Preliminary evaluation of the fire-related debris flows on Storm King Mountain, Glenwood Springs, Colorado
No abstract available.
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Geology topics
Research about Colorado
Source-linked reports with geographic coverage including Colorado.
The effect of acidic, metal-enriched drainage from the Wightman Fork and Alamosa River on the composition of selected wetlands in San Luis Valley, Colorado
The biogeochemistry of selected wetlands in the San Luis Valley, Colorado, was examined to assess the effect of acidic, metal-enriched water draining mineralized areas near and around the Summitville Mine. The sampling protocols, analytical methods, and chemical composition of water and stream bed sediment from the Wightman Fork and Alamosa River as well as water, surface sediment or cores, and rooted aquatic vegetation from wetland sites within and west of the Alamosa National Wildlife Refuge are presented. The data indicate that As, Co, Cr, Cu, Ni, and Zn are tracers of drainage from mineralized areas around the Summitville Mine. Sediments and aquatic plants in wetlands in the San Luis Valley that receive surface water from the Alamosa River tend to have larger concentrations of certain tracer elements (e.g., Co and Cu) than wetlands that receive water from other sources. Larger concentrations of Cu, Ni, and Zn in the sediments of wetlands receiving Alamosa River water appear to be related to the presence of larger amounts of Fe oxyhydroxides. However, there is little to no variation in the concentrations of tracer elements with depth in wetlands that receive Alamosa River water. This observation suggests that the geochemistry of these wetlands has not been significantly affected by recent mining activities at the Summitville Mine.
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Hydrologic assessment of a riparian section along Boulder Creek near Boulder, Colorado, September 1989-September 1991
Native woody riparian species, primarily plains cottonwood ( Populus fremontii ), are regenerating at less than historical rates along Boulder Creek, a regulated stream near Boulder, Colorado. Loss of native riparian habitats might cause a decline in numbers of some native wildlife species. Previous studies have indicated that streamflow regulation can adversely affect native riparian vegetation reproduction. Surface- and ground-water data were collected from September 1989 to September 1991 along a riparian section of Boulder Creek to assist ecologists in assessing woody plant-recruitment characteristics. Annual mean streamflows in Boulder Creek at Cottonwood Grove of 34.5 cubic feet per second for water year 1990 (October 1, 1989- September 30, 1990) and 34.1 cubic feet per second for water year 1991 were 53 percent less than a site on Boulder Creek about 5 miles upstream from the study area. Diversions dating from 1882 caused most of the decrease. The alluvial aquifer in the study area averaged 5 feet in thickness and consisted of gravel- to cobble-size particles derived from crystalline rock of Precambrian age. The direction of ground-water movement was similar to the direction of streamflow. Ground-water movement in the northeastern part of the grove was affected by a pond constructed at a lower elevation than the stream channel. Water levels in the alluvial aquifer adjacent to the stream pre- dominantly were affected by stream stage, whereas farther from the channel, ground-water levels were affected by other processes such as evapotrans- piration, infiltration, and recharge from urban runoff.
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Water quality of storm runoff and comparison of procedures for estimating storm-runoff loads, volume, event-mean concentrations, and the mean load for a storm for selected properties and constituents for Colorado Springs, southeastern Colorado, 1992
The U.S. Environmental Protection Agency requires that municipalities that have a population of 100,000 or greater obtain National Pollutant Discharge Elimination System permits to characterize the quality of their storm runoff. In 1992, the U.S. Geological Survey, in cooperation with the Colorado Springs City Engineering Division, began a study to characterize the water quality of storm runoff and to evaluate procedures for the estimation of storm-runoff loads, volume and event-mean concentrations for selected properties and constituents. Precipitation, streamflow, and water-quality data were collected during 1992 at five sites in Colorado Springs. Thirty-five samples were collected, seven at each of the five sites. At each site, three samples were collected for permitting purposes; two of the samples were collected during rainfall runoff, and one sample was collected during snowmelt runoff. Four additional samples were collected at each site to obtain a large enough sample size to estimate storm-runoff loads, volume, and event-mean concentrations for selected properties and constituents using linear-regression procedures developed using data from the Nationwide Urban Runoff Program (NURP). Storm-water samples were analyzed for as many as 186 properties and constituents. The constituents measured include total-recoverable metals, vola-tile-organic compounds, acid-base/neutral organic compounds, and pesticides. Storm runoff sampled had large concentrations of chemical oxygen demand and 5-day biochemical oxygen demand. Chemical oxygen demand ranged from 100 to 830 milligrams per liter, and 5.-day biochemical oxygen demand ranged from 14 to 260 milligrams per liter. Total-organic carbon concentrations ranged from 18 to 240 milligrams per liter. The total-recoverable metals lead and zinc had the largest concentrations of the total-recoverable metals analyzed. Concentrations of lead ranged from 23 to 350 micrograms per liter, and concentrations of zinc ranged from 110 to 1,400 micrograms per liter. The data for 30 storms representing rainfall runoff from 5 drainage basins were used to develop single-storm local-regression models. The response variables, storm-runoff loads, volume, and event-mean concentrations were modeled using explanatory variables for climatic, physical, and land-use characteristics. The r2 for models that use ordinary least-squares regression ranged from 0.57 to 0.86 for storm-runoff loads and volume and from 0.25 to 0.63 for storm-runoff event-mean concentrations. Except for cadmium, standard errors of estimate ranged from 43 to 115 percent for storm- runoff loads and volume and from 35 to 66 percent for storm-runoff event-mean concentrations. Eleven of the 30 concentrations collected during rainfall runoff for total-recoverable cadmium were censored (less than) concentrations. Ordinary least-squares regression should not be used with censored data; however, censored data can be included with uncensored data using tobit regression. Standard errors of estimate for storm-runoff load and event-mean concentration for total-recoverable cadmium, computed using tobit regression, are 247 and 171 percent. Estimates from single-storm regional-regression models, developed from the Nationwide Urban Runoff Program data base, were compared with observed storm-runoff loads, volume, and event-mean concentrations determined from samples collected in the study area. Single-storm regional-regression models tended to overestimate storm-runoff loads, volume, and event-mean con-centrations. Therefore, single-storm local- and regional-regression models were combined using model-adjustment procedures to take advantage of the strengths of both models while minimizing the deficiencies of each model. Procedures were used to develop single-stormregression equations that were adjusted using local data and estimates from single-storm regional-regression equations. Single-storm regression models developed using model- adjustment proce
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Hydrogeology and simulation of flow between the alluvial and bedrock aquifers in the upper Black Squirrel Creek basin, El Paso County, Colorado
Anticipated increases in pumping from the bedrock aquifers in El Paso County potentially could affect the direction and rate of flow between the alluvial and bedrock aquifers and lower water levels in the overlying alluvial aquifer. The alluvial aquifer underlies about 90 square miles in the upper Black Squirrel Creek Basin of eastern El Paso County. The alluvial aquifer consists of unconsolidated alluvial deposits that unconformably overlie siltstones, sandstones, and conglomerate (bedrock aquifers) and claystone, shale, and coal (bedrock confining units) of the Denver Basin. The bedrock aquifers (Dawson, Denver, Arapahoe, and Laramie-Fox Hills aquifers) are separated by confining units (upper and lower Denver and the Laramie confining units) and overlie a relatively thick and impermeable Pierre confining unit. The Pierre confining unit is assumed to be a no-flow boundary at the base of the alluvial/ bedrock aquifer system. During 1949-90, substantial water-level declines, as large as 50 feet, in the alluvial aquifer resulted from withdrawals from the alluvial aquifer for irrigation and municipal supplies. Average recharge to the alluvial aquifer from infiltration of precipitation and surface water was an estimated 11.97 cubic feet per second and from the underlying bedrock aquifers was an estimated 0.87 cubic foot per second. Water-level data from eight bedrock observation wells and eight nearby alluvial wells indicate that, locally, the alluvial and bedrock aquifers probably are hydraulically connected and that the alluvial aquifer in the upper Black Squirrel Creek Basin receives recharge from the Denver and Arapahoe aquifers but-locally recharges the Laramie-Fox Hills aquifer. Subsurface-temperature profiles were evaluated as a means of estimating specific discharge across the bedrock surface (the base of the alluvial aquifer). However, assumptions of the analytical method were not met by field conditions and, thus, analyses of subsurface-temperature profiles did not reliably estimate specific discharge across the bedrock surface. The vertical hydraulic diffusivity of a siltstone and sandstone in the lower Denver confining unit was estimated, by an aquifer test, to be about 8 x 10'4 square foot per day. Physical and chemical characteristics of water from the bedrock aquifers in the study area generally differ from the physical and chemical characteristics of water from the alluvial aquifer, except for the physical and chemical characteristics of water from one bedrock well, which is completed in the Laramie-Fox Hills aquifer. In the southern part of the study area, physical and chemical characteristics of ground water indicate downward flow of water from the alluvial aquifer to the Laramie-Fox Hills aquifer. A three-dimensional numerical model was used to evaluate flow of water between the alluvial aquifer and underlying bedrock. Simulation of steady-state conditions indicates that flow from the bedrock aquifers to the alluvial aquifer was about 7 percent of recharge to the alluvial aquifer, about 0.87 cubic foot per second. The potential effects of withdrawal from the alluvial and bedrock aquifers at estimated (October 1989 to September 1990) rates and from the bedrock aquifers at two larger hypothetical rates were simulated for a 50-year projection period. The model simulations indicate that water levels in the alluvial aquifer will decline an average of 8.6 feet after 50 years of pumping at estimated October 1989 to September 1990 rates. Increases in withdrawals from the bedrock aquifers in El Paso County were simulated to: (1) Capture flow that currently discharges from the bedrock aquifers to springs and streams in upland areas and to the alluvial aquifer, (2) induce flow downward from the alluvial aquifer, and (3) accelerate the rate of waterlevel decline in the alluvial aquifer.
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Characterization of selected radionuclides in sediment and surface water in Standley Lake, Great Western Reservoir, and Mower Reservoir, Jefferson County, Colorado, 1992
Lake sediment and surface water from Standley Lake, Great Western Reservoir, and Mower Reservoir, near Denver, Colorado, were sampled and analyzed for selected radionuclides during August through October, 1992. Sample concentrations were summarized and compared to results from a study conducted in 1983-84. Median plutonium-239,240 (239,240Pu) concentrations in lake-sediment grab samples from Standley Lake, Great Western Reservoir, and Mower Reservoir were 0.037, 0.105, and 0.351 picocuries per gram (pCi/g). The maximum concen- tration of 239,240Pu dissolved in lake water was 0.009 picocuries per liter, substantially below limits suggested by the Colorado Department of Health and the Environment. Dissolved concentrations of gross alpha and uranium isotopes were below National Drinking Water Standards in all water samples. There was no statistically significant difference between 239,240Pu concentration in lake-sediment grab samples collected from Standley Lake in 1983-84 and in 1992; however, there was a small, but statistically significant, difference at Great Western Reservoir (p<0.05). In 1992 at Great Western Reservoir, median 239,240Pu concentrations were 0.040 pCi/g lower than in 1983-84. There was a small, but statistically significant (p<0.05) difference in 239,240Pu concentrations in lake- bottom-sediment cores collected in 1983-84 and in 1992. Measured concentrations tended to be higher in 1983-84 than in 1992. The differences were greatest at concentrations above 1.5 pCi/g; in those samples concentrations were 10 to 30% higher in 1983-84 than in 1992.
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Ecosystem trends in the Colorado Rockies
Biological conservation is increasingly moving toward an ecosystem and landscape approach, recognizing the prohibitive cost and difficulty of a species-by-species approach (LaRoe 1993). Also, statewide (e.g., Gap Analysis Program) and national surveys (e.g., Environmental Monitoring and Assessment Program or EMAP) are conducted at a scale and level of resolution that do not meet the needs of most small land-management units that require detailed information at the ecosystem and landscape scale (Stohlgren 1994). The Colorado Rockies are an ideal outdoor laboratory for ecosystem science and management. The escalating environmental threats described in this article compelled us to design a landscape-scale assessment of the status and trends of biotic resources.
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The biogeochemistry of wetlands in the San Luis Valley, Colorado: The effects of acid drainage from natural and mine sources
The Summitville Mine, located near the old mining town of Summitville in Rio Grande County, Colorado, operated between July 1986 and December 1992 as a large-tonnage open-pit heap-leach gold mine. During its 6 years of existence the trace metal levels in drainage water from the mine site were elevated over historical (pre-1986) levels (Moran and Wentz, 1974) due to input from three sources—heap leach water, seeps that occur throughout the mine workings, and an increase in the metal load of water coming from the old Reynolds Adit. Mine-drainage waters flow into Wightman Fork, a small tributary of the Alamosa River, which in turn flows east into the San Luis Valley. The increase in the trace metal burden of the Alamosa River watershed is of concern to farmers, land owners, and Federal and State wildlife agencies. The information presented here is largely abstracted from reports previously published (Balistrieri and others, 1995; Gough and others, 1995).
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Lead isotope compositions as guides to early gold mineralization: The North Amethyst vein system, Creede district, Colorado
The North Amethyst vein system, which is hosted by approximately 27 Ma Carpenter Ridge Tuff and approximately 26 Ma Nelson Mountain Tuff, has two mineral associations separated by brecciation and sedimentation in the veins. The early association consists of quartz, rhodonite, hematite, magnetite, electrum (Au (sub 0.3-0.5) Ag (sub 0.7-0.5)) , and Mn carbonate, Au-Ag sulfide, Ag sulfosalt, and base metal sulfide minerals. The later mineral association cuts the Mn- and Au-bearing assemblages and consists of quartz, calcite, sericite, chlorite, hematite, adularia, fluorite, base metal sulfides, and Ag-bearing tetrahedrite.Our detailed studies show that the Pb isotope compositions of paragenetically early galenas associated with Au-rich mineralization in the North Amethyst vein system are relatively unradiogenic ( 206 Pb/ 204 Pb: 18.826-18.881, 207 Pb/ 204 Pb: 15.588-15.602, and 208 Pb/ 204 Pb: 37.790-37.926) compared to Pb isotope compositions of galenas formed later at about 25 Ma during Ag and base metal mineralization ( 206 Pb/ 204 Pb: 19.041-19.115, 207 Pb/ 204 Pb: 15.627- 15.672, and 208 Pb/ 204 Pb: 37.829-38.057). New Pb isotope data for the central and southern parts of the Creede district, which are located 5 to 7 km south of the North Amethyst area, agree with the results of a regional study by Doe et al. (1979) that included five samples from the main part of the Creede district. Galenas and adularia from the central and southern Creede district and galenas from the Bondholder district, 7 km north of the North Amethyst area, are similar to the Pb isotope compositions of galenas formed later in the North Amethyst area during Ag and base metal mineralization. Galenas from the Alpha-Corsair vein, which was mined for Ag prior to 1910, are isotopically similar to galenas associated with North Amethyst Au-stage mineralization. This isotopic similarity suggests that unexplored segments of the Alpha-Corsair structure may have the same mineralogy as the North Amethyst Au stage; thus, the Alpha-Corsair structure has the potential for high gold contents.Pb isotope compositions from the late stage of the North Amethyst vein system and from the Bondholder and central and southern Creede mining districts are more radiogenic than the host volcanic rocks of the central cluster of the San Juan volcanic field. Our Pb isotope results indicate that early Au mineralization of the North Amethyst area may represent the product of an older and relatively local hydrothermal system distinct from that of the younger base metal and Ag mineralization found throughout the region. Fluids that deposited Au minerals may have derived their Pb isotope composition by a greater degree of interaction with shallow, relatively less radiogenic volcanic wall rocks. The younger, base metal and Ag-rich mineralization that overprints the Au mineralization in the North Amethyst area clearly has a more radiogenic isotopic signature, which implies that the later mineralization derived a greater component of its Pb from Proterozoic source rocks, or sediments derived from them.Paragenetically early sulfide-rich vein assemblages have the least radiogenic galenas and generally also have the highest Au contents. Thus, identification of paragenetically early vein assemblages with relatively unradiogenic Pb isotope compositions similar to those of the North Amethyst area provides an additional exploration tool for Au in the central San Juan Mountains area.
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Mineralogy, paragenesis, and mineral zoning of the Bulldog Mountain vein system, Creede District, Colorado
The Bulldog Mountain vein system, Creede district, Colorado, is one of four major epithermal vein systems from which the bulk of the district's historical Ag-Pb-Zn-Cu production has come. Ores deposited along the vein system were discovered in 1965 and were mined from 1969 to 1985.Six temporally gradational mineralization stages have been identified along the Bulldog Mountain vein system, each with a characteristic suite of minerals deposited or leached and a characteristic distribution within the vein system; some of these stages are also strongly zoned within the vein system. Stage A was dominated by deposition of rhodochrosite along the lower levels of the Bulldog Mountain ore zone. Stage B in the northern parts of the ore zone is characterized by abundant fine-grained sphalerite and galena, with lesser tetrahedrite and minor chlorite and hematite. With increasing elevation to the south, stage B ores become progressively more barite and silver rich, with alternating barite and fine-grained sphalerite + galena generations; native silver + or - acanthite assemblages are also locally abundant within southern stage B barite sulfide ores, whereas chalcopyrite and other Cu and Ag sulfides and sulfosalts are present erratically in minor amounts. Stage C in the upper and northern portions of the ore zone is characterized by abundant quartz and fluorite, minor adularia, hematite, Mn siderite, sphalerite, and galena, and major leaching of earlier barite; to the south, some barite and sulfides may have been deposited. Stage D sphalerite and galena were deposited in the upper and northern portions of the ore zone; a barite- and silver-rich facies of this stage may also be present in the southern portions of the vein system. Late in stage D, mineralogically complex assemblages containing chalcopyrite, tetrahedrite, polybasite, bornite, pyrargyrite, and a variety of other sulfides and sulfosalts were deposited in modest amounts throughout the vein system. This complex assemblage marked the transition to stage E. During stage E, the final sulfide stage, abundant botryoidal pyrite and marcasite with lesser stibnite, sphalerite, and sulfosalts were deposited primarily along the top of the Bulldog Mountain ore zone. Stage F, the final mineralization stage along the vein system, is marked by wire silver and concurrent leaching of earlier sulfides and sulfosalts; this stage may reflect the transition to a supergene environment.The sequence of mineralization stages identified in this study along the Bulldog Mountain system can be correlated with corresponding stages identified by other researchers along the OH and P veins, and the southern Amethyst vein system. Mineral zoning patterns identified along the Bulldog Mountain vein system also parallel larger scale zoning patterns across the central and southern Creede district.The complex variations in mineral assemblages documented in time and space along the Bulldog Mountain vein system were produced by the combined effects of many processes. Large-scale changes in vein mineralogy over time produced discrete mineralization stages. Short-term mineralogical fluctuations produced complex interbanding of mineralogically distinct generations. Fluid chemistry evolution within the vein system produced large-scale lateral zoning patterns within certain stages. Hypogene leaching substantially modified the distributions of some minerals. Finally, structural activity, mineral deposition, and mineral leaching modified fluid flow pathways repeatedly during mineralization, and so added to the complex mineral distribution patterns within the vein system.
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Phenotypic divergence of secondary sexual traits among sage grouse, Centrocercus urophasianus , populations
S age grouse, Centrocercus urophasianus , in an isolated montane basin near Gunnison, Colorado differ in several morphological and behavioural traits from conspecifics studied in other areas of the species' range. Both sexes in Gunnison are smaller than sage grouse elsewhere, and males possess differences in feather morphology as well. The mating behaviour of male sage grouse in three populations was examined to determine whether male strut displays of Gunnison sage grouse were behaviourally distinct. Behavioural analyses revealed Gunnison males perform strut displays at a slower rate than males in the two other sage grouse populations sampled. In addition, Gunnison males' strut displays contain unique visual and acoustical aspects. The most distinguishing attributes of Gunnison sage grouse were male secondary sexual characteristics including traits that correlate with mating success in other populations. Thus, phenotypic differences observed in the Gunnison population represent a divergence in expression of traits that are likely to be influenced by sexual selection. Recent models of speciation suggest that species characterized by intense sexual selection, such as those with lek mating systems, have the potential for rapid inter-populational divergence in male traits and female preferences leading to speciation.
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Hydrological controls on dissolved organic carbon during snowmelt in the Snake River near Montezuma, Colorado
A quantitative understanding of the factors controlling the variation of dissolved organic carbon (DOC) in headwater streams is of scientific concern for at least two reasons. First, quantifying the overall carbon budgets of lotic systems is needed for a fundamental understanding of these systems. Second, DOC interacts strongly with other dissolved substances (heavy metals in particular) and plays an important role in the transport of contaminants. In the Snake River near Montezuma, Colorado, measurements of DOC from 1980 to 1986 show rapid decreases in concentration from a peak very early in the snowmelt period. Peak DOC concentrations occur approximately one month prior to peak discharge in the stream. The decline in DOC with time is approximately exponential, suggesting that a simple flushing mechanism can explain the response. We examined hydrological mechanisms to explain the observed variability of DOC in the Snake River by simulating the hydrological response of the catchment using TOPMODEL and routing the predicted flows through a simple model that accounted for temporal changes in DOC. Conceptually the DOC model represents a terrestrial (soil) reservoir in which DOC builds up during low flow periods and is flushed out by infiltrating meltwaters. The model reproduces the main features of the observed variation in DOC in the Snake River and thus lays the foundation for quantitatively linking hydrological processes with carbon cycling through upland catchments. Model results imply that a significant fraction of the soils in the Snake River catchment contribute DOC to the stream during peak discharge. Our work represents one of the first attempts to quantitatively describe the hydrological controls on DOC dynamics in a headwater stream. These controls are studied through the model by imposing mass balance constraints on both the flux of water through the various DOC source areas and the amount of DOC that can accumulate in these areas.
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Specific surface area of a crushed welded tuff before and after aqueous dissolution
Specific surface areas were measured for several reference minerals (anorthoclase, labradorite and augite), welded tuff and stream sediments from Snowshoe Mountain, near Creede, Colorado. Crushed and sieved tuff had an unexpectedly small variation in specific surface area over a range of size fractions. Replicate surface area measurements of the largest and smallest tuff particle size fractions examined (1−0.3mm and<0.212mm) were 2.3 ± 0.2m 2 /g for each size fraction. Reference minerals prepared in the same way as the tuff had smaller specific surface areas than that of the tuff of the same size fraction. Higher than expected tuff specific surface areas appear to be due to porous matrix. Tuff, reacted in solutions with pH values from 2 to 6, had little change in specific surface area in comparison with unreacted tuff. Tuff, reacted with solutions having high acid concentrations (0.1 M hydrochloric acid or sulfuric-hydrofluoric acid), exhibited a marked increase in specific surface area compared to unreacted tuff.
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Mineralogy of a calc-silicate locality near Genesee Park, Jefferson County, Colorado
No abstract available.
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Complete Bouguer gravity anomaly, isostatic-residual gravity, horizontal gradient, and terrain maps of Colorado
No abstract available.
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Preliminary surficial geologic map of the Rocky Flats Plant and vicinity, Jefferson and Boulder counties, Colorado
No abstract available.
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Aeromagnetic map of parts of the Denver, Greeley, and Pueblo 1 x 2 degree quadrangles, Colorado
No abstract available.
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