Geology topics

Research about Colorado

Source-linked reports with geographic coverage including Colorado.

At least 361 records · Page 20Linked to original sources

USGS2019

Supporting the development and use of native plant materials for restoration on the Colorado Plateau (Fiscal Year 18 Report)

Introduction A primary focus of the Colorado Plateau Native Plant Program (CPNPP) is to identify and develop appropriate native plant materials (NPMs) for current and future restoration projects. Multiple efforts have characterized the myriad challenges inherent in providing appropriate seed resources to enable effective, widespread restoration and identified a broad suite of research activities to provide the information necessary to overcome those challenges (e.g., Plant Conservation Alliance 2015; Breed et al. 2018). Many of the most complex information needs relate to identifying the appropriate plant species and populations that can successfully establish in dryland environments, like the Colorado Plateau, where low and highly variable precipitation is standard. Providing this information requires synergistic research efforts in which results from earlier investigations inform the design of subsequent investigations. Southwest Biological Science Center’s (SBSC’s) research activities in FY18 followed the FY18 Statement of Work (“Research supporting native plant materials development for the Colorado Plateau Native Plant Program, FY18”) to support a research framework that is continually adapting based on the needs of the restoration community and results from previous investigations; the long-term research framework is now outlined in the 2019-2023 5-Year Research Strategy (discussed below; hereafter referred to as the 5-Year Research Strategy). This research framework provides support for the National Seed Strategy for Rehabilitation and Restoration (Plant Conservation Alliance, 2015), Department of Interior Secretarial Order #3347 (Conservation Stewardship and Outdoor Recreation), and Bureau of Land Management Leadership Priority #1 (Create a conservation stewardship legacy second only to Teddy Roosevelt). The overall focus of activities in FY18 centered on landscape genetics and planning for common garden and other research projects. These activities were supported by two biological technicians that were hired and trained by Dr. Rob Massatti and Dr. Daniel Winkler. Many of the field-related activities, including plant trait measurement and seed/tissue collecting, were assigned to these technicians, which freed Dr. Massatti to work on other research objectives, including the time-consuming activities of processing and analyzing genetic data. A major challenge to field work in FY18 was the drought conditions that pervaded the Plateau during the spring field season. Due to low winter and spring precipitation, many plant communities did not green up in the spring, which prevented the biological technicians from collecting plant trait data, tissues samples, and seeds in many areas. To cope with the dry conditions, the technicians searched sites across a wider range of environmental space and considered a broader suite of species from which to collect data (i.e., species that may be included in research projects in future years). Monsoonal precipitation starting in July supported a late summer/fall field season and allowed the technicians to follow a more normal work plan. While Dr. Massatti was the only scientist supported by the SBSC-CPNPP agreement in FY18, other scientists, including Drs. John Bradford, Seth Munson, Mike Duniway, Sasha Reed, Daniel Winkler, and Jayne Belnap, spent a considerable amount of time discussing individual projects and the newly developed 5-Year Research Strategy. Some of these discussions resulted in a publication by Dr. Winkler, in addition to a large group of researchers, practitioners, and others who work on the Colorado Plateau, concerning the restoration challenges facing the Plateau into the future and the types of efforts that may support successful restoration (Winkler et al., 2018).

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USGS2019

Natural resource management decision-making under climate uncertainty: Building social-ecological resilience in southwestern Colorado

The goal of this project was to facilitate climate change adaptation that contributes to social-ecological resilience, ecosystem and species conservation, and sustainable human communities in southwestern Colorado. The team developed and piloted integrated adaptation planning tools and principles that merge the strengths of the iterative scenario process, the Adaptation for Conservation Targets (ACT) planning framework, institutional analysis, and climate modeling. These tools and principles generated practical strategies and scientific knowledge to advance climate change adaptation in both the Gunnison River Basin and San Juan River Basin and, potentially, other landscapes. A key objective of this project was to work with decision-makers to develop social-ecological adaptation strategies and coordinate actions to reduce the impacts of a changing climate on nature and people. To accomplish this, the project blended science (biophysical and social) and participatory approaches to integrate expert knowledge, land management decision making, and local needs. These adaptation strategies and their creation process were documented by the project team to assist communities and scientists elsewhere who are grappling with the challenges posed by climate change.

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USGS2018

Geologic map of the Pagosa Springs 7.5' quadrangle, Archuleta County, Colorado

The geologic map of the Pagosa Springs 7.5’ quadrangle in southwestern Colorado includes the town of Pagosa Springs that is partly known for its hot springs. The quadrangle is southwest of the San Juan volcanic mountains (Oligocene) and north of the San Juan Basin. All bedrock units exposed in the map area are Upper Cretaceous in age except a minor canyon outcrop of Jurassic rock. Early Holocene deposits are mainly alluvial gravels and outwash on terraces. Structure is simple: shale and sandstone beds dip at low angles east-to-northeast as a broad limb of the north-northwest striking Archuleta anticline. Three geologic cross sections controlled by drill holes are included and depict Mesozoic bedrock and faults down to and including shallow Precambrian basement rock. A brief geologic history of the region is described.

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USGS2018

Real-time streambed scour monitoring at two bridges over the Gunnison River in western Colorado, 2016–17

The Colorado Department of Transportation maintains roadways crossing over large streams and rivers where sediment transport and channel alignment changes can affect the structural stability of bridges. Structural stability during and immediately after peak streamflow can be assessed by measuring streambed scour; however, placing personnel or boats in the water during high-streamflow events using traditional methods can be difficult, hazardous, and time consuming. To address this need, the U.S. Geological Survey, in cooperation with Colorado Department of Transportation, installed instrumentation at two bridges in western Colorado to measure streambed elevations in real-time during snowmelt-runoff periods (May through June) in 2016 and 2017. The bridges include U.S. Highway 50 eastbound over the Gunnison River at milepost 70.0 (bridge I–04–K) and Colorado Highway 141 over the Gunnison River at milepost 153.7 (bridge I–03–A). Bridge I–04–K was outfitted with two echosounders, each mounted on the north side of pier 3. Data collected during the 2016 snowmelt runoff did not indicate scour had occurred. Data collected during 2017 snowmelt runoff indicated minor scour and fill occurred under the downstream echosounder. Bridge I–03–A was outfitted with two echosounders, each mounted on opposite sides of pier 4, at the transition of the upstream nose to the straight section of the pier wall. Data recorded during 2016 did not indicate any scour under the echosounders. Debris accumulation around the nose of the pier and under the echosounders resulted in inconsistent streambed elevation data. Data recorded during 2017 did not indicate any scour under the echosounders. Probing of the pier wall and streambed interface and underwater photographs obtained in 2016 revealed undermining along the length of the pier wall. The undermining extended side-to-side to a depth of about 2 feet. Underwater photographs were obtained again in 2017; no changes from the previous year were observed. Cross-section surveys were completed at each bridge to measure and document changes in channel geometry during the study. Surveys were performed in spring 2016 before snowmelt runoff, spring 2017 before snowmelt runoff, and fall 2017. Streambed elevations from cross-section surveys at both bridges were evaluated using two-tailed, paired t-tests and Wilcoxon rank sum tests to identify significant changes between the surveys. Both tests indicated significant changes in mean streambed elevations for the cross-sections and around the monitored piers at bridges I–04–K and I–03–A during the 2-year study.

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USGS2018

When ignimbrite meets water: Megascale gas-escape structures formed during welding

Diverse welding, crystallization, and structural features develop when a hot ignimbrite encounters external water, depending largely on volatile-rock ratios. Such processes are spectacularly documented by a regional ignimbrite, where ponded within an older caldera in the San Juan Mountains, Colorado. Interaction of hot pyroclastic flows with moist underlying sediments or standing water in a stream valley or shallow-lakeshore environment produced mega-scale gas-escape structures, quenched adjacent tuff, inhibited welding, and generated nonplanar crystallization zones. This site provides a context for reviewing examples of ignimbrite-water interaction elsewhere.

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USGS2018

Biophysical assessment for indemnity selection of Federal Lands in Colorado

Information on the biophysical features of Federal lands identified as suitable for transfer to the State of Colorado was requested by the Bureau of Land Management (BLM). This information is intended for use in conducting an Environmental Assessment prior to the transfer of ownership (conveyance) to the State. The Colorado State Land Board filed a selective application to obtain public land and mineral estate in lieu of lands to which the State of Colorado was entitled but did not receive at the time of statehood. To address this legal obligation, 339 parcels of Federal lands (organized into 89 indemnity units [IUs]), currently under management by the BLM, have been identified as suitable for transfer to the State. The IUs include 23,130 acres of surface and mineral estate and 6,150 acres of mineral estate only. The specific land parcels to be transferred to the State will be finalized after an Environmental Assessment and other evaluations are completed. To provide the biophysical information necessary for conducting a future Environmental Assessment of the potential effects of the proposed land transfer, information on ecological communities, soil characteristics, and land use was summarized at three levels: (1) all of Colorado, (2) lands under the jurisdiction of the BLM, and (3) the 89 IUs. Information was also synthesized and summarized for 179 plant and animal species or subspecies of management concern to evaluate which species had the potential for occurrence on IUs. Datasets summarized for Colorado and for indemnity units and methodological details for all data summaries are provided in U.S. Geological Survey data releases available online at https://doi.org/10.5066/F7GT5MGV and https://doi.org/10.5066/F7C24VQ0 .

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USGS2018

Groundwater chemistry and water-level elevations in bedrock aquifers of the Piceance and Yellow Creek watersheds, Rio Blanco County, Colorado, 2013–16

The Piceance and Yellow Creek watersheds in Rio Blanco County, Colorado, are known to contain important energy resources (oil shale and natural gas) and mineral resources (nahcolite). The primary sources of fresh groundwater in the Piceance and Yellow Creek watersheds are bedrock aquifers in the Uinta and Green River Formations. The aquifers are divided into an upper and lower aquifer separated by a regionally extensive semiconfining layer. These aquifers provide water to streams and springs in the watersheds and are an important resource to people living and working in the area. Development of energy and mineral resources has the potential to affect the quality of groundwater in several ways. The Bureau of Land Management and the U.S. Geological Survey began groundwater monitoring in 2010 to characterize the groundwater quality and water-level elevations of shallow bedrock aquifers in the Piceance and Yellow Creek watersheds. The purpose of this report is to present ground-water chemistry and water-level elevations collected during 2013–16. Comparisons are made to data that were collected from the bedrock aquifers from 2010 to 2012 to identify the potential for changes in water quality and water-level elevations. Appreciable changes in water-level elevations and hydraulic gradient were observed in early April 2015 in two wells completed in the upper and lower aquifers. The hydraulic gradient between the two wells was consistently downward from the upper aquifer to the lower aquifer during 2010–15; however, in early April 2015, the gradient changed from downward to upward between the two aquifers. Overall, water-level elevations declined by about 14 and 11 feet in the upper and lower aquifers, respectively, from 2013 to 2016. Previously published data estimated groundwater ages at 1,200 years old in the upper aquifer and 9,600 years old in the lower aquifer. These groundwater ages indicate that ground-water was recharged over thousands of years. With such long periods of time for aquifer recharge, declines in water-level elevation over short time steps (a few months) have important implications for sustainable management of this resource. Solution mining activities or drilling for oil and natural gas in the area could be related to the changes observed in water-level elevations in these wells; however, further investigation would be needed to evaluate causation. Changes in major-ion chemistry were evaluated in the bedrock aquifer using time series plots of select major-ion data from 2010 to 2016. Major-ion chemistry was variable for a single well from 2010 to 2016 where alkalinity and sulfate were the most variable constituents. One possible explanation for the observed changes in major-ion chemistry may be that the sample depth for that well no longer represents the most appreciable flow in the borehole. On a larger scale, potential changes in flow within the borehole may indicate changes in the regional flow system. Methane and volatile organic compound concentrations were evaluated using a similar approach to that of major ions and had similar findings. Methane concentrations in wells sampled from 2010 to 2016 were generally constant. The only exception was observed at a single well where the range of methane concentrations was from 57.4 (2010) to 4.02 milligrams per liter (2013). This is the same well where changes in water-level elevation, hydraulic gradient, and major-ion chemistry were observed, providing multiple lines of evidence to indicate change in the bedrock aquifers. Sampling of a well located in an area with little energy development but where faults or fractures could provide a path for the migration of fluids indicate mixing of groundwater between the upper and lower aquifers.

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USGS2018

Time-varying predatory behavior is primary predictor of fine-scale movement of wildland-urban cougars

Background While many species have suffered from the detrimental impacts of increasing human population growth, some species, such as cougars ( Puma concolor ), have been observed using human-modified landscapes. However, human-modified habitat can be a source of both increased risk and increased food availability, particularly for large carnivores. Assessing preferential use of the landscape is important for managing wildlife and can be particularly useful in transitional habitats, such as at the wildland-urban interface. Preferential use is often evaluated using resource selection functions (RSFs), which are focused on quantifying habitat preference using either a temporally static framework or researcher-defined temporal delineations. Many applications of RSFs do not incorporate time-varying landscape availability or temporally-varying behavior, which may mask conflict and avoidance behavior. Methods Contemporary approaches to incorporate landscape availability into the assessment of habitat selection include spatio-temporal point process models, step selection functions, and continuous-time Markov chain (CTMC) models; in contrast with the other methods, the CTMC model allows for explicit inference on animal movement in continuous-time. We used a hierarchical version of the CTMC framework to model speed and directionality of fine-scale movement by a population of cougars inhabiting the Front Range of Colorado, U.S.A., an area exhibiting rapid population growth and increased recreational use, as a function of individual variation and time-varying responses to landscape covariates. Results We found evidence for individual- and daily temporal-variability in cougar response to landscape characteristics. Distance to nearest kill site emerged as the most important driver of movement at a population-level. We also detected seasonal differences in average response to elevation, heat loading, and distance to roads. Motility was also a function of amount of development, with cougars moving faster in developed areas than in undeveloped areas. Conclusions The time-varying framework allowed us to detect temporal variability that would be masked in a generalized linear model, and improved the within-sample predictive ability of the model. The high degree of individual variation suggests that, if agencies want to minimize human-wildlife conflict management options should be varied and flexible. However, due to the effect of recursive behavior on cougar movement, likely related to the location and timing of potential kill-sites, kill-site identification tools may be useful for identifying areas of potential conflict.

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USGS2018

Estimating the probability of movement and partitioning seasonal survival in an amphibian metapopulation

Movement of individuals has been described as one of the best studied, but least understood concepts in ecology. The magnitude of movements, routes, and probability of movement have significant application to conservation. Information about movement can inform efforts to model species persistence and is particularly applicable in situations where specific threats (e.g., disease) may depend on the movement of hosts and potential vectors. We estimated the probability of movement (breeding dispersal and permanent emigration) in a metapopulation of 16 breeding sites for boreal toads ( Anaxyrus boreasboreas ). We used a multi‐state mark–recapture approach unique in its complexity (16 sites over 18 yr) to address questions related to these movements and variation in resident survival. We found that individuals had a 1–2% probability of dispersing in a particular year and that approximately 10–20% of marked individuals were transient and observed in the metapopulation only once. Resident survival probabilities differed by season, with 71–90% survival from emergence from hibernation through early post‐breeding and >97% survival from mid‐/late active season through hibernation. Movement‐related probabilities are needed to predict species range expansions and contractions, estimate population and metapopulation dynamics, understand host–pathogen and native–invasive species interactions, and to evaluate the relative effects of proposed management actions.

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USGS2018

Flood-inundation maps for the South Platte River at Fort Morgan, Colorado, 2018

In 2017, the U.S. Geological Survey (USGS), in cooperation with the Colorado Water Conservation Board (CWCB), studied floods in the historic record to produce a library of flood-inundation maps for the South Platte River at Fort Morgan, Colorado. Digital flood-inundation maps for a 4.5-mile (7.2-kilometers) reach of the South Platte River at Fort Morgan from Morgan County Road 16 to Morgan County Road 20.5, were created. The flood-inundation maps depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the U.S. Geological Survey streamgage on the South Platte River at Fort Morgan (streamgage number 06759500). Water-surface profiles were computed for the stream reach by means of a one-dimensional, step-backwater model. The September 15, 2013, and May 20, 2017, floods were used to calibrate the model, and the June 15, 2015, and May 29, 2017, floods were used to independently validate the model. Nine pressure transducers were deployed to record the stage at nine different locations along the reach and to document the floods of May 20 and 29, 2017, at the South Platte River at Fort Morgan streamgage. The hydraulic model was then used to compute 16 water-surface profiles for flood stages at 1-foot (ft; 0.3-meter [m]) intervals referenced to the streamgage datum and ranging from 12 ft (3.66 m) or below bankfull to 27 ft (8.23 m), which is 1 ft (0.3 m) greater than the highest recorded water level (25.73 ft [7.84 m] on September 15, 2013) at the South Platte River at Fort Morgan streamgage during its period of record; the 2013 flood exceeds the major flood stage of 21.5 ft (6.55 m) by more than 4 ft (1.2 m), as defined by the National Weather Service. The simulated water-surface profiles were then combined with a geographic information system digital elevation model (derived from light detection and ranging data having a 0.37-ft [0.11-m] vertical accuracy and 3.28-ft [1.00-m] horizontal resolution) to delineate the area flooded for stages ranging from 12 to 27 ft (3.66 to 8.23 m). These flood-inundation maps, in conjunction with the real-time stage data from the USGS streamgage on the South Platte River at Fort Morgan, are intended to help guide the general public in taking individual safety precautions and provide emergency management personnel with a tool to efficiently manage emergency flood operations and post flood recovery efforts.

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USGS2018

Responding to risky neighbors: Testing for spatial spillover effects for defensible space in a fire-prone WUI community

Often, factors that determine the risk of an environmental hazard occur at landscape scales, and risk mitigation requires action by multiple private property owners. How property owners respond to risk mitigation on neighboring lands depends on whether mitigation actions are strategic complements or strategic substitutes. We test for these neighbor interactions with a case study on wildfire risk mitigation on private properties. We use two measures of wildfire risk mitigation—an assessment by a wildfire professional and a self-assessment by homeowners. Taken together, the two assessments provide the first empirical explanation for strategic complements in wildfire risk mitigation and a more complete picture of how homeowners respond to this landscape-scale risk. We find homeowners that mitigate risk on their land are more likely to have neighbors that do the same, and homeowners that fail to mitigate risk are more likely to have neighbors that fail to do so as well. Due to spatial spillovers, motivating a few key residents to take action could reduce risk across the landscape.

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USGS2018

Fire, flood, and drought: Extreme climate events alter flow paths and stream chemistry

Extreme climate events—such as hurricanes, droughts, extreme precipitation, and wildfires—have the potential to alter watershed processes and stream response. Yet due to the destructive and hazardous nature and unpredictability of such events, capturing their hydrochemical signal is challenging. A 5‐year postwildfire study of stream chemistry in the Fourmile Creek watershed, Colorado Front Range, USA, focused on high‐frequency storm sampling. During the study, the watershed was impacted by three additional extreme climate events—drought and two periods of extreme rainfall totals. These events altered concentration‐discharge relationships in ways that elucidate how hydrologic flow paths and source material availability affect stream water chemistry. Reduced infiltration after wildfire led to overland flow during thunderstorms, which conveyed ash and soil into streams. This resulted in elevated stream concentrations of constituents elevated in ash—Ca, K, Mg, alkalinity, and dissolved organic carbon—along with sediment and nitrate. Subsurface flow paths were bypassed, leading to low concentrations of Na and SiO 2 , which are bedrock derived and not elevated in ash. During drought conditions, when stream discharge was <20% of average, concentrations of sediment, dissolved organic carbon, and Ca fell below average concentrations, but SiO 2 did not. Extreme rainfall totals saturated the subsurface and led to prolonged elevated stream discharge. Concentration‐discharge relationships for bedrock‐derived constituents, such as Ca and SiO 2 , were altered in that time period, while those for dissolved organic carbon were not. Previous disturbances, including historical mining, also affect stream chemistry, and water‐quality impairment can be exacerbated by extreme climate events.

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USGS2018

Development of an aerial population survey method for elk (Cervus elaphus) in Rocky Mountain National Park, Colorado

Executive Summary Since the early 1990s, substantial effort and funding have been expended to conduct research to guide development of a 20-year Elk and Vegetation Management Plan for Rocky Mountain National Park (RMNP) in Colorado. One goal of the plan is to maintain the elk ( Cervus elaphus ) population size at the lower end of the natural range of variation. To implement management actions called for in the plan, accurate and reliable population estimates are needed, as well as a better understanding of the spatial and temporal distribution of elk. The previous aerial survey protocol and population estimation model used by the park had not been updated since the model’s initial calibration more than 15 years ago and the model was developed with an insufficient number (n=44) of observations. Thus we initiated research to reevaluate, update, and improve elk population estimation protocols for RMNP. We considered several alternative survey and analysis methods, and concluded that a hybrid population-estimation model using a simultaneous double-observer technique with sighting covariates was the most appropriate and effective aerial survey methodology for this population and the environmental conditions in RMNP. Instructional protocols for conducting these surveys in the future, along with datasheets, are provided in this report’s appendixes. To develop an improved method for aerial elk surveys, we used elk radio-collar location data from our study and other studies, and applied geographic information system analyses to define the survey area and develop effective, repeatable survey transect lines. We used telemetry data from radio-collared elk to inform our understanding of the temporal and spatial scale of elk movements across the park boundary, elk use of tree cover during potential survey hours, and elk use of different elevations within their range. Determining where elk were during surveys helped to fine-tune a survey design that improved spatial cover-age and decreased costs where possible, while standardizing the method to make it repeatable from year to year. We conducted aerial helicopter surveys to test our methodology in an adaptive, iterative process during three winters: 2007–2008, 2008–2009, and 2009–2010. We gained new information on each survey and used results to refine subsequent surveys. Our results confirm that elk movements were highly dynamic with respect to park boundary crossings; an average of six round trips from the park to Estes Park, Colorado, and back per month were taken by global positioning system-collared bull elk. We observed a strong diurnal temporal pattern of bull elk use of trees; elk were found in dense tree cover from 15:00−22:00 but not as often during morning and early afternoon hours when surveys were conducted. We used information on elk use of different altitudes to refine and establish a more efficient survey area. During the time of our study, a concurrent study in the park deployed 120 very high frequency radio collars on elk cows. We used those collar locations during our flights to increase sample size and to evaluate the level of precision we would gain by using “known fates analysis” (in which elk were known to be in the survey area, out of the survey area, or deceased based on radio-collar locations collected simultaneously during aerial surveys). Using radio-collar locations reduced bias by 1.1–8.8 percent and increased precision (that is, reduced the width of confidence intervals). This report provides final population estimates analyzed with and without radio-collar data to demonstrate what is gained by using marked individuals.

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USGS2018

Streamflow and selenium loads during synoptic sampling of the Gunnison River and its tributaries near Delta, Colorado, November 2015

In response to the need for more information about selenium (Se) sources and transport, the U.S. Geological Survey, in cooperation with the Colorado Water Conservation Board, completed a study that characterized Se loads in a reach of the Gunnison River between Delta and Grand Junction, Colo. This report identifies where possible dissolved Se loading is occurring in a study reach in the Lower Gunnison River Basin between Delta and Grand Junction on November 19, 2015. The combined Se loads from the Gunnison River at Delta (site 3) and the Uncompahgre River at Delta (site 4) were about 95 percent of the load at the furthest downstream main-stem sample location at the Gunnison River below Roubideau Creek near Delta (site 20) (31.6 and 33.4 pounds per day, respectively), indicating that about 5 percent of the total load (1.8 pounds) was potentially contributed from diffuse groundwater inflow. Main-stem streamflow accounting during November 2015 in a downstream direction was not supportive of substantial net gains or losses in the main-stem water balance. The cumulative load from measured tributary inflows downstream from the Uncompahgre River confluence only amounted to 1.2 pounds of the main-stem loads (1.8 pounds gain) from site 4 to the end of the synoptic reach at site 20. The remaining 33 percent (about 0.6 pounds) of Se load increase was not accounted for by known tributary inflow. Yet, the small changes in the streamflow mass balance in the same reach does not strongly support a net inflow explanation for the apparent gain in load. Based on the results of the loading and streamflow analysis, when errors in the loading estimates are considered, there is no conclusive evidence of an appreciable amount of Se load that is unaccounted for in the study reach of the Gunnison River as was originally hypothesized. Differences determined from comparisons of cumulative tributary loads and Gunnison River main-stem loads for this study are within error estimates of the main-stem loads.

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USGS2018

Geologic map of the Fort Morgan 7.5' quadrangle, Morgan County, Colorado

The Fort Morgan 7.5′ quadrangle is located on the semiarid plains of northeastern Colorado, along the South Platte River corridor where the river has incised into Upper Cretaceous Pierre Shale. The Pierre Shale is largely covered by surficial deposits that formed from alluvial, eolian, and hillslope processes operating in concert with environmental changes from the late Pliocene to the present. The South Platte River, originating high in the Colorado Rocky Mountains, has played a major role in shaping surficial geology in the map area, which is several tens of kilometers downstream from where headwater tributaries join the river. Recurrent glaciation (and deglaciation) of basin headwaters has affected river discharge and sediment supply far downstream, influencing deposition of alluvium and river incision in the Fort Morgan quadrangle. Distribution and characteristics of the alluvial deposits indicate that during the Pleistocene the course of the river within the map area shifted progressively southward as it incised, and by late middle Pleistocene the river was south of its present position, cutting and filling a deep paleochannel near the south edge of the quadrangle. The river shifted back to the north during the late Pleistocene. Kiowa and Bijou Creeks are unglaciated tributaries originating in the Colorado Piedmont east of the Front Range that also have played a major role in shaping surficial geology of the map area. Periodically during the late Pleistocene, major flood events on these tributaries deposited large volumes of sediment at and near their confluences, forming a broad, low-gradient fan composed of sidestream alluvium that could have occasionally dammed the river for short periods of time. Wildcat Creek, also originating on the Colorado Piedmont, and the small drainage of Cris Lee Draw dissect the map area north of the river. Eolian sand deposits of the Sterling (north of river) and Fort Morgan (south of river) dune fields cover much of the quadrangle and record past episodes of sand mobilization during times of prolonged drought. With the onset of irrigation and damming during historical times, the South Platte River has changed from a broad, shallow, and sandy braided river with highly variable seasonal discharge to a much narrower, deeper river with braided-meandering transition morphology and more uniform discharge.

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USGS2018

Influences of the invasive tamarisk leaf beetle (Diorhabda carinulata) on avian diets along the Dolores River in Southwestern Colorado USA

The tamarisk leaf beetle ( Diorhabda carinulata ), introduced from Eurasia in 2001 as a biological control agent for the invasive plant Tamarix ramosissima , has spread widely throughout the western USA. With D. carinulata now very abundant, scientists and restoration managers have questioned what influence this introduced arthropod might have upon the avian component of riparian ecosystems. From 2009 through 2012 we studied the consequences of biological invasions of the introduced tamarisk shrub and tamarisk leaf beetles on the diets of native birds along the Dolores River in southwestern Colorado, USA. We examined avian foraging behavior, sampled the arthropod community, documented bird diets and the use of invasive tamarisk shrubs and tamarisk leaf beetles by birds. We documented D. carinulata abundance, on what plants the beetles occurred, and to what degree they were consumed by birds as compared to other arthropods. We hypothesized that if D. carinulata is an important new avian food source, birds should consume beetles at least in proportion to their abundance. We also hypothesized that birds should forage more in tamarisk in the late summer when tamarisk leaf beetle larvae are more abundant than in early summer, and that birds should select beetle-damaged tamarisk shrubs. We found that D. carinulata composed 24.0 percent (± 19.9–27.4%) and 35.4% biomass of all collected arthropods. From the gut contents of 188 birds (25 passerine species), only four species ( n = 11 birds) contained tamarisk leaf beetle parts. Although D. carinulata comprised one-quarter of total insect abundance, frequency of occurrence in bird gut contents was only 2.1% by abundance and 3.4% biomass. Birds used tamarisk shrubs for foraging in proportion to their availability, but foraging frequency did not increase during the late summer when more tamarisk leaf beetles were present and birds avoided beetle-damaged tamarisk shrubs. Despite D. carinulata being the most abundant arthropod in the environment, these invasive beetles were not frequently consumed by birds and seem not to provide a significant contribution to avian diets.

Colorado↗

USGS2018

Wildland–urban interface residents’ relationships with wildfire: Variation within and across communities

Social science offers rich descriptions of relationships between wildland–urban interface residents and wildfire, but syntheses across different contexts might gloss over important differences. We investigate the potential extent of such differences using data collected consistently in sixty-eight Colorado communities and hierarchical modeling. We find substantial variation across responses for all considered measures, much of which occurs at the community-level. Our results show that many aspects of relationships with wildfire meaningfully differ both within and across communities. Our analysis suggests that some wildfire social science results will be relatively consistent across communities, whereas others will not, and this study contributes evidence to broader efforts for understanding which is which. As such, it provides important guidance for transferring the lessons of wildfire social science studies across contexts, and for practitioners who seek to understand the breadth of viewpoints within the communities with which they work.

Colorado↗

USGS2018

Influence of climate on alpine stream chemistry and water sources

The resilience of alpine/subalpine watersheds may be viewed as the resistance of streamflow or stream chemistry to change under varying climatic conditions, which is governed by the relative size (volume) and transit time of surface and subsurface water sources. Here, we use end‐member mixing analysis in Andrews Creek, an alpine stream in Rocky Mountain National Park, Colorado, from water year 1994 to 2015, to explore how the partitioning of water sources and associated hydrologic resilience change in response to climate. Our results indicate that four water sources are significant contributors to Andrews Creek, including snow, rain, soil water, and talus groundwater. Seasonal patterns in source‐water contributions reflected the seasonal hydrologic cycle, which is driven by the accumulation and melting of seasonal snowpack. Flushing of soil water had a large effect on stream chemistry during spring snowmelt, despite making only a small contribution to streamflow volume. Snow had a large influence on stream chemistry as well, contributing large amounts of water with low concentrations of weathering products. Interannual patterns in end‐member contributions reflected responses to drought and wet periods. Moderate and significant correlations exist between annual end‐member contributions and regional‐scale climate indices (the Palmer Drought Severity Index, the Palmer Hydrologic Drought Index, and the Modified Palmer Drought Severity Index). From water year 1994 to 2015, the percent contribution from the talus‐groundwater end member to Andrews Creek increased an average of 0.5% per year (p < 0.0001), whereas the percent contributions from snow plus rain decreased by a similar amount (p = 0.001). Our results show how water and solute sources in alpine environments shift in response to climate variability and highlight the role of talus groundwater and soil water in providing hydrologic resilience to the system.

Colorado↗