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Research about Colorado

Source-linked reports with geographic coverage including Colorado.

At least 793 records · Page 44Linked to original sources
USGS2009

Quaternary incision rates and drainage evolution of the Uncompahgre and Gunnison Rivers, western Colorado, as calibrated by the Lava Creek B ash

The Quaternary erosional history of western Colorado is documented in terraces of the Colorado, Gunnison, and Uncompahgre Rivers that contain the Lava Creek B ash (0.64 Ma). This paper reports an important new ash locality that dates ca. 100-m-high river gravels associated with the paleo-confluence of the Gunnison and Uncompahgre Rivers upstream from Grand Junction. Provenance analysis reveals paleo-Gunnison River gravels (containing granite and gneiss clasts) and paleo-Uncompahgre River gravels (containing Uncompahgre Group quartzite and San Juan volcanic field rocks). The paleo-Uncompahgre River gravels are 3 m directly beneath Lava Creek B ash, and the areal distribution of terraces indicates that this area was the paleo-confluence between the Gunnison and Uncompahgre Rivers. This confluence has shifted 11 km to the east since 0.64 Ma due to events related to stream piracy and drainage reorganization. Gunnison terrace straths near the paleo-confluence are estimated to be 106 m above the modern strath, giving an estimated incision rate of 165 m/Ma. Because of excellent age and geologic control, this is one of the best incision-rate data points in the upper Colorado River system. It is similar to previously reported regional rates, but is substantially lower than upstream incision rates in the Black Canyon of the Gunnison River. This dated Gunnison River terrace anchors the projection of Lava Creek B-bearing Grand Mesa pediment surfaces (e.g., Petrie Mesa) to regional base level and helps constrain a regional reconstruction of the 0.64-Ma profile of the paleo-Gunnison River. This reconstruction shows dramatic differences in incision rate in the Gunnison River system since 0.64 Ma, and that a transient knickpoint migrated past Sawmill Mesa prior to 0.64 Ma. This incision data point has important implications for evaluating major Quaternary changes in the configuration of this part of the Rocky Mountain drainage system. It also provides evidence for a young, disequilibrium drainage system that is responding to base-level changes downstream driven by a stream capture event, which in turn may have been driven by tectonic or climatic perturbations.

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USGS2009

Investigating hydraulic connections and the origin of water in a mine tunnel using stable isotopes and hydrographs

Turquoise Lake is a water-supply reservoir located north of the historic Sugarloaf Mining district near Leadville, Colorado, USA. Elevated water levels in the reservoir may increase flow of low-quality water from abandoned mine tunnels in the Sugarloaf District and degrade water quality downstream. The objective of this study was to understand the sources of water to Dinero mine drainage tunnel and evaluate whether or not there was a direct hydrologic connection between Dinero mine tunnel and Turquoise Lake from late 2002 to early 2008. This study utilized hydrograph data from nearby draining mine tunnels and the lake, and stable isotope (δ 18 O and δ 2 H) data from the lake, nearby draining mine tunnels, imported water, and springs to characterize water sources in the study area. Hydrograph results indicate that flow from the Dinero mine tunnel decreased 26% (2006) and 10% (2007) when lake elevation (above mean sea level) decreased below approximately 3004 m (approximately 9855 feet). Results of isotope analysis delineated two meteoric water lines in the study area. One line characterizes surface water and water imported to the study area from the western side of the Continental Divide. The other line characterizes groundwater including draining mine tunnels, springs, and seeps. Isotope mixing calculations indicate that water from Turquoise Lake or seasonal groundwater recharge from snowmelt represents approximately 10% or less of the water in Dinero mine tunnel. However, most of the water in Dinero mine tunnel is from deep groundwater having minimal isotopic variation. The asymmetric shape of the Dinero mine tunnel hydrograph may indicate that a limited mine pool exists behind a collapse in the tunnel and attenutates seasonal recharge. Alternatively, a conceptual model is presented (and supported with MODFLOW simulations) that is consistent with current and previous data collected in the study area, and illustrates how fluctuating lake levels change the local water-table elevation which can affect discharge from the Dinero mine tunnel without physical transfer of water between the two locations.

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USGS2009

Historical fire and multidecadal drought as context for piñon - Juniper woodland restoration in western Colorado

Fire is known to structure tree populations, but the role of broad-scale climate variability is less clear. For example, the influence of climatic “teleconnections” (the relationship between oceanic–atmospheric fluctuations and anomalous weather patterns across broad scales) on forest age structure is relatively unexplored. We sampled semiarid piñon–juniper ( Pinus edulis – Juniperus osteosperma ) woodlands in western Colorado, USA, to test the hypothesis that woodland age structures are shaped by climate, including links to oceanic–atmospheric fluctuations, and by past fires and livestock grazing. Low-severity surface fire was lacking, as fire scars were absent, and did not influence woodland densities, but stand-replacing fires served as long-rotation (>400–600 years), stand-initiating events. Old-growth stands (>300 years old) were found in 75% of plots, consistent with a long fire rotation. Juniper and piñon age structures suggest contrasting responses during the past several centuries to dry and wet episodes linked to the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO). Juniper density increased slightly during periods of drought, positive (warm) AMO (after ∼10-year lag), and negative (cool) PDO. In contrast, piñon populations may still be recovering from a long, drought-filled period (AD 1620–1820), with pulses of recovery favored during cool AMO, warm PDO, and above-average moisture periods. Analysis of 20th-century tree establishment and instrumental climate data corroborate the long-term relationships between age structure and climate. After Euro–American settlement (AD 1881), livestock grazing reduced understory grasses and forbs, reducing competition with tree seedlings and facilitating climate-induced increases in piñons. Thus tree populations in these woodlands are in flux, affected by drought and wet periods linked to oceanic–atmospheric variability, Euro–American livestock grazing, and long-rotation, high-severity fires. Reductions in livestock grazing levels may aid ecological restoration efforts. However, given long-term fluctuations in tree density and composition, and expected further drought, thinning or burning to reduce tree populations may be misdirected.

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USGS2009

Boundary of the Eagle River watershed valley-fill aquifer, Eagle County, north-central Colorado, 2006-2007

This vector data set delineates the approximate boundary of the Eagle River watershed valley-fill aquifer (ERWVFA). This data set was developed by a cooperative project between the U.S. Geological Survey, Eagle County, the Eagle River Water and Sanitation District, the Town of Eagle, the Town of Gypsum, and the Upper Eagle Regional Water Authority. This project was designed to evaluate potential land-development effects on groundwater and surface-water resources so that informed land-use and water management decisions can be made. The boundary of the ERWVFA was developed by combining information from two data sources. The first data source was a 1:250,000-scale geologic map of the Leadville quadrangle developed by Day and others (1999). The location of Quaternary sediments was used as a first approximation of the ERWVFA. The boundary of the ERWVFA was further refined by overlaying the geologic map with Digital Raster Graphic (DRG) scanned images of 1:24,000 topographic maps (U.S. Geological Survey, 2001). Where appropriate, the boundary of the ERWVFA was remapped to correspond with the edge of the valley-fill aquifer marked by an abrupt change in topography at the edge of the valley floor throughout the Eagle River watershed. The boundary of the ERWVFA more closely resembles a hydrogeomorphic region presented by Rupert (2003, p. 8) because it is based upon general geographic extents of geologic materials and not on an actual aquifer location as would be determined through a rigorous hydrogeologic investigation.

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USGS2009

Depth to water, saturated thickness, and other geospatial datasets used in the design and installation of a groundwater monitoring-well network in the High Plains Aquifer, Colorado

These datasets were compiled in support of U.S. Geological Survey Data Series 456, Design and Installation of a Groundwater Monitoring-Well Network in the High Plains Aquifer, Colorado. These datasets were developed as part of a cooperative project between the U.S. Geological Survey and the Colorado Department of Agriculture. The purpose of the project was to design a 30-well network and install 20 of the 30 wells to characterize water quality in the High Plains aquifer in areas of irrigated agriculture in Colorado. The five datasets are described as follows and are further described in Data Series 456: (1) ds472_dtw: This dataset represents the depth to groundwater in the High Plains Aquifer in Colorado in 2000. This grid was used to determine areas where the depth to water was less than 200 feet below land surface. (2) Ds472_sat: This dataset represents the saturated thickness of the High Plains aquifer within Colorado in 2000. This grid was used to determine areas where the saturated thickness was greater than 50 feet. (3) Ds472_equalareas: This dataset includes 30 equal-area polygons overlying the High Plains Aquifer in Colorado having a depth to water less than 200 feet, a saturated thickness greater than 50 feet, and underlying irrigated agricultural lands. (4) Ds472_randomsites: This dataset includes 90 randomly-generated potential groundwater sampling sites. This dataset provides a first, second, and third choice placed within the 30 equal area polygons of dataset dsXX_equalareas. (5) Ds472_welldata: This dataset includes point locations and well completion data for the 20 wells installed as part of this project. The datasets that pertain to this report can be found on the U.S. Geological Survey's NSDI (National Spatial Data Infrastructure) Node, the links are provided on the sidebar.

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USGS2009

Hazards management in Grand County, Colorado— Fire fuels characterization

The USGS Fire Science Initiative is designed to identify potential wildfire risks and related hazards and to mitigate their effects on people, property, and natural resources. The USGS Rocky Mountain Geographic Science Center (RMGSC) plays an integral role in the fire science demonstration project targeting Grand County, Colo., which uses remote sensing imagery, other geospatial data, and advanced classification techniques to produce inventories and assessments of the current state of the ecosystem. The data gathered - extent of tree mortality and insect infestation, changes in fire fuels, susceptibility to post-fire effects, distribution of wildland-urban interface areas, etc. - will give much needed information to decisionmakers on the Federal, State, and local levels.

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USGS2009

Geology highlights for Ride the Rockies 2009

The author provides a brief description of the geology along the route for each day of the ride, from June 14 through June 19, 2009. Ride the Rockies begins and ends in Glenwood Springs, with stops in Hotchkiss, Gunnison, Salida, Leadville, Aspen, and back to Glenwood Springs, Colorado. A small, generalized geologic map also is shown.

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USGS2009

The Iron Hill (Powderhorn) carbonatite complex, Gunnison County, Colorado — A potential source of several uncommon mineral resources

A similar version of this slide show was presented on three occasions during 2008: two times to local chapters of the Society for Mining, Metallurgy, and Exploration (SME), as part of SME's Henry Krumb lecture series, and the third time at the Northwest Mining Association's 114th Annual Meeting, held December 1-5, 2008, in Sparks (Reno), Nevada. In 2006, the U.S. Geological Survey (USGS) initiated a study of the diverse and uncommon mineral resources associated with carbonatites and associated alkaline igneous rocks. Most of these deposit types have not been studied by the USGS during the last 25 years, and many of these mineral resources have important applications in modern technology. The author chose to begin this study at Iron Hill in southwestern Colorado because it is the site of a classic carbonatite complex, which is thought to host the largest known resources of titanium and niobium in the United States.

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USGS2009

Transient electromagnetic soundings near Great Sand Dunes National Park and Preserve, San Luis Valley, Colorado (2006 field season)

Time-domain electromagnetic (TEM) soundings were made near Great Sand Dunes National Park and Preserve in the San Luis Valley of southern Colorado to obtain subsurface information of use to hydrologic modeling. Seventeen soundings were made to the east and north of the sand dunes. Using a small loop TEM system, maximum exploration depths of about 75 to 150 m were obtained. In general, layered earth interpretations of the data found that resistivity decreases with depth. Comparison of soundings with geologic logs from nearby wells found that zones logged as having increased clay content usually corresponded with a significant resistivity decrease in the TEM determined model. This result supports the use of TEM soundings to map the location of the top of the clay unit deposited at the bottom of the ancient Lake Alamosa that filled the San Luis Valley from Pliocene to middle Pleistocene time.

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USGS2009

Geochemistry of standard mine waters, Gunnison County, Colorado, July 2009

In many hard-rock-mining districts water flowing from abandoned mine adits is a primary source of metals to receiving streams. Understanding the generation of adit discharge is an important step in developing remediation plans. In 2006, the U.S. Environmental Protection Agency listed the Standard Mine in the Elk Creek drainage basin near Crested Butte, Colorado as a superfund site because drainage from the Standard Mine enters Elk Creek, contributing dissolved and suspended loads of zinc, cadmium, copper, and other metals to the stream. Elk Creek flows into Coal Creek, which is a source of drinking water for the town of Crested Butte. In 2006 and 2007, the U.S. Geological Survey undertook a hydrogeologic investigation of the Standard Mine and vicinity and identified areas of the underground workings for additional work. Mine drainage, underground-water samples, and selected spring water samples were collected in July 2009 for analysis of inorganic solutes as part of a follow-up study. Water analyses are reported for mine-effluent samples from Levels 1 and 5 of the Standard Mine, underground samples from Levels 2 and 3 of the Standard Mine, two spring samples, and an Elk Creek sample. Reported analyses include field measurements (pH, specific conductance, water temperature, dissolved oxygen, and redox potential), major constituents and trace elements, and oxygen and hydrogen isotopic determinations. Overall, water samples collected in 2009 at the same sites as were collected in 2006 have similar chemical compositions. Similar to 2006, water in Level 3 did not flow out the portal but was observed to flow into open workings to lower parts of the mine. Many dissolved constituent concentrations, including calcium, magnesium, sulfate, manganese, zinc, and cadmium, in Level 3 waters substantially are lower than in Level 1 effluent. Concentrations of these dissolved constituents in water samples collected from Level 2 approach or exceed concentrations of Level 1 effluent suggesting that water-rock interaction between Levels 3 and 1 can account for the elevated concentration of metals and other constituents in Level 1 portal effluent. Ore minerals (sphalerite, argentiferous galena, and chalcopyrite) are the likely sources of zinc, cadmium, lead, and copper and are present within the mine in unmined portions of the vein system, within plugged ore chutes, and in muck piles.

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USGS2009

Salinization of the upper Colorado River - Fingerprinting geologic salt sources

Salt in the upper Colorado River is of concern for a number of political and socioeconomic reasons. Salinity limits in the 1974 U.S. agreement with Mexico require the United States to deliver Colorado River water of a particular quality to the border. Irrigation of crops, protection of wildlife habitat, and treatment for municipal water along the course of the river also place restrictions on the river's salt content. Most of the salt in the upper Colorado River at Cisco, Utah, comes from interactions of water with rock formations, their derived soil, and alluvium. Half of the salt comes from the Mancos Shale and the Eagle Valley Evaporite. Anthropogenic activities in the river basin (for example, mining, farming, petroleum exploration, and urban development) can greatly accelerate the release of constituents from these geologic materials, thus increasing the salt load of nearby streams and rivers. Evaporative concentration further concentrates these salts in several watersheds where agricultural land is extensively irrigated. Sulfur and oxygen isotopes of sulfate show the greatest promise for fingerprinting the geologic sources of salts to the upper Colorado River and its major tributaries and estimating the relative contribution from each geologic formation. Knowing the salt source, its contribution, and whether the salt is released during natural weathering or during anthropogenic activities, such as irrigation and urban development, will facilitate efforts to lower the salt content of the upper Colorado River.

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USGS2009

Groundwater quality, age, and probability of contamination, Eagle River watershed valley-fill aquifer, north-central Colorado, 2006-2007

The Eagle River watershed is located near the destination resort town of Vail, Colorado. The area has a fastgrowing permanent population, and the resort industry is rapidly expanding. A large percentage of the land undergoing development to support that growth overlies the Eagle River watershed valley-fill aquifer (ERWVFA), which likely has a high predisposition to groundwater contamination. As development continues, local organizations need tools to evaluate potential land-development effects on ground- and surface-water resources so that informed land-use and water management decisions can be made. To help develop these tools, the U.S. Geological Survey (USGS), in cooperation with Eagle County, the Eagle River Water and Sanitation District, the Town of Eagle, the Town of Gypsum, and the Upper Eagle Regional Water Authority, conducted a study in 2006-2007 of the groundwater quality, age, and probability of contamination in the ERWVFA, north-central Colorado. Ground- and surface-water quality samples were analyzed for major ions, nutrients, stable isotopes of hydrogen and oxygen in water, tritium, dissolved gases, chlorofluorocarbons (CFCs), and volatile organic compounds (VOCs) determined with very low-level laboratory methods. The major-ion data indicate that groundwaters in the ERWVFA can be classified into two major groups: groundwater that was recharged by infiltration of surface water, and groundwater that had less immediate recharge from surface water and had elevated sulfate concentrations. Sulfate concentrations exceeded the USEPA National Secondary Drinking Water Regulations (250 milligrams per liter) in many wells near Eagle, Gypsum, and Dotsero. The predominant source of sulfate to groundwater in the Eagle River watershed is the Eagle Valley Evaporite, which is a gypsum deposit of Pennsylvanian age located predominantly in the western one-half of Eagle County.

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USGS2009

Regional regression equations for estimation of natural streamflow statistics in Colorado

The U.S. Geological Survey (USGS), in cooperation with the Colorado Water Conservation Board and the Colorado Department of Transportation, developed regional regression equations for estimation of various streamflow statistics that are representative of natural streamflow conditions at ungaged sites in Colorado. The equations define the statistical relations between streamflow statistics (response variables) and basin and climatic characteristics (predictor variables). The equations were developed using generalized least-squares and weighted least-squares multilinear regression reliant on logarithmic variable transformation. Streamflow statistics were derived from at least 10 years of streamflow data through about 2007 from selected USGS streamflow-gaging stations in the study area that are representative of natural-flow conditions. Basin and climatic characteristics used for equation development are drainage area, mean watershed elevation, mean watershed slope, percentage of drainage area above 7,500 feet of elevation, mean annual precipitation, and 6-hour, 100-year precipitation. For each of five hydrologic regions in Colorado, peak-streamflow equations that are based on peak-streamflow data from selected stations are presented for the 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year instantaneous-peak streamflows. For four of the five hydrologic regions, equations based on daily-mean streamflow data from selected stations are presented for 7-day minimum 2-, 10-, and 50-year streamflows and for 7-day maximum 2-, 10-, and 50-year streamflows. Other equations presented for the same four hydrologic regions include those for estimation of annual- and monthly-mean streamflow and streamflow-duration statistics for exceedances of 10, 25, 50, 75, and 90 percent. All equations are reported along with salient diagnostic statistics, ranges of basin and climatic characteristics on which each equation is based, and commentary of potential bias, which is not otherwise removed by log-transformation of the variables of the equations from interpretation of residual plots. The predictor-variable ranges can be used to assess equation applicability for ungaged sites in Colorado.

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USGS2009

The history of aggregate development in the Denver, CO area

At the start of the 20 th century Denver's population was 203,795. Most streets were unpaved. Buildings were constructed of wood frame or masonry. Transport was by horse-drawn-wagon or rail. Statewide, aggregate consumption was less than 0.25 metric tons per person per year. One hundred years later Denver had a population of 2,365,345. Today Denver is a major metropolitan area at the crossroads of two interstates, home to a new international airport, and in the process of expanding its light rail transit system. The skyline is punctuated with skyscrapers. The urban center is surrounded with edge cities. These changes required huge amounts of aggregate. Statewide, aggregate consumption increased 50 fold to over 13 metric tons per person per year. Denver has a large potential supply of aggregate, but sand and gravel quality decreases downstream from the mountain front and potential sources of crushed stone occur in areas prized for their scenic beauty. These issues, along with urban encroachment and citizen opposition, have complicated aggregate development and have paved a new path for future aggregate development including sustainable resource management and reclamation techniques.

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USGS2009

Acid neutralizing capacity and leachate results for igneous rocks, with associated carbon contents of derived soils, Animas River AML site, Silverton, Colorado

Mine planning efforts have historically overlooked the possible acid neutralizing capacity (ANC) that local igneous rocks can provide to help neutralize acidmine drainage. As a result, limestone has been traditionally hauled to mine sites for use in neutralizing acid drainage. Local igneous rocks, when used as part of mine life-cycle planning and acid mitigation strategy, may reduce the need to transport limestone to mine sites because these rocks can contain acid neutralizing minerals. Igneous hydrothermal events often introduce moderately altered mineral assemblages peripheral to more intensely altered rocks that host metal-bearing veins and ore bodies. These less altered rocks can contain ANC minerals (calcite-chlorite-epidote) and are referred to as a propylitic assemblage. In addition, the carbon contents of soils in areas of new mining or those areas undergoing restoration have been historically unknown. Soil organic carbon is an important constituent to characterize as a soil recovery benchmark that can be referred to during mine cycle planning and restoration. <br/> This study addresses the mineralogy, ANC, and leachate chemistry of propylitic volcanic rocks that host polymetallic mineralization in the Animas River watershed near the historical Silverton, Colorado, mining area. Acid titration tests on volcanic rocks containing calcite (2 &ndash; 20 wt %) and chlorite (6 &ndash; 25 wt %), have ANC ranging from 4 &ndash; 146 kg/ton CaCO<sub>3</sub> equivalence. Results from a 6-month duration, kinetic reaction vessel test containing layered pyritic mine waste and underlying ANC volcanic rock (saturated with deionized water) indicate that acid generating mine waste (pH 2.4) has not overwhelmed the ANC of propylitic volcanic rocks (pH 5.8). Sequential leachate laboratory experiments evaluated the concentration of metals liberated during leaching. Leachate concentrations of Cu-Zn-As-Pb for ANC volcanic rock are one-to-three orders of magnitude lower when compared to leached solution from mine waste used in the kinetic reaction vessel test. This finding suggests that mine waste and not ANC rock may generate the majority of leachable metals in a field scenario. <br/> The organic carbon content of naturally reclaimed soils derived from weathering of propylitically-altered andesite was determined in catchments where ANC studies were initiated. Soils were found to have total carbon concentrations (TOC) that exceed global average soil TOC abundances by as much as 1.5 &ndash; 5 times. These data support an environmental management system involving use of ANC rocks as part of life-cycle mine planning to reduce post-mine closure acid mitigation measures. Carbon contents of undisturbed soils in mined catchments can possibly be used to validate post-reclamation success and help quantify carbon sequestration for CO<sub>2</sub> emission offset trading as carbon markets mature.

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USGS2009

Environmental effects of hydrothermal alteration and historical mining on water and sediment quality in Central Colorado

The U.S. Geological Survey conducted an environmental assessment of 198 catchments in a 54,000-km2 area of central Colorado, much of which is on Federal land. The Colorado Mineral Belt, a northeast-trending zone of historical base- and precious-metal mining, cuts diagonally across the study area. The investigation was intended to test the hypothesis that degraded water and sediment quality are restricted to catchments in which historical mining has occurred. Water, streambed sediment, and aquatic insects were collected from (1) catchments underlain by single lithogeochemical units, some of which were hydrothermally altered, that had not been prospected or mined; (2) catchments that contained evidence of prospecting, most of which contain hydrothermally altered rock, but no historical mining; and (3) catchments, all of which contain hydrothermally altered rock, where historical but now inactive mines occur. Geochemical data determined from catchments that did not contain hydrothermal alteration or historical mines met water quality criteria and sediment quality guidelines. Base-metal concentrations from these types of catchments showed small geochemical variations that reflect host lithology. Hydrothermal alteration and mineralization typically are associated with igneous rocks that have intruded older bedrock in a catchment. This alteration was regionally mapped and characterized primarily through the analysis of remote sensing data acquired by the ASTER satellite sensor. Base-metal concentrations among unaltered rock types showed small geochemical variations that reflect host lithology. Base-metal concentrations were elevated in sediment from catchments underlain by hydrothermally altered rock. Classification of catchments on the basis of mineral deposit types proved to be an efficient and accurate method for discriminating catchments that have degraded water and sediment quality. Only about 4.5 percent of the study area has been affected by historical mining, whereas a larger part of the study area is underlain by hydrothermally altered rock that has weathered to produce water and sediment with naturally elevated geochemical baselines.

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USGS2009

U.S. Geological Survey research in Handcart Gulch, Colorado—An alpine watershed with natural acid-rock drainage

Handcart Gulch is an alpine watershed along the Continental Divide in the Colorado Rocky Mountain Front Range. It contains an unmined mineral deposit typical of many hydrothermal mineral deposits in the intermountain west, composed primarily of pyrite with trace metals including copper and molybdenum. Springs and the trunk stream have a natural pH value of 3 to 4. The U.S. Geological Survey began integrated research activities at the site in 2003 with the objective of better understanding geologic, geochemical, and hydrologic controls on naturally occurring acid-rock drainage in alpine watersheds. Characterizing the role of groundwater was of particular interest because mountain watersheds containing metallic mineral deposits are often underlain by complexly deformed crystalline rocks in which groundwater flow is poorly understood. Site infrastructure currently includes 4 deep monitoring wells high in the watershed (300&ndash; 1,200 ft deep), 4 bedrock (100&ndash;170 ft deep) and 5 shallow (10&ndash;30 ft deep) monitoring wells along the trunk stream, a stream gage, and a meteorological station. Work to date at the site includes: geologic mapping and structural analysis; surface sample and drill core mineralogic characterization; geophysical borehole logging; aquifer testing; monitoring of groundwater hydraulic heads and streamflows; a stream tracer dilution study; repeated sampling of surface and groundwater for geochemical analyses, including major and trace elements, several isotopes, and groundwater age dating; and construction of groundwater flow models. The unique dataset collected at Handcart Gulch has yielded several important findings about bedrock groundwater flow at the site. Most importantly, we find that bedrock bulk permeability is nontrivial and that bedrock groundwater apparently constitutes a substantial fraction of the hydrologic budget. This means that bedrock groundwater commonly may be an underappreciated component of the hydrologic system in studies of alpine watersheds. Additionally, despite the complexity of the fracture controlled aquifer system, it appears that it can be represented with a relatively simple conceptual model and can be treated as an equivalent porous medium at the watershed scale. Interpretation of existing data, collection of new monitoring data, and efforts to link geochemical and hydrologic processes through modeling are ongoing at the site.

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