Geology topics

Research about Colorado

Source-linked reports with geographic coverage including Colorado.

At least 73 records · Page 4Linked to original sources

USGS2025

Antigone canadensis (Sandhill Crane) foraging patterns influenced by crop type, roost distance, and tillage intensity during spring and autumn migration at a primary stopover area

The San Luis Valley in Colorado, USA, an agriculturally dominated stopover area, is used by the Rocky Mountain population of Antigone canadensis tabida (Greater Sandhill Crane) and some midcontinental individuals of A. c. canadensis (Lesser Sandhill Crane) during migration. While the numbers of both subspecies are stable, the effects of continued water scarcity and declines in grain output on the energetics of cranes in the San Luis Valley are unclear. We conducted roadside counts of A. c. tabida and A. c. canadensis on agricultural fields to determine the effects of crop type, roost distance, and tillage intensity on their selection and abundance on crop fields. Antigone canadensis varied in their use of the San Luis Valley for foraging. In autumn, both subspecies selected barley and other grains over other crop types. In spring, cranes preferred to forage in barley fields, and selection declined as distance to roosts increased. Both subspecies also selected barley fields that were lightly or not tilled. We modeled covariates on abundance for A. c. tabida only and found that more cranes were found close to roosts early in the season in autumn. As the season progressed, the number of A. c. tabida increased as roost distance increased. In spring, abundance was influenced by an interaction between time and crop, with the highest numbers found on barley and pasture around mid-March. Our results suggest that A. canadensis may switch to other crop types as resources are depleted near roosts but appear to prefer to fly farther for grains. Grains that are left idle or moderately tilled and are located near roosts will help ensure A. canadensis are able to maintain adequate nutrient reserves at agriculturally dominated stopover areas during migration.

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USGS2025

Variability in hydrologic response to wildfire between snow zones in forested headwaters

Rising temperatures and shifting fire regimes in the western United States are pushing fires upslope into areas of deep winter snowpack, where we have little knowledge of the likely hydrologic impacts of wildfire. We quantified differences in the timing and magnitude of stormflow responses to summer rainstorms among six catchments of varying levels of burn severity and seasonal snowpack cover for years 1–3 after the 2020 Cameron Peak fire. Our objectives were to (1) examine whether responsiveness, magnitude, and timing of stormflow responses to rainfall vary between burned and unburned catchments and between snow zones, and (2) identify the factors that affect these responses. We evaluated whether differences in storm hydrograph peak flow, total flow, stage rise, and lag to peak time differed by snow zone and burn category using generalised linear models. Additional predictors in these models are the maximum 60-min rainfall intensity for each storm, the cumulative potential water deficit prior to the storm, and the year post-fire. These models showed that the high snow zone (HSZ) has higher total stormflow than the low snow zone (LSZ), likely due to the higher soil moisture content in that area. In both snow zones, the biggest driver of the magnitude of the stormflow response was MI 60 . Burn category did not have a clear impact on stormflow response in the HSZ, but it did impact stage rise at the severely burned catchment in the LSZ. This was the only site that had widespread overland flow post-fire. These results demonstrate that the stormflow responses to fire vary between snow zones, indicating a need to account for elevation and snow persistence in post-fire risk assessments.

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USGS2025

Cenozoic stratigraphy of Colorado

As a successor to previous Colorado stratigraphy charts (MS-53 Colorado Stratigraphic Chart and MS-54 Cretaceous Stratigraphy of Colorado), this Colorado Geological Survey (CGS) publication resulted from a collaboration between the CGS, USGS, and the Denver Museum of Nature and Science (DMNS). The chart was designed to illustrate Cenozoic stratigraphy spanning the state’s many sedimentary basins. It builds upon the work of dozens of colleagues and updates Richard Pearl’s seminal 1974 stratigraphy chart. The chart leverages the community’s stratigraphic work in both the subsurface and outcrop, and depicts new geochronologic constraints for many units. To facilitate comparison of strata to external forcing factors, the chart employs a linear timescale. Each unit’s dominant depositional environment is depicted, as are major mountain building events, erosional events, and regional unconformities.

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USGS2025

Data gap analysis for estimation of agricultural return flows in the Upper Gunnison River Basin, Colorado

The Gunnison River and many tributaries in the Upper Gunnison River Basin provide water to irrigate agricultural crops. The application of irrigation water can recharge some aquifers locally by water percolating below the root zone and eventually flowing back to the stream or river through the subsurface. Diverting surface water for irrigation reduces streamflow during the irrigation season but can provide temporary storage of water and supplement streamflow after the snowmelt runoff season. Understanding the timing and quantity of agricultural return flows could help resource managers make informed decisions and adapt to potential changes in water management and availability that could affect irrigation practices. In 2024, the U.S. Geological Survey, in cooperation with the Upper Gunnison River Water Conservancy District, began a study to characterize agricultural return flows in the Upper Gunnison River Basin by using endmember mixing analysis and developing a groundwater model. Both approaches require data from multiple sources, but data gaps exist in the East River study reach and other reaches of interest (Ohio Creek, Tomichi Creek, and Cochetopa Creek). The East River Basin, which is the initial focus of the study, has fewer data gaps than the other basins. Data gaps could be addressed by installing additional surface water and groundwater monitoring sites, making regular streamflow measurements on tributaries, and completing tests to characterize local aquifer properties.

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USGS2025

Structural analysis of brittle-plastic shear zones in the Sangre de Cristo Range, southern Colorado USA: Superposition of Rio Grande rift extension on Laramide contraction

The Sangre de Cristo Range in southern Colorado exposes some of the deepest Cenozoic structural levels in the Rocky Mountain region, including mylonitic shear zones associated with both the Laramide orogeny and Rio Grande rift. We investigated the relation between Laramide contraction and Rio Grande rift extension with detailed geologic mapping, kinematic analysis, and geochronometry in a 50 km 2 area centered on the Independence Mine shear zone (IMSZ). The 15−100-m-thick IMSZ is one of several shallowly to moderately (∼45° ± 20°) W-SW−dipping brittle-plastic shear zones along the western flank of the range. These shear zones display microstructural evidence of initiation as top-NE contractional mylonite zones, consistent with regional Laramide kinematics, which have been pervasively overprinted by shear fabrics indicating top-SW extensional reactivation. Both top-NE and top-SW shear fabrics involve cataclasis and quartz dislocation creep, although top-SW shear is more commonly localized along phyllosilicate-lined shear bands. Shear zones are hosted predominately within Proterozoic gneiss, and contain abundant chlorite and white mica derived from alteration of hornblende and feldspar, which indicates that weakening driven by fluid reactions played an important role in localizing strain. Extensional overprinting appears to be most pervasive along more steeply dipping portions of shear zones and where secondary phyllosilicates form an interconnected weak phase, which suggests that reactivation was primarily controlled by geometry and rheological contrasts inherited from contraction. One top-SW shear zone adjacent to the IMSZ cuts a late Oligocene gabbro stock, and monazite grains synkinematic with top-SW shear in the IMSZ yielded late Oligocene to Early Miocene U-Th-Pb dates that correspond with initiation of the Rio Grande rift. Reactivation of weak reverse faults may represent an important structural control during initial extension in the middle crust, prior to slip along the high-angle Sangre de Cristo normal fault system.

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USGS2025

Assessing the effects of climate and visitor use on amphibian occupancy in a protected landscape with long-term data

Determining where animals are, and if they are persisting across protected landscapes, is necessary to implement appropriate management and conservation actions. For long-lived animals and those with boom-and-bust life histories, perspective across time contributes to discerning temporal trends in occupancy and persistence, and potentially in identifying mechanisms affecting those parameters. Long-term data are particularly useful in protected areas to quantify indicators of change that may be less obvious or occur more slowly. We used long-term amphibian data from Rocky Mountain National Park (RMNP) in a Bayesian occupancy modeling framework to estimate changes in occupancy, colonization, and persistence of amphibians over three decades and to explore the effects of climate, landscape change, and visitor use as mechanisms behind observed changes. Our results indicate that colonization and persistence are low and/or declining for Pseudacris maculata , Lithobates sylvaticus , and Ambystoma mavortium , and that occupied catchments are increasingly isolated. We found visitor use to have a consistently negative effect on occupancy and persistence of amphibians in RMNP, and that all species are more likely to occupy catchments with more complex habitat and a higher proportion of wetlands. While these results are sobering, they also provide a way forward where mitigation efforts can target identified drivers of change.

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USGS2025

Land-use and socioeconomic time-series reveal legacy of redlining on present-day gentrification within a growing United States city

Home Owners’ Loan Corporation (HOLC) maps illustrated patterns of segregation in United States cites in the 1930s. As the causes and drivers of demographic and land-use segregation vary over years, these maps provide an important spatial lens in determining how patterns of segregation spatially and temporally developed during the past century. Using a high-resolution land-use time series (1937-2018) of Denver, Colorado, USA, in conjunction with 80 years of U.S. Census data, we found divergent land-use and demographics patterns across HOLC categories were both pre-existent to the establishment of HOLC mapping and continued to develop over time. Over this period, areas deemed “declining” or “hazardous” had more diverse land use compared to “desirable” areas. “Desirable” areas were dominated by one land-use type (single-family residential), while single-family residential diminished in prominence in the “declining/hazardous” areas. This divergence became more established decades after HOLC mapping, with impact to racial metrics and low-income households. We found changes in these demographic patterns also occurred between 2000 and 2019, highlighting how processes like gentrification can develop from both rapid demographic and land-use changes. This study demonstrates how the legacy of urban segregation develops over decades and can simultaneously persist in some neighborhoods while providing openings for fast-paced gentrification in others.

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USGS2025

Genetics of wild, whirling disease resistant rainbow trout populations in Colorado

Introduction: Myxobolus cerebralis , the parasite responsible for salmonid whirling disease, was unintentionally introduced to and became established in Colorado in the 1990s. Mortality of young-of-year fish due to infection by M. cerebralis resulted in recruitment failure and subsequent significant declines in Rainbow Trout ( Oncorhynchus mykiss ) populations. The complex multistage lifecycle of M. cerebralis makes it difficult to eradicate and manage, and hatchery control strategies do not work in the wild. A viable method that has been utilized for wild populations is enhancing host resistance. Myxobolus cerebralis resistant Rainbow Trout were discovered at a hatchery in Germany and subsequently incorporated into Colorado's brood stock program. Since 2004, M. cerebralis resistant strains have been stocked into all major Colorado coldwater drainages to re-establish Rainbow Trout populations after whirling disease-related declines, with documented survival and reproduction of stocked disease resistant fish. Methods and results: Genetic population assignment tests (via putatively neutral microsatellite markers) were used to monitor the stocked populations and indicated that, after only a few years, many of the individuals in these populations unexpectedly assigned to genetic strains that were historically susceptible to M. cerebralis . To further investigate the genetic composition of these fish, a single nucleotide polymorphism (SNP) panel was used to determine the percent genetic composition of resistant strain in these individuals. Microsatellites and SNPs provided similar results, indicating a low percentage of ancestry from the resistant strain in these fish, but they continued to survive exposure to M. cerebralis , suggesting that these individuals possessed genetic loci necessary for resistance. Finally, a quantitative trait locus (QTL) region (termed WDRES-9) was used to identify individuals with alleles associated with disease resistance. Implementation of the WDRES-9 QTL test allowed for more accurate determination of M. cerebralis resistant individuals within wild populations and better described their variability in resistance.

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USGS2025

The role of bedrock circulation depth and porosity in mountain streamflow response to prolonged drought

Quantitative understanding is lacking on how the depth of active groundwater circulation in bedrock affects mountain streamflow response to a multi‐year drought. We use an integrated hydrological model to explore the sensitivity of a variety of streamflow metrics to bedrock circulation depth and porosity under a plausible extreme drought scenario lasting up to 5 years. Endmember depth versus hydraulic conductivity relationships and porosity values for fractured crystalline rock are simulated. With drought, a deeper circulation system with higher drainable porosity more effectively buffers minimum flow and significantly limits perennial stream loss in comparison to a shallow circulation system. Streamflow buffering is accomplished through extensive groundwater storage loss. However, deeper circulation systems experience prolonged recovery from drought in comparison to storage‐limited shallow systems. Research highlights the importance of characterizing the deeper bedrock hydrogeology in mountainous watersheds to better understand and predict drought impacts on stream ecosystem health and water resource sustainability.

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USGS2025

Reduction of red bed sedimentary rocks in connection with energy metal ore formation: A case study from the Sinbad seep, Mesa County, Colorado

The Paradox Basin’s Sinbad seep is a modern analog for ancient bleaching of red bed sediments by introduced alkaline, reducing brines. This bleaching, involving reductive alteration of former red beds, is essential ground preparation that enables the altered rocks to trap Cu, U, and V from later oxidized fluids, forming ore deposits. Study of Sinbad thus offers insights into these metallic mineralization processes in the Paradox and other sedimentary basins. The Sinbad seep occurs where shallow groundwater interacts with organic-rich petroleum source rocks, flows up a fault, and discharges into Salt Creek. Ratios of Na/Cl, Na/Br, and Cl/Br, plus high sulfate concentrations, indicate that the salinity of the seep water originated from dissolution of halite and gypsum during topographically driven flow of meteoric water across a diapir of the Pennsylvanian Paradox Formation, rather than from deep basinal brines. In contact with the organic-rich shales of the Paradox, these SO 4 -rich waters become reduced through bacterial reduction, producing H 2 S. The waters react with red beds of the Permian Cutler Formation, causing pervasive bleaching. The bleaching at Sinbad is characterized by iron-conservative reduction of ferric iron in diagenetic hematite and detrital ilmenite and magnetite to Fe sulfides. The ferrous iron is retained in these sulfides likely as sorbed Fe. Associated alteration includes precipitation of quartz and feldspar overgrowths, partial dissolution of detrital quartz and feldspar caused by pressure solution, formation of clay and authigenic rutile, and precipitation of carbonate and gypsum. The Fe sulfides rapidly degenerate to a mixture of jarosite and iron oxides on weathering at the surface. Among the major-oxide elements and most trace elements, there is no statistical difference between unbleached and bleached samples. The exceptions are uranium and sulfur, which are somewhat greater in bleached samples. Fission track radiography illuminates that uranium is preferentially concentrated in iron oxide cements, iron sorbed into detrital clasts, and finely disseminated iron oxide in illite cement in bleached samples. A leaching experiment suggests that uranium may be more easily available for mobilization from rocks that have undergone bleaching alteration, making them potential U sources. In addition, bleached rocks form effective traps for U, V, and some Cu mineralization.

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USGS2025

Reevaluating the depositional model of the Cenomanian–Turonian Bridge Creek Limestone Member near Pueblo, Colorado, U.S.A.: Roles of changing sedimentation rate on the formation of limestone–marl bedding couplets

Although interbedded limestone–marl couplets in many hemipelagic and pelagic deposits have been commonly attributed to orbital-driven climate cycles, the driving mechanisms of these couplets remain largely controversial. This situation arises from the fact that detailed sedimentologic and petrographic facies characteristics of these fine-grained deposits have rarely been examined closely. In this study we conduct an integrated sedimentologic and petrographic analysis to disentangle causes of the limestone–marl bedding couplets in the Cenomanian–Turonian Bridge Creek Limestone Member (BCL) of the Greenhorn Formation using cores and outcrop near Pueblo, Colorado. By integrating existing geochemical datasets, each of the three general lithologies in the BCL including limestone, marl, and calcareous mudstone can be divided into two facies, a more bioturbated vs. a more laminated facies, in addition to bentonite beds. The variability in sedimentary, bioturbation, and petrographic characteristics of different sedimentary facies types, as well as constraints from the existing orbital time scale, in the BCL indicate changes in sediment accumulation rate or the amount of time recorded by different facies—the limestone, marl, and calcareous facies are interpreted to reflect increasing sedimentation rate. The sedimentary and petrographic facies variations, including but not limited to lithological alternations, in the BCL are interpreted to result from the combined influence of various processes such as bottom currents, bioturbation, early diagenesis, and episodic volcanic input, with some of the above-mentioned processes likely modulated by short-term relative changes in sea level. Results of this study highlight the need for detailed sedimentologic and petrographic studies and consideration of short-term changes in sedimentation rate to fully resolve the causes of the apparent limestone–marl bedding couplets and reliably reconstruct short-term changes in depositional and environmental conditions from the BCL and other similar successions.

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USGS2025

Exploring the science and data foundation for Federal public lands decisions

Public lands provide diverse resources, values, and services worldwide. Laws and policies typically require consideration of science in public lands decisions, and resource managers are committed to science-informed decision-making. However, it can be challenging for managers to use, and document the use of, science and data in their decisions. To better understand science and data use in Federal public lands decisions in the United States, we assessed the number, type, and age of documents cited in 70 Environmental Assessments (EAs) completed by the Bureau of Land Management (BLM) in Colorado from 2015–2019. We focused on the BLM, as they manage the largest area of public lands in the United States. We selected Colorado as our study area, as actions proposed on BLM lands in Colorado are representative of those across the nation. Fifty percent of citations were categorized as science and 23% as data. EAs contained an average of 17 citations (range 0–111), with documents analyzing effects of oil and gas development and recreation actions including the highest and lowest mean number of citations (41 and 6, respectively). Of individual resource analysis sections within EAs, 24% contained ≥1 science citation and 21% contained ≥1 data citation. Journal articles were the most cited type of document (26% of citations) followed by non-BLM inventories (13%). Forty-seven percent of citations were relatively recent (2010 or later); the oldest citation was from 1927. Commonly analyzed resources with the highest mean number of citations were socioeconomics, mineral resources, and noise. Fourteen of 33 commonly analyzed resources included <1 citation on average. Actions and resources with no or few citations represent opportunities for strengthening the transparent use of science and data in public lands decision-making.

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USGS2025

Tracing metal sources and groundwater flow paths in the Upper Animas River watershed using rare earth elements and stable isotopes

Groundwater flow paths and processes that govern metal mobility and transport are difficult to characterize in mountainous bedrock watersheds. Despite the difficulty in holistic characterization, conceptual understanding of subsurface hydrologic and geochemical processes is key to developing remediation plans for locations affected by acid mine drainage, such as the Upper Animas River watershed in southwestern Colorado, USA. Stable isotopes of water and rare earth elements were utilized to evaluate groundwater flow and metal sources within this complex catchment. Stable isotope samples collected from draining mine adits and springs display systematic spatial variation wherein sample sites at higher elevations have greater seasonal variability than sites at lower elevations. The Upper Cement Creek watershed, where multiple draining mines are present, displays the lowest seasonal variation in stable isotopic signatures, potentially indicating the presence of a large, well-mixed volume of groundwater storage or interbasin groundwater flow. Rare earth elements display statistically significant variation between different alteration styles in the catchment. Overprinting of regional propylitic alteration is evident based on enrichment of middle rare earth elements in acidic springs and mines that are not spatially associated with surficial exposures of acid generating alteration styles. Europium anomaly and middle rare earth enrichment signatures from two flooded mine tunnels on opposite sides of a watershed divide indicate connections to the same subsurface flooded mine workings.

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USGS2025

Quantifying the effect of petrogenic carbon on SOC turnover for two Rocky Mountain soils: When are petrogenic carbon corrections required?

Petrogenic organic carbon (OC petro ), derived from sedimentary rocks, is an often overlooked and poorly quantified source of soil organic carbon (SOC), which may influence measured or modeled SOC composition, age, and stability. In this study, we exploited differences in thermochemical stability between OC petro and biogenic SOC (OC bio ) using stepped elemental analysis to quantify the fractional contribution of OC petro to total SOC (f petro ), and we conducted a sensitivity analysis to estimate the effects of OC petro on modeled SOC transit times and system ages. Specifically, we compared the effects of accounting for OC petro inputs in SOC turnover modeling (using SoilR) for two montane meadow soils that are underlain by Cretaceous Mancos Shale. At these sites, we estimate that OC petro comprises 7%–9% of the total SOC stock (f petro = 0.07–0.09). However, accounting for OC petro as a mixture of inert and passive C or as completely inert C had negligible effects on SOC transit times and system ages, suggesting that there is a threshold of OC petro content under which there is minimal effect on calculated SOC turnover. Based on our sensitivity analysis, we estimate this threshold to be f petro = 0.125, further supporting that the accurate calculation of OC petro remains an important factor in estimating SOC turnover.

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USGS2025

Groundwater hydrology, groundwater and surface-water interactions, water quality, and groundwater-flow simulations for the Wet Mountain Valley alluvial aquifer, Custer and Fremont Counties, Colorado, 2017–19

In 2017, the U.S. Geological Survey, in cooperation with the Upper Arkansas Water Conservancy District, began a study to provide a comprehensive analysis of the Wet Mountain Valley alluvial aquifer, Custer and Fremont Counties, Colorado. The study included collection of data pertaining to groundwater hydrology, groundwater and surface-water interactions, and water quality in the alluvial aquifer. In addition to providing foundational information on the hydrology of the alluvial aquifer, a numerical groundwater-flow model was developed to estimate the potential effects of additional storage of groundwater in the alluvial aquifer. Groundwater-level elevation data from 30 wells were used to estimate groundwater-flow directions in the alluvial aquifer, which were generally from the southwest to northeast, away from the Sangre de Cristo Mountains and towards perennial streams in the center of the valley. Although some seasonal variation was apparent in groundwater-level elevation records, no statistically significant seasonal trends were indicated. Statistically significant long-term trends were indicated in groundwater-level elevation records for 8 of the 30 wells, and of these wells with statistically significant trends, all but 1 indicated a negative trend of groundwater-level elevations. Spatial evaluation of wells with statistically significant negative groundwater-level elevation trends showed many are in areas of denser well drilling for domestic or other uses, indicating increasing groundwater use could potentially be causing groundwater-level elevation declines. There were instances of wells with no statistically significant groundwater-level elevation trends also located in areas of greater density of well completions. Additional investigations may be necessary to more fully characterize the processes responsible for negative groundwater-level elevation trends. Streamflow gain or loss calculations were completed for low flow in 2017–19 and for high flow in 2018 in nine reaches of streams within the study area. Stream reaches of the upper Texas Creek, upper Grape Creek, upper-middle Grape Creek, and Taylor Creek displayed consistent streamflow loss in each period from 2017 to 2019. These stream reaches represent long-term sources of recharge to the alluvial aquifer. Streamflow gain or loss varies through time in other stream reaches (lower Texas Creek, lower-middle Grape Creek, lower Grape Creek below Westcliffe, and lower Grape Creek above DeWeese Reservoir). The temporally variable behavior indicates these stream reaches may be sources of groundwater recharge or areas of groundwater discharge, likely depending on temporal dynamics between the elevation of the water table and the stream. Water-quality samples were collected from 10 groundwater wells and 10 stream sites during September through November 2019. All groundwater and stream samples were analyzed for major and trace elements and stable isotopes of water. A subset of groundwater samples was also analyzed for the environmental tracers sulfur hexafluoride, tritium, and noble gases. Comparison of water-quality results to U.S. Environmental Protection Agency drinking water-quality standards indicated no constituents exceeded primary standards for human health. Spatial evaluation of water quality indicated the concentrations of various constituents are likely controlled by groundwater and surface-water interactions and by spatial variability in bedrock geology underlying the alluvial aquifer. Specifically, streams shown to gain from groundwater had water chemistry constituent compositions similar to groundwater, whereas streams exiting the Sangre de Cristo Mountains tended to have compositions consistent with snowmelt. Groundwater geochemistry appeared to be partially controlled by oxidation-reduction processes and by proximity to igneous rocks in the Wet Mountains. Environmental tracers used to estimate groundwater age indicated all sampled groundwater contained tracers representing modern recharge (approximately less than 65 years old) but mixing of premodern recharge (approximately more than 65 years old) also occurs. Spatial evaluation of environmental tracers indicated large faults may be conduits for upwelling of older groundwater. No trends were observed in groundwater age with well depth, indicating all sampled wells are located within the zone of active groundwater flow. The presence of modern groundwater in wells with statistically significant negative groundwater-level elevation trends indicates groundwater storage depletions may be partially offset by capture of modern recharge. Repeated sampling of groundwater age would be necessary, however, to determine if any trends in groundwater age exist, which may indicate changing groundwater recharge, storage, or discharge. Additional investigations could also consider quantifying groundwater age in deeper wells to more fully define the depth of active groundwater flow. A numerical groundwater-flow model was developed to estimate components of the water budget, simulate groundwater and surface-water interactions, and evaluate the potential effects of aquifer storage and recovery. Simulated groundwater-level elevations from the calibrated groundwater-flow model are similar to the observed pattern of groundwater-level elevations with higher elevations in the western part of the study area along the Sangre de Cristo Mountains. Simulated water-budget components indicate most of the recharge to the alluvial aquifer is derived from streamflow losses, which is consistent with observations of losing streams along the mountain front. The largest groundwater discharge component of the alluvial aquifer was to streams in the center of the valley, where observations of stream gain or loss indicated the predominance of gaining conditions. Comparison of groundwater and surface-water interactions between the calibrated groundwater-flow model for 2000-19 (the base-case model) and a simulation including additional recharge, representing potential aquifer storage and recovery operations, indicated the additional recharge distributed throughout the area had minimal effects on streamflow in the nearby Grape Creek. An analysis of subregional groundwater budgets showed approximately 54 percent of the additional recharge flowed back to nearby Grape Creek, and the other 46 percent was distributed laterally into adjacent cells in the alluvial aquifer. The comparison of simulations and subregional water budget show the additional recharge did not substantially alter groundwater-level elevations or basin wide groundwater storage. Although the analysis of additional recharge provided in the numerical groundwater-flow model considers only one of many possible recharge scenarios, the model provides a useful tool that could be modified for various scenarios to understand potential effects of managed aquifer recharge.

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USGS2025

Light absorbing particles deposited to snow cover across the Upper Colorado River Basin, Colorado Rocky Mountains, 2013-16: Interannual variations from multiple natural and anthropogenic sources

Atmospheric particulate matter (PM) as light-absorbing particles (LAPs) deposited to snow cover can result in early onset and rapid snow melting, challenging management of downstream water resources. We identified LAPs in 38 snow samples (water years 2013–2016) from the mountainous Upper Colorado River basin by comparing among laboratory-measured spectral reflectance, chemical, physical, and magnetic properties. Dust sample reflectance, averaged over the wavelength range of 0.35–2.50 μm, varied by a factor of 1.9 (range, 0.2300–0.4444) and was suppressed mainly by three components: (a) carbonaceous matter measured as total organic carbon (1.6–22.5 wt. %) including inferred black carbon, natural organic matter, and carbon-based synthetic, black road-tire-wear particles, (b) dark rock and mineral particles, indicated by amounts of magnetite (0.11–0.37 wt. %) as their proxy, and (c) ferric oxide minerals identified by reflectance spectroscopy and magnetic properties. Fundamental compositional differences were associated with different iron oxide groups defined by dominant hematite, goethite, or magnetite. These differences in iron oxide mineralogy are attributed to temporally varying source-area contributions implying strong interannual changes in regional source behavior, dust-storm frequency, and (or) transport tracks. Observations of dust-storm activity in the western U.S. and particle-size averages for all samples (median, 25 μm) indicated that regional dust from deserts dominated mineral-dust masses. Fugitive contaminants, nevertheless, contributed important amounts of LAPs from many types of anthropogenic sources.

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USGS2025

Landslide-channel feedbacks amplify channel widening during floods

Channel widening is a major hazard during floods, particularly in confined mountainous catchments. However, channel widening during floods is not well understood and not always explained by hydraulic variables alone. Floods in mountainous regions often coincide with landslides triggered by heavy rainfall, yet landslide-channel interactions during a flood event are not well known or documented. Here we demonstrate with an example from the Great Colorado Flood in 2013, a 1000 year precipitation event, how landslide-channel feedbacks can substantially amplify channel widening and flood risk. We use a combination of DEM differencing, field analysis, and multiphase flow modeling to document landslide-channel interaction during the flood event in which sediment delivered by landslides temporarily dammed the channel before failing and generating substantial channel widening. We propose that such landslide-flood interactions will become increasingly important to account for in flood hazard assessment as flooding and landsliding both increase with extreme rainfall under climate change.

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USGS2025

Relationship of atmospheric nitrogen deposition to soil nitrogen cycling along an elevation gradient in the Colorado Front Range

Microbial processing of atmospheric nitrogen (N) deposition regulates the retention and mobilization of N in soils, with important implications for water quality. Understanding the links between N deposition, microbial communities, N transformations, and water quality is critical as N deposition shifts toward reduced N and remains persistently high in many regions. Here, we investigated these connections along an elevation transect in the Colorado Front Range. Although rates of N deposition and pools of extractable N increased down the elevation transect, soil microbial communities and N transformation rates did not follow clear elevational patterns. The subalpine microbial community was distinct, corresponding to a high C:N ratio and low pH, while the microbial communities at the lower elevation sites were all very similar. Net nitrification, mineralization, and nitrification potential rates were highest at the Plains (1,700 m) and Montane (2,527 m) sites, suggesting that these ecosystems mobilize N. In contrast, the net immobilization of N observed at the Foothills (1,978 m) and Subalpine (3,015 m) sites suggests that these ecosystems retain N deposition. The contrast in N transformation rates between the plains and foothills, both of which receive elevated N deposition, may be due to spatial heterogeneity not captured in this study and warrants further investigation. Stream N concentrations from the subalpine to the foothills were consistently low, indicating that these soils are currently able to process and retain N deposition, but this may be disrupted if drought, wildfire, or land-use change alter the ability of the soils to retain N.

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