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At least 217 records · Page 12Linked to original sources
USGS2011

Evolution of overpressured and underpressured oil and gas reservoirs, Anadarko Basin of Oklahoma, Texas, and Kansas

Departures of resistivity logs from a normal compaction gradient indicate that overpressure previously extended north of the present-day overpressured zone. These indicators of paleopressure, which are strongest in the deep basin, are mapped to the Kansas-Oklahoma border in shales of Desmoinesian age. The broad area of paleopressure has contracted to the deep basin, and today the overpressured deep basin, as determined from drillstem tests, is bounded on the north by strata with near normal pressures (hydrostatic), grading to the northwest to pressures that are less than hydrostatic (underpressured). Thus the pressure regime in the northwest portion of the Anadarko Basin has evolved from paleo-overpressure to present-day underpressure. Using pressure data from drillstem tests, we constructed cross sections and potentiometric maps that illustrate the extent and nature of present-day underpressuring. Downcutting and exposure of Lower Permian and Pennsylvanian strata along, and east of, the Nemaha fault zone in central Oklahoma form the discharge locus where pressure reaches near atmospheric. From east to west, hydraulic head increases by several hundred feet in each rock formation, whereas elevation increases by thousands of feet. The resulting underpressuring of the aquifer-supported oil and gas fields, which also increases from east to west, is a consequence of the vertical separation between surface elevation and hydraulic head. A 1,000-ft thick cap of Permian evaporites and shales isolates the underlying strata from the surface, preventing re-establishment of a normal hydrostatic gradient. Thus, the present-day pressure regime of oil and gas reservoirs, overpressured in the deep basin and underpressured on the northwest flank of the basin, is the result of two distinct geologic events-rapid burial and uplift/erosion-widely separated in time.

Open-File Report↗
USGS2023

Connecting flood-related fluvial erosion and deposition with vulnerable downstream road-stream crossings

Fluvial erosion is increasingly responsible for infrastructure and building damages associated with floods as the intensity of extreme rainfalls hit rural and urban rivers in a variety of climate settings across the United States. Extreme floods in 2016 and 2018 caused widespread culvert blockages and road failures, including extensive damage along steep tributaries and ravines in the Marengo River, Wisconsin, watershed during 2016 and 2018. A study conducted by the U.S. Geological Survey (USGS), Wisconsin Wetlands Association (WWA), Ashland County, and the Northwest Wisconsin Regional Planning Commission (NWRPC) investigated the special concern of fluvial erosion hazards (FEHs) associated with gullying, streamside landslides, and the loss of wetland storage in headwaters. In 2019, a pilot study was begun to map and classify ephemeral and perennial streams and wetlands in terms of their sensitivity to FEHs. This study combined data from field-based rapid geomorphic assessments (RGAs) coupled with a stream network-wide geographic information system (GIS) approach for mapping stream segments, referred to as fluvial process zones (FPZ), sensitive to erosion, deposition, and channel change. The GIS approach used nationally available 10-meter (m) resolution topology and an extended stream network to map FPZs based on Strahler stream order, stream power, channel slope, presence of adjacent steep valley sides and headwater flats, and adjacent landform setting. Bankfull channel widths derived from RGA-based hydraulic geometry curves combined with drainage areas, an estimate of bankfull flow, and channel slope were used to calculate specific stream power for the FPZs. Lastly, the FPZs were characterized by their location within three major landform settings that affect erosion potential. The resulting vulnerability maps provided a screening framework to identify FPZs that are sensitive to incision, gullying and mass wasting along steep headwater ephemeral channels, as well as downstream perennial channels that have the potential for valley-side landslides, coarse sediment deposition, and channel change. Lastly, each FPZ was characterized in terms of hydrologic alteration associated with ditching. The vulnerability mapping products and rankings of sensitivity of FPZs will ultimately be used by Ashland County and their collaborators to prioritize natural flood management projects that mitigate FEHs, restore hydrology, and reconnect channels with adjacent wetlands and floodplains.

Wisconsin↗
USGS1998

Tectonic controls on magmatism in the Geysers-Clear Lake region: Evidence from new geophysical models

In order to study magmatism and geothermal systems in The Geysers–Clear Lake region, we developed a detailed three-dimensional tomographic velocity model based on local earthquakes. This high-resolution model resolves the velocity structure of the crust in the region to depths of approximately 12 km. The most significant velocity contrasts in The Geysers–Clear Lake region occur in the steam production area, where high velocities are associated with a Quaternary granitic pluton, and in the Mount Hannah region, where low velocities occur in a 5-km-thick section of Mesozoic argillites. In addition, a more regional tomographic model was developed using traveltimes from earthquakes covering most of northern California. This regional model sampled the whole crust, but at a lower resolution than the local model. The regional model outlines low velocities at depths of 8–12 km in The Geysers–Clear Lake area, which extend eastward to the Coast Range thrust. These low velocities are inferred to be related to unmetamorphosed Mesozoic sedimentary rocks. In addition, the regional velocity model indicates high velocities in the lower crust beneath the Clear Lake volcanic field, which we interpret to be associated with mafic underplating. No large silicic magma chamber is noted in either the local or regional tomographic models. A three-dimensional gravity model also has been developed in the area of the tomographic imaging. Our gravity model demonstrates that all density contrasts can be accounted for in the upper 5–7 km of the crust. Two-dimensional magnetotelluric models of data from a regional, east-west profile indicate high resistivities associated with the granitic pluton in The Geysers production area and low resistivities in the low-velocity section of Mesozoic argillites near Mount Hannah. No indication of midcrustal magma bodies is present in the magnetotelluric data. On the basis of heat flow and geologic evidence, Holocene intrusive activity is thought to have occurred near the Northwest Geysers, Mount Hannah, Sulphur Bank Mine, and perhaps other areas. The geophysical data provide no conclusive evidence for such activity, but the detailed velocity model is suggestive of intrusive activity near Mount Hannah similar to that in the “felsite” of The Geysers production area. The geophysical models, seismicity patterns, distribution of volcanic vents, heat flow, and other data indicate that small, young intrusive bodies that were injected along a northeast trend from The Geysers to Clear Lake probably control the thermal regime.

Geological Society of America Bulletin↗
USGS1983

The Alaska Mineral Resource Assessment Program: Background information to accompany folio of geologic and mineral resource maps of the Ambler River quadrangle, Alaska

The Ambler River quadrangle, consisting of 14,290 km2 (5,520 mi2) in northwest Alaska, was investigated by an interdisciplinary research team for the purpose of assessing the mineral resource potential of the quadrangle. This report provides background information for a folio of maps on the geology, reconnaissance geochemistry, aeromagnetics, Landsat imagery, and mineral resource evaluation of the quadrangle. A summary of the geologic history, radiometric dates, and fossil localities and a comprehensive bibliography are also included. The quadrangle contains jade reserves, now being mined, and potentially significant resources of copper, zinc, lead, and silver.

Alaska↗
USGS2020

Assessment of multi-stressors on compositional turnover of diatom, invertebrate and fish assemblages along an urban gradient in Pacific Northwest streams (USA)

This study is part of the regional stream-quality assessment (RSQA) conducted by the U.S. Geological Survey (USGS) National Water Quality Assessment (NAWQA) project. The purpose of this study is to examine small streams along land-use and stressor gradients at the regional scale and to evaluate the relative importance of instream stressors on diatom, macroinvertebrate, and fish assemblages. In 2015, the RSQA project assessed stream quality in 82 wadeable streams that were selected along an urban land-use gradient in the Pacific Northwest Region (PNW) of the United States. This study evaluates the effects of four major categories of measured instream stressors – flow (i.e. alteration), water quality, habitat, and contaminants (in water and sediment) – on stream biota. We used gradient forest (GF) models to evaluate taxon specific responses to the various stressors for the three biotic assemblages. Results for diatom, invertebrate and fish assemblages showed that several environmental variables including substrate size, dissolved oxygen, and two or more different contaminants were selected in each of the GF models. In general, all three assemblages were negatively associated with any contaminant measures above zero, except the more tolerant taxa in each assemblage, which responded positively to contaminants. Total nitrogen (TN) and total phosphorus (TP) were important in both the diatom and invertebrate GF models but not in the fish models, which were related to temperature and stream flow. TP and TN were the top two variables for diatom GF models and various taxa responded at a range of nutrient concentrations; however, some taxa responded at low concentrations, for example around 0.02 for TP and 0.5 mg/L for TN. In general, the three biotic assemblages responded to multiple stressors following general patterns of known sensitive versus tolerant taxa for each of the biotic groups studied, yet the GF models allow us to explore taxon specific responses. For example, most of the sensitive Ephemeroptera, Plecoptera, Trichoptera invertebrate taxa (EPT) responded negatively when any contaminant increased above zero; yet some taxa such as the tolerant Trichoptera Cheumatopsyche responded positively to contaminants and many of the other stressors. The findings of this study demonstrate the value of using multiple assemblages to monitoring stressor gradients associated with urban stream systems and the importance of evaluating the responses of individual taxa to stressors.

Washington, Oregon↗
USGS1995

Preliminary Geologic Map of the Thousand Oaks 7.5' Quadrangle, Southern California: A Digital Database

Thousand Oaks is located in Arroyo Conejo, a region spanning both southeastern Ventura County and extreme northwest Los Angeles County in southern California. It was discovered in 1542 by Spanish explorer Juan Rodriquez Cabrillo and eventually became part of the Spanish Rancho El Conejo land grant (conejo means 'rabbit' in Spanish, of which there are many in the area). It is located in the Santa Monica Mountains in the northwestern part of the greater Los Angeles area. The area is bordered by the San Fernando Valley and the city of Los Angeles to the east, Simi Hills to the north, Las Posas Hills and the Santa Rosa Valley to the northwest, Conejo Mountain (also known as Conejo Hills) and Oxnard Plain to the west, and the Santa Monica Mountains and Malibu to the southwest. The geology of the surrounding Santa Monica Mountains is dominated by a sequence of Tertiary sedimentary and volcanic rocks. These include the Tertiary Modelo Formation and the upper part of the Topanga Formation, other minor Tertiary rocks, and Miocene volcanic and intrusive rocks of the Conejo Formation. The basement units within the Santa Monica Mountains are a series of Jurassic and Cretaceous sedimentary rocks. The volcanic rocks of the Conejo Formation underlies much of the surrounding watersheds. The younger Tertiary sedimentary Modelo and Upper Topanga Formations flank the Conejo to the north and south. On the north slope of the Santa Monica Mountains where the Arroyo Conejo and Thousand Oaks are located, the Tertiary formations are gently folded. The south flank of the Santa Monica Mountains is structurally dominated by the Malibu Coast Fault that runs along the foot of the mountains. This fault, and associated structures, creates a complex geologic setting on the south flank of the Santa Monica Mountains. The active nature of the Malibu Coast fault and associated structures accounts for the steep and rugged coastal topography. The most widely exposed rock units in the area are the Plio-Pleistocene marine and nonmarine Pico and Saugus formations, which crop out on the southern flank of South Mountain-Oak Ridge and on the Las Posas uplands and Las Posas Hills. Locally, the Pico Formation consists of marine siltstone and silty shale with minor sandstone and pebbly sandstone. The Saugus Formation overlies and interfingers with the Pico Formation and is composed of interbedded shallow-marine to brackish water sandstone, siltstone, pebble-cobble conglomerate, and coquina beds that grade laterally and vertically into non-marine sandstone, siltstone, and conglomerate. A local member of the Saugus Formation is exposed in the southeast corner of the map area. It is predominantly a volcanic breccia conglomerate that resembles the Conejo Volcanics breccia, but is believed to represent remnants of landslide debris shed from the Conejo Formation into a local trough during Saugus time. Eroded from, and overlying, these bedrock formations are a series of recent alluvial units. These alluvial units include Quaternary alluvium comprised of alluvium, stream deposits, alluvial fan and floodplain deposits, beach deposits, dissected older alluvial deposits. Also present are Quaternary landslides and colluvium composed of landslide deposits and colluvium deposits. The colluvium represents relatively thick continuous deposits of soil and rock fragments that are common on the steep slopes of the coastal canyons, and generally feed the many landslides, soil slips, and debris flows.

Open-File Report↗
USGS2014

Geologic map of the Kechumstuk fault zone in the Mount Veta area, Fortymile mining district, east-central Alaska

This map was developed by the U.S. Geological Survey Mineral Resources Program to depict the fundamental geologic features for the western part of the Fortymile mining district of east-central Alaska, and to delineate the location of known bedrock mineral prospects and their relationship to rock types and structural features. This geospatial map database presents a 1:63,360-scale geologic map for the Kechumstuk fault zone and surrounding area, which lies 55 km northwest of Chicken, Alaska. The Kechumstuk fault zone is a northeast-trending zone of faults that transects the crystalline basement rocks of the Yukon-Tanana Upland of the western part of the Fortymile mining district. The crystalline basement rocks include Paleozoic metasedimentary and metaigneous rocks as well as granitoid intrusions of Triassic, Jurassic, and Cretaceous age. The geologic units represented by polygons in this dataset are based on new geologic mapping and geochronological data coupled with an interpretation of regional and new geophysical data collected by the Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys. The geochronological data are reported in the accompanying geologic map text and represent new U-Pb dates on zircons collected from the igneous and metaigneous units within the map area.

Alaska↗
USGS1968

Geology and geochemistry of the Wanamu-Blue Mountains area, Waini SW, Guyana

The Wanamu-Blue Mountains area is situated in the Northwest District of Guyana, about 110 miles northwest of Georgetown. The Blue Mountains are low, but rugged, hills that have developed on mafic metamorphic rocks that occur in an arcuate "mantle" around a granite batholith, the Aranka-Wanamu Granite. The area lies within the Precambrian Guiana Shield and is entirely covered with tropical rain forest. The geology of the area is complex and is made up of an assemblage of metamorphic rocks consisting of phyllites, quartzites, amphibolites, and epidiorites that are intruded by serpentinites. The serpentinites occur as thin, tabular, dike-like bodies that trend northwest across the area. The serpentinites contain abundant magnetite, but very little chromite or sulfide minerals. Lletasomatic reaction zones have developed around the serpentinite bodies at their contacts with country rock. These reaction zones consist of aureoles of actinolite schist, chloritic hornfels, and talcose zones in the phyllites.

Wanamu-Blue Mountains↗
USGS2013

NW CSC annual report fiscal year 2013

The Northwest Climate Science Center (NW CSC) was established in 2010 as one of eight regional Climate Science Centers created by the Department of the Interior (DOI). The NW CSC encompasses Washing-ton, Oregon, Idaho, and western Montana and has overlapping boundaries with three Landscape Conservation Cooperatives (LCCs): the Great Northern, the Great Basin, and the North Pacific. With guidance from its Executive Stakeholder Advisory Committee (ESAC), the NW CSC and its partner LCCs are addressing the highest priority regional climate science needs of Northwest natural and cultural resource managers. Climate Science Centers tap into the scientific expertise of both the U.S. Geological Survey (USGS) and academic institutions. The NW CSC is supported by an academic consortium with the capacity to generate climate science and tools in a coordinated fashion, serving stakeholders across the Northwest region. This consortium is primarily represented by Oregon State University (OSU), the University of Id-ho (UI), and the University of Washington (UW). The academic consortium and USGS provide capabilities in climate science, ecology, impacts and vulnerability assessment, modeling, adaptation planning, and advanced information technology, all necessary to address and respond to climate change in the Northwest. University members also recruit and train graduate students and early-career scientists. This Annual Report summarizes progress for the goals set out in the NW CSC Strategic Plan for 2012-2015 (http://www.doi.gov/csc/northwest/upload/Northwest-CSC-Strategic-Plan.cfm) and the NW CSC Work-plan for Fiscal Year (FY) 2013 (October 1, 2012 through September 30, 2013). The report follows the structure of the Strategic Plan, which describes the five core services (Executive, Science, Data, Communications, and Education and Training) provided by the NW CSC in support of the stated vision: Our Vision: To become nationally recognized as a best-practice model for the provision of climate science and decision support tools to address conservation and management issues in the Pacific Northwest Region.

Report↗
USGS2014

Key subsurface data help to refine Trinity aquifer hydrostratigraphic units, south-central Texas

The geologic framework and hydrologic characteristics of aquifers are important components for studying the nation’s subsurface heterogeneity and predicting its hydraulic budgets. Detailed study of an aquifer’s subsurface hydrostratigraphy is needed to understand both its geologic and hydrologic frameworks. Surface hydrostratigraphic mapping can also help characterize the spatial distribution and hydraulic connectivity of an aquifer’s permeable zones. Advances in three-dimensional (3-D) mapping and modeling have also enabled geoscientists to visualize the spatial relations between the saturated and unsaturated lithologies. This detailed study of two borehole cores, collected in 2001 on the Camp Stanley Storage Activity (CSSA) area, provided the foundation for revising a number of hydrostratigraphic units representing the middle zone of the Trinity aquifer. The CSSA area is a restricted military facility that encompasses approximately 4,000 acres and is located in Boerne, Texas, northwest of the city of San Antonio. Studying both the surface and subsurface geology of the CSSA area are integral parts of a U.S. Geological Survey project funded through the National Cooperative Geologic Mapping Program. This modification of hydrostratigraphic units is being applied to all subsurface data used to construct a proposed 3-D EarthVision model of the CSSA area and areas to the south and west.

Texas↗
USGS1974

Generalized geology and structure of the Winkelman 15-minute quadrangle and vicinity, Pinal and Gila Counties, Arizona

A. northwest-trending belt of steeply east-dipping Precambrian and Paleozoic sedimentary rocks extends across the Winkelman 15-minute quadrangle and separates areas of contrasting structures. To the southwest for 60 mi is an expanse of Precambrian basement, largely granite; to the northeast the Precambrian and Paleozoic sedimentary rocks are gently tilted and intricately faulted. The structure within the Winkelman 15-minute quadrangle is interpreted as a monocline separated into en echelon segments by strike-slip and normal faults. Other monoclines lie-to the north and northwest. Most of the tilting that formed the monoclines occurred after deposition of the early(?) Miocene San Manuel Formation. Structural features that repeat the Precambrian and Paleozoic sedimentary rocks within the area and that resemble high-angle faults are believed to have formed as low-angle thrusts, tilted to their present nearly vertical position during development of the monoclines. Structural features that are younger than the monoclines include low-angle gravity slide surfaces which are older than the high-angle normal faults that formed the basin-and-range topography on which the Pliocene sediments were deposited.

Arizona↗
USGS2016

Geologic map of the Sauvie Island quadrangle, Multnomah and Columbia Counties, Oregon, and Clark County, Washington

Introduction The Sauvie Island 7.5' quadrangle is situated in the Puget-Willamette Lowland northwest of downtown Portland, Oreg. This lowland, which extends from Puget Sound to west-central Oregon, is a complex structural and topographic trough between the Coast Range and the Cascade Range. Since late Eocene time, the Cascade Range has been the locus of a discontinuously active volcanic arc associated with underthrusting of oceanic lithosphere beneath the North American continent along the Cascadia Subduction Zone. The Coast Range, which occupies the fore-arc position within the Cascadia arc-trench system, consists of a complex assemblage of Eocene to Miocene volcanic and marine sedimentary rocks. The Sauvie Island quadrangle lies along the southwest margin of the Portland Basin, a 2,000-km 2 topographic and structural depression. The basin boundary is an abrupt topographic break at the base of the Tualatin Mountains, which separates the Portland and Tualatin Basins. The Tualatin Mountains are underlain by lava flows of the Miocene Columbia River Basalt Group that have been folded into an asymmetric anticline. Oligocene marine sedimentary rocks, not exposed at the surface, are inferred to underlie the basalt flows. The abrupt basin boundary marks the location of the northwest-striking Portland Hills Fault Zone, which is probably an active structure. The Columbia River flows west and north through the Portland Basin at nearly sea level. The Willamette River enters the Columbia near the southeast corner of the map area. Seismic-reflection profiles and lithologic logs of water wells show as much as 550 m of late Miocene and younger sediments in the deepest part of the basin east of the quadrangle. Deposits exposed at the surface consist chiefly of Holocene and late Pleistocene fluvial and eolian sediments and man-made fill. This map contributes to a U.S. Geological Survey program to improve the geologic database for the Portland region of the Pacific Northwest urban corridor. The map and ancillary data will support assessments of seismic risk, ground-failure hazards, and resource availability.

Oregon, Washington↗
USGS2010

Reconnaissance geologic map of the Hyampom 15' quadrangle, Trinity County, California

The Hyampom 15' quadrangle lies west of the Hayfork 15' quadrangle in the southern part of the Klamath Mountains geologic province of northern California. It spans parts of four generally northwest-trending tectono- stratigraphic terranes of the Klamath Mountains, the Eastern Hayfork, Western Hayfork, Rattlesnake Creek, and Western Jurassic terranes, as well as, in the southwest corner of the quadrangle, a small part of the Pickett Peak terrane of the Coast Range province. Remnants of the Cretaceous Great Valley overlap sequence that once covered much of the pre-Cretaceous bedrock of the quadrangle are now found only as a few small patches in the northeast corner of the quadrangle. Fluvial and lacustrine deposits of the mid-Tertiary Weaverville Formation crop out in the vicinity of the village of Hyampom. The Eastern Hayfork terrane is a broken formation and m-lange of volcanic and sedimentary rocks that include blocks of chert and limestone. The chert has not been sampled; however, chert from the same terrane in the Hayfork quadrangle contains radiolarians of Permian and Triassic ages, but none clearly of Jurassic age. Limestone at two localities contains late Paleozoic foraminifers. Some of the limestone from the Eastern Klamath terrane in the Hayfork quadrangle contains faunas of Tethyan affinity. The Western Hayfork terrane is part of an andesitic volcanic arc that was accreted to the western edge of the Eastern Hayfork terrane. It consists mainly of metavolcaniclastic andesitic agglomerate and tuff, as well as argillite and chert, and it includes the dioritic Ironside Mountain batholith that intruded during Middle Jurassic time (about 170 Ma). This intrusive body provides the principal constraint on the age of the terrane. The Rattlesnake Creek terrane is a melange consisting mostly of highly dismembered ophiolite. It includes slabs of serpentinized ultramafic rock, basaltic volcanic rocks, radiolarian chert of Triassic and Jurassic ages, limestone containing Late Triassic conodonts and Permian or Triassic foraminifers, and small exotic(?) plutons. The plutons probably are similar to ones to the southeast beyond the quadrangle boundary that yielded isotopic ages ranging from 193 Ma to 207 Ma. The Rattlesnake Creek terrane contains several areas of well- bedded sedimentary rocks (rcs) that somewhat resemble the Galice(?) Formation and may be inliers of the Western Jurassic terrane. The Western Jurassic terrane in the Hyampom quadrangle appears to consist only of a narrow tectonic sliver of slaty to semischistose detrital sedimentary rocks of the Late Jurassic Galice(?) Formation. The isotopic age of metamorphism of the rocks is about 150 Ma, which probably indicates when the terrane was accreted to the Rattlesnake Creek terrane. The Pickett Peak terrane, which is the most westerly of the succession of terranes in the Hyampom quadrangle, is the accreted eastern margin of the Coast Ranges province. It mainly consists of semischistose and schistose metagraywacke of the South Fork Mountain Schist and locally contains the blueschist-facies mineral lawsonite. Isotopic analysis indicates a metamorphic age of 120 to 115 Ma. During the Cretaceous period, much of the southern fringe of the Klamath Mountains was onlapped by sedimentary strata of the Great Valley sequence. However, much of the onlapping Cretaceous strata has since been eroded away, and in the Hyampom quadrangle only a few small remnants are found in the northeast corner near Big Bar. Near the west edge of the quadrangle, in the vicinity of the village of Hyampom, weakly consolidated fluvial and lacustrine rocks and coaly deposits of Oligocene and (or) Miocene age are present. These rocks are similar to the Weaverville Formation that occurs in separate sedimentary basins to the east in the Weaverville and Hayfork 15? quadrangles. This map of the Hyampom 15' quadrangle is a digital version of U.S. Geological Survey Miscellaneous Field Study.

California↗
USGS2014

Spawning patterns of Pacific Lamprey in tributaries to the Willamette River, Oregon

Addressing the ongoing decline of Pacific Lamprey Entosphenus tridentatus across its range along the west coast of North America requires an understanding of all life history phases. Currently, spawning surveys (redd counts) are a common tool used to monitor returning adult salmonids, but the methods are in their infancy for Pacific Lamprey. To better understand the spawning phase, our objective was to assess temporal spawning trends, redd abundance, habitat use, and spatial patterns of spawning at multiple spatial scales for Pacific Lamprey in the Willamette River basin, Oregon. Although redd density varied considerably across surveyed reaches, the observed temporal patterns of spawning were related to physical habitat and hydrologic conditions. As has been documented in studies in other basins in the Pacific Northwest, we found that redds were often constructed in pool tailouts dominated by gravel, similar to habitat used by spawning salmonids. Across the entire Willamette Basin, Pacific Lampreys appeared to select reaches with alluvial geology, likely because this is where gravel suitable for spawning accumulated. At the tributary scale, spawning patterns were not as strong, and in reaches with nonalluvial geology redds were more spatially clumped than in reaches with alluvial geology. These results can be used to help identify and conserve Pacific Lamprey spawning habitat across the Pacific Northwest.

Oregon↗
USGS2024

Geologic map and structure sections along the southern part of the Bartlett Springs Fault Zone and adjacent areas from Cache Creek to Lake Berryessa, northern Coast Ranges, California

Introduction Located in the Coast Ranges of northern California, the Bartlett Springs Fault Zone is the easternmost fault in the San Andreas Fault system in northern California. The fault is a right-lateral, strike-slip structure considered capable of producing an earthquake of moment magnitude 7. The purpose of this mapping is to better characterize the geology and earthquake hazards associated with the southern part of the Bartlett Springs Fault Zone and to help identify any evidence of active uplift on the faults bounding the Coast Ranges. Although the area immediately surrounding the Bartlett Springs Fault Zone is sparsely populated, its southern segment presents a potential seismic hazard to northern California communities as far away as the San Francisco Bay region and Sacramento. There are also nearby water resources, mineral resources, and public lands used for public recreation. The Coast Ranges of northern California are a series of northwest-southeast-oriented mountain ranges and valleys located north of the San Francisco Bay region, between the Pacific Ocean to the west and the Sacramento Valley to the east. The region has rugged terrain, high mountain peaks that reach more than 2,400 meters above sea level, isolated and narrow valley bottoms on which most human settlements are located, and large drainage systems that tend to follow the northwest-southeast-oriented topographic grain. The physiographic character of the region is shaped by its bedrock geology, deformational history, and active faulting. The basement rocks of the northern Coast Ranges consist of the Franciscan Complex and the Great Valley complex, the latter of which consists of two informal units, the Coast Range ophiolite and the Great Valley sequence. The Franciscan Complex and the Great Valley complex are in structural contact along the Coast Range Fault, a regional-scale structure and fundamental crustal boundary. The Franciscan Complex and the Great Valley complex are superposed by active, northwest-southeast-striking strike-slip faults that are associated with seismicity swarms. These active strike-slip faults can produce moderate to large earthquakes that have moment magnitudes of 7–8. In places, these active structures bound large ranges and valleys, suggesting that much of the modern topographic expression is the result of active deformation processes. This report contains new 1:24,000-scale geologic mapping along the southern part of the Bartlett Springs Fault Zone between Clear Lake and Lake Berryessa. The map area spans 738 square kilometers in northern Napa County, southern Lake County, and parts of Yolo and Colusa Counties. The south and east borders of the map are 90 kilometers north of San Francisco and 70 kilometers west of Sacramento, respectively. The map area is within the Knoxville mining district, which has a history of mercury and gold mining dating back to the mid-19th century. The two main towns in the region, Lower Lake and Clearlake, California, are west-northwest of the map area. Approximately 71,000 people live in the cities and rural communities located within a 40-kilometer radius of the center of the map area. The bedrock geology, cross sections, and structural data presented herein are critical for evaluating the long-term evolution of the Bartlett Springs Fault Zone. This work will supplement studies on local seismic hazards, liquefaction potential, landslide hazards, earthquake geology, natural resources, groundwater resources, engineering geology, and tectonic history by providing the background information for site-specific investigations on these subjects.

California↗
USGS2010

Geology of the Selk crater region on Titan from Cassini VIMS observations

Observations of Titan obtained by the Cassini Visual and Infrared Mapping Spectrometer (VIMS) have revealed Selk crater, a geologically young, bright-rimmed, impact crater located ???800. km north-northwest of the Huygens landing site. The crater rim-crest diameter is ???90. km; its floor diameter is ???60. km. A central pit/peak, 20-30. km in diameter, is seen; the ratio of the size of this feature to the crater diameter is consistent with similarly sized craters on Ganymede and Callisto, all of which are dome craters. The VIMS data, unfortunately, are not of sufficient resolution to detect such a dome. The inner rim of Selk crater is fluted, probably by eolian erosion, while the outer flank and presumed ejecta blanket appear dissected by drainages (particularly to the east), likely the result of fluvial erosion. Terracing is observed on the northern and western walls of Selk crater within a 10-15. km wide terrace zone identified in VIMS data; the terrace zone is bright in SAR data, consistent with it being a rough surface. The terrace zone is slightly wider than those observed on Ganymede and Callisto and may reflect differences in thermal structure and/or composition of the lithosphere. The polygonal appearance of the crater likely results from two preexisting planes of weakness (oriented at azimuths of 21?? and 122?? east of north). A unit of generally bright terrain that exhibits similar infrared-color variation and contrast to Selk crater extends east-southeast from the crater several hundred kilometers. We informally refer to this terrain as the Selk "bench." Both Selk and the bench are surrounded by the infrared-dark Belet dune field. Hypotheses for the genesis of the optically bright terrain of the bench include: wind shadowing in the lee of Selk crater preventing the encroachment of dunes, impact-induced cryovolcanism, flow of a fluidized-ejecta blanket (similar to the bright crater outflows observed on Venus), and erosion of a streamlined upland formed in the lee of Selk crater by fluid flow. Vestigial circular outlines in this feature just east of Selk's ejecta blanket suggest that this might be a remnant of an ancient, cratered crust. Evidently the southern margin of the feature has sufficient relief to prevent the encroachment of dunes from the Belet dune field. We conclude that this feature either represents a relatively high-viscosity, fluidized-ejecta flow (a class intermediate to ejecta blankets and long venusian-style ejecta flows) or a streamlined upland remnant that formed downstream from the crater by erosive fluid flow from the west-northwest. ?? 2010 Elsevier Inc.

Icarus↗
USGS2018

Extreme‐value geoelectric amplitude and polarization across the northeast United States

Maps are presented of extreme‐value geoelectric field amplitude and horizontal polarization for the Northeast United States. These maps are derived from geoelectric time series calculated for sites across the Northeast by frequency‐domain multiplication (time‐domain convolution) of 172 magnetotelluric impedance tensors, acquired during a survey, with decades‐long, 1‐min resolution time series of geomagnetic variation, acquired at three magnetic observatories. The maps show that, during intense magnetic storms, high geoelectric amplitude hazards are realized across electrically resistive, igneous and metamorphic rock of the Appalachian Mountains and the New England Highlands, while low geoelectric hazards are realized across electrically conductive, sedimentary rock of the Appalachian Plateau and the Mid‐Atlantic Coastal Plain. From statistical extrapolation, once‐per‐century (100‐year) geoelectric amplitudes are highest at a site in Virginia at 25.44 V/km (followed by a site in Maine at 21.75 V/km and a site in Connecticut at 19.39 V/km); 100‐year geoelectric amplitude exceeds 10 V/km at 12 sites across the northeast; geoelectric amplitude is lowest at a site in Virginia at 0.05 V/km. Average errors for these values are estimated to be about 38%, or much less than the more than 2 orders of magnitude range seen in geoelectric amplitudes from one survey site to another across the northeast. It is noteworthy that geoelectric fields tend to be most (least) polarized at locations with high (low) geoelectric hazard. Furthermore, geoelectric fields over the Appalachians tend to be polarized southeast‐to‐northwest, or generally in a direction orthogonal to the southwest‐to‐northeast geological strike. Results reported here inform utility companies in projects for evaluating and managing the response of power grid systems to the deleterious effects of geomagnetic disturbance.

Connecticut, Delaware, Maine, Maryland, Massachuse↗
USGS1998

Paleoslope analysis of slump folds in the devonian flysch of Maine

Ancient submarine slide and slump deposits in the Devonian flysch of central and northern Maine show considerable variation in fold style, from symmetric to asymmetric to sheath geometries. Building on earlier work by Farrell and Eaton, we suggest that the spectrum of fold styles reflects the degree of simple shear within each slump deposit. We present a stereographic approach to paleoslope analysis that exploits fold hinge attitudes, axial surface attitudes, sheath axes, vergence, S‐ and Z‐asymmetry—depending on the style of slump folding. Our paleoslope determinations from widely scattered locations across the Devonian foreland basin in Maine show a regionally consistent pattern of westerly to northwesterly slopes.

Journal of Geology↗