Approximately 150 meters (500 feet) of Grande Ronde Basalt and 140 meters (450 feet) of Wanapum Basalt of the Columbia River Basalt Group are exposed in the Bull Run Watershed. In Bull Run, the Grande Ronde Basalt is divided into three mappable units: "low Mg" R2 (at least one flow), "low Mg" N2 (approximately four flows), and "high Mg" N2 (two to three flows}. The Wanapum Basalt is represented by two members: Frenchman Springs Member (six flows) and Priest Rapids Member (one flow). These units are identified by instrumental neutron activation analysis, paleomagnetism based on measurements with a fluxgate magnetometer, petrography, lithology, jointing, and stratigraphic position.

The Clackamas River drainage within the western Cascade Range is approximately aligned with a northwest trending lineation defined by the Portland Hills and the Brothers Fault zone. This area is occupied by an extensive Columbia River Basalt sequence that is deeply incised by the Clackamas River and its tributaries. Two major basalt units of the Yakima Basalt Subgroup, including the Grande Ronde Basalt and the Frenchman Springs Member of the Wanapurn Basalt, are distinguishable in a 515 meter to 550 meter accumulation. Of particular interest is the presence of five trending right-lateral strike-slip faults is consistent with a stress model of north-south compression and east-west extension.

Nitrate concentration in excess of national drinking-water standards (10 mg/l) are present in the shallow alluvial aquifer and Saddle Mountains Basalt (SMB) aquifer in the Lower Umatilla Basin, Oregon. To determine sources responsible for elevated nitrate concentrations in the SMB aquifer mass-balance and reaction-path models (NETPATH and PHREEQE) were used to understand observed geochemical trends. Nitrate-nitrogen isotopes were used to distinguish potential nitrate sources in the shallow alluvial aquifer. NETPATH-validated simple water/rock reactions in the SMB aquifers in Irrigon (dissolving glass, precipitating smectite, dissolving or precipitating calcite, and cation exchange) using constituents (calcium, magnesium, sodium and carbon). Diversity of composition for the shallow alluvial water and limited number of wells available made obtaining a mass balanced solution for the SMB aquifer near Boardman impossible. Irrigon basalt groundwaters were consistent with the PHREEQE models prediction of natural hydrochemical trends, where Boardman basalt groundwaters plotted consistently with impacted alluvial groundwater. Nitrogen-isotopic values of nitrate (o 15NNo3) were measured in the shallow alluvial groundwater from 17 wells in 4 land-use settings, 3 lysimeter samples and 1 surface water effluent sample. The landuse setting and corresponding average ranges for nitrate concentrations (as N) and 015NNo3 values for wells near: commercial fertilizer-irrigated fields range from 25-87 mg/l, +3.5 to +4.6 per mil; explosive washout lagoons ranged from 10-18 mg/l, +4.6 to +4.9 per mil; potato waste water application ranged from 6.4-17.8 mg/l, +4.4 to +35 per mil; past confined animal feeding operations (CAFO) ranged from 16-56 mg/l, +4.9 to 10.4 per mil; lysimeters 5.4-39.9 mg/l, +9.1 to +21.9 per mil; surface water effluent ranged from 60-61 mg/l, +3.5 to 6.5 per mil; and varying landuse ranged from 9.3-19.5 mg/l, +2.7 to +7.1 per mil. Commercial fertilizer 0 15NNo3 signatures are consistent for this source. Explosive 015NNa3 values are consistent with an atmospheric signature. CAFO o15NNo3 signatures probably result from mixing between currently applied commercial fertilizer and past CAFO's. High 015NNo3 Signatures (+22 to +35 per mil) imply denitrification. Potato waste water and varying land-use 015NNo3 signatures indicate probable mixing of nitratenitrogen sources in the groundwater.

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.

The Chehalem Mountains area, encompassing 70 square kilometers, is at the western extent of the Columbia River Basalt Group as mapped in western Oregon. The flows in the study area were identified as belonging to subdivisions of the Columbia River Basalt Group on the basis of physical characteristics and trace element geochemistry. The basalt flows are poorly exposed in the area and weathering is deep and extensive where the flows have been exposed. Where erosion has exposed the underlying marine sedimentary rocks, the basalt has failed in landslides.

The Hood River Valley, located 100 kilometers east of Portland, Oregon, is in the transition zone between two geologic provinces--the High Cascades and the Columbia Plateau. The entire valley is probably underlain by Columbia River Basalt, but it crops out only on steep hillsides and in stream valleys. The base of the basalt is not exposed in the thesis area. The basalt is overlain by Pliocene and Quaternary basalt and andesite, volcanic sediments and glacial debris. The stratigraphy of the Columbia River Basalt is useful in determining the path of the basalt flows into western Oregon, in mapping the structure and in reconstructing the tectonic development of the northern Oregon Cascades.

Approximately 16 square km of Columbia River basalt are exposed in the Salmon River area to the south and to the west of Mount Hood, Oregon. A maximum composite basalt section composed of 15 flows and totaling 461 m is exposed in discontinuous areas of outcrop.

The study area is located in northwestern Columbia County, and covers an area of approximately 70 square kilometers. The purpose of the study was to investigate the possible correlation of the Scappoose and Astoria Formations and determine their stratigraphic relationship to the Columbia River Basalt Group through mapping, geochemistry and petrography.

Explosion structures occur in flows of Grande Ronde Basalt in the study area near Troy, Oregon. Data from nineteen stratigraphic sites indicate that the maximum number of flows that contain explosion structures at any one site is six. In the informally named Troy flow, explosion structures are widespread.

The Dooley Rhyolite Breccia in northeast Oregon was erupted between 12 and 16 million years ago, from central vents and linear feeder dikes within the Dooley Mountain quadrangle. The peraluminous, high-silica rhyolites of the formation were erupted over an irregular highland of eroded pre-Tertiary metamorphic rocks locally overlain by intracanyon, Eocene Clarno-type basalt flow(s) . The Dooley Rhyolite Braccia is exposed in a tectonically disrupted, north-south trending graben across the Elkhorn Range. The formation is variable in thickness with maximum thickness exceeding 660 meters in the south and 600 meters in the north half of the quadrangle. Volumetrically the formation is dominated by block lava flows with lessor associated volcaniclastic and pyroclastic rocks. Although initial and waning phases of eruption of the formation produced ash-flow tuffs which extend well beyond the quadrangle boundaries, volcanism within the quadrangle appears to have been primarily effusive. At least nine geochemically distinct rhyolite subunits belonging to four related chemical groups have been identified in the formation stratigraphy which appear to represent unique eruptive episodes. Chronologic geochemical patterns within the formation are consistent with a petrogenetic model of repeated partial melting and eruption from multiple silicic magma chambers in an attenuated continental crust. Basalts correlative with the Powder River Basalt and the Strawberry Volcanics overlie the Dooley Rhyolite Braccia on the north flank of Dooley Mountain. Cale-alkaline basalts correlative with the Strawberry Volcanics are overlain by thoeliitic basalts of uncertain affinity on the south flank of the mountain. These basalt flows on respective flanks of the mountain were not continuous across the quadrangle. Rhyolitic volcanism in the Dooley Mountain quadrangle is contemporary with the strawberry Volcanics and the Picture Gorge Basalt of the Columbia River Basalt Group.