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A geologic study of the Parrett Mountain area, located twenty miles (32 kms) south-southwest of Portland, Oregon, was initiated by the Oregon Water Resources Department. The main goal was to create a stratigraphic and structural model of Parrett Mountain in order to better understand the local basalt aquifers present there. Previous geologic studies of the area revealed the mountain to be composed of Columbia River basalt. Field mapping and hand lithologic and geochemical analyses allowed the basalt to be subdivided into eleven basalt flows. These flows are as follows: (from oldest to youngest) the Wapshilla Ridge (WpR) , the Ortley-Grouse Creek (undifferentiated) (OGC), the Umtanum (U), the Winter Water (WW), and the Sentinel Bluffs (SB) basalt units of the Grande Ronde Basalt and the Ginkgo (Gk) flow of the Frenchman Springs Member of the Wanapum Basalt. All the basalt flows were found to be laterally extensive throughout the entire area creating a stacked pancake-layered structure. Thickness variations in the Wapshilla Ridge, Ortley- Grouse Creek and Ginkgo basalt flows reflect paleotopographic relief present during the emplacement of the basalt flows. Sedimentary interbeds appear to be highly localized, occurring sporadically throughout the entire area stratigraphic column. Faults were identified based on geologic map compilation, cross section analysis, and topographic linear features. They trend N-S, E-W, NE and NW and are believed to dissect the entire basalt column. All faults have been designated with a normal sense of displacement, except those known to be thrust or r~verse. Cross-cutting relationships suggest the NS-trending faults are the youngest and the NWtrending faults are the oldest. The faulting created twenty-four separate basalt blocks, each represented by a distinct strike and dip. Flowtop morphology, stratigraphic layering, and the local geologic structures influence local groundwater systems. All flow boundaries yield water to at least one well on the mountain. The most commonly used aquifers are the U/OGC boundary, interflow zones within the OGC, the OGC/WpR boundary and permeable zones within the WpR. Faulting is believed to promote recharge of the groundwater systems by increasing the vertical infiltration of percolating precipitation through the highly fractured fault zone.

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. High grade metamorphic rocks belonging to the Shuswap Complex crop out in the southern Okanagan region of British Columbia. An area of these rocks previously mapped by Bostock (1940) as the Vaseaux Formation was studied. A local structural lithologic succession is postulated comprising. of four units, whose present thicknesses are variable but do not generally exceed 100 ft. Four phases of penetrative deformation are recognized. The first, recumbent isoclinal with northerly trends, was succeeded by a second recumbent isoclinal phase, with northwesterly trends. Phase 3 produced easterly trending upright close folds, and later open upright northwesterly and northerly trending folds characterize phase 4. Five intrusive events punctuate the structural history. Two precede phase 2 and three postdate it. Rb-Sr isotopic dating of these intrusions provides a Tertiary age for phase 4, and a pre-mid-Jurassic age for phase 2. The existence of a mid-Jurassic metamorphism can also be inferred from the isotopic data. Based on interpretations of data from adjacent areas it appears that phases 1, 2 and 3, and related events are all facets of the Lower Mississippian Caribooan Orogeny. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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The series Californicae is a natural grouping of Iris species native to Oregon, Washington and California. Natural and experimental hybridization is characteristic of the series which has led to confusing taxonomies for some species. Populations of species belonging to this series and found on the northwestern slopes of the Siskiyou Mountains cf southwestern Oregon and adjacent California were investigated. Methods used were numerical classification techniques for morphological characters including both discriminant and K-means cluster analyses and a chemotaxonomi c analysis of flavonoid pigments using thin layer chromatography.

The Ellensburg Formation, preserved in the Nile basin 50 km northwest of Yakima, Washington, consists of a series of middle to late Miocene epiclastic and pyroclastic rock assemblages rich in porphyritic hornblende-biotite dacite. Geochemical, petrographic, and stratigraphic correlations indicate that Old Scab Mountain, a dacite porphyry intrusion, located at the western margin of the basin (lat. 46°53'30", long. 121°13'00"), is the probable source for much of the upper Ellensburg volcaniclastic material in the basin. The dacite intrusion exposed at Old Scab Mountain was emplaced at depths of 1 to 3 km and underlaid a now eroded volcanic edifice. This volcanic center is interpreted to have been active during the time of deposition of the upper Ellensburg Formation. AK-Ar age of 8.75 ± 0.20 Ma for an adjacent sill of similar dacite suggests an age for Old Scab Mountain between 9 to 7 Ma (Smith, 1988a). This age corresponds with the upper Ellensburg Formation which stratigraphically overlies Grande Ronde Basalt lava flows of the Columbia River Basalt Group, within the basin. Stratigraphic reconstruction of the Nile basin deposits indicates a dome collapse eruptive style. Progressive dome growth was punctuated by short-lived eruptions resulting in dome collapse and deposition of debris-avalanche and lahar deposits. These deposits were remobilized by fluvial processes which generated thick conglomerates and interstratified volcanic sandstones. Upper Ellensburg deposits and dacite of Old Scab Mountain are calc-alkaline and medium-K in composition. Silica content ranges from 53 to 67 weight percent Si02 for upper Ellensburg deposits and 66 to 67 weight percent Si02 for dacite of Old Scab Mountain. Older deposits composing the lower Ellensburg Formation are interbedded with and underlie the Grande Ronde Basalt. The lower Ellensburg deposits are typically more tholeiitic, range from 56 to 74 weight percent Si02 , and show slightly higher trace element concentrations than the upper Ellensburg deposits. These deposits were possibly derived from other dacite centers located near the headwaters of the adjacent Naches basin.

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.