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• 1. [Article] Stream temperatures, riparian vegetation, and channel morphology in the Upper Grande Ronde River Watershed, Oregon

  The Upper Grande Ronde River Watershed in northeastern Oregon is considered important habitat for threatened stocks of chinook salmon (Oncorhynchus tshawytscha). Documented reductions in channel complexity ...

  Citation × Citation Citation Abstract Copy Title: Stream temperatures, riparian vegetation, and channel morphology in the Upper Grande Ronde River Watershed, Oregon Author: Bohle, Todd S. The Upper Grande Ronde River Watershed in northeastern Oregon is considered important habitat for threatened stocks of chinook salmon (Oncorhynchus tshawytscha). Documented reductions in channel complexity and riparian vegetation within the watershed have increased concern over loss of viable habitat. An important component of salmonid habitat is stream temperature during critical summer periods. In general, annual maximum stream temperatures and diurnal fluctuations in the Upper Grande Ronde River were found to reflect local reach characteristics, position in the drainage, and large-scale changes in valley shape. Stream temperatures on the Grande Ronde River at a distance of 71 km from the watershed divide exceeded 14°C, the "upper preferred temperature" for chinook salmon, more than 90% of time in July of 1991 and in July and August of 1992. While the occurrence of temperatures above 14°C were less common in the headwaters of the Grande Ronde River, downstream of a large meadow (i.e., Vey Meadow) (29 km from the divide) 14°C was exceeded at least 60% of the time during the same three month period. Seven-day maximum stream temperatures on the Upper Grande Ronde River ranged between 17.9°C and 26.6°C in 1991 and between 19.1°C and 26.7°C in 1992. Diel fluctuations on the mainstem were greatest immediately below Vey Meadow (about 12°C) but tended to stabilize at approximately 8°C at distances of over 49 km from the divide. Maximum stream temperatures in tributaries of the Upper Grande Ronde River varied by as much as 11°C (during 1992), reflecting large differences in stream cover, aspect, and flow. The timing of annual maximums seemed to be strongly linked to aspect during 1992. In addition, the high-elevation, forested tributaries had annual maximum stream temperatures and diel fluctuations which were 3°C lower than those associated with more open, low-elevation sites. Relationships between stream temperatures, riparian vegetation, and channel morphology characteristics were evaluated for 11 tributary reaches. Differences in stream cover, average flow velocity, bankfull depth and percent undercut bank were found to be significantly (p <0.1) related to maximum stream temperatures and/or average August diel fluctuations based on linear regression models. A stream temperature prediction model (i.e., TEMP-86) was found to be an accurate predictor of average hourly strew temperatures through short 250-m long reaches. An average WSTAT (a measure of model accuracy) of -0.18°C was calculated based on 11 reaches though two reaches led to consistent over- and under-predictions of downstream temperatures. A series of temperature simulations using TEMP-86 and combinations of wetted width and percent stream cover suggest that lower maximum daily stream temperatures would be observed through altered reaches if concurrent changes in both parameters occurred. Title: Stream temperatures, riparian vegetation, and channel morphology in the Upper Grande Ronde River Watershed, Oregon Author: Bohle, Todd S. The Upper Grande Ronde River Watershed in northeastern Oregon is considered important habitat for threatened stocks of chinook salmon (Oncorhynchus tshawytscha). Documented reductions in channel complexity and riparian vegetation within the watershed have increased concern over loss of viable habitat. An important component of salmonid habitat is stream temperature during critical summer periods. In general, annual maximum stream temperatures and diurnal fluctuations in the Upper Grande Ronde River were found to reflect local reach characteristics, position in the drainage, and large-scale changes in valley shape. Stream temperatures on the Grande Ronde River at a distance of 71 km from the watershed divide exceeded 14°C, the "upper preferred temperature" for chinook salmon, more than 90% of time in July of 1991 and in July and August of 1992. While the occurrence of temperatures above 14°C were less common in the headwaters of the Grande Ronde River, downstream of a large meadow (i.e., Vey Meadow) (29 km from the divide) 14°C was exceeded at least 60% of the time during the same three month period. Seven-day maximum stream temperatures on the Upper Grande Ronde River ranged between 17.9°C and 26.6°C in 1991 and between 19.1°C and 26.7°C in 1992. Diel fluctuations on the mainstem were greatest immediately below Vey Meadow (about 12°C) but tended to stabilize at approximately 8°C at distances of over 49 km from the divide. Maximum stream temperatures in tributaries of the Upper Grande Ronde River varied by as much as 11°C (during 1992), reflecting large differences in stream cover, aspect, and flow. The timing of annual maximums seemed to be strongly linked to aspect during 1992. In addition, the high-elevation, forested tributaries had annual maximum stream temperatures and diel fluctuations which were 3°C lower than those associated with more open, low-elevation sites. Relationships between stream temperatures, riparian vegetation, and channel morphology characteristics were evaluated for 11 tributary reaches. Differences in stream cover, average flow velocity, bankfull depth and percent undercut bank were found to be significantly (p <0.1) related to maximum stream temperatures and/or average August diel fluctuations based on linear regression models. A stream temperature prediction model (i.e., TEMP-86) was found to be an accurate predictor of average hourly strew temperatures through short 250-m long reaches. An average WSTAT (a measure of model accuracy) of -0.18°C was calculated based on 11 reaches though two reaches led to consistent over- and under-predictions of downstream temperatures. A series of temperature simulations using TEMP-86 and combinations of wetted width and percent stream cover suggest that lower maximum daily stream temperatures would be observed through altered reaches if concurrent changes in both parameters occurred. Close

• 2. [Article] An economic comparison of alternative bluegrass residue management practices in Oregon's Grande Ronde Valley

  Published February 2009. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/cata...

  Citation × Citation Citation Abstract Copy Title: An economic comparison of alternative bluegrass residue management practices in Oregon's Grande Ronde Valley Author: Walenta, Darrin L., 1968-, Gow, Laura R., Diebel, Penelope L., 1961-, Oregon State University. Agricultural Experiment Station Published February 2009. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalog Title: An economic comparison of alternative bluegrass residue management practices in Oregon's Grande Ronde Valley Author: Walenta, Darrin L., 1968-, Gow, Laura R., Diebel, Penelope L., 1961-, Oregon State University. Agricultural Experiment Station Published February 2009. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalog Close

• 3. [Article] Evaluation and cost analysis of alternative residue management methods for Kentucky bluegrass seed production in the Grande Ronde Valley

  The production of high quality grass seed is important to the agricultural economy of the Grande Ronde Valley (GRV) of eastern Oregon. The predominate grass seed crops grown in the area are Kentucky bluegrass ...

  Citation × Citation Citation Abstract Copy Title: Evaluation and cost analysis of alternative residue management methods for Kentucky bluegrass seed production in the Grande Ronde Valley Author: Walenta, Darrin L., 1968-, Diebel, Penelope L., 1961-, Gow, Laura R., Kiemnec, Gary L. The production of high quality grass seed is important to the agricultural economy of the Grande Ronde Valley (GRV) of eastern Oregon. The predominate grass seed crops grown in the area are Kentucky bluegrass and fine fescues. Historically, open-field burning has been an effective, economical means by which to remove residue and maintain seed yield and quality. The continued concern for air quality and public health have led to the adoption of alternative residue management methods that place less reliance on open-field burning of full straw residue loads. Title: Evaluation and cost analysis of alternative residue management methods for Kentucky bluegrass seed production in the Grande Ronde Valley Author: Walenta, Darrin L., 1968-, Diebel, Penelope L., 1961-, Gow, Laura R., Kiemnec, Gary L. The production of high quality grass seed is important to the agricultural economy of the Grande Ronde Valley (GRV) of eastern Oregon. The predominate grass seed crops grown in the area are Kentucky bluegrass and fine fescues. Historically, open-field burning has been an effective, economical means by which to remove residue and maintain seed yield and quality. The continued concern for air quality and public health have led to the adoption of alternative residue management methods that place less reliance on open-field burning of full straw residue loads. Close

• 4. [Article] From the Willamette to the Coast Range

  Citation × Citation Citation Abstract Copy Title: From the Willamette to the Coast Range Author: Adams, James Davis (J.D.) Title: From the Willamette to the Coast Range Author: Adams, James Davis (J.D.) Close

• 5. [Article] Ecological characteristics of montane floodplain plant communities in the Upper Grande Ronde basin, Oregon

  Citation × Citation Citation Abstract Copy Title: Ecological characteristics of montane floodplain plant communities in the Upper Grande Ronde basin, Oregon Author: Otting, Nicholas J. Title: Ecological characteristics of montane floodplain plant communities in the Upper Grande Ronde basin, Oregon Author: Otting, Nicholas J. Close

• 6. [Article] Historical changes in anadromous fish habitat in the Upper Grande Ronde River, Oregon, 1941-1990

  The U.S. Bureau of Fisheries (now National Marine Fisheries Service) conducted stream habitat surveys in the Upper Grande Ronde River Basin in 1941. This survey was part of an extensive inventory of stream ...

  Citation × Citation Citation Abstract Copy Title: Historical changes in anadromous fish habitat in the Upper Grande Ronde River, Oregon, 1941-1990 Author: McIntosh, Bruce A. The U.S. Bureau of Fisheries (now National Marine Fisheries Service) conducted stream habitat surveys in the Upper Grande Ronde River Basin in 1941. This survey was part of an extensive inventory of stream habitat conditions for anadromous salmonids (Oncorhynchus spp.) throughout the Columbia River Basin. The survey systematically inventoried 158 km of streams within the 3000 km2 watershed. Stream habitat was degraded from land-use activities (riparian timber harvest, splash dams, stream channelization, livestock grazing, and mining) prior to the 1941 survey. A 1990 resurvey determined how stream habitat conditions had continued to change. The historical survey and the 1990 resurvey inventoried streams according to pool and substrate characteristics. Pools were classified by size and depth criteria, while substrate was divided into size-classes. Losses in total pools/km (> 20m2 area and > 0.5 m depth) ranged from 43 to 83% (mean = 65%, 12.2 to 4.31km), while the loss in large pools/km (> 20m2 and > 1.0 m depth) ranged from 20 to 89% (mean = 68%, 6.2 to 2.0/1cm) for individual streams. The loss of variability in pool frequencies from 1941 to 1990 (total pools/km a2 = 43.9 to 2.8, large pools/km a2 = 23.2 to 3.2) demonstrates that stream channels have become less diverse. Classifying streams by reach types indicated that the decline in pool frequencies was not significantly related to geomorphic constraints. Substrate composition appears to have shifted toward smaller size-classes, with an increase in fine sediments (< 6mm) in the headwaters. Livestock grazing declined 78% (229,000 to 51,000 aum) from 1911 to 1990, while annual timber harvest increased 172% (36 to 98 mmbf) from the pre-survey period (1896-1940) to the post-survey period (1940-1990). Road densities have increased concurrent with timber harvest, currently averaging 4 miles/mile2. Base discharge has increased 51% (18.5 to 28.0 cfs), while there has been a 27% decrease in annual precipitation (22.0" to 16.0") and snowpack (April 1 water equivalent) (15.0" to 10.5") from 1941 to 1990. In an era of presumably improving management (1941-1990), large-scale losses in the fish habitat necessary for the continued viability of resident and anadromous fish populations continued to occur. Title: Historical changes in anadromous fish habitat in the Upper Grande Ronde River, Oregon, 1941-1990 Author: McIntosh, Bruce A. The U.S. Bureau of Fisheries (now National Marine Fisheries Service) conducted stream habitat surveys in the Upper Grande Ronde River Basin in 1941. This survey was part of an extensive inventory of stream habitat conditions for anadromous salmonids (Oncorhynchus spp.) throughout the Columbia River Basin. The survey systematically inventoried 158 km of streams within the 3000 km2 watershed. Stream habitat was degraded from land-use activities (riparian timber harvest, splash dams, stream channelization, livestock grazing, and mining) prior to the 1941 survey. A 1990 resurvey determined how stream habitat conditions had continued to change. The historical survey and the 1990 resurvey inventoried streams according to pool and substrate characteristics. Pools were classified by size and depth criteria, while substrate was divided into size-classes. Losses in total pools/km (> 20m2 area and > 0.5 m depth) ranged from 43 to 83% (mean = 65%, 12.2 to 4.31km), while the loss in large pools/km (> 20m2 and > 1.0 m depth) ranged from 20 to 89% (mean = 68%, 6.2 to 2.0/1cm) for individual streams. The loss of variability in pool frequencies from 1941 to 1990 (total pools/km a2 = 43.9 to 2.8, large pools/km a2 = 23.2 to 3.2) demonstrates that stream channels have become less diverse. Classifying streams by reach types indicated that the decline in pool frequencies was not significantly related to geomorphic constraints. Substrate composition appears to have shifted toward smaller size-classes, with an increase in fine sediments (< 6mm) in the headwaters. Livestock grazing declined 78% (229,000 to 51,000 aum) from 1911 to 1990, while annual timber harvest increased 172% (36 to 98 mmbf) from the pre-survey period (1896-1940) to the post-survey period (1940-1990). Road densities have increased concurrent with timber harvest, currently averaging 4 miles/mile2. Base discharge has increased 51% (18.5 to 28.0 cfs), while there has been a 27% decrease in annual precipitation (22.0" to 16.0") and snowpack (April 1 water equivalent) (15.0" to 10.5") from 1941 to 1990. In an era of presumably improving management (1941-1990), large-scale losses in the fish habitat necessary for the continued viability of resident and anadromous fish populations continued to occur. Close

• 7. [Article] Basin level ecological regions of the upper Grande Ronde River

  Citation × Citation Citation Abstract Copy Title: Basin level ecological regions of the upper Grande Ronde River Author: Thiele, Sandra Anne Title: Basin level ecological regions of the upper Grande Ronde River Author: Thiele, Sandra Anne Close

• 8. [Article] Year 2000 Timber Sales - Confederated Tribes on Grand Ronde : Biological Opinion

  The Natural Resources Division (NRD) of the Confederated Tribes of Grand Ronde (CTGR), in cooperation with the Bureau of Indian Affairs (BIA), proposes the regeneration harvest and commercial thinning ...

  Citation × Citation Citation Abstract Copy Title: Year 2000 Timber Sales - Confederated Tribes on Grand Ronde : Biological Opinion The Natural Resources Division (NRD) of the Confederated Tribes of Grand Ronde (CTGR), in cooperation with the Bureau of Indian Affairs (BIA), proposes the regeneration harvest and commercial thinning of four timber sales on the Reservation of The Confederated Tribes of Grand Ronde (CTGR). The CTGR has a 20-year management agreement with the BIA. For the purposes of this consultation the BIA is the action agency. The proposed timber harvest units are in the South Yamhill River subbasin, which supports two species listed by the National Marine Fisheries Service (NMFS) as threatened under the Federal Endangered Species Act (ESA). Upper Willamette River (UWR) chinook salmon (Oncorhynchus tshawytscha) were listed as threatened under the ESA on May 24, 1999. Upper Willamette River (UWR) steelhead (Oncorhynchus mykiss) were listed as threatened under the ESA on March 25, 1999. Critical habitat for both of these species was designated on February 16, 2000 (effective on March 17, 2000). According to the BA, UWR chinook do not currently reside in the action area and there is no recorded data indicating they were present historically. The nearest known occurrence of UWR chinook is near the confluence of Salt creek and the South Yamhill River, over 40 stream miles from the Reservation. Juvenile UWR steelhead reside within the action area and are known to occur in streams on the reservation. Based on the presence of juveniles, CTGR staff suspect that adult UWR steelhead spawn in streams on the Reservation, although little spawning survey work has been done. Title: Year 2000 Timber Sales - Confederated Tribes on Grand Ronde : Biological Opinion The Natural Resources Division (NRD) of the Confederated Tribes of Grand Ronde (CTGR), in cooperation with the Bureau of Indian Affairs (BIA), proposes the regeneration harvest and commercial thinning of four timber sales on the Reservation of The Confederated Tribes of Grand Ronde (CTGR). The CTGR has a 20-year management agreement with the BIA. For the purposes of this consultation the BIA is the action agency. The proposed timber harvest units are in the South Yamhill River subbasin, which supports two species listed by the National Marine Fisheries Service (NMFS) as threatened under the Federal Endangered Species Act (ESA). Upper Willamette River (UWR) chinook salmon (Oncorhynchus tshawytscha) were listed as threatened under the ESA on May 24, 1999. Upper Willamette River (UWR) steelhead (Oncorhynchus mykiss) were listed as threatened under the ESA on March 25, 1999. Critical habitat for both of these species was designated on February 16, 2000 (effective on March 17, 2000). According to the BA, UWR chinook do not currently reside in the action area and there is no recorded data indicating they were present historically. The nearest known occurrence of UWR chinook is near the confluence of Salt creek and the South Yamhill River, over 40 stream miles from the Reservation. Juvenile UWR steelhead reside within the action area and are known to occur in streams on the reservation. Based on the presence of juveniles, CTGR staff suspect that adult UWR steelhead spawn in streams on the Reservation, although little spawning survey work has been done. Close

• 9. [Article] Strontium isotopic and trace element geochemistry of the Saddle Mountains and Grande Rondé basalts of the Columbia River basalt group

  Citation × Citation Citation Abstract Copy Title: Strontium isotopic and trace element geochemistry of the Saddle Mountains and Grande Rondé basalts of the Columbia River basalt group Author: Nelson, Dennis O. Title: Strontium isotopic and trace element geochemistry of the Saddle Mountains and Grande Rondé basalts of the Columbia River basalt group Author: Nelson, Dennis O. Close

• 10. [Article] The geology of the Elk Mountain-Porter Ridge area, Clatsop County, northwest Oregon

  Eight Tertiary sedimentary and volcanic units crop out in the thesis area. From oldest to youngest they are the: Sager Creek formation (informal); Pittsburg Bluff Formation; Northrup Creek formation (informal); ...

  Citation × Citation Citation Abstract Copy Title: The geology of the Elk Mountain-Porter Ridge area, Clatsop County, northwest Oregon Author: Goalen, Jeffrey Scott Eight Tertiary sedimentary and volcanic units crop out in the thesis area. From oldest to youngest they are the: Sager Creek formation (informal); Pittsburg Bluff Formation; Northrup Creek formation (informal); Smuggler Cove formation (informal); Wickiup Mountain and Cannon Beach members (both informal) of the Astoria Formation; the Grande Ronde Basalt, and Frenchman Springs Member of the Wanapum Basalt, both of the Columbia River Basalt Group. Also, areally limited, unnamed sedimentary strata interbedded between flows of the Columbia River Basalt Group crop out in the study area. Quaternary deposits consist of alluvium, colluvium, and landslide debris. Rhythmically-bedded, foram-bearing, carbonaceous to micaceous mudstone and graded, fine-grained, feldspathic turbidite sandstone are the dominant lithologies of the upper Eocene (Refugian) Sager Creek formation. Plane-laminae and climbing ripple-laminae typical of Bouma b,c, and d intervals are common in the thin turbidite sandstone beds. Contemporaneous, rare, thick, sandstones may represent submarine feeder channels that supplied the more widespread, thinly-bedded overbank turbidite sandstones. Foraminiferal paleobathymetry indicates that deposition was in bathyal water depths. Sager Creek deposition was followed by a regression or offlap of the late Eocene to early Oligocene (Refugian) sea as indicated by the molluscan fossils and thick, bioturbated sandstone of the predominantly shallow-marine Pittsburg Bluff Formation. The lower part of the formation consists of outer shelf, glauconitic, fossiliferous sandstone and subordinate mudstone. Higher in the section are middle-shelf, fine-grained, bioturbated, tuffaceous, arkosic sandstones. These sandstones contain minor glauconite, wave- and storm-generated molluscan shell hash beds, carbonized wood fragments, and calcareous concretions. Deposition occurred in 20 - 50 m open-marine shelf water depths; however, the depositional environment may have shallowed to a bay-like setting (Moore, 1982, written communication). The upper part of the unit consists of thin- to medium-bedded, carbonaceous siltstone and mudstone with minor ashfall tuffs. Therefore, deposition of the Pittsburg Bluff Formation occurred as a shallowing-upward, then deepening depositional episode, punctuated by contemporaneous, intermittent eruption of nearby calc-alkaline western Cascade volcanoes. The deep-marine Oligocene to lower Miocene (Zemorrian to Saucesian) Northrup Creek formation is predominantly composed of thinly-laminated mudstone interbedded with thin, very fine-grained, graded, micaceous arkosic sandstone. Bouma c-d-e and a-b-e sequences are common in the turbidite sandstone; Bouma a-e intervals occur locally in sandstone/mudstone couplets. Paleocurrent indicators suggest that the predominant transport direction of these turbidite deposits was northeast to southwest. Abraded, carbonaceous plant debris and mica are abundant in the sandstone laminations. The upper part of the formation consists of thick, mollusk-bearing, moderately- to well-sorted, arkosic sandstone and minor polymict grit beds. A shallowing-upward, high-energy, shallow-marine shelf environment of deposition is indicated for the upper part of the formation. Contemporaneous with shelf and slope deposition of the Sager Creek, Pittsburg Bluff and Northrup Creek formations, the deep-water late Eocene to early Miocene Smuggler Cove formation was deposited as a distal or lateral correlative in a low-energy, outer shelf to slope setting. This foram-bearing unit consists of thick, bioturbated, bathyal, tuffaceous mudstone and siltstone with minor thin- to thick-bedded ashfall and current-reworked tuff. A marine onlap is indicated by the conformable relationship between the upper sandstone unit of the Northrup Creek formation and the overlying Smuggler Cove formation in the eastern part of the thesis area. The overlying lower to middle Miocene Astoria Formation contains two members in the thesis area: a high-energy, shallow shelf, fine- to medium-grained, fossiliferous, micaceous arkosic sandstone (Wickiup Mountain member), and an overlying, thinly-laminated, deepmarine mudstone (Cannon Beach member). Diatom floras indicate that a thermal "oceanographic irregularity" (water warmer than normal) may have occurred during deposition of the Cannon Beach member. At least six, and possibly eight, flows of the middle Miocene Grande Ronde Basalt (Columbia River Basalt Group) are present in the thesis area. Individual flows have been ascribed to the (N1?), R2, and N2 magnetozones. Geochemically, the flows consist of low MgO high Ti02, low MgO low Ti02, and high MgO subtypes. These subaerial to submarine flows are correlated to Mangan and others (1986) chemical subtypes 2D, 5C, 5A, and 4A of the Columbia Plateau-derived Grande Ronde Basalt of eastern Washington and eastern Oregon. The correlations are based on similarity of age, major element chemistry, stratigraphic position, and magnetic polarity. Field evidence suggests that thick, submarine pillow and breccia complexes generated sufficient pressure to autoinvasively inject into the Eocene to middle Miocene sedimentary strata of the Plympton/Porter ridge and Elk Mountain areas. This process apparently formed many randomly-oriented dike- and sill-like intrusions in the western part of the thesis area. However, in the eastern and central parts of the thesis area, three sub-parallel dikes (the Northrup, Beneke, and Fishhawk Falls dikes) extend along linear trends for tens of kilometers. This suggests that their emplacement was, in part, influenced by earlier or contemporaneous regional tectonism. At least two, and as many as five, flows of the Frenchman Springs Member of the Wanapum Basalt occur in the thesis area: one to two abundantly plagioclase-phyric Basalt of Ginkgo flow(s), and one to three Basalt of Sand Hollow flows (terminology after Beeson and Tolan, 1985). These flows consist of subaqueous pillow palagonite breccia and vesicular, columnar-jointed, subaerial basalt. No Frenchman Springs flows are invasive in the thesis area. Local middle Miocene sedimentary interbeds between flows of Grande Ronde and Frenchman Springs Basalt are lithologically and sedimentologically diverse. Common lithologies are fine- to mediumgrained, arkosic sandstone, coarse-grained basaltic sandstone, and structureless mudstone. Depositional environments represented by these strata are fluvial, marginal-marine, and shallow-marine. Thicknesses of individual interbeds range from 0.2 to 50 m. The thesis area is located on the northwest flank of the Oregon Coast Range anticline, adjacent to the Nehalem Arch. Large-scale northeast-trending oblique to strike-slip left-lateral faults coupled with northwest-trending oblique to strike-slip right-lateral faults dominate the structure of the area. These faults may have formed as conjugate shears (Riedel shear) caused by north-south compressive stress related to the oblique subduction of the Juan de Fuca Plate beneath the North American Plate. Five episodes of deformation are suggested by faults, dike orientations, unconformities, and other geological relationships within the thesis area: a late Eocene north-south compressional episode, an early Oligocene to early Miocene uplift, a middle Miocene northwest-southeast extensional episode, a post-middle Miocene to Pliocene (?) north-south compressional episode, and a north-south extensional event that occurred between the post-middle Miocene and Recent. Although crushed rock (for road and revetment construction) is currently the primary mineral resource within the thesis area, several potential fault traps on this northwest flank of the Nehalem Arch may contain significant reserves of natural gas. This conclusion is based upon field, laboratory, and subsurface (well) data. The Clark and Wilson sandstone of the middle to late Eocene Cowlitz Formation, the producing unit at the nearby Mist gas field, represents the most attractive target horizon. Additionally, the porous and permeable upper sandstone unit of the Northrup Creek formation could contain shallow hydrocarbon reserves beneath the northern part of the area. Title: The geology of the Elk Mountain-Porter Ridge area, Clatsop County, northwest Oregon Author: Goalen, Jeffrey Scott Eight Tertiary sedimentary and volcanic units crop out in the thesis area. From oldest to youngest they are the: Sager Creek formation (informal); Pittsburg Bluff Formation; Northrup Creek formation (informal); Smuggler Cove formation (informal); Wickiup Mountain and Cannon Beach members (both informal) of the Astoria Formation; the Grande Ronde Basalt, and Frenchman Springs Member of the Wanapum Basalt, both of the Columbia River Basalt Group. Also, areally limited, unnamed sedimentary strata interbedded between flows of the Columbia River Basalt Group crop out in the study area. Quaternary deposits consist of alluvium, colluvium, and landslide debris. Rhythmically-bedded, foram-bearing, carbonaceous to micaceous mudstone and graded, fine-grained, feldspathic turbidite sandstone are the dominant lithologies of the upper Eocene (Refugian) Sager Creek formation. Plane-laminae and climbing ripple-laminae typical of Bouma b,c, and d intervals are common in the thin turbidite sandstone beds. Contemporaneous, rare, thick, sandstones may represent submarine feeder channels that supplied the more widespread, thinly-bedded overbank turbidite sandstones. Foraminiferal paleobathymetry indicates that deposition was in bathyal water depths. Sager Creek deposition was followed by a regression or offlap of the late Eocene to early Oligocene (Refugian) sea as indicated by the molluscan fossils and thick, bioturbated sandstone of the predominantly shallow-marine Pittsburg Bluff Formation. The lower part of the formation consists of outer shelf, glauconitic, fossiliferous sandstone and subordinate mudstone. Higher in the section are middle-shelf, fine-grained, bioturbated, tuffaceous, arkosic sandstones. These sandstones contain minor glauconite, wave- and storm-generated molluscan shell hash beds, carbonized wood fragments, and calcareous concretions. Deposition occurred in 20 - 50 m open-marine shelf water depths; however, the depositional environment may have shallowed to a bay-like setting (Moore, 1982, written communication). The upper part of the unit consists of thin- to medium-bedded, carbonaceous siltstone and mudstone with minor ashfall tuffs. Therefore, deposition of the Pittsburg Bluff Formation occurred as a shallowing-upward, then deepening depositional episode, punctuated by contemporaneous, intermittent eruption of nearby calc-alkaline western Cascade volcanoes. The deep-marine Oligocene to lower Miocene (Zemorrian to Saucesian) Northrup Creek formation is predominantly composed of thinly-laminated mudstone interbedded with thin, very fine-grained, graded, micaceous arkosic sandstone. Bouma c-d-e and a-b-e sequences are common in the turbidite sandstone; Bouma a-e intervals occur locally in sandstone/mudstone couplets. Paleocurrent indicators suggest that the predominant transport direction of these turbidite deposits was northeast to southwest. Abraded, carbonaceous plant debris and mica are abundant in the sandstone laminations. The upper part of the formation consists of thick, mollusk-bearing, moderately- to well-sorted, arkosic sandstone and minor polymict grit beds. A shallowing-upward, high-energy, shallow-marine shelf environment of deposition is indicated for the upper part of the formation. Contemporaneous with shelf and slope deposition of the Sager Creek, Pittsburg Bluff and Northrup Creek formations, the deep-water late Eocene to early Miocene Smuggler Cove formation was deposited as a distal or lateral correlative in a low-energy, outer shelf to slope setting. This foram-bearing unit consists of thick, bioturbated, bathyal, tuffaceous mudstone and siltstone with minor thin- to thick-bedded ashfall and current-reworked tuff. A marine onlap is indicated by the conformable relationship between the upper sandstone unit of the Northrup Creek formation and the overlying Smuggler Cove formation in the eastern part of the thesis area. The overlying lower to middle Miocene Astoria Formation contains two members in the thesis area: a high-energy, shallow shelf, fine- to medium-grained, fossiliferous, micaceous arkosic sandstone (Wickiup Mountain member), and an overlying, thinly-laminated, deepmarine mudstone (Cannon Beach member). Diatom floras indicate that a thermal "oceanographic irregularity" (water warmer than normal) may have occurred during deposition of the Cannon Beach member. At least six, and possibly eight, flows of the middle Miocene Grande Ronde Basalt (Columbia River Basalt Group) are present in the thesis area. Individual flows have been ascribed to the (N1?), R2, and N2 magnetozones. Geochemically, the flows consist of low MgO high Ti02, low MgO low Ti02, and high MgO subtypes. These subaerial to submarine flows are correlated to Mangan and others (1986) chemical subtypes 2D, 5C, 5A, and 4A of the Columbia Plateau-derived Grande Ronde Basalt of eastern Washington and eastern Oregon. The correlations are based on similarity of age, major element chemistry, stratigraphic position, and magnetic polarity. Field evidence suggests that thick, submarine pillow and breccia complexes generated sufficient pressure to autoinvasively inject into the Eocene to middle Miocene sedimentary strata of the Plympton/Porter ridge and Elk Mountain areas. This process apparently formed many randomly-oriented dike- and sill-like intrusions in the western part of the thesis area. However, in the eastern and central parts of the thesis area, three sub-parallel dikes (the Northrup, Beneke, and Fishhawk Falls dikes) extend along linear trends for tens of kilometers. This suggests that their emplacement was, in part, influenced by earlier or contemporaneous regional tectonism. At least two, and as many as five, flows of the Frenchman Springs Member of the Wanapum Basalt occur in the thesis area: one to two abundantly plagioclase-phyric Basalt of Ginkgo flow(s), and one to three Basalt of Sand Hollow flows (terminology after Beeson and Tolan, 1985). These flows consist of subaqueous pillow palagonite breccia and vesicular, columnar-jointed, subaerial basalt. No Frenchman Springs flows are invasive in the thesis area. Local middle Miocene sedimentary interbeds between flows of Grande Ronde and Frenchman Springs Basalt are lithologically and sedimentologically diverse. Common lithologies are fine- to mediumgrained, arkosic sandstone, coarse-grained basaltic sandstone, and structureless mudstone. Depositional environments represented by these strata are fluvial, marginal-marine, and shallow-marine. Thicknesses of individual interbeds range from 0.2 to 50 m. The thesis area is located on the northwest flank of the Oregon Coast Range anticline, adjacent to the Nehalem Arch. Large-scale northeast-trending oblique to strike-slip left-lateral faults coupled with northwest-trending oblique to strike-slip right-lateral faults dominate the structure of the area. These faults may have formed as conjugate shears (Riedel shear) caused by north-south compressive stress related to the oblique subduction of the Juan de Fuca Plate beneath the North American Plate. Five episodes of deformation are suggested by faults, dike orientations, unconformities, and other geological relationships within the thesis area: a late Eocene north-south compressional episode, an early Oligocene to early Miocene uplift, a middle Miocene northwest-southeast extensional episode, a post-middle Miocene to Pliocene (?) north-south compressional episode, and a north-south extensional event that occurred between the post-middle Miocene and Recent. Although crushed rock (for road and revetment construction) is currently the primary mineral resource within the thesis area, several potential fault traps on this northwest flank of the Nehalem Arch may contain significant reserves of natural gas. This conclusion is based upon field, laboratory, and subsurface (well) data. The Clark and Wilson sandstone of the middle to late Eocene Cowlitz Formation, the producing unit at the nearby Mist gas field, represents the most attractive target horizon. Additionally, the porous and permeable upper sandstone unit of the Northrup Creek formation could contain shallow hydrocarbon reserves beneath the northern part of the area. Close