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A summary of the stratigraphic occurrence of the Miocene molluscan faunas exposed in marine sandstone seacliffs on the SW Oregon coast. The more common and biostratigraphically significant species are illustrated. - Philip Harris
The Pomona Member of the Saddle Mountains Basalt (Columbia River Basalt Group) occurs as an intracanyon flow greater than 75m (250ft) thick along the S side of the Columbia River Gorge between Mitchell Point and Shellrock Mountain, Oregon. Best exposures are at Mitchell Point, where this flow caps more than 70m (230ft) of cobble conglomerate that partially fills a canyon cut into flows of the underlying Frenchman Springs Member. These exposures provide a necessary link between outcrops of the Pomona Member in the Columbia Plateau and western Washington. Post-Frenchman Springs, pre-Pomona canyon cutting implies deformation in the ancestral Cascade Range between about 14.5 and 12Ma ago.-Author
Earthquakes struck the Klamath Falls area on Monday night, September 20, 1993, resulting in two deaths and extensive damage. The quakes were felt as far away as Coos Bay to the west, Eugene to the north, Lakeview to the east, and Chico, California, to the south. A foreshock recorded at 8:16 p.m. had a Richter magnitude of 3.9. The first of two main shocks, measuring 5.9 on the Richter scale, rumbled through Klamath Falls at 8:28 p.m. Following 16 smaller jolts with magnitudes between 2.2 and 3.8, the largest quake struck at 10:45 p.m. This earthquake, measuring 6.0 on the Richter scale, is the largest to hit Oregon since the 1873 Port Orford/Crescent City earthquake (Jacobson, 1986). Oregon has been shaken by stronger quakes, but those quakes originated beneath the Pacific Ocean west of Port Orford.
This report describes the Cenozoic geology of the Willamette Lowland physiographic province, and the geologic framework of the regional ground-water flow system. Five regional hydrogeologic units are identified and described. The report includes maps showing the altitude of the top and the thickness of each hydrogeologic unit.
The use of groundwater in Oregon is expected to increase owing to continued population growth and to surface water supplies that are inadequate to meet present or future demand. The major groundwater issues in Oregon are: conjunctive use of surface and groundwater; contamination from hazardous wastes, leakage from underground gasoline and diesel tanks, naturally occurring brackish water, and high concentrations of dissolved iron; groundwater availability; and Indian water rights. Before 1987, the Oregon Water Resources Department, in cooperation with the U.S. Geological Survey (USGS), maintained a network of about 400 observation wells in Oregon to monitor fluctuations in groundwater levels. Water levels currently are measured cooperatively only in active project areas. The USGS has conducted more than 120 hydrologic investigations in Oregon. During fiscal year 1987, the USGS entered into cooperative agreements with 23 local, State, and Federal agencies to conduct hydrologic investigations in Oregon; six investigations included quantitative studies of groundwater. Examples of these groundwater studies are: groundwater hydrology of the Portland basin; groundwater hydrology in the Umatilla Plateau; and iron geochemistry of a sand dune aquifer near Coos Bay. (Lantz-PTT)
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The Dixonville 7.5 minute quadrangle is situated near the edge of two major geologic and tectonic provinces the northernmost Klamath Mountains and the southeastern part of the Oregon Coast Ranges (Figure 1). Rocks of the Klamath Mountains province that lie within the study area include ultramafic, mafic, intermediate and siliceous igneous types (Diller, 1898, Ramp, 1972, Ryberg, 1984). Similar rock associations that lie to the southwest yield Late Jurassic and earliest Cretaceous radiometric ages (Dott, 1965, Saleeby, et al., 1982, Hotz, 1971, Harper and Wright, 1984). These rocks, which are part of the Western Klamath terrane (Western Jurassic belt of (Irwin, 1964), are considered to have formed within an extensive volcanic arc and rifted arc complex (Harper and Wright, 1984) that lay along western North America during the Late Jurassic (Garcia, 1979, Garcia, 1982, Saleeby, et al., 1982, Ryberg, 1984). Imbricate thrust faulting and collapse of the arc during the Nevadan orogeny, which ranged in age between about 150 to 145 Ma in the Klamath region (Coleman, 1972, Saleeby, et al., 1982, Harper and Wright, 1984) was syntectonic with, or closely followed by deposition of the volcano-lithic clastic rocks of the Myrtle Group. The Myrtle Group consists of Upper Jurassic and Lower to middle Cretaceous turbidity and mass flow deposits considered to be either arc basin and/or post-orogenic flysh basins that were syntectonic with the waning phases of arc collapse (Imlay et al., 1959, Ryberg, 1984, Garcia, 1982, Roure.and Blanchet, 1983). The intermediate and mafic igneous rocks of the Rogue arc and the pre-Nevadan sedimentary cover (the Galice Formation, (Garcia, 1979) are intruded by siliceous and intermediate plutonic rocks principally of quartz diorite and granodiorite composition (Dott, 1965, Saleeby, et al., 1982, Garcia, 1982, Harper and Wright, 1984). The plutonic rocks are locally tectonized into amphibolite, gneiss, banded gneiss and augen gneiss. Similar metamorphic rocks have yielded metamorphic ages of 165 to 150 Ma (Coleman, 1972, Hotz, 1971, Saleeby, et al., 1982, Coleman and Lanphere, 1991). The Jurassic arc rocks and sedimentary cover occur as a tectonic outlier in this region (Figure 2) as they are bound to the northwest and southeast by melange, broken formation and semi-schists of the Dothan Formation and Dothan Formation(?) that are considered part of a late Mesozoic accretion complex (Ramp, 1972, Blake, et al., 1985). The plutonism that accompanied arc formation and tectonic collapse of the arc does not intrude the structurally underlying Dothan Formation, indicating major fault displacements since the Early Cretaceous. Semischistose and schistose rocks of the accretion complex have yielded metamorphic ages of around 125-140 Ma where they have been studied to the southwest (Coleman and Lanphere, 1971, Dott, 1965, Coleman, 1972). These rocks were unroofed and unconformably overlain by marine deposits by late early Eocene time (Baldwin, 1974). The early Tertiary history of this region is controversial. The most recent interpretation is that during the Paleocene and early Eocene the convergent margin was undergoing transtension or forearc extension as suggested by the voluminous extrusion of pillow basalt and related dike complexes (Wells, et al., 1984, Snavely, 1987). This episode was followed shortly by thrust and strike-slip faulting in the late early Eocene (Ryberg, 1984). During the Eocene, the Mesozoic convergent margin association of arc, clastic basin, and accretion complex was partly unroofed and faulted against early Cenozoic rocks of the Oregon Coast Ranges (Ramp, 1972, Baldwin, 1974, Champ, 1969, Ryberg, 1984). Faults that are typical of this period of deformation include high-angle reverse faults with a very strong component of strike-slip displacement characterized by a low-angle rake of striae. Thrust and oblique-slip faults are ubiquitous in early Tertiary rocks to the northwest (Ryberg, 1984, Niem and Niem, 1990). The late Mesozoic and early Cenozoic arc and forearc rocks are unconformably overlain to the east by the late Eocene and younger, mainly continental fluvial deposits and pyroclastic flows of the Cascade arc (Peck, et al., 1964, Baldwin, 1974, Walker and MacLeod, 1991). Minor fossiliferous shallow marine sandstone is locally present. The volcanic sequence consists of a homoclinal section of about 1 to 2 kilometers of andesitic to rhyolitic flows and ash flow tuff. The section is gently east-tilted and is slightly disrupted by NE trending faults with apparent normal separation.
The U.S. Geological Survey developed equipment to measure stream velocity simultaneously with 10 current meters arranged in a vertical and to measure velocity closer to the streambed than attainable with conventional equipment. With the 10 current meters, synchronous velocities were recorded for a period of 66 minutes at 10 different depths in one vertical of one gaging-station cross section. In addition, with a current meter installed on a special bracket to allow measurements to 0.5 foot above streambed, data were obtained at two to four verticals in four gaging-station cross sections. The mean velocity determined for the 66-minute period of record was 3.30 fps (feet per second). The graphic record of velocity was analyzed on a minute-by-minute basis. It was noted that the shape of the vertical velocity curves (plot of horizontal flow velocities measured in a vertical) changed from one minute to the next, but the change seemed to be random. Velocities obtained at different depths in the, profile fluctuated significantly, with the 1-minute velocities obtained at 0.05 depth (5 percent of total depths measured from the surface at indicated vertical) showing the smallest range--0.66 fps--and those at 0.55 depth the largest range--l.22 fps. The standard deviation, expressed in feet per second, of the velocity at each point in the vertical tended to increase with depth--from 0.16 fps at 0.05 depth to a maximum of 0.24 fps at 0.75 depth. The standard deviation, expressed as a percentage of the mean velocity, ranged from about 4 percent near the surface to 11 percent at 0.95 depth. In spite of the fluctuation in mean velocity that occurred during the 66 minutes and observation period of 4 minutes yields a mean velocity that differs from the 66-minute mean by less than one-half of a percent. Determining the mean velocity by averaging the 10-point observations of the 66minute run proved to be as accurate as by plotting the vertical velocity curvy (from the averaged 10 points) and then integrating the depth-velocity profile. In comparing the velocity obtained by integrating the depth-velocity profile with the 10-point mean velocity for other field data, collected beyond that obtained during the 66-minute run, the difference ranged from -1.3 to +1.7 percent and averaged -0.2 percent. Extension of the curve below the 0.95 depth by use of a power function proved to be fairly accurate (when compared with actual measurements within this reach made with the special current-meter bracket). However, the extension did not improve significantly the accuracy of the integrated-curve mean velocity. Both the one- and two-point methods were found to agree with the 10-point velocity. In computing mean river velocity, values determined by the two-point method ranged from -1.4 to +1.6 percent when compared with the base integrated-curve mean river velocity. The one-point method yielded results that ranged from -1.9 to +4.4 percent and averaged 40.1 percent. In determining river flow by use of the midsection and mean-section methods, the mean-section method uniformly yields lower flows for the same dart.. The range in difference is from -0.2 percent to -1.6 percent, with an average difference of -0.6 percent.
The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geology-based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States, focusing on the distribution, quantity, and availability of oil and natural gas resources. The USGS has completed an assessment of the undiscovered oil and gas potential of the Eastern Oregon and Washington Province of Oregon and Washington (USGS Province 5005). The province is a priority Energy Policy and Conservation Act (EPCA) province for the National Assessment because of its potential for oil and gas resources. The assessment of this province is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (stratigraphy, sedimentology, petrophysical properties), and hydrocarbon traps (trap formation and timing). In the Eastern Oregon and Washington Province, the USGS used this geologic framework to define one total petroleum system and two assessment units within the total petroleum system, and quantitatively estimated the undiscovered gas resources within each assessment unit.
This report includes well specifications, drillers ' logs, and temperature logs of geothermal test wells drilled at 7 sites near Mt. Hood, Oreg. The wells were drilled in 1979 and 1980 under contract to the U.S. Geological Survey. The project, funded by the U.S. Department of Energy, was part of an interagency effort to determine the geothermal potential of Mt. Hood. The agencies involved were, U.S. Department of Energy, U.S. Forest Service, U.S. Geological Survey, and Oregon Department of Geology and Mineral Industries. (USGS)
Stratigraphic and chronologic information collected for Quaternary deposits in the Willamette Valley, Oregon, provides a revised stratigraphic framework that serves as a basis for a 1:250,000-scale map, as well as for thickness estimates of widespread Quaternary geologic units. We have mapped 11 separate Quaternary units that are differentiated on the basis of stratigraphic, topographic, pedogenic, and hydrogeologic properties. In summation, these units reflect four distinct episodes in the Quaternary geologic development of the Willamette Valley: 1) Fluvial sands and gravels that underlie terraces flanking lowland margins and tributary valleys were probably deposited between 2.5 and 0.5 million years ago. They are the oldest widespread surficial Quaternary deposits in the valley. Their present positions and preservation are undoubtedly due to postdepositional tectonic deformation - either by direct tectonic uplift of valley margins, or by regional tectonic controls on local base level. 2) Tertiary and Quaternary excavation or tectonic lowering of the Willamette Valley accommodated as much as 500 m (meters) of lacustrine and fluvial fill. Beneath the lowland floor, much of the upper 10 to 50 m of fill is Quaternary sand and gravel deposited by braided channel systems in subhorizontal sheets 2 to 10 m thick. These deposits grade to gravel fans 40 to 100 m thick where major Cascade Range rivers enter the valley and are traced farther upstream as much thinner valley trains of coarse gravel. The sand and gravel deposits have ages that range from greater than 420,000 to about 12,000 years old. A widely distributed layer of sand and gravel deposited at about 12 ka (kiloannum, thousands of years before the present) is looser and probably more permeable than older sand and gravel. Stratigraphic exposures and drillers' logs indicate that this late Pleistocene unit is mostly between 5 and 20 m thick where it has not been subsequently eroded by the Willamette River and its major tributaries. 3) Between 15,000 and 12,700 years ago, dozens of floods from Glacial Lake Missoula flowed up the Willamette Valley from the Columbia River, depositing up to 35 m of gravel, sand, silt, and clay. 4) Subsequent to 12,000 years ago, Willamette River sediment and flow regimes changed significantly: the Pleistocene braided river systems that had formed vast plains of sand and gravel evolved to incised and meandering rivers that are constructing today's fine-grained floodplains and gravelly channel deposits. Sub-surface channel facies of this unit are loose and unconsolidated and are highly permeable zones of substantial groundwater flow that is likely to be well connected to surface flow in the Willamette River and major tributaries. Stratigraphic exposures and drillers' logs indicate that this unit is mostly between 5 and 15 m thick.
Over the last 20 years there has been a shift from dryland to irrigated agriculture in parts of Gilliam, Morrow, and Umatilla Counties in northeastern Oregon. Some irrigation water used in this area obtained from surface sources, but a significant amount is obtained from wells. The principal aquifer in the area is the Columbia River Basalt Group. Wells in the basalt are commonly drilled to depths of 500 to 1,200 ft and many produce more than 1,000 gal/min. A cooperative ground-water modeling study by the U.S. Geological Survey and Oregon Water Resources Department has resulted in the compilation of data from drillers logs and well inspections for wells completed in the basalt aquifer. Water-level measurements have been made in some wells in the area since the 1950's. The wells with longest periods of record are those that are part of a Statewide network of observation wells measured by the U. S. Geological Survey and Oregon Water Resources Department. This report includes a table of well information, representative hydrographs, and well location maps. (USGS)
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This report pt·esents a description of the stratigraphy, structure, and petrology of the volcanic rocks of the central and northern parts of the Western Cascade Range of Oregon. The study is a part of a long-range cooperative program between the U.S. Geological Survey and the Oregon State Department of Geology and Mineral Industries to prepare a geologic map of Oregon. The map area, about 7,500 square miles, lies in the densely forested western slope of the Cascade Range. It is bounded approximately by lat 43° N. and lat 45°30' N. on the south and north, the crest of the range on the east, and long 123° W. and the edge of the Willamette Valley on the west. The geology, which was mapped by reconnaissance methods, is chiefly based on examination of rock exposures along roads. The Cascade Range in Oregon comprises two physiographic divisions: the Western Cascade Range, which includes a wide, deeply dissected belt of volcanic formations making up the western slope of the range, and the High Cascade Range, which includes chiefly younger cones and lava flows forming the nearly undissected crest of the range. The volcanic rocks of the Western Cascade Range are deformed and partially altered flows and pyroclastic rocks that range in age from late Eocene t·o lute Miocene, as determined chiefly from fossil plants from more than 50 localities. These volcanic rocks overlie or interfinger westward with marine sedimentary rocks, and in the southwestern part of the map area they overlie pre-Tertiary plutonic and metamorphic rocks of the Klamath Mountains.
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