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At least 1,279 records · Page 71Linked to original sources
USGS2016

Demonstration of the Cascadia G‐FAST geodetic earthquake early warning system for the Nisqually, Washington, earthquake

A prototype earthquake early warning (EEW) system is currently in development in the Pacific Northwest. We have taken a two‐stage approach to EEW: (1) detection and initial characterization using strong‐motion data with the Earthquake Alarm Systems (ElarmS) seismic early warning package and (2) the triggering of geodetic modeling modules using Global Navigation Satellite Systems data that help provide robust estimates of large‐magnitude earthquakes. In this article we demonstrate the performance of the latter, the Geodetic First Approximation of Size and Time (G‐FAST) geodetic early warning system, using simulated displacements for the 2001 M w 6.8 Nisqually earthquake. We test the timing and performance of the two G‐FAST source characterization modules, peak ground displacement scaling, and Centroid Moment Tensor‐driven finite‐fault‐slip modeling under ideal, latent, noisy, and incomplete data conditions. We show good agreement between source parameters computed by G‐FAST with previously published and postprocessed seismic and geodetic results for all test cases and modeling modules, and we discuss the challenges with integration into the U.S. Geological Survey’s ShakeAlert EEW system.

Washington↗
USGS2006

Volcanic hazards at Atitlan volcano, Guatemala

Atitlan Volcano is in the Guatemalan Highlands, along a west-northwest trending chain of volcanoes parallel to the mid-American trench. The volcano perches on the southern rim of the Atitlan caldera, which contains Lake Atitlan. Since the major caldera-forming eruption 85 thousand years ago (ka), three stratovolcanoes--San Pedro, Toliman, and Atitlan--have formed in and around the caldera. Atitlan is the youngest and most active of the three volcanoes. Atitlan Volcano is a composite volcano, with a steep-sided, symmetrical cone comprising alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs. Eruptions of Atitlan began more than 10 ka [1] and, since the arrival of the Spanish in the mid-1400's, eruptions have occurred in six eruptive clusters (1469, 1505, 1579, 1663, 1717, 1826-1856). Owing to its distance from population centers and the limited written record from 200 to 500 years ago, only an incomplete sample of the volcano's behavior is documented prior to the 1800's. The geologic record provides a more complete sample of the volcano's behavior since the 19th century. Geologic and historical data suggest that the intensity and pattern of activity at Atitlan Volcano is similar to that of Fuego Volcano, 44 km to the east, where active eruptions have been observed throughout the historical period. Because of Atitlan's moderately explosive nature and frequency of eruptions, there is a need for local and regional hazard planning and mitigation efforts. Tourism has flourished in the area; economic pressure has pushed agricultural activity higher up the slopes of Atitlan and closer to the source of possible future volcanic activity. This report summarizes the hazards posed by Atitlan Volcano in the event of renewed activity but does not imply that an eruption is imminent. However, the recognition of potential activity will facilitate hazard and emergency preparedness.

Open-File Report↗
USGS1953

Stratigraphic sections of the Phosphoria formation in Montana, 1951

The U.S. Geological Survey has recently measured and sampled the Phosphoria formation at many localities in Montana and other western states. These data will not be fully synthesized and analyzed for several years, but segments of the data, accompanied by little or no interpretation, are published as preliminary reports as they are assembled. This report, which contains abstracts of the sections measured in southwestern Montana (fig. 1), during 1951, is the fifth Montana report of this series. The field and laboratory procedures adopted in these investigations are described in a previous report (McKelvey and others, 1953). Many people have taken part in this investigation. Crushing and splitting of the samples in the field were done by T. K. Rigby. The laboratory preparation of samples for chemical analysis was done in Denver, Colo., under the direction of W. P. Huleatt. The P 2 0 5 and acid insoluble analyses were made for the Survey by the U.S. Bureau of Mines at the Northwest Electrodevelopment Laboratory, Albany, Oreg., under the direction of S. M. Sheldon and M. L. Wright.

Montana↗
USGS1978

Geology and coal resources of the Hanging Woman Creek Study Area, Big Horn and Powder River Counties, Montana

In an area of 7,200 acres (29 sq km) In the Hanging Woman Creek study area, the Anderson coal bed contains potentially surface minable resources of 378 million short tons (343 million metric tons) of subbituminous C coal that ranges in thickness from 26 to 33 feet (7.9-10.1 m) at depths of less than 200 feet (60 m). Additional potentially surface minable resources of 55 million short tons (50 million metric tons) are contained in the 9-12 foot (2.7-3.7 m) thick Dietz coal bed which lies 50-100 feet (15-30 m) below the Anderson. Analyses of coal from 5 core holes indicates that the Anderson bed contains 0.4 percent sulfur, 5 percent ash, and has a heating value of 8,540 Btu/lb (4,750 Kcal/kg). The trace element content of the coal is generally similar to other coals in the Powder River Basin. The two coal beds are in the Fort Union Formation of Paleocene age which consists of sandstone, siltstone, shale, coal beds, and locally impure limestone. A northeast-trending normal fault through the middle of the area, downthrown on the southeast side, has displaced the generally flat lying strata as much as 300 feet (91 m). Most of the minable coal lies northwest of this fault.

Montana↗
USGS2024

Influence of inherited structure on flexural extension in foreland basin systems: Evidence from the northern Arkoma basin and southern Ozark dome, USA

Extensional faults are key components of foreland basin systems. They form within the upper crust in response to flexure of the lithosphere and accommodate subsidence within the foredeep and forebulge depozones. Such faults are excellent proxies for orogenic system evolution and control the distribution of natural resources and hazards. However, the spatiotemporal evolution of flexural extension has not been documented previously at a regional scale, thereby limiting our understanding of underlying geodynamic controls. Here, we resolve late Paleozoic flexural extension in the northern Arkoma basin and southern Ozark dome, USA. We synthesize a large database of previous mapping, existing research, subsurface data, and geophysical data into 3D geologic and 2D kinematic models. Mesh surfaces representing several key horizons from the Carboniferous Period (ca. 335-306 Ma) were constructed. These surfaces were built from oil and gas well tops (n = ∼10,000) and surface geologic map contacts using an advanced kriging method. The mesh surfaces are offset by a complex 3D fault network, allowing detailed analysis of along-strike and down-dip variations in fault displacement. Analysis of the 3D model reveals a regular and repeated fault segmentation pattern wherein E -W striking, left- and foreland-stepping en échelon normal faults are segmented by inherited NE striking basement faults. Maximum vertical separation along the E -W normal faults is generally focused between the inherited NE-trending faults. This suggests that the inherited basement faults delocalized extensional strain during late Paleozoic normal faulting. Maximum vertical separation and fault localization may correlate to areas with high-amplitude positive magnetic anomalies interpreted as Mesoproterozoic granitic rocks. Speculative covariance of magnetic anomalies and fault displacements implies that the relatively strong basement granite concentrated stress, leading to localized faulting within the relatively thin sedimentary cover. Lastly, we show that flexural extension migrated southeast to northwest from the Chesterian-Morrowan (ca. 335-319 Ma) to the Desmoinesian (ca. 306 Ma). The migratory flexural extension may be explained by diachronous loading during Pangean assembly, or by synchronous loading but variable load compensation due to inherent factors.

Arkansas, Oklahoma↗
USGS1999

Cenozoic basins of the Death Valley extended terrane as reflected in regional-scale gravity anomalies

The contrast in density between basin-filling deposits and underlying basement rocks in the Basin and Range province produces a distinctive pattern of gravity anomalies that roughly correlates with basin-and-range topography. This is especially apparent in the Death Valley extended terrane, where minima in residual gravity closely correspond to well-known extensional basins, such as Owens Valley, Saline Valley, Pahrump Valley, and Death Valley itself. A three-dimensional calculation of the thickness and shape of Cenozoic deposits throughout the Basin and Range based on digital gravity, geologic, and topographic information is here interpreted in terms of the depths and shapes of extensional basins in the Death Valley region. In most basins, the gravity inversion predicts a much more complex basement than might be assumed from the surface topography. Death Valley itself is, to first order, a two-dimensional feature; as reflected by the topography of the bounding ranges down to 400–800 m below the valley floor, it is a long, narrow, and continuous valley along its entire length of 200 km. This apparent uniformity, however, belies a complex basement surface beneath the Cenozoic cover as revealed by the gravity inversion. The floor of Death Valley is pockmarked with four deep (3–5 km), steep-sided depressions that may have formed as relatively small pull-apart structures superimposed on the more uniform extension that created the twodimensional aspects of Death Valley. Lateral dimensions of these subbasins suggest a minimum of 10 km of northwest extension across Death Valley. If a regionally continuous detachment surface lies beneath Death Valley, it must lie deeper than the subbasins, that is, below a depth of 3–5 km. Similar deep, steep-sided subbasins are seen elsewhere in the Death Valley extended terrane, notably at Saline Valley, Panamint Valley, Pahrump Valley, the Amargosa Desert, and Fremont Valley, but are noticeably absent from the Mojave Desert block south of the Garlock fault zone where extensional rates are lower. The floor of the caldera complex at the southwest Nevada volcanic field is predicted by the gravity inversion to be extraordinarily deep (>8 km) and rugged. Deep, linear basins that branch out of the caldera complex may reflect modification of extensional strain due to massive injections of magma into the middle and upper crust.

California, Nevada↗
USGS2023

Analysis of aquifer framework and properties, North Magee Street well field, Southampton, New York

The U.S. Geological Survey, in cooperation with the Suffolk County Water Authority, evaluated the groundwater-flow characteristics and aquifer properties of the North Magee Street well field north of the village of Southampton, New York. Characteristics and properties included groundwater-flow direction, potential groundwater-contributing areas to the well field production wells, and aquifer transmissivity and storage. The groundwater flow and aquifer properties were also evaluated to allow Suffolk County Water Authority to better assess the potential source of dissolved halocarbons (refrigerants, such as chlorofluorocarbons). The well field production wells are screened in the upper glacial aquifer and an observation well is screened in the Magothy aquifer. Based on depth and available logs, groundwater from wells screened in the upper glacial aquifer was classified as under water-table (unconfined) conditions, and groundwater from wells screened in the Magothy aquifer was classified as being under semiconfined conditions. Groundwater flows radially to the well field during production and in a northwesterly direction under the effect of the regional flow regime. A previously published particle tracking analysis identified the following recharge contributing areas nearby the well field: (1) contributing areas to surface-water bodies of the Peconic Estuary, (2) contributing areas to surface-water bodies of the South Shore Estuary Reserve, (3) a contributing area to the Atlantic Ocean, and (4) a contributing area to another Suffolk County Water Authority well field. Five other pumping well contributing areas were identified within the study area, including those of various wells pumped for golf-course irrigation. Analysis of drawdown and recovery data collected during the multiple-well aquifer test, through the application of a Neuman analytical model, provided estimates of upper glacial aquifer characteristics and properties. Inclusion of lateral aquifer boundaries was not necessary for the analysis to result in satisfactory matches with the observed water-level responses. Aquifer transmissivity was estimated to be 170,000 feet squared per day. Storativity was estimated to be 0.02 (dimensionless), and specific yield was estimated to be 0.08 (dimensionless), consistent with the inferred degree of confinement and well field characteristics.

New York↗
USGS2013

Reconnaissance geologic map of the Kuskokwim Bay region, southwest Alaska

The rocks of the map area range from Proterozoic age metamorphic rocks of the Kanektok metamorphic complex (Kilbuck terrane) to Quaternary age mafic volcanic rocks of Nunivak Island. The map area encompasses much of the type area of the Togiak-Tikchik Complex. The geologic maps used to construct this compilation were, for the most part, reconnaissance studies done in the time period from the 1950s to 1990s. Pioneering work in the map area by J.M. Hoare and W.L. Coonrad forms the basis for much of this map, either directly or as the stepping off point for later studies compiled here. Physiographically, the map area ranges from glaciated mountains, as much as 1,500 m high, in the Ahklun Mountains to the coastal lowlands of northern Bristol Bay and the Kuskokwim River delta. The mountains and the finger lakes (drowned fiords) on the east have been strongly affected by Pleistocene and Holocene glaciation. Within the map area are a number of major faults. The Togiak-Tikchik Fault and its extension to the northeast, the Holitna Fault, are considered extensions of the Denali fault system of central Alaska. Other sub-parallel faults include the Golden Gate, Sawpit, Goodnews, and East Kulukak Faults. Northwest-trending strike-slip faults crosscut and offset northeast-trending fault systems. Rocks of the area are assigned to a number of distinctive lithologic packages. Most distinctive among these packages are the high-grade metamorphic rocks of the Kanektok metamorphic complex or Kilbuck terrane, composed of a high-grade metamorphic orthogneiss core surrounded by greenschist and amphibolite facies schist, gneiss, and rare marble and quartzite. These rocks have yielded radiometric ages strongly suggestive of a 2.05 Ga emplacement age. Poorly known Paleozoic rocks, including Ordovician to Devonian and Permian limestone, are found east of the Kanektok metamorphic complex. A Triassic(?) ophiolite complex is on the southeast side of Kuskokwim Bay; otherwise only minor Triassic rock units are known. The most widespread rocks of the area are Jurassic and Early Cretaceous(?) volcanic and volcaniclastic rocks. The Kuskokwim Group flysch is restricted largely to the northeast part of the map area. It consists primarily of shelf and minor nearshore facies rocks. Primarily exposed in the lowlands west of the Ahklun Mountains, extensive latest Tertiary and Quaternary alkalic basalt flows and lesser pyroclastic rocks form much of the bedrock of the remaining area. On Saint Matthew Island, Cretaceous volcanic and pyroclastic rocks occur that are not found elsewhere within the map area. The Kuskokwim Group and older rocks, including on Saint Matthew Island, but not the Kanektok metamorphic complex, are intruded by widely dispersed Late Cretaceous and (or) Early Tertiary granitic rocks. Much of the lowland area is mantled by unconsolidated deposits that include glacial, alluvial and fluvial, marine, estuarine, and eolian deposits. These formed during several episodes of Quaternary glaciation.

Alaska↗
USGS2012

Conceptual and numerical models of the glacial aquifer system north of Aberdeen, South Dakota

This U.S. Geological Survey report documents a conceptual and numerical model of the glacial aquifer system north of Aberdeen, South Dakota, that can be used to evaluate and manage the city of Aberdeen's water resources. The glacial aquifer system in the model area includes the Elm, Middle James, and Deep James aquifers, with intervening confining units composed of glacial till. The Elm aquifer ranged in thickness from less than 1 to about 95 feet (ft), with an average thickness of about 24 ft; the Middle James aquifer ranged in thickness from less than 1 to 91 ft, with an average thickness of 13 ft; and the Deep James aquifer ranged in thickness from less than 1 to 165 ft, with an average thickness of 23 ft. The confining units between the aquifers consisted of glacial till and ranged in thickness from 0 to 280 ft. The general direction of groundwater flow in the Elm aquifer in the model area was from northwest to southeast following the topography. Groundwater flow in the Middle James aquifer was to the southeast. Sparse data indicated a fairly flat potentiometric surface for the Deep James aquifer. Horizontal hydraulic conductivity for the Elm aquifer determined from aquifer tests ranged from 97 to 418 feet per day (ft/d), and a confined storage coefficient was determined to be 2.4x10 -5 . Estimates of the vertical hydraulic conductivity of the sediments separating the Elm River from the Elm aquifer, determined from the analysis of temperature gradients, ranged from 0.14 to 2.48 ft/d. Average annual precipitation in the model area was 19.6 inches per year (in/yr), and agriculture was the primary land use. Recharge to the Elm aquifer was by infiltration of precipitation through overlying outwash, lake sediments, and glacial till. The annual recharge for the model area, calculated by using a soil-water-balance method for water year (WY) 1975-2009, ranged from 0.028 inch in WY 1980 to 4.52 inches in WY 1986, with a mean of 1.56 inches. The annual potential evapotranspiration, calculated in soil-water-balance analysis, ranged from 21.8 inches in WY 1983 to 27.0 inches in WY 1985, with a mean of 24.6 inches. Water use from the glacial aquifer system primarily was from the Elm aquifer for irrigation, municipal, and suburban water supplies, and the annual rate ranged from 1.0 to 2.4 cubic feet per second (ft 3 /s). The MODFLOW-2005 numerical model represented the Elm aquifer, the Middle James aquifer, and the Deep James aquifer with model layers 1-3 respectively separated by confining layers 1-2 respectively. Groundwater flow was simulated with 75 stress periods beginning October 1, 1974, and ending September 30, 2009. Model grid spacing was 200 by 200 ft and boundaries were represented by specified-head boundaries and no-flow boundaries. The model used parameter estimation that focused on minimizing the difference between 954 observed and simulated hydraulic heads for 135 wells. Calibrated mean horizontal hydraulic conductivity values for model layers 1-3 were 94, 41, and 30 ft/d respectively. Vertical hydraulic conductivity values for confining layers 1 and 2 were 0.0002 and 0.0003 ft/d, respectively. Calibrated specific yield for model layer 1was 0.1 and specific storage ranged from 0.0003 to 0.0005 per foot. Calibrated mean recharge rates ranged from 2.5 in/yr where glacial till thickness was less than 10 ft to 0.8 in/yr where glacial till thickness was greater than 30 ft. Calibrated mean annual evapotranspiration rate was 8.8 in/yr. Simulated net streamflow gain from model layer 1 was 3.1 ft 3 /s.

South Dakota↗
USGS2018

Hydrologic assessment of the Edwin B. Forsythe National Wildlife Refuge

The Edwin B. Forsythe National Wildlife Refuge (hereafter Forsythe refuge or the refuge) is situated along the central New Jersey coast and provides a mixture of freshwater and saltwater habitats for numerous bird, wildlife, and plant species. Little data and information were previously available regarding the freshwater dynamics that support the refuge’s ecosystems. In cooperation with the U.S. Fish and Wildlife Service, the U.S. Geological Survey conducted an assessment of the hydrologic resources and processes in the refuge and surrounding areas to provide baseline information for evaluating restoration projects and future changes in the hydrologic system associated with climate change and other anthropogenic stressors. During spring 2015, water levels were measured at groundwater and surface-water sites in and near the Forsythe refuge. These water-level measurements, along with surface-water elevations obtained from digital elevation models, were used to construct water-table-elevation and depth-to-water maps of the refuge and surrounding areas. Water-table elevations in the refuge ranged from sea level to approximately 65 feet above sea level; in most of the refuge, the water-table elevation was within 3 feet of sea level. The water-table-elevation map indicates that the direction of shallow groundwater flow at the regional scale is generally from west to east (much of it from the northwest to the southeast), and groundwater moves downgradient from the uplands toward major groundwater discharge areas consisting of coastal streams and wetlands. The depth to water is estimated to be less than 2 feet for approximately 86 percent of the refuge, which coincides closely with the percentage of wetland area in the refuge. Depth to water in excess of 20 feet below land surface is limited to higher elevation areas of the refuge. Streamflow data collected at continuous-record streamgages and partial-record stations within the Mullica-Toms Basin were summarized. Hydrograph separation of streamflow data for eight streamgages (2004–13) reveals that base flow accounts for 68–94 percent of streamflow in basins upstream from the refuge. The high base-flow inputs underscore the importance of groundwater as a source of freshwater that supports both the streams that flow into the refuge and the hydroecology of the contributing basins. Mean annual flow typically ranged from 1.7 to 2.1 cubic feet per second per square mile at the streamgages (2004–13) and between 1.2 and 2.3 cubic feet per second per square mile at the partial-record stations (1965–2015) but was notably greater or lower than these ranges at several stations. Mean annual water budgets were estimated for multiple regions of the refuge for 2004–13 using data compiled from nearby meteorological stations and groundwater flows derived from previously calibrated groundwater-flow models. Precipitation, groundwater recharge, and evapotranspiration were estimated from available data; direct runoff was calculated as the residual component of the water balance. Groundwater recharge rates were greatest in the upland-dominated areas of the refuge with estimates of 14.4 to 18.9 inches per year, which are equivalent to 30 to 40 percent of precipitation. Groundwater recharge rates were nearly zero in the central coastal areas because these areas are major groundwater discharge zones, the water table is near land surface, the subsurface is close to saturation and cannot accept much recharge, and much of the area is underlain by thick marsh deposits likely with low permeability. Estimates of evapotranspiration varied from about 26 inches per year in the upland-dominated areas to more than 35 inches per year in the coastal wetlands, equivalent to 55–79 percent of mean annual precipitation, indicating that it is a major component of the hydrodynamics of the Forsythe refuge. On the basis of output from previously calibrated groundwater-flow models, nearly all of the groundwater exiting the surficial aquifer system in the central coastal areas of the refuge is discharged to wetlands, which highlights the importance of groundwater discharge in supporting the ecosystems of the Forsythe refuge. In the central coastal areas, horizontal flow contributes more than 90 percent of the groundwater flow to the surficial system, indicating that the upbasin areas are a substantial source of water that ultimately discharges to streams and wetlands in the refuge.

New Jersey↗
USGS2003

Geophysical and isotopic constraints on crustal structure related to mineral trends in north-central Nevada and implications for tectonic history

We combined information from Sr and Pb isotope data and magnetotelluric models to develop a new magnetic and gravity interpretation of the crustal structure of north - central Nevada to better understand the origin of mineral trends . The new interpretation suggests a crustal structure that is composed of Precambrian continental crust, transitional crust, and primarily oceanic crust that are separated by northwest- and northeast-striking fault zones. The magnetic expression of the buried Precambrian continental crust is recognized for the first time. Low magnetic values primarily reflect magnetite-poor crystalline crust rather than elevated temperatures at depth. Northwest- and northeast-striking crustal boundaries are defined by isotopic data and abrupt gradients in gravity and magnetic data. The Carlin and Battle Mountain-Eureka mineral trends are associated with two of three northwest-striking boundaries. The Carlin boundary is primarily defined by a change in density and isotopic character of the lower to middle crust. The Battle Mountain-Eureka boundary coincides with a density contrast in the upper crust and a change in isotopic character in the lower to middle crust. Magnetotelluric models suggest that the Battle Mountain-Eureka boundary represents a crustal fault zone for most of its extent, but that deep-rooted faulting is more complex near and northwest of Battle Mountain. Crustal fault zones inferred from the magnetotelluric models near the Carlin trend are oblique to it, suggesting that they may not have been controlled by the deep boundary seen in the gravity and isotopic data. The third northwest-trending boundary is related to the western edge of the buried Precambrian continent in west- central Nevada , but lacks an associated mineral trend . A northeast-striking boundary forms the northern limit of Precambrian continental and transitional crust. The boundaries may have originated as rift or transform faults during Precambrian breakup of Rodinia or as faults accommodating lateral movements or accretion during later Paleozoic tectonic events. Comparing the crustal structure to tectonic elements produced by successively younger events shows that it had a profound influence on subsequent sedimentation, deformation, magmatism, extension, and most important, mineralization.

Nevada↗
USGS1977

Spherulitic rhyolite dike from Goat Island, southeastern Alaska

Spherulites, as much as 4 mm in diameter, locally constitute almost 50 percent by volume of a dark-red rhyolite dike that intrudes porphyritic pyroxene gabbro along the northeast coast of Goat Island, 3.2 km northwest of Hydaburg, southeastern Alaska. The largest spherulites are composed mainly of o-quartz, whereas the smallest consist of a microcrystalline intergrowth of tridymite and alkali feldspar. Textural relations indicate that the radial and concentrically zoned structures are the products.of devitrification of glassy lava. The mineralogy of the dike is similar to that of other spherulitic rhyolites except that quartz occurs to the exclusion of cristobalite. The posteruptive formation of the spherulites has also resulted in alkali transfer, the groundmass of the dike being enriched in both sodium and potassium relative to the spherulites.

Alaska↗
USGS2012

Tectonic history of the north portion of the San Andreas fault system, California, inferred from gravity and magnetic anomalies

Geologic and geophysical data for the San Andreas fault system north of San Francisco suggest that the eastern boundary of the Pacific plate migrated eastward from its presumed original position at the base of the continental slope to its present position along the San Andreas transform fault by means of a series of eastward jumps of the Mendocino triple junction. These eastward jumps total a distance of about 150 km since 29 Ma. Correlation of right-laterally displaced gravity and magnetic anomalies that now have components at San Francisco and on the shelf north of Point Arena indicates that the presently active strand of the San Andreas fault north of the San Francisco peninsula formed recently at about 5 Ma when the triple junction jumped eastward a minimum of 100 km to its present location at the north end of the San Andreas fault. Prior to 5 Ma the triple junction was located at the north end of a proposed northwesterly extension of the Pilarcitos fault. This jump took place at what is now about latitude 38°20′N on the North American plate and may have occurred during part of the time when the relative motion between the North American and Pacific plates rotated 20° clockwise, resulting in transpression along the earlier transcurrent San Andreas fault system. The proposed 150-km eastward movement of the triple junction explains the submarine topography near Cape Mendocino where the continental shelf south of the Mendocino fault extends about 130 km farther west than does the shelf directly north of the fault.

Journal of Geophysical Research Solid Earth↗
USGS1979

Geology and porphyry copper-type alteration-mineralization of igneous rocks at the Christmas Mine, Gila County, Arizona

The Christmas copper deposit, located in southern Gila County, Arizona, is part of the major porphyry copper province of southwestern North America. Although Christmas is known for skarn deposits in Paleozoic carbonate rocks, ore-grade porphyry-type copper mineralization also occurs in a composite granodioritic intrusive complex and adjacent mafic volcanic country rocks. This study considers the nature, distribution, and genesis of alteration-mineralization in the igneous rock environment at Christmas. At the southeast end of the Dripping Spring Mountains, the Pennsylvanian Naco Limestone is unconformably overlain by the Cretaceous Williamson Canyon Volcanics, a westward-thinning sequence of basaltic volcanic breccia and lava flows, and subordinate clastic sedimentary rocks. Paleozoic and Mesozoic strata are intruded by Laramide-age dikes, sills, and small stocks of hornblende andesite porphyry and hornblende rhyodacite porphyry, and the mineralized Christmas intrusive complex. Rocks of the elongate Christmas stock, intruded along an east-northeast-trending fracture zone, are grouped into early, veined quartz diorite (Dark Phase), biotite granodiorite porphyry (Light Phase), and granodiorite; and late, unveined dacite porphyry and granodiorite porphyry. Biotite rhyodacite porphyry dikes extending east and west from the vicinity of the stock are probably coeval with biotite granodiorite porphyry. Accumulated normal displacement of approximately 1 km along the northwest-trending Christmas-Joker fault system has juxtaposed contrasting levels (lower, intrusive-carbonate rock environment and upper, intrusive-volcanic rock environment) within the porphyry copper system. K-Ar age determinations and whole-rock chemical analyses of the major intrusive rock types indicate that Laramide calc-alkaline magmatism and ore deposition at Christmas evolved over an extended period from within the Late Cretaceous (~75-80 m.y. ago) to early Paleocene (~63-61 m.y. ago). The sequence of igneous rocks is progressively more alkaline and silicic from basalt to granodiorite. Early (Stage I) chalcopyrite-bornite (-molybdenite) mineralization and genetically related K-silicate alteration are centered on the Christmas stock. K-silicate alteration is manifested by pervasive hornblende-destructive biotitization in the stock, biotitization of basaltic volcanic wall rocks, and a continuous stockwork of K-feldspar veinlets and quartz-K-feldspar veins in the stock and quartz-sulfide veins in volcanic rocks. Younger (Stage II) pyrite-chalcopyrite mineralization and quartz-sericite-chlorite alteration occur in a zone overlapping with but largely peripheral to the zone of Stage I stockwork veins. Within the Christmas intrusive complex, K-silicate-altered rocks in the central stock are flanked east and west by zones of fracture-controlled quartz-sericite alteration and strong pyritization. In volcanic rocks quartz-chlorite-pyrite-chalcopyrite veins are superimposed on earlier biotitization and crosscut Stage I quartz-sulfide veins. Beyond the zones of quartz-sericite alteration, biotite rhyodacite porphyry dikes contain the propylitic alteration assemblage epidote-chlorite-albite-sphene. Chemical analyses indicate the following changes during pervasive alteration of igneous rocks: (1) addition of Si, K, H, S, and Cu, and loss of Fe 3+ and Ca during intense biotitization of basalt; (2) loss of Na and Ca, increase of Fe3+/Fe2+, and strong H-metasomatism during sericitization of quartz diorite; and (3) increase in Ca, Na, and Fe3+/Fe2+, and loss of K during intense propylitization of biotite rhyodacite porphyry dikes. Thorough biotitization of biotite granodiorite porphyry in the Christmas stock was largely an isochemical process. Fluid-inclusion petrography reveals that Stage I veins are characterized by low to moderate populations of moderate-salinity and gas-rich inclusions, and sparse but ubiquitous halite-bearing inclusions. Moderate-salinity an

Open-File Report↗
USGS2002

Miocene extension and fault-related folding in the Highland Range, southern Nevada: A three-dimensional perspective

The Highland Range of southern Nevada contains a major anticline and syncline that constitute the westernmost segments of the Black Mountains accommodation zone in the highly extended Colorado River extensional corridor. The folds are defined by thick tilted sections of Miocene volcanic and sedimentary strata that accumulated immediately prior to and during regional extension. The folds are generally symmetrical, with interlimb angles that exceed 90??, subhorizontal hingelines, and steeply inclined axial surfaces. East- and west-dipping normal faults dominate the west- and east-tilted limbs of the folds, respectively. The limbs of the folds are parts of major half grabens. Tilt fanning within these half grabens and 15 new 40Ar/39Ar dates bracket major extension between about 16.5 and 11 Ma. Tilting of the opposing fold limbs occurred simultaneously and was contemporaneous with extension. The anticline and syncline are therefore interpreted as fault-related extensional folds produced by the partial, along-strike overlap of oppositely dipping normal-fault systems and attendant tilt-block domains. The anticline developed between overlapping listric normal faults that dip toward one another, including the east-dipping McCullough Range and west-dipping Keyhole Canyon faults. Each limb of the anticline is a rollover fold developed in the hanging wall of the inwardly dipping listric normal faults. The syncline formed between overlapping outwardly dipping listric faults, as adjacent fault blocks were tilted toward one another. The dominant folding style was fault-bend folding, with drag-folding and displacement-gradient folding playing subsidiary roles. The anticline and syncline significantly affected depositional patterns, with synextensional units, including two major ash-flow tuffs, thinning toward the anticlinal hinge and thickening toward the synclinal hinge. The Black Mountains accommodation zone is largely composed of intersecting northwest-trending anticlines and northeast-trending synclines, both occurring at a variety of scales depending on the amount of overlap between the opposing normal-fault systems. This three-dimensional geometry contrasts with the typical style of folding in contractional settings and may characterize extensional accommodation zones that include the partial along-strike overlap of multiple, oppositely dipping normal faults. The folds in the Highland Range serve as well-exposed analogues of similar features in hydrocarbon-rich areas of submerged continental margins. ?? 2002 Elsevier Science Ltd. All rights reserved.

Journal of Structural Geology↗
USGS2010

Attributes for MRB_E2RF1 Catchments by Major River Basins in the Conterminous United States: NLCD 2001 Tree Canopy

This tabular data set represents the mean percent tree canopy from the Canopy Layer of the National Land Cover Dataset 2001 (LaMotte and Wieczorek, 2010), compiled for every MRB_E2RF1 catchment of Major River Basins (MRBs, Crawford and others, 2006). The source data set represents tree canopy percentage for the conterminous United States for 2001. The Canopy Layer of the National Land Cover Data Set for 2001 was produced through a cooperative project conducted by the Multi-Resolution Land Characteristics (MRLC) Consortium. The MRLC Consortium is a partnership of Federal agencies (http://www.mrlc.gov), consisting of the U.S. Geological Survey (USGS), the National Oceanic and Atmospheric Administration (NOAA), the U.S. Environmental Protection Agency (USEPA), the U.S. Department of Agriculture (USDA), the U.S. Forest Service (USFS), the National Park Service (NPS), the U.S. Fish and Wildlife Service (USFWS), the Bureau of Land Management (BLM), and the USDA Natural Resources Conservation Service (NRCS). The MRB_E2RF1 catchments are based on a modified version of the U.S. Environmental Protection Agency's (USEPA) ERF1_2 and include enhancements to support national and regional-scale surface-water quality modeling (Nolan and others, 2002; Brakebill and others, 2011). Data were compiled for every MRB_E2RF1 catchment for the conterminous United States covering New England and Mid-Atlantic (MRB1), South Atlantic-Gulf and Tennessee (MRB2), the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy (MRB3), the Missouri (MRB4), the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf (MRB5), the Rio Grande, Colorado, and the Great basin (MRB6), the Pacific Northwest (MRB7) river basins, and California (MRB8).

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USGS2010

Attributes for MRB_E2RF1 Catchments by Major River Basins in the Conterminous United States: NLCD 2001 Imperviousness

This tabular data set represents the mean percent impervious surface from the Imperviousness Layer of the National Land Cover Dataset 2001, (LaMotte and Wieczorek, 2010), compiled for every MRB_E2RF1 catchment of selected Major River Basins (MRBs, Crawford and others, 2006). The source data set represents imperviousness for the conterminous United States for 2001. The Imperviousness Layer of the National Land Cover Data Set for 2001 was produced through a cooperative project conducted by the Multi-Resolution Land Characteristics (MRLC) Consortium. The MRLC Consortium is a partnership of Federal agencies (http://www.mrlc.gov), consisting of the U.S. Geological Survey (USGS), the National Oceanic and Atmospheric Administration (NOAA), the U.S. Environmental Protection Agency (USEPA), the U.S. Department of Agriculture (USDA), the U.S. Forest Service (USFS), the National Park Service (NPS), the U.S. Fish and Wildlife Service (USFWS), the Bureau of Land Management (BLM), and the USDA Natural Resources Conservation Service (NRCS). The MRB_E2RF1 catchments are based on a modified version of the U.S. Environmental Protection Agency's (USEPA) ERF1_2 and include enhancements to support national and regional-scale surface-water quality modeling (Nolan and others, 2002;Brakebill and others, 2011). Data were compiled for every MRB_E2RF1 catchment for the conterminous United States covering New England and Mid-Atlantic (MRB1), South Atlantic-Gulf and Tennessee (MRB2), the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy (MRB3), the Missouri (MRB4), the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf (MRB5), the Rio Grande, Colorado, and the Great basin (MRB6), the Pacific Northwest (MRB7) river basins, and California (MRB8).

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USGS1972

Orbital-science investigation: Part H: sketch map of the region around the candidate Littrow Apollo landing sites

The photograph in figure 25-59 and the corresponding map (fig. 25-60) show the geology of part of the lunar surface just east of the Littrow rilles at the eastern edge of Mare Serenitatis. The most striking feature of the region is the extremely low albedo of the area mapped as Eld in the western half of the map. The low albedo is believed to be caused by a thin layer of pyroclastic volcanic material at the surface. Another notable feature is the fresh-appearing ridges that cross the mare and the adjacent terra. The fine-braided texture of these ridges contrasts markedly with the rounded, subdued topography more common to such features, an indication that the ridges here may be unusually young. Also evident is a well-exposed succession of marelike plains units, which probably represent different stages in the filling of the Serenitatis basin. Several sets of rilles are present; most are roughly tangential to the basin and terminate against the different plains units according to the relative ages. In the northwest corner of the map is a relatively fresh volcanic crater chain (Cch) from which material appears to have been ejected over the surrounding terrain, forming rays of volcanic ejecta. The area thus includes an unusually wide variety of lunar features.

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