Lummi and Eliza Islands form the northeast part of the San Juan Island group in northwest Washington. Lummi is a long, narrow island characterized by a rocky, mountainous southern half and a low, northern half. Eliza is a small T-shaped island southeast of Lummi Island. Lummi Island is underlain by igneous, metamorphic, and sedimentary rocks of Paleozoic to Lower Cenozoic age. The oldest rocks are believed to be those of the Lummi Island Metamorphic and Igneous Complex which form a small, isolated knob in the middle of the island. These are hornblendic rocks, intruded by quartz-albite rocks and cut by numerous aplite and lamprophyric dikes. The age and origin of these rocks is unknown but they may be older "basement" rocks brought to their present position through faulting. Shale, graywacke and granule conglomerate of the Carter Point formation (Paleozoic or Mesozoic) underly most of southern Lummi Island. These rocks show all the characteristics of the typical "graywacke suite" such as great thickness, clastic character, rhythmic bedding, and graded bedding. The only fossils found were a few carbonized plant stems imbedded in fine-grained graywacke. The rocks forming the bedrock of Eliza Island may be a more metamorphosed equivalent of these. Overlying the Carter Point formation on the southeast side of Lummi Island and directly underlying the sandstone at the northern end are the Reil Harbor volcanics. Although they occur in five isolated outcrops these rocks are grouped together on the basis of lithology and outcrop features. In contrast to an earlier intrusive interpretation these occur as submarine (pillow) lavas and interbedded breccia with tuffaceous - argillaceous rocks rather than as dikes or sills. The lavas of some of the outcrops are spilitic and in most cases are extremely altered. The breccias are dominantly volcanic - clastic types which show some reworking. The age of the volcanics and underlying Carter Point formation is unknown; however, interbedded sedimentary rocks contain radiolarian tests suggestive of Mesozoic age. Northern Lummi Island is underlain by plant-bearing lithic-feldspathic arenites and conglomerates of the Chuckanut formation (Paleocene). These are believed to have a continental fluviatile origin on the basis of: absence of marine fossils; conspicuous amounts of hematite imbedded in the sandstone; moderate sorting and rounding; apparent large-scale heterogeneity evidenced by internal structures such as prominant cross bedding and cut - fill structures, and the dominance of sandstone and conglomerate facies. The Carter Point formation and the overlying volcanics on the southeast side of Lummi Island strike N 40 W and dip 45 degrees NW. Drag folds suggest that southern Lummi Island represents the eastern limb of a northwest plunging anticline. The Chuckanut formation and the underlying Reil Harbor vol-canics at the north end of the island have been folded into three synclines which strike northwest-southeast and plunge gently northwest. During the Pleistocene, northern Lummi Island was blanketed with glacial drift while the higher knobs here and the rocks of southern Lummi were grooved, polished or eroded by the glaciers. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Northwest-southeast Miocene uplift with subsequent erosion has bared rocks of Paleozoic, Mesozoic and Cenozoic ages in the western Skagit Delta region. Pleistocene glaciation followed by recent alluviation has buried much of the bedrock leaving rock exposures only on islands in Skagit Bay or as low hills projecting through the alluvium. A low-grade metamorphosed sequence of graywacke, conglomerate, breccia, argillite, and spilite, all of probable Paleozoic age, make up the oldest rocks of the area. Mesozoic rocks, composed of graywacke and argillite, crop out in hills northwest and southeast of the town of La Conner. The contact between Paleozoic and Mesozoic rocks is not exposed but an unconformity is believed to separate the two. No fossils were found in either sequence. Because Paleozoic(?) and Mesozoic(?) rocks can not be correlated with any other known units, new names have been assigned by the writer. The Paleozoic(?) sequence is called the Goat Island Formation and the Mesozoic(?) sequence is called the La Conner Formation. Along the North Fork of the Skagit River a conglomerate sequence with interbedded sandstones and siltstones makes up disconnected, low, tree covered hills. Lithologically this sequence can be divided into two formations separated by a probable unconformity. Microfossils in the upper unit indicate a Lower Tertiary age but definite correlation with described units in other areas is not possible. The lower formation is here designated the Delta Rocks Formation while the upper is called the Ika Formation. Serpentinites make up the whole of Goat Island and adjacent parts of Fidalgo Island. On southern Fidalgo Island another serpentinite encloses an unusual hydrothermal vein containing calcite, celestite, and strontianite. These ultrabasic rocks are considered part of the Fidalgo Formation and are of probable Triassic age. A small outcrop of marine Pleistocene occurs at the east end of Goat Island and contains an assemblage of invertebrates. Vashon till and outwash cover most of Fidalgo Island and Pleasant Ridge. Pre-Tertiary deformation has been intense with both Paleozoic and Mesozoic sequences folded, sheared and faulted. Cenozoic deformation has been restricted to Miocene concentric folding. Axes of both pre-Tertiary and Tertiary folding are aligned essentially east-west. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Red Mountain formation (Lower Pennsylvanian?) of the Chilliwack group (Carboniferous) was mapped in five areas of northwestern Washington. Except for a few outcrops of Devonian strata, the formation represents the oldest known sedimentary rocks in this region. It consists primarily of argillite, graywacke, chert, tuff and limestone, and is overlain by conglomerate of the Black Mountain formation (Lower Permian). The base of the formation is nowhere exposed. Correlation of the Red Mountain formation is dependent essentially on the presence of large crinoid stems, foraminifera, and similarity of stratigraphic relationships. Limestones of the upper portion of the formation represent deposition under conditions of marked tectonic stability, whereas enclosing strata are indicative of deposition in an unstable, subsiding realm. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Horse Heaven Hills uplift in south-central Washington consists of distinct northwest and northeast trends which merge in the lower Yakima Valley. The northwest trend is adjacent to and parallels the Rattlesnake-Wallula alignment (RAW; a part of the Olympic-Wallowa lineament). The northwest trend and northeast trend consist of aligned or en echelon anticlines and monoclines whose axes are generally oriented in the direction of the trend. At the intersection, folds in the northeast trend plunge onto and are terminated by folds of the northwest trend.

The Snoqualmie pass area lies about 50 mi (80 km) east of Seattle, Washington, along the crest of the Cascade Range. Five stratified units, forming a composite section over 22,000 ft (6700 m) thick, are recognized in the area. They were deformed and later intruded by granodiorite and quartz monzonite porphyry of the Snoqualmie batholith (middle Miocene). The oldest unit, the Denny Formation (Permian), 7000 ft (2100 m) thick, consists of interstratified basalt, andesite and dacite volcanic rocks and limestone and chert beds. This formation is unconformably overlain by a thick conformable sequence of early Tertiary strata which are subdivided, from oldest to youngest, into the Guye Formation, Mount Catherine Tuff, and Naches Formations (Paleocene to early Oligocene). The Guye Formation, 6500 ft (1980 m) thick, consists of carbonaceous mudstone, quartzofeldspathic siltstone and sandstone, and chert conglomerate. The Mount Catherine Tuff, 900 ft (274 m) thick, consists of interstratified dacitic and rhyolitic crystal-vitric welded tuff. The Naches Formation, more than 6000 ft (1830 m) thick, is composed of carbonaceous mudstone and quartzofeldspathic siltstone and sandstone with interstratified andesitic lava and pyroclastic rock. The Denny Mountain Formation, informally named, 1800 ft (550 m) thick,(Oligocene or early Miocene) overlies the Guye Formation along a major angular unconformity. This unit consists of interstratified dacitic and andesitic tuff, volcanic breccia, and intercalated andesitic lava. The rocks of all stratified formations except the Denny Mountain Formation were deformed at different times before emplacement of the Snoqualmie batholith. During batholithic emplacement, four stages of deformation are recognized: (1) development of an anticline in the Guye, Mount Catherine Tuff, and Naches Formations, (2) break-up of this anticline and downfaulting of limbs with displacements up to 2 mi (3.2 km), (3) uplift of blocks of the Denny Formation and juxtaposition of these with younger formational units, and (4) uplift of additional blocks of the Denny Formation along trends that cut obliquely across stratigraphic contacts and previous structural trends. Intrusion of the Snoqualmie granodiorite and quartz monzonite porphyry into limestone beds of the Denny Formation has formed local deposits of skarn containing principally magnetite and lesser amounts of chalcopyrite.

Over 1150 m of middle to late Eocene nonmarine arkose, lithic arkose, mudstone, and siltstone, referred to here as the Chambers Creek beds, are int~r.stratified with, and overlain by over 1600 m of late Eocene-Oligocsne(?) andesitic volcaniclastic and subordinate volcanic rocks assigned to the Ohanapecosh Formation, in a dissected structural high in the southern Washington Cascade Range, about 18 km south-southeast of the town of Packwood.

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.

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 Wind River gold prospect is located in TSN, R7E of Skamania County, Washington, and is an epithermal gold-quartz vein system hosted in volcanic rocks of the Ohanapecosh Formation, a late Eocene to middle Oligocene unit of calcalkaline chemical composition. Andesitic pyroclastic rocks of the Ohanapecosh Formation are the host of mineralization in the study area, and form the lowest of several stratigraphic subunits. These pyroclastic rocks are overlain by two sequences of lava flows which cap the ridges and are folded by an anticlinal warp over the length of Paradise Ridge, plunging gently to the southeast. Toward the west, the number of flows decreases and the proportion of intercalated pyroclastic rocks increases. Numerous dikes cut the pyroclastic rocks at the Wind River prospect. Geochemical data show these dikes to have been feeders for the overlying lava flows. Differing degrees of alteration of the dikes relative to the most intensely altered pyroclastic rocks which they cut indicates a complex history of overlapping hydrothermal and volcanic activity at the prospect.

No description available.