The Ellensburg Formation of south-central Washington and north-central Oregon has been described by many workers from the time of the original description by Russell (1893) to recent work by Schmincke (1964). However, detailed information concerning the stratigraphy and petrography of the Ellensburg Formation in south-central Washington and north-central Oregon is not available. This study is among the first detailed studies made for a member of the Ellensburg Formation; it provides a specific comparison with the type Ellensburg of central Washington.

Hyaloclastic sediment forms an identifiable stratigraphic interval within the Troutdale Formation that can be traced from the Bridal Veil channel to the Portland basin. Hyaloclastic sediment composed chiefly vitric sands is found interbedded with muds, sandy muds and gravels penetrated by wells in northeast Portland are correlated with the upper member of the Troutdale Formation. These beds are characteristic of the informal upper member of the Troutdale Formation in the Bridal Veil channel of the ancestral Columbia River (Tolan and Beeson, 1984) and the type area of the Troutdale Formation exposed along the Sandy River (Trimble, 1963). Fluvially deposited hyaloclastic beds within the upper Troutdale Formation are interpreted to be the result of interaction of Cascadian basaltic lavas with an ancestral Columbia River (Tolan and Beeson, 1984; Trimble, 1963). Glass clasts taken from well and outcrop samples have nearly identical trace and minor element geochemical content as determined by instrumental neutron activation analysis.

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.

Rainier, Oregon, has experienced problems in the development of residential and commercial sites, utilities, and transportation facilities as a result of slope instability. This study of slope stability at Rainier was conducted at the request of city officials.

Red Butte is located 60 km south of Vale, Oregon, about 20 km west of the Oregon/Idaho border. The butte is within the Owyhee Upland physiographic province of eastern Oregon which lies at the intersection of the Western Snake River Plain, the High Lava Plains, and the Northern Basin and Range provinces. The butte is composed of Miocene to Pliocene lacustrine and fluvial volcaniclastic sediments. The topography of the butte is controlled by silicification of the sandstones and mudstones which cap it. Silicification and hydrothermal alteration are both structurally and stratigraphically controlled. North-trending normal faults dominate the area, and show progressively less offset in younger units. Strong northwest and minor northeast faults also cut the area. Anomalous concentrations of Au, As, Sb, and Hg occur in banded quartz, quartz-adularia veins and rarely in calcite-quartz veins cutting basalts. The silicified mudstones at the butte top are generally barren. An hydrothermal explosion crater exposed on the southeast side of the butte lies at the intersection of north and northwest-trending faults. Banded quartz veins, quartz-adularia veins, and quartz-cemented breccias are exposed in the walls of the explosion crater. There is evidence of multiple brecciation events. A few mudstones exposed in the crater wall have an exhalative texture, contain pyrite des seminated along bedding, and contain trace amounts of Au. The Red Butte system developed as a hot spring venting into a lake, possibly within a caldera. Periodic influxes of air fall tuffs and coarser clastic sediments diluted accumulating fine grained clastic and chemical sediments. As hot, silica saturated fluids rose into cooler lake waters they were cooled and diluted, resulting in silica flocculation near the vents and silicification of the lake sediments as they were deposited. Faults cutting the butte acted as conduits for the hydrothermal fluids. Overpressuring, caused by silica sealing of open fractures, resulted in explosions, generally followed by resealing of the system. Simultaneous faulting, sedimentation, and hot spring activity occurred at different rates throughout the life of the system. Late in the life of the system, the local water table dropped, and the lake was replaced by a high-energy fluvial system. As the water table dropped below the surface, zones of low pH alteration and bleaching were developed above the hydrothermal vents, implying boiling at depth. The large explosion crater and bedded explosion breccia on the southeast side of the butte were formed in these last stages of hydrothermal activity.

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.

The geologic history and sedimentary till of the Tualatin Basin after Columbia River Basalt Group (CRBG) emplacement is assessed and related to groundwater characteristics. The 334 m deep HBD-1 core from the Hillsboro Airport, provides the primary information for sediment characterization and is supported by over 2400 well logs and cores, and four seismic lines. The sedimentary section above the 26 m thick paleosol on the CRBG in HBD-I is divided into two main groups: a 25 m thick section of Missoula flood sediments called the Willamette Silt overlies a 263 m thick finegrained sequence of fluvial Neogene sediments. Pollen, diatom and paleomagnetic data support dividing the Neogene sediments into a 230 m thick Pleistocene package and an underlying, 75 m thick Pliocene to upper Miocene unit. Heavy mineral and INAA chemical analyses indicate that the Neogene sediments were primarily derived from local highlands surrounding the Tualatin Valley. The structure of the top CRBG in the Tualatin Basin exhibits two provinces, a larger northern subbasin with few faults cutting the Neogene sediments above the CRBG and a smaller, more complexly faulted, subbasin south and east of the Beaverton Fault. Neogene sedimentation rates increased ten fold from the late Miocene-Pliocene to the Pleistocene, concomitant with increased basin subsidence. Comparison of Neogene basin evolution among Willamette Valley depositional centers reveals similarities among gravity and seismic reflection characters and subsidence timing between the Tualatin Basin and the northern Willamette Basin and out of phase with the Portland Basin. The Tualatin River CRBG nickpoint near the river's mouth has remained essentially unchanged since the Missoula floods filled the basin 12,700 years ago. This has kept the river from cutting back into the valley resulting in the low gradient evident today. Elevated orthophosphate levels in the upper 140 m of the Neogene sediment section indicate that the sediments are a natural source of phosphorus supplied to groundwater. Groundwater conditions in the lower Neogene sediments promote stabilization of phosphorus as vivianite. The unconfined Willamette Silt aquifer and the underlying confined Neogene aquifers are distinct, separate hydrogeologic units and usually yield less than 40 1pm.

The continental terrace west of Oregon between 43° 50'N and 44° 40' N latitude is 50 to 55 miles wide. It consists of a continental shelf, 16 to 35 miles wide, and a continental slope, 16 to 37 miles wide. The eastern portion of the shelf is a smooth, sediment covered area that slopes very gently west. The western portion of the shelf contains four rocky bank areas. The banks are topographically irregular and appear to be of structural origin. West of the banks the shelf edge occurs at depths of 71 to 90 fathoms. The continental slope extends from the edge of the shelf to the abyssal plain at depths of 1530 to 1610 fathoms. A smooth upper slope of less than three degrees extending to depths of 117 to 250 fathoms occurs north and south of Heceta Bank. West of Heceta Bank the upper slope is formed by a scarp that slopes 10° to 16° to 560 to 725 fathoms. West of the upper slope there is an area of irregular topography, including benches, hills and scarps, which extends to depths of 380 to 1100 fathoms. The lower part of the slope is formed by a north-striking scarp which is 3000 to 6000 feet high and slopes 04° to 15°. The bathymetry indicates that the continental slope was formed by step-type, block faulting. Sediments form a thin surface layer over much of: the terrace. Detrital sand, similar to the coastal sand, covers the shelf from the shoreline to approximately 50 fathoms. The deeper areas on the shelf and upper part of the slope are covered by glauconitic sands and silts on the topographic highs and olive green, clayey silts in the topographic lows. The intermediate and lower portions of the slope are blanketed with olive-green, clayey silt. In these sediments the sand fraction, which generally comprises less than five percent of the sample, is composed chiefly of diatoms, Foraminifera, Radiolaria, and sponge spicules. Sands are also present on the intermediate and deep portions of the slope. Dredge hauls west of Newport obtained sand composed mainly of detrital grains which may have been derived from an underlying friable sandstone. Thin layers of sand occur in cores from other portions of the slope. These sands may have been derived by down slope movement of sediment from the upper slope and the shelf. Sedimentary rocks of Upper Miocene and Pliocene age crop out on the shelf banks and on the continental slope. The banks consist of a sequence of diatomaceous, clayey siltstones with interbeds and concretions of calcareous siltstones. Glauconite sandstone, gray wacke sandstone, and limestone breccia are exposed along with the siltstone, on the northern end of Heceta Bank. Most of the rocks obtamed from the slope are similar to those from the shelf. Friable, wacke sandstone is exposed on the slope west of Newport. Foraminifera, the sand fraction compositions, and textural analyses all indicate that the sediment forming the siltstones from the shelf were deposited at lower littoral to lower bathyal depths. The sediments forming the rocks were deposited in one or more sedimentary basins during the Miocene and Pliocene. The subsidence continued until the. Late Pliocene when the area began to rise. The area was uplifted as much as 1000 fathoms by the Late Pleistocene when the shelf was eroded by transgressions and regressions resulting from sea level changes. The last rise in sea level resulted in the erosion of the shelf to its present form and the deposition of a thin layer of sediment. Sand is presently being deposited on the shallow areas adjacent to the continent, and silt and clay are being laid down on the slope and the sheltered areas of the outer shelf. / Graduation date: 1965

Sequence stratigraphic analysis of the southern Tyee basin, Oregon Coast Range, reveals that the lower to middle Eocene forearc and subduction zone strata comprise four depositional sequences. Sequence I (lower Umpqua Group) represents a partially subducted accretionary wedge. Sequence II (upper Umpqua Group) is a deltaic sequence that filled irregular lows and thinned over submarine highs created by intrabasin, imbricate thrust faulting. Farther north, Sequences I and II rapidly thin and distally onlap oceanic basalt islands and searnounts of the Siletz River Volcanics to form a condensed section and then thicken again northward. These sequences are overlain by a tectonism-forced transgressive systems tract deposited during an onlap caused by tectonic subsidence and dockwise basin rotation approximately 50 Ma. By middle Eocene, sandy submarine fans and wave-dominated deltas of Sequences III and IV (Tyee, Elkton, Bateman, and Spencer formations) prograded northward down the axis of the Tyee forearc basin and across the structural trend of the Umpqua Group. Organic geochemistry indicates that most units are thermally immature and contain lean, gas-prone Type III kerogen. However, some beds (coals) are sufficiently organic-rich to be sources of biogenic and thermogenic methane discovered in numerous seeps. Reservoir-quality porosities and permeabilities are identified in a few delta front and turbidite sandstones of Sequences II and III, although zeolite, clay, and quartz diagenesis has destroyed most potential sandstone reservoirs. The overall hydrocarbon potential of the basin is moderately low. Several requirements f or commercial accumulations of hydrocarbons, however, probably exist locally within and adjacent to the basin. Three speculative petroleum systems are identified. The first includes the southern part of the basin near the border with the Mesozoic Klamath Mountains and is related to a proposed subduction zone maturation mechanism along thrust faults. The second is centered in the northern part of the study area and may be associated with basin-center gas in an overpressured zone. The third occurs near the eastern border of the basin where maturation is related to local heating by sills and migration of hydrothermal fluids associated with mid- Tertiary volcanism in the Western Cascade arc. / Graduation date: 1995

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.