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Geologic map of the Caetano caldera, Lander and Eureka counties, Nevada
The Eocene (34 Ma) Caetano caldera in north-central Nevada offers an exceptional opportunity to study the physical and petrogenetic evolution of a large (20 km by 10–18 km pre-extensional dimensions) silicic magma chamber, from precursor magmatism to caldera collapse and intrusion of resurgent plutons. Caldera-related rocks shown on this map include two units of crystal-rich intracaldera tuff totaling over 4 km thickness, caldera collapse breccias, tuff dikes that fed the eruption, hydrothermally altered post-eruption rocks, and two generations of resurgent granitic intrusions (John et al., 2008). The map also depicts middle Miocene (about 16–12 Ma) normal faults and synextensional basins that accommodated >100 percent extension and tilted the caldera into a series of ~40° east-dipping blocks, producing exceptional 3-D exposures of the caldera interior (Colgan et al., 2008). This 1:75,000-scale map is a compilation of published maps and extensive new mapping by the authors (fig. 1), and supersedes a preliminary 1:100,000-scale map published by Colgan et al. (2008) and John et al. (2008). New mapping focused on the margins of the Caetano caldera, the distribution and lithology of rocks within the caldera, and on the Miocene normal faults and sedimentary basins that record Neogene extensional faulting. The definition of geologic units and their distribution within the caldera is based entirely on new mapping, except in the northern Toiyabe Range, where mapping by Gilluly and Gates (1965) was modified with new field observations. The distribution of pre-Cenozoic rocks outside the caldera was largely compiled from existing sources with minor modifications, with the exception of the northeastern caldera margin (west of the Cortez Hills Mine), which was remapped in the course of this work and published as a stand-alone 1:6000-scale map (Moore and Henry, 2010).
Geologic map of the Bateman Spring Quadrangle, Lander County, Nevada
This 1:24,000-scale geologic map of the Bateman Spring 7.5-minute quadrangle in Lander County, Nevada contains descriptions of 24 geologic units and one cross section. Accompanying text includes full unit descriptions and references. This quadrangle includes lower Paleozoic siliciclastic sedimentary rocks of the Roberts Mountain allochthon, Miocene intrusive dikes, alluvial deposits of the northern Shoshone Range piedmont, and riverine deposits of the Reese and Humboldt rivers. Significant findings include: refined age estimates for the Ordovician-Cambrian Valmy Formation and Devonian Slaven Chert, based on new fossil information; and detailed mapping of late Quaternary fault traces along the Shoshone Range fault system.
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.
Geologic map of the Verdi Peak Quadrangle, Elko County, Nevada
A 1:24,000-scale, full-color geologic map of the Verdi Peak 7.5-minute quadrangle in Elko County, Nevada, with one cross section and descriptions of 19 rock units. Accompanying text describes the geology of the quadrangle.
Surface Rupture Map of the 2020 M 6.5 Monte Cristo Range earthquake, Esmeralda and Mineral counties, Nevada
The 15 May 2020, M6.5 Monte Cristo Range earthquake was the largest earthquake in Nevada in over 66 years and occurred in a sparsely populated area of western Nevada about 74 km southeast of the town of Hawthorne. The earthquake produced surface rupture distributed across a 28-km-long zone along the eastward projection of the Candelaria fault in the Mina deflection of the central Walker Lane. Post-event field surveys mapped surface ruptures and measured displacements, which reached up to ~20 cm of oblique slip. Additional detailed mapping was completed using centimeter-resolution orthomosaics generated from Uncrewed Aerial Vehicle surveys. The rupture observations and displacement data are compiled into this 1:14,000-scale map, data tables, and accompanying digital dataset. The rupture consists of two distinct deformational domains roughly separated by U.S. Highway 95: ENE-trending ruptures with normal and left-oblique displacements in the western domain, and N- to NNE-trending ruptures with normal and right-oblique displacement in the eastern domain. The complex pattern of surface rupture is consistent with the projections of mapped bedrock and Quaternary faults in the area and illustrates the kinematics of slip partitioning at the junction of variably oriented structures in the shallow subsurface.
Geologic map of the Silver Zone Pass quadrangle, Elko County, Nevada
This 1:24,000-scale geologic map of the Silver Zone Pass quadrangle lies in the southern Toano Range in Elko County, Nevada. Metamorphic and sedimentary strata of the quadrangle range from Neoproterozoic to Permian in age. Important intrusions include the Late Jurassic (ca. 159 Ma) Silver Zone Pass pluton and Cretaceous Toano Spring pluton. In particular, the Silver Zone Pass pluton involves undeformed dikes that crosscut metamorphic foliations and the pluton is associated with pluton-margin anticlines. Interpretation of these characteristics suggests that the pluton was syn-kinematic with respect to metamorphism and strain, thus requiring a phase of Late Jurassic deformation. A Miocene rhyolite lava is of particular interest as one of the few topaz-bearing volcanic rocks in Nevada. A major detachment fault places non-metamorphosed Paleozoic rocks over low-grade Paleozoic and Proterozoic rocks. High-angle normal faults tilted the range in several blocks, and Miocene Humboldt Formation were deposited on, and faulted against, bedrock. Rocks of the Toano Range are bounded by broad valleys on the east and west, with the eastern basin being at much lower elevation than the western basin. Pleistocene lakes, which created distinctive beach deposits, occupied both basins, with Lake Bonneville on the east and Lake Waring on the west. Silver Zone Pass owes its low relief to the enhanced weathering and erosion of the rock within the pass, a granodiorite pluton. The weathering has created some unusual landforms such as tors.
Reconnaissance map of the Cenozoic geology in the Carlin basin area, Elko and Eureka counties, Nevada
The middle Miocene Carlin sedimentary basin encompasses a large area between the Adobe Range to the east, the Piñon Range to the south, the southern Independence Mountains and Marys Mountain to the west, and Swales Mountain to the north. The town of Carlin is in the southern part of the basin. The geologic map includes detailed to more reconnaissance mapping of Cenozoic units in the main part of the basin, including different facies of the middle Miocene Humboldt Formation. The mapping was part of a broader study of the Miocene and younger paleogeographic evolution of the region. Earlier work obtained numerous 40 Ar/ 39 Ar and tephra correlation dates on sedimentary and volcanic units in the basin. The basin connected to the east into the Elko sedimentary basin and to the northwest and northeast into similar smaller basins between present-day mountain ranges. Early sediments, largely fluvial, began to accumulate in the lowlands between the surrounding ranges at about 16.5 Ma. The sediments were derived from Paleozoic sedimentary and middle Tertiary volcanic units in the nearby highlands, and flow patterns indicate a general southward flow towards present-day Pine Valley. The eruption of the Palisade Canyon–Marys Mountain rhyolite flows at the southwest end of the basin at 15.3 Ma blocked the southward flow, and a lake began to form in the basin. As the lake grew in extent, sedimentary units around the fringes of the lake included a mixture of inflowing fluvial sediments mixed with the pyroclastic-fall, ash-rich sediments deposited in the lake. The lake margin expanded, and stratigraphic sections record the progressive transition from fluvial to mixed fluvial and lacustrine, and finally to entirely lacustrine. The volcanic rock dam was breached at about 14.7 Ma, the lake drained, and fluvial sediments blanketed the entire basin for an unknown period of time after that. Sedimentation progressively buried existing highlands and bridged gaps between adjacent basins. For example, the Carlin and Elko basins connected across the southern Adobe Range. Normal faulting produced numerous, mostly north- to north-northeast-striking faults that cut the sedimentary units and surrounding highlands largely after sedimentation ceased. The largest fault formed in the eastern third of the basin and tilted all of the sedimentary units in the western two-thirds of the basin, as well as the eastern part of Marys Mountain, to the east. Some offset took place during sedimentation. Many other normal faults of smaller extent and offset cut the sedimentary units. The integration of streams draining the Elko and Carlin basins began after about 9.8 Ma. The streams, which together comprised the early stages of the Humboldt River, flowed regionally southwestward beyond the Carlin basin. As many as thirteen, downward-stepping strath terraces in the Carlin basin record the progressive downcutting into and removal of the middle Miocene sediments. Gravel deposits form a thin veneer on some of the higher terraces. Clasts in those gravel deposits, as well as the overall terrace pattern, indicate southward drainage towards the Humboldt River. The erosion gradually re-exposed the flanks of the surrounding highlands. A brief pause in downcutting allowed the formation of a small lake in the Hemphillian (late Miocene), represented by lacustrine units northwest of Carlin. The sedimentary rocks of the Carlin basin conceal a large segment of the world-class, late Eocene Carlin gold trend, which extends from the southern Independence Mountains south into the Piñon Range. Sedimentation largely buried the Gold Quarry and Mike gold deposits in the northwestern part of the basin. Later faulting and erosion re-exposed the Gold Quarry deposit, but the Mike deposit remains buried. The basin’s sedimentary units conceal potential Paleozoic host rocks, and the sedimentary facies and post-sedimentation faults shown on the map may help guide interpretations of geophysical and other exploration data in the Carlin basin. The current map publication was supported by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number G19AC00383.
Map showing drill-hole depths, lithologic intercepts, and partial isopachs of basin fill in the Winnemucca 1 degree by 2 degrees quadrangle, Nevada
The purpose of this map is to aid in the mineral-resource assessment and exploration of covered host rocks by displaying and interpreting data that can be used to estimate the depth of basin fill in the Winnemucca 1° by 2° quadrangle, Nevada. Publicly available information used in making this map includes water, petroleum, and geothermal well data, gravity data and models, seismic profiles, and geologic and geomorphic reports. Wells logs used for this map of the Winnemucca quadrangle are from the following sources: (1) logs of more than 1,000 water wells reported to the State of Nevada Division of Water Resources, which are on file with them in Reno and at the with U.S. Geological Survey in Carson City, (2) 44 petroleum wells collected by the Nevada Bureau of Mines (Lintz, 1957; Schilling and Garside, 1968; Garside and Schilling, 1977, Garside and others, 1977; 1988), and (3) Two geothermal wells reported in Zoback (1979) and Flynn and others (1982). Data from isostatic residual and Bouguer gravity maps by Wagini (1985) contributed to the interpretation of basin configuration. Gravity models of Dixie Valley (Schaefer, 1982, and Speed, 1976) and Grass Valley (Grannell and Noble, 1977) and seismic profiles of Grass and Pine Valleys (Potter and others, 1987) helped refine basis interpretations in those areas. The geologic base map of Paleozoic and Mesozoic igneous and sedimentary rocks, Tertiary volcanic and sedimentary rocks, and Cenozoic structures was simplified from Stewart and Carlson (1976b).
Geologic map of the South Jackson Mountains Wilderness Study Area, Humboldt County, Nevada
The Federal Land Policy and Management Act (Public Law 94-579, October 21, 1976) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct mineral surveys on certain areas to determine their mineral values, if any, that may be present. Results must be made available to the public and be submitted to the President and the Congress. This report presents the results of a mineral survey of the South Jackson Mountains (NV-020-603) Wilderness Study Area, Humboldt County, Nevada. The South Jackson Mountains Wilderness Study Area is in south-central Humboldt County, approximately 50 miles northwest of Winnemucca, Nevada. The boundaries originally specified for the wilderness study area encompassed an area of 60,211 acres. The draft Environmental Impact Statement issued in 1983 by the U.S. Bureau of Land Management (BLM) identified 20,094 acres within the wilderness study area as potentially suitable for inclusion into the National Wilderness Preservation System. Subsequent (August 27, 1984) deletions by the BLM have resulted in the present study area of approximately 10,300 acres. The boundaries of the study area are approximated by the range crestline to the east and the 4,400-ft contour along the west side of the range from King Lear Peak north to the divide between Hobo and Christiorsson Canyons.
Maps showing mineral resource potential of the Virgin Mountains Instant Study Area, Clark County, Nevada
The Virgin Mountains Instant Study Area contains about 30,000 acres (12,000 ha) in southeastern Nevada. In accordance with the Federal Land Policy and Management Act (P.L. 94-579), the U.S. Bureau of Mines examined mines, prospects, and mineralized zones, and the U.S. Geological Survey made regional geologic, geophysical, and geochemical investigations. Tungsten and sheet mica have been produced from the study area, and oil and gas lease applications have been filed on 20,300 acres (8,200 ha). Sixteen mining claims are presently held.
Preliminary geologic map of the Nevada and Arizona parts of the Mount Manchester quadrangle
This map was prepared as part of the STATEMAP component of the National Cooperative Geologic Mapping Program in cooperation with the U.S. Geological Survey.
Mineral Resources of the Antelope Wilderness Study Area, Nye County, Nevada
At the request of the U.S. Bureau of land Management, 83,100 acres of the Antelope Wilderness Study Area (NV-4)60-231/241) was studied. In this report the studied area is called the 'wilderness study area', or simply the 'study area.' No identified mineral or energy resources occur within the study area. The southern part of the area has moderate mineral resource potential for undiscovered gold and silver, and the Woodruff Formation in the southern part of the area has high resource potential for undiscovered vanadium, zinc, selenium, molybdenum, and silver (fig. 1). This assessment is based on field geochemical studies in 1984 and 1985 by the U.S. Bureau of Mines and field geochemical studies and geologic mapping by the U.S. Geological Survey in 1984 and 1985. The remainder of the study area has low resource potential for undiscovered gold, silver, lead, zinc, manganese, tin, and molybdenum. The study area also has low resource potential for undiscovered oil and gas resources. The Antelope Wilderness Study Area is about midway between Tonopah and Eureka, Nev., in the northern Hot Creek Range and southern Antelope Range of central Nevada. It is accessible by unimproved dirt roads extending 20 mi (miles) north from U.S. Highway 6 and 40 mi south from U.S. Highway 50 (fig. 2). Most of the study area consists of rugged mountainous terrain having approximately 2,600 ft (feet) of relief. The mountain range is a block tilted gently to the east and bounded on both sides by normal faults that dip steeply to moderately west and have major displacements. Most of the study area is underlain by a thick sequence of Tertiary volcanic rocks that predominantly consist of silicic ash-flow tuff, the Windous Butte Formation. Paleozoic and lower Mesozoic (see geologic time chart in appendix) marine sediments occur along the southern margin of the study area, and lower Paleozoic rocks are exposed in the northeast corner. The areas of exposed Paleozoic-Mesozoic rocks along the southern margin of the study area have moderate mineral resource potential for gold and silver in sediment-hosted, disseminated, epithermal (low-temperature) gold-silver deposits (fig. 1). These rocks consist of folded and thrust-faulted, fine-grained clastic sediments and limestone and dolomite that locally have been brecciated and hydrothermally altered. The alteration (locally, strong silicification) and geochemical associations of these rocks indicate a favorable environment for such deposits. Exploration for disseminated gold deposits in the same geologic environment is currently being conducted just south of the study area. The remainder of the study area has low resource potential for epithermal gold and silver vein deposits in the Tertiary volcanic rocks. The Cenozoic sedimentary basins adjacent to the fault-bounded mountain block have moderate potential for petroleum resources; the study area itself has low potential for petroleum resources.
Quantifying the eroded and deposited mass of mercury-contaminated sediment by using terrestrial laser scanning at the confluence of Humbug Creek and the South Yuba River, Nevada County, California, 2011–13
High-resolution, terrestrial laser scanning, also known as ground-based lidar (light detection and ranging), was used to quantify the volume of mercury-contaminated sediment eroded from an outcrop of historical placer-mining debris at the confluence of Humbug Creek and the South Yuba River in the Sierra Nevada foothills, about 17 kilometers northeast of Grass Valley, California, and delivered to a zone below an observed flood stage of the South Yuba River. Substantial quantities of mercury were used and lost to the environment from historical placer gold mining activities on the western slope of the Sierra Nevada, California, and recent studies have documented continued persistence of mercury and methylmercury concentrations in water, sediment, fish, and predatory invertebrates in the Yuba River drainage basin in relation to suspected mercury sources. To identify areas that have high levels of mercury contamination as possible remediation targets in the Yuba River drainage basin and other areas in the Sierra Nevada, the U.S. Geological Survey worked in cooperation with the Bureau of Land Management on this and other detailed studies. Malakoff Diggings, one of the largest hydraulic gold mines in the Sierra Nevada, is 3.5 kilometers north of the study site in the Humbug Creek subbasin. Terrestrial laser scanning was used to produce centimeter-scale, three-dimensional maps of the complex outcrop surface, which was composed of an upper erosional area (cliff and over-steepened slope) and a lower depositional area (colluvial slope). The outcrop could not be mapped non-destructively or in sufficient detail by traditional surveying techniques. The study site, which was approximately 70 meters long, 30 meters wide and 20 meters high, was surveyed four times in 2 years (December 15, 2011; October 25, 2012; January 4, 2013; and November 22, 2013) to determine volumetric differences in the upper erosional and lower depositional areas between surveys. Measured changes in volume for the upper erosional area and lower depositional area were multiplied by the corresponding sediment density so that a mass-balance relationship, between the eroded and deposited sediment during each period, could be used to estimate the amount of mercury-contaminated sediment that was transported to below the base of the colluvial slope, where it could be mobilized by the South Yuba River during a flood having a 5-to-10-year recurrence interval. On December 2, 2012, a flood of this estimated magnitude reached the base of the colluvial slope. Between the first and second surveys (December 15, 2011–October 25, 2012), an estimated mass of 18±9.2 kilograms of sediment was transported from steeper slopes to the gently sloping river bank below the base of the colluvial slope. Between the second and third surveys (October 25, 2012–January 4, 2013), an atmospheric river caused heavy precipitation at the study site during late November and early December 2012. This short-duration, high-intensity rain resulted in a large amount of erosion and deposition at the study site and also caused high streamflow (flood stage) in the South Yuba River. From October 2012 to January 2013, 51±31 kilograms of sediment was transported to below the base of the colluvial slope, that is, below the high-water mark of December 2, 2012. Between the third and fourth surveys (January 4, 2013–November 22, 2013), an additional 10±26 kilograms of sediment was transported to below the base of the colluvial slope. During the 24 months of the study, the total mass of sediment delivered below the base of the colluvial slope and the high-water mark of December 2, 2012, was 79±66 kilograms. In any given year there is a 10–20-percent chance (5-to-10-year recurrence interval) of a flood equal to or greater than that of the December 2, 2012, flood, which could transport mercury-contaminated sediment at the study site into the South Yuba River. Hydraulically modeled estimates of the South Yuba River stage during floods having a 50- and 100-year recurrence interval (2- and 1-percent annual exceedance probability, respectively) indicated that resulting river stages could be 2.2–3.0 meters above the base of the colluvial slope, or 2.2–3.0 meters above the high-water mark of December 2, 2012. Such high river stages would be likely to inundate the lower half of the colluvial slope and mobilize a substantial volume of mercury-contaminated sediment to downstream areas.
Discovering blind geothermal systems in the Great Basin Region: An integrated geologic and geophysical approach for establishing geothermal play fairways: All phases
Most geothermal resources in the Great Basin region of the western USA are blind, and thus the discovery of new commercial-grade systems requires synthesis of favorable characteristics for geothermal activity. The geothermal play fairway concept involves integration of multiple parameters indicative of geothermal activity to identify promising areas for new development. This project integrated multiple datasets to apply the play fairway concept and assess geothermal potential in a large region of the Great Basin in Nevada. It is therefore referred to as the Nevada play fairway project. This project was a strong collaborative effort between several organizations, led by the Nevada Bureau of Mines and Geology at the University of Nevada, Reno, but with key support from the U.S. Geological Survey, ATLAS Geosciences, Inc,, Hi-Q Geophysical, Inc., Lawrence Berkeley National Laboratory, Utah Geological Survey, and Innovative Geothermal Ltd. In Budget Period 1 of this project, available data for nine geologic, geochemical, and geophysical parameters were initially synthesized to produce a new detailed geothermal potential map of 96,000 km2 from west-central to eastern Nevada (Figure 1). These parameters were grouped into subsets and individually weighted (Figure 2) to delineate rankings for local permeability, intermediate permeability, regional permeability, and thermal potential, which collectively defined geothermal play fairways (i.e., most likely locations for significant geothermal fluid flow). This initial work was aimed at reducing the risks in regional exploration and therefore facilitating discovery of new commercial-grade systems in blind settings, as well as in areas with surface expressions of geothermal activity. Budget Period 2 of the project involved detailed analysis of some of the most promising areas identified in Phase 1. Twenty-four highly prospective areas, including both known undeveloped systems and previously undiscovered potential blind systems, were identified for further analysis (Figures 3 and 4). After reconnaissance of these areas, five of the most promising sites were selected for detailed studies. Multiple techniques were employed in the detailed studies, including geologic mapping, shallow temperature surveys, gravity surveys, Lidar, geochemical studies, seismic reflection analysis, and 3D modeling. The goal of the detailed studies was to identify specific areas with the highest likelihood for high permeability and thermal fluids, such that drill sites could be targeted. Three main sets of predictive maps were generated for each detailed study area: 1) play fairway maps, 2) play fairway error maps, and 3) direct evidence maps. Local- and intermediate-scale permeability models were revised to reflect results of the detailed geologic, geophysical, and geochemical analyses. Budget Period 3 of the project involved more detailed geophysical analyses and temperature-gradient (TG) drilling in southeastern Gabbs Valley and northern Granite Springs Valley (Figure 4), deemed the two most promising sites, with the goal of providing preliminary validation of the play fairway methodology. In southeastern Gabbs Valley, the collocation of a favorable structural setting (displacement transfer zone and fault intersections), Quaternary faults, intersecting and terminating gravity gradients, magnetic low, shallow (2 m) temperature anomaly, low resistivity anomaly, and promising geothermometry from nearby water wells provided evidence for a blind system. Drilling of six TG holes defines an apparent geothermal system at this locality with temperatures as high as 124°C at 152 m. This system is blind, with no surface hot springs, fumaroles, or paleo-geothermal deposits. For northern Granite Springs Valley, a favorable structural setting (termination of a major Quaternary normal fault), terminating gravity gradient, magnetic gradient, newly discovered sinter deposits, nearby warm water wells, previously drilled TG holes in the vicinity, and promising geothermometry suggest a hidden system. Drilling of six new TG holes yields temperatures of ~96°C at ~250 m, suggesting the presence of a geothermal system. Major lessons learned in the course of this project include: 1) initially identified sites commonly include multiple favorable structural settings at a finer scale; 2) promising sites in Cenozoic basins cannot be recognized without detailed geophysical surveys; and 3) play fairway analysis should be refined as the exploration program vectors into the most promising sites and finer-scale data are acquired. In addition to producing copious amounts of data, this project resulted in 16 published papers, 10 abstracts, more than 40 presentations across the U.S. and abroad (including several keynote addresses), 2 Masters theses, and 7 media reports.
Digital mining claim density map for federal lands in Nevada: 1996
This report describes a digital map generated by the U.S. Geological Survey (USGS) to provide digital spatial mining claim density information for federal lands in Nevada as of March 1997. Mining claim data is earth science information deemed to be relevant to the assessment of historic, current, and future ecological, economic, and social systems. There is no paper map included in this Open-File report. In accordance with the Federal Land Policy and Management Act of 1976 (FLPMA), all unpatented mining claims, mill, and tunnel sites must be recorded at the appropriate Bureau of Land Management (BLM) State office. BLM maintains a cumulative computer listing of mining claims in the MCRS database with locations given by meridian, township, range, and section. A mining claim is considered closed when the claim is relinquished or a formal BLM decision declaring the mining claim null and void has been issued and the appeal period has expired. All other mining claims filed with BLM are considered to be open and actively held. The digital map (figure 1.) with the mining claim density database available in this report are suitable for geographic information system (GIS)-based regional assessments at a scale of 1:100,000 or smaller.
Summary geochemical maps for samples of rock, stream sediment, and nonmagnetic heavy-mineral concentrate, Pyramid Roadless Area, El Dorado County, California
The Wilderness Act (Public Law 88-577, September 3, 1964) and related acts require the U.S. Geological Survey and the U.S. Bureau of Mines to survey certain areas on Federal lands to determine their mineral resource potential. Results must be made available to the public and be submitted to the President and the Congress. This report presents the results of a geochemical survey of the Pyramid Roadless Area (5203) in the Eldorado National Forest and Lake Tahoe Basin Management Unit, El Dorado County, California. This roadless area was classified as a further planning area during the Second Roadless Area Review and Evaluation (RARE II) by the U.S. Forest Service, January 1979. The Pyramid Roadless Area lies near the crest of the Sierra Nevada about 75 miles east of Sacramento, California. the area, which is adjacent to and almost encircles the Desolation Wilderness, encompasses approximately 31,400 acres in Eldorado National Forest and the Lake Tahoe Basin Management Unit in El Dorado County, California. The area is dominated by deep rugged canyons that run eastward from the Sierra Nevada crest to Lake Tahoe basin and westward toward the Sacramento Valley. Elevations range from about 5,500 feet along Big Silver Creek on the west side of the study area to 8,895 feet at Echo Peak along the southeastern side of the roadless area. Geochemical sampling was conducted during 1982. This report summarizes the results of that investigation and provides details of the geochemical evaluation used in producing the final mineral resource assessment of the study area (Armstrong and others, 1983).
Great Basin geoscience data base
This CD-ROM serves as the archive for 73 digital GIS data set for the Great Basin. The data sets cover Nevada, eastern California, southeastern Oregon, southern Idaho, and western Utah. Some of the data sets are incomplete for the total area. On the CD-ROM, the data are provided in three formats, a prototype Federal Data Exchange standard format, the ESRI PC ARCVIEW1 format for viewing the data, and the ESRI ARC/INFO export format. Extensive documentation is provided to describe the data, the sources, and data enhancements. The following data are provided. One group of coverages comes primarily from 1:2,000,000-scale National Atlas data and can be assembled for use as base maps. These various forms of topographic information. In addition, public land system data sets are provided from the 1:2,500,000-scale Geologic Map of the United States and 1:500,000-scale geologic maps of Nevada, Oregon, and Utah. Geochemical data from the National Uranium Resource Evaluation (NURE) program are provided for most of the Great Basin. Geophysical data are provided for most of the Great Basin, typically gridded data with a spacing of 1 km. The geophysical data sets include aeromagnetics, gravity, radiometric data, and several derivative products. The thematic data sets include geochronology, calderas, pluvial lakes, tectonic extension domains, distribution of pre-Cenozoic terranes, limonite anomalies, Landsat linear features, mineral sites, and Bureau of Land Management exploration and mining permits.