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At least 559 records · Page 31Linked to original sources
USGS1985

Significance of tourmaline-rich rocks in the Grenville Complex of St. Lawrence County, New York

Feldspathic quartzite and metapelite of Middle Proterozic age north of Gouverneur, N.Y., contain abundant dravite-uvite (magnesian tourmaline). These rocks, more than 1,000 feet thick, are regionally metamorphosed to the upper amphibolite facies, are pyritic, and locally contain porphyroblastic scapolite. The rocks are underlain by talctremolite schist and a thick sequence of calcitic and dolomitic marble, and are overlain by quartz, calc-silicate carbonate rock, and a pyroxene scapolite unit. All rocks are part of the metasedimentary Grenville Complex. Individual tourmaline-rich layers in the quartzite are as thick as 3 cm and contain as much as 50 percent finegrained, brownish-green dravite. Subjacent talc schist contains fine-grained amber dravite, and silicated marble locally contains brown porphyroblasts of uvite. Gneissic granite, pegmatite, and migmatitic segregations cutting the tourmaline-bearing quartzite, gneisses, and schists are rich in black schorl. Tourmalines from the tourmaline-rich quartzite and other metasedimentary and metaigneous rocks were analyzed by means of an electron microprobe. The compositions of tourmalines in the North Gouverneur area are clearly a function of the bulk composition of the rock. Tourmaline compositions in the quartzite have a wide range in FeO/(Fe+MgO) ratios, from 0.15 to 0.58, which are distinct from the ratios for tourmalines in granitic and pegmatitic rocks that range from 0.55 to 0.75. Tourmalines in the area have Na2O contents that range from 0.85 to 4.25 weight percent. Aluminum in all tourmalines ranges widely from about 25 to 37 weight percent AI 2O3 . The most heterogeneous tourmaline compositions are in the quartzites, although most compositions cluster in the dravite-uvite solid solution series. Substitutions involving Na, Ca, Mg, Fe, and Al result in the following compositional schemes: Na+Fe = Al+vacancy, and Na = Ca. Such coupled substitutions probably represent valid constraints for tourmalines from North Gouverneur. The abundance of magnesian tourmaline in the metasedimentary rocks of the North Gouverneur area is comparable to that of tourmaline-rich rocks associated with sedimenthosted massive sulfide deposits for example, Sullivan Mine, British Columbia. A recently described large lead-zinc deposit at Dugald River, Australia, is associated with tourmaline- and scapolite-bearing rocks similar in many respects to those north of Gouverneur. Compared with known tourmaline compositions in the Sullivan Mine area, tourmalines from North Gouverneur have comparable FeO and MgO values. We suggest that other tourmaline components such as a low TiO2 content, variable Na/(Na + Ca + K) ratios, and the antipathetic correlation of Na and Ca might also be useful in discriminating tourmalines associated with ore deposits. Ore bodies at the nearby Balmat-Edwards mining district are in marbles associated with rocks of evaporitic origin. The boron- and scapolite-rich rocks under consideration in this study possibly also are related to an evaporite-producing environment. Similar rocks that have an evaporite origin are associated with stratabound sulfide deposits at many places.

Bulletin↗
USGS2010

Western Mineral and Environmental Resources Science Center--providing comprehensive earth science for complex societal issues

Minerals in the environment and products manufactured from mineral materials are all around us and we use and come into contact with them every day. They impact our way of life and the health of all that lives. Minerals are critical to the Nation's economy and knowing where future mineral resources will come from is important for sustaining the Nation's economy and national security. The U.S. Geological Survey (USGS) Mineral Resources Program (MRP) provides scientific information for objective resource assessments and unbiased research results on mineral resource potential, production and consumption statistics, as well as environmental consequences of mining. The MRP conducts this research to provide information needed for land planners and decisionmakers about where mineral commodities are known and suspected in the earth's crust and about the environmental consequences of extracting those commodities. As part of the MRP scientists of the Western Mineral and Environmental Resources Science Center (WMERSC or 'Center' herein) coordinate the development of national, geologic, geochemical, geophysical, and mineral-resource databases and the migration of existing databases to standard models and formats that are available to both internal and external users. The unique expertise developed by Center scientists over many decades in response to mineral-resource-related issues is now in great demand to support applications such as public health research and remediation of environmental hazards that result from mining and mining-related activities. Western Mineral and Environmental Resources Science Center Results of WMERSC research provide timely and unbiased analyses of minerals and inorganic materials to (1) improve stewardship of public lands and resources; (2) support national and international economic and security policies; (3) sustain prosperity and improve our quality of life; and (4) protect and improve public health, safety, and environmental quality. The MRP supports approximately 40 USGS research specialists who utilize cooperative agreements with universities, industry, and other governmental agencies to support their collaborative research and information exchange. Scientists of the WMERSC study how and where non-fuel mineral resources form and are concentrated in the earth's crust, where mineral resources might be found in the future, and how mineral materials interact with the environment to affect human and ecosystem health. Natural systems (ecosystems) are complex - our understanding of how ecosystems operate requires collecting and synthesizing large amounts of geologic, geochemical, biologic, hydrologic, and meteorological information. Scientists in the Center strive to understand the interplay of various processes and how they affect the structure, composition, and health of ecosystems. Such understanding, which is then summarized in publicly available reports, is used to address and solve a wide variety of issues that are important to society and the economy. WMERSC scientists have extensive national and international experience in these scientific specialties and capabilities - they have collaborated with many Federal, State, and local agencies; with various private sector organizations; as well as with foreign countries and organizations. Nearly every scientific and societal challenge requires a different combination of scientific skills and capabilities. With their breadth of scientific specialties and capabilities, the scientists of the WMERSC can provide scientifically sound approaches to a wide range of societal challenges and issues. The following sections describe examples of important issues that have been addressed by scientists in the Center, the methods employed, and the relevant conclusions. New directions are inevitable as societal needs change over time. Scientists of the WMERSC have a diverse set of skills and capabilities and are proficient in the collection and integration of

Circular↗
USGS1969

Platinum, palladium, and rhodium analyses of ultramafic and mafic rocks from the Stillwater Complex, Montana

Analyses by a combination fire- assay-solution-optical-emission spectrographic method of 137 rocks from the Stillwater Complex, Mont., indicate that platinum, palladium, and rhodium are preferentially concentrated in chromitite zones. The A chromitite zone (21 samples) has an average of 988.9 ppb (pans per billion, 10 -9 ) Pt, 2290.2 ppb Pd, and 245.9 ppb Rh and reaches a maximum (to date) of 8,000 ppb Pt, 11,000 ppb Pd, and 1,700 ppb Rh.

Montana↗
USGS2024

Pesticide concentrations of surface water and suspended sediment in Yolo By-Pass and Cache Slough Complex, California, 2019–2021

Managed flow pulses in the north Sacramento-San Joaquin Delta are an adaptive management tool used in efforts to enhance food availability in delta smelt ( Hypomesus transpacificus ) habitat as part of the North Delta Food Subsidies Action. The California Department of Water Resources (DWR) monitors non-managed seasonal and local flow pulses and managed flow pulses from agricultural drainage or main stem Sacramento River water redirected through Yolo By-Pass. Augmented flow pulses are hypothesized to improve net positive flow during summer and fall in Yolo By-Pass and enhance plankton availability in delta smelt habitat in Cache Slough complex. However, flow pulses may also result in unintended negative effects of increased pesticides that are transported through Yolo By-Pass. Here, we evaluate pesticides in surface water and suspended sediment correlated with flow pulses in Yolo By-Pass during the 2019–21 calendar years. Surface-water and suspended-sediment samples were collected by DWR personnel. Water samples were analyzed at the U.S. Geological Survey Organic Chemistry Research Laboratory in Sacramento, California, for a suite of as many as 178 current-use pesticides and pesticide degradates using gas chromatography with mass spectrometry (GC/MS), gas chromatography with tandem mass spectrometry, and liquid chromatography with tandem mass spectrometry. Suspended sediments filtered from water samples were analyzed for a suite of as many as 173 current-use pesticides and pesticide degradates. There were 52 different current-use pesticides and pesticide degradates detected in water samples collected throughout the study. Concentrations ranged from below method detection limits to 4,070 nanograms per liter. Five different compounds in water samples were detected with concentrations above U.S. Environmental Protection Agency aquatic life benchmarks. In suspended-sediment samples collected throughout the study, eight different current-use pesticides and pesticide degradates were detected. Total pesticide concentrations were highest at surface-water sites in the northern end of Yolo By-Pass and decreased farther downstream during the same sampling events. Total pesticide concentrations generally were higher for most surface-water sites immediately before or during the managed flow pulse in 2019 versus after the flow pulse. Finally, mean total pesticide concentrations for each surface-water site generally were higher during all of 2019 than 2021, regardless of sampling period.

California↗
USGS2009

U.S. Geological Survey Groundwater Modeling Software: Making Sense of a Complex Natural Resource

Computer models of groundwater systems simulate the flow of groundwater, including water levels, and the transport of chemical constituents and thermal energy. Groundwater models afford hydrologists a framework on which to organize their knowledge and understanding of groundwater systems, and they provide insights water-resources managers need to plan effectively for future water demands. Building on decades of experience, the U.S. Geological Survey (USGS) continues to lead in the development and application of computer software that allows groundwater models to address scientific and management questions of increasing complexity.

Fact Sheet↗
USGS2016

Mercury cycling in the Hells Canyon Complex of the Snake River, Idaho and Oregon

Introduction The Hells Canyon Complex (HCC) is a hydroelectric project built and operated by the Idaho Power Company (IPC) that consists of three dams on the Snake River along the Oregon and Idaho border (fig. 1). The dams have resulted in the creation of Brownlee, Oxbow, and Hells Canyon Reservoirs, which have a combined storage capacity of more than 1.5 million acre-feet and span about 90 miles of the Snake River. The Snake River upstream of and through the HCC historically has been impaired by water-quality issues related to excessive contributions of nutrients, algae, sediment, and other pollutants. In addition, historical data collected since the 1960s from the Snake River and tributaries near the HCC have documented high concentrations of mercury in fish tissue and sediment (Harris and Beals, 2013). Data collected from more recent investigations within the HCC continue to indicate elevated concentrations of mercury and methylmercury in the water column, bottom sediments, and biota (Clark and Maret, 1998; Essig, 2010; Fosness and others, 2013). As a result, Brownlee and Hells Canyon Reservoirs are listed as impaired for mercury by the State of Idaho, and the Snake River from the Oregon and Idaho border through the HCC downstream to the Oregon and Washington border is listed as impaired for mercury by the State of Oregon.

Idaho, Oregon↗
USGS2002

Geologic map of the Stillwater Complex, Montana: A digital database

This report provides a digital version of the Geologic map of the Stillwater Complex, Montana by Page and Nokleberg (1974). Paper copies of the four geologic map sheets from the original report were scanned and initially attributed by Optronics Specialty Co., Inc. (Northridge, CA) and remitted to the U.S. Geological Survey for further attribution and publication of the geospatial digital files. The resulting digital geologic dataset can be queried in a geographic information system (GIS) in many ways to produce a variety of geological maps.

Montana↗
USGS2002

Spatial digital database of the geologic map of Catalina Core Complex and San Pedro Trough, Pima, Pinal, Gila, Graham, and Cochise Counties, Arizona

The geologic map of Catalina Core Complex and San Pedro Trough by Dickinson (1992) was digitized for input into a geographic information system (GIS) by the U.S. Geological Survey staff and contractors in 2000-2001. This digital geospatial database is one of many being created by the U.S. Geological Survey as an ongoing effort to provide geologic information in a geographic information system (GIS) for use in spatial analysis. The resulting digital geologic map database data can be queried in many ways to produce a variety of geologic maps and derivative products. Digital base map data (topography, roads, towns, rivers, lakes, and so forth) are not included; they may be obtained from a variety of commercial and government sources. This database is not meant to be used or displayed at any scale larger than 1:125,000 (for example, 1:100,000 or 1:24,000). The digital geologic map plot files that are provided herein are representations of the database. The map area is located in southern Arizona. This report lists the geologic map units, the methods used to convert the geologic map data into a digital format, the ArcInfo GIS file structures and relationships, and explains how to download the digital files from the U.S. Geological Survey public access World Wide Web site on the Internet. The manuscript and digital data review by Lorre Moyer (USGS) is greatly appreciated.

Arizona↗
USGS2006

2005 annual progress report: Elk and bison grazing ecology in the Great Sand Dunes complex of lands

In 2000 the U.S. Congress authorized the expansion of the former Great Sand Dunes National Monument by establishing a new Great Sand Dunes National Park and Preserve in its place, and establishing the Baca National Wildlife Refuge. The establishment of Great Sand Dunes National Park and Preserve and the new Baca National Wildlife Refuge in the San Luis Valley (SLV), Colorado was one of the most significant land conservation actions in the western U.S. in recent years. The action was a result of cooperation between the National Park Service (NPS), U.S. Fish and Wildlife Service (USFWS), Bureau of Land Management (BLM), U.S. Forest Service (USDA-FS), and The Nature Conservancy (TNC). The new national park, when fully implemented, will consist of 107,265 acres, the new national preserve 41,872 acres, and the new national wildlife refuge (USFWS lands) 92,180 acres (fig. 1). The area encompassed by this designation protects a number of natural wonders and features including a unique ecosystem of natural sand dunes, the entire watershed of surface and groundwaters that are necessary to preserve and recharge the dunes and adjacent wetlands, a unique stunted forest, and other valuable riparian vegetation communities that support a host of associated wildlife and bird species. When the National Park was initially established, there were concerns about overconcentrations and impacts on native plant communities of the unhunted segments of a large and possibly growing elk (Cervus elaphus) population. This led to the designation of the Preserve as a compromise solution, where the elk could be harvested. The Preserve Unit, however, will not address all the ungulate management challenges. In order to reduce the current elk population, harvests of elk may need to be aggressive. But aggressive special hunts of elk to achieve population reductions can result in elk avoidance of certain areas or elk seeking refuge in areas where they cannot be hunted, while removals of whole herd segments and abandonment or alterations of migration routes can occur (Smith and Robbins, 1994; Boyce and others, 1991). Elk may seek refuge from hunting in the newly expanded Park Unit and TNC lands where they might overconcentrate and impact unique vegetation communities. In these sites of refugia, or preferred loafing sites, elk and bison could accelerate a decline in woody riparian shrubs and trees. This decline may also be due to changes in hydrology, climatic, or dunal processes, but ungulate herbivory might exacerbate the effects of those processes. To address the questions and needs of local resource managers, a multi-agency research project was initiated in 2005 to study the ecology, forage relations, and habitat relations of elk and bison in the Great Sand Dunes–Sangre de Cristo–Baca complex of lands. Meetings and discussions of what this research should include were started in 2001 with representatives from NPS, USFWS, TNC, the Colorado Division of Wildlife (CDOW), and USDA-FS/BLM. The final study plan was successfully funded in 2004 with research scheduled to start in 2005. The research was designed to encompass three major study elements: (1) animal movements and population dynamics, (2) vegetation and nutrient effects from ungulate herbivory, and (3) development of ecological models, using empirical data collected from the first two components, that will include estimates of elk carrying capacity and management scenarios for resource managers.

Colorado↗
USGS2009

The Iron Hill (Powderhorn) carbonatite complex, Gunnison County, Colorado — A potential source of several uncommon mineral resources

A similar version of this slide show was presented on three occasions during 2008: two times to local chapters of the Society for Mining, Metallurgy, and Exploration (SME), as part of SME's Henry Krumb lecture series, and the third time at the Northwest Mining Association's 114th Annual Meeting, held December 1-5, 2008, in Sparks (Reno), Nevada. In 2006, the U.S. Geological Survey (USGS) initiated a study of the diverse and uncommon mineral resources associated with carbonatites and associated alkaline igneous rocks. Most of these deposit types have not been studied by the USGS during the last 25 years, and many of these mineral resources have important applications in modern technology. The author chose to begin this study at Iron Hill in southwestern Colorado because it is the site of a classic carbonatite complex, which is thought to host the largest known resources of titanium and niobium in the United States.

Colorado↗
USGS2011

Species accounts for the Alamosa/Monte Vista/Baca National Wildlife Refuge Complex

As part of an interagency agreement between the U.S. Geological Survey (USGS) and the U.S. Fish and Wildlife Service (USFWS), the Alamosa/Monte Vista/Baca National Wildlife Refuge Complex requested help with the synthesis of scientific information for 10 focal species and their habitat requirements in response to common Refuge management activities in the San Luis Valley, Colorado. This information will be instrumental in developing the Service's Comprehensive Conservation Plan (CCP), which is required by law for each unit of the National Wildlife Refuge System. After consultation with Refuge managers and USGS staff, the 10 species chosen for detailed literature reviews and synthesis of information were the following: (1) American Avocet ( Recurvirostra americana ); (2) Wilson's Phalarope ( Phalaropus tricolor Porzana carolina ); (4) White-faced Ibis ( Plegadis chihi ); (5) Black Tern ( Chlidonias niger ); (6) Short-eared Owl ( Asio flammeus ); (7) Brewer's Sparrow ( Spizella breweri ); (8) Savannah Sparrow ( Passerculus sandwichensis ); (9) Northern Leopard Frog [ Lithobates (=Rana) pipiens ]; and, (10) Tadpole Shrimp ( Triops longicaudatus ).

Colorado↗
USGS2013

Postwildfire debris-flow hazard assessment of the area burned by the 2013 West Fork Fire Complex, southwestern Colorado

This report presents a preliminary emergency assessment of the debris-flow hazards from drainage basins burned by the 2013 West Fork Fire Complex near South Fork in southwestern Colorado. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence, potential volume of debris flows, and the combined debris-flow hazard ranking along the drainage network within and just downstream from the burned area, and to estimate the same for 54 drainage basins of interest within the perimeter of the burned area. Input data for the debris-flow models included topographic variables, soil characteristics, burn severity, and rainfall totals and intensities for a (1) 2-year-recurrence, 1-hour-duration rainfall, referred to as a 2-year storm; (2) 10-year-recurrence, 1-hour-duration rainfall, referred to as a 10-year storm; and (3) 25-year-recurrence, 1-hour-duration rainfall, referred to as a 25-year storm. Estimated debris-flow probabilities at the pour points of the 54 drainage basins of interest ranged from less than 1 to 65 percent in response to the 2-year storm; from 1 to 77 percent in response to the 10-year storm; and from 1 to 83 percent in response to the 25-year storm. Twelve of the 54 drainage basins of interest have a 30-percent probability or greater of producing a debris flow in response to the 25-year storm. Estimated debris-flow volumes for all rainfalls modeled range from a low of 2,400 cubic meters to a high of greater than 100,000 cubic meters. Estimated debris-flow volumes increase with basin size and distance along the drainage network, but some smaller drainages also were predicted to produce substantial debris flows. One of the 54 drainage basins of interest had the highest combined hazard ranking, while 9 other basins had the second highest combined hazard ranking. Of these 10 basins with the 2 highest combined hazard rankings, 7 basins had predicted debris-flow volumes exceeding 100,000 cubic meters, while 3 had predicted probabilities of debris flows exceeding 60 percent. The 10 basins with high combined hazard ranking include 3 tributaries in the headwaters of Trout Creek, four tributaries to the West Fork San Juan River, Hope Creek draining toward a county road on the eastern edge of the burn, Lake Fork draining to U.S. Highway 160, and Leopard Creek on the northern edge of the burn. The probabilities and volumes for the modeled storms indicate a potential for debris-flow impacts on structures, reservoirs, roads, bridges, and culverts located within and immediately downstream from the burned area. U.S. Highway 160, on the eastern edge of the burn area, also is susceptible to impacts from debris flows.

Colorado↗
USGS1978

Geology of the Arco-Big Southern Butte area, eastern Snake River Plain, and potential volcanic hazards to the radioactive waste management complex, and other waste storage and reactor facilities at the Idaho National Engineering Laboratory, Idaho

The Arco-Big Southern Butte area of the eastern Snake River Plain, Idaho, includes a volcanic rift zone and more than 70 Holocene and late Quaternary basalt volcanoes. The Arco volcanic rift zone extends southeast for 50 km from Arco to about 10 km southeast of Big Southern Butte. The rift zone is the locus of extensional faults, graben, fissure basaltic volcanic vents, several rhyolite domes at Big Southern Butte, and a ferrolatite volcano at Cedar Butte. Limited radiometric age data and geological field criteria suggest that all volcanism in the area is younger than 700,000 years; at least 67 separate basaltic eruptions are estimated to have occurred within the last 200,000 years. The average volcanic recurrence interval for the Arco-Big Southern Butte area is approximately one eruption per 3,000 years. Radioactive waste storage and reactor facilities at the Idaho National Engineering Laboratory may be subject to potential volcanic hazards. The geologic history and inferred past volcanic events in the Arco-Big Southern Butte area provide a basis for assessing the volcanic hazard. It is recommended that a radiometric age-dating study be performed on rocks in cored drill holes to provide a more precise estimate of the eruption recurrence interval for the region surrounding and including the Radioactive Waste Management Complex. It is also recommended that several geophysical monitoring systems (dry tilt and seismic) be installed to provide adequate warning of future volcanic eruptions.

Idaho↗
USGS1988

Zircon morphology and U-Pb geochronology of seven metaluminous and peralkaline post-orogenic granite complexes of the Arabian Shield, Kingdom of Saudi Arabia

The U-Pb zircon method was used to determine the ages of seven metaluminous-to-peralkaline post-orogenic granites located throughout the Late Proterozoic Arabian Shield of Saudi Arabia. Zircons from the metaluminous rocks are prismatic, with length-to-width ratios of about 2-4:1 and small pyramidal terminations. In contrast, zircons from three of the four peralkaline complexes either lack well developed prismatic faces (are pseudo-octahedral) or are anhedral. Some of the zircons from the peralkaline granites contain inherited radiogenic lead. This complicates interpretation of the isotopic data and. in many cases, may make the U-Pb method unsuitable for determining the age of a peralkaline granite. Zircons in the metaluminous granites do not contain inheritance and thus, best-fit chords calculated through the data have upper concordia intercepts that indicate the age of intrusion, and lower intercepts that indicate simple episodic lead loss. The results show that these granites were emplaced during multiple intrusive episodes from 670 to 510 Ma (Late Proterozoic to Cambrian).

Open-File Report↗
USGS1989

XAP, a program for deconvolution and analysis of complex X-ray spectra

The X-ray analysis program (XAP) is a spectral-deconvolution program written in BASIC and specifically designed to analyze complex spectra produced by energy-dispersive X-ray analytical systems (EDS). XAP compensates for spectrometer drift, utilizes digital filtering to remove background from spectra, and solves for element abundances by least-squares, multiple-regression analysis. Rather than base analyses on only a few channels, broad spectral regions of a sample are reconstructed from standard reference spectra. The effects of this approach are (1) elimination of tedious spectrometer adjustments, (2) removal of background independent of sample composition, and (3) automatic correction for peak overlaps. Although the program was written specifically to operate a KEVEX 7000 X-ray fluorescence analytical system, it could be adapted (with minor modifications) to analyze spectra produced by scanning electron microscopes, electron microprobes, and probes, and X-ray defractometer patterns obtained from whole-rock powders.

Open-File Report↗
USGS1980

Drake Peak — A structurally complex rhyolite center in southeastern Oregon

The Drake Peak volcanic center of middle Miocene age, located about 25 km northeast of Lakeview, Oreg., is a structurally complex eruptive center that resulted from several episodes of intrusion and extrusion of rhyolite. Two thousand meters of andesite and basalt flows, lahars, and volcaniclastic rocks of late Eocene age, and of basaltic andesite, tuff, and flood basalts of Eocene to middle Miocene age were structurally domed by the piston-like intrusion of a large body of rhyolite. The eruption of rhyolite flows at 14.3±2 million years followed the structural doming, and upper Miocene tuffs and basalt flows lapped against the dome and the rhyolite. A felsitic rhyolite ring intrusion 3 km in diameter, emplaced during the doming, is now exposed in the deeply eroded core of the dome. The rhyolites range in Si02 content from 69 to 76 percent and are peraluminous. The nonporphyritic ring intrusion is more silicic than the flows erupted later, which contain up to 23 percent phenocrysts of plagioclase, hypersthene, biotite, clinopyroxene, and quartz. The progressive depletion of Mg, Ca, Sr, Fe, Ti, and Al and the enrichment in silicon and rubidium are compatible with the generation of the observed rhyolite types by tapping a compositionally zoned magma chamber.

Oregon↗
USGS2001

Mountain Meadows Dacite: Oligocene intrusive complex that welds together the Los Angeles Basin, northwestern Peninsular Ranges, and central Transverse Ranges, California

Dikes and irregular intrusive bodies of distinctive Oligocene biotite dacite and serially related hornblende latite and felsite occur widely in the central and eastern San Gabriel Mountains, southern California, and are related to the Telegraph Peak granodiorite pluton. Identical dacite is locally present beneath Middle Miocene Topanga Group Glendora Volcanics at the northeastern edge of the Los Angeles Basin, where it is termed Mountain Meadows Dacite. This study mapped the western and southwestern limits of the dacite distribution to understand the provenance of derived redeposited clasts, to perceive Neogene offsets on several large strike-slip faults, to test published palinspastic reconstructions, and to better understand the tectonic boundaries that separate contrasting pre-Tertiary rock terranes where the Peninsular Ranges meet the central and western Transverse Ranges and the Los Angeles Basin. Transported and redeposited clasts of dacite-latite occur in deformed lower Miocene and lower middle Miocene sandy conglomerates (nonmarine, nearshore, and infrequent upper bathyal) close to the northern and northeastern margins of the Los Angeles Basin for a distance of nearly 60 km. Tie-lines between distinctive source suites and clast occurrences indicate that large tracts of the ancestral San Gabriel Mountains were elevated along range-bounding faults as early as 16–15 Ma. The tie-lines prohibit very large strike-slip offsets on those faults. Transport of eroded dacite began south of the range as early as 18 Ma. Published and unpublished data about rocks adjacent to the active Santa Monica-Hollywood-Raymond oblique reverse left-lateral fault indicate that cumulative left slip totals 13–14 km and total offset postdates 7 Ma. This cumulative slip, with assembly of stratigraphic and paleogeographic data, invalidates prior estimates of 60 to 90 km of left slip on these faults beginning about 17–16 Ma. A new and different palinspastic reconstruction of a region southwest of the San Andreas Fault Zone is proposed. Our reconstruction incorporates 20° of clockwise rotation of tracts north of the Raymond Fault from the easternmost Santa Monica Mountains to the Vasquez Creek Fault (San Gabriel south branch). We interpret the Vasquez Creek Fault as a reverse and right-lateral tear fault. Right slip on the tear becomes reverse dip slip on the northeast-striking Clamshell-Sawpit fault complex, interpreted as an offset part of the Mount Lukens Fault. This explains the absence of evidence for lateral offset of the Glendora Volcanics and associated younger marine strata where those are broken farther east by the eastern Sierra Madre reverse fault system. About 34 km of right slip is suggested for all breaks of the San Gabriel fault system. New paleogeographic maps of the Paleogene basin margin and of a Middle Miocene marine embayment and strandline derive in part from our palinspastic reconstruction. These appealingly simple maps fit well with data from the central Los Angeles Basin to the south and southwest.

California↗
USGS2005

Monitoring the natural attenuation of petroleum in ground water at the former naval complex, Operable Unit A, Adak Island, Alaska, May and June 2003

During May and June 2003, the U.S. Geological Survey installed monitoring wells and collected data to characterize the effectiveness of natural attenuation processes for remediating petroleum-contaminated ground water at Operable Unit A of the former Naval complex on Adak Island, Alaska. In addition, the evidence for petroleum biodegradation in ground water was evaluated at selected petroleum sites, plans for future natural attenuation monitoring were suggested for the selected petroleum sites, and the natural attenuation monitoring strategy for the Downtown area of Adak Island was reviewed and refinements were suggested. U.S. Geological Survey personnel measured water levels and collected ground-water samples from about 100 temporary boreholes and 50 monitoring wells. Most samples were analyzed on-site for concentrations of selected petroleum compounds and natural attenuation parameters such as dissolved oxygen, ferrous iron, and carbon dioxide. The U.S. Geological Survey evaluated the data on-site, selected new monitoring well locations, and installed, developed, and sampled 10 monitoring wells. The review and suggestions for the natural attenuation monitoring strategy focused on how to better achieve monitoring objectives specified in the Record of Decision for Adak Island petroleum sites. To achieve the monitoring objective of verifying that natural attenuation is occurring, the monitoring plans for each monitored natural attenuation site need to include sampling of at least one strategically placed well at the downgradient margin of the contaminant plume margin, preferably where contaminant concentrations are detectable but less than the cleanup level. Collection of natural attenuation parameter data and sampling background wells is no longer needed to achieve the monitoring objective of demonstrating the occurrence of natural attenuation. To achieve the objective of monitoring locations where chemical concentrations exceed specified cleanup levels, at least one natural attenuation well within or immediately downgradient from the contaminant source area at each site needs to be monitored. Achieving the Record of Decision-specified final monitoring objective of estimating the rate of natural attenuation to demonstrate achievement of cleanup levels within 75 years will be problematic. Demonstrating (predicting) achievement of cleanup levels within any timeframe in a technically defensible manner will be difficult to achieve using any type of short-term monitoring and evaluation, and will be particularly difficult to achieve through monitoring and evaluation of dissolved-phase petroleum only. Overall, natural attenuation processes appear to have greatly limited the extent of ground-water contamination at most sites investigated and have limited the risk that petroleum contaminants pose to downgradient receptors. Clarification or refinement of the monitoring objective to demonstrate cleanup within 75 years would be a reasonable prelude to developing a monitoring and data evaluation strategy to meet the objective.

Scientific Investigations Report↗