Geology topics
Research about Nevada
Source-linked reports with geographic coverage including Nevada.
Principal facts for gravity stations in the Antelope Valley-Bedell Flat area, west-central Nevada
In April 2000 the U.S. Geological Survey (USGS) established 211 gravity stations in the Antelope Valley and Bedell Flat area of west-central Nevada (see figure 1). The stations were located about 15 miles north of Reno, Nevada, southwest of Dogskin Mountain, and east of Petersen Mountain, concentrated in Antelope Valley and Bedell Flat (figure 2). The ranges in this area primarily consist of normal-faulted Cretaceous granitic rocks, with some volcanic and metavolcanic rocks. The purpose of the survey was to characterize the hydrogeologic framework of Antelope Valley and Bedell Flat in support of future hydrologic investigations. The information developed during this study can be used in groundwater models. Gravity data were collected between latitude 39°37.5' and 40°00' N and longitude 119°37.5' and 120°00' W. The stations were located on the Seven Lakes Mountain, Dogskin Mountain, Granite Peak, Bedell Flat, Fraser Flat, and Reno NE 7.5 minute quadrangles. All data were tied to secondary base station RENO-A located on the campus of the University of Nevada at Reno (UNR) in Reno, Nevada (latitude 39°32.30' N, longitude 119°48.70' W, observed gravity value 979674.69 mGal). The value for observed gravity was calculated by multiple ties to the base station RENO (latitude 39°32.30' N, longitude 119°48.70' W, observed gravity value 979674.65 mGal), also on the UNR campus. The isostatic gravity map (figure 3) includes additional data sets from the following sources: 202 stations from a Geological Survey digital data set (Ponce, 1997), and 126 stations from Thomas C. Carpenter (written commun., 1998).
Regional ground-water evapotranspiration and ground-water budgets, Great Basin, Nevada
PART A: Ground-water evapotranspiration data from five sites in Nevada and seven sites in Owens Valley, California, were used to develop equations for estimating ground-water evapotranspiration as a function of phreatophyte plant cover or as a function of the depth to ground water. Equations are given for estimating mean daily seasonal and annual ground-water evapotranspiration. The equations that estimate ground-water evapotranspiration as a function of plant cover can be used to estimate regional-scale ground-water evapotranspiration using vegetation indices derived from satellite data for areas where the depth to ground water is poorly known. Equations that estimate ground-water evapotranspiration as a function of the depth to ground water can be used where the depth to ground water is known, but for which information on plant cover is lacking. PART B: Previous ground-water studies estimated groundwater evapotranspiration by phreatophytes and bare soil in Nevada on the basis of results of field studies published in 1912 and 1932. More recent studies of evapotranspiration by rangeland phreatophytes, using micrometeorological methods as discussed in Chapter A of this report, provide new data on which to base estimates of ground-water evapotranspiration. An approach correlating ground-water evapotranspiration with plant cover is used in conjunction with a modified soil-adjusted vegetation index derived from Landsat data to develop a method for estimating the magnitude and distribution of ground-water evapotranspiration at a regional scale. Large areas of phreatophytes near Duckwater and Lockes in Railroad Valley are believed to subsist on ground water discharged from nearby regional springs. Ground-water evapotranspiration by the Duckwater phreatophytes of about 11,500 acre-feet estimated by the method described in this report compares well with measured discharge of about 13,500 acre-feet from the springs near Duckwater. Measured discharge from springs near Lockes was about 2,400 acre-feet; estimated ground-water evapotranspiration using the proposed method was about 2,450 acre-feet. PART C: Previous estimates of ground-water budgets in Nevada were based on methods and data that now are more than 60 years old. Newer methods, data, and technologies were used in the present study to estimate ground-water recharge from precipitation and ground-water discharge by evapotranspiration by phreatophytes for 16 contiguous valleys in eastern Nevada. Annual ground-water recharge to these valleys was estimated to be about 855,000 acre-feet and annual ground-water evapotranspiration was estimated to be about 790,000 acrefeet; both are a little more than two times greater than previous estimates. The imbalance of recharge over evapotranspiration represents recharge that either (1) leaves the area as interbasin flow or (2) is derived from precipitation that falls on terrain within the topographic boundary of the study area but contributes to discharge from hydrologic systems that lie outside these topographic limits. A vegetation index derived from Landsat-satellite data was used to estimate phreatophyte plant cover on the floors of the 16 valleys. The estimated phreatophyte plant cover then was used to estimate annual ground-water evapotranspiration. Detailed estimates of summer, winter, and annual ground-water evapotranspiration for areas with different ranges of phreatophyte plant cover were prepared for each valley. The estimated ground-water discharge from 15 valleys, combined with independent estimates of interbasin ground-water flow into or from a valley, were used to calculate the percentage of recharge derived from precipitation within the topographic boundary of each valley. These percentages then were used to estimate ground-water recharge from precipitation within each valley. Ground-water budgets for all 16 valleys were based on the estimated recharge from precipitation and estimated evapotranspiration. Any imba
Quality assurance and analysis of water levels in wells on Pahute Mesa and vicinity, Nevada Test Site, Nye County, Nevada
Periodic and continual water-level data from 1963 to 1998 were compiled and quality assured for 65 observation wells on Pahute Mesa and vicinity, Nye County, Nevada. As part of the quality assurance of all water levels, ancillary data pertinent to computing hydraulic heads in wells were compiled and analyzed. Quality-assured water levels that were not necessarily in error but which did not represent static heads in the regional aquifer system, or required some other qualification, were flagged. Water levels flagged include those recovering from recent pumping or well construction, water levels affected by nuclear tests, and measurements affected by borehole deviations. A cursory examination of about 30 wells with available water-level and down-hole temperature data indicate that water levels in most wells on Pahute Mesa would not be significantly affected by temperature if corrected to 95 degrees Fahrenheit. Wells with large corrections (greater than 10 feet) are those with long water columns (greater than 1,500 feet of water above the assumed point of inflow) in combination with mean water-column temperatures exceeding 105 degrees Fahrenheit. Water-level fluctuations in wells on Pahute Mesa are caused by several factors including infiltration of precipitation, barometric pressure, Earth tides, ground-water pumpage, and seismic events caused by tectonic activity and underground nuclear testing. No observed water-level fluctuations were attributed to a naturally occurring earthquake. The magnitude and duration of changes in water levels caused by nuclear tests are affected by the test size and the distance from a well to the test. Identifying water levels that might be affected by past nuclear tests is difficult because pre-testing water-level data are sparse. Hydrologically significant trends were found in 13 of 25 wells with multiple years of water-level record. The largest change in water levels (1,029 feet in 25 years) occurred in well U-19v PS 1D as a result of the Almendro nuclear test. Likely explanations for trends in most of the wells are either changes in precipitation patterns that affect recharge rates to the ground-water system, pumping effects from water-supply well U-20 WW, or a combination of these two factors.
Water budget estimates for the 14 hydrographic areas in the middle Humboldt River basin, north-central Nevada
Water budgets were developed for the 14 hydrographic areas in the middle Humboldt River Basin of north-central Nevada. The water budgets include estimates of average annual precipitation, runoff, water yield, ground-water recharge and subsurface flow, and evapotranspiration (ET) determined from recently developed or revised methods. Ground-water pumping is not included in the budget estimates. The estimated budgets represent average annual volumes over a 30-year reference period ( 1961-90) and are compared to water budgets developed more than 30 years ago. Annual inflow to the middle Humboldt River basin is about 5 million acre-feet. An estimated 4.6 million is from precipitation in the 14 hydrographic areas and about 350,000 acre-feet is inflow from the Humboldt River. Annual outflow is about 5.1 million acre-feet, of which ET accounts for 4.8 million acre-feet, and outflow of the Humboldt River is about 300,000 acre-feet. Average annual precipitation in the hydrographic areas for 1961-90 ranged from 105 to 128 percent of that for the 1912-63 period. The annual volume ofET in the 14 areas was 102 to almost 134 percent of that previously estimated, although the percentage of annual precipitation lost to ET is similar. About 15 percent of the annual precipitation in mountain-block areas becomes water yield (either ground water or runoff) as compared to previous estimates of 11 percent. On the basis of mass-balance calculations, ground-water recharge on average is about 145 percent of previous estimates.
Near surface infiltration monitoring neutron moisture logging, Yucca Mountain, Nevada
No abstract available.
The Goldfield mining district, Nevada: an acid sulfate bonanza gold deposit
This paper provides an introduction to the geology, ore deposits, and fluid geochemistry of the Goldfield mining district, Esmerelda and Nye Counties, Nevada. Also included is a brief interpretation of mineral maps of the western half of the district which were recently produced from remotely sensed imagery acquired by the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) systems operated by NASA JPL.
Blue tilapia, Orechromis aureus, predation on native fishes of the Muddy River, Nevada
No abstract available
Geologic map of the Lamoille Quadrangle, Elko County, Nevada
A 1:24,000-scale, full-color geologic map of the Lamoille 7.5-minute quadrangle in Elko County, Nevada, with one cross section and descriptions of 17 geologic units.
U-Th-Pb dating of hydrothermal minerals from Carlin-type gold deposits, Nevada- Results and evaluation
No abstract available.
The East Range, northwestern Nevada: A neglected key to the tectonic history of the region
The East Range occupies a strategic position at the western edge of the exposed western facies terrane near the Paleozoic continental margin. There a Cambrian and Ordovician deep-water sequence including the Preble and Valmy Formations is overlain by middle to upper Paleozoic strata that are assigned to three separate stratigraphic sequences on published geologic maps of the range. The three sequences, which include the Havallah sequence, the Inskip Formation, and the Harmony Formation, originally were perceived to be of different ages and lithic composition. The strata assigned to the Havallah are now known to contain conodonts of Late Devonian to Permian ages, and fusulinids of Permian age; those assigned to the Inskip contain conodonts of Early Mississippian and Permian ages and corals of Mississippian age. Strata assigned to the Harmony are undated paleontologically. All three are composed mainly of siliceous deep-water sedimentary deposits. Lower beds of the Havallah and Inskip totalling hundreds of meters in thickness are composed of arkosic sandstone and conglomerate identical to that composing most of the Harmony. The Havallah and Inskip lie disconformably on the quartzitic, middle part of the Valmy Formation. The Harmony lies concordantly on distinctive chert beds at the top of the Valmy Formation. Assuming the latter contact is disconformable rather than a bedding-parallel fault, the East Range displays the stratigraphic bases of all three arkosic map units. The disconformable relation of the Havallah and Inskip to the Valmy Formation indicates elevation of deep-water deposits, subaerial erosion down to Middle Ordovician, and in Late Devonian a return to deep immersion. There is no evidence here of Late Devonian to Early Mississippian folding. Major folds in the East Range must be of Jurassic or younger age because Upper Triassic strata are involved. Evidence of large-scale thrust-faulting is notably scarce. The existence of the Willow Creek thrust shown on published maps of the East Range was based on the mistaken belief that strata below the Valmy Formation are of Triassic age whereas they are actually of Cambrian and earliest Ordovician age.
Implications of celsian in the Ruby Mountains, Elko County, Nevada
The Ba-feldspar celsian [BaAl 2 Si 2 O 8 ] has been found in quartz-skarn-sulfide deposits at the American Beauty and Summit View Mines in the Ruby Mountains, Nevada. The celsian is present in quartz-skarn-polymetallic sulfide ores formed during Jurassic and Tertiary phases of skarn formation. Well-shaped microcrystals of celsian, along with sulfide minerals and apatite, fill cavities in quartz and are related to a retrogressive hydrothermal mineral paragenesis that took place during a final stage of contact-metamorphic mineralization at temperatures of approximately 300 ° C. Prismatic crystals of celsian were subsequently fragmented and rounded during superposed ductile deformation of the enclosing quartz and became part of a Tertiary mylonitic fabric at the American Beauty Mine.
Chronology of polyphase extension in the Windermere Hills, northeast Nevada
Fission-track and 40 Ar/ 39 Ar dating and chemical correlation of volcanic strata exposed in the Windermere Hills and northern Pequop Mountains, northeast Nevada, indicate a protracted, polyphase history of Tertiary (late Eocene–late Miocene) extension along the northern margin of a major Cordilleran metamorphic core complex. Early extension is recorded by a west-tilted half graben filled with early Oligocene (34.79 ± 0.18–39.18 ± 0.12 Ma) sedimentary rocks in the eastern Windermere Hills above the low-angle Black Mountain detachment fault. The early Oligocene half graben conformably overlies a widespread suite of late Eocene (39.18 ± 0.12–40.38 ± 0.06 Ma) calc-alkaline volcanic rocks, reflecting a temporal link between early extension at a high structural level and the end of the ignimbrite flare-up. These strata are cut by east-west–striking normal faults, which are exposed along, and parallel to, the northern margin of the metamorphic complex. Available age data (e.g., between 14.93 ± 0.08 and 34.79 ± 0.18 Ma) permit the interpretation that the east-west–striking faults formed at the same time as, or after, large-magnitude unroofing of high-grade rocks. We interpret the east-west–striking faults to accommodate differential uplift of greenschist-grade metamorphic rocks in the upper crust, above a lateral ramp in a west-northwest–directed mylonitic shear zone. Subsequent extension in the Windermere Hills is defined by deep, rapidly filled half grabens of middle Miocene (<7.42 ± 2.0 to 14.93 ± 0.08 Ma) age that unconformably overlie older faults and synextensional deposits. These are the youngest half grabens in the region and are inferred to be initiated by extensional stresses imparted to the base of the lithosphere by a laterally spreading mantle plume (e.g., the Yellowstone hotspot) located in southeastern Oregon at this time.