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At least 739 records · Page 41Linked to original sources
USGS2016

Water temperature effects from simulated dam operations and structures in the Middle Fork Willamette River, western Oregon

Significant Findings Streamflow and water temperature in the Middle Fork Willamette River (MFWR), western Oregon, have been regulated and altered since the construction of Lookout Point, Dexter, and Hills Creek Dams in 1954 and 1961, respectively. Each year, summer releases from the dams typically are cooler than pre-dam conditions, with the reverse (warmer than pre-dam conditions) occurring in autumn. This pattern has been detrimental to habitat of endangered Upper Willamette River (UWR) Chinook salmon ( Oncorhynchus tshawytscha ) and UWR winter steelhead ( O. mykiss ) throughout multiple life stages. In this study, scenarios testing different dam-operation strategies and hypothetical dam-outlet structures were simulated using CE-QUAL-W2 hydrodynamic/temperature models of the MFWR system from Hills Creek Lake (HCR) to Lookout Point (LOP) and Dexter (DEX) Lakes to explore and understand the efficacy of potential flow and temperature mitigation options. Model scenarios were run in constructed wet, normal, and dry hydrologic calendar years, and designed to minimize the effects of Hills Creek and Lookout Point Dams on river temperature by prioritizing warmer lake surface releases in May–August and cooler, deep releases in September–December. Operational scenarios consisted of a range of modified release rate rules, relaxation of power-generation constraints, variations in the timing of refill and drawdown, and maintenance of different summer maximum lake levels at HCR and LOP. Structural scenarios included various combinations of hypothetical floating outlets near the lake surface and hypothetical new outlets at depth. Scenario results were compared to scenarios using existing operational rules that give temperature management some priority ( Base ), scenarios using pre-2012 operational rules that prioritized power generation over temperature management ( NoBlend ), and estimated temperatures from a without-dams condition ( WoDams ). Results of the tested model scenarios led to the following conclusions: The existing outlets at Lookout Point Dam, because of the range of depths, allow for greater temperature control than the two existing outlets at Hills Creek Dam that are relatively deep. Temperature control at HCR through operational scenarios generally was minimal near Hills Creek Dam, but improved downstream toward the head of LOP when decreased release rates held HCR at a low lake elevation year-round. Inflows from unregulated streams between HCR and LOP helped to dilute the effects of HCR and achieve more natural stream temperatures before the MFWR entered LOP. The relative benefit of any particular scenario depended on the location in the MFWR system used to assess the potential change, with most scenarios involving changes to Hills Creek Dam being less effective with increasing downstream distance, such as downstream of DEX. To achieve as much temperature control as the most successful structural scenarios, which were able to resemble without-dam conditions for part of the year, most operational scenarios had to be free of any power-generation requirements at Lookout Point Dam. Downstream of DEX, scenarios incorporating a hypothetical floating outlet at either HCR or LOP resulted in similar temperatures, with both scenarios causing a delay in the estimated spring Chinook egg emergence by about 9–10 days compared to base-case temperature-management scenarios.

Oregon↗
USGS2017

Semiautomatic approaches to account for 3-D distortion of the electric field from local, near-surface structures in 3-D resistivity inversions of 3-D regional magnetotelluric data

This report summarizes the results of three-dimensional (3-D) resistivity inversion simulations that were performed to account for local 3-D distortion of the electric field in the presence of 3-D regional structure, without any a priori information on the actual 3-D distribution of the known subsurface geology. The methodology used a 3-D geologic model to create a 3-D resistivity forward (“known”) model that depicted the subsurface resistivity structure expected for the input geologic configuration. The calculated magnetotelluric response of the modeled resistivity structure was assumed to represent observed magnetotelluric data and was subsequently used as input into a 3-D resistivity inverse model that used an iterative 3-D algorithm to estimate 3-D distortions without any a priori geologic information. A publicly available inversion code, WSINV3DMT, was used for all of the simulated inversions, initially using the default parameters, and subsequently using adjusted inversion parameters. A semiautomatic approach of accounting for the static shift using various selections of the highest frequencies and initial models was also tested. The resulting 3-D resistivity inversion simulation was compared to the “known” model and the results evaluated. The inversion approach that produced the lowest misfit to the various local 3-D distortions was an inversion that employed an initial model volume resistivity that was nearest to the maximum resistivities in the near-surface layer.

Open-File Report↗
USGS2017

Water temperature effects from simulated changes to dam operations and structures in the Middle and South Santiam Rivers, Oregon

Green Peter and Foster Dams on the Middle and South Santiam Rivers, Oregon, have altered the annual downstream water temperature profile (cycle). Operation of the dams has resulted in cooler summer releases and warmer autumn releases relative to pre-dam conditions, and that alteration can hinder recovery of various life stages of threatened spring-run Chinook salmon ( Oncorhyncus tshawytscha ) and winter steelhead ( O. mykiss ). Lake level management and the use of multiple outlets from varying depths at the dams can enable the maintenance of a temperature regime more closely resembling that in which the fish evolved by releasing warm surface water during summer and cooler, deeper water in the autumn. At Green Peter and Foster Dams, the outlet configuration is such that temperature control is often limited by hydropower production at the dams. Previously calibrated CE-QUAL-W2 water temperature models of Green Peter and Foster Lakes were used to simulate the downstream thermal effects from hypothetical structures and modified operations at the dams. Scenarios with no minimum power production requirements allowed some releases through shallower and deeper outlets (summer and autumn) to achieve better temperature control throughout the year and less year-to-year variability in autumn release temperatures. Scenarios including a hypothetical outlet floating 1 meter below the lake surface resulted in greater ability to release warm water during summer compared to existing structures. Later in Autumn (October 15–December 31), a limited amount of temperature control was realized downstream from Foster Dam by scenarios limited to operational changes with existing structures, resulting in 15-day averages within 1.0 degree Celsius of current operations.

Oregon↗
USGS2022

Evaluation of fish behavior at the entrances to a Selective Water Withdrawal structure in Lake Billy Chinook, Oregon, 2021

Imaging sonar was used to assess the behavior, abundance, and timing of fish at the entrances to the Selective Water Withdrawal (SWW) intake structure located in the forebay of Round Butte Dam, Oregon during the spring of 2021. The purposes of the SWW are (1) to direct surface currents in the forebay to attract and collect downriver migrating juvenile salmonid smolts (Chinook salmon [ Oncorhynchus tshawytscha ], sockeye salmon [ O. nerka ], and steelhead [ O. mykiss ]) from Lake Billy Chinook and (2) to enable operators of the SWW to withdraw water from surface and benthic elevations in the reservoir to manage downriver water temperatures. Part of the evaluation, to determine how well the structure performs at collecting juvenile salmonids, needs (A) to regularly assess how fish are approaching the entrance, and (B) to determine if operational flows could be optimized to increase the attraction of smolts present in the forebay of Lake Billy Chinook. The primary goals of this study were (1) to assess the abundance and behaviors of smolt-size fish observed near the SWW and (2) to provide data of the effect of two-night generation operation timing conditions on movements and behaviors of fish near the entrance to the SWW structure. The purpose of this assessment is to improve downstream passage solutions. Two imaging sonar units were deployed during the spring 2021 smolt out-migration period. One unit monitored fish movements near the south entrance and one unit monitored movements near the north entrance of the SWW. Both smolt and bull trout ( Salvelinus confluentus )-size fish were regularly observed near the entrances with greater abundances observed during night, corresponding with greater discharge through the SWW than during the day when discharge was reduced. Differences in fish abundance were observed between the night generation operation timing conditions, with increased fish counts observed when elevated discharge was extended to 6:00 a.m., rather than when discharges have been traditionally reduced in the early morning at 4:00 a.m. Fish of all size groups were primarily observed near the center of the SWW, and greater abundances of fish were observed at the south entrance. Increased counts of bull trout-size fish coincided with the increased abundances of smolt-size fish. Overall, the results indicate that (A) smolt-size fish were more abundant near the entrance of the SWW during periods of increased discharge, (B) bull trout-size fish were present at the SWW, and (C) fish were more numerous at the SWW when night generation operation timing was extended later into the morning hours rather than the traditional operation timing flow reduction.

Oregon↗
USGS2023

Influence of a guide net on the presence and behavior of fish near the selective water withdrawal structure in Lake Billy Chinook, Oregon, 2022

Imaging sonar was used to assess the influence of a fish guidance net, installed at the entrances to the selective water withdrawal (SWW) intake structure, in the forebay of Round Butte Dam, Oregon, on behavior, abundance, and timing of fish during the spring of 2022. The purposes of the SWW are (1) to direct surface currents in the forebay to attract and collect downriver migrating juvenile salmonid smolts (Chinook salmon [ Oncorhynchus tshawytscha ], sockeye salmon [ O. nerka ], and steelhead [ O. mykiss ]) from Lake Billy Chinook and (2) to enable operators of the SWW to withdraw water from surface and benthic elevations in the reservoir to manage downriver water temperatures. Part of the evaluation to determine how well the structure performs at collecting juvenile salmonids is (1) to regularly assess how fish are approaching the entrance, and (2) determine if operational flows and the installation of a guidance (lead) net near the SWW structure entrance can be optimized to increase the attraction of smolts present in the forebay of Lake Billy Chinook. The goal of this study was to provide data about the effects of the installation of a lead net on the movements and behaviors of juvenile salmonids near the entrance to the SWW to help inform decisions to improve downstream passage solutions. Two imaging sonar units were deployed during the spring 2022 smolt out-migration period. One unit monitored fish movements near the south entrance and one unit monitored movements near the north entrance of the SWW, with the lead net between the two entrances. Both smolt and bull trout ( Salvelinus confluentus )-size fish were regularly observed near the entrances, with greater abundances observed at night, corresponding with greater discharge through the SWW, as opposed to during the day when discharge was reduced. Smolt-size fish groups were primarily observed near the interior halves of each SWW entrance, and greater abundances of fish were observed at the south entrance. Increased counts of bull trout-size fish coincided with the increased abundances of smolt-size fish. Overall, the results indicate that (1) smolt-size fish were more abundant near the entrance of the SWW during periods of increased discharge, (2) bull trout-size fish were present at the SWW, and (3) a greater percentage of smolt-size fish were observed directed toward the entrances of the SWW during periods of increased discharge. The addition of the lead net may assist in orienting fish toward the entrances to the SWW.

Oregon↗
USGS2025

Benthic habitat map of Olowalu Reef, Maui, Hawaii—Geomorphological structure, biological cover, and geologic zonation determined with spectral, lidar, and acoustic data

The fringing coral reef off Olowalu, Maui, Hawaii, has been identified as a local conservation priority site. In 2007, the National Oceanic and Atmospheric Administration (NOAA) produced a benthic habitat map of the Hawaiian Islands that was used as a foundation for this study. To support place-based management of the reef in the future, the U.S. Geological Survey (USGS) mapped the geologic zone, major and dominant geomorphological structure, biological cover type, and percent of biological cover for 11 square kilometers (km 2 ) of Olowalu Reef at a minimum mapping unit (MMU) of 100 square meters (m 2 ) to create a benthic habitat map. Heads-up digitization was employed on 0.50-meter (m) natural color satellite orthoimagery with ancillary 1-m acoustic backscatter imagery from single-scan sonar (sound navigation and ranging). A 1-m, 4-m, and 8-m digital bathymetric model (DBM) was interpolated from bathymetric lidar (light detection and ranging), and various geomorphometric layers derived from the DBMs were used for habitat interpretation. Still-frame imagery of the seafloor extracted from vessel-towed underwater video transects on Olowalu Reef served as ground validation points ( n =870) during active mapping and accuracy assessment points ( n =216) for thematic accuracy assessment. Thematic accuracy was cross-validated by the Hawai‘i Department of Land and Natural Resources Division of Aquatic Resources. Final thematic accuracy was 88.8 percent for major structure, 85.6 percent for dominant structure, 86.0 percent for major biological cover, and 78.6 percent for type and percent of major biological cover. Reef and hardbottom constituted 52 percent of the total mapped habitat, comprising mostly aggregate reef (31 percent) and pavement (11 percent), with large swaths of spur-and-groove (9 percent). Of this hardbottom, 17 percent was covered with moderate (10 to <50 percent) coral and 27 percent with high coral cover (50 to <90 percent). High (50 to <90 percent) macroalgae cover dominated the continuous sand sheets in offshore bank/shelf zones. The map created in this study supplements the NOAA 2007 map and expands on the observations made by USGS sampling of the reef. The NOAA 2007 map and our map differed in total areal extent by a negligible 6 m 2 and were in general thematic agreement. Our map is intended to serve as a baseline for public access, general research, local-level management, and reef change for future studies.

Hawaii↗
USGS1951

Rocks and structure of the Quartz Spring area, northern Panamint Range, California

The Quartz Spring area covers about 50 square miles in the northern part of the Panamint Range, Inyo County, California. It lies near the southwestern border of the Basin and Range Province. The paper describes the stratigraphy, igneous petrology, and the main structures of the area. The formations, as defined by the stratigraphy, and the structure are shown on a large scale topographic map and in structure sections. The stratigraphy, except for Quaternary deposits that cover about one-fourth of the area, consists of Paleozoic sedimentary rocks preponderantly dolomite and limestone, representing each system from Cambrian to Carboniferous, as outlined below. No surface of erosion (unconformity) has been recognized between any of the formations or systems within the area.

Open-File Report↗
USGS1961

Structure and stratigraphy of the Pybus-Gambier area, Alaska

The Pybus-Gambier area comprises about 215 square miles of uninhabited land on the southeastern coast of Admiralty Island, southeastern Alaska. The section consists of more than 20,000 feet of intensely folded sedimentary, volcanic, and metamorphic rocks, all probably of marine origin, ranging in age from Silurian(?) to Early Cretaceous, unconformably overlain by more than 10,000 feet of gently dipping nonmarine, coarse-grained sedimentary rocks, and basalt and andesite flows of Eocene age. Diorite plutons and associated contact metamorphic rocks occur in the little-know northwestern part of the area. The section here is subdivided into nine formations, eight of which are named for the first time, as follows: Gambier Bay formation of Middle(?) Devonian age, composed of greenschist, phyllite, marble, and metachert; Hood Bay formation or Silurian and Devonian age, composed of dark, carbonaceous, thin-bedded chert, argillite, limestone, and graywacke; Cannery formation of Permian age, composed of thin-bedded chert, argillite, and graywacke; Pybus dolomite of Permian age, composed of fossiliferous, cherty dolomite; Hyd formation of Late Triassic age, composed of a basal chert breccia, a limestone member, a thin-bedded argillite member, and a spilitic volcanic member; Seymour Canal formation of Late Cretaceous and Early Cretaceous age, composed of argillite, graywacke, and conglomerate; Brothers volcanic of Early Cretaceous age, composed of andesitic flows and breccia; unnamed conglomerate and sandstone of Eocene age, and Admiralty Island volcanics of Eocene age, composed of basaltic and andesitic flows. A marked angular unconformity occurs at the base of the Tertiary section, and unconformities of less angularity occur as follows: at the base of the Cannery formation; at the base of the Hyd formation, and at the base of the Seymour Canal formation. In general, pre-Seymour Canal deformation seems to have been mild, but the intensity of the post-Gambier Bay - pre-Cannery deformation is uncertain. The complex structure of the pre-Tertiary rocks seem to be the product chiefly of the post-Seymour Canal - pre-Eocene formation. The structure of the pre-Tertiary rocks is studied by graphical statistical analysis of the preferred orientation of the planar and linear structural elements. This analysis indicates that the post-Seymour Canal - pre-Eocene deformation consisted chiefly of three episodes of folding, all of which appear to have resulted from sub-horizontal, northeast-southwest compression. The first episode produced isoclinal folds in bedding, and in places associated axial plane foliation, that had north-northwesterly striking axial planes in eastern Pybus-Gambier area, but generally northeasterly striking axial planes west of False Point Pybus. Compression during the second episode deformed the first folds in the west where their axial planes were oriented about parallel to the compression into complex second folds in both bedding and axial plane foliation, having northwesterly striking axial planes. The second folds are absent in the east where the axial planes and limbs of the first folds were oriented about normal to the second compression. The divergence of the axial planes of the first folds in the west from those in the east may have been caused by the crowding of the first folds in the west against the irregular western margin of the geosyncline during the first compression. Northweststriking thrust and reverse faults occur between domains in which the axial planes of the first folds are strongly divergent. The third episode produced kink folds, having axial planes with subvertical dips but widely varying strikes, that are confined to the thinly fissile schists and phyllites of the Gambier Bay formation. The episodes of folding in the Gambier Bay formation are accompanied by metamorphic recrystallization not found in either younger or possibly coeval (Hood Bay formation) pre-Tertiary rocks. If these episodes are contemporaneous with those in nonmetamorphic pre-Tertiary rocks, then the metamorphism dies out both vertically and laterally, and may be part of the regional decrease in metamorphism westward away from the Coast Range batholith, located about 25 miles to the east. The gently dipping Tertiary strata have been broken into fault blocks by subvertical, north-and north-east striking, normal and reverse faults.

Alaska↗
USGS1975

Sediments, structural framework, petroleum potential, environmental conditions, and operational considerations of the United States South Atlantic Outer Continental Shelf

The area designated for possible oil and gas lease sale in Bureau of Land Management memorandum 3310 #43 (722) and referred to therein as part of the United States South Atlantic Outer Continental Shelf (OCS) contains about 98,000 square kilometres of the continental margin seaward of the 3 mile offshore limit and within the 600 metre isobath. The designated area, offshore of North Carolina, South Carolina, Georgia, and Florida, encompasses parts of three physiographic provinces: the Continental Shelf, the Florida-Hatteras Slope, and the Blake Plateau. The structural framework of the U.3. South Atlantic region is dominated by the Southeast Georgia Embayment --an east-plunging depression recessed into the Atlantic Coastal Plain and shelf between Cape Fear, North Carolina and Jacksonville, Florida. The embayment is bounded to the north by the Cape Fear Arch and to southeast by the Peninsular Arch. Refraction data indicate a minor basement(?) ridge beneath the outer shelf between 30° and 32°N at 80°W. Drill hole data also suggest a gentle fold or accretionary structure (reef?) off the east coast of Florida. Several other structural features have been identified by refraction and reflection techniques and drilling. These are the Yamacraw Uplift, Burton High, Stone Arch, and the Suwannee Channel. Gravity and magnetic anomalies within the area probably result from emplacement of magma bodies along linear features representing fundamental crustal boundaries. Of these anomalies, the most prominent, is a segment of the East Coast Magnetic Anomaly which crosses the coast at Brunswick, Georgia. This anomaly has been interpreted as representing an ancient continental boundary where two formerly separate continental plates collided and were welded together. There may be as much as 5,000 m of sedimentary rocks in the Southeast Georgia Embayment out to the 600 m isobath. Basement rocks beneath the Southeast Georgia Embayment are expected to be similar to those exposed in the Appalachian Piedmont province. Triassic deposits are likely to exist beneath the inner Continental Shelf, and probably consist of nonmarine arkosic sandstones, shales, basalt flows, and diabase intrusions deposited in relatively narrow northeast-trending grabens. Jurassic marine carbonates in the Bahamas grade northward to carbonates, shales, sand, and arkose in North Carolina. Salt may be present in the basal Jurassic section in the Southeast Georgia Embayment. Up to 4,000 m of Jurassic-Lower Cretaceous rocks are expected out to the 600 m water depth. Lower Cretaceous rocks in southern Florida are shallow-water marine limestone and dolomites with beds of anhydrite. In coastal North Carolina the Lower Cretaceous is a marine section made up of shales, sand, and sandy limestone. The Upper Cretaceous is composed almost entirely of marine carbonates in southern Florida grading northward to nonmarine to marginal marine, sandstones and shales with minor amounts of carbonates. In general, Upper Cretaceous rocks will probably maintain a fairly constant thickness (600 m) on the Continental Shelf and grade downdip from terrigeneous sands and shales to more marine chalks, limestones, and dolomites. The Cenozoic rocks are predominantly shallow-water marine carbonates in Florida grading northward into a marginal marine to marine clastic facies composed of sands, marls, and limestones. The offshore Cenozoic section is expected to range in thickness from 600 to 1100 m.

Florida, Georgia, South Carolina↗
USGS1976

Preliminary survey of modern glaciolacustrine sediments for earthquake-induced deformational structures, south-central Alaska

Bottom sediments of four lakes in South-Central Alaska were studied in the summer of 1975 for evidence of earthquake-induced deformation. The lakes are: Summit, Upper Trail, and Skilak, all on the Kenai Peninsula, and Eklutna, northeast of Anchorage (fig. 1). Interest in these lakes was stimulated by hypotheses developed from a study of sediments in Van Norman Reservoir, California, after the 1971 San Fernando earthquake (Sims, 1973). During that study three zones of deformational structures were found and correlated with moderate earthquakes that shook the San Fernando area in 1930, 1952, and 1971. Results of that study, coupled with the experimental formation of deformational structures similar to those from Van Norman Reservoir, led to a search for similar structures in Pleistocene and Holocene lakes and lake sediments in other seismically active areas. The lakes for this study were chosen specifically because of their location within the area affected by the 1964 Prince William Sound earthquake, and the probability of obtaining varved sediments which would allow counting of years between sedimentologic events.

Alaska↗
USGS1978

The utility of petroleum seismic exploration data in delineating structural features within salt anticlines

The Salt Valley anticline, in the Paradox Basin of southeastern Utah, is under investigation for use as a location for storage of solid nuclear waste. Delineation of thin, nonsalt interbeds within the upper reaches of the salt body is extremely important because the nature and character of any such fluid- or gas-saturated horizons would be critical to the mode of emplacement of wastes into the structure. Analysis of 50 km of conventional seismic-reflection data, in the vicinity of the anticline, indicates that mapping of thin beds at shallow depths may well be possible using a specially designed adaptation of state-of-the-art seismic oil-exploration procedures. Computer ray-trace modeling of thin beds in salt reveals that the frequency and spatial resolution required to map the details of interbeds at shallow depths (less than 750 m) may be on the order of 500 Hz, with surface-spread lengths of less than 350 m. Consideration should be given to the burial of sources and receivers in order to attenuate surface noise and to record the desired high frequencies. Correlation of the seismic-reflection data with available well data and surface geology reveals the complex, structurally initiated diapir, whose upward flow was maintained by rapid contemporaneous deposition of continental clastic sediments on its flanks. Severe collapse faulting near the crests of these structures has distorted the seismic response. Evidence exists, however, that intrasalt thin beds of anhydrite, dolomite, and black shale are mappable on seismic record sections either as short, discontinuous reflected events or as amplitude anomalies that result from focusing of the reflected seismic energy by the thin beds; computer modeling of the folded interbeds confirms both of these as possible causes of seismic response from within the salt diapir. Prediction of the seismic signatures of the interbeds can be made from computer-model studies. Petroleum seismic-reflection data are unsatisfactory for mapping the thin beds because of the lack of sufficient resolution to provide direct evidence of the presence of the thin beds. However, indirect evidence, present in these data as discontinuous seismic events, suggests that two geophysical techniques designed for this specific problem would allow direct detection of the interbeds in salt. These techniques are vertical seismic profiling and shallow, short-offset, high-frequency, seismic-reflection recording.

Open-File Report↗
USGS1982

Disturbed zones: Indicators of deep-seated subsurface faults in the Valley and Ridge and Appalachian structural front of Pennsylvania

Field studies of geologic structures in the Valley and Ridge and adjacent parts of the Appalachian Plateau provinces in Pennsylvania have shown a new type of structure, formerly poorly understood and frequently unmapped, is a significant indicator of deep-seated subsurface faulting. These structures, herein called disturbed zones, are formed by movement between closely spaced pairs of thrust faults. Disturbed zones are characterized at the surface by long, narrow, intensely folded and faulted zones of rocks in a relatively undisturbed stratigraphic sequence. These zones are frequently kilometers to tens of kilometers long and tens to hundreds of meters wide. Although disturbed zones generally occur in sequences of alternating siltstone and shale beds, they can also occur in other lithologies including massively-bedded sandstones and carbonates. Disturbed zones are not only easily recognized in outcrop but their presence can also be inferred on geologic maps by disharmonic fold patterns, which necessitates a detachment between adjacent units that show the disharmony. A number of geologic problems can be clarified by understanding the principles of the sequence of formation and the method of location of disturbed zones, including the interpretation of some published geologic cross sections and maps. The intense folding and faulting which accompanies the formation of a typical disturbed zone produces a region of fracture porosity which, if sealed off from the surface, might well serve as a commercially-exploitable hydrocarbon trap. We believe that the careful mapping of concentrations of disturbed zones can serve as an important exploration method which is much less expensive than speculation seismic lines.

Pennsylvania↗
USGS1983

Stratigraphy, structure, and palinspastic synthesis of the western Brooks Range, northwestern Alaska

This report is an effort to describe and decipher the mid-Paleozoic to Lower Cretaceous stratigraphy and the orogenic evolution of the western Brooks Range. The western Brooks Range primarily is composed of stacks of complexly deformed thrust sheets that contain mostly coeval sequences of rocks with slightly different lithologic facies. In order to simplify the thrust-faulted stratigraphy and palinspastic restoration, the rocks are grouped into eight principal structural levels. The lowest structural level is believed to be autochthonous or parautochthonous and above that, each succeeding level is designated allochthon one through seven. Allochthon seven is composed of the remnants of an extensive ophiolite sheet. Allochthon six is composed of pillow basalt with subordinate intermediate volcanic rocks, chert, and Devonian limestone. It is not certain whether this allochthon was formed in a continental or oceanic setting. Allochthons five through one consist of distinctive and coeval sequences of Devonian to Lower Cretaceous sedimentary rocks that were deposited in a continental setting. The present geographic distribution of each structural level is shown on the allochthon map of the western Brooks Range. The stratigraphy of the southern part of northern Alaska has been reconstructed by systematically unstacking lower allochthons to the north of higher allochthons. The palinspastic map that results from this procedure shows that the minimum thrust displacement between allochthon seven and the autochthon is approximately 700 to 800 km. Schematic cross sections drawn across the palinspastic map show how the stratigraphy of the southern part of northern. Alaska most likely appeared prior to the orogeny. During Devonian and Mississippian time, the sedimentary sequences that are now part of allochthons one to five are inferred to have been deposited in an ensialic basin with both northern and southern margins. During Pennsylvanian time, the sequences seem to have become part of a southward-sloping continental shelf when a southern land area moved away from northern Alaska by an inferred plate tectonic process of rifting or strike-slip motion. In Early Jurassic time just prior to the Brooks Range orogeny, northern Alaska probably was an extensive continental shelf with oceanic conditions to the south and land to the north. The Brooks Range orogeny seems to have begun in the Middle Jurassic as the Arctic Alaska plate was underthrust (subducted) southward beneath oceanic crust of allochthon seven. At progressively later stages in the underthrusting process, the upper parts of the continental shelf were detached from the subthrust basement on which they were deposited, resulting in the other allochthons of the western Brooks Range. The period of major thrusting ceased by Albian time in the Early Cretaceous. During middle and Late Cretaceous time, epeirogenic uplift in the Brooks Range caused large quantities of clastic detritus to be shed into successor basins to the north and south. Broad folds and reverse faults in Upper Cretaceous sediments north of the Brooks Range provide evidence for a later period(s) of less intense deformation in northern Alaska.

Open-File Report↗
USGS1983

Instrumentation for measuring and recording streamflow data at river-control structures

Instrumentation was developed in the mid to late 60 's to resolve the dilemma of intolerably high percentages of missing streamflow records on certain large and highly controlled streams in industrialized parts of the United States. Analysis of the field situation at specific problem sites quickly suggested that conventional stream gaging techniques should be supplanted by new instruments, designed to measure key hydraulic data at the nearest stream control structures. The key data were found universally to include some combination of a length measurement to specify the vertical height of a gate opening in a dam; measurement of pressure head differential in a turbine; a count of lockages; and precise measurement of time, to give one master reference scale to which all measurements could be keyed. The instruments designed to collect such key data are the shaft position digitizer, the shaft output follower, the STACOM manometer, the lock pressure switch, and the digital data collection console. Although their design was prompted by the need to collect data at river control structures their potential for field use is not that restrictive. Several of these instruments have already found widespread use in the hydrologic data collection program at large. In the 12-1/2 yr period from June 1968 to December 1980 nineteen different river control structures were instrumented. The general experience to date has been a marked improvement in completeness of record, with the average performance somewhere in the 80 percentile range. Performance percentiles at individual sites have ranged from the mid 90 's to about 70. Maintenance records show the instruments to be virtually trouble free, except for the unpredictable acts of nature and man. (Author 's abstract)

Open-File Report↗
USGS1986

Operating manual for the digital data-collection system for flow-control structures

This manual was written to help the user operate and maintain the digital data collection system for flow control structures. The system is used to measure daily discharge through river control dams. These dams commonly have tainter gates which are raised and lowered to keep the upper pool level relatively constant as the river flow changes. In order to measure the flow through such a structure, the positions of the tainter gates and the headwater and tailwater elevations must be known. From these data, the flow through the structure can be calculated. A typical digital data collection system is shown. Digitizing devices are mounted on the hoisting mechanism of each gate, as well as at the headwater and tailwater gages. Data from these digitizers are then routed by electrical cables to a central console where they are displayed and recorded on paper tape. If the dam has locks, a pressure-sensitive switch located in the lock activates a counter in the console which keeps track of the number of times the lock is drained and filled. (USGS)

Open-File Report↗
USGS1989

Humic substances in the Suwannee River, Georgia; interactions, properties, and proposed structures

Humic substances as a collective term and humic and fulvic acids as specific terms are not household words. For about a century, these terms belonged to the domain of the soil scientist. Even^though their chemical structures remained elusive, they were recognized as important entities in soil. During the past decade or so, there has been a renewed interest in humic substances in soil and water. Such interest has been the result of improved analytical instrumentation, and by a need to understand the structure and function of natural organic substances in water. A responsibility of the U.S. Geological Survey is to assess the Nation's water resources; this includes water quality, which is the study of material in water. Such material may be suspended, colloidal, or in true solution. Because humic substances are a major carbon source in water, they have received attention by Geological Survey scientists. This attention has been a major focus by members of the Geological Survey's organic-chemistry group. For more than a decade, this group has collected samples, made analyses, and worked toward determining the structures and function of humic substances in water. Their work has brought worldwide recognition to the field, and in 1981, through Geological Survey support, they helped organize the International Humic Substances Society, which held its first meeting in Estes Park, Colorado, in August 1983. At the second meeting of the Society in Birmingham, England, in August 1984, it became apparent that Geological Survey scientists were rapidly advancing the study of the chemistry of humic substances. It seemed appropriate, therefore, to publish this Open-File report on humic and fulvic acids from the Suwannee River in Georgia. The results represent our most definitive findings to date (1986). Though this work is not conclusive, it is state-of-the-science. Hopefully, our reporting on this work will aid in moving the science of humic substances forward as others read of our progress, findings, and theories. If so, this Open-File report will have served its purpose.

Georgia↗
USGS1999

Geometry, structure, and concealed lithology of the San Rafael Basin, southeastern Arizona

The contiguous United States has been well explored for exposed conventional mineral deposits. Therefore, it is likely that many economically viable and strategically significant conventional undiscovered mineral deposits will be found in bedrock concealed beneath basin sediments. Mineral resource assessments must incorporate an understanding of the geometry, structure, and concealed lithology of basins in order to be accurate. This report presents an analysis of the basin geometry and structure of the San Rafael basin in southeastern Arizona. In addition, a new methodology for inferring concealed lithology is presented and applied in the San Rafael basin. Gravity data is used to model the geometry of the basin using recent models of sediment density vs. depth developed in the region. This modeling indicates that the basin has a maximum depth of approximately 1.05 km plus or minus 0.10 km. In the southern portion, the basin can be modeled as an asymmetric graben faulted on the western margin. The northern portion of the basin is structurally more complex and may have high angle faults on the western, northern, and eastern margin. Near-ground closely spaced Earth’s total intensity magnetic field data is used to locate concealed faults within the basin. This data is also used to infer lithology concealed by shallow basin sediments. Airborne Earth’s total intensity magnetic field data is used to help infer concealed lithology in deep portions of the basin. The product of integrating all data and interpretations is a map which presents the geometry of the basin, faults and contacts concealed by basin sediments, and an estimate of the bedrock lithology concealed by basin sediment. Based on basin geometry and concealed lithology, the San Rafael basin has a high potential for concealed mineral deposits on its western and northern margin. In particular, a newly discovered magnetic anomaly in the northern portion of the basin can be modeled as a granitic intrusion with highly altered margins and may represent a potential mineral resource target. Based on the permeability and porosity of upper basin fill found in nearby basins, the San Rafael basin may contain an aquifer up to 300 meters thick over a substantial area of the basin.

Arizona↗
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↗