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At least 325 records · Page 18Linked to original sources
USGS1995

Preliminary geologic map of the Mount Hood 30- by 60-minute Quadrangle, Northern Cascade Range, Oregon

This map shows the geology of the central and eastern parts of the Cascade Range in northern Oregon. The Quaternary andesitic stratovolcano of Mount Hood dominates the northwest quarter of the quadrangle, but nearly the entire area is underlain by arc-related volcanic and volcaniclastic rocks of the Cascade Range. Most stratigraphic units were emplaced since middle Miocene time, and all are Oligocene or younger. Despite the proximity of the map area to the Portland metropolitan area, large parts remained virtually unstudied or known only from limited reconnaissance until the late 1970s. A notable exception is the area surrounding Mount Hood, where mapping and chemical analyses by Wise (1969) provided a framework for geologic interpretation. Mapping since 1975 was conducted first to understand the stratigraphy and structure of the Columbia River Basalt Group (Anderson, 1978; Vogt, 1981; J.L. Anderson, in Swanson and others, 1981; Vandiver-Powell, 1978; Burck, 1986) and later to examine the geothermal potential of Mount Hood (Priest and others, 1982). Additional mapping was completed in 1985 for a geologic map of the Cascade Range in Oregon (Sherrod and Smith, 1989). From 1987 to 1990, detailed mapping was conducted in three 15-minute quadrangles on a limited basis (D.R. Sherrod, unpublished mapping) (see fig. 1 for index to mapping). An ongoing volcanic hazards study of Mount Hood by the U.S. Geological Survey (Scott and others, 1994) has provided the catalyst for completing the geologic map of the Mount Hood 30-minute by 60-minute quadrangle. As of June 1994, only two broad areas still remain largely unmapped. One of these areas, labeled 'unmapped' on the geologic map, lies in the Salmon River valley south of Zigzag along the west margin of the quadrangle. Although strata of the Columbia River Basalt Group in the Salmon River valley were mapped in detail by Burck (1986), the overlying middle and upper(?) Miocene lava flows, volcaniclastic strata, and intrusions have never been studied. The other poorly known area, the Mutton Mountains in the southeastern part of the map area, consists of Oligocene and lower Miocene volcanic and volcaniclastic rocks. Overlying lava flows of the Columbia River Basalt Group were mapped in some detail by Anderson (in Swanson and others, 1981).

Open-File Report↗
USGS2011

Geologic map of the Ganiki Planitia quadrangle (V-14), Venus

The Ganiki Planitia (V-14) quadrangle on Venus, which extends from 25° N. to 50° N. and from 180° E. to 210° E., derives its name from the extensive suite of plains that dominates the geology of the northern part of the region. With a surface area of nearly 6.5 x 10 6 km 2 (roughly two-thirds that of the United States), the quadrangle is located northwest of the Beta-Atla-Themis volcanic zone and southeast of the Atalanta Planitia lowlands, areas proposed to be the result of large scale mantle upwelling and downwelling, respectively. The region immediately south of Ganiki Planitia is dominated by Atla Regio, a major volcanic rise beneath which localized upwelling appears to be ongoing, whereas the area just to the north is dominated by the orderly system of north-trending deformation belts that characterize Vinmara Planitia. The Ganiki Planitia quadrangle thus lies at the intersection between several physiographic regions where extensive mantle flow-induced tectonic and volcanic processes are thought to have occurred. The geology of the V-14 quadrangle is characterized by a complex array of volcanic, tectonic, and impact-derived features. There are eleven impact craters with diameters from 4 to 64 km, as well as four diffuse 'splotch' features interpreted to be the product of near-surface bolide explosions. Tectonic activity has produced heavily deformed tesserae, belts of complex deformation and rifts as well as a distributed system of fractures and wrinkle ridges. Volcanic activity has produced extensive regional plains deposits, and in the northwest corner of the quadrangle these plains host the initial (or terminal) 700 km of the Baltis Vallis canali, an enigmatic volcanic feature with a net length of ~7,000 km that is the longest channel on Venus. Major volcanic centers in V-14 include eight large volcanoes and eight coronae; all but one of these sixteen features was noted during a previous global survey. The V-14 quadrangle contains an abundance of minor volcanic features including individual shield volcanoes and localized fissure eruptions as well as many small annular structures and domes, which often serve as the source for local lava flows. The topographic and geophysical characteristics of the Ganiki Planitia quadrangle are less complex than the surface geology, but they yield equally valuable information about the region’s formation and evolution. Referenced to the mean planetary radius of 6051.84 km, the average elevation in the quadrangle is -0.26±0.86 km (2σ) with a full range of -2.58 km to 1.85 km. The highest 2.5 percent of elevations in the quadrangle (above 0.60 km) are associated primarily with the major tessera blocks and the peaks of a few volcanic edifices, whereas the lowest 2.5 percent (below -1.12 km) mostly occur within corona interiors and in the northwest corner of the quadrangle where the plains begin to merge into the Atalanta Planitia lowlands. At the ~4.6 km/pixel scale of the topography data, the mean point-to-point topographic slope is 0.63° and topographic slopes greater than 2° cover less than 5 percent of the region. Overall, the topography of the Ganiki Planitia quadrangle can be characterized as flat, low lying, and nearly devoid of abrupt topographic variation. Complementing this gentle topography, the geoid anomaly has a generally linear gradient that decreases north-northwest from a high of ~20 m at the southern edge of the quadrangle (the northern border of the Atla Regio anomaly) to a low of -30 to -40 m along the northern edge (Konopliv and others, 1999). The vertical component of the gravity anomaly varies from ~50 mGal to -40 mGal, and integrated analysis of the gravity and topography data indicates that dynamically supported regions and areas of thickened crust are both present within the quadrangle. Because the Ganiki Planitia quadrangle is a plains-dominated lowland area that lies between several major physiographic provinces (namely, Atla Regio, Atalanta Planitia, and Vinmara Planitia), a geologic map of the region may yield insight into a wide array of important problems in Venusian geology. The current mapping effort and analysis complements previous efforts to characterize aspects of the region’s geology, for example stratigraphy near parabolic halo crater sites, volcanic plains emplacement, wrinkle ridges, volcanic feature distribution, volcano deformation, coronae characteristics, lithospheric flexure, and various features along a 30±7.58° N. geotraverse. Our current research focuses on addressing four specific questions. Has the dominant style of volcanic expression within the quadrangle varied in a systematic fashion over time? Does the tectonic deformation within the quadrangle record significant regional patterns that vary spatially or temporally, and if so what are the scales, orientations and sources of the stress fields driving this deformation? If mantle upwelling and downwelling have played a significant role in the formation of Atla Regio and Atalanta Planitia as has been proposed, does the geology of Ganiki Planitia record evidence of northwest-directed lateral mantle flow connecting the two sites? Finally, can integration of the tectonic and volcanic histories preserved within the quadrangle help constrain competing resurfacing models for Venus?

Scientific Investigations Map↗
USGS2002

Arctic Refuge coastal plain terrestrial wildlife research summaries

In 1980, when the U.S. Congress enacted the Alaska National Interest Lands Conservation Act (ANILCA), it also mandated a study of the coastal plain of the Arctic National Wildlife Refuge. Section 1002 of ANILCA stated that a comprehensive inventory of fish and wildlife resources would be conducted on 1.5 million acres of the Arctic Refuge coastal plain (1002 Area). Potential petroleum reserves in the 1002 Area were also to be evaluated from surface geological studies and seismic exploration surveys. Results of these studies and recommendations for future management of the Arctic Refuge coastal plain were to be prepared in a report to Congress. In 1987, the Department of the Interior published the Arctic National Wildlife Refuge, Alaska, Coastal Plain Resource Assessment - Report and Recommendations to the Congress of the United States and Final Environmental Impact Statement. This report to Congress identified the potential for oil and gas production (updated* most recently by the U.S. Geological Survey in 2001), described the biological resources, and evaluated the potential adverse effects to fish and wildlife resources. The 1987 report analyzed the potential environmental consequences of five management alternatives for the coastal plain, ranging from wilderness designation to opening the entire area to lease for oil and gas developement. The report's summary recommended opening the 1002 Area to an orderly oil and gas leasing program, but cautioned that adverse effects to some wildlife populations were possible. Congress did not act on this recommendation nor any other alternative for the 1002 Area, and scientists continued studies of key wildlife species and habitats on the coastal plain of the Arctic Refuge and surrounding areas. This report contains updated summaries of those scientific investigations of caribou, muskoxen, predators (grizzly bears, wolves, golden eagles), polar bears, snow geese, and their wildlife habitats. Contributions to this report were made by scientists affiliated with the U.S. Geological Survey; U.S. Fish and Wildlife Service; Alaska Department of Fish and Game; University of Alaska-Fairbanks; Canadian Wildlife Service; Yukon Department of Renewable Resources; and the Northwest Territories Department of Resources, Wildlife, and Economic Development. Sections of the report presenting new information on caribou and forage plants were peer-reviewed by three independent, non-affiliated scientists. The remaining sections summarize previously published peer-reviewed scientific papers and were reviewed by a single independent scientist. The U.S. Geological Survey and the U.S. Fish and Wildlife Service collaborated in the publication of this report.

Alaska, Northwest Territories, Yukon Territory↗
USGS2021

Three-dimensional geologic map of the Brady geothermal area, Nevada

The three-dimensional (3D) geologic map characterizes the subsurface in the Brady geothermal area in the northern Hot Springs Mountains of northwestern Nevada. We built the 3D map by integrating the results from detailed geologic mapping, seismic-reflection, potential-field-geophysical, and lithologic well-logging investigations completed in the study area. This effort was undertaken to investigate the geologic structure in the geothermal field and geologic controls on hydrothermal circulation. This characterization of the controls on hydrothermal circulation is applicable to the assessment, exploration, and development of analogous geothermal resources. The 3D map area is 4 kilometers (km) wide along the west-northwest-to-east-southeast axis and 6 km wide along the north-northeast-to-south-southwest axis and extends to 1.0 km below sea level, approximately 2.5 km below the land surface. We describe the geologic units and structures in the map area, discuss the methods used to integrate the geologic and geophysical information into the 3D geologic interpretation, and calculate several geologic factors that may aid in our understanding of hydrothermal circulation. Map sheet 1 provides horizontal and vertical section views and oblique perspective views from several angles of the 3D geologic map. Map sheet 2 provides views of derivative calculations based on the 3D geologic data, 3D density of faults, 3D density of fault intersections and terminations, slip tendency on 3D faults, and dilation tendency on 3D faults. We provide digital data for all elements of the map, such as individual 3D fault and stratigraphic surfaces, 3D fault density, 3D fault intersection density, 3D slip tendency on fault surfaces, and 3D dilation tendency on fault surfaces. A brief movie displaying the 3D map is available at https://doi.org/10.3133/sim3469 .

Nevada↗
USGS2006

Abstracts of the Annual Meeting of Planetary Geologic Mappers, Nampa, Idaho 2006

Approximately 18 people attended this year's mappers meeting, and many more submitted abstracts and maps in absentia. The meeting was held on the campus of Northwest Nazarene University (NNU), and was graciously hosted by NNU's School of Health and Science. Planetary mapper Dr. Jim Zimbelman is an alumnus of NNU, and he was pivotal in organizing the meeting at this location. Oral and poster presentations were given on Friday, June 30. Drs. Bill Bonnichsen and Marty Godchaux led field excursions on July 1 and 2. USGS Astrogeology Team Chief Scientist Lisa Gaddis led the meeting with a brief discussion of the status of the planetary mapping program at USGS, and a more detailed description of the Lunar Mapping Program. She indicated that there is now a functioning website (http://astrogeology.usgs.gov/Projects/PlanetaryMapping/Lunar/) which shows which lunar quadrangles are available to be mapped. Like other USGS-published maps, proposals to complete a lunar geologic map must be submitted to the regular Planetary Geology & Geophysics (PGG) program for peer review. Jim Skinner (USGS) later presented the progress of the 1:2.5M-scale map of the lunar Copernicus quadrangle, and demonstrated the wide range of data that are available to support these maps. Gaddis and Skinner encouraged the community to submit proposals for generating lunar geologic maps, and reminded us that, as for all planetary maps, the project must be science-driven. Venus mapper Jim Zimbelman of the Smithsonian Institution (SI) presented the progress for his V-15 and V-16 quadrangles; Vicki Hansen (University of Minnesota Duluth) showed her preliminary work on V-45. Zimbelman addressed an issue that has been plaguing the community: 'delinquent Venus mappers'. In short, there were a number of Venus maps funded in the early 1990s under the Venus Data Analysis Program (VDAP). Unfortunately, funding for this program was cut before many Venus maps could be completed, resulting in about 10 Venus maps that were initially assigned but have shown little or no progress in many years. Zimbelman announced that he was not going to be able to complete quadrangle V-27 that he was assigned under VDAP, and was therefore returning that quadrangle to the community; he invited people to propose to PGG to map this quadrangle. Dave Williams of Arizona State University (ASU) reported on the progress of his global Io map. His mapping team recently received the completed, controlled global mosaic (using Voyager and Galileo images) from the USGS; this will be the basemap for their geologic mapping. Furthermore, the three team members (Laszlo Keszthelyi, David Crown and Dave Williams) have calibrated their individual mapping techniques by each mapping the same region for comparison. Thomas Doggett (ASU) showed progress on the global Europa map that was awarded to Ron Greeley. There was some consternation expressed on the methodology for determining relative ages of the lineaments; it was suggested that Vicki Hansen contact Patricio Figueredo (Exxon) directly, because Figueredo is the one who has been developing the lineament mapping techniques. Mars remains the most popular planet to map. Kevin Williams (SI) and Corey Fortezzo (SI) presented progress on their 1:500K maps in the Margaritifer Terra region of Mars. Jim Zimbelman described his 1:1M Medusae Fossae map, which is nearing completion. Peter Mouginis-Mark (University of Hawai'i) reported progress on his 1:200K maps of Tooting crater and of the Olympus Mons summit caldera. Jim Skinner discussed the progress of his and Ken Herkenhoff?s (USGS) map (1:500K) on the Olympia Cavi region of Mars? north pole, and Eric Kolb (USGS) presented work that he and Ken Tanaka (USGS) are completing on the Martian south pole. David Crown of the Planetary Science Institute (PSI) reported on numerous 1:500K and 1:1M maps in the Hellas and Hesperia regions of Mars. Frank Chuang (PSI) discussed progress on mapping the Deuteronilus Mensae reg

Open-File Report↗
USGS1998

Low-flow water-quality characterization of the Gore Creek watershed, upper Colorado River basin, Colorado, August 1996

The Upper Colorado River Basin (UCOL) is one of 59 National Water-Quality Assessment (NAWQA) study units designed to assess the status and trends of the Nation?s water quality (Leahy and others, 1990). The UCOL study unit began operation in 1994, and surface-water-quality data collection at a network of 14 sites began in October 1995 (Apodaca and others, 1996; Spahr and others, 1996). Gore Creek, which flows through Vail, Colorado, originates in pristine alpine headwaters and is designated a gold-medal trout fishery. The creek drains an area of about 102 square miles and is a tributary to the Eagle River. Gore Creek at the mouth near Minturn (site 13 in fig. 1) is one of the 14 sites in the UCOL network. This site was selected to evaluate water quality resulting from urban development and recreational land use. The Gore Creek watershed has undergone rapid land-use changes since the 1960?s as the Vail area shifted from traditional mountain ranchlands to a four-season resort community. Residential, recreational, commercial, and transportation development continues near Gore Creek and its tributaries to support the increasing permanent and tourist population of the area. Interstate 70 runs through the watershed from Vail Pass near site 14, along the eastern side of Black Gore Creek, and along the northern side of the main stem of Gore Creek to the mouth of the watershed (fig. 1). A major local concern is how increasing urbanization/recreation affects the water quality, gold-medal trout fishery, and aesthetic values of Gore Creek. An evaluation of the spatial characteristics of water quality in the watershed upstream from site 13 at the mouth of Gore Creek (fig. 1) can provide local water and land managers with information necessary to establish water policy and make land-use planning decisions to maintain or improve water quality. Historical data collected at the mouth of Gore Creek provide information about water quality resulting from land use, but a synoptic sampling is needed to determine the distribution and sources of water-quality constituents at one point in time. In August 1996, a low-flow synoptic sampling for analyses of water-quality properties and constituents at sites in the Gore Creek watershed was done by the U.S. Geological Survey, in cooperation with the Town of Vail, Eagle River Water and Sanitation District, Upper Eagle River Water Authority, and Northwest Colorado Council of Governments, to evaluate the water quality of Gore Creek. The August low-flow period can be important from water-quality and stream ecology perspectives. There is less water available to dilute any contaminants entering the streams, and stream temperatures are highest during August. Physical habitat for aquatic plants and animals is smaller than during most other times of the year. To address these more extreme water-quality and ecological conditions, the synoptic sampling was conducted during the summer low-flow period. Specific objectives of this sampling included: 1. Establish a current data set representing the spatial characteristics of low-flow water-quality conditions in the Gore Creek watershed, and 2. Develop some understanding of land-use and water-quality relations in the watershed. This fact sheet presents hydrologic background information and an analysis of general water-quality properties and constituents, trace elements, and nutrients collected in water samples during low-flow synoptic sampling of the Gore Creek watershed. The U.S. Geological Survey also is conducting a study of the algae and macroinvertebrate communities and physical habitat of streams in the Gore Creek watershed during low flow. This study is designed to provide information about land-use and stream ecology relations in the watershed.

Colorado↗
USGS1974

Correlation between geophysical data and rock types in the Piedmont and coastal plain of northeast Virginia and related areas

Physical, chemical, and mineralogic characteristics of rock units in parts of the northeast Virginia Piedmont are reflected in the aeromagnelic, aeroradioactivity, and gravity data for this area. Magnetic anomalies show the areal distribution of rocks containing magnetite. Aeroradiometric anomalies in the Piedmont and Coastal Plain provinces are directly related to the K 2 O content of the formations. In the crystalline rocks of the Piedmont this is reflected in their muscovite and microcline content, whereas in the Coastal Plain province it is related to the glauconite content of the Aquia Formation. Locally, in the crystalline rocks of the Piedmont, uranium- and thorium-bearing mineral content is of greater importance than K 2 O-bearing mineral content in producing aeroradiometric anomalies. The region also is characterized by (1) a northern gravity high, (2) a southern gravity high presumed to be caused by mafic rocks, and (3) an intervening zone characterized by low gravity relief and underlain by schist and gneiss. Geologic and geophysical extrapolation southward toward the Arvonia area show that the Chopawamsic Formation and the volcanic rocks of the Evington group are coeval. Also, on the northwest side of these volcanic rocks is a belt of small rootless mafic and ultramafic rocks diapirically ceplaced in folded rocks of Early Cambrian (?) age.

Virginia↗
USGS2001

Geologic map of Colorado National Monument and adjacent areas, Mesa County, Colorado

New 1:24,000-scale geologic mapping in the Colorado National Monument Quadrangle and adjacent areas, in support of the USGS Western Colorado I-70 Corridor Cooperative Geologic Mapping Project, provides new interpretations of and data for the stratigraphy, structure, geologic hazards in the area from the Colorado River in Grand Valley onto the Uncompahgre Plateau. The plateau drops abruptly along northwest-trending structures toward the northeast 800 m to the Redlands area and the Colorado River in Grand Valley. In addition to common alluvial and colluvial deposits, surficial deposits include Holocene and late Pleistocene charcoal-bearing valley-fill deposits, late to middle Pleistocene river-gravel terrace deposits, Holocene to middle Pleistocene younger, intermediate, and old fan-alluvium deposits, late to middle Pleistocene local gravel deposits, Holocene to late Pleistocene rock-fall deposits, Holocene to middle Pleistocene young and old landslide deposits, Holocene to late Pleistocene sheetwash deposits and eolian deposits, and Holocene Cienga-type deposits. Only the lowest part of the Upper Cretaceous Mancos Shale is exposed in the map area near the Colorado River. The Upper and Lower? Cretaceous Dakota Formation and the Lower Cretaceous Burro Canyon Formation form resistant dipslopes in the Grand Valley and a prominent ridge on the plateau. Less resistant strata of the Upper Jurassic Morrison Formation consisting of the Brushy Basin, Salt Wash, and Tidwell Members form slopes on the plateau and low areas below the mountain front of the plateau. The Middle Jurassic Wanakah Formation nomenclature replaces the previously used Summerville Formation. Because an upper part of the Middle Jurassic Entrada Formation is not obviously correlated with strata found elsewhere, it is therefore not formally named; however, the lower rounded cliff former Slickrock Member is clearly present. The Lower Jurassic silica-cemented Kayenta Formation forms the cap rock for the Lower Jurassic carbonate-cemented Wingate Sandstone, which forms the impressive cliffs of the monument. The Upper Triassic Chinle Formation was deposited on the eroded and weathered Middle Proterozoic meta-igneous gneiss, pegmatite dikes, and migmatitic gneiss. Structurally the area is deceptively challenging. Nearly flat-lying strata on the plateau are folded by northwest-trending fault-propagation folds into at least two S-shaped folds along the mountain front of the plateau. Strata under Grand Valley dip at about 6 degrees to the northeast. In the absence of local evidence, the uplifted plateau is attributed to Laramide deformation by dated analogous structures elsewhere in the Colorado Plateau. The major exposed fault records high-angle reverse relationships in the basement rocks but dissipates strain as a triangular zone of distributed microfractures and cataclastic flow into overlying Mesozoic strata that absorb the fault strain, leaving only folds. Evidence for younger, probably late Pliocene or early Pleistocene, uplift does exist at the antecedent Unaweep Canyon south and east of the map area. To what degree this younger deformation affected the map area is unknown. Several geologic hazards affect the area. Middle and late Pleistocene landslides involving the smectite-bearing Brushy Basin Member of the Morrison Formation are extensive on the plateau and common in the Redlands below the plateau. Expansive clay in the Brushy Basin and other strata create foundation stability problems for roads and homes. Flash floods create a serious hazard to people on foot in narrow canyons in the monument and to homes close to water courses downstream from narrow restrictions close to the monument boundary.

Colorado↗
USGS2014

Structural control of ore deposition at Kasaan Peninsula, southeastern Alaska

Copper‐bearing magnetite deposits and associated copper deposits at Kasaan Peninsula , Prince of Wales Island, southeastern Alaska , have been known for many years and have been mined to some extent for their copper content. At the beginning of World War II, the development of war industries in the Pacific northwest focused attention on the deposits as possible sources of iron ore . From 1942 through 1944 the United States Geological Survey made detailed studies of most of the ore deposits and at a few of the more promising localities diamond‐drilling operations were carried on by the United States Bureau of Mines. The deposits are for the most part small and irregular but of relatively high grade. The chief ore minerals are magnetite, pyrite, and chalcopyrite, and the gangue consists largely of skarn minerals, including garnet, epidote, diopside, and hornblende. The deposits are presumably of pyrometasomatic origin, but whereas deposits of this type are commonly replacement bodies in limestone, at Kasaan Peninsula limestone seemingly was a poor host rock for the ore.

Alaska↗
USGS2015

Regional seismic-wave propagation from the M5.8 23 August 2011, Mineral, Virginia, earthquake

The M5.8 23 August 2011 Mineral, Virginia, earthquake was felt over nearly the entire eastern United States and was recorded by a wide array of seismic broadband instruments. The earthquake occurred ~200 km southeast of the boundary between two distinct geologic belts, the Piedmont and Blue Ridge terranes to the southeast and the Valley and Ridge Province to the northwest. At a dominant period of 3 s, coherent postcritical P-wave (i.e., direct longitudinal waves trapped in the crustal waveguide) arrivals persist to a much greater distance for propagation paths toward the northwest quadrant than toward other directions; this is probably related to the relatively high crustal thickness beneath and west of the Appalachian Mountains. The seismic surface-wave arrivals comprise two distinct classes: those with weakly dispersed Rayleigh waves and those with strongly dispersed Rayleigh waves. We attribute the character of Rayleigh wave arrivals in the first class to wave propagation through a predominantly crystalline crust (Blue Ridge Mountains and Piedmont terranes) with a relatively thin veneer of sedimentary rock, whereas the temporal extent of the Rayleigh wave arrivals in the second class are well explained as the effect of the thick sedimentary cover of the Valley and Ridge Province and adjacent Appalachian Plateau province to its northwest. Broadband surface-wave ground velocity is amplified along both north-northwest and northeast azimuths from the Mineral, Virginia, source. The former may arise from lateral focusing effects arising from locally thick sedimentary cover in the Appalachian Basin, and the latter may result from directivity effects due to a northeast rupture propagation along the finite fault plane.

GSA Special Papers↗
USGS1974

Expectable Earthquakes and their ground motions in the Van Norman Reservoirs Area

The upper and lower Van Norman dams, in northwesternmost San Fernando Valley about 20 mi (32 km) northwest of downtown Los Angeles, were severely damaged during the 1971 San Fernando earthquake. An investigation of the geologic-seismologic setting of the Van Norman area indicates that an earthquake of at least M 7.7 may be expected in the Van Norman area. The expectable transitory effects in the Van Norman area of such an earthquake are as follows: peak horizontal acceleration of at least 1.15 g, peak velocity of displacement of 4.43 ft/sec (135 cm/sec), peak displacement of 2.3 ft (70 cm), and duration of shaking at accelerations greater than 0.05 g, 40 sec. A great earthquake (M 8+) on the San Andreas fault, 25 mi distant, also is expectable. Transitory effects in the Van Norman area from such an earthquake are estimated as follows: peak horizontal acceleration of 0.5 g, peak velocity of 1.97 ft/sec (60 cm/sec), displacement of 1.31 ft (40 cm), and duration of shaking at accelerations greater than 0.05 g, 80 sec. The permanent effects of the expectable local earthquake could include simultaneous fault movement at the lower damsite, the upper damsite, and the site proposed for a replacement dam halfway between the upper and lower dams. The maximum differential displacements due to such movements are estimated at 16.4 ft (5 m) at the lower damsite and about 9.6 ft (2.93 m) at the upper and proposed damsites. The 1971 San Fernando earthquake (M 6?) was accompanied by the most intense ground motions ever recorded instrumentally for a natural earthquake. At the lower Van Norman dam, horizontal accelerations exceeded 0.6 g, and shaking greater than 0.25 g lasted for about 13 see; at Pacoima dam, 6 mi (10 km) northeast of the lower dam, high-frequency peak horizontal accelerations of 1.25 g were recorded in two directions, and shaking greater than 0.25 g lasted for about 7 sec. Permanent effects of the earthquake include slope failures in the embankments of the upper and lower Van Norman dams, rupturing of the ground surface by faulting along parts of the zone of old faults that extends easterly through the reservoir area and across the northern part of the valley, folding or arching of the ground surface, and differential horizontal displacement of the terrane north and south of the fault zone. Although a zone of old faults extends through the reservoir area, the 1971 surface ruptures apparently did not; however, arching and horizontal displacements caused small relative displacements of the abutment areas of each of the three damsites. The 1971 arching coincided with preexisting topographic highs, and the surface ruptures coincided with eroded fault scarps and a buried ground-water impediment formed by pre-1971 faulting in young valley fill. This coincidence with evidence of past deformation indicates that the 1971 deformations were the result of a continuing geologic process that is expected to produce similar deformations during future events. The 1971 San Fernando earthquake probably was not the largest that has occurred in this area during the last approximately 200 years, as indicated by a buried fault like scarp about 200 years old that is higher than, and aligned with, 1971 fault scarps. In addition, the San Fernando zone of 1971 ruptures is part of a regional tectonic system that includes the San Andreas and associated faults; one of these, the White Wolf fault north of the San Andreas, is symmetrical in structural attitude with the San Fernando zone and ruptured the ground surface during the 1952 Kern County earthquake (M 7.7). Other large earthquakes associated with surface rupturing on faults of this system include the 1857 Fort Tejon earthquake (M 8+) and possibly the 1852 Big Pine earthquake. Several other historic earthquakes in this general area are not known to be associated with surface ruptures, but were large enough to cause damage in the northern San Fernando Valley. The Van Norman rese

Circular↗
USGS1981

Maps showing aeromagnetic survey and geologic interpretation of the Chignik and Sutwik Island quadrangles, Alaska

An aeromagnetic survey over part of the Chignik and Sutwik Island quadrangles, on the southern Alaska Peninsula, was flown in 1977 as part of the Alaska mineral resource assessment program (AMRAP). Maps at scales 1:250,000 and 1:63,360 have been released on open-file (U.s. Geological Survey, 1978a, 1978b). This report includes the aeromagnetic map superimposed on the topographic base (sheet 1) and an interpretation map superimposed on the topographic and simplified geologic base (sheet 2). This discussion provides an interpretation of the aeromagnetic data with respect to regional geology, occurrence of ore deposits and prospects, and potential oil and gas resources. The survey was flown along northwest-southeast lines, spaced about 1.6 km apart, at a nominal elevation of about 300 m above the land surface. A proton-precession magnetometer was used for the survey, and the resulting digital data were computer contoured at intervals of 10 and 50 gammas (sheet 1). The International Geomagnetic Reference Field (IGRF) of 1965, updated to 1977, was removed from the total field data.

Alaska↗
USGS1976

The source of hydrothermal solutions at Puerto Maunabo and its bearing on the base-metal-potassium feldspar association in Puerto Rico

A quartz oligoclase porphyry exposed near Puerto Maunabo may provide evidence to further our understanding of the base-metal-potassium feldspar association known to occur in many of the porphyry-type copper deposits of Puerto Rico. The porphyry appears to be a magmatic differentiate on the border of the San Lorenzo batholith that may represent a source of mineralizing hydrothermal solutions. The porphyry intrudes an albitized quartz diorite border phase of the batholith that contains large roof pendants of metavolcanic rock. These roof pendants are mostly metamorphosed to greenschist metamorphic facies, but in the vicinity of Puerto Maunabo south of the porphyry, they reach amphibolite metamorphic facies; north of the porphyry, similar xenolithic lenses of metavolcanic rock appear to have been converted entirely to an oligoclase quartz felsite. The layered albitized quartz felsite has the same composition and texture as irregular veinlets in the albitized quartz diorite and as the groundmass in the porphyry. The K + ions arid basic ions of Fe +2 , Cu +2 , Mg +2 apparently were mobilized during final magmatic crystallization and then escaped as hydrothermal solutions that followed open conduits within a zone of structural weakness which also permitted the emplacement of the porphyry. The volcanic rock of Cerro Piedra Hueca, in contact with the albitized quartz diorite, and generally along strike west of the porphyry, has been altered to a quartz sericite rock entirely devoid of mafic silicates. This is the southeasternmost exposure of hydrothermally altered volcanic rock in the regional zone of northwest-trending faults that contains the principal porphyry-type copper deposits of Puerto Rico. The texture, mineralogy, and geologic environment of the porphyry at Puerto Maunabo are similar to those of the ore-bearing porphyries but differ in one important aspect. Most ore-bearing porphyries contain hydrothermal potassium feldspar and reddish-brown biotite intimately associated with the base-metal sulfides. In the porphyry of Puerto Maunabo, potassium feldspar is conspicuously absent, and only a trace of biotite is present; the only sulfide present is pyrite. The physical and chemical environment required to precipitate K + ions, either as potassium feldspar or biotite, apparently is very similar to that required to precipitate base-metal sulfides. At Puerto Maunabo, these conditions evidently did not prevail, and potassium and the base metals may have been carried in solution to a more favorable environment.

Puerto Maunabo↗
USGS2019

Bathymetric contour map, surface area and capacity table, and bathymetric change map for Sugar Creek Lake near Moberly, Missouri, 2018

Managers of water-supply lakes need an accurate estimate of the lake capacity to ensure that enough water is available for uses such as: providing consistent recreation pool levels, preserving downstream aquatic habitat, flood abatement, water supply, and power generation. Lake capacity is particularly important for managers of water-supply lakes during periods of drought, unexpected population growth, or exceptionally high water use in the area supplied by the lake. Sedimentation, primarily from runoff into the lake, will cause a loss of storage capacity as a lake ages; as a result, the capacity table for the lake (if one exists) will overestimate the actual capacity. Lake bathymetric changes can be demonstrated through periodic surveying, and rates of sediment accumulation can be calculated so that managers can better regulate the water supply. The U. S. Geological Survey, in cooperation with the Missouri Department of Natural Resources, completed a bathymetric survey of Sugar Creek Lake in December 2003. Sugar Creek Lake, constructed in 1922, is about 4 miles northwest of Moberly, Missouri, in Randolph County and has a surface area of about 330 acres at the spillway elevation of 746.8 feet. The lake primarily is used for recreation and drinking-water supply for the town of Moberly, Missouri. In September 2018, the U. S. Geological Survey, in cooperation with the Missouri Department of Natural Resources and the City of Moberly, Missouri, surveyed the bathymetry of Sugar Creek Lake to prepare an updated bathymetric map and a surface area and capacity table. The 2003 survey was compared with the 2018 survey to document the changes in the bathymetric surface. The comparison found that in the 14.7 years between the two surveys the lake had lost 230 acre-feet of capacity and had an average sediment accumulation of 0.96 feet.

Missouri↗
USGS2001

Interpretive geologic cross sections for the Death Valley regional flow system and surrounding areas, Nevada and California

This report presents a network of 28 geologic cross sections that portray subsurface geologic relations within the Death Valley regional ground-water system, a ground-water basin that encompasses a 3? x 3? area (approximately 70,000 km2) in southern Nevada and eastern California. The cross sections transect that part of the southern Great Basin that includes Death Valley, the Nevada Test Site, and the potential high-level nuclear waste underground repository at Yucca Mountain. The specific geometric relationships portrayed on the cross sections are discussed in the context of four general sub-regions that have stratigraphic similarities and general consistency of structural style: (1) the Nevada Test Site vicinity; (2) the Spring Mountains, Pahrump Valley and Amargosa Desert region; (3) the Death Valley region; and (4) the area east of the Nevada Test Site. The subsurface geologic interpretations portrayed on the cross sections are based on an integration of existing geologic maps, measured stratigraphic sections, published cross sections, well data, and geophysical data and interpretations. The estimated top of pre-Cenozoic rocks in the cross sections is based on inversion of gravity data, but the deeper parts of the sections are based on geologic conceptual models and are more speculative. The region transected by the cross sections includes part of the southern Basin and Range Province, the northwest-trending Walker Lane belt, the Death Valley region, and the northern Mojave Desert. The region is structurally complex, where a locally thick Tertiary volcanic and sedimentary section unconformably overlies previously deformed Proterozoic through Paleozoic rocks. All of these rocks have been deformed by complex Neogene ex-tensional normal and strike-slip faults. These cross sections form a three-dimensional network that portrays the interpreted stratigraphic and structural relations in the region; the sections form part of the geologic framework that will be incorporated in a complex numerical model of ground-water flow in the Death Valley region.

California, Nevada↗
USGS2006

Geologic map of the Lacamas Creek quadrangle, Clark County, Washington

The Lacamas Creek 7.5 minute quadrangle is in southwestern Washington, approximately 25 km northeast of Portland, Oregon, along the eastern margin of the Portland Basin, which is part of the Puget-Willamette Lowland that separates the Cascade Range from the Oregon Coast Range. Since late Eocene time, the Cascade Range has been the locus of an episodically active volcanic arc associated with underthrusting of oceanic lithosphere beneath the North American continent along the Cascadia Subduction Zone. Lava flows that erupted early in the history of the arc underlie the eastern half of the Lacamas Creek quadrangle, forming a dissected terrain, with elevations as high as 2050 ft (625 m), that slopes irregularly but steeply to the southwest. These basalt and basaltic andesite flows erupted in early Oligocene time from one or more vents located outside the map area. The flows dip gently (less than 5 degrees) west to southwest. In the western part of the map area, volcanic bedrock is unconformably overlain by middle Miocene to early Pleistocene(?) sediments that accumulated as the Portland Basin subsided. These sediments consist mostly of detritus carried into the Portland Basin by the ancestral Columbia River. Northwest-striking faults offset the Paleogene basin floor as well as the lower part of the basin fill. In middle Pleistocene time, basalt and basaltic andesite erupted from three small volcanoes in the southern half of the map area. These vents are in the northern part of the Boring volcanic field, which comprises several dozen late Pliocene and younger monogenetic volcanoes scattered throughout the greater Portland region. In latest Pleistocene time, the Missoula floods of glacial-outburst origin inundated the Portland Basin. The floods deposited poorly sorted gravels in the southwestern part of the Lacamas Creek quadrangle that grade northward into finer grained sediments. This map is a contribution to a program designed to improve geologic knowledge of the Portland Basin region of the Pacific Northwest urban corridor, the densely populated Cascadia forearc region of western Washington and Oregon. More detailed information on the bedrock and surficial geology of the basin and its surrounding area is necessary to refine assessments of seismic risk, ground-failure hazards and resource availability in this rapidly growing region.

Scientific Investigations Map↗
USGS1999

Water-resources investigations in Wisconsin, 1999

The statewide average precipitation of 31.23 inches for the 1998 water year was 0.42 inches less than the normal annual precipitation of 31.65 inches for water years 1961-90. Average precipitation values ranged from 69 percent of normal at both the Willow Reservoir WVI weather station in north central Wisconsin and Crivitz High Falls WPS weather station in northeast Wisconsin to 141 percent of normal at the Dodgeville 1 NE WWTP and Muscoda weather stations in southwest Wisconsin (from tables provided by Lyle Anderson, Program Assistant, UW-Extension, Geological and Natural History Survey, written commun., 1999). Runoff differed for rivers throughout the State and ranged from 54 percent in northwest Wisconsin to 146 percent in southeast Wisconsin. Runoff was lowest (54 percent of the average annual runoff from 1975-98) for the Nemadji River near South Superior and highest (146 percent of the average annual runoff from 1976-79, 1981-98) for the Underwood Creek at Wauwatosa station which monitors a small urban basin (drainage area is 18.2 square miles) in southeastern Wisconsin. Departures of runoff in the 1998 water year as a percent of long-term average runoff in the State (determined using stations with drainage areas greater than 150 square miles and at least 20 years of record) are shown in Figure 4. Annual discharges for the individual water years (1916-98) at the Oconto River near Gillett, Jump River at Sheldon, and Sugar River near Brodhead are shown in Figure 5. The comparison of monthly and annual discharges for the 1998 water year to discharge for a 83-year base period at the same three gaging stations are shown in Figure 6. Low flows occurred at 21 gaging stations where the annual minimum 7-consecutive day average flows (Q7) had recurrence intervals of 5 or more years. Precipitation was well below normal from July through September in northern Wisconsin. Monthly precipitation values were 4.46, 5.69, and 4.24 inches below normal in northwestern, north central, and northeastern Wisconsin, respectively, in the July through September period (from tables provided by Lyle Anderson, Program Assistant, UW-Extension, Geological and Natural History Survey, written commun., 1999). The precipitation for the April to October period was

Wisconsin↗
USGS1974

Summary of activities, U.S. Geological Survey Saudi Arabian project, 1950 to 1974

The U. S. Geological Survey (USGS) first began work in the Kingdom of Saudi Arabia in 1950 under the sponsorship of the Ministry of Finance and National Economy. The basic objective of the work was to investigate the mineral and water resource potential in western Saudi Arabia, but little was known of the region and it therefore was necessary to prepare geographic and geologic maps. Aerial photographs were taken and controlled mosaics produced, some paid for by the USGS but most paid for by the Saudi Arabian government, and reconnaissance geologic mapping was undertaken until the USGS team left Saudi Arabia in 1955. This mapping, in cooperation with mapping of the Arabian American Oil Company, was compiled as a series of scale 1:500,000 geographic and geologic maps in Arabic and English covering all of Saudi Arabia. A total of 42 of these maps were prepared. Three scale 1:2,000,000 geographic and geologic maps in Arabic and English, covering the Arabian Peninsula, also were prepared from this work. All of the maps were printed in the United States and published by the USGS, the last in 1963. Other work done by the USGS between 1950 and 1955 included locating and examining ancient mines, indentifying the Wadi Fatima oolitic iron deposit and other iron deposits in northwest Saudi Arabia, and advising on many water supply problems including those for Riyadh, Qizan, Qunfudhah, Rabigh, Yenbo, Umm Lejh, and Al Wajh. The mapping work and the geologic investigations laid the groundwork for the more detailed studies that followed.

Open-File Report↗