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• 41. [Article] The Making of Seaside’s “Indian Place”: Contested and Enduring Native Spaces on the Nineteenth Century Oregon Coast

  During the mid nineteenth century, non-Native settlement and activities disrupted and changed historic Chinook and Clatsop communities at the mouth of the Columbia River. Indian Place in what would be ...

  Citation × Citation Citation Abstract Copy Title: The Making of Seaside’s “Indian Place”: Contested and Enduring Native Spaces on the Nineteenth Century Oregon Coast Author: Deur, Douglas Year: 2016 During the mid nineteenth century, non-Native settlement and activities disrupted and changed historic Chinook and Clatsop communities at the mouth of the Columbia River. Indian Place in what would be Seaside, Oregon, became home to a number of displaced peoples and an enclave where “the living gathered with the remains of the dead,” for “modest protection from the apocalyptic changes that so radically disrupted tribal lands, lives, and worldviews.” Douglas Deur documents tribal migration to the Indian Place during the late nineteenth and early twentieth centuries and calls attention to many of its significant early residents. Transitional communities such as Indian Place, Deur attests, “defined the nineteenth- and early-twentieth-century Native experience in northwestern Oregon and beyond.” While the Indian Place no longer exists, it remains an “important [conduit] for tribal cultural knowledge, values, and practices that endure today.” Title: The Making of Seaside’s “Indian Place”: Contested and Enduring Native Spaces on the Nineteenth Century Oregon Coast Author: Deur, Douglas Year: 2016 During the mid nineteenth century, non-Native settlement and activities disrupted and changed historic Chinook and Clatsop communities at the mouth of the Columbia River. Indian Place in what would be Seaside, Oregon, became home to a number of displaced peoples and an enclave where “the living gathered with the remains of the dead,” for “modest protection from the apocalyptic changes that so radically disrupted tribal lands, lives, and worldviews.” Douglas Deur documents tribal migration to the Indian Place during the late nineteenth and early twentieth centuries and calls attention to many of its significant early residents. Transitional communities such as Indian Place, Deur attests, “defined the nineteenth- and early-twentieth-century Native experience in northwestern Oregon and beyond.” While the Indian Place no longer exists, it remains an “important [conduit] for tribal cultural knowledge, values, and practices that endure today.” Close

• 42. [Article] Geophysical and geochemical analyses of selected Miocene coastal basalt features, Clatsop County, Oregon

  The proximity of Miocene Columbia River basalts to the "locally-erupted" coastal Miocene basalts in northwestern Oregon, and the compelling similarities between the two groups, suggest that the coastal ...

  Citation × Citation Citation Abstract Copy Title: Geophysical and geochemical analyses of selected Miocene coastal basalt features, Clatsop County, Oregon Author: Pfaff, Virginia Josette Year: 1980 The proximity of Miocene Columbia River basalts to the "locally-erupted" coastal Miocene basalts in northwestern Oregon, and the compelling similarities between the two groups, suggest that the coastal basalts, rather than being locally erupted, may be the westward extension of plateau basalts derived from eastern Oregon and Washington. The local-origin hypothesis is based largely on the interpretation of coastal dikes and sills as representing vent areas; however, a complex mechanism, as yet unsatisfactorily defined, would be required to cause the eruption of virtually identical magmas simultaneously from source areas 500 km apart. This study, therefore, has investigated the coastal basalt intrusions both laterally and vertically. Geochemical and paleomagnetic analysis was used to determine the occurrence and distribution of basalt units; gravity surveys enabled an examination of the subsurface extensions of basalt intrusions in sedimentary rocks. Title: Geophysical and geochemical analyses of selected Miocene coastal basalt features, Clatsop County, Oregon Author: Pfaff, Virginia Josette Year: 1980 The proximity of Miocene Columbia River basalts to the "locally-erupted" coastal Miocene basalts in northwestern Oregon, and the compelling similarities between the two groups, suggest that the coastal basalts, rather than being locally erupted, may be the westward extension of plateau basalts derived from eastern Oregon and Washington. The local-origin hypothesis is based largely on the interpretation of coastal dikes and sills as representing vent areas; however, a complex mechanism, as yet unsatisfactorily defined, would be required to cause the eruption of virtually identical magmas simultaneously from source areas 500 km apart. This study, therefore, has investigated the coastal basalt intrusions both laterally and vertically. Geochemical and paleomagnetic analysis was used to determine the occurrence and distribution of basalt units; gravity surveys enabled an examination of the subsurface extensions of basalt intrusions in sedimentary rocks. Close

• 43. [Article] Consumptive use of surface water by Willamette Basin municipalities

  The consumptive water use of six cities in the Willamette Basin of northwestern Oregon was evaluated for the period 1960-66. Consumptive use ratios were obtained by analyzing data from monthly water supply ...

  Citation × Citation Citation Abstract Copy Title: Consumptive use of surface water by Willamette Basin municipalities Author: Mittelstadt, Richard Lee The consumptive water use of six cities in the Willamette Basin of northwestern Oregon was evaluated for the period 1960-66. Consumptive use ratios were obtained by analyzing data from monthly water supply and sewage flow records. The average annual consumptive use for the six cities was found to be 26 percent, and the average monthly ratios varied from essentially zero in the winter months to as high as 53 percent in July and August. The principal factors affecting consumptive use were found to be weather conditions, lawn watering, water system losses, cost of water, air conditioning, and proportion of water used for industrial purposes. While not affecting consumptive use, per se, sewer infiltration, storm runoff, and incomplete water or sewer systems can affect the calculated consumptive use ratios. The extent to which a water right is consumptive is inferred by the use to which the water is put. On the basis of existing water law and past court decisions, it is concluded that a city has the legal right to consume the full amount of its municipal water right providing the water is used strictly in accordance with the conditions of its permit. Title: Consumptive use of surface water by Willamette Basin municipalities Author: Mittelstadt, Richard Lee The consumptive water use of six cities in the Willamette Basin of northwestern Oregon was evaluated for the period 1960-66. Consumptive use ratios were obtained by analyzing data from monthly water supply and sewage flow records. The average annual consumptive use for the six cities was found to be 26 percent, and the average monthly ratios varied from essentially zero in the winter months to as high as 53 percent in July and August. The principal factors affecting consumptive use were found to be weather conditions, lawn watering, water system losses, cost of water, air conditioning, and proportion of water used for industrial purposes. While not affecting consumptive use, per se, sewer infiltration, storm runoff, and incomplete water or sewer systems can affect the calculated consumptive use ratios. The extent to which a water right is consumptive is inferred by the use to which the water is put. On the basis of existing water law and past court decisions, it is concluded that a city has the legal right to consume the full amount of its municipal water right providing the water is used strictly in accordance with the conditions of its permit. Close

• 44. [Article] Long Trails Project: Identifying Opportunities, Solving Problems, and Exploring Implementation

  This document presents the final report of the Long Trails Project, a partnership with the Oregon Parks Department and USP 549: Regional Planning and Metropolitan Growth Management, a course offered to ...

  Citation × Citation Citation Abstract Copy Title: Long Trails Project: Identifying Opportunities, Solving Problems, and Exploring Implementation Author: Portland State University Year: 2012 This document presents the final report of the Long Trails Project, a partnership with the Oregon Parks Department and USP 549: Regional Planning and Metropolitan Growth Management, a course offered to graduate planning students in the Toulan School of Urban Studies and Planning at Portland State University. It is divided into 5 sections: (1.) History of Long Trails and Regional Trail Networks (2.) Long Trails in Northwestern Oregon (3.) The Demand for Long Trails-based Recreation (4.) Long Trails and Community Economic Development (5.) Long Trails Implementation. This technical report is edited by Dr. Ethan Seltzer Title: Long Trails Project: Identifying Opportunities, Solving Problems, and Exploring Implementation Author: Portland State University Year: 2012 This document presents the final report of the Long Trails Project, a partnership with the Oregon Parks Department and USP 549: Regional Planning and Metropolitan Growth Management, a course offered to graduate planning students in the Toulan School of Urban Studies and Planning at Portland State University. It is divided into 5 sections: (1.) History of Long Trails and Regional Trail Networks (2.) Long Trails in Northwestern Oregon (3.) The Demand for Long Trails-based Recreation (4.) Long Trails and Community Economic Development (5.) Long Trails Implementation. This technical report is edited by Dr. Ethan Seltzer Close

• 45. [Article] Spatial Patterns of Sediment Transport in the Upper Willamette River, Oregon

  The Willamette is a gravel-bed river that drains ~28,800 square kilometers between the Coast Range and Cascade Range in northwestern Oregon before entering the Columbia River near Portland. In the last ...

  Citation × Citation Citation Abstract Copy Title: Spatial Patterns of Sediment Transport in the Upper Willamette River, Oregon Author: Langston, Trevor Year: 2015 The Willamette is a gravel-bed river that drains ~28,800 square kilometers between the Coast Range and Cascade Range in northwestern Oregon before entering the Columbia River near Portland. In the last 150 years, natural and anthropogenic drivers have altered the sediment transport regime, drastically reducing the geomorphic complexity of the river. The purpose of this research is to assess longitudinal trends in sediment transport within the modern flow regime. Sediment transport rates are highly discrete in space, exhibit similar longitudinal patters across flows and increase non-linearly with flow. The highest sediment transport rates are found where the channel is confined due to disconnection of the floodplain and the river runs against high resistance terraces. The spatial distributions of sediment transport rates and active gravel are tightly linked. Sediment sampling revealed slight downstream fining in the surface grain size. Sediment size did not correlate with stream power. Title: Spatial Patterns of Sediment Transport in the Upper Willamette River, Oregon Author: Langston, Trevor Year: 2015 The Willamette is a gravel-bed river that drains ~28,800 square kilometers between the Coast Range and Cascade Range in northwestern Oregon before entering the Columbia River near Portland. In the last 150 years, natural and anthropogenic drivers have altered the sediment transport regime, drastically reducing the geomorphic complexity of the river. The purpose of this research is to assess longitudinal trends in sediment transport within the modern flow regime. Sediment transport rates are highly discrete in space, exhibit similar longitudinal patters across flows and increase non-linearly with flow. The highest sediment transport rates are found where the channel is confined due to disconnection of the floodplain and the river runs against high resistance terraces. The spatial distributions of sediment transport rates and active gravel are tightly linked. Sediment sampling revealed slight downstream fining in the surface grain size. Sediment size did not correlate with stream power. Close

• 46. [Article] Texture analysis riparian coniferous forest ADAR imagery to identify potential ecological indicators for monitoring

  The Airborne Data Acquisition and Registration (ADAR) remote sensing system captured one-meter resolution imagery of 25 different riparian sites in drift Creek Basin of coastal northwestern Oregon, USA. ...

  Citation × Citation Citation Abstract Copy Title: Texture analysis riparian coniferous forest ADAR imagery to identify potential ecological indicators for monitoring Author: Fiorella, M., Barker, Jerry R., Ringold, P.L., Bradshaw, Gay, Bollman, Mike The Airborne Data Acquisition and Registration (ADAR) remote sensing system captured one-meter resolution imagery of 25 different riparian sites in drift Creek Basin of coastal northwestern Oregon, USA. The multispectral, digital data characterized riparian areas with the intent to develop ecological indicators for long-term monitoring. Title: Texture analysis riparian coniferous forest ADAR imagery to identify potential ecological indicators for monitoring Author: Fiorella, M., Barker, Jerry R., Ringold, P.L., Bradshaw, Gay, Bollman, Mike The Airborne Data Acquisition and Registration (ADAR) remote sensing system captured one-meter resolution imagery of 25 different riparian sites in drift Creek Basin of coastal northwestern Oregon, USA. The multispectral, digital data characterized riparian areas with the intent to develop ecological indicators for long-term monitoring. Close

• 47. [Article] Post-breeding habitat selection by songbirds in the headwaters of the Trask River, northwestern Oregon

  Little is known on the importance of riparian areas to birds near small headwater streams in mesic forests. Progress towards understanding limiting factors that affect bird populations has been difficult ...

  Citation × Citation Citation Abstract Copy Title: Post-breeding habitat selection by songbirds in the headwaters of the Trask River, northwestern Oregon Author: Jenkins, Stephanie R. Little is known on the importance of riparian areas to birds near small headwater streams in mesic forests. Progress towards understanding limiting factors that affect bird populations has been difficult because of lack of information beyond the breeding period. I compared bird assemblages between headwater riparian and upland areas throughout the post-breeding period by capturing birds using mist-nets in six paired riparian and upland locations along six headwater streams of the Trask River in northwestern Oregon. In order to assess whether birds prefer headwater riparian areas, I also examined factors affecting habitat selection by juvenile Swainson's thrushes (n=37) using radio telemetry. While riparian and upland locations had similar coarse wood volume and fruiting and tall (> 1.3 m tall) shrub cover, riparian locations had less shrub cover (< 1.3 m tall) and different shrub composition than upland locations. Total capture rate was double that of upland in riparian locations, while bird species richness was similar. Similar numbers of birds were captured in mist-nets oriented perpendicular and parallel to the stream suggesting that birds were not using riparian areas as movement corridors. Adult capture rate was greater in riparian locations than adjacent uplands while results of juvenile capture rates were ambiguous. Riparian locations supported higher capture rates of Swainson's thrushes and winter wrens than adjacent uplands. Higher arthropod abundance in riparian locations may best explain higher capture rates in riparian locations. Radio-tagged juvenile Swainson's thrushes were more likely to select habitat that was near streams with high proportions of deciduous mid-story cover 1.5 - 15 m in the vertical strata and large volumes of coarse wood; possibly due to cover from predation and sources of food (i.e., fruits and arthropods). I observed higher survival (97.3%) than reported in previous studies on independent juveniles which suggests that headwater streams contribute positively to the demography of the Swainson's thrush in the Pacific Northwest. In comparison with adjacent upland, headwater riparian areas appeared to be disproportionately used by songbirds during the post-breeding period even though vegetation differences were minimal. To assess if current policies sufficiently protect avian biodiversity, further research should evaluate how manipulation of vegetation affects bird distribution in headwater areas. Title: Post-breeding habitat selection by songbirds in the headwaters of the Trask River, northwestern Oregon Author: Jenkins, Stephanie R. Little is known on the importance of riparian areas to birds near small headwater streams in mesic forests. Progress towards understanding limiting factors that affect bird populations has been difficult because of lack of information beyond the breeding period. I compared bird assemblages between headwater riparian and upland areas throughout the post-breeding period by capturing birds using mist-nets in six paired riparian and upland locations along six headwater streams of the Trask River in northwestern Oregon. In order to assess whether birds prefer headwater riparian areas, I also examined factors affecting habitat selection by juvenile Swainson's thrushes (n=37) using radio telemetry. While riparian and upland locations had similar coarse wood volume and fruiting and tall (> 1.3 m tall) shrub cover, riparian locations had less shrub cover (< 1.3 m tall) and different shrub composition than upland locations. Total capture rate was double that of upland in riparian locations, while bird species richness was similar. Similar numbers of birds were captured in mist-nets oriented perpendicular and parallel to the stream suggesting that birds were not using riparian areas as movement corridors. Adult capture rate was greater in riparian locations than adjacent uplands while results of juvenile capture rates were ambiguous. Riparian locations supported higher capture rates of Swainson's thrushes and winter wrens than adjacent uplands. Higher arthropod abundance in riparian locations may best explain higher capture rates in riparian locations. Radio-tagged juvenile Swainson's thrushes were more likely to select habitat that was near streams with high proportions of deciduous mid-story cover 1.5 - 15 m in the vertical strata and large volumes of coarse wood; possibly due to cover from predation and sources of food (i.e., fruits and arthropods). I observed higher survival (97.3%) than reported in previous studies on independent juveniles which suggests that headwater streams contribute positively to the demography of the Swainson's thrush in the Pacific Northwest. In comparison with adjacent upland, headwater riparian areas appeared to be disproportionately used by songbirds during the post-breeding period even though vegetation differences were minimal. To assess if current policies sufficiently protect avian biodiversity, further research should evaluate how manipulation of vegetation affects bird distribution in headwater areas. Close

• 48. [Article] Geochemical Evolution of Ferruginous Bauxite Deposits in Northwestern Oregon and Southwestern Washington

  Ferruginous bauxite deposits developed from flows of the Columbia River Basalt Group in northwestern Oregon and southwestern Washington. Samples of the iron pisolite and the gibbsite nodular zones from ...

  Citation × Citation Citation Abstract Copy Title: Geochemical Evolution of Ferruginous Bauxite Deposits in Northwestern Oregon and Southwestern Washington Author: Fassio, Joseph Michael Year: 1990 Ferruginous bauxite deposits developed from flows of the Columbia River Basalt Group in northwestern Oregon and southwestern Washington. Samples of the iron pisolite and the gibbsite nodular zones from the upper portion of the weathering profile of drill core from Columbia County, Oregon and Cowlitz County, Washington, were analyzed by instrumental neutron activation. The mineralogy was determined using Xray diffraction and Mossbauer spectroscopy. The gibbsite nodular zone is above the clay-rich saprolite or relic basalt zone. The nodules contain relic vesicles and well preserved relic plagioclase microlites. Gibbsite occurs with poorly crystalline goethite and hematite in the gibbsite nodular zone. Clays are absent in this part of the profile . The iron pisolite zone is at the top of the profile above the gibbsite nodular zone. Both maghemite and goethite pisolites occur in the lower part of the zone while maghemite pisolites are dominant in the upper part of the pisolite zone. The parent flow is the Frenchman Springs Member of the Wanapum Basalt for the Columbia County profile and the Pomona Member of the Saddle Mountains Basalt for the Cowlitz County profile. Distribution of the major, minor and trace elements through the profile shows three distinct sympathetic patterns consisting of lanthanide elements and Na; As, Sbi Th, Hf, and Ta; and transition metals Fe, Ti, V, and Cr. Ratios between the high-field strength elements Ta and Hf are nearly constant through the profile, and Hf appears to be the least mobile elements of the elements analyzed in the profile. Ratios of other elements were calculated against Hf, based on the assumption that it has remained largely immobile during weathering, to show element enrichment and depletion in the profile independent of mass-volume changes. Transition metals and Al show a progressive depletion through the upper gibbsite nodular and iron pisolite zone due to leaching in the profile. Lanthanide elements (except Ce), As, and Sb show an obvious enrichment in the iron pisolite zone relative to the gibbsite nodular zone. Volume reduction during weathering was calculated based on the immobility of Hf. In the gibbsite nodular zone, the volume reduction calculated for bulk samples is greater than for gibbsite nodule separates suggesting that a greater volume reduction occurred the matrix material surrounding the nodules. Ratios between gibbsite nodules and parent basalt of the immobile elements Hf, Ta, Fe, Ti, Th and Cr suggest that the nodules, where the relic textures are preserved, have undergone volume reduction. Based on the immobility of Hf, the gibbsite nodules lost approximately 40% of the original volume. The volume factors based on the immobility of Hf show that the pisolite zone experienced a greater volume reduction than the gibbsite nodular zone. Absolute gains and losses relative to the parent basalt show the following relative order of depletion: Na > La > Eu > Sm > Co > Mn > Ce > Sc > Ta > V > Cr > Lu > Th > Fe > Ga > Al. The lesser mobility of Ce and Lu relative to other lanthanide elements suggests fractionation of lanthanide elements in the bauxite profile. Aluminum is both enriched and depleted at different depths in the gibbsite nodular zone suggesting that Al is mobilized from the matrix and possibly the pisolite zone into Al enriched gibbsite nodules. Volume reduction and destruction of relic textures in the pisolite zone is accompanied by small-scale mobilization of Th, Cr, Fe, Hf, Ga, Sc, and Ta during the formation of iron pisolites. Formation of the iron pisolite zone above the gibbsite nodular zone may indicate a change in climate from a heavy year round to a seasonal rainfall pattern. Title: Geochemical Evolution of Ferruginous Bauxite Deposits in Northwestern Oregon and Southwestern Washington Author: Fassio, Joseph Michael Year: 1990 Ferruginous bauxite deposits developed from flows of the Columbia River Basalt Group in northwestern Oregon and southwestern Washington. Samples of the iron pisolite and the gibbsite nodular zones from the upper portion of the weathering profile of drill core from Columbia County, Oregon and Cowlitz County, Washington, were analyzed by instrumental neutron activation. The mineralogy was determined using Xray diffraction and Mossbauer spectroscopy. The gibbsite nodular zone is above the clay-rich saprolite or relic basalt zone. The nodules contain relic vesicles and well preserved relic plagioclase microlites. Gibbsite occurs with poorly crystalline goethite and hematite in the gibbsite nodular zone. Clays are absent in this part of the profile . The iron pisolite zone is at the top of the profile above the gibbsite nodular zone. Both maghemite and goethite pisolites occur in the lower part of the zone while maghemite pisolites are dominant in the upper part of the pisolite zone. The parent flow is the Frenchman Springs Member of the Wanapum Basalt for the Columbia County profile and the Pomona Member of the Saddle Mountains Basalt for the Cowlitz County profile. Distribution of the major, minor and trace elements through the profile shows three distinct sympathetic patterns consisting of lanthanide elements and Na; As, Sbi Th, Hf, and Ta; and transition metals Fe, Ti, V, and Cr. Ratios between the high-field strength elements Ta and Hf are nearly constant through the profile, and Hf appears to be the least mobile elements of the elements analyzed in the profile. Ratios of other elements were calculated against Hf, based on the assumption that it has remained largely immobile during weathering, to show element enrichment and depletion in the profile independent of mass-volume changes. Transition metals and Al show a progressive depletion through the upper gibbsite nodular and iron pisolite zone due to leaching in the profile. Lanthanide elements (except Ce), As, and Sb show an obvious enrichment in the iron pisolite zone relative to the gibbsite nodular zone. Volume reduction during weathering was calculated based on the immobility of Hf. In the gibbsite nodular zone, the volume reduction calculated for bulk samples is greater than for gibbsite nodule separates suggesting that a greater volume reduction occurred the matrix material surrounding the nodules. Ratios between gibbsite nodules and parent basalt of the immobile elements Hf, Ta, Fe, Ti, Th and Cr suggest that the nodules, where the relic textures are preserved, have undergone volume reduction. Based on the immobility of Hf, the gibbsite nodules lost approximately 40% of the original volume. The volume factors based on the immobility of Hf show that the pisolite zone experienced a greater volume reduction than the gibbsite nodular zone. Absolute gains and losses relative to the parent basalt show the following relative order of depletion: Na > La > Eu > Sm > Co > Mn > Ce > Sc > Ta > V > Cr > Lu > Th > Fe > Ga > Al. The lesser mobility of Ce and Lu relative to other lanthanide elements suggests fractionation of lanthanide elements in the bauxite profile. Aluminum is both enriched and depleted at different depths in the gibbsite nodular zone suggesting that Al is mobilized from the matrix and possibly the pisolite zone into Al enriched gibbsite nodules. Volume reduction and destruction of relic textures in the pisolite zone is accompanied by small-scale mobilization of Th, Cr, Fe, Hf, Ga, Sc, and Ta during the formation of iron pisolites. Formation of the iron pisolite zone above the gibbsite nodular zone may indicate a change in climate from a heavy year round to a seasonal rainfall pattern. Close

• 49. [Article] Geology, structure, and tectonic history of the Tualatin Basin, northwestern Oregon

  The northwest-trending Neogene Tualatin basin in northwestern Oregon is a pull-apart basin with approximately 750 m of post-middle Miocene structural relief. Gently tilted uplands capped by Columbia River ...

  Citation × Citation Citation Abstract Copy Title: Geology, structure, and tectonic history of the Tualatin Basin, northwestern Oregon Author: Popowski, Thomas Allan The northwest-trending Neogene Tualatin basin in northwestern Oregon is a pull-apart basin with approximately 750 m of post-middle Miocene structural relief. Gently tilted uplands capped by Columbia River Basalt Group surround the synclinal basin on all sides. Integrated gravity, aeromagnetic, and seismic reflection data indicated that the basin is underlain by 3 to 4 km of sub-horizontal, upper lower Eocene to middle Miocene age sedimentary and volcanic rocks. Up to 300 m of Columbia River Basalt overlie these older strata, in turn overlain by up to 400 m of late Miocene to Pleistocene, dominantly fluvio-lacustrine sediments. Late middle Eocene strong oblique convergence across the continental margin generated regional northeast-trending fissures in the forearc through which the Tillamook Volcanics and basalt of Waverly Heights erupted. Sinistral strike-slip faults, including the proto-Gales Creek-Mt. Angel structural zone, segmented the forearc into discrete blocks which rotated clockwise independently. A right-step in the Gales Creek-Mt. Angel system generated northeast-directed folding and faulting adjacent to the restraining bend, deforming rocks as young as upper Tillamook Volcanics. Regional uplift culminated in a late Eocene unconformity which removed the arkosic Spencer Formation northeast of the Gales Creek-Mt. Angel system, prior to subsidence of the forearc and burial by late Eocene and Oligocene tuffaceous sedimentary strata. The distribution of middle Miocene Columbia River Basalt Group flows shows no evidence of a structural or topographic Tualatin basin at that time. The syncline initiated along the present southwestern margin of the basin in late Miocene time, in response to uplift of the Coast Range and Portland Hills anticlines to the southwest and northeast, respectively. A late Pliocene decrease in convergence and consequent relative increase in the oblique component of convergence reactivated the Gales Creek-Mt. Angel structural zone as a dextral shear zone. The right-step acted as a releasing bend, allowing extension, increased subsidence and normal faulting along the basin margins, and volcanism within the basin. Subsequent development of transverse folds and reverse faults, northwest-trending riedel shears, northeast-trending antithetic faults, and basin-marginal normal faults, is consistent with classification of the Tualatin basin as a pull-apart basin in a dextral wrench system. Title: Geology, structure, and tectonic history of the Tualatin Basin, northwestern Oregon Author: Popowski, Thomas Allan The northwest-trending Neogene Tualatin basin in northwestern Oregon is a pull-apart basin with approximately 750 m of post-middle Miocene structural relief. Gently tilted uplands capped by Columbia River Basalt Group surround the synclinal basin on all sides. Integrated gravity, aeromagnetic, and seismic reflection data indicated that the basin is underlain by 3 to 4 km of sub-horizontal, upper lower Eocene to middle Miocene age sedimentary and volcanic rocks. Up to 300 m of Columbia River Basalt overlie these older strata, in turn overlain by up to 400 m of late Miocene to Pleistocene, dominantly fluvio-lacustrine sediments. Late middle Eocene strong oblique convergence across the continental margin generated regional northeast-trending fissures in the forearc through which the Tillamook Volcanics and basalt of Waverly Heights erupted. Sinistral strike-slip faults, including the proto-Gales Creek-Mt. Angel structural zone, segmented the forearc into discrete blocks which rotated clockwise independently. A right-step in the Gales Creek-Mt. Angel system generated northeast-directed folding and faulting adjacent to the restraining bend, deforming rocks as young as upper Tillamook Volcanics. Regional uplift culminated in a late Eocene unconformity which removed the arkosic Spencer Formation northeast of the Gales Creek-Mt. Angel system, prior to subsidence of the forearc and burial by late Eocene and Oligocene tuffaceous sedimentary strata. The distribution of middle Miocene Columbia River Basalt Group flows shows no evidence of a structural or topographic Tualatin basin at that time. The syncline initiated along the present southwestern margin of the basin in late Miocene time, in response to uplift of the Coast Range and Portland Hills anticlines to the southwest and northeast, respectively. A late Pliocene decrease in convergence and consequent relative increase in the oblique component of convergence reactivated the Gales Creek-Mt. Angel structural zone as a dextral shear zone. The right-step acted as a releasing bend, allowing extension, increased subsidence and normal faulting along the basin margins, and volcanism within the basin. Subsequent development of transverse folds and reverse faults, northwest-trending riedel shears, northeast-trending antithetic faults, and basin-marginal normal faults, is consistent with classification of the Tualatin basin as a pull-apart basin in a dextral wrench system. Close

• 50. [Image] 4. Northwestern Electric Co. Portland, Oregon. View of cement being poured into wooden forms for foundation. Reinforcing rods visable.; 11381; P3858

  	4. Northwestern Electric Co. Portland, Oregon. View of cement being poured into wooden forms for foundation. Reinforcing rods visable.
  	Citation × Citation Citation Abstract Copy Title: 4. Northwestern Electric Co. Portland, Oregon. View of cement being poured into wooden forms for foundation. Reinforcing rods visable.; 11381; P3858 Year: 1880 4. Northwestern Electric Co. Portland, Oregon. View of cement being poured into wooden forms for foundation. Reinforcing rods visable. Title: 4. Northwestern Electric Co. Portland, Oregon. View of cement being poured into wooden forms for foundation. Reinforcing rods visable.; 11381; P3858 Year: 1880 4. Northwestern Electric Co. Portland, Oregon. View of cement being poured into wooden forms for foundation. Reinforcing rods visable. Close