Graduation date: 1953

The Coyote Hills are located about 46 kilometers north-northwest of Lakeview, Oregon, within the Basin and Range physiographic province. These hills represent a complex volcanic center of bimodal calc-alkaline igneous activity. The oldest rocks recorded in the Tertiary succession are horn-blende- bearing andesite and aphanitic basalt flows, laharic breccias, conglomerates, tuffaceous sandstones, and lithic wackes of the late Eocene to early Oligocene Lower Andesite formation. During middle to early late Oligocene time, voluminous eruptions of predominately basaltic andesite formed a large shield volcano. This unit, the Upper Basalt formation, was followed, after a short hiatus, by the Coyote Hills rhyolite of late Oligocene to early Miocene age. The Coyote Hills rhyolite represents a complex spectrum of multi-phase silicic volcanism and comagmatic near-surface plutonism. Magma compositions varied from dacite to rhyolite and include lava flows, volcanic plugs, a flow dome complex, and a hypabyssal quartz monzonite intrusion. Volcanic activity that post-dates formation of the bimodal Coyote Hills complex culminated with the lower slopes of the shield volcano onlapped by the middle Miocene Steens Basalt, the late middle to early late Miocene Plush tuff, and the late Miocene to early Pliocene Upper basalt. A prominent northwest and northeast-trending fault and fracture system formed after emplacement of the Coyote Hills rhyolite, and as early as late Oligocene to early Miocene in time. Basin and Range faults post-date the Steens Basalt and have caused some minor displacement of the younger rocks. Penecontemporaneous with silicic volcanism of the Coyote Hills rhyolite was a period of hydrothermal activity. Fluids ascended favorable structures, altered the surrounding country rocks, and deposited minor quantities of epithermal gold-silver-copper-mercury-molybdenum(?)- lead(?), and zinc(?) in structurally controlled quartz-pyrite veinlets and as disseminations. Because of the association of mineralization with silicic volcanics in time and space, it is concluded that the two processes were genetically related. The hydrothermal system in the Coyote Hills is related to the late stages of silicic volcanism. Evidence for a genetic relation includes the close association of rock type, and chemical and mineral zonations within the district. Geological and geochemical evidence that includes rock type and alteration patterns, and mineral and trace element zonations, collectively suggest that only the highest level of the hydrothermal system has been exposed. It is entirely possible that a large vein or disseminated-type deposit containing both base and precious metals is present at depth. / Graduation date: 1981

xi, 60 p. : ill. (some col.), maps (some col.). A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / I present an alternative approach to determine the magnitude and direction of extension in the Basin and Range Province at the north end of Summer Lake basin using GIS techniques. Offset across 161 faults and tilting of 56 fault blocks were estimated to calculate extension as a function of azimuth in this area. The orientation of a representative set of slickenlines was collected in the field to assign average values for the GIS analysis. Azimuthal variation of extension is consistent with a strain ellipse indicating plane strain with extension of 1.5 to 5.5 percent along the maximum extension direction of N75E and no extension along the minimum N15W axis. Blocks tilt on average 60° from the maximum extension direction, suggesting the underlying detachment dips -N15E. This technique allows strain associated with the numerous small faults to be added to the sparse large faults for a complete regional analysis. / Committee in Charge: Dr. Ray Weldon, Chair; Dr. David Schmidt; Dr. Marli Miller

Stone stripes are linear accumulations of rock debris separated by finer material and oriented down the steepest available slope. In north central Oregon, the stone stripes are composed of basalt fragments and occur where the soil mantle averages less than 1 m in depth. They are best developed in areas of higher elevation, usually from about 900 to 1100 m, and are most prominent on convex to straight slopes of 15 to 30 degrees. The stripes vary from a few meters to over 150 in length, and their widths range from 0.3 to over 3 m. The depth of the stone stripes ranges from 20 to over 65 cm. Morphological investigations of stone stripes in north central Oregon reveal that: (1) surface rock orientation is not very strongly related to slope direction or gradient; (2) stripe depth does not seem to be connected to width of the stripe nor to position on the slope; (3) vertical sorting occurs in a rock size ratio of about 5:3:2 from surface, to middle, to base; (4) the introduction of cattle has resulted in considerable stripe modification; and (5) vegetation encroachment and infilling with soil are stabilizing the stripes from the edges inward. The stone stripes found throughout north central Oregon are of such a size and magnitude that they cannot be adequately explained by geomorphic processes currently operating in the region. Although these processes are sufficient to cause some stripe movement and modification, the initial striped patterns were probably developed under periglacial conditions during the cooler, moister phases of the Quaternary. Evidence which lends credence to a cold climate origin for these stone stripes includes: (1) other forms of patterned ground, i.e." sorted circles, nets, and polygons; (2) soil mounds; (3) talus slopes; (4) terracettes; (5) convex slopes; and (6) stripe stabilization through vegetation encroachment, soil infilling, and heavy lichen growth.

The Willamette Pass area is situated at the intersection of two hypothesized structural features, the Western Cascade-High Cascade boundary and the Eugene-Denio lineament. It is of interest due to its designation by the U.S. Department of the Interior as a Known Geothermal Resource Area.

This thesis is a study of the geology of the southeast quarter of the Bone Mountain Quadrangle. The bedrock geology mapped includes about 56 square miles.The Klamath Mountain and Coast Range Provinces of southwestern Oregon are represented in the area. Rocks in the area include the Rogue, Dothan Riddle, Days Creek, upper member of the Umpqua and Tyee Formations. The ages of these rocks range from Late Jurassic to middle Eocene. Late Jurassic ultramafic and mafic intrusive rocks associated with the Rogue Formation occur in the Klamath Province. The metavolcanics of the Rogue Format ion and an associated linear belt of mafic intrusive rocks have been thrust northwestward over the Late Jurassic-Early Cretaceous Riddle Formation. Ultramafics occur along the fault. Graywackes, siltstones, and conglomerate lenses of the Dothan Formation have been downfaulted relative to the Rogue Formation along a southeasterly dipping fault. The Dothan Formation is steeply dipping to the southeast and contains numerous folds inclined to the northwest. The genetic relationships of faulting are problematic. The Myrtle Group conglomerates, siltstones and sandstones are greatly folded and dip to the northwest. Internal structures are intense and diagnostic fauna of Late Jurassic to Early Cretaceous age indicates separate lithologic units of shallow water deposition. Tertiary sedimentary rocks include the upper member of the Umpqua and Tyee Formations of middle Eocene age. The formations are gently dipping to the northwest with coal beds and fauna indicating a near shore depositional environment.

The North Fork stock is a composite intrusive body of Late Jurassic-Early Cretaceous age which outcrops in the Blue Mountains of northeastern Oregon. The upper 600 m of the intrusion are exposed over an area of approximately 36 km squared along the canyon walls of the North Fork of the John Day River in Grant and Umatilla counties. The stock intrudes metasediments, metavolcanics, and metagabbros associated with the Permian-Triassic Elkhorn Ridge Argillite. Contact metamorphism of the Elkhorn Ridge Argillite is developed to the hornblende-hornfels facies throughout most of the exposed area of this unit in the study area. The contact aureole of the North Fork stock extends away from the intrusive margins and ultimately grades into regionally metamorphosed greenschist- and amphibolite facies rocks. The metamorphic rocks exhibit a pronounced regional trend of foliation which is disrupted where it intersects intrusive contacts at steep angles.

The geology of the Castle Rock area aids in the understanding of Cenozoic volcanic stratigraphy and structures in an area where these volcanic rocks thin near the margins of the pre-Tertiary basement rocks and structural trends are overlapping. The Castle Rock area is unique in several aspects and is important in understanding and interpreting the geology in adjacent regions which have all been studied, at least on a regional basis. Intrusive ash-flow bodies of the Dinner Creek Ash-Flow Tuff, well-exposed sections of complexly interstratified volcanic rocks and well-exposed faults, and of high amount of erosional relief are features which make this area a unique and important addition to the understanding of the stratigraphy of eastern Oregon.

Field work in the southeast quarter of the Dutchman ·Butte Quadrangle, which lies within the Klamath Mountains geomorphic province of southwestern Oregon, was completed during the summers of 1973 and 1974. The objectives of the study were fourfold: (1) to produce a geologic map of the southeast quarter of the Dutchman Butte Quadrangle, (2) to determine the nature of the contact between the Dothan and Rogue formations, (3) to construct a stratigraphic column of the Dothan Formation in the area, and (4) to attempt to determine the nature of the deformation occurring in the area.

The original purpose of this study was a detailed structural analysis of the Jurassic Otter Point Formation in order to determine if the Canyonville Fault Zone, which forms the northern boundary of the Klamath Mountains in the Riddle - Canyonville area (Benson and Perttu, 1980), extends westward to the coast and, if possible, to characterize the structure of the Otter Point Formation. Further, a detailed examination of the structural and stratigraphic relationships between the Otter Point Formation and the Eocene Roseburg and Lookingglass Formations was to be performed in an attempt to determine the tectonic history of the area.