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At least 145 records · Page 8Linked to original sources
USGS2002

Preliminary report on geophysical data in Yavapai County, Arizona

Recently acquired geophysical data provide information on the geologic framework and its effect of groundwater flow and on stream/aquifer interaction in Yavapai County, Arizona. High-resolution aeromagnetic data reflect diverse rock types at and below the topographic surface and have permitted a preliminary interpretation of faults and underlying rock types (in particular, volcanic) that will provide new insights on the geologic framework, critical input to future hydrologic investigations. Aeromagnetic data map the western end of the Bear Wallow Canyon fault into the sedimentary fill of Verde Valley. Regional gravity data indicate potentially significant accumulations of low-density basin fill in Big Chino, Verde, and Williamson Valleys. Electrical and seismic data were also collected and help evaluate the approximate depth and extent of recent alluvium overlying Tertiary and Paleozoic sediments. These data will be used to ascertain the potential contribution of shallow ground-water subflow that cannot be measured by gages or flow meters and whether stream flow in losing reaches is moving as subflow or is being lost to the subsurface. The geophysical data will help produce a more robust groundwater flow model of the region.

Arizona↗
USGS1999

An interpretation of the 1997 airborne electromagnetic (AEM) survey, Fort Huachuca vicinity, Cochise County, Arizona

In March of 1997, an airborne electromagnetic (AEM) survey of the Fort Huachuca Military Reservation and immediate surrounds was conducted. This survey was sponsored by the U.S. Army and contracted through the Geologic Division of the U.S. Geological Survey (USGS). Data were gathered by Geoterrex-Dighem Ltd. of Ottawa, Canada. The survey aircraft is surrounded by a coil through which a large current pulse is passed. This pulse induces currents in the Earth which are recorded by a set of three mutually perpendicular coils towed in a "bird" about 100 m behind and below the aircraft. The bird also records the Earth's magnetic field. The system samples the Earth response to the electromagnetic pulse about every 16 m along the aircraft flight path. For this survey, the bulk of the flightpaths were spaced about 400 m apart and oriented in a northeast-southwest direction extending from bedrock over the Huachuca Mountains to bedrock over the Tombstone Hills. A preliminary report on the unprocessed data collected in the field was delivered to the U.S. Army by USGS in July 1997 (USGS Open-File Report 97–457). The final data were delivered in March, 1998 by the contractor to USGS and thence to the U.S. Army. The present report represents the final interpretive report from USGS. The objectives of the survey were to: 1) define the structure of the San Pedro basin in the Sierra Vista-Fort Huachuca-Huachuca City area, including the depth and shape of the basin, and to delineate large faults that may be active within the basin fill and therefore important in the hydrologic regime; 2) define near surface and subsurface areas that contain a large volume fraction of silt and clay in the basin fill and which both reduce the volume of available storage for water and reduce the permeability of the aquifer; and 3) to evaluate the use of the time domain electromagnetic method in the southwest desert setting as a means of mapping depth to water.

Arizona↗
USGS1996

Aftermath of Hurricane Fran in North Carolina; preliminary data on flooding and water quality

Floods resulting from Hurricane Fran, which passed through North Carolina on September 5-6, 1996, were some of the most severe and widespread in the State in recent memory. The U.S. Geological Survey (USGS) is responsible for the collection and interpretation of water-resources information, including flood data, for the Nation. As such, the USGS, in cooperation with the North Carolina Department of Environment, Health, and Natural Resources, the U.S. Army Corps of Engineers, and numerous other State and local agencies, is continuing to document the effects of Hurricane Fran on the water resources of North Carolina. The purpose of this report is to present preliminary, selected information on the flooding and associated water-quality conditions which followed Hurricane Fran in North Carolina

North Carolina↗
USGS1999

An interpretation of the 1997 airborne electromagnetic (AEM) survey, Fort Huachuca vicinity, Cochise County, Arizona

Executive Summary -- In March of 1997, an airborne electromagnetic (AEM) survey of the Fort Huachuca Military Reservation and immediate surrounds (location map, http://geopubs.wr.usgs.gov/open-file/of99-007-b/index.jpg) was conducted. This survey was sponsored by the U.S. Army and contracted through the Geologic Division of the U.S. Geological Survey (USGS). Data were gathered by Geoterrex-Dighem Ltd. of Ottawa, Canada. The survey aircraft is surrounded by a coil through which a large current pulse is passed. This pulse induces currents in the Earth which are recorded by a set of three mutually perpendicular coils towed in a 'bird' about 100 m behind and below the aircraft. The bird also records the Earth's magnetic field. The system samples the Earth response to the electromagnetic pulse about every 16 m along the aircraft flight path. For this survey, the bulk of the flightpaths were spaced about 400 m apart and oriented in a northeast-southwest direction extending from bedrock over the Huachuca Mountains to bedrock over the Tombstone Hills. A preliminary report on the unprocessed data collected in the field was delivered to the U.S. Army by USGS in July 1997 (USGS Open-File Report 97?457). The final data were delivered in March, 1998 by the contractor to USGS and thence to the U.S. Army. The present report represents the final interpretive report from USGS. The objectives of the survey were to: 1) define the structure of the San Pedro basin in the Sierra Vista-Fort Huachuca-Huachuca City area, including the depth and shape of the basin, and to delineate large faults that may be active within the basin fill and therefore important in the hydrologic regime; 2) define near surface and subsurface areas that contain a large volume fraction of silt and clay in the basin fill and which both reduce the volume of available storage for water and reduce the permeability of the aquifer; and 3) to evaluate the use of the time domain electromagnetic method in the southwest desert setting as a means of mapping depth to water. Chapter one, written by M.E. Gettings, reports the results of the analysis of the aeromagnetic anomaly data. Depths to magnetic rocks computed from these data are in good agreement with depths from gravity anomaly models (Gettings and Houser, in prep.) and confirm and refine the location of the bedrock highs which reach to within 200 m of the surface in several parts of the study area. The highly faulted and generally shallow character of the basin within the study area deduced from the gravity studies is also evident in the aeromagnetic data. The caldera ring fault delimiting the buried structural southwest edge of the Tombstone caldera is expressed in the magnetic data and deeper intrusives extending outside the caldera to the southwest are inferred. Several magnetic bodies occur at shallow depths within the Precambrian granite of the Huachuca Mountains along the eastern foothills of the mountains. These are inferred to be Tertiary intrusives but remain to be confirmed by field work if any of their uppermost dikes or apotheses are exposed. Faults delineating the east-west trending bedrock high beneath the city of Sierra Vista appear to be shallow and should be investigated for surface expressions. Chapter two, written by Jeff Wynn, analyzes and interprets the conductivity depth transforms (CDTs) and provides a general evaluation of the data quality. He concludes that there is a good general correlation between the uppermost conductor seen in the CDTs and water table depth in many cases. Detailed comparisons between the ground-based vertical electric soundings (VES) and the CDTs are reported in this chapter. The two sets of data compare well in general for most sounding sites where the VES data are not noisy.

Arizona↗
USGS2008

40Ar/39Ar data for white mica, biotite, and K-feldspar samples from low-grade metamorphic rocks in the Westminster Terrane and adjacent rocks, Maryland

This report contains reduced 40 Ar/ 39 Ar data of white mica and K-feldspar mineral separates and matrix of a whole rock phyllite, all from low-grade metamorphic rocks of the Westminster terrane and adjacent strata in central Maryland. This report presents these data in a preliminary form, but in more detail than can be accommodated in todays professional journals. Also included in this report is information on the location of the samples and a brief description of the samples. The data contained herein are not interpreted in a geological context, and care should be taken by readers unfamiliar with argon isotopic data in the use of these results; many of the individual apparent ages are not geologically meaningful. This report is primarily a detailed source document for subsequent publications that will integrate these data into a geological context.

Maryland↗
USGS2007

Mercury at the Oat Hill Extension Mine and James Creek, Napa County, California: Tailings, sediment, water, and biota, 2003-2004

The Oat Hill Extension (OHE) Mine is one of several mercury mines located in the James Creek/Pope Creek watershed that produced mercury from the 1870's until 1944 (U.S. Bureau of Mines, 1965). The OHE Mine developed veins and mineralized fault zones hosted in sandstone that extended eastward from the Oat Hill Mine. Waste material from the Oat Hill Mine was reprocessed at the OHE Mine using gravity separation methods to obtain cinnabar concentrates that were processed in a retort. The U.S. Bureau of Land Management requested that the U.S. Geological Survey measure and characterize mercury and other chemical constituents that are potentially relevant to ecological impairment of biota in tailings, sediment, and water at the OHE Mine and in the tributaries of James Creek that drain the mine area (termed Drainage A and B ) (Figs. 1 and 2). This report summarizes such data obtained from sampling of tailings and sediments at the OHE on October 17, 2003; water, sediment, and biota from James Creek on May 20, 2004; and biota on October 29, 2004. These data are interpreted to provide a preliminary assessment of the potential ecological impact of the mine on the James Creek watershed. The mine tailings are unusual in that they have not been roasted and contain relatively high concentrations of mercury (400 to 1200 ppm) compared to unroasted waste rock at other mines. These tailings have contaminated a tributary to James Creek with mercury primarily by erosion, on the basis of higher concentration of mercury (780 ng/L) measured in unfiltered (total mercury, Hg T ) spring water flowing from the OHE to James Creek compared to 5 to 14 ng/L Hg T measured in James Creek itself. Tailing piles (presumably from past Oat Hill mine dumping) near the USBLM property boundary and upstream of the main OHE mine drainage channel ( Drainage A ; Fig. 2) also likely emit mercury, on the basis of their mercury composition (930 to 1200 ppm). The OHE spring water is likely an appreciable source of sulfate and carbonate to James Creek, because the spring water was enriched in sulfate (130 mg/L) and carbonate (430 mg/L as CaCO 3 ) compared to James Creek water (70 to 100 mg/L SO 4 2- and 110 to 170 mg/L as CaCO 3 ) at the time of sampling. Concentrations of mercury in active channel sediment from James Creek are variable and potentially high, on the basis of chemical analysis (2.5 to 17 _g/g-wet sediment) and easily visible cinnabar grains in panned concentrates. Average (geometric mean) organic mercury (presumably monomethyl mercury (MMHg); §2.3.3) concentrations in several invertebrate taxa collected from the James Creek watershed locations were higher than invertebrates taken from a Northern California location lacking a known point source of mercury. The mean proportion of MMHg to total mercury in James Creek predatory insect samples was 40 percent (1 standard deviation = 30 percent); only 40 percent of all insect samples had a MMHg/Hg T proportion greater than 0.5. The low proportions of MMHg measured in invertebrates in James Creek and the presence of cinnabar in the creek suggest that some invertebrates may have anomolously high Hg concentrations as a result of the injestion or adhesion of extremely fine-grained cinnabar particles. Interpretation of Hg T in frogs and fish as an indicator of mercury reactivity, biouptake, or trophic transfer is limited, pending MMHg measuremens, by the possibility of these whole-body samples having contained cinnabar particles at the time of analysis. To minimize this limitation, the gastrointestinal tracts and external surfaces of all amphibians, where cinnabar most likely resides, were carefully flushed to remove any visible particles. However, extremely fine-grained, invisible, adhesive cinnabar particles likely exist in the amphibians' habitats. Hg T in foothill yellow-legged frogs collected from the James Creek study area, ranging from 0.1 to 0.6 μg/g Hg, was on average twice that of an extensive database compiled from Hg T in frogs studied throughout Northern California. Average concentrations of Hg T in frogs from James Creek were similar upstream (0.18 μg/g) and downstream (0.15 μg/g) of the confluence with Tributary 1 and at the lower Corona Mine adit drainage (0.14 μg/g). Frogs may be susceptible to trophic transfer of MMHg from invertebrates, but further study is required to rule out cinnabar ‘contamination.’ Hg T concentrations in rainbow trout collected from James Creek upstream and downstream of Tributary 1 averaged 0.10 μg/g and 0.13 μg/g, respectively. Compared to invertebrates, trout Hg T was less variable, suggesting that trout were less contaminated with cinnabar. California roach had significantly higher Hg T on average than trout (0.16 vs. 0.12 μg/g), and can be considered moderately contaminated compared to the same species from other sites in Northern California, which average 0.12 μg/g Hg. While limited measurements of mercury in water, sediment, and fish exceed, in some samples, predefined ecologically protective criteria for mine-impacted California systems, they do not clearly demonstrate that the biota residing in James Creek in the vicinity of the OHE are ecologically impaired. The potential for ecological impairment is clearly evident from invertebrate methyl mercury results and may manifest in other biological ecosystem residents that have yet to be studied (e.g., piscivorous birds). Methyl mercury concentrations in flowing water and sediment from James Creek and the tributary that drains the OHE are relatively low, ranging from 0.04 to 0.08 ng/L, although these data should be cautiously interpreted (see §3.2). While the results of this investigation suggest that the OHE contributes inorganic mercury to James Creek, they do not indicate the extent to which the OHE site is ecologically impairing biota relative to other sources of mercury. Improved sampling and analytical methods are recommended for future study.

California↗
USGS2008

Audiomagnetotelluric data and preliminary two-dimensional models from Spring, Dry Lake, and Delamar Valleys, Nevada

This report presents audiomagnetotelluric (AMT) data along fourteen profiles in Spring, Delamar, and Dry Lake Valleys, and the corresponding preliminary two-dimensional (2-D) inverse models. The AMT method is a valuable tool for estimating the electrical resistivity of the Earth over depth ranges from a few meters to less than one kilometer, and it is important for revealing subsurface structure and stratigraphy within the Basin and Range province of eastern Nevada, which can be used to define the geohydrologic framework of the region. We collected AMT data by using the Geometrics StrataGem EH4 system. Profiles were 0.7 - 3.2 km in length with station spacing of 50-400 m. Data were recorded in a coordinate system parallel to and perpendicular to the regional geologic-strike direction with Z positive down. We show AMT station locations, sounding curves of apparent resistivity, phase, and coherency, and 2-D models of subsurface resistivity along the profiles. The 2-D inverse models are computed from the transverse electric (TE), transverse magnetic (TM), and TE+TM mode data by using a conjugate gradient, finite-difference method. Preliminary interpretation of the 2-D models defines the structural framework of the basins and the resistivity contrasts between alluvial basin-fill, volcanic units, and carbonate basement rocks.

Nevada↗
USGS1946

Stratigraphy and structure of the area of the Killik, Chandler, Anaktuvuk, and Colville Rivers, Alaska

This report deals with results of field and laboratory studies carried out to May 1946 by the Geological Survey, largely as part of the Navy Department's program of petroleum investigations in northern Alaska. The immediate purpose of the work has been to collect and interpret stratigraphic and structural data pertinent to drilling in the Umiat area. Field studies were made during the summers of 1944 and 1945 in the drainage areas of the Colville, Killik, Chandler, and. Anaktuvuk Rivers (fig. 1). Paleontologic and microlithologic studies, together with stratigrahica1 and structural analysis of the areas, were carried out in the petroleum laboratory in Fairbanks. This work led. to preparation of a preliminary report submitted. in December, 1945. Additional detailed studies, in the Survey laboratories and offices in Washington, D. C., have resulted in some modification of earlier conclusions and changes in illustrations. The changes are minor and have no significant bearing on drilling in the Umiat area. The present report is accompanied. by revised conies of figures 1, 2, 3 (sheet 1) and. 5. These illustrations should be substituted for the comparable figures of the preliminary report. Figures 3 (sheet 2), 4, and. 6 of the earlier report stand unchanged and should, be added to the illustrations accompanying the present report. It is believed that work to date has revealed the general geologic picture of the area and. that the sequence of Upper Cretaceous rocks is established. The section of rocks in Umiat Test No. 1 has been approximately located within the sequence. This report, and the work on which it is based was done under the supervision of George O. Gates, who has contributed. much to the study.

Alaska↗
USGS1985

Geologic characteristics of sediment- and volcanic-hosted disseminated gold deposits - Search for an occurrence model

The current expansion of resource information, particularly on "disseminated" gold, and the improved technologies now available for resource investigations should place us in an enhanced position for developing a better predictive methodology for meeting one of the important responsibilities of the U.S. Geological Survey-to examine and assess the mineral resources of the geologic terranes composing the public (and privately owned) lands of the United States. The first step is systematic organization of these data. Geologic-occurrence models are an effective systematic method by which to organize large amounts of resource information into a logical sequence facilitating its use more effectively in meeting several industry and Survey objectives, which include the exploration for resources and the assessment of resource potential for land-use decisions. Such models also provide a scientific basis for metallogenesis research, which considers the observable features or attributes of ore occurrence and their "fit" into the Earth's resource puzzle. The use of models in making resource assessments/appraisals was addressed by Shawe (1981), who reported the results of a workshop on methods for resource appraisal of Wilderness and Conterminous United States Mineral Appraisal Program (CUSMAP; 1:250,000-scale quadrangles) areas. The Survey's main objective in the 1982 workshop was to evaluate the status of knowledge about disseminated or very fine grained gold deposits and, if possible, to develop an occurrence model(s). This report on the workshop proceedings has three main objectives: (1) Education through the publication of a summary review and presentation of new thinking and observations about the scientific bases for those geologic processes and environments that foster disseminated gold-ore formation; (2) systematic organization of available geologic, geochemical, and geophysical information for a range of typical disseminated gold deposits (including recognition of gaps in those data); and (3) assessment of current understanding (as presented in objective 2) toward formulating an empirical ore-occurrence model for this type of deposit. As such, this volume represents a preliminary first step at classification and provides a source of pertinent background information. Readers of this volume will soon discover, however, that full agreement has not yet been achieved in the interpretation of some of the geologic evidence. The resulting variations in tentative occurrence models for these controversial deposits ultimately will be resolved by filling the gaps in information that have already been identified. Thus, this volume does not report a U.S. Geological Survey consensus; the conclusions expressed in each chapter represent the particular interpretations of the various workshop participants.

Arizona, California, Idaho, Nevada, Utah↗
USGS2002

Logs and data from trenches across the Hayward Fault at Tyson's Lagoon (Tule Pond), Fremont, Alameda County, California

INTRODUCTION The purpose of this publication is to make available detailed trench logs (sheets 1, 2), radiocarbon dates (table 1) and pollen data (fig. 1) obtained as a result of an intensive subsurface investigation of the Hayward Fault at Tyson's Lagoon (Tule Pond) from August to November 2000 (figs. 1, 2 on sheet 1). The Hayward Fault is recognized to be among the most hazardous in the United States (Working Group on California Earthquake Probabilities, 1999). This document makes available geologic evidence for historical and prehistoric surfacerupturing earthquakes that were recorded at the site. Prehistoric earthquakes deduced from geologic evidence are called paleoearthquakes. Establishing a chronology of paleoearthquakes is of immediate use in resolving the level of hazard posed by the Hayward Fault for producing large earthquakes in the future. Preliminary findings of this investigation have been presented in Lienkaemper and others (2001). A formal report on our conclusions based on these data is in preparation. The investigation at Tyson's Lagoon is ongoing, so these products should not be considered final. Lienkaemper, Dawson, and Personius interpreted the geology and logged the trenches. Seitz and Reidy performed analyses on radiocarbon and pollen samples, respectively. Schwartz led the critical-review field team. Previous trenching work was done at Tyson's Lagoon (figs. 2, 3 on sheet 1). Lienkaemper (1992) references the location of most of those trenches. The earlier trenching was generally for the evaluation of local faultrupture hazard, except for the study of Williams (1993), which was a paleoearthquake investigation. An unpublished study by J.N. Alt in 1998 (shown on our site map as trenches 98A and 98B, fig. 3, on sheet 1), also sought evidence of paleoearthquakes. Alt's study and one by Woodward-Clyde and Associates (1970; trenches 70A to 70G, fig. 3) were located south of Walnut Avenue in one of the few areas that still remain undisturbed and were, thus, useful in planning our work in 2000.

Miscellaneous Field Studies Map↗
USGS2015

Preliminary interpretation of industry two-dimensional seismic data from Susitna Basin, south-central Alaska

Located approximately 80 kilometers northwest of Anchorage, Alaska, the Susitna Basin is a complex sedimentary basin whose tectonic history has been poorly understood. Recent interpretation of two-dimensional seismic reflection data integrated with well, aeromagnetic, and gravity data provides new insights into the structural and stratigraphic nature of the basin. This report presents an interpretation of 41 two-dimensional seismic reflection lines, acquired by industry from the 1960s to the 1980s. Our interpretation of the seismic data focused mainly on picking two Eocene stratigraphic units and a presumed base of Tertiary horizon. Based on our interpretation of the seismic data, the structural features in the basin appear to be generally contractional, as evidenced by the presence of many reverse faults, thrust faults, and folds, with the contraction mainly oriented east-west. This result is contrary to prior inferences of most previous geologic studies that showed normal faults. Several regional reverse faults have been identified in the seismic data and appear to divide the basin into three regions or “sides”: east, west, and south. The eastern seismic lines show evidence of numerous short-wavelength antiforms that appear to correspond to a series of northeast-trending lineations observed in aeromagnetic data, which have been interpreted as being due to folding of Paleogene volcanic strata. The eastern side of the basin is also cut by a number of reverse faults and thrust faults, the majority of which strike north-south. The western side of the Susitna Basin is cut by a series of regional reverse faults and is characterized by synformal structures in two fault blocks between the Kahiltna River and Skwentna faults. These synforms are progressively deeper to the west in the footwalls of the east-vergent Skwentna and northeast-vergent Beluga Mountain reverse faults. Although the seismic data are limited to the south, we interpret a potential regional south-southeast-directed reverse fault striking east-northeast on the east side of the basin that may cross the entire southern portion of the basin.

Alaska↗
USGS1996

Compilation and preliminary interpretations of hydrologic and water-quality data from the Railroad Industrial Area, Fairbanks, Alaska, 1993-94

Commercial and industrial activities in the Railroad Industrial Area in Fairbanks, Alaska, have resulted in accidental releases of chemicals to the subsurface. Such releases have generated concern regarding local ground-water quality and the potential impact on nearby water-supply wells. Consequently, a study is being conducted to characterize the environmental and hydrologic conditions in the area. Existing reports from numerous previous investigations in the area were reviewed and relevant information from these documents was compiled. Both ground- and surface-water elevations were measured approximately monthly at as many as 50 sites during mass measurements. Selected sites were measured more frequently to assess short-term changes in the ground- and surface-water systems. Supplemental data were also collected outside of the study area to aid in interpretation. Ground water was sampled and analyzed to define the extent of the area affected by petroleum hydrocarbons and chlorinated solvents. Data show that water levels in nearby rivers and sloughs have a considerable influence on ground-water flow in the study area. Seasonal and shorter term changes in river stage frequently alter and even reverse the direction of ground-water flow. The local ground-water system typically has an upward flow component, but this component is reversed in the upper part of the aquifer during periods of high water levels in the Chena River. These periodic changes in the magnitude and direction of ground-water flow have a considerable influence on the transport of dissolved hydrocarbons in the subsurface. Both petroleum hydrocarbons and chlorinated solvents were found in ground water at the study area. Typical degradation products of these compounds were also found, indicating that biodegradation by indigenous microorganisms is occurring.

Water-Resources Investigations Report↗
USGS2007

Audiomagnetotelluric Data and Two-Dimensional Models from Spring, Snake, and Three Lakes Valleys, Nevada

Audiomagnetotelluric (AMT) data along thirteen profiles in Spring, Snake, and Three Lakes Valleys, and the corresponding two-dimensional (2-D) inverse models, are presented. The AMT method is a valuable tool for estimating the electrical resistivity of the Earth over depth ranges of a few meters to roughly one kilometer. It is important for revealing subsurface structure and stratigraphy within the Basin and Range province of eastern Nevada that can be used to define the geohydrologic framework of the region. We collected AMT data using the Geometrics StrataGem EH4 system. Profiles were 1.2 to 4.6 km in length with station spacing of 100-400 m. Data were recorded in a coordinate system parallel to and perpendicular to the assumed regional geologic strike direction. We show station locations, sounding curves of apparent resistivity, phase, and coherency, and 2-D models. The 2-D inverse models are computed from the transverse electric (TE), transverse magnetic (TM), and TE+TM mode data using the conjugate gradient, finite-difference method of Rodi and Mackie (2001). Preliminary interpretation of these models defines the structural framework of the basins and the resistivity contrasts between alluvial basin-fill, volcanic units, and carbonate/clastic rocks.

Open-File Report↗
USGS2002

June 2002 floods in the Red River of the North basin in northeastern North Dakota and northwestern Minnesota

The Red River of the North is a complex river system in the north-central plains of the United States. The river continues to affect the people and property within its basin. During June of 2002, major flooding occurred for the third time in 5 years in the Red River of the North Basin, especially on tributaries in northwestern Minnesota. The worst damage occurred in Roseau, Minn., where about 95 percent of the town was inundated. Extensive damage to roads, bridges, and crops occurred throughout the flooded area in northwestern Minnesota and northeastern North Dakota. Roseau County, Minn., was designated a major disaster area on June 14, 2002, by President Bush and later twelve more counties were added to the disaster declaration. Unlike the 1997 floods, which were the result of record-high, region-wide snowpacks and a late spring blizzard, the June 2002 floods were the result of heavy rainfall that swept across the region on June 9-10 and again on June 22-24, 2002. Flooding in the Red River of the North Basin commonly is caused by spring snowmelt, and the severity of the flooding is affected by (1) substantial precipitation in the fall that produces high levels of soil moisture; (2) above-normal snowfall in the winter; (3) moist, frozen ground that prohibits infiltration of moisture; (4) a late spring thaw; (5) above-normal precipitation during spring thaw; and (6) ice jams (temporary dams of ice) on rivers and streams. Flooding during June 2002, however, was not caused by most factors usually associated with major flooding in the Red River Basin. In fact, precipitation had been below normal since late last summer and as of June 1, 2002, the flooded area was in a moderate drought based on the Palmer Drought Severity Index. The U.S. Geological Survey (USGS), one of the principal Federal agencies responsible for the collection and interpretation of water-resources data, works with other Federal, State, and local agencies to ensure that accurate and timely data are available for making decisions regarding the public's welfare (a listing of cooperators in the Red River Basin is given at the end of this report). This report presents preliminary meteorologic data provided by the National Weather Service, Grand Forks Office and water-resources 2002 flood data that were obtained from selected streamflow-gaging stations located in the Red River of the North Basin (fig. 1). Historical peak stages and peak discharges and the June 2002 peak stages, peak discharges, and recurrence intervals are shown in table 1. The streamflow-gaging stations are listed in downstream order by station number, and station locations are shown in figure 1. The June 2002 peak stages and peak discharges given in this preliminary report may be revised as site surveys are completed and additional field data are reviewed in the upcoming months. The peak discharges are used to determine the probability, often expressed in recurrence intervals, that a given discharge will be exceeded in the future. For example, a flood that has a 1-percent chance of exceedance in any given year would, on the long-term average, be expected to occur only about once a century; therefore, the flood would be termed a "100-year flood." However, the chance of such a flood occurring in any given year is 1 percent. Thus, a 100-year flood can occur in successive years at the same location. In some instances, recurrence interval estimates can be based on periods of regulated flow or made with historic adjustments when historic data are available.

Minnesota, North Dakota↗
USGS1983

A seismic study of Yucca Mountain and vicinity, southern Nevada; data report and preliminary results

From 1980 to 1982, the U.S. Geological Survey conducted seismic refraction studies at the Nevada Test Site to aid in an investigation of the regional crustal structure at a possible nuclear waste repository site near Yucca Mountain. Two regionally distributed deployments and one north-south deployment recorded nuclear events. First arrival times from these deployments were plotted on a location map and contoured to determine traveltime delays. The results indicate delays as large as 0.5 s in the Yucca Mountain and Crater Flat areas relative to the Jackass Flats area. A fourth east-west deployment recorded a chemical explosion and was interpreted using a two-dimensional computer raytracing technique. Delays as high as 0.7 s were observed over Crater Flat and Yucca Mountain. The crustal model derived from this profile indicates that Paleozoic rocks, which outcrop to the east at Skull Mountain and the Calico Hills, and to the west at Bare Mountain, lie at a minimum depth of 3 km beneath part of Yucca Mountain. These results confirm earlier estimates based on the modeling of detailed gravity data. A mid-crustal boundary at 15 ? 2 km beneath Yucca Mountain is evidenced by a prominent reflection recorded beyond 43 km range at 1.5 s reduced time. Other mid-crustal boundaries have been identified at 24 and 30 km and the total crustal thickness is 35 km.

Open-File Report↗
USGS2012

Geologic map of the Cook Inlet region, Alaska, including parts of the Talkeetna, Talkeetna Mountains, Tyonek, Anchorage, Lake Clark, Kenai, Seward, Iliamna, Seldovia, Mount Katmai, and Afognak 1:250,000-scale quadrangles

In 1976, L.B. Magoon, W.L. Adkinson, and R.M. Egbert published a major geologic map of the Cook Inlet region, which has served well as a compilation of existing information and a guide for future research and mapping. The map in this report updates Magoon and others (1976) and incorporates new and additional mapping and interpretation. This map is also a revision of areas of overlap with the geologic map completed for central Alaska (Wilson and others, 1998). Text from that compilation remains appropriate and is summarized here; many compromises have been made in strongly held beliefs to allow construction of this compilation. Yet our willingness to make interpretations and compromises does not allow resolution of all mapping conflicts. Nonetheless, we hope that geologists who have mapped in this region will recognize that, in incorporating their work, our regional correlations may have required some generalization or lumping of map units. Many sources were used to produce this geologic map and, in most cases, data from available maps were combined, without generalization, and new data were added where available. A preliminary version of this map was published as U.S. Geological Survey Open-File Report 2009–1108. The main differences between the versions concern revised mapping of surfical deposits in the northern and eastern parts of the map area. Minor error corrections have been made also.

Alaska↗