Geology topics
Research about Colorado
Source-linked reports with geographic coverage including Colorado.
Channel-pattern adjustments and geomorphic characteristics of Elkhead Creek, Colorado, 1937-97
Onsite channel surveys and sediment measurements made in 1997, aerial photographs taken from 1937 through 1993, and streamflow-gaging- station record from 1954 to 1996 were used to determine the probable cause of accelerated streambed and streambank erosion in the lower reaches of Elkhead Creek, a perennial, meandering tributary of the Yampa River. Concern about the possible effects of Elkhead Reservoir, constructed in 1974, has been expressed by landowners living downstream. Evidence cited as an indication of reservoir related effects include the trapping of bedload transported sediment in the reservoir, vertical incision of the streambed, and lateral erosion causing loss of agricultural land. A large deltaic deposit composed of approximately 163 acre-ft of bedload-transported sediment formed in Elkhead Reservoir between 1974 and 1993, the contemporary bankfull stage of Elkhead Creek is several feet below the elevation of a broad terrace that previously was the flood plain, and lateral erosion at meander bends occurs at a higher rate than in previous periods at some locations. Elkhead Creek meander migration rates were used as a measure of lateral instability in the study reaches. Meander migration rates based on changes in channel centerline position were calculated for three periods from five sets of rectified aerial photographs for reaches upstream and downstream from the reservoir. The creek upstream from Elkhead Reservoir was unaffected by impoundment and was used as the control reach. Mean meander migration rates in the downstream study reach were 1.2 ft/yr from 1938 to 1953, 2.5 ft/yr from 1954 to 1970, and 4.8 ft/yr from 1978 to 1993, compared to rates of 0.5 ft/yr, 1.6 ft/yr, and 6.6 ft/yr for the same periods in the upstream study reach. Sediment and channel-geometry measurements and estimated hydraulic conditions at eight cross sections indicate that most of the sediment sizes represented in the streambed are mobile at frequently occurring streamflows; those streamflows are less than or equal to the bankfull discharge of approximately 1,800 to 2,200 cubic feet per second. Discharge data from 1954 through 1996 recorded at a site upstream from the reservoir were examined to determine the effect of hydrology on meander migration rates. The discharge data were assumed to be representative of the total streamflow and flood hydrology of both the upstream and downstream reaches because Elkhead Reservoir normally has a full pool. Mean annual streamflow increased 122 percent, and the mean annual flood increased 130 percent from the pre-regulation period (1954 to 1970) to the post-regulation period (1978 to 1993), a possible explanation for much of the increase observed in meander migration rate in both the upstream and downstream reaches in the period after reservoir construction. Channel instability, quantified by meander migration rates, has increased throughout Elkhead Creek since 1977. The most probable cause is a combination of external factors affecting the 2 Channel-Pattern Adjustments and Geomorphic Characteristics of Elkhead Creek, Colorado, 1937-97 entire watershed, such as changes in annual runoff and flood magnitude and sedimentation in Elkhead Reservoir. Local land-use practices, such as intentional meander cutoff and riparian vegetation removal, also can decrease channel stability, but these factors were not addressed in this study.
Reconfigured-Channel Monitoring and Assessment Program
A U.S. Geological Survey program to monitor and assess channel reconfiguration activity is described. A data base available on the world wide web will enable land-management agencies and other interested parties to evaluate the long-term success of various channel reconfiguration projects. A demonstration project on the Lake Fork of the Gunnison River, Colorado, illustrates the program objectives and approach.
Characterization of selected biological, chemical, and physical conditions at fixed sites in the Upper Colorado River Basin, Colorado, 1995-98
Biological community samples were collected at 15 sites in the Upper Colorado River Basin (UCOL) in Colorado as part of the National Water-Quality Assessment (NAWQA) Program. Sites sampled in two physiographic provinces, the Southern Rocky Mountains and the Colorado Plateau, represented agriculture, mining, urban and recreation, and mixed land uses and background conditions. Nine measures of water quality, which include information on nutrients, specific conductance (a surrogate for salinity), trace elements in streambed sediment, pesticides in fish tissue, fish communities, and macroinvertebrate richness and composition and stream habitat were used for comparisons among sites within the two physiographic provinces. Sampling sites from three other NAWQA study units—the Rio Grande Valley, the South Platte River Basin, and the Upper Snake River Basin study units—were categorized on the basis of land use and stream size in order to develop a larger data set for comparison to sites in the UCOL. Three categories of land use—forested (includes mining, urban and recreation, and background), agriculture, and mixed—were used for comparison to the UCOL fixed sites. Results indicated that all sites other than the Colorado River below Baker Gulch (a background site) showed some water-quality characteristics to be significantly affected. Results indicated that the concentrations of cadmium and zinc in streambed sediment at mining land-use sites in the Southern Rocky Mountains physiographic province generally were orders of magnitude higher than streambed-sediment concentrations at the background site. Streambed-sediment concentrations at mining land-use sites in the UCOL were greater than the 75 th percentile of concentrations from sites in the three other NAWQA study units. Fish communities and habitat conditions were degraded at mining land-use sites compared to the background site. Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness and the percentage of EPT were lower at mining land-use sites than at the background site and were less than the 50 th percentile of those for sites from the three other NAWQA study units. Nutrient concentrations at urban and recreation sites in the Southern Rocky Mountain physiographic province generally were greater than concentrations at the background site and generally were between the 25 th and 90 th percentile of concentrations for sites from the three other NAWQA study units. Habitat conditions and fish communities at urban and recreation sites were slightly degraded compared to the background site. EPT richness and the percentage of EPT were lower at urban and recreation sites than at the background site and were between the 25 th and 75 th percentile of those for sites from the three other NAWQA study units. The percentage of Chironomidae, which may be indicative of pollutant-tolerant organisms, was higher at urban and recreation sites than at the background site. Mixed land-use sites in the Southern Rocky Mountains physiographic province had similar nutrient concentrations and similar cadmium and zinc streambed-sediment concentrations. Fish-community degradation index values were very different among the three mixed land-use sites in the Southern Rocky Mountains physiographic province. Larger percentages of omnivores and anomalies such as lesions and deformities at two mixed land-use sites resulted in higher degradation values of the fish community. Agriculture land-use sites had higher concentrations of nutrients and selenium than the background site in the Colorado Plateau physiographic province. Concentrations of p,p '-DDE in fish tissue at agriculture sites were higher than the 75 th percentile of concentrations for sites from the three other NAWQA study units. Fish communities had degradation values near the 75 th percentile for agriculture sites. The percentage of EPT was low at agriculture sites when compared to the background site. Two mixed land-use sites in the Colorado Plateau physiographic province had similar concentrations of nutrients, selenium, and p,p '-DDE, and similar EPT richness and composition. These two sites were located downstream from agricultural and urban activities. Some water-quality measures at these two sites indicated degradation compared to a mixed land-use site upstream from most of the agriculture and urban activities in the Colorado Plateau physiographic province.
Comparison of two approaches for determining ground-water discharge and pumpage in the lower Arkansas River Basin, Colorado, 1997-98
In March 1994, the Colorado Division of Water Resources (CDWR) adopted “Rules Governing the Measurement of Tributary Ground Water Diversions Located in the Arkansas River Basin” (Office of the State Engineer, 1994); these initial rules were amended in February 1996 (Office of the State Engineer, 1996). The amended rules require users of wells that divert tributary ground water to annually report the water pumped monthly by each well. The rules allow a well owner to report the pumpage measured by a totalizing flowmeter (TFM) or pumpage determined from electrical power data and a power conversion coefficient (PCC) (Hurr and Litke, 1989). Opinions by representatives of the State of Kansas, presented before the Special Master hearing a court case [State of Kansas v. State of Colorado, No. 105 Original (1996)] concerning post-Compact well pumping, stated that the PCC approach does not provide the same level of accuracy and reliability as a TFM when used to determine pumpage. In 1997, the U.S. Geological Survey (USGS), in cooperation with the CDWR, began a 2-year study to compare ground-water pumpage estimates made using the TFM and the PCC approaches. The study area was along the Arkansas River between Pueblo, Colorado, and the Colorado-Kansas State line (fig. 1). The two approaches for estimating ground-water discharge and pumpage were compared for more than 100 wells completed in the alluvial aquifer of the Arkansas River Basin. The TFM approach uses an inline flowmeter to directly measure instantaneous discharge and the total volume of water pumped at a well. The PCC approach uses electrical power consumption records and a power conversion coefficient to estimate the pumpage at ground-water wells. This executive summary describes the results of the comparison of the two approaches. Specifically, (1) the differences in instantaneous discharge measured with three portable flowmeters and measured with an inline TFM are evaluated, and the statistical differences in paired instantaneous discharge between the two approaches are determined; (2) short- and long-term variations in the PCC’s are presented; (3) differences in pumpage between the two approaches are evaluated, and the statistical differences in pumpage between the two approaches are determined; (4) potential sources of discrepancy between pumpage estimates are discussed; and (5) differences in total network pumpage using the two approaches are presented. During the irrigation seasons of 1997 and 1998, instantaneous discharge and electrical power demand were measured at randomly selected wells to determine PCC’s. At more than 100 wells, the PCC’s determined during the 1998 season were applied to total electrical power consumption data that was recorded between the initial and final readings at each network well site in 1998 to estimate total ground-water pumpage. At each site, an inline TFM was installed in a full-flowing, acceptable test section of pipe on the discharge side of the pump where the measurement of discharge was made. Measurements of instantaneous ground-water discharge also were made using three different types of portable flowmeters. The average velocity multiplied by the cross-sectional area of the discharge pipe was used to compute the discharge in gallons per minute. Whenever possible, discharge measurements were made at each network site using all three types of portable flowmeters.
Coal mining in the 21st century: Yampa coal field, northwest Colorado
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The Fish Canyon Tuff: a standard for geochronology
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Defining models and measuring aggregate quality for gravel deposits of the Front Range Urban Corridor, Colorado
No abstract available.
Vegetation responses to natural regulation of elk in Rocky Mountain National Park
Little experimental information is available on the relationship between herbivory by native ungulates and vegetation in relatively undisturbed environments. A quasi-experimental situation exists in Rocky Mountain National Park, where elk (Cervus elaphus) populations have increased about 3-fold since 1968, following their release from artificial controls within the park boundaries. We reviewed data collected on vegetation transects established and monitored over the 25-year period from 1968 through 1992. Data were subjected to rigorous statistical analysis to detect trends following the release of elk from artificial controls. Increases in elk habitat use and decreases in deer habitat use were observed on all transects over the 25-year period. Significant increases in moss and lichen cover occurred in three offour vegetation types. Percent cover of bare ground, forbs (particularly Selaginella densa), and Carex spp. increased on grassland transects. Increases in timothy (Phleum pratense) were observed on meadow transects. Graminoid and litter cover increased on sagebrush transects, and shrub and litter cover increased on bitterbrush transects. We concluded the lack of control (fenced) plots in this sampling design, the types ofmeasures, the small number of replicates, and nonrandom placement of plots limit the inferences and sensitivity from the work. Unique strengths ofthe work included the long time period (25 years), good distribution of samples, consistency ofthe observer (D. Stevens), and placement of the plots in the most heavily grazed sites. Some grazing-induced responses were detected. Grazing-resistant species such as sedges (native), timothy (exotic), and club mosses increased and the amount of bare ground increased on some grazed sites. However, the changes within this sampling program alone were not alarming. The amount of bare ground increase was minor (4%), and grass and shrub cover increased in the shrub plots. The inferential power ofthis sample design was limited to the study plots only. Other factors (climate change, succession) were not controlled for using fenced plots and the sensitivity ofthe methods and plots to detect change were limited. For example, the low number oftransects in willow was not adequate to monitor conditions on the entire winter range. Lacking controls, observed changes may have been due to other factors (climate trends, beaver dam abandonment, stream channel changes), not elk herbivory alone. We recommend using a new sampling design that would include controls, pretreatment data, random site selection, and much more replication.
Effects of ultraviolet radiation on boreal toads in Colorado
Field exposures of Bufo boreas embryos to fractions of ambient UV-B radiation at two sites in Rocky Mountain National Park, Colorado, USA, were conducted to evaluate UV-B as a possible cause of recent severe declines of this species. There were no differences in hatching success of B. boreas embryos exposed to 0–100% of ambient UV-B radiation at either study site, results that are different from those of recent studies in Oregon that found increased mortality of B. boreas embryos exposed to ambient UV-B. The reasons for these differing results are not apparent, and several possible explanations exist, including differences in experimental design, presence or absence of a pathogenic fungus, and geographic genetic variation. Bufo boreas embryos were probably not receiving higher doses of UV-B radiation during the experiments in Oregon compared to the experiments in this study. Results of this study do not support UV-B radiation alone as the cause of the decline of B. boreas during the past 20 yr in the southern Rocky Mountains, but UV-B cannot be dismissed because of the contradictory results from other studies.
Nitrogen and carbon soil dynamics in response to climate change in a high-elevation ecosystem in the Rocky Mountains, U.S.A.
We have implemented a long-term snow-fence experiment at the Niwot Ridge Long-Term Ecological Research (NWT) site in the Colorado Front Range of the Rocky Mountains, U.S.A., to assess the effects of climate change on alpine ecology and biogeochemical cycles. The responses of carbon (C) and nitrogen (N) dynamics in high-elevation mountains to changes in climate are investigated by manipulating the length and duration of snow cover with the 2.6 × 60 m snow fence, providing a proxy for climate change. Results from the first year of operation in 1994 showed that the period of continuous snow cover was increased by 90 d. The deeper and earlier snowpack behind the fence insulated soils from winter air temperatures, resulting in a 9°C increase in annual minimum temperature at the soil surface. The extended period of snow cover resulted in subnivial microbial activity playing a major role in annual C and N cycling. The amount of C mineralized under the snow as measured by CO 2 production was 22 g m -2 in 1993 and 35 g m -2 in 1994, accounting for 20% of annual net primary above-ground production before construction of the snow fence in 1993 and 31% after to snow fence was constructed in 1994. In a similar fashion, maximum subnivial N 2 O flux increased 3-fold behind the snow fence, from 75 μg N m -2 d -1 in 1993 to 250 μg N m -2 d -1 in 1994. The amount of N lost from denitrification was greater than the annual atmospheric input of N in snowfall. Surface litter decomposition studies show that there was a significant increase in the litter mass loss under deep and early snow, with no significant change under medium and little snow conditions. Changes in climate that result in differences in snow duration, depth, and extent may therefore produce large changes in the C and N soil dynamics of alpine ecosystems.
Methodology and implications of maximum paleodischarge estimates for mountain channels, upper Animas River basin, Colorado, U.S.A.
Historical and geologic records may be used to enhance magnitude estimates for extreme floods along mountain channels, as demonstrated in this study from the San Juan Mountains of Colorado. Historical photographs and local newspaper accounts from the October 1911 flood indicate the likely extent of flooding and damage. A checklist designed to organize and numerically score evidence of flooding was used in 15 field reconnaissance surveys in the upper Animas River valley of southwestern Colorado. Step-backwater flow modeling estimated the discharges necessary to create longitudinal flood bars observed at 6 additional field sites. According to these analyses, maximum unit discharge peaks at approximately 1.3 m3 s-1 km-2 around 2200 m elevation, with decreased unit discharges at both higher and lower elevations. These results (1) are consistent with Jarrett's (1987, 1990, 1993) maximum 2300-m elevation limit for flash-flooding in the Colorado Rocky Mountains, and (2) suggest that current Probable Maximum Flood (PMF) estimates based on a 24-h rainfall of 30 cm at elevations above 2700 m are unrealistically large. The methodology used for this study should be readily applicable to other mountain regions where systematic streamflow records are of short duration or nonexistent.
Soil relative dating of moraine and outwash-terrace sequences in the northern part of the upper Arkansas Valley, central Colorado, U.S.A.
Profile development indices for soils developed in moraines and outwash near Twin Lakes and in outwash near Leadville support the correlation of moraines with subdued morphology and two high outwash terraces with the Bull Lake glaciation (ca. 130-160 ka) and the correlation of hummocky moraines and two low outwash terraces with the Pinedale glaciation (ca. 14-47 ka). Elsewhere in the northern part of the upper Arkansas Valley, glacial sequences are correlated by mapping outwash terraces near the mouths of major tributaries of the Arkansas River. Near Twin Lakes, indices for soils on low, outer lateral moraines suggest that the older Pinedale glaciers extended beyond the margin of high, younger Pinedale lateral moraines with hummocky topography. A few subdued moraines near Twin Lakes and Leadville probably record one or more glaciations significantly older than the Bull Lake. The downvalley extent of Pinedale glaciers in the Mosquito Range on the east side of the Arkansas Valley is uncertain: most likely, Pinedale glaciers were almost as extensive as Bull Lake glaciers but built no prominent terminal moraines at their maximum positions.
Point and line geologic structure information in "Structure, outcrop, and subcrop of the geologic structure information for the Arapahoe and Laramie-Fox Hills aquifers."
This digital geospatial data set consists of points and lines representing symbolization of geologic structure information for the Arapahoe and Laramie-Fox Hills aquifers. The symbols were developed as part of the report in "Structure, Outcrop, and Subcrop of the Bedrock Aquifers Along the Western Margin of the Denver Basin, Colorado" (Robson and others, 1998).
Structure contours of base of Laramie-Fox Hills and Arapahoe aquifers
This digital geospatial data set consists of structure contours of the base of the Laramie-Fox Hills aquifer and the base of the Arapahoe aquifer along the Front Range of Colorado. The U.S. Geological Survey developed this data set as part of a project described in the report, "Structure, Outcrop, and Subcrop of the Bedrock Aquifers Along the Western Margin of the Denver Basin, Colorado" (Robson and others, 1998).
Structure contours of top of Laramie-Fox Hills aquifer in "Structure, outcrop, and subcrop of the bedrock aquifers along the western margin of Denver Basin, Colorado." Hydrologic Atlas 742
This digital geospatial data set consists of structure contours of the top of the Laramie-Fox Hills aquifer along the Front Range of Colorado. The U.S. Geological Survey developed this data set as part of a project described in the report, "Structure, Outcrop, and Subcrop of the Bedrock Aquifers Along the Western Margin of the Denver Basin, Colorado" (Robson and others, 1998).
Study-area boundary for "Structure, outcrop, and subcrop of the bedrock aquifers along the western margin of the Denver Basin, Colorado." Hydrologic Atlas 742
This digital geospatial data set consists of outlines of the study area in the report "Structure, Outcrop, and Subcrop of the Bedrock Aquifers Along the Western Margin of the Denver Basin, Colorado" (Robson and others, 1998).
Location of wells shown in "Structure, outcrop,, and subcrop of the bedrock aquifers along the western margin of the Denver Basin, Colorado." Hydrologic Atlas 742
This digital geospatial data set consists of locations of coal, oil, gas and water wells shown as data points in the report, "Structure, Outcrop, and Subcrop of the Bedrock Aquifers Along the Western Margin of the Denver Basin, Colorado" (Robson and others, 1998).