Abstract The rocks of the Olympic Peninsula and their counterparts to the south in the Coast Ranges of southern Washington and Oregon comprise one or more Tertiary accreted terranes which are part of the collage of terranes that make up most of northwestern Washington (Coney and others, 1980). The Olympic Mountains in Olympic National Park are one of the best examples of an accreted subduction complex of Tertiary age found in the conterminous United States. The Hurricane Ridge Road, south of Port Angeles, crosses parts of the complex where the observercan see spectacular outcrops of pillow basalt, pelagic interbeds, and submarine fan deposits, as well as the complex structures engendered during accretion of these rocks to the continental margin of North America. Terrane (or tectonostratigraphic terrane) as used in this guide refers to a discrete structural block with stratigraphic and/or structural coherence; it is separated from its neighboring terranes by faults. Moreover, a large terrane that was coherent during its later geologic history, can be subdivided into smaller terranes whose earlier geologic histories differ.
In the high mountain area of the Olympic Mountains, Washington, there are many troughlike depressions on and essentially parallel to ridge tops. The troughs are mostly developed on rocks with strong planar anisotropy: slate, sandstone, and phyllite. Similar features in Europe, Japan, and New Zealand have been variously ascribed to erosion, slow movement along deep-seated shear planes, creep, and tectonic movements. In the Olympics, many depressions parallel structure; one wall is steeply dipping rocks, the other shattered, gently dipping rocks. These depressions seem to be the gaps left between undisturbed steeply dipping rocks and beds or cleavage bent valley-ward by creep. A few troughs may be the result of slow down-slope movement along deep-seated shear planes; this is a favorite explanation of eastern European workers. The Olympic ridge-top depressions testify to the importance of gravity in the degradation of high mountains carved from weak rocks.
Research Article| January 01, 1984 Ages and stratigraphy of lower and middle Tertiary sedimentary and volcanic rocks of the central Cascades, Washington: Application to the tectonic history of the Straight Creek fault R. W. TABOR; R. W. TABOR 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar V. A. FRIZZELL, JR.; V. A. FRIZZELL, JR. 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar J. A. VANCE; J. A. VANCE 2University of Washington, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar C. W. NAESER C. W. NAESER 3U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information R. W. TABOR 1U.S. Geological Survey, Menlo Park, California 94025 V. A. FRIZZELL, JR. 1U.S. Geological Survey, Menlo Park, California 94025 J. A. VANCE 2University of Washington, Seattle, Washington 98195 C. W. NAESER 3U.S. Geological Survey, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1984) 95 (1): 26–44. https://doi.org/10.1130/0016-7606(1984)95<26:AASOLA>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation R. W. TABOR, V. A. FRIZZELL, J. A. VANCE, C. W. NAESER; Ages and stratigraphy of lower and middle Tertiary sedimentary and volcanic rocks of the central Cascades, Washington: Application to the tectonic history of the Straight Creek fault. GSA Bulletin 1984;; 95 (1): 26–44. doi: https://doi.org/10.1130/0016-7606(1984)95<26:AASOLA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract In the central Cascade Range of Washington, three structural blocks of early Tertiary sedimentary and volcanic rocks help to define the position and history of the southern segment of the Straight Creek fault. East of the fault, in the Teanaway River block, the early Eocene fluviatile feld-spathic sandstone of the Swauk Formation is interbedded with largely dacitic volcanic rocks of the Silver Pass Volcanic Member. Zircon fission-track ages on the Silver Pass are about 52 m.y. Overlying the tightly folded Swauk and Silver Pass is the Teanaway Formation, a gently dipping accumulation of basalt, andesite, rare dacite, and rhyolite that yields middle Eocene (about 47 m.y.) whole-rock K-Ar ages. Conformably overlying the Teanaway is the Roslyn Formation, a coal-bearing fluviatile feld-spathic sandstone of probable middle to late Eocene age.The late Eocene and Oligocene(?) Naches Formation, exposed west of the Straight Creek fault in the Cabin Creek block, is rich in fluviatile feldspathic sandstone and rhyolite flows and tuffs in its lower part but grades upward into a sequence dominated by basalt but with some andesite. The basal Guye Sedimentary Member of the Naches Formation underlies and is interbedded with the Mount Catherine Rhyolite Member in the Snoqualmie Pass area. On the basis of zircon fission-track ages on silicic tuffs and whole-rock K-Ar ages on basalt, the basal part of the Naches is about 40 to 44 m.y. old. The formation is tightly folded and complexly faulted along the Straight Creek fault.The Straight Creek fault intersects the Olympic-Wallowa lineament in the strongly deformed Manastash River block. In this block, fluviatile coal-bearing feldspathic sandstone of the Manastash Formation is overlain by principally dacitic volcanic rocks of the Taneum Formation. Overlying the Taneum is the basalt of Frost Mountain. We correlate this threefold sequence, feldspathic sandstone-dacite-basalt, with the sequence in the Teanaway River block.Small patches of rhyolitic ash-flow tuff, dated at 33 m.y. (late Oligocene) and interbedded feldspathic sandstone overlie the Roslyn and Teanaway Formations in the Teanaway River block and are probably correlative with the late Oligocene Wenatchee Formation exposed in the Chiwaukum graben east of the Teanaway River block as well as with the late Oligocene volcanic rocks (30 m.y.) along the Cascade crest to the southwest. These latter rocks are little deformed and unconformably overlie the Naches Formation.The ages and depositional record in the three blocks indicate a Tertiary history of dominantly vertical movement along the Straight Creek fault and its southeasterly splays that merge with the Olympic-Wallowa lineament. The horst-and-graben structure of the blocks, as well as enechelon fold axes in the Swauk Formation, suggests some post–early Eocene, right-lateral shear along the fault, although there is no direct evidence of lateral offset. Vertical movement, significant since early Eocene Swauk deposition, followed late Eocene Naches deposition but tapered off by late Oligocene time and ceased by Miocene time, when the fault was intruded by the 25-m.y.-old Snoqualmie batholith and other plutons. However, structures with Olympic-Wallowa lineament trends appear to have influenced folding of the Miocene Yakima Basalt Subgroup. 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The northern part of the North Cascades National Park in northern Washington is north of the Skagit River between Mount Shuksan on the West and Ross Lake on the east. The area occupies approximately 500 square miles of steep mountains and thickly forested valleys centered on the precipitous Picket Range. Old metamorphic rocks and young volcanic and sedimentary rocks are intruded by large masses of granitic rocks that together form a diverse, complicated, but well-exposed geologic section. The granitic rocks are the most abundant in the area; they intrude most of the other rocks, and they separate one suite of rocks in the eastern part of the area from a second suite in the western part. In the eastern part of the area, the oldest rocks are the Custer Gneiss of McTaggart and Thompson, a thick sequence of biotite and hornblende gneisses and schists. We have divided these rocks into three generalized units: light-colored gneiss, banded gneiss, and amphibole-rich gneiss. To the northeast of these rocks lies a metagabbro. This rock type is complex and is made up of several types of gabbro, diorite, amphibolite, ultramafic rocks, and quartz diorite that crop out along the Ross Lake fault zone. To the northeast of these rocks and also along the Ross Lake fault zone is the phyllite and schist of Ross Lake. These rocks are the highly sheared and metamorphosed equivalents of the plagioclase arkose and argillite sequence of Jurassic and Cretaceous age that is so widespread on the east side of Ross Lake. The Cretaceous Hozomeen Group of Cairnes lies along Ross Lake northeast of the phyllite and schist and consists mainly of slightly metamorphosed greenstones with subordinate chert and phyllite. The phyllite in this unit is similar to that in the underlying phyllite and schist of Ross Lake with which it appears to be interbedded. The youngest rocks in the eastern part of the area are the Skagit Volcanics a thick sequence of welded tuff-breccia with some flows and air-laid tuffs. These rocks, which are probably early Tertiary in age, overlie the Hozomeen Group and the Custer Gneiss along the Canadian border. In the western part of the area the oldest rocks are greenschist and phyllite of Mount Shuksan. These fine-grained foliated and crinkled rocks commonly contain narrow lenses or layers of quartz. They are unconformably overlain by the Chuckanut Formation in the southern part of the area. This formation, which is of Paleocene and Late Cretaceous age, is made up mainly of gently dipping plagioclase arkose with some interbedded black argillite and conglomerate. The Hannegan Volcanics overlie the Chuckanut in the northern part of the area and the greenschist and phyllite of Mount Shuksan in the central part. The Hannegan Volcanics which are of early Tertiary age, consist principally of air-laid volcanic breccias and tuffs, but also include some flows and one small porphyry stock. The Chilliwack composite batholith consists of several types of granitic rocks, which were intruded at different times in the Tertiary. The two principal rock types are granodiorite and quartz diorite, but small bodies of quartz monzonite diorite, and alaskite are found in many parts of the area. Contacts between the various rock types may be either abrupt or gradational. All rocks of the Chilliwack batholith are younger than the other rock types except the Skagit and Hannegan Volcanics, which are in part younger than rocks of the batholith. At least two periods of deformation are indicated by the tight folding of the older Custer Gneiss and the greenschist and phyllite of Mount Shuksan and the gentle folding of the younger Chuckanut Formation. At least three periods of faulting occurred, one before and two after the intrusion of the Chilliwack batholith. The two largest fault structures are the Ross Lake fault zone and a long northeast-striking fault that extends for 20 miles from Mount Shuksan down the Chilliwack Valley. The Ross Lake fault zone is pro
This map is an interpretation of a 6-ft-resolution lidar-derived digital elevation model combined with geology by Derek B. Booth and Kathy Goetz Troost. Field work by Booth and Troost was located on the 1:24,000-scale topographic map of the Vashon and Des Moines 7.5' quadrangles that were published in 1997 and 1995, respectively. Much of the geology was interpreted from landforms portrayed on the topographic maps, supplemented by field exposures, where available. In 2001, the Puget Sound Lidar Consortium (see http://pugetsoundlidar.org/) obtained a lidar-derived digital elevation model (DEM) for Vashon Island and the Des Moines quadrangle. For a brief description of lidar and this data acquisition program, see Haugerud and others (2003). This new DEM has a horizontal resolution of 6 ft (1.83 m) and mean vertical accuracy of about 1 ft (about 0.3 m). The greater resolution and accuracy of the lidar DEM facilitated a much-improved interpretation of many aspects of the surficial geology, especially the distribution and relative age of landforms and the materials inferred to comprise them. Booth and Troost were joined by Tabor to interpret the new lidar DEM but have done no futher field work for this map. This map, the Vashon quadrangle and selected adjacent areas, encompasses most of Vashon Island, Maury Island, and Three Tree Point in the south-central Puget Sound. One small area in the Vashon quadrangle on the east side of Puget Sound is excluded from this map but included on the adjacent Seattle quadrangle (Booth and others, 2005). The map displays a wide variety of surficial geologic deposits, which reflect many geologic environments and processes. Multiple ice-sheet glaciations and intervening nonglacial intervals have constructed a complexly layered sequence of deposits that underlie both islands to a depth of more than 300 m below sea level. These deposits not only record glacial and nonglacial history but also control the flow and availability of ground water, determine the susceptibility of the slopes to landslides, and provide economic reserves of sand and gravel. The islands are surrounded by channels of Puget Sound, some as deep as the islands are high (>600 ft (~200 m)). The shorelines provide many kilometers of well-exposed coastal outcrops that reveal abundant lithologic and stratigraphic details not ordinarily displayed in the heavily vegetated Puget Lowland.
The Snoqualmie Pass quadrangle lies at the north edge of a Tertiary volcanic and sedimentary cover, where the regional structural uplift to the north elevated the older rocks to erosional levels. Much of the quadrangle is underlain by folded Eocene volcanic rocks and fluvial deposts of an extensional event, and these rocks are overlain by Cascade arc volcanic rocks: mildly deformed Oligocene-Miocene rocks and undeformed younger volcanic rocks. Melanges of Paleozoic and Mesozoic rocks are exposed in structural highs in the northern part of the quadrangle. The quadrangle is traversed north to south by the Straight Creek Fault, and the probably partially coincident Darringon-Devils Mountain Fault. A rich Quaternary stratigraphy reveals events of the Frazer glaciation.
Paleogeographic reconstructions for Oregon and Washington during Paleogene time illustrate a major transition from a dominantly compressional (prior to middle Eocene time) to an extensional tectonic regime. This transition resulted in the development of three phases of Paleogene basin evolution in the United States Pacific Northwest. During the initial phase, basins formed along the continental margin during collision of oceanic islands. Sediments in these basins were derived from nearby orogenic highlands. The second phase of basin development began in middle Eocene time and consisted of rapid subsidence of individual basins that formed within a broad forearc region. Nonmarine basins that formed during this phase were caused by extension possibly associated with transcurrent faulting. Rapid sedimentation in both marine and nonmarine basins during this time consisted dominantly of sandstone derived from Cretaceous plutonic sources far to the east. The final stage of basin development was the modification of previous basin configurations by the growth of the Cascade volcanic arc, which was initiated in early Oligocene time. The rising Cascade Range diverted streams carrying eastern-derived material, thereby reducing overall sedimentation rates in the coastal basins and providing a local source of volcanic detritus.
