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This presentation describes USGS geologic mapping in western Oregon, geologic map products, a thumbnail sketch of geologic history, a discussion of new mapping in progress in northwest Oregon, a tour of northwest Oregon geologic units, their relation to new American Viticultural Areas, and online sources of information.
Geologic formations in Oregon, east of the crest of the Cascade Range, have been grouped according to similarities in their hydrogeologic and geologic properties into six major aquifer units. Two of the units, the Mesozoic-Paleozoic and the John Day-Clarno aquifers, are low-permeability aquifers, have hydraulic conductivities generally less than 1 ft/d (feet per day), and are generally capable of yielding only a few gallons per minute to wells. These are important aquifer units, nevertheless, because they are the only economical source of domestic water present in east-central Oregon where they outcrop. Four of the aquifer units contain beds or zones of high permeability materials with hydraulic conductivities that commonly range between 5 and 50 ft/d. In many localities where these units are present, they are capable of yielding 200 gallons/min or more to wells. These productive aquifer units are the Columbia River Basalt, the Cenozoic volcanic and sedimentary , Cenozoic sedimentary, and the Quaternary sediment aquifers, respectively. North of the Blue Mountains, the Columbia River Basalt aquifer is a major aquifer of regional extent and, in that area, heavy withdrawals, chiefly for irrigation, have resulted in regional groundwater level declines. South of the Blue Mountains, the basalt underlies rugged terrane, is not developed, and little is known about its hydraulic properties. Other major aquifer units are heavily developed in localized areas or in basins throughout eastern Oregon. (USGS)
Geologic structure plays an important role in controlling fluid flow in geothermal systems. In particular, very complex structural settings, consisting of many closely spaced and intersecting faults, host many geothermal systems. To elucidate the key geologic factors that affect fault-controlled geothermal circulation, it is critical to precisely characterize the structural and stratigraphic geometries in these complex settings. Here, we present a methodology and the results of 3D geologic analyses of two geothermal systems in the Basin and Range, USA. This methodology is a quantitative and geologically focused technique that can be used to precisely characterize geothermal areas, in a time when future geothermal growth demands increased exploration precision and efficiency. Surficial and subsurface geologic and geophysical data are synthesized in the construction of detailed 3D geologic maps of geothermal areas. Based on these 3D geologic maps, we examine several geologic attributes that control permeability development and geothermal fluid flow along faults. We use the stress state of faults and the distribution of structural discontinuities (i.e., fault intersections and fault terminations) to identify locations of upflow along faults in these geothermal systems. These results and the methodology presented herein are directly applicable to structurally controlled geothermal fields in the Basin and Range and worldwide. As development focus shifts toward blind geothermal resources, integration of precisely characterized subsurface structural information into exploration methods will be increasingly critical to continued growth in geothermal exploration and development.
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Introduction This report describes and makes available a geologic digital spatial database (orgeo) representing the geologic map of Oregon (Walker and MacLeod, 1991). The original paper publication was printed as a single map sheet at a scale of 1:500,000, accompanied by a second sheet containing map unit descriptions and ancillary data. A digital version of the Walker and MacLeod (1991) map was included in Raines and others (1996). The dataset provided by this open-file report supersedes the earlier published digital version (Raines and others, 1996). This digital spatial database is one of many being created by the U.S. Geological Survey as an ongoing effort to provide geologic information for use in spatial analysis in a geographic information system (GIS). This database can be queried in many ways to produce a variety of geologic maps. This database is not meant to be used or displayed at any scale larger than 1:500,000 (for example, 1:100,000). This report describes the methods used to convert the geologic map data into a digital format, describes the ArcInfo GIS file structures and relationships, and explains how to download the digital files from the U.S. Geological Survey public access World Wide Web site on the Internet. Scanned images of the printed map (Walker and MacLeod, 1991), their correlation of map units, and their explanation of map symbols are also available for download.
New geologic mapping (Wells and others, 2020b) and geophysical mapping (Blakely and others, 2000; McPhee and others, 2014; Wells and others, 2020a) document kilometers of Cenozoic right-lateral offset along the Gales Creek Fault Zone, a major, northwest-striking fault zone forming the boundary between the Tualatin Valley and the Coast Range. The Bureau of Reclamation’s (Reclamation) Scoggins Dam (fig. 1), in the Coast Range foothills west of Forest Grove, Oregon, lies within the Gales Creek Fault Zone as mapped by Wells and others (2020a, 2020b; fig. 2). Active faults of the Gales Creek Fault Zone defined by paleoseismic trenching (Redwine and others, 2017, 2019b, Horst and others, 2018, 2019, 2021, and Wells and others, 2020a) are presently mapped as projecting through the existing dam. The Pacific Northwest Region of Reclamation requested assistance with geologic studies around Scoggins Dam to provide better understanding of fault locations and their activity, which are needed to design a modification of the dam (Maguire, 2019a, b). The scope of this project includes detailed geology of the existing Scoggins Dam site, Henry Hagg Lake, the reservoir behind the dam, and Scoggins Valley downstream of the existing dam, particularly around a potential new dam site, where Scoggins Creek cuts through a narrow gap formed by a resistant felsic tuff bed that crosses the valley.
Fragile geologic features (FGFs), which are extant on the landscape but vulnerable to earthquake ground shaking, may provide geological constraints on the intensity of prior shaking. These empirical constraints are particularly important in regions such as the Pacific Northwest that have not experienced a megathrust earthquake in written history. Here, we describe our field survey of FGFs in southern Oregon. We documented 58 features with fragile geometric characteristics, as determined from field measurements of size and strength, historical photographs, and light detection and ranging point clouds. Among the surveyed FGFs, sea stacks have particular advantages for use as ground‐motion constraints: (1) they are frequently tall and thin; (2) they are widely distributed parallel to the coast, proximal to the trench and the likely megathrust rupture surface; and (3) they are formed by sea cliff retreat, meaning that their ages may be coarsely estimated as a function of distance from the coast. About 40% of the surveyed sea stacks appear to have survived multiple Cascadia megathrust earthquakes. Using a quasi‐static analysis, we estimate the minimum horizontal ground accelerations that could fracture the rock pillars. We provide context for the quasi‐static results by comparing them with predictions from kinematic simulations and ground‐motion prediction equations. Among the sea stacks old enough to have survived multiple megathrust earthquakes ( n = 16), eight yield breaking accelerations lower than the predictions, although they generally overlap within uncertainty. FGFs with the lowest breaking accelerations are distributed uniformly over 130 km of coastline. Results for inland features, such as speleothems, are in close agreement with the predictions. We conclude that FGFs show promise for investigating both past earthquake shaking and its spatial variability along the coasts of Oregon and Washington, where sea stacks are often prevalent. Future work can refine our understanding of FGF age and evolution.
This bibliography of Klamath Mountains geology was begun, although not in a systematic or comprehensive way, when, in 1953, I was assigned the task of preparing a report on the geology and mineral resources of the drainage basins of the Trinity, Klamath, and Eel Rivers in northwestern California. During the following 40 or more years, I maintained an active interest in the Klamath Mountains region and continued to collect bibliographic references to the various reports and maps of Klamath geology that came to my attention. When I retired in 1989 and became a Geologist Emeritus with the Geological Survey, I had a large amount of bibliographic material in my files. Believing that a comprehensive bibliography of a region is a valuable research tool, I have expended substantial effort to make this bibliography of the Klamath Mountains as complete as is reasonably feasible. My aim was to include all published reports and maps that pertain primarily to the Klamath Mountains, as well as all pertinent doctoral and master's theses. In addition, I included reports in which the Klamath Mountains are of significance but not the primary focus; these latter kinds are mostly reports that correlate the Klamath terranes with those of other provinces, that compare the genesis of Klamath rocks with those elsewhere, or that include the Klamath Mountains in a continental framework. Reports describing the geology of the overlap sequences such as the Great Valley sequence, Hornbrook Formation, and Tertiary sediments and volcanics are included where those rocks lie within the limits of the Klamath Mountains province, but are only selectively included where the overlap sequences are mainly peripheral to the province. The alphabetical part of the bibliography consists of approximately 1700 entries. The list of primary references probably is virtually complete through 1994 and includes some 1995 references. The earliest reference is to James Dwight Dana in 1849. In order to restrict the size of the topical part of the bibliography to reasonable limits, each reference is listed under only one subject although many references may be applicable to two or more subjects. Titles in the topical section are abbreviated to conserve space and still retain identity. The bibliography was compiled from a variety of sources. Some of the references have not been checked against the original publications for accuracy. Caveat emptor! I would appreciate being informed of any errors or ommissions in order that a corrected and updated version of the bibliography may be prepared. I thank Nancy Blair for assistance in verifying some of the references, and thank Mary Donato and Robert Brown for helpful suggestions regarding the topical part of the bibliography. Since the first version of this bibliography was released in 1995, the total number of entries has increased from approximately 1700 to 1937, which indicates a continued high interest in the geology of the Klamath Mountains province. The total number of entries includes 73 Ph.D. theses and 123 Masters theses representing 26 universities.
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