-based transfer functions to infer nitrate. We developed a diatom calibration set using surface sediment samples from 46 high-elevation lakes across the Rocky Mountains of the western US, a region spanning an N deposition gradient from very low to moderate levels (<1 to 3.2 kg Nr ha−1 year−1 in wet deposition). Out of the fourteen measured environmental variables for these 46 lakes, ordination analysis identified that nitrate, specific conductance, total phosphorus, and hypolimnetic water temperature were related to diatom distributions. A transfer function was developed for nitrate and applied to a sedimentary diatom profile from Heart Lake in the central Rockies. The model coefficient of determination (bootstrapping validation) of 0.61 suggested potential for diatom-inferred reconstructions of lakewater nitrate concentrations over time, but a comparison of observed versus diatom-inferred nitrate values revealed the poor performance of this model at low nitrate concentrations. Resource physiology experiments revealed that nitrogen requirements of two key taxa were opposite to nitrate optima defined in the transfer function. Our data set reveals two underlying ecological constraints that impede the development of nitrate transfer functions in oligotrophic lakes: (1) even in lakes with nitrate concentrations below quantification (<1 μg L−1), diatom assemblages were already dominated by species indicative of moderate N enrichment; (2) N-limited oligotrophic lakes switch to P limitation after receiving only modest inputs of reactive N, shifting the controls on diatom species changes along the length of the nitrate gradient. These constraints suggest that quantitative inferences of nitrate from diatom assemblages will likely require experimental approaches.

Impacts of climate change on August stream discharge in the Central-Rocky Mountains

In the snowmelt dominated hydrology of arid western US landscapes, late summer low streamflow is the most vulnerable period for aquatic ecosystem habitats and trout populations. This study analyzes mean August discharge at 153 streams throughout the Central Rocky Mountains of North America (CRMs) for changes in discharge from 1950–2008. The purpose of this study was to determine if: (1) Mean August stream discharge values have decreased over the last half-century; (2) Low discharge values are occurring more frequently; (3) Climatic variables are influencing August discharge trends. Here we use a strict selection process to characterize gauging stations based on amount of anthropogenic impact in order to identify heavily impacted rivers and understand the relationship between climatic variables and discharge trends. Using historic United States Geologic Survey discharge data, we analyzed data for trends of 40–59 years. Combining of these records along with aerial photos and water rights records we selected gauging stations based on the length and continuity of discharge records and categorized each based on the amount of diversion. Variables that could potentially influence discharge such as change in vegetation and Pacific Decadal Oscillation (PDO) were examined, but we found that that both did not significantly influence August discharge patterns. Our analyses indicate that non-regulated watersheds are experiencing substantial declines in stream discharge and we have found that 89% of all non-regulated stations exhibit a declining slope. Additionally our results here indicate a significant (α ≤ 0.10) decline in discharge from 1951–2008 for the CRMs. Correlations results at our pristine sites show a negative relationship between air temperatures and discharge and these results coupled with increasing air temperature trends pose serious concern for aquatic ecosystems in CRMs.

Testing the Feasibility of Using the ForSAFE-VEG Model to Map the Critical Load of Nitrogen to Protect Plant Biodiversity in the Rocky Mountains Region, USA

The ForSAFE-VEG model was used to estimate atmospheric nitrogen deposition and climate effects on soil chemistry and ground vegetation in alpine and subalpine zones of the northern and central Rocky Mountains region in the USA from 1750 to 2500. Model simulations for a generalized site illustrated how the critical load of atmospheric nitrogen deposition could be estimated to protect plant biodiversity. The results appear reasonable compared with past model applications in northern Europe. Atmospheric N deposition critical loads estimated to protect plant biodiversity were 1 to 2 kg N/ha/year. This range could be greater, depending on the values selected for critical site-specific parameters (precipitation, temperature, soil chemistry, plant nutrient uptake, and any eventual harvest of biomass) and the amount of biodiversity change allowed.

Mapping Grizzly Bear Habitats for Conservation Planning in the Central Interior of British Columbia

The Central Interior and Sub-Boreal Interior ecoprovinces of British Columbia represent an important transitional population of grizzly bears (Ursus arctos L.) occupying the area between two major mountain systems (Coastal Ranges and Central Rockies), as well as defining the boundary of extirpated range in the Fraser Plateau South. To assist ecoregional planning in the area, grizzly bear habitat models were produced for density, mortality risk, and source-sink habitat. Bear density was based on population estimates for each management unit and downscaling approaches using local habitat suitability rankings; mortality risk was modelled using 339 mortality locations from 2004 to 2007 and a suite of environmental and anthropogenic factors as predictors. Both models were combined to form a two-dimensional framework of habitat states representing source-like and sink-like habitats that help prioritize areas for protection and restoration (road decommissioning), respectively, as well as provide a basis for comparing with other biodiversity features. Irreplaceability values based on rare biota and unique habitats measured as the sum of runs in Marxan were significantly higher in grizzly bear source habitats than sink habitats suggesting that protection of grizzly bear source habitats would confer an umbrella or surrogate effect to other biodiversity.

Obsidian Source Use in the Greater Yellowstone Area, Wyoming Basin, and Central Rocky Mountains

Using x-ray fluorescence (XRF) analysis from nearly 2,300 sourced obsidian artifacts in western Wyoming, southwestern Montana, and eastern Idaho, we demonstrate regional diachronic changes in access to and preference for particular obsidian sources throughout the West. We focus on both (I) long-term patterns of obsidian use that may inform us about the timing of precontact migrations of Numic (Shoshone) speakers into the Rocky Mountains and (2) the extent to which later contact among Native inhabitants and European immigrants was a mechanism for reducing elements of precontact mobility and exchange in the postcontact era. We view indigenous responses to contact in the study area as an active, strategic process with measurable material consequences. Despite a well-documented increase in mobility among local Native groups as a result of the introduction of the horse, our study demonstrates a restriction and reduction in Historic period source use in western Wyoming. We propose that changes in obsidian source use are a reflection of ethnogenesis and development of ethnographic bands as a response to culture contact among indigenous inhabitants and with Europeans.

Lithosphere-asthenosphere interaction beneath the western United States from the joint inversion of body-wave traveltimes and surface-wave phase velocities

SUMMARY The relation between the complex geological history of the western margin of the North American plate and the processes in the mantle is still not fully documented and understood. Several pre-USArray local seismic studies showed how the characteristics of key geological features such as the Colorado Plateau and the Yellowstone Snake River Plains are linked to their deep mantle structure. Recent body-wave models based on the deployment of the high density, large aperture USArray have provided far more details on the mantle structure while surface-wave tomography (ballistic waves and noise correlations) informs us on the shallow structure. Here we combine constraints from these two data sets to image and study the link between the geology of the western United States, the shallow structure of the Earth and the convective processes in mantle. Our multiphase DNA10-S model provides new constraints on the extent of the Archean lithosphere imaged as a large, deeply rooted fast body that encompasses the stable Great Plains and a large portion of the Northern and Central Rocky Mountains. Widespread slow anomalies are found in the lower crust and upper mantle, suggesting that low-density rocks isostatically sustain part of the high topography of the western United States. The Yellowstone anomaly is imaged as a large slow body rising from the lower mantle, intruding the overlying lithosphere and controlling locally the seismicity and the topography. The large E–W extent of the USArray used in this study allows imaging the ‘slab graveyard’, a sequence of Farallon fragments aligned with the currently subducting Juan de Fuca Slab, north of the Mendocino Triple Junction. The lithospheric root of the Colorado Plateau has apparently been weakened and partly removed through dripping. The distribution of the slower regions around the Colorado Plateau and other rigid blocks follows closely the trend of Cenozoic volcanic fields and ancient lithospheric sutures, suggesting that the later exert a control on the locus of magmato-tectonic activity today. The DNA velocity models are available for download and slicing at http://dna.berkeley.edu.

Holocene record of precipitation seasonality from lake calcite δ18O in the central Rocky Mountains, United States

A context for recent hydroclimatic extremes and variability is provided by a ∼10 k.y. sediment carbonate oxygen isotope (δ 18 O) record at 5–100 yr resolution from Bison Lake, 3255 m above sea level, in northwestern Colorado (United States). Winter precipitation is the primary water source for the alpine headwater lake in the Upper Colorado River Basin and lake water δ 18 O measurements reflect seasonal variations in precipitation δ 18 O. Holocene lake water δ 18 O variations are inferred from endogenic sedimentary calcite δ 18 O based on comparisons with historic watershed discharge records and tree-ring reconstructions. Drought periods (i.e., drier winters and/or a more rain-dominated seasonal precipitation balance) generally correspond with higher calcite δ 18 O values, and vice-versa. Early to middle Holocene δ 18 O values are higher, implying a rain-dominated seasonal precipitation balance. Lower, more variable δ 18 O values after ca. 3500 yr ago indicate a snow-dominated but more seasonally variable precipitation balance. The middle to late Holocene δ 18 O record corresponds with records of El Nino Southern Oscillation intensification that supports a teleconnection between Rocky Mountain climate and North Pacific sea-surface temperatures at decade to century time scales.