Preliminary geologic map of the Whitney Pocket 7.5-minute quadrangle, Clark County, Nevada
No abstract available.
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Geology topics
Research about Nevada
Source-linked reports with geographic coverage including Nevada.
Water resources data, Nevada, water year 1992
This report for Nevada is one of a series of annual reports that document hydrologic data gathered from the U.S. Geological Survey's surface-water and ground-water data-collection networks in each State, Puerto Rico, and the Trust Territories. These records of streams, canals, drains and springs, lakes and reservoirs, and observation wells provide the hydrologic information needed by State, local, and Federal agencies and the private sector for developing and managing our Nation's land and water resources.
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Preliminary hydrogeologic assessment of boreholes UE-25c #1, UE-25c #2, and UE-25c #3, Yucca Mountain, Nye County, Nevada
Boreholes UE-25c #1, UE-25c #2, and UE-25c #3 (collectively called the C-holes) each were drilled to a depth of 914.4 meters at Yucca Mountain, on the Nevada Test Site, in 1983 and 1984 for the purpose of conducting aquifer and tracer tests. Each of the boreholes penetrated the Paintbrush Tuff and the tuffs and lavas of Calico Hills and bottomed in the Crater Flat Tuff. The geologic units penetrated consist of devitrified to vitrophyric, nonwelded to densely welded, ash-flow tuff, tuff breccia, ash-fall tuff, and bedded tuff. Below the water table, which is at an average depth of 401.6 meters below land surface, the rocks are argillic and zeolitic. The geologic units at the C-hole complex strike N. 2° W. and dip 15° to 21° NE. They are cut by several faults, including the Paintbrush Canyon Fault, a prominent normal fault oriented S. 9° W., 52.2° NW. The rocks at the C-hole complex are fractured extensively, with most fractures oriented approximately perpendicular to the direction of regional least horizontal principal stress. In the Crater Flat Tuff and the tuffs and lavas of Calico Hills, fractures strike predominantly between S. 20° E. and S. 20° W. and secondarily between S. 20° E. and S. 60° E. In the Topopah Spring Member of the Paintbrush Tuff, however, southeasterly striking fractures predominate. Most fractures are steeply dipping, although shallowly dipping fractures occur in nonwelded and reworked tuff intervals of the Crater Flat Tuff. Mineral-filled fractures are common in the tuff breccia zone of the Tram Member of the Crater Flat Tuff, and, also, in the welded tuff zone of the Bullfrog Member of the Crater Flat Tuff. The fracture density of geologic units in the C-holes was estimated to range from 1.3 to 7.6 fractures per cubic meter. Most of these estimates appear to be the correct order of magnitude when compared to transect measurements and core data from other boreholes 1.3 orders of magnitude too low. Geophysical data and laboratory analyses were used to determine matrix hydrologic properties of the tuffs and lavas of Calico Hills and the Crater Flat Tuff in the C-holes. The porosity ranged from 12 to 43 percent and, on the average, was larger in nonwelded to partially welded, ash-flow tuff, ashfall tuff, and reworked tuff than in moderately to densely welded ash-flow tuff. The pore-scale horizontal permeability of nine samples ranged from 5.7x10 -3 to 2.9 millidarcies, and the pore-scale vertical permeability of these samples ranged from 3.7x10 -3 to 1.5 millidarcies. Ratios of pore-scale horizontal to vertical permeability generally ranged from 0.7 to 2. Although the number of samples was small, values of pore-scale permeability determined were consistent with samples from other boreholes at Yucca Mountain. The specific storage of nonwelded to partially welded ash-flow tuff, ash-fall tuff, and reworked tuff was estimated from porosity and elasticity to be 2x10 -6 per meter, twice the specific storage of moderately to densely welded ash-flow tuff and tuff breccia. The storativity of geologic units, based on their average thickness (corrected for bedding dip) and specific storage, was estimated to range from 1x10 -5 to 2x10 -4 .
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Water-level changes and directions of ground-water flow in the shallow aquifer, Fallon area, Churchill County, Nevada
The Truckee-Carson-Pyramid Lake Water Rights Settlement Act of 1990 directed the U.S. Fish and Wildlife Service to acquire water for wetland areas in the Carson Desert. The public is concerned that this acquisition of water rights and delivery of the water directly to the wetland areas would reduce recharge to the shallow ground water in the Fallen area and cause domestic wells to go dry. In January 1992, the U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service, began a study of the shallow ground-water system in the Fallen area in Churchill County, Nevada. A network of 126 wells in the study area was monitored. Water levels were measured in wells before, during, and after the 1992 irrigation season. Water levels in 24 of the wells were measured every 2 weeks beginning in January 1992. Many wells in the network had been monitored during earlier investigations, allowing determination of changes in water level during the last 15 years. Newlands Project water deliveries to the study area began soon after the turn of the century. Since then, water levels have risen more than 15 feet across much of the study area. Water lost from unlined irrigation canals caused Big Soda Lake to rise nearly 60 feet; ground-water levels near the lake have risen 30 to 40 feet. The depth to water in most irrigated areas is now less than 10 feet. The net change in water level over the 15- year period between early 1977 and early 1992 has been small in spite of 6 years of drought. Water levels in most wells for which data are available declined less than 1 foot. Some wells in the south and north parts of the study area showed rises in water level during this period. The lake level in Big Soda Lake declined slightly more than 3 feet between 1971 and 1992. Between January and November 1992, water levels in most wells declined, generally less than 2 feet. The maximum measured decline over this period was 2.68 feet in a well in the Stillwater area. Between April and July, however, water levels rose in irrigated areas typically 1 to 2 feet. When the upper reaches of the T-Line Canal were lined in 1983-84 to reduce seepage to ground water, the water levels declined from 7.5 feet to more than 10 feet in wells near the canal. Water levels in a well near an unlined reach of the canal are essentially unchanged from what they were before the upper reaches of the canal were lined. The altitude of the water table ranges from 4,025 feet above sea level 11 miles west of Fallon to 3,865 feet in the Stillwater Marsh area. The hydraulic gradient is small and ranges from about 6 to 9 feet per mile from west to east. The principal recharge area is in the west part of the study area along the Carson River and major canals. Ground water flows eastward and divides; some flow goes northeast toward the Carson Sink and Stillwater areas, and some goes southeast to Carson Lake. Carson Lake is a regional discharge area. Future declines in water level can be expected in irrigated areas if canals are lined or if the amount of water carried in the canals is greatly reduced. The amount and rate of water-level change at a particular site will depend on sitespecific geohydrologic factors. The effect of these water-level changes at a specific shallow well will depend on the depth and condition of the well.
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Three-dimensional lithostratigraphic model at Yucca Mountain, Nevada: A framework for fluid transport modeling and engineering design
A three-dimensional lithostratigraphic model of the central block of Yucca Mountain, Nevada, illustrates how some activities can serve both site characterization and design and construction of the Exploratory Studies Facility (ESF). Site-characterization activities supported by this model include characterizing the three-dimensional geometry of lithologic units and faults, and providing boundary conditions for geostatistical models and site-scale fluid flow modeling. This model supports the conceptual design as well as construction efforts for the proposed ramps of the ESF and potential high-level nuclear waste repository.
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Toxicity of trace element and salinity mixtures to striped bass ( Morone saxatilis ) and Daphnia magna
Acute toxicity tests with reconstituted water were conducted to investigate the relationship between water hardness, salinity, and a mixture of trace elements found in irrigation drain waters entering Stillwater Wildlife Management Area (SWMA), near Fallon, Nevada. The SWMA has been the site of many fish kills in recent years, and previous toxicity studies indicated that one drain water, Pintail Bay, was acutely toxic to organisms acclimated or cultured in fresh water or salt water. This toxicity could reflect both the ionic composition of this saline water and the presence of trace elements. The lowest water salinity tested with Daphnia magna was near the upper salinity tolerance of these organisms; therefore, we were unable to differentiate between the toxic effects of ion composition and those of trace elements. In toxicity tests conducted with striped bass ( Morone saxatilis ), we found that the extent to which salinity was lethal to striped bass depended on the ion composition of that salinity. Survival of striped bass increased as hardness increased. In addition, a trace element mixture was toxic to striped bass, even though the concentrations of individual elements were below expected acutely lethal concentrations. Although salinity is an important water quality characteristic, the ionic composition of the water must be considered when one assesses the hazard of irrigation drain waters to aquatic organisms.
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Morphology and genesis of carbonate soils on the Kyle Canyon fan, Nevada, U.S.A.
The physical and chemical properties of soils formed in an arid climate on calcareous alluvium of the Kyle Canyon alluvial fan, southern Nevada, were studied in order to infer the rates and relative importance of various soil-forming processes. These studies included field and microscopic observations and analyses of thin sections, major oxides, extractable iron, and clay minerals. The results are interpreted to reflect five major pedogenic processes: (1) The calcic horizons and calcretes of Kyle Canyon soils form by precipitation of CaCO 3 , derived from eolian dust and alluvium, as clast coats, matrix cement, and massive layers. (2) The A and uppermost B horizons are essentially dust-derived, for they contain large amounts of detrital material not present in the alluvial parent material, and their major-oxide content is similar to that of modern dust. (3) Clay particles are translocated from A into B horizons. (4) Iron-bearing minerals in the near-surface B horizons are slowly oxidized. (5) Carbonate and aluminosilicate grains are both displaced and replaced by pedogenic CaCO 3 ; the silica released by replacement of aluminosilicates may be locally precipitated as amorphous or opaline silica and (or) incorporated into newly formed palygorskite and sepiolite. Rates of soil development at Kyle Canyon are approximate due to uncertainties in age estimates. Some soil field properties change at rates that are similar to rates for soils formed in rhyolitic parent material near Mercury, Nevada. The rate of accumulation of CaCO 3 (3–5 g m −2 yr −1 ) at Kyle Canyon is an order of magnitude faster than that near Mercury, but is comparable to rates calculated for soils in southern New Mexico and Utah.
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Two-temperature method for measuring emissivity
Spectral emissivity can be uniquely determined from radiance measurements if the object can be observed at two different temperatures. The advantage of this approach is that the spectral emissivity is determined without a priori assumptions about spectral shape. Because the different temperatures are obtained by observing the scene at two times in the diurnal cycle (optimally after midday and midnight), the method assumes that emissivity is temporally invariant. This is valid for rocks and dry soils, not well established for vegetation, and not true when changes in soil moisture occur between the measurements. Accurate image registration and satisfactory signal:noise are critical factors that limit extensive use of this method.
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Consumption of atmospheric methane by desert soils
Atmospheric concentrations of methane, a greenhouse gas, are increasing at a rate of about 1% yr -1 (refs 1–4). Oxidation by methylotrophic bacteria in soil is the largest terrestrial sink for atmospheric CH 4 , and is estimated to consume about 30 x 10 12 g CH 4 yr -1 (refs 4–6). Spatial and temporal variability in the rate of soil CH 4 consumption are incompletely understood 6–19 , as are the apparent inhibitory 12,13,18 or enhancing 20 effects of changes in land use. Dry deserts, which constitute 20% of total land surface, are not currently included in global soil uptake estimates. Here we describe measurements of the rate of uptake of atmospheric CH 4 by undisturbed desert soils. We observed rates as great as 4.38 mg CH 4 m -2 day -1 ; 50% of the measured rates were between 0.24 and 0.92 mg CH 4 m -2 d -1 . Uptake of CH 4 by desert soil is enhanced by rainfall after an initial soil-drainage period—opposite to the response of temperate forest soils 12 . Methane is consumed to a depth of about 2 m, allowing for deep removal of atmospheric CH 4 if near-surface conditions are unfavourable for consumption. On the basis of an annual average CH 4 consumption rate of 0.66 mg CH 4 m -2 d -1 , we estimate that the global CH 4 sink term needs to be increased by about 7 x 10 12 g yr -1 to account for the contribution of desert soils.
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Continuous 500,000-year climate record from vein calcite in Devils Hole, Nevada
Oxygen-18 (δ 18 O) variations in a 36-centimeter-long core (DH-11) of vein calcite from Devils Hole, Nevada, yield an uninterrupted 500,000-year paleotemperature record that closely mimics all major features in the Vostok (Antarctica) paleotemperature and marine δ 18 O ice-volume records. The chronology for this continental record is based on 21 replicated mass-spectrometric uranium-series dates. Between the middle and latest Pleistocene, the duration of the last four glacial cycles recorded in the calcite increased from 80,000 to 130,000 years; this variation suggests that major climate changes were aperiodic. The timing of specific climatic events indicates that orbitally controlled variations in solar insolation were not a major factor in triggering deglaciations. Interglacial climates lasted about 20,000 years. Collectively, these observations are inconsistent with the Milankovitch hypothesis for the origin of the Pleistocene glacial cycles but they are consistent with the thesis that these cycles originated from internal nonlinear feedbacks within the atmosphere-ice sheet-ocean system.
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Mass-spectrometric 230Th-234U-238U dating of the Devils Hole calcite vein
The Devils Hole calcite vein contains a long-term climatic record, but requires accurate chronologic control for its interpretation. Mass-spectrometric U-series ages for samples from core DH-11 yielded 230 Th ages with precisions ranging from less than 1,000 years (2σ) for samples younger than ∼140 ka (thousands of years ago) to less than 50,000 years for the oldest samples (∼566 ka). The 234 U/ 238 U ages could be determined to a precision of ∼20,000 years for all ages. Calcite accumulated continuously from 566 ka until ∼60 ka at an average rate of 0.7 millimeter per 10 3 years. The precise agreement between replicate analyses and the concordance of the 230 Th/ 238 U and 234 U/ 238 U ages for the oldest samples indicate that the DH-11 samples were closed systems and validate the dating technique in general.
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Paleomagnetic data bearing on the origin of arcuate structures in the French Peak-Massachusetts Mountain area of southern Nevada
The eastern margin of the Yucca Flat basin, in southern Nevada, is bounded by north-northwest-striking tilted fault blocks of the Halfpint Range whose strikes curve as much as 90° clockwise into east-northeast strikes in the French Peak-Massachusetts Mountain (FPMM) area. This pattern of arcuate structures has been attributed to clockwise drag along a postulated northwest-trending, right-lateral shear zone. The flexure model implies that rocks within the FPMM area were rotated strongly clockwise about a vertical axis. Directions of remanent magnetization of the middle Miocene Ammonia Tanks and Rainier Mesa Members of the Timber Mountain Tuff and of the Topopah Spring Member of the Paintbrush Tuff indicate no systematic vertical-axis rotation in the FPMM area and disprove the flexure model. After tilt correction, declinations of 29 site means obtained from the three ash-flow sheets in the FPMM area are not systematically different than declinations of 17 site means from the Halfpint Range or declinations of 16 site means from little-deformed mesa areas to the west. The paleomagnetic data thus indicate that structures in the FPMM area initiated with arcuate trends and were not originally straight elements that were rotated by right-lateral drag. The structures probably formed under the influence of spatially variable stress fields. The FPMM area lies in an accommodation zone between domains of oppositely tilted extensional fault blocks. Interaction between stress fields associated with propagating normal-fault zones may have been responsible for the arcuate structures in the FPMM area.
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A relation among geology, tectonics, and velocity structure, western to central Nevada Basin and Range
In the northwestern to central Nevada Basin and Range, there are correlations between velocity and specific geologic structures of the crust. Mapped range-bounding faults at the surface can be traced to appreciable (10 km) depths based on velocity variations and are consistent with subsurface projections of the faults based on seismic reflection images. The limiting depth of the faults, as indicated by the velocity variations, corresponds to the maximum depth of earthquakes along the seismic profile. Correlations between velocity and the surface geology show that in the upper crust the pre-Cenozoic rocks are underlain by high-velocity (6.0 km/s) rocks, whereas the Tertiary ranges are underlain by lower-velocity (4.0-5.7 km/s) rocks to depths as great as 10 km. Although the Tertiary rocks differ in composition from the Mesozoic rocks, the lower-velocity Tertiary rocks may also be attributed to rock masses which are broken (4.0-5.7 km/s), and the higher-velocity Mesozoic rocks (6.0 km/s) may be attributed to largely unbroken rock masses. The regional seismicity pattern is consistent with this interpretation, as earthquakes are largely confined within or near the base of the low-velocity rocks. These low-velocity, highly fractured rocks are laterally distributed in discrete zones, suggesting that extension is not uniformly distributed but occurs in discrete, highly extended zones. Beneath these highly extended zones, the lower-crustal layers show structural evidence of extension, and velocity measurements suggest that the lowermost crust has been magmatically underplated. The superposition of Tertiary volcanic rocks, highly fractured upper crust, and lower-crustal magmatic underplating suggests that the Tertiary volcanic rocks originated from lower-crustal magmas that migrated to the surface via the highly extended zones. The velocity structure of one of the highly extended zones and the Lahonton Basin resembles that of many continental rifts. The velocity structure beneath central Nevada, however, is much more like normal continental crust. On the basis of isotopic studies, it is concluded that the transition between highly extended crust and more normal crust occurs in the area inferred to be the edge of the North American craton.
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Precipitation estimation in mountainous terrain using multivariate geostatistics. Part I: structural analysis
Values of average annual precipitation (AAP) are desired for hydrologic studies within a watershed containing Yucca Mountain, Nevada, a potential site for a high-level nuclear-waste repository. Reliable values of AAP are not yet available for most areas within this watershed because of a sparsity of precipitation measurements and the need to obtain measurements over a sufficient length of time. To estimate AAP over the entire watershed, historical precipitation data and station elevations were obtained from a network of 62 stations in southern Nevada and southeastern California. Multivariate geostatistics (cokriging) was selected as an estimation method because of a significant (p = 0.05) correlation of r = .75 between the natural log of AAP and station elevation. A sample direct variogram for the transformed variable, TAAP = ln [(AAP) 1000], was fitted with an isotropic, spherical model defined by a small nugget value of 5000, a range of 190 000 ft, and a sill value equal to the sample variance of 163 151. Elevations for 1531 additional locations were obtained from topographic maps to improve the accuracy of cokriged estimates. A sample direct variogram for elevation was fitted with an isotropic model consisting of a nugget value of 5500 and three nested transition structures: a Gaussian structure with a range of 61 000 ft, a spherical structure with a range of 70 000 ft, and a quasi-stationary, linear structure. The use of an isotropic, stationary model for elevation was considered valid within a sliding-neighborhood radius of 120 000 ft. The problem of fitting a positive-definite, nonlinear model of coregionalization to an inconsistent sample cross variogram for TAAP and elevation was solved by a modified use of the Cauchy-Schwarz inequality. A selected cross-variogram model consisted of two nested structures: a Gaussian structure with a range of 61 000 ft and a spherical structure with a range of 190 000 ft. Cross validation was used for model selection and for comparing the geostatistical model with six alternate estimation methods. Multivariate geostatistics provided the best cross-validation results.
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Precipitation estimation in mountainous terrain using multivariate geostatistics. Part II: isohyetal maps
Values of average annual precipitation (AAP) may be important for hydrologic characterization of a potential high-level nuclear-waste repository site at Yucca Mountain, Nevada. Reliable measurements of AAP are sparse in the vicinity of Yucca Mountain, and estimates of AAP were needed for an isohyetal mapping over a 2600-square-mile watershed containing Yucca Mountain. Estimates were obtained with a multivariate geostatistical model developed using AAP and elevation data from a network of 42 precipitation stations in southern Nevada and southeastern California. An additional 1531 elevations were obtained to improve estimation accuracy. Isohyets representing estimates obtained using univariate geostatistics (kriging) defined a smooth and continuous surface. Isohyets representing estimates obtained using multivariate geostatistics (cokriging) defined an irregular surface that more accurately represented expected local orographic influences on AAP. Cokriging results included a maximum estimate within the study area of 335 mm at an elevation of 7400 ft, an average estimate of 157 mm for the study area, and an average estimate of 172 mm at eight locations in the vicinity of the potential repository site. Kriging estimates tended to be lower in comparison because the increased AAP expected for remote mountainous topography was not adequately represented by the available sample. Regression results between cokriging estimates and elevation were similar to regression results between measured AAP and elevation. The position of the cokriging 250-mm isohyet relative to the boundaries of pinyon pine and juniper woodlands provided indirect evidence of improved estimation accuracy because the cokriging result agreed well with investigations by others concerning the relationship between elevation, vegetation, and climate in the Great Basin. Calculated estimation variances were also mapped and compared to evaluate improvements in estimation accuracy. Cokriging estimation variances were reduced by an average of 54% relative to kriging variances within the study area. Cokriging reduced estimation variances at the potential repository site by 55% relative to kriging. The usefulness of an existing network of stations for measuring AAP within the study area was evaluated using cokriging variances, and twenty additional stations were located for the purpose of improving the accuracy of future isohyetal mappings. Using the expanded network of stations, the maximum cokriging estimation variance within the study area was reduced by 78% relative to the existing network, and the average estimation variance was reduced by 52%.
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Mapping thermal maturity in the Chainman shale, near Eureka, Nevada, with Landsat Thematic Mapper images
The purpose of this study was to determine if there is a correlation between measurements of organic matter (OM) maturity and laboratory measurements of visible and near-infrared spectral reflectance, and if Landsat Thematic Mapper (TM) images could be used to map maturity. The maturity of Mississippian Chainman Shale samples collected in east-central Nevada and west-central Utah was determined by using vitrinite reflectance and Rock-Eval pyrolysis. To establish the relations between maturity and spectral reflectance in the visible and near-infrared (VNIR) wavelength region, VNIR reflectance spectra of fresh and weathered whole-rock sample surfaces were measured in the laboratory. The spectra were convolved digitally with the Landsat TM filter band passes to facilitate th analysis, especially the relative sensitivities of individual band passes and ratios of band passes to spectral reflectance variations related to OM maturity. With increasing maturity, overall VNIR diffuse reflectance and mineral-absorption-feature intensities decrease, and the shape of the spectra changes from concave-downward to nearly flat. The spectral shape differences between mature and supermature samples remains distinctive in reflectance spectra of weathered surfaces. TM 4/TM 5 values correspond well to vitrinite reflectance and hydrogen index variations, and therefore this ratio was used to evaluate a TM image of the Eureka, Nevada, area for mapping thermal maturity differences in the Chainman Shale. First, the contribution of vegetation to the TM response was minimized using a linear regression technique, and then a TM 4/TM 5 density-sliced image was produced. Field evaluation of the TM 4/TM 5 density-sliced image shows that all the high values in the Chainman Shale, which correspond to high maturity, are located in the Diamond Mountains; in contrast, Chainman Shale in the northwestern Pancake Range exhibits low to moderate values. These results are consistent with published local maturity determinations. Locally, the presence of limonitic arenaceous exposures and colluvium causes anomalously low TM 4/TM 5 values, but these areas can be identified in TM images because of their diagnostic VNIR reflectance spectra.
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Mesozoic and Tertiary rocks near Elko, Nevada: Evidence for Jurassic to Eocene folding and low-angle faulting
No abstract available.
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