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Research about Montrose County, Colorado

Source-linked reports with geographic coverage including Montrose County, Colorado.

At least 19 recordsLinked to original sources
USGS2025

Living with wildfire in Montrose County, Colorado: 2023 Data report

During 2022–2024, the Wildfire Research (WiRē) Center partnered with the West Region Wildfire Council (WRWC) to learn more about parcel-level wildfire risk in Montrose County, Colorado. This research project was part of a larger, sustained collaboration between WiRē and the WRWC, moving the focus from areas typically characterized as fire-prone due to heavily treed and steep topography, into an area with relatively gentle topography and lighter fuels. The study area borders and includes northern portions of Ouray County that fall within the service area of Montrose County Fire Protection District. The area was of particular interest to the WRWC because it lacks some of the social infrastructure typically leveraged to build community relationships, such as Homeowners Associations, and the WRWC sought to build understanding in order to provide a foundation to foster stronger ties to pursue wildfire risk reduction. The study also presented an opportunity to help assess interest in the WRWC’s cost share program intended to facilitate risk mitigation action on private properties.

Colorado↗
USGS2024

Hydrogeologic conceptual model of groundwater occurrence and brine discharge to the Dolores River in the Paradox Valley, Montrose County, Colorado

Salinity, or total dissolved solids (TDS), of the Colorado River is a major concern in the southwestern United States where the river provides water to about 40 million people for municipal and industrial use and is used to irrigate about 5.5 million acres of land. Much of the salinity in the Colorado River Basin is derived from natural interactions of surface water and groundwater with various geologic materials (rocks, soils, and alluvial deposits). The Dolores River in southwest Colorado is a major tributary of the Colorado River that historically accounts for about 6 percent of the salinity load to the Upper Colorado River Basin with the Paradox Valley being the primary source of salinity to the Dolores River. The Paradox Valley, one of several salt-anticline valleys in the region, is a fault-bounded topographic basin aligned with and exposing an underlying salt-anticline core. Salt deposits in the Pennsylvanian Paradox Formation of the Hermosa Group form an elongated salt diapir oriented northwest to southeast that is up to 12,000 feet (ft) thick beneath the present valley floor. Surface erosion, groundwater circulation, and weathering during Tertiary and Quaternary valley formation contributed to development of a cap rock, collapse features, breccia, and brine at the top of the exposed salt diapir. Today (2023), brine occurring in the brecciated cap rock and underlying salt deposits is in hydraulic connection with an overlying freshwater alluvial aquifer, and depending on seasonal river stage and hydrologic conditions, the brine discharges to the Dolores River causing the observed increase in salinity as the river crosses the Paradox Valley. To reduce salinity concentrations in the Dolores River, the Bureau of Reclamation (Reclamation) operates the Paradox Valley Unit (PVU). The PVU project consists of nine shallow brine pumping wells near the Dolores River and one deep disposal well where the brine is injected for disposal. When operational, the PVU pumping wells extract brine from the base of the alluvial aquifer that is piped and injected into a deep disposal well about 3 miles southwest of the PVU. The PVU became fully operational July 1, 1996, and by 2015, operation of the PVU had reduced salinity concentrations in the Dolores River by as much as 70 percent compared to pre-PVU conditions. In response to a 4.5 magnitude earthquake, injection operations, and thus PVU pumping, were ceased from March 2019 to June 2022. A trial period of PVU operation began in June 2022 with a reduced injection rate, and thus PVU pumping rate, of about two-thirds capacity to gather additional information and guide future operational decisions. In cooperation with Reclamation, the U.S. Geological Survey (USGS) developed this report to present the current (2023) understanding of groundwater and brine occurrence and discharge to the Dolores River in the Paradox Valley. Results from the compilation of spatial datasets, groundwater sampling and age dating, and aquifer tests are presented to provide improved understanding of the Paradox Valley hydrogeology, to supply datasets for a numerical groundwater-flow and brine-transport model, and to support future operations of the PVU. The hydrogeologic data provided herein, along with the most recent loading analysis for the Dolores River in the Paradox Valley, and a previous conceptual model for brine discharge to the river are used to present a conceptual understanding of groundwater occurrence in the Paradox Valley.

Colorado↗
USGS2024

Simulation of groundwater flow and brine discharge to the Dolores River in the Paradox Valley, Montrose County, Colorado

Salinity, or total dissolved solids (TDS), of the Colorado River affects agricultural, municipal, and industrial water users and is an important concern in the Western United States. In the Paradox Valley of southwestern Colorado, natural discharge of sodium-chloride brine to the Dolores River from the underlying core of a salt-valley anticline accounts for about 6 percent of the salinity load to the Colorado River. Formation of the Paradox Valley began during the Miocene, and subsequent erosion exposed the Pennsylvania Paradox Formation in the core of the anticline where a cap rock, collapse features, breccia, and sodium-chloride saturated brine developed at the top of the exposed salt diapir. The discharge of brine to the Dolores River is affected by these dissolution features, along with seasonal hydrologic conditions and density-dependent flow between older dense brine and the younger fresh groundwater in the overlying alluvial aquifer. To reduce TDS concentrations in the Dolores River through the Paradox Valley, the Bureau of Reclamation has pumped brine from a series of shallow wells adjacent to the river since July 1996. The pumped brine is collected and piped to a deep disposal well where it is injected into the Mississippian Leadville Limestone at a depth of about 4,570-meters below land surface. The pumping and injection operation is collectively known as the Paradox Valley Unit (PVU), and by 2015, the PVU had substantially reduced TDS concentrations in the Dolores River by about 70 percent. Since 2019, injection-pressure limits and related seismic activity have constrained deep-well injection and thus brine pumping at the PVU. In cooperation with the Bureau of Reclamation, the U.S. Geological Survey developed a MODFLOW-6 three-dimensional, variable-density groundwater flow and TDS transport model of the Paradox Valley to evaluate the effects of PVU pumping operations on brine discharge to the Dolores River and to guide additional research. The finite-difference model grid consists of 76 rows and 48 columns oriented from northwest to southeast in alignment with valley topography and groundwater-flow directions in the near-surface freshwater alluvial aquifer. A 7-layer hydrogeologic framework was developed from existing datasets to represent the alluvial aquifer, cap rock, collapse breccia, and groundwater flow and TDS transport from the underlying Paradox Formation salt to the Dolores River. The model represents a 33-year transient calibration period from 1987 through 2020 that includes pre-PVU conditions from 1987 through June 1996 and post-PVU conditions from July 1996 through 2020. A 1,000-year simulation of groundwater flow and coupled TDS transport computed the initial conditions for the subsequent 33-year transient simulation. Observations of precipitation, streamflow, evaporation, agricultural land use, and PVU brine pumping rates were used to specify appropriate boundary conditions to the model representing time-varying recharge, tributary streamflow, groundwater underflow, evapotranspiration (ET), and PVU pumping. Values for average monthly streamflow and TDS concentration at the upstream streamgage, the Dolores River at Bedrock (USGS streamgage 09169500), were specified as model input where the Dolores River enters Paradox Valley. Observed pumping from the PVU, water levels and TDS concentrations in groundwater, and streamflow and estimated TDS concentrations at the downstream streamgage, the Dolores River near Bedrock (USGS streamgage 09171100), were calibration targets that constrained the manual calibration of model parameters representing aquifer hydraulic conductivity, storage, streambed conductance, recharge, and (ET). Two primary model-calibration targets were the match between observed and simulated TDS mass flux from PVU pumping wells and the match between estimated and simulated TDS mass flux to the Dolores River. The simulated TDS mass withdrawn by pumping wells is calculated by the model as the product of the assigned pumping rate and simulated groundwater TDS concentrations. Because actual pumping rates were assigned as simulated values, the total simulated PVU pumping for the 33-year calibration is within 0.5 percent of the observed values. However, simulated concentrations and thus mass flux of TDS withdrawn by the PVU pumping wells were consistently about 26 percent less than observed values for all the simulated time periods (33-year simulation, pre-PVU, and post-PVU). The representation of brine inflow was explored through additional modeling to evaluate the effect of the simulated brine source on groundwater TDS concentrations. Results indicated that a saturated-salt constant-flux brine source best replicated the magnitude and transient pattern observed for TDS mass flux from PVU pumping wells. The simulated TDS mass flux to the Dolores River is compared to estimates based on observed streamflow and specific conductance (SC) data for the downstream streamgage. The calibrated model provided a close fit of simulated to measured streamflow at the downstream streamgage, and the calibrated model fit to estimated TDS concentrations at the downstream streamgage was reasonable. The greatest differences between simulated and estimated values occurred during drought periods from June 2000 to March 2003, May 2012 to June 2013, and October 2013 to October 2014, when simulated TDS concentrations in the river were greater than estimated concentrations. In general, simulated TDS mass flux to the river for the pre-PVU period is in good agreement with estimated values (2-percent difference), but the model overestimated TDS mass flux to the river by about 41 percent during the post-PVU period. The model uncertainty with respect to TDS mass flux to the river indicates other processes or model parameters not well represented by the model are affecting the system, especially during drought. During model calibration, the most sensitive parameters were identified as vertical hydraulic conductivity of the alluvial aquifer, conductance of the Dolores River streambed, ET extinction depth and rate, and recharge rate. Five 5-year scenarios of conditions for 2021–25 were simulated to assist evaluation of alternative strategies to manage the discharge of brine into the Dolores River. The first scenario simulates no PVU pumping and serves as a base case for comparison to the other scenarios. Two scenarios simulate the effects of varying withdrawal timing at an annual rate about one-third less than during 2010 through 2018. During high-flow spring snowmelt runoff periods when brine discharge is naturally minimized, PVU pumping does not substantially affect salinity in the Dolores River, and comparison of these two scenarios indicates that scheduling brine withdrawals during times of low river stage is nearly as effective at reducing TDS mass flux to the river as pumping brine year-round. Cessation of pumping during periods of high river stage may be advantageous for system maintenance, brine injection, and seismic-risk reduction. The fourth scenario tested the effect of reducing irrigation-return flow on brine discharge and predicted a slight reduction of TDS mass flux to the Dolores River, but not as great a reduction as that of using the PVU to remove brine. The fifth scenario simulated 5 years of drought conditions without PVU pumping and indicates brine discharge during drought about 15 percent greater than during average hydrologic conditions. Results from scenario 5 are consistent with the calibrated model results and indicate that aquifer properties and ET processes and parameters may be affecting simulation results during drought. The Paradox Valley groundwater model provides a reasonable overall match to observed conditions in the Dolores River. The model is useful for evaluating relative differences between brine management scenarios to inform PVU operational decisions and to identify gaps in data and process understanding. Representation of the brine source, hydraulic-conductivity parameters, and recharge and ET processes were identified as potential areas for additional field and modeling research. Additional research in the Paradox Valley might include field-data collection that provides additional information on the hydrogeologic framework, groundwater levels, groundwater TDS concentrations, stream characteristics, and aquifer properties. Additional modeling efforts could benefit from applying advanced tools for model development, calibration, and visualization including parameter-estimation and sensitivity analysis. Statistical evaluation of known model uncertainties such as hydraulic conductivity, streambed conductance, representations of the brine source, recharge, and ET could improve the match between simulated and estimated TDS mass flux from PVU pumping wells and to the Dolores River further informing model predictions and system understanding for the Paradox Valley.

Colorado↗
USGS2019

Controls on spatial and temporal variations of brine discharge to the Dolores River in the Paradox Valley, Colorado, 2016–18

The Paradox Valley in southwestern Colorado is a collapsed anticline formed by movement of the salt-rich Paradox Formation at the core of the anticline. The salinity of the Dolores River, a tributary of the Colorado River, increases substantially as it crosses the valley because of discharge of brine-rich groundwater derived from the underlying salts. Although the brine is naturally occurring, it increases the salinity of the Colorado River, which is a major concern to downstream agricultural, municipal, and industrial water users. The U.S. Geological Survey in cooperation with the Bureau of Reclamation conducted a study to improve the characterization of processes controlling spatial and temporal variations in brine discharge to the Dolores River. For the study, three geophysical surveys were conducted in March, May, and September 2017, and water levels were monitored in selected ponds and groundwater wells from November 2016 to May 2018. The study also utilized streamflow and specific conductance data from two U.S. Geological Survey streamflow-gaging stations on the Dolores River to estimate salt load to the river. River-based continuous resistivity profiling and frequency domain electromagnetic induction surveys made during low-flow conditions indicated a zone of brine-rich groundwater close to the riverbed along an approximately 4-kilometer reach of the river. Under high-flow conditions, the brine was depressed as much as 2 meters below the riverbed, and brine discharge to the river was reduced to a minimum. Direct current electrical resistivity surveys show that the freshwater lens overlying the brine is much thicker (up to 10 meters) on the west bank than on the east bank (less than 5 meters). A large low-conductivity anomaly at river distance 6,800 meters was observed in all surveys and may represent a freshwater discharge zone or a losing reach of the river. Filling and draining of the wildlife ponds on the west side of the river had a negligible effect on salt loads in the river during the study period. Groundwater monitoring showed there was active exchange of water between the river and the adjacent alluvial aquifer. When river stage was low, groundwater flowed towards the river, and brine discharge to the river increased. When the river stage was high, the gradient was reversed, and fresh surface water recharged the alluvial aquifer minimizing brine discharge. Most of the salt load to the river occurred during the winter and appeared to be enhanced by diurnal stage fluctuations. A conceptual model of brine discharge to the river is presented at three scales. Groundwater at the regional scale drives dissolution of salt in the Paradox Formation and flow of brine into the base of the alluvial aquifer. Surface water–groundwater interactions at the scale of the alluvial aquifer control brine discharge to the river seasonally and interannually. At the finest scale, diurnal fluctuations in river stage drive exchange of freshwater with saltier pore water in the hyporheic zone, which appears to increase brine discharge to the river during winter.

Colorado↗
USGS2016

Response of selenium concentrations in groundwater to seasonal canal leakage, lower Gunnison River Basin, Colorado, 2013

Selenium is a water-quality concern in the lower Gunnison River Basin because irrigation water interacting with seleniferous soils derived from the Mancos Shale Formation has mobilized selenium and increased its concentrations in surface water. Understanding the occurrence of elevated selenium concentrations in groundwater is necessary because groundwater discharge is an important source of selenium in surface water in the basin. In 2013, the U.S. Geological Survey, in cooperation with the Bureau of Reclamation and the Colorado Water Conservation Board, began a study to understand how changes in groundwater levels attributed to canal leakage affected the concentrations and speciation of dissolved selenium in groundwater. The purpose of this report is to characterize the groundwater adjacent to an unlined leaky canal. Two locations, near the East Canal (W-N1 and W-N2) and farther from the East Canal (W-M1 and W-M2), were selected for nested monitoring well installations. The pressure exerted by changes in canal stage was more readily transferred to the deep groundwater measured in the W-N1 near the canal than the shallow groundwater at the W-N2 well. No definitive relation could be made between canal water-level elevation and water-level elevations in monitoring wells farther from the canal (W-M1 and W-M2). Water flowing through the East Canal before the irrigation season had much higher selenium concentrations (140 micrograms per liter) than water in the canal during the irrigation season (3.02 micrograms per liter). Total selenium concentrations in the monitoring wells near the canal initially increased to 51.8 micrograms per liter in W-N1 and 1.66 micrograms per liter in W-N2. The initial increase in groundwater selenium concentrations presumably resulted from the dissolution of salts in the unsaturated zone by rising groundwater levels associated with canal leakage. The subsequent decrease in total selenium concentrations resulted from a combination of dilution by canal leakage and selenium reduction processes. Total selenium concentrations in monitoring wells located farther from the canal were not directly affected by canal leakage. Selenite/total selenium mass ratios in the East Canal samples ranged from about 0.02 to 0.13, indicating that about 2 to 13 percent of the total selenium in canal samples was composed of selenite. The increase in total selenium at W-N1 from before the irrigation season to the early irrigation season was accompanied by a decrease in the percentage of selenite from about 10 to 1 percent, indicating that selenate was added to the groundwater. A nitrate pulse occurred with the selenate pulse in W-N1 at the beginning of the irrigation season but apparently dissipated to a low enough concentration during the irrigation season to allow for selenate reduction to occur, as indicated by the relatively high percentages of selenite in W-N1 during the late irrigation season. W-N2 generally contained higher percentages of selenite than W-N1. Percentages of selenite in W-M1 did not change in response to filling the canal and generally composed less than 1 percent of the total selenium in that well. The predominance of selenate in W-M1, and apparent lack of selenate reduction, cannot be explained by a lack of anoxic conditions in the groundwater because all the available dissolved-oxygen data indicate that concentrations were less than 0.5 milligrams per liter. The most likely explanation for the lack of selenate reduction in W-M1 is that the exceptionally high concentrations of nitrate in the groundwater (about 340 to 390 milligrams per liter as nitrogen) inhibited selenate reduction. These high nitrate concentrations presumably come from the Mancos Shale and its weathering products because there was no evidence for a human source of nitrate at the lower Gunnison River Basin wetland. The high concentrations of selenate in W-M1 may persist and eventually discharge to surface water unless nitrate concentrations are reduced to low enough levels to permit substantial selenate reduction to occur. Well W-M2 contained relatively low concentrations of total selenium and high percentages of selenite before and at the onset of the irrigation season. An increase in total selenium concentration associated with a drying and wetting period later in the summer was accompanied by a decrease in the percentage of selenite to near 0 percent, indicating that selenate was added to the groundwater. This pattern is consistent with the examples of increasing concentrations of total selenium in the other wells and presumably resulted from the dissolution of selenate-bearing salts in the unsaturated zone by rising water levels in W-M2.

Colorado↗
USGS1992

Geochemical effects of deep-well injection of the Paradox Valley brine into Paleozoic carbonate rocks, Colorado, U.S.A.

Brine seepage into the Dolores River from ground water in Paradox Valley, Colorado constitutes a major source of salt to the Colorado River. Plants are enderway to remove this source of salt by drawing down the Paradox Valley brine (PVB) and forcibly injecting it into a deep disposal well (4.8 km). Experiments were conducted to determine the effects of deep-well injection of PVB. The results show that PVB is near saturation with anhydrite at 25°C, and that heating results in anhydrite precipitation. The amount and the rate at which anhydrite forms is temperature, pressure, and substrate dependent. Paradox Valley brine heated in the presence of Precambrian rocks from the drill core produces the same amount of anhydrite as PVB heated alone, but at a greatly accelerated rate. A 30% dilution of PVB with Dolores River water completely eliminates anhydrite precipitation when the fluid is heated with the Precambrian rocks. Interaction of PVB and Leadville Limestone is characterized by dolomitization of calcite by brine Mg which releases Ca to solution. This added Ca reacts with SO 4 to form increased amounts of anhydrite. A 20% dilution of PVB by Dolores River water has no effect on dolomitization and reduces the amount of anhydrite only slightly. A 65% dilution of PVB by Dolores River water still does not prevent dolomitization but does suppress anhydrite formation. Computer modeling of PVB by programs utilizing the Pitzer ion-interaction parameters is in general agreement with the experimental results. Ion-activity products calculated by both SOLMINEQ and PHRQPITZ are close to equilibrium with both anhydrite and dolomite whenever these phases are present experimentally, although the calculations over-estimate by a factor of 2 the degree of saturation. Some discrepancies in the calculated results between the two programs are due largely to differences in mineral solubility data.

Colorado↗
USGS1958

Exploration for uranium-vanadium deposits by the U.S. Geological Survey in the Club Mesa area, Uravan district, Montrose County, Colorado

The Club Mesa area is in the western part of the Uravan district, Montrose County, Colo.; it covers about 6 square miles in Tps. 47 and 48 N., R. 17 W., New Mexico principal meridian. (See index map.) The area is immediately west of Uravan, Colo., and is bounded approximately by the San Miguel River to the north and northeast, the Dolores River to the northwest, Saucer Basin to the southwest, and Hieroglyphic Canyon to the southeast. Club Mesa is one of the most productive areas for uranium-vanadium ore in southwestern Colorago. The average grade of this ore has ranged from about 0.25 to 1.50 percent U 3 O 8 and 1.5 to 5.0 percent V 2 O 5 .

Colorado↗
USGS1957

Distribution of elements in the Salt Wash member of the Morrison Formation in the Jo Dandy area, Montrose County, Colorado

A study of the distribution of elements in the Salt Wash member of the Morrison formation of Jurassic age from samples taken in the Jo Dandy area, Montrose County, Colo., was made to determine average chemical composition of mudstone and sandstone and to determine the magnitude of variations in concentrations of elements within similar rock types. Analytical data were obtained by semiquantitative spectrographic and radiometric methods. Results of the study show that variations in concentrations of about 20 elements commonly detected by semiquantititive spectrographic analyses of sedimentary rocks are small for a specific rock type; therefore, considerable confidence may be placed upon the average chemical appears to be no significant relation between chemical composition of mudstone or sandstone and distance from known uranium-vanadium ore or mineralization rock. Mudstone generally contains greater concentrations of the elements studied than sandstone. The chemical composition of red mudstone is similar to the chemical composition of green mudstone except that red mudstone was found to contain almost twice as much calcium as green mudstone in the Jo Dandy area. Samples of the unoxidized sandstone from the Jo Dandy area contain about twice as much calcium, three times as much strontium, but only about one-half as much as zirconium as oxidized sandstone; except for these elements the chemical compositions of both categories of sandstone are similar. Samples of sandstone of the Salt Wash member in the Jo Dandy area contain more potassium, magnesium, vanadium, and nickel than “average sandstone” of the Salt Wash member. The distribution of bismuth in rocks of the Jo Dandy area suggests that bismuth and perhaps part of the potassium and magnesium found in rocks of the Salk Wash member were either derived from solutions which ascended from the underlying salt- and gypsum-bearing Paradox member that was incorporated with rocks of the Salt Wash during sedimentation.

Colorado↗
USGS1956

Duttonite, a new quadrivalent vanadium oxide from the Peanut mine, Montrose County, Colorado

Duttonite, a new quadrivalent vanadium oxide from the Peanut mine, Montrose County, Colo., has the formula VO(OH) 2 . The mineral occurs as crusts and coatings of pale-brown transparent platy crystals, as one of the first oxidation products of montroseite ore. It is associated with melanovanadite and abundant crystals of hexagonal native selenium. Duttonite is biaxial positive, 2V is about 60°, dispersion is r < v , moderate; X = a , pale pinkish brown; Y = c , pale yellow-brown; Z = b , pale brown; α = 1.810 ± 0.003, β = 1.900 ± 0.003, γ > 2.01. The hardness is about 2.5; the calculated specific gravity is 3.24. The chemical analysis shows, in percent: V 2 o 3 2.6, V 2 O 4 75.3, FeO 0.4, H 2 O 18.1, insoluble 4.2, total 100.6. Duttonite is monoclinic, a o = 8.80 ± 0.02A, b o - 3.95 ± 0.01A, c o - 5.96 ± 0.02A, β = 90°40 1 ± 5 1 . The space group is I 2/ c , ( C 6 2 h ); the cell contents are 4[VO(OH) 2 ]. The crystals are strongly pseudo-orthorhombic, and the structure departs only slightly from the space group Imcm . Duttonite is named for Captain Clarence Edward Dutton (1841-1912). A detailed study of the geology, geochemistry, and mineralogy of the vanadium-uranium ore at the Peanut mine, Montrose County, Colo., was begun early in 1954 by Carl H. Roach of the U. S. Geological Survey. A number of rare and new minerals were found in the ore and the study of these samples was undertaken by Mary E. Thompson. Duttonite is the first new vanadium mineral to be described from the Peanut mine. It is named for Captain Clarence Edward Dutton (1841-1912), who was one of the first geologists to work in the Colorado Plateau region and who was a member of the U. s. Geological Survey from 1879-91. We are indebted to the following members of the Geological Surbey: K. E. Valentine for spectrographic analyses of duttonite, and M. E. Mrose and H. T. Evans, Jr., for measurement of the unit cell constants. This work is part of a program being conducted by the U. S. Geological Survey on behalf of the Division of Raw Materials of the U. S. Atomic Energy Commission.

Colorado↗
USGS1955

Carnotite resources of San Miguel bench, Montrose County, Colorado

San Miguel bench includes about 4 square miles in the southern part of T. 48 N., R. 17 W., New Mexico principal meridian, Montrose County, Colorado. Production of carnotite ore from the area has been about 15,000 short tons having an estimated average grade of 0.31 percent U 3 O 8 and 1.6 percent V 2 O 5 . Nearly all of the carnotite deposits occur in a single continuous sandstone bed near the top of the Salt Wash member of the Jurassic Morrison formation. These deposits consist chiefly of sandstone impregnated with uranium- and vanadium-bearing minerals. They are irregular tabular-shaped masses ranging in size from a few short tons to 30,000 short tons or more of minable carnotite ore. During the period November 27, 1951, to April 17, 1953, the U.S. Geological Survey drilled 309 holes totaling 92,194 feet on the San Miguel bench. Reserves total about 43,000 short tons of material 1 foot or more thick and contain 0.10 percent or More U 3 O 8 or 1.0 percent or more V 2 O 5 . Of these reserves 3,300 short tons occur in private land. These reserves are in ten deposits found by Geological Survey drilling. Potential reserves (reserves based on geologic evidence only) are predicted to total about 15,000 short tons, averaging 0.30 percent U 3 O 8 and 1.6 percent V 2 O 5 . No additional drilling in the San Miguel bench is planned by the Geological Survey. Some drilling by private enterprise is recommended.

Colorado↗
USGS1954

Exploration for uranium deposits in the Atkinson Mesa area, Montrose County, Colorado

The U.S. Geological Survey explored the Atkinson Mesa area for uranium- and vanadium-bearing deposits from July 2, 1951, to June 18, 1953, with 397 diamond-drill holes that totaled 261,251 feet. Sedimentary rocks of Mesozoic age are exposed in the Atkinson Mesa area. They are: the Brushy Basin member of the Upper Jurassic Morrison formation, the Lower Cretaceous Burro Canyon formation, and the Upper and Lower Cretaceous Dakota sandstone. All of the large uranium-vanadium deposits discovered by Geological Survey drilling are in a series of sandstone lenses in the upper part of the Salt Wash member of the Jurassic Morrison formation. The deposits are mainly tabular and blanket-like, but some elongate pod-shaped masses, locally called "rolls" may be present. The mineralized material consists of sandstone impregnated with a uranium mineral which is probably coffinite, spme carnotite, and vanadium minerals, thought to be mainly corvusite and montroseite. In addition,, some mudstone and carbonaceous material is similarly impregnated. Near masses of mineralized material the sandstone is light gray or light brown, is generally over 40 feet thick, and usually contains some carbonaceous material and abundant disseminated pyrite or limonite stain. Similarly, the mudstone in contact with the ore-bearing sandstone near bodies of mineralized rock is commonly blue gray, as compared to its dominant red color away from ore deposits. Presence and degree of these features are useful guides in exploring for new deposits.

Colorado↗
USGS1954

Exploration for uranium deposits in the Spring Creek Mesa area, Montrose County, Colorado

The U.S. Geological Survey explored the Spring Creek Mesa area from July 11, 1951, to August 14, 1953. During that period, 280 diamond-drill holes were completed for a total of 180,287 feet. Sedimentary rocks of Mesozoic age are exposed in and adjacent to the Spring Creek Mesa area. These rocks consist of, from oldest to youngest: the Upper Jurassic Morrison formation, the Lower Cretaceous Burro Canyon formation, and the Upper Cretaceous Dakota formation. The Morrison formation consists of two members in the Spring Creek Mesa area: the lower is the Salt Wash member and the upper is the Brusby Basin member. All of the large uranium-bearing deposits discovered by the Geological Survey drilling in the Spring Creek Mesa area are in a series of coalescing sandstone lenses in the uppermost part of the Salt Wash member of the Morrison formation. Most of the ore deposits are believed to be irregular tabular or lens-shaped masses and probably lie parallel to the bedding, although in detail, they may crosscut the bedding. Also, ore deposits that take the form of narrow elongate concretionary-like structures, locally called “rolls”, may be present in the Spring Creek Mesa area. The mineralized material consists mostly of sandstone which has been selectively impregnated and in part replaced by uranium and vanadium minerals. Also, rich concentrations of uranium and vanadium are commonly associated with thin mudstone seams, beds of mudstone pebbles, and carbonaceous material of various types. Two suites of ore minerals are present in the ore deposits - - an oxidized suite of secondary uranium and vanadium minerals and a relatively unoxidized suite of “primary” uranium and vanadium minerals. The following geologic criteria are useful as guides to ore in the Spring Creek Mesa area: 1. Large ore deposits generally occur where the “ore-bearing sandstone” is more than 40 feet thick. 2. The color of the mudstone associated with the “ore-bearing sandstone” in the vicinity of large ore deposits is commonly gray instead of the usual red. 3. The “ore-bearing sandstone” is normally a light red, but in the vicinity of oxidized ore deposits it is light brown and in the vicinity of relatively unoxidized ore deposits it is gray. 4. The “ore-bearing sandstone” in the vicinity of relatively unoxidized ore deposits commonly contains sparse to abundant disseminated pyrite. In the vicinity of oxidized deposits it commonly contains abundant limonite spots and widespread limonite staining.

Colorado↗
USGS1954

Geology of the Paradox quadrangle, Montrose county, Colorado

The Paradox quadrangle is one of eighteen 7 1/2-minute quadrangles covering the principal carnotite-producing area of southwestern Colorado. The geology of these quadrangles was mapped by the U.S. Geological Survey for the Atomic Energy Commission as part of a comprehensive study of carnotite deposits. The rocks exposed in the eighteen quadrangles consist of crystalline rocks of pre-Cambrian age and sedimentary rocks that range in age from late Paleozoic to Quaternary. Over much of the area the sedimentary rocks are flat lying, but in places the rocks are disrupted by high-angle faults, and northwest-trending folds. Conspicuous among the folds are large anticlines having cores of intrusive salt and gypsum. Most of the carnotite deposits are confined to the Salt Wash sandstone member of the Jurassic Morrison formation, Within this sandstone, most of the deposits are spottily distributed through an arcuate zone known as the "Uravan Mineral Belt". Individual deposits range in size from irregular masses containing only a few tons of ore to large, tabular masses containing thousands of tons. The ore consists largely of sandstone selectively impregnated and in part replaced by uranium and vanadium minerals. Most of the deposits appear to be related to certain sedimentary structures in sandstones of favorable composition.

Colorado↗
USGS1954

Geology of the Roc Creek quadrangle, Montrose county, Colorado

The Roc Creek quadrangle is one of eighteen 7 1/2-minute quadrangles covering the principal carnotite-producing area of southwestern Colorado. The geology of these quadrangles was mapped by the U.S. Geological Survey for the U.S. Atomic Energy Commission as part of a comprehensive study of carnotite deposits. The rocks exposed in the eighteen quadrangles consist of crystalline rocks of pre-Cambrian age and sedimentary rocks that range in age from late Paleozoic to Quaternary. Over much of the area the sedimentary rocks are flat lying, but in places the rocks are disrupted by high-angle faults and northwest-trending folds. Conspicuous among the folds are large anticlines having cores of intrusive salt and gypsum. Most of the carnotite deposits are confined to the Salt Wash sandstone member of the Jurassic Morrison formation. Within this sandstone, most of the deposits are spottily distributed through an arcuate zone known as the "Uravan mineral belt". Individual deposits range in size from irregular masses containing only a few tons of ore to large, tabular masses containing many thousands of tons. The ore consists largely of sandstone selectively impregnated and in part replaced by uranium and vanadium minerals. Most of the deposits appear to be related to certain sedimentary in sandstones of favorable composition.

Colorado↗