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At least 955 records · Page 53Linked to original sources
USGS1994

The northern Nevada rift: Regional tectono-magmatic relations and Middle Miocene stress direction

As defined by the most recent aeromagnetic surveys, the north-northwest-trending northern Nevada rift zone extends for at least 500 km from southern Nevada to the Oregon Nevada border. At several places along the rift, the magnetic anomaly is clearly related to north-northwest-trending dikes and flows that, based on new radiometric dating, erupted between 17 and 14 Ma and probably during an even shorter time interval. The tectonic significance of the rift is dramatized by its length, its coincidence in time and space (at its northern terminus) with the oldest silicic caldera complex along the Yellowstone hot-spot trend, and its parallelism with the subduction zone along the North American coast prior to the establishment of the San Andreas fault.

Geological Society of America Bulletin↗
USGS2008

Digital data for volcano hazards at Newberry Volcano, Oregon

Newberry volcano is a broad shield volcano located in central Oregon, the product of thousands of eruptions, beginning about 600,000 years ago. At least 25 vents on the flanks and summit have been active during the past 10,000 years. The most recent eruption 1,300 years ago produced the Big Obsidian Flow. Thus, the volcano's long history and recent activity indicate that Newberry will erupt in the future. Newberry Crater, a volcanic depression or caldera has been the focus of Newberry's volcanic activity for at least the past 10,000 years. Newberry National Volcanic Monument, which is managed by the U.S. Forest Service, includes the caldera and extends to the Deschutes River. Newberry volcano is quiet. Local earthquake activity (seismicity) has been trifling throughout historic time. Subterranean heat is still present, as indicated by hot springs in the caldera and high temperatures encountered during exploratory drilling for geothermal energy. The report USGS Open-File Report 97-513 (Sherrod and others, 1997) describes the kinds of hazardous geologic events that might occur in the future at Newberry volcano. A hazard-zonation map is included to show the areas that will most likely be affected by renewed eruptions. When Newberry volcano becomes restless, the eruptive scenarios described herein can inform planners, emergency response personnel, and citizens about the kinds and sizes of events to expect. The geographic information system (GIS) volcano hazard data layers used to produce the Newberry volcano hazard map in USGS Open-File Report 97-513 are included in this data set. Scientists at the USGS Cascades Volcano Observatory created a GIS data layer to depict zones subject to the effects of an explosive pyroclastic eruption (tephra fallout, pyroclastic flows, and ballistics), lava flows, volcanic gasses, and lahars/floods in Paulina Creek. A separate GIS data layer depicts drill holes on the flanks of Newberry Volcano that were used to estimate the probability of coverage by future lava flows.

Open-File Report↗
USGS1985

Gas hydrates on the northern California continental margin

The inner continental margin of northern California is underlain by a well-defined and extensive acoustic reflector that crosses other reflectors and mimics the surface of the sea floor. This bottom-simulating reflector (BSR) lies at a typical subsurface depth of about 250 m and has been mapped continuously beneath the Klamath Plateau and upper slope (water depths of 800 to 1200 m) for a distance of more than 130 km; it covers an area of at least 3000 km 2 . Limited data show that the BSR extends northward into Oregon and seaward at least to the base of the slope (3000 m). The water depths, subsurface depths, and pervasive nature of the BSR all suggest that it represents the base of a natural-gas hydrate. Using standard phase boundary diagrams for hydrate stability, we estimate the local geothermal gradient within the gas hydrate to be about 55 °C/km. This value is higher than that of most subduction margins and may be a result of the youthfulness of the subducting oceanic crust. This acoustically inferred gas hydrate is the first to be mapped on the western conterminous United States continental margin.

California↗
USGS2004

Magmatic intrusion west of Three Sisters, central Oregon, USA: The perspective from spring geochemistry

A geochemical investigation of springs near Three Sisters volcanoes was conducted in response to the detection of crustal uplift west of the peaks. Dilute, low-temperature springs near the center of uplift show 3 He/ 4 He ratios ≥7 R A ( R A is the ratio in air), and transport in total ∼16 MW of heat and ∼180 g/s of magmatic carbon (as CO 2 ). These anomalous conditions clearly reflect the influence of magma, but they seemingly predate the onset of the present uplift and derive from a previous event. Episodes of intrusion may thus be more common in this area than the age of eruptive vents would imply.

Geology↗
USGS1993

Damages from the 20 September earthquakes near Klamath Falls, Oregon

The Klamath Falls earthquakes of 8:28PM PDT (magnitude 5.9) and 10:45 PM PDT (magnitude 6.0) on September 20, 1993, were felt over an area of about 130,000 sq km in southwestern Oregon and northern California. Losses due to property damage are preliminary estimated to be about 7.5 million. A motorist died when the car he was driving was crushed by a boulder in an earthquake-induced rockfall, and an elderly woman died of a heart attack that was apparently triggered by one of the earthquakes. Most of the damage resulting from the earthquakes was reported from Klamath Falls, approximately 20 km from the source region of earthquakes. As has commonly been the case with earthquakes in other parts of the United States, the degree of damage was highly uneven in Klamath Falls. Most of the town escaped with little damage to buildings or building contents. Losses were concentrated in the downtown area, but even there most of the buildings were not damaged. The unevenness of damage in earthquakes results primarily from large differences in the seismic resistance of individual buildings and differences in the seismic response due to different soil conditions and geology beneath buildings.

Oregon↗
USGS2010

Attributes for NHDPlus Catchments (Version 1.1) for the Conterminous United States: Mean Annual R-factor, 1971-2000

This data set represents the average annual R-factor, rainfall-runoff erosivity measure, compiled for every catchment of NHDPlus for the conterminous United States. The source data are from Christopher Daly of the Spatial Climate Analysis Service, Oregon State University, and George Taylor of the Oregon Climate Service, Oregon State University (2002), who developed spatially distributed estimates of R-factor for the period 1971-2000 for the conterminous United States. The NHDPlus Version 1.1 is an integrated suite of application-ready geospatial datasets that incorporates many of the best features of the National Hydrography Dataset (NHD) and the National Elevation Dataset (NED). The NHDPlus includes a stream network (based on the 1:100,00-scale NHD), improved networking, naming, and value-added attributes (VAAs). NHDPlus also includes elevation-derived catchments (drainage areas) produced using a drainage enforcement technique first widely used in New England, and thus referred to as "the New England Method." This technique involves "burning in" the 1:100,000-scale NHD and when available building "walls" using the National Watershed Boundary Dataset (WBD). The resulting modified digital elevation model (HydroDEM) is used to produce hydrologic derivatives that agree with the NHD and WBD. Over the past two years, an interdisciplinary team from the U.S. Geological Survey (USGS), and the U.S. Environmental Protection Agency (USEPA), and contractors, found that this method produces the best quality NHD catchments using an automated process (USEPA, 2007). The NHDPlus dataset is organized by 18 Production Units that cover the conterminous United States. The NHDPlus version 1.1 data are grouped by the U.S. Geologic Survey's Major River Basins (MRBs, Crawford and others, 2006). MRB1, covering the New England and Mid-Atlantic River basins, contains NHDPlus Production Units 1 and 2. MRB2, covering the South Atlantic-Gulf and Tennessee River basins, contains NHDPlus Production Units 3 and 6. MRB3, covering the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy River basins, contains NHDPlus Production Units 4, 5, 7 and 9. MRB4, covering the Missouri River basins, contains NHDPlus Production Units 10-lower and 10-upper. MRB5, covering the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf River basins, contains NHDPlus Production Units 8, 11 and 12. MRB6, covering the Rio Grande, Colorado and Great Basin River basins, contains NHDPlus Production Units 13, 14, 15 and 16. MRB7, covering the Pacific Northwest River basins, contains NHDPlus Production Unit 17. MRB8, covering California River basins, contains NHDPlus Production Unit 18.

Data Series↗
USGS2020

Procedures for developing multi-period response spectra at non-conterminous United States sites

This study complements proposals to the Provisions Update Committee of the Building Seismic Safety Council that would incorporate multi-period response spectra (MPRS) in the 2020 edition of the NEHRP Recommended Seismic Provisions for New Buildings and Other Structures (2020 NEHRP Provisions) and related proposals to the ASCE 7-22 Seismic Subcommittee of the American Society of Civil Engineers for incorporation of MPRS in ASCE Standard, ASCE/SEI 7-22, Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE 7-22). Ultimately, the intent is that the proposed MPRS and related design requirements of ASCE 7-22 would be adopted, by reference, as part of the 2024 International Building Code. The technical basis and associated methods herein enable the U.S. Geological Survey (USGS) to develop MPRS for sites in non-conterminous U.S. regions for which seismic hazard analyses have not yet been updated by the USGS to fully define all 22 periods and eight site classes of interest in the MPRS related proposals for the 2020 NEHRP Provisions and ASCE 7-22. These regions include Alaska, Hawaii, Guam and the Northern Mariana Islands, Puerto Rico and the U.S. Virgin Islands, and American Samoa. The methods developed can be used to derive MPRS using only the three currently available ground motion parameters S S , S 1 , and T L for all nonconterminous United States regions of interest. The methods include models that characterize generic shapes of Risk-Targeted Maximum Considered Earthquake (MCE R ) ground motions as a function of these three parameters. For deriving MPRS that represent probabilistic MCE R ground motions, models are based on statistical analyses of large sample sets of probabilistic MCE R response spectra for Western United States (WUS) and Cascadia sites in California, Oregon, Washington (including Puget Sound), Idaho, and Nevada. For deriving MPRS that represent deterministic MCE R ground motions, models are based on sets of deterministic MCE R response spectra calculated using WUS shallow crustal ground motion models for earthquake magnitudes and shaking levels typical of sites governed by deterministic MCE R ground motions.

Alaska, American Samoa, Hawaii, Guam and the North↗
USGS1991

Neogene rotations and quasicontinuous deformation of the Pacific Northwest continental margin

Paleomagnetically determined rotations about vertical axes of 15 to 12 Ma flows of the Miocene Columbia River Basalt Group of Oregon and Washington decrease smoothly with distance from the plate margin, consistent with a simple physical model for continental deformation that assumes the lithosphere behaves as a thin layer of fluid. The average rate of northward translation of the continental margin since 15 Ma calculated from the rotations, using this model, is about 15 mm/yr, which suggests that much of the tangential motion between the Juan de Fuca and North American plates since middle Miocene time has been taken up by deformation of North America. The fluid-like character of the large-scale deformation implies that the brittle upper crust follows the motions of the deeper parts of the lithosphere.

Geology↗
USGS2012

User’s guide and metada for the PICES Nonindigenous Species Information System

Introduction Welcome to the PICES Nonindigenous Species Information System, a Microsoft Access database that displays the biogeographic distributions, invasion status, vectors, and key life history attributes of the approximately 740 reported nonindigenous species (NIS) in the estuarine and near-coastal habitats of the North Pacific and Hawaii. This database was developed by the U.S. Environmental Protection Agency and the U.S. Geological Survey under the auspices of Working Group 21 (Invasive Species) of the North Pacific Marine Science Organization (PCIES). The PICES database contains the data used to generate the “Atlas of Nonindigenous Marine and Estuarine Species in the North Pacific” (Lee and Reusser, 2012; herein referred to as the “Atlas”). The User’s Guide provides instructions on how to use the PICES database as well as metadata for the database and the Atlas. We note that for most users, the Atlas provides a simpler approach to accessing key information on NIS in the PICES countries than the database, though the database does provide additional information on species and sources as well as allowing users to extract information on specific taxa and/or locations (see Section 4). The PICES database also includes species reported from the PICES Rapid Assessment Surveys (RAS). PICES sponsored four rapid assessment surveys with the objective of quickly characterizing the native, non-native, and cryptogenic species present in different locations. Surveys were sponsored in Dalian, China in 2008, Jeju, Korea in 2009, Newport, Oregon, USA in 2010, and Peter the Great Bay, near Vladivostok and Nakhodka, Russia in 2011 ( http://www.pices.int/publications/pices_press/volume19/v19_n1/pp_30-31_Kobe-WS_f.pdf , http://www.pices.int/publications/pices_press/volume20/v20_n1/pp_26-29_RAS-2011.pdf ). The PICES database contains the RAS species that were made available in time for inclusion. Thus, the database does not capture all the species found in these surveys. In addition, much of the information on the RAS species was provided by the experts conducting the survey, and their distributions, environmental requirements, and life history attributes were not evaluated to the same level of detail by the PICES authors as the North Pacific NIS. In lieu of the more extensive review as conduced with the Atlas species, the information on the RAS species needs to be considered preliminary. Additionally, it is important to use the “Map All Distributions” option (see Section 3.6.6) when mapping their distribution or conducting a query. The general reference for the RAS surveys in the PICES database is “PICES Working Group 21, YEAR SURVEY”. The overall goal of both the database and Atlas was to simplify and standardize the dissemination of distributional, habitat, and life history characteristics of near-coastal and estuarine nonindigenous species. This database provides a means of querying these data and displaying the information in a consistent format. The specific classes of information the database captures include: Regional and global ranges of native and nonindigenous near-coastal and estuarine species at different hierarchical spatial scales. Habitat and physiological requirements of near-coastal and estuarine species. Life history characteristics of near-coastal and estuarine species. Invasion history and vectors for nonindigenous species. This standardized and synthesized data in the database and the Atlas provide the basic information needed to address a number of managerial and scientific needs. Thus, users will be able to: Create a baseline on the extent of invasion by region in order to assess new invasions. Use existing geographical patterns of invasion to gain some insights into potential new invaders. Use existing geographical patters of invasion to gain some insights into mechanisms affecting relative invasibility of different areas. Use life history attributes and environmental requirements of the reported nonindigenous species to evaluate traits of invaders. Understand the potential spread of invaders based on their habitat and environmental requirements. Understand importance of different vectors of introduction of nonindigenous species by region. The data in the Atlas of Nonindigenous Marine and Estuarine Species in the North Pacific (Lee and Reusser, 2012) are up-to-date as of June 2012. Updates to the PICES database were made in September 2012.

Report↗
USGS2006

Late Pleistocene outburst flooding from pluvial Lake Alvord into the Owyhee River, Oregon

At least one large, late Pleistocene flood traveled into the Owyhee River as a result of a rise and subsequent outburst from pluvial Lake Alvord in southeastern Oregon. Lake Alvord breached Big Sand Gap in its eastern rim after reaching an elevation of 1292 m, releasing 11.3 km3 of water into the adjacent Coyote Basin as it eroded the Big Sand Gap outlet channel to an elevation of about 1280 m. The outflow filled and then spilled out of Coyote Basin through two outlets at 1278 m and into Crooked Creek drainage, ultimately flowing into the Owyhee and Snake Rivers. Along Crooked Creek, the resulting flood eroded canyons, stripped bedrock surfaces, and deposited numerous boulder bars containing imbricated clasts up to 4.1 m in diameter, some of which are located over 30 m above the present-day channel. Critical depth calculations at Big Sand Gap show that maximum outflow from a 1292- to 1280-m drop in Lake Alvord was ??? 10,000 m3 s- 1. Flooding became confined to a single channel approximately 40 km downstream of Big Sand Gap, where step-backwater calculations show that a much larger peak discharge of 40,000 m3 s- 1 is required to match the highest geologic evidence of the flood in this channel. This inconsistency can be explained by (1) a single 10,000 m3 s- 1 flood that caused at least 13 m of vertical incision in the channel (hence enlarging the channel cross-section); (2) multiple floods of 10,000 m3 s- 1 or less, each producing some incision of the channel; or (3) an earlier flood of 40,000 m3 s- 1 creating the highest flood deposits and crossed drainage divides observed along Crooked Creek drainage, followed by a later 10,000 m3 s- 1 flood associated with the most recent shorelines in Alvord and Coyote Basins. Well-developed shorelines of Lake Alvord at 1280 m and in Coyote Basin at 1278 m suggest that after the initial flood, postflood overflow persisted for an extended period, connecting Alvord and Coyote Basins with the Owyhee River of the Columbia River drainage. Surficial weathering characteristics and planktonic freshwater diatoms in Lake Alvord sediment stratigraphically below Mt. St. Helens set Sg tephra, suggest deep open-basin conditions at ??? 13-14 ka (14C yr) and that the flood and prominent shorelines date to about this time. But geomorphic and sedimentological evidence also show that Alvord and Coyote Basins held older, higher-elevation lakes that may have released earlier floods down Crooked Creek. ?? 2006 Elsevier B.V. All rights reserved.

Geomorphology↗
USGS2021

Late Cenozoic tephrochronology of the Mount Diablo area within the evolving plate-tectonic boundary zone of northern California

We present a tephrochronologic/chronostratigraphic database for the Mount Diablo area and greater San Francisco Bay region that provides a spatial and temporal framework for geologic studies in the region, including stratigraphy, paleogeography, tectonics, quantification of earth surface processes, recurrence of natural hazards, and climate change. We identified and correlated 34 tephra layers within this region using the chemical composition of their volcanic glasses, stratigraphic sequence, and isotopic and other dating techniques. Tephra layers range in age from ca. 65 ka to ca. 29 Ma, as determined by direct radiometric techniques or by correlation to sites where they have been dated. The tephra layers are of Quaternary or Neogene age except for two that are of Oligocene age. We correlated the tephra layers among numerous sites throughout northern California. Source areas of the tephra layers are the Snake River–Yellowstone hotspot trend of northern Nevada, southern Idaho, and western Wyoming; the Nevadaplano caldera complex of central Nevada; the Jemez Mountains–Valles Caldera in northwestern New Mexico; the Southern Nevada volcanic field and related source areas in eastern California and west-central Nevada; the Quien Sabe–Sonoma volcanic centers of the California Coast Ranges; and the young Cascade Range volcanic centers of northeastern California and Oregon.

GSA Memoirs↗
USGS2014

Technical review of managed underground storage of water study of the upper Catherine Creek watershed, Union County, northeastern Oregon

Because of water diversions during summer, flow in Catherine Creek, a tributary to the Grande Ronde River in northeastern Oregon, is insufficient to sustain several aquatic species for which the stream is listed as critical habitat. A feasibility study for managed underground storage (MUS) in the upper Catherine Creek watershed in Union County, Oregon, was undertaken by Anderson Perry and Associates, Inc., to address the issue of low flows in summer. The results of the study were released as a report titled “Upper Catherine Creek Storage Feasibility Study for Grande Ronde Model Watershed,” which evaluated the possibility of diverting Catherine Creek streamflow during winter (when stream discharge is high), storing the water by infiltration or injection into an aquifer adjacent to the stream, and discharging the water back to the stream in summer to augment low flows. The method of MUS would be accomplished using either (1) aquifer storage and recovery (ASR) that allows for the injection of water that meets drinking-water-quality standards into an aquifer for later recovery and use, or (2) artificial recharge (AR) that involves the intentional addition of water diverted from another source to a groundwater reservoir. Concerns by resource managers that the actions taken to improve water availability for upper Catherine Creek be effective, cost-efficient, long-term, and based on sound analysis led the National Fish and Wildlife Foundation to request that the U.S. Geological Survey conduct an independent review and evaluation of the feasibility study. This report contains the results of that review. The primary objectives of the Anderson Perry and Associates study reviewed here included (1) identifying potentially fatal flaws with the concept of using AR and (or) ASR to augment the streamflow of Catherine Creek, (2) identifying potentially favorable locations for augmenting streamflow, (3) developing and evaluating alternatives for implementing AR and (or) ASR, and (4) identifying next steps and estimated costs for implementation. The Anderson Perry study was not intended as a comprehensive evaluation of feasibility, but, rather, an effort to develop a concept and preliminary evaluation of feasibility. Additionally, the feasibility study was limited to using existing data from which additional data needs were to be identified. The feasibility study mostly accomplished the goals of identifying potential fatal flaws and developing a project implementation plan. However, a more practical discussion of conclusions regarding the feasibility, likelihood for success, achievement of goals, and overall project costs could have received greater emphasis and would be of value to decision makers. With regard to objective (2), the subject report analyzed information from several possible sites examined for an MUS system. Sufficient cause is provided in the subject report to identify the basalt aquifer in the Milk Creek sub-area as having the greatest potential for MUS. Therefore, this review is primarily focused on the Milk Creek sub-area and the basalt aquifer.

Oregon↗
USGS1960

Gravity survey in part of the Snake River Plain, Idaho — A preliminary report

During the early summer of 1959, a total of 1,187 gravity stations were occupied on the western part of the Snake River plain in Idaho. An area of 2,000 square miles extending from Glenns Ferry, Idaho, to Caldwell, Idaho, was covered with a station density of one station per two square miles. An additional 1,200 square miles of surrounding area, mainly from Caldwell, Idaho, to the Oregon-Idaho state line, was covered with a density of one station per seven square miles. The mean reproducibility of the observed gravities of these stations was 0.05 milligal, with a maximum discrepancy of 0.2 milligal. Gravity data were reduced to simple Bouguer values using a combined free-air and Bouguer correction of 0.06 milligal per foot. The only anomalies found with closure in excess of 10 milligals are two elongated highs, orientated northwest-southeast, with the northwestern high offset to the northeast by 10 miles. The smaller of these highs extends from Meridian, Idaho, to Nyssa, Oregon, and the larger extends from Swan Falls, Idaho, to Glenns Ferry, Idaho. The maximum value recorded is a simple Bouguer value of -66.5 milligals with respect to the International Ellipsoid. Gradients on the sides of these highs are largest on the northeast sides, reaching six milligals per mile in places. Graticule interpretations of a profile across the southeastern high using a density contrast of 0.3 gm per cubic centimeter indicate an accumulation of lava reaching a thickness of at least 28,000 feet. The Snake River investigation was made for the purpose of searching out, defining, and interpreting gravity anomalies present on the western part of the Snake River lava plain in Idaho. In particular, it was desired to further define gradients associated with the gravity high shown by the regional work of Bonini and Lavin (1957). It was not planned to cover any specific area, but rather to let the observed anomalies determine the course of the field work. The study was undertaken as part of a project on Volcanism and Crustal Deformation, supervised by L. C. Pakiser of the U.S. Geological Survey. Professor Rodgers of the Geophysics Department of the Colorado School of Mines acted as an advisor.

Idaho↗
USGS2012

Evolution of the caldera‐forming eruption at Crater Lake, Oregon, indicated by component analysis of lithic fragments

Crater Lake caldera (8 × 10 km), formed 6845 years B. P. ( 14 C age) during the climactic eruption of the volcanic edifice known as Mount Mazama, is intermediate in size between small calderas associated with central vent eruptions and large calderas that have ring fracture vent systems. Our quantitative study of lithic fragments in the ejecta confirms the existing model of changes in vent configuration during the climactic eruption of Mount Mazama. Initial activity was from a single vent that produced a rhyodacite pumice fall from a Plinian column. Altered preexisting volcanic rocks are the predominant lithic type in the Plinian deposit, and their extensive hydrothermal alteration is considered as evidence of their relatively deep origin. The Wineglass Welded Tuff lies atop the Plinian deposit and contains a higher proportion of fresh volcanic rocks, suggesting enlargement of the single vent by slumping of its walls. This same vent enlargement caused the Plinian eruption column to collapse and feed valley‐hugging pyroclastic flows that deposited the Wineglass Welded Tuff. When enough material was erupted from the shallow magma chamber that its roof was no longer adequately supported, Mount Mazama collapsed to form the caldera, while highly energetic pyroclastic flows produced the climactic ignimbrite. A lag breccia that represents the proximal facies of the compositionally zoned climactic ignimbrite lies atop the Wineglass Welded Tuff and contains predominantly altered volcanic rocks of deeper origin, accompanied by minor granitoids from the magma chamber walls. Azimuthal differences in lithic component proportions in the lag breccia correlate well with the geology of the caldera walls, indicating that the climactic ignimbrite was ejected by multiple vents along a ring fracture system. Systematic lithic component changes within the lag breccia suggest different quarrying levels that reflect waxing and waning of the discharge rate during the caldera collapse phase of the climactic eruption. Our lithic component analysis demonstrates that calderas that may be too small to experience structural resurgence, such as Crater Lake, nevertheless may form by syneruptive subsidence along ring fractures.

Oregon↗
USGS2017

Emplacement of Holocene silicic lava flows and domes at Newberry, South Sister, and Medicine Lake volcanoes, California and Oregon

This field guide for the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Scientific Assembly 2017 focuses on Holocene glassy silicic lava flows and domes on three volcanoes in the Cascade Range in Oregon and California: Newberry, South Sister, and Medicine Lake volcanoes. Although obsidian-rich lava flows have been of interest to geologists, archaeologists, pumice miners, and rock hounds for more than a century, many of their emplacement characteristics had not been scientifically observed until two very recent eruptions in Chile. Even with the new observations, several eruptive processes discussed in this field trip guide can only be inferred from their final products. This makes for lively debates at outcrops, just as there have been in the literature for the past 30 years. Of the three volcanoes discussed in this field guide, one (South Sister) lies along the main axis defined by major peaks of the Cascade Range, whereas the other two lie in extensional tectonic settings east of the axis. These two tectonic environments influence volcano morphology and the magmatic and volcanic processes that form silicic lava flows and domes. The geomorphic and textural features of glass-rich extrusions provide many clues about their emplacement and the magma bodies that fed them. The scope of this field guide does not include a full geologic history or comprehensive explanation of hazards associated with a particular volcano or volcanic field. The geochemistry, petrology, tectonics, and eruption history of Newberry, South Sister, and Medicine Lake volcanic centers have been extensively studied and are discussed on other field excursions. Instead, we seek to explore the structural, textural, and geochemical evolution of well-preserved individual lava flows—the goal is to understand the geologic processes, rather than the development, of a specific volcano.

California, Oregon↗
USGS1999

Sources and transport of phosphorus and nitrogen during low-flow conditions in the Tualatin River, Oregon, 1991-93

In the 1980s significant nutrient-related water-quality problems that impacted beneficial uses were identified in the Tualatin River during the low-flow summer months, defined as .May 1 to October 31. Unsightly algal blooms resulted in fluctuations in oxygen concentrations and pH conditions; reduction of phosphorus concentrations was determined to the effective control mechanism for these conditions. Elevated ammonia concentrations also contributed to low oxygen concentrations. Because standards for beneficial uses were not being met, the Oregon Department of Environmental Quality established Total Maximum Daily Loads (TMDLs) for phosphorus and ammonia in the Tualatin Basin, as required by the Clean Water Act. To provide necessary context for the TMDL process, data were collected during the period 1991-93 to characterize the sources and transport of water, phosphorus, and major forms of nitrogen in the main-stem Tualatin River during the summer. A significant source of water to the river was not accounted for by surface-water inputs, and was consistent with direct discharge of ground water to the main-stem river channel. Ground water is also the primary source of water for the tributaries during the summer low-flow season. Because large natural supplies of highly mobile phosphorus exist in the upper 500 feet of valley-fill sediments throughout the Tualatin Basin, ground water in the basin is naturally enriched with phosphorus. While improvement in wastewater treatment efficiencies and land management practices have resulted in significant reductions in nutrient concentrations in the Tualatin River, phosphorus concentrations continue to exceed TMDL criterion concentrations. The presence of significant geologic sources of phosphorus in the basin will confound the achievement of current TMDL criteria for phosphorus in the Tualatin River and its tributaries. In contrast, natural sources of all forms of nitrogen to the Tualatin River are insignificant relative to the effluent from the wastewater treatment plants in the basin. Efficient wastewater treatment is, therefore, an effective means for controlling ammonia concentrations in the main-stem river.

Oregon↗
USGS1998

Response of a small Oregon estuary to coseismic subsidence and postseismic uplift in the past 300 years

The Sixes River estuary, south coastal Oregon, sits above the locked portion of the Cascadia subduction zone, which intermittently releases in subduction-zone earthquakes. One such Cascadia earthquake ∼300 years ago caused subsidence and a tsunami at the Sixes estuary. The subsidence raised the river's base level, resulting in an ∼3 km upstream shift of the head of tide of the estuary. At the upper end of the expanded estuary, more than 4 m of overbank sediment was deposited in the first decades or century after subsidence. Subsequent incision through the overbank deposits accompanied the gradual emergence of the estuary, and attendant downstream shift of the head of tide, as relative sea level fell in response to interseismic uplift.

Geology↗
USGS1915

Springs of California

In 1903 the United States Geological Survey began an investigation of the underground water of California, generally with financial cooperation on the part of the State. Since that year ten papers on the underground water of the State have been issued by the Survey, each representing an investigation that has been completed. The field work which is to serve as the basis for two additional papers has also been done and the reports are in preparation. Investigations have been begun in two other areas in the State and their results will eventually be assembled and published. Since a period soon after the inception of the California work those responsible for its conduct have realized the desirability of a special study of the springs, particularly those which yield mineral waters and which are utilized to a greater or less extent by citizens of the State and by tourists as recreation and health resorts. It did not become practicable to begin this work until the summer of 1908, when Mr. G. A. Waring, who had assisted in some of the earlier California studies and had investigated for the Survey certain areas in southern Oregon and Washington, was assigned to the task of collecting and assembling the necessary data. California, with an area of 158,000 square miles, is the second largest State in the Union. It exhibits wide geographic diversity, since it includes the lowest area in the United States Death Valley, 276 feet below sea level and the highest Mount Whitney, 14,501 feet above the sea; and accompanying this geographic diversity there is a corresponding range in scenic effects, climate, and vegetation. The records obtained at meteorological stations in the Salton Sink indicate a maximum temperature of 130° in the shade, the highest of record within the continental United States. It is probable that minimum temperatures on the higher peaks, like Mount Whitney and Mount Shasta, approach the minimum within our boundaries. Rainfall records in the most arid sections of the southern deserts of the State represent the extreme of aridity in the United States, with averages of less than 3 inches per annum and periods of 12 months or more with only traces of rain, whereas the precipitation in northwestern California is very heavy, an annual average of close to 100 inches being recorded at a few stations in Mendocino and Del Norte counties. The immensity of the area of the State has made the collection of the field data required for the report a task of considerable magnitude, though its diversity has added greatly to the interest of the work. In the original plan it was estimated that two years of field studies would prove sufficient. Mr. Waring succeeded in visiting the more important localities during this period, although some of his examinations were, of necessity, rather cursory. In midsummer, 1910, after the completion of the field work and the assembling of the greater portion of his data in manuscript form he was called by the Government of Brazil to take charge of general water supply investigations in the northeastern arid portion of that South American republic. The task of reviewing, editing, and supplementing in some respects, the results of his studies was thus unavoidably left to others. This task was rendered light by the systematic form in which Mr. Waring's material was left. It was a matter of regret to Mr. Waring, as it has been to those associated with him, that the financial limitations which controlled his work made it impracticable to procure the large number of new analyses which are particularly important in a paper of this type, in which waters of unusual chemical characteristics are discussed. Such analyses as are available have been assembled from all possible sources and combined with those which were prepared especially in connection with this investigation. The result, although it is in some respects unsatisfactory, furnishes a basis for a general view of the characteristics of the spring waters and serves to permit, their classification in a general way. Mr. Herman Stabler has reviewed the chemical data and rearranged and interpreted the available analyses. It is hoped that the report, setting forth as it does the results of impartial observations upon one of the important present and more important prospective resources of the State, will prove of value to its citizens as well as to its visitors, and that the assembled material will not be without interest to physicians, chemists, geologists, and teachers who may have especial need for the information contained in the volume.

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