Northern Cascade Mountains Research Articles

Eocene dike orientations across the Washington Cascades in response to a major strike-slip faulting episode and ridge-trench interaction

Abstract The northern Cascade Mountains in Washington (USA) preserve an exceptional shallow to mid-crustal record of Eocene transtension marked by dextral strike-slip faulting, intrusion of dike swarms and plutons, rapid non-marine sedimentation, and ductile flow and rapid cooling in parts of the North Cascades crystalline core. Transtension occurred during ridge-trench interaction with the formation of a slab window, and slab rollback and break-off occurred shortly after collision of the Siletzia oceanic plateau at ca. 50 Ma. Dike swarms intruded a ≥1250 km2 region between ca. 49.3 Ma and 44.9 Ma, and orientations of more than 1500 measured dikes coupled with geochronologic data provide important snapshots of the regional strain field. The mafic Teanaway dikes are the southernmost and most voluminous of the swarms. They strike NE (mean = 036°) and average ~15 m in thickness. To the north, rhyolitic to basaltic dikes overlap spatially with 49.3–46.5 Ma, mainly granodioritic plutons, but they typically predate the nearby plutons by ca. 500 k.y. The average orientations of five of the six dike domains range from 010° to 058°; W-NW–to NW–striking dikes characterize one domain and are found in lesser amounts in a few other domains. Overall, the mean strike for all Eocene dikes is 035°, and the average extension direction (305°–125°) is oblique to the strike (~320°) of the North Cascades orogen. Extension by diking reached ~45% in one >7-km-long transect through the Teanaway swarm and ranged from ~5% to locally ~79% in shorter transects across other swarms, which corresponds to a minimum of ~12 km of extension. The dominant NE-striking dikes are compatible with the dextral motion on the N- to NW-striking (~355–320°) regional strike-slip faults. Some of the W–NW- to NW-striking dikes were arguably influenced by pre-existing faults, shear fractures, and foliations, and potentially in one swarm where both NE- and lesser W-NW–striking dikes are present, by a switch in principal stress axes induced by dike emplacement. Alternatively, the W-NW–to NW-striking dikes may reflect a younger regional strain field, as ca. 49.3–47.5 Ma U-Pb zircon ages of the NE-striking dikes are older than those of the few dated W-NW–to NW-trending dikes. In one scenario, NE-striking dikes intruded during an interval when strain mainly reflected dextral strike-slip faulting, and the younger dikes record a switch to more arc-normal extension. Diking ended as magmatism migrated into a N-S–trending belt west of the North Cascades core that marks the initiation of the ancestral Cascade arc.

A multi-century, tree-ring-derived perspective of the North Cascades (USA) 2014–2016 snow drought

Cool-season precipitation is a critical component of western North American water supplies. In recent decades, snow water equivalent (snowpack) has declined dramatically, culminating in record lows along the northern Cascade Range, USA, during the winters of 2014 and 2015. Given the brevity of observational records, the extent to which these recent trends exceed historical ranges of variability remains poorly understood. Here, we use a network of 30 tree-ring chronologies to reconstruct April 1 snowpack in the northern Cascade Mountains (Washington, USA) over the past ca. 400 years that accounts for 62% of the instrumental period variability. The reconstruction is characterized by considerable interannual- to interdecadal-scale variability. Yet, the most conspicuous feature is a decline that began in the mid-1970s concurrent with a shift to above-average air temperature which is accelerated through to the most recent years of the record. The 2014–2016 snow drought, especially snow conditions during the 2015 winter, across the northern Cascades is unprecedented within the context of the last 400 years. The reconstruction is characterized by considerable interannual- to interdecadal-scale variability, but a conspicuous decline emerged in the mid-1970s and accelerated through to the most recent years of the record to levels below the pre-industrial envelope of variability. This decline culminated in the 2014–2016 northern Cascade Mountains snow drought, which is unprecedented within the context of the last 400 years. Not only is the twentieth–twenty-first century period characterized by the rapid decline in snowpack conditions, it is also highly volatile. Extreme flips in snowpack conditions (year-to-year changes between 95th percentiles) during the twentieth and twenty-first centuries were anomalous within the context of the record. These patterns described for the North Cascades are concurrent with anomalously low snowpack in the Sierra Nevada Mountains of California, and thus part of a broader trend toward reduced snowpack in western North America. This decline will fundamentally impact regional drought and hydrography in North Cascadia and is likely the combined result of rising temperatures, weakening

Effects of the Light Environment and Stand History on Beargrass (Xerophyllum tenax) Morphology and Demography

Beargrass (Xerophyllum tenax [Pursh] Nutt.) is an herbaceous, evergreen perennial found in higher elevations of the northern Rocky, Sierra Nevada, Klamath, Siskiyou, Cascade and Olympic Mountains and in coastal areas from Washington to northern California. It is used by Native Americans for basketry and is an important floral green, but the conditions needed for reproduction and commercially valuable characteristics are not well known. We studied how the light environment affects size, morphology, color, and reproduction of a lowland, southeastern Olympic Peninsula beargrass population. We examined beargrass crown size distribution in relation to current and past overstory structure and found that beargrass plants had longer, greener leaves, lower crown density, smaller basal diameter, and fewer vegetative offshoots in shaded areas compared to more open areas. Flowering was less and there were fewer seedlings in shaded areas. Beargrass did not reproduce sexually in areas with < 0.3 of full photosynthetically active radiation (equivalent to at least 50% tree cover in our stand). Beargrass abundance matched the locations of anthropogenically maintained woodland openings that have since become forested preventing beargrass reproduction, suggesting that many plants have survived in the shade for more than 60 years. Overstory removal and prescribed burning in a portion of the stand stimulated sexual and asexual reproduction. We concluded that plants in shaded areas, although of somewhat higher commercial quality, are likely to recover more slowly from foliar harvest, and are less likely to be replaced after mortality. Population sustainability requires periodically or permanently open stand conditions.

ASSESSING ELK POPULATION STATUS AND POTENTIAL PERFORMANCE IN THE NOOKSACK AREA, WASHINGTON

Abstract Augmentation is a viable method of increasing the size of small populations if habitat quality is adequate. We examined a hierarchy of demographic responses to habitat quality, including individual nutritional condition, juvenile survival, adult fecundity, and adult survival to determine if the habitat of the Nooksack elk herd, a remnant elk population located in the northern Cascade Mountains of Washington, could support additional elk. Total ingesta-free body fat levels of lactating cow elk (11.5–13.6%), the most nutritionally challenged segment of the population, indicated that elk consumed diets at the high end of marginal quality. Juvenile survival during summer was moderate (0.66) relative to other elk populations, while annual adult survival was high (0.94). Pregnancy averaged 0.89, and early autumn calf:cow ratios ranged from 60 ± 9 to 69 ± 15 calves/100 cows. Levels of condition (approximately 56% of potential), juvenile survival (73% of potential), adult fecundity (99% of potential), an...

Detecting translational landslide scars using segmentation of Landsat ETM+ and DEM data in the northern Cascade Mountains, British Columbia

Extensive landslide inventories are often utilized for hazard assessment studies and when investigating medium- to long-term evolution of alpine terrain. The predominant methodology for collecting these databases is aerial photographic interpretation, which can be time-consuming and expensive. Earlier work has demonstrated that spectral response patterns for satellite images, when used alone, are unreliable at detecting most types of landslides. Principal difficulties are related to inadequate image resolution and spectral methods of classifying image data that are not sensitive to the characteristics that identify landslide features such as their shape and topographic expression. This study in the Cascade Mountains of coastal British Columbia attempts to overcome the latter problem through image segmentation and the use of geomorphometric data derived from a digital elevation model (DEM). Image segmentation involved grouping pixels into discrete objects based on similarities and differences in their reflectance and the use of shape criteria. A hierarchical classification system was then developed such that the normalized difference vegetation index (NDVI) and slope data eliminated all areas in the image that were both vegetated and on a gradient of less than 15°. The remaining "unvegetated steeplands" were classified using a supervised classification based on spectral, geomorphic, and shape criteria. The technique produced an overall accuracy of 75% in the detection of landslides that were over 1 ha in area.

Holocene Treeline and Climate Change in the Subalpine Zone near Stoyoma Mountain, Cascade Mountains, Southwestern British Columbia, Canada

Multiproxy paleoecological investigation of a small lake in the high subalpine zone near Stoyoma Mountain, northern Cascade Mountains of British Columbia, reveals significant change in vegetation, limnic conditions, and inferred climate throughout the Holocene (last 10,000 radiocarbon years). Three zones of distinct pollen, plant macrofossil, and chironomid assemblages are apparent in the sediment core from 3M Pond (informal name). A dry, sparsely vegetated spruce parkland and a warm-adapted chironomid community existed in and around the study sites in the early Holocene (ca. 10,000 to 7000 14C yr BP). Between 7000 and 3500 14C yr BP, Engelmann spruce–subalpine fir forest conditions established and then declined around 3M Pond leading to modern subalpine parkland conditions from 3500 14C yr BP to present. Chironomid communities at 3M Pond between 7000 and 3500 14C yr BP are indicative of warmer waters than present, but show a transition to modern assemblages. Three climatic regimes are identified near Stoyoma Mountain: (1) the early Holocene xerothermic period (10,000 to 7000 14C yr BP, (2) a period of climatic transition in the mid-Holocene (7000 to 3500 14C yr BP), and (3) cool, modern neoglacial conditions (after 3500 14C yr BP). These findings confirm vegetation and inferred climate changes identified at Cabin Lake, British Columbia (a nearby lake in the subalpine forest). Changes in treeline position, plant communities, chironomid communities, and inferred climate are nearly synchronous and validate the multiproxy approach for paleoecological reconstruction. Chironomid-based paleotemperature reconstructions confirm earlier evidence that the early Holocene was significantly warmer than present, with estimated summer water surface temperatures up to 4°C higher than today.

Integrating Physical and Chemical Characteristics of Lakes into the Glacially Influenced Landscape of the Northern Cascade Mountains, Washington State, USA.

/ A basic knowledge of the physical and chemical characteristics of lakes is needed by management to make informed decisions to protect water resources. In this study we investigated some of the physical and chemical characteristics of 58 lakes in alpine, subalpine, and forest vegetation zones in a natural area (North Cascades National Park Service Complex) between 1989 and 1993. The objectives of the study were to: (1) document the time of ice-out relative to lake elevation; (2) determine how a sharp climate gradient west and east of the hydrologic divide affected the time of ice-out for subalpine lakes; and (3) assess how lake water quality was associated with lake elevation, lake depth, and basin geology. As expected, lake ice-out times occurred earlier with decreasing elevation. East-slope subalpine lakes iced-out earlier than did west-slope subalpine lakes because the east slope of the study area was drier and warmer than the west slope. On average, the lakes were relatively cold, neutral in pH, and low in dissolved substances and concentrations of nitrogen and phosphorus. Although some shallow lakes (depth <10 m) exhibited the highest alkalinities, conductivities, and concentrations of phosphorus and nitrogen, most shallow lakes exhibited low values for these variables that were comparable to values observed in deep lakes. Geology did not play a major role in segregating the lakes based on water quality. Overall, lake temperature, pH, alkalinity, conductivity, and concentrations of total phosphorus and total Kjeldahl N increased with decreasing elevation. These changes in water quality with decreasing elevation in this temperate mountainous region corresponded with warmer air temperatures and increased vegetation biomass, soil depth and maturity, and dissolved substances and nutrients.KEY WORDS: Limnology; Mountain lakes; Water quality; North Cascades National Park Service Complex; National Park Servicehttp://link.springer-ny.com/link/service/journals/00267/bibs/24n2p219.html

Palaeoecology of postglacial treeline shifts in the northern Cascade Mountains, Canada

Postglacial changes in vegetation and chironomid communities at a subalpine lake in the Engelmann Spruce–Subalpine Fir zone in the northern Cascade Mountains, British Columbia, indicate patterns of treeline and climate fluctuation during the Holocene. In late-glacial sediments of Cabin Lake, pollen assemblages representative of alpine vegetation and cold-stenothermous chironomids indicate cold conditions prior to the Holocene. In the early Holocene (10,090 to 7000 14C yr BP) co-occurrence of spruce–fir parkland and a warm-adapted chironomid community indicates a warm and probably dry climate. In the mid-Holocene, inferred forest closure suggests that precipitation increased, and a mixture of warm- and cold-adapted chironomids indicates temperatures warmer than present, but cooler than in the early Holocene. This period between 7000 and 3200 14C yr BP represents a transitional climate in which temperature gradually declined, culminating in cool neoglacial conditions. This transitional interval may correspond with the `mesothermic period' proposed for lowland sites in southern British Columbia. Palaeobotanical evidence suggests that moist subalpine forest began to establish around 4800 14C yr BP with minimum temperatures and maximum precipitation between 2435 and ca. 1700 14C yr BP, corresponding with neoglacial advances throughout the northern Cordillera. A cool late Holocene (3200 14C yr BP to present) is also supported by a further decline in warm-adapted chironomids. Comparisons with other study sites in the Pacific Northwest reveal that regional climatic changes were a major factor in driving biotic changes in this area.

Phytoplankton assemblages in high-elevation lakes in the northern Cascade Mountains, Washington State USA

Phytoplankton assemblages in high-elevation lakes of North Cascades National Park Service Complex were studied during the open-water period in 1989. Collectively, 93 taxa were identified in 55 samples from 51 lakes. Based on cell densities, cyanobacteria had the highest relative abundance (36.7 %), followed by chlorophytes (29.8 %), and chrysophytes (19.6 %). Aphanocapsa delicatissima had the highest proportional abundance (14.0 %). Only 15.1% percent of the taxa occurred in more than 20 samples. Phytoplankton cell densities increased following a gradient of increasing lake-water temperature, alkalinity, and concentration of total Kjeldahl-N with decreasing lake elevation. Chrysophytes and cyanobacteria were quantitatively (relative abundance) the most important taxa in alpine and subalpine lakes, whereas cyanobacteria had the highest relative abundances in high-forest and low-forest lakes. Chlorophytes had their highest relative abundance in high-forest lakes. Although low in relative abundance, diatoms and dinoflagellates were most abundant in alpine lakes. An ordination by correspondence analysis indicated that most alpine, subalpine, and high-forest lakes had similar floras. Although a few subalpine lakes exhibited deviations from this pattern, the main differences in phytoplankton composition were found in a group of low-forest and high-forest lakes. Canonical correspondence analysis (CCA) provided evidence that the distribution of samples and taxa in ordination space was correlated with a gradient of decreasing lake elevation and increasing water temperature, alkalinity, and concentration of nitrogen. When CCA was used to examine relationships among phytoplankton taxa and vegetation zones, a continuous distribution of taxa was found from the low-forest zone to the subalpine zone, with a large number of taxa occurring primarily in the subalpine and high-forest zones. Three phytoplankton taxa occurred primarily in alpine lakes, whereas five taxa co-occurred in alpine, subalpine, and high forest zones. Collectively, lake elevation and associated changes in water quality and concentrations of nutrients, especially nitrogen, appeared to be the primary physical and chemical factors influencing the taxonomic structures of phytoplankton assemblages.

Rotifer abundance and distribution in the northern Cascade mountains, Washington, USA

Few studies of rotifers have focused on North American western mountain systems. In this study of Cascade mountain lakes in Washington state, both cluster analysis and detrended correspondence analysis (DCA) grouped lakes with the same dominant rotifer taxon. With both statistical techniques, each cluster of lakes was associated with characteristic physico-chemical variables and dominant crustacean zooplankton. Small, microphagous, loricate (hard-bodied) rotifers (Keratella or Kellicottia) dominated lakes in 4 of the clusters: these lakes generally had low to moderate nutrient concentrations and low cladoceran densities. Conochilus anicornis dominated lakes in a fifth cluster; these lakes had relatively high levels of alkalinity and conductivity and also had high densities of cladocerans and diaptomids. Collotheca mutabilis dominated a single lake which composed a sixth cluster; this was a large deep lake with low alkalinity and conductivity. No significant relationships were evident between vertebrate predation and rotifer taxa.

Distribution of nearshore macroinvertebrates in lakes of the Northern Cascade Mountains, Washington, USA

Various attributes of high mountain lake ecosystems were found to affect distributions of nearshore macroinvertebrates in 41 oligotrophic lakes of North Cascades National Park Service Complex, Washington, USA. Eighty-eight taxa representing 16 taxonomic groups were collected from study lakes, and each of 63 taxa (72 %) were collected from eight or fewer lakes. Eighty-six percent of all taxa were collected from forest zone lakes, 61% from subalpine zone lakes, and 16 % from alpine zone lakes. Number of taxa per lake was positively correlated to water temperature and inversely related to elevation. Low-elevation forest lakes had the highest number of taxa and maximum temperatures per lake, while lakes with the lowest number of taxa and maximum temperatures occurred in the alpine zone. The distributions of gastropods and the beetle Potamonectes griseostriatus were found to vary according to their water chemistry requirements. Gastropods were restricted to three low-elevation forest lakes with the highest pH, alkalinity, and calcium ion concentration levels, and P. griseostriatus was not present in forest lakes due, in part, to this species requirement for acidic conditions not typically found in lakes of this zone. Microhabitat substrate composition varied by vegetation zone. Low-elevation forest lakes had the highest percent of microhabitats with organic substrates, and these types of substrates decreased in higher elevation forest lakes, and in subalpine and alpine zone lakes. Conversely, the predominance of inorganic substrates in microhabitats increased in higher elevation forest lakes and in the subalpine and alpine zones. The presence of macroinvertebrates in lakes closely paralleled these changes in microhabitat substrate composition and could be associated with the substrate preferences of organisms. Vertebrate predators (i.e., two salamander species and trout) influenced the distributions of three taxa. The relationship between physiographic characteristics of the terrestrial environment of lakes and characteristics of nearshore lake habitat was elucidated using discriminant analysis. Aquatic-based predictor variables representing lake habitat were used to predict the membership of lakes in classification categories which were based on characteristics of a lake's terrestrial environment. In this analysis, no lakes were misclassified, and calculation of the number of lakes expected to be correctly placed into classification categories by chance alone was low enough to conclude that the classification equations developed using aquatic-based variables were useful in assigning lakes to the terrestrially-based classification categories.

Changes in Soil Physical Properties due to Cable Yarding and their Hydrologic Implications

Abstract This study was performed to measure changes in soil properties due to cable yarding and to estimate the resulting changes in hydrologic response. Soils were sampled before and after a commercial logging operation in the northern Cascade Mountains of Washington. The samples were analyzed for saturated hydraulic conductivity (Ks), moisture release characteristics, and bulk density (BD). Postlogging Ks values ranged from 1.08 to 497 cm/h and were significantly less than prelogging values, which ranged from 10.8 to 623 cm/h. Postlogging bulk densities ranged from 0.34 to 1.13 g/cm³ and were significantly greater than prelogging values, which ranged from 0.10 to 0.95 g/cm³. Because of the high Ks values it was concluded that Horton overland flow is not a dominant process even after disturbance. A 32.7% reduction in available water storage was found due to decreases in noncapillary porosity and surface horizon thickness. From this, increases in saturation overland flow and/or subsurface flow are predicted on skid trails. Overall impacts on the cutting unit however are considered small. West. J. Appl. For. 7(2):36-39.

Ancient borderland terranes of the North American Cordillera: Correlation and microplate tectonics

Enigmatic Paleozoic and Precambrian sequences rich in volcanic and plutonic rocks form discrete terranes along the outer border of the North American Cordillera. These borderland terranes occur in California in the northern Sierra Nevada and Klamath Mountains, in central Oregon and eastern Oregon–westernmost Idaho, in Washington in the Northern Cascade Mountains and San Juan Islands, in British Columbia in Vancouver Island, and in Alaska in the Alexander Archipelago. The difficulty in relating the geology of the borderland terranes to that of the North American continent, the recognition of ophiolites and suture zones separating the terranes from the continent, plus the Asiatic affinity of certain of the borderland faunas indicate that the terranes are allochthonous relative to the North American continent. Furthermore, major differences in stratigraphy, magmatic activity, tectonic activity, metamorphism, and particularly the ages and types of basement between the terranes — when considered together with discordant paleomagnetic data — suggest that at least six lithospheric plates are represented. The terranes in the Klamath Mountains have an Ordovician ultramafic rock (ophiolite) basement. The Oregon terranes have ultramafic complexes (ophiolites) in close association with volcanic rocks (volcanic arcs) that form the basement. In the Northern Cascade Mountains and San Juan Islands, the terranes have, respectively, Precambrian and Ordovician crystalline metaplutonic (magmatic arc) basement. The terrane in the southern part of the Alexander Archipelago has a Precambrian crystalline meta-volcanic-metasedimentary (remnant arc) basement, but an Ordovician basaltic-andesitic basement (initial deposits of an upward-shoaling island arc) appears farther north. Transcurrent faults segment and truncate parts of the Cordillera, but since the borderlands are in themselves composed of several plates, models of a single allochthonous plate are difficult to apply. More likely, during Precambrian and Paleozoic time, multiple microcontinental plates and volcanic arcs moved outboard and inboard (away from and toward North America) to accommodate a succession of marginal ocean basins opening and closing behind migrating arcs. This was followed in Mesozoic and Cenozoic time by large-scale northwestward drift.

Chemical weathering in the temperate glacial environment of the Northern Cascade Mountains

Chemical weathering activity in the South Cascade Glacier area of the Northern Cascades is both intensive and extensive. The presence of chemical weathering is shown by (1) pedogenic clay assemblages which vary according to bedrock mineralogy, (2) distinctive water types which co-exist with discrete bedrock types and (3) the striking chemical transformation of water as it runs over bedrock. The weathering mechanisms are primarily carbonation and oxidation. Even though zoned soils are rare or absent, pedogenic minerals such as vermiculite, smectite, gibbsite and lepidocrocite accumulate locally. Cationic denudation of the South Cascade Glacier watershed (930 mE/m 2yr) is substantially higher than the world average (390 mE/m 2yr), indicating the intensity of chemical weathering in such an environment. Evidently the low average temperatures generally associated with an active glacier do not inhibit chemical weathering reactions. On the contrary, the turbulent well-aerated water flows prevalent in such an environment promote weathering by constantly replenishing the acid potential of the water. Also, the mechanical effects of glaciation apparently expedite the chemical weathering process by continuously reviving the fresh surface area of rock exposed to water. A crucial limiting factor in chemical weathering seems to be the supply of water and hydrogen ion from the atmosphere. By virtue of the fact that the temperate glacial environment represents an extreme of hydrologic activity, it may, therefore, represent an extreme of chemical weathering activity even in the absence of normal biologic and pedogenic processes associated with the soil.

Ages of Zircons from the Northern Cascade Mountains, Washington

Pre-Late Cretaceous crystalline rocks in the core of the Northern Cascade Mountains of Washington are predominantly heterogeneous supracrustal gneiss and schist, and dioritic, quartz dioritic, and trondhjemitic plutons and bodies of orthogneiss. Migmatite derived from plutonic and supracrustal rocks is also widespread. Isotopic age determinations of zircons indicate that, of the supracrustal gneiss and schist, the Swakane Gneiss and possibly the Skagit Gneiss may have been deposited > 1,650 m.y. ago. Alternatively, some of these rocks may be younger but were derived at least in part from a >l,650-m.y.-old source terrane. A second group of supracrustal rocks, the Younger gneissic rocks of the Holden area, includes a metavolcanic unit about 265 m.y. old. Plutonic rocks and orthogneisses comprise four main age groups: 1,452 to 2,000 m.y., pyroxene gneiss of the Yellow Aster Complex; about 460 m.y., the Turtleback Complex of the San Juan Islands and younger orthogneiss of the Yellow Aster Complex; 220 m.y., plutonic and gneissic rocks of the Marblemount belt (Marblemount Meta-Quartz Diorite, Dumbell Mountain plutons); and 92 m.y., the Eldorado Orthogneiss. Strongly metamorphosed rocks of the Chelan Complex, chiefly quartz dioritic, have zircon Pb 206 /U 238 ages ranging from 100 to 183 m.y. These ages appear to be discordant, and the Chelan Complex may represent remobilized rocks from the 220-m.y.-old Marblemount belt. Ages of metamorphic minerals, zircons from pegmatitic material associated with migmatite, and zircons from synkinematic intrusive rocks indicate two major episodes of metamorphism in the Northern Cascade terrane, one about 415 m.y. ago and the other, 60 to 90 m.y. ago. Both episodes culminated in metamorphism to amphibolite facies grade—and in the case of the older episode, metamorphism to granulite facies grade—and both resulted in extensive migmatization of pre-existing rocks.

Plagioclase compositions and non-anatectic origin of migmatitic gneisses in Northern Cascade mountains of Washington State

Regionally developed migmatitic gneisses make up most of the Skagit Gneiss, though there are some orthogneisses also, derived from pre- to late-metamorphic intrusives. The migmatites contain countless, though quantitatively subordinate, remnants of biotite schists, less abundant amphibolitic rocks, and minor varieties of metasediments. Biotite schists (fine-grained paragneisses) predominantly are plagioclase-rich, having the compositions of highly immature graywackes; quartz-rich varieties are minor, and alumina-excess rocks very rare. There are para- and ortho-amphibolites, the latter of basaltic-gabbroic parentage. Leucocratic hornblende schists are largely meta-sedimentary. Apart from subordinate varieties in which K-feldspar is a major constituent, the leucocratic migmatitic gneisses have (leuco-) trondhjemitic and, to a lesser extent, quartz-dioritic compositions.

GRANITIZATION, MIGMATIZATION, AND FUSION IN THE NORTHERN ENTIAT MOUNTAINS, WASHINGTON

A tabular quartz diorite complex extends along the Entiat Mountains, which form a southeast-trending spur of the Northern Cascade Mountains. The country rocks of the complex are biotite gneiss, probably derived from arkosic sedimentary rocks, and hornblende schist, probably derived from basic volcanic rocks. Their present mineral composition is typical of the upper epidote amphibolite and amphibolite facies of regional metamorphism. During regional metamorphism the biotite gneiss was granitized to biotite-quartz diorite gneiss and the hornblende schist to hornblende-quartz diorite gneiss. The metamorphic origin of these quartz diorite gneisses involving relatively little replacement is shown by their chemical and mineralogical similarity to the original biotite gneiss and hornblende schist, by their enclosing long, thin, undisturbed layers of country rocks, and by their association with migmatites formed by metamorphic processes. Here and there in the quartz diorite gneisses massive rocks with hypidiomorphic granular “igneous” textures have formed principally by recrystallization, and these features are associated with small-scale swirling of the foliation and some intrusive features, which show that the gneiss was rendered plastic and mobile during granitization. Migmatites containing replacement bodies and secretions of leucocratic quartz diorite occur in the biotite gneiss and in most of the rocks of the complex—particularly in the biotite-quartz diorite gneiss. During the formation of the complex, the felsic material contained in the leucocratic rocks, principally sodium, potassium, and silicon, was generated by metamorphic differentiation. During the granitization, anatectic magmas were formed by fusion of hornblende-quartz diorite gneiss, and some similar magma intruded from below. Melting without metamorphic differentiation is indicated by the chemical similarity between the anatectic quartz diorite and the parent hornblende-quartz diorite gneiss. Smearing out of inclusions and crystals and the tabular, sill-like nature of the bodies indicate that fusion may have been triggered by differential movement and shearing. The anatectic rocks contain inclusions of hornblende schist that survived both the granitization to hornblende-quartz diorite and the fusion. Crystallization differentiation of the anatectic magmas yielded potassium-rich pegmatites and local granodioritic masses. Regional metamorphism continued after the anatectic magmas in the sills had solidified; felsic metamorphic differentiates occur in leucocratic quartz diorite that partly replaces the borders of the sills. The leucocratic material was plastic and facilitated differential movement between the sill and its walls.

Forest and Adjacent Burn in the Tillamook Burn Area of Northwestern Oregon

The approximately 300,000 acre Tillamook Burn in the northern Oregon Coast Range has been the scene of three major fires. The area burned first in 1933, in a holocaustic fire that covered 244,706 acres and destroyed approximately ten billion board feet of timber (Morris, 1936). Most of the area burned again in 1939, and again in 1945. The later fires killed many patches of forest missed or subject to ground fires only in the preceding fires, and increased the total acreage by extending the boundaries at various places. Descriptions and statistics of the 1933 fire include those by Morris (1936), Isaac (1936), McArdle (1933), Cronemiller (1933) and others. The fires were exceedingly severe and entirely destroyed the forest vegetation over most of the area, with one major exception. One block of unburned timber, approximately 25,000 acres in size, remained in the center of the Burn area following the 1933 fire. The two subsequent major fires reduced this so-called green island to approximately 2,500 acres, the major reduction occurring in 1939. While there were some ground and spot fires in the edges of this remaining stand of forest, the bulk of it was free of any fire damage. This forest is now being logged. Quantitative studies of forest communities in Oregon as a whole are rare and none exist in the literature for the northern half of the Oregon Coast Range. The only records of the pre-Burn forest in this part of the Coast Range were early timber cruises. The study reported here was carried out in the summers of 1955 and 1956 to obtain information on various habitats and environmental conditions within this remaining forest and on the relative importance of its component species. For purposes of comparison, similar data were taken in adjacent areas in the Burn which had been burned only in 1945. The author wishes to thank the Stimson Lumber Company for allowing this work to be done on their holdings, and the State Forester's Office in Salem, Oregon for generous assistance in providing maps and aerial photographs, and information about the Tillamook fires. DESCRIPTION AND HISTORY OF AREA The topography in the part of the Oregon Coast Range occupied by the main Burn is rugged, consisting of narrow ridges and steep-walled valleys. The topography is highly dissected by streams which have eroded down through soft Cenozoic sandstones and around intrusive lava masses which form the skeletons of the sharp ridges. Slopes of 30? to 50? are common and the more or less level areas of the ridge tops are frequently less than '4 mile in width. General elevations of the higher points range from 2800 to 3500 feet above sea level, while the main valleys of two major streams of the area lie approximately 600-1000 feet above sea level. The area of this study lies in the southwest portion of Township 1 North, Range 6 West and in the extreme northwest portion of Township 1 South, Range 6 West, Willamette Meridian. It lies along a major ridge running south-southwest, north-northeast between the heads of two major streams, as shown in Figure 1. The ridge crest varies in elevation from 2900 to 3500 feet above sea level. Several prominent secondary ridges protrude toward the northwest and southeast at more or less right angles to the line of the main ridge. Figure 2 shows the northwest slope of the area analyzed, the general appearance of this portion of the Burn, and the relative locations of the forest and burn areas studied. The coniferous forest of the Oregon Coast Range is included in the Cedar-Hemlock association of the Coast Forest Formation by Weaver and Clements (1938), in the Pacific Douglas fir of the Cedar-Hemlock Forest by Shantz and Zon (1924), and in the Pacific Coastal Forest Formation by Boosting (1956). Over most of its area it is characterized by tall, often luxuriant forests containing such species as Douglas fir (Pseudotsuga taxifolia), western hemlock (Tsuga heterophylla), western red cedar (Thuja plicata) and various true firs (Abies spp.), with Sitka spruce (Picea sitchensis) occurring on lower slopes near the Pacific Ocean. In Oregon, this forest occurs over much of the Coast Range and the western slopes of the middle and northern Cascade Mountains. The behavior of these forest species in succession has been studied by various workers. Prob1 This work was largely supported by National Science Foundation Grant No. G-1702.

Geology of Oregon and Washington and Its Relation to Occurrence of Oil and Gas

Oregon and Washington contain the following topographic provinces, each with distinctive geological features: Coast Range, Cascade Mountains, Puget Sound-Willamette trough, Okanogan Highlands, Blue Mountains, Klamath Mountains, Olympic Mountains, and Columbia Plateau. The northern Cascades of Washington, the Okanogan Highlands, the Klamath Mountains and a part of the Blue Mountains are composed largely of thick sections of folded Paleozoic and early Mesozoic marine sediments which have been intensely metamorphosed and deformed. Associated with these are granites and other intrusive rocks. The formations in eastern Oregon and Washington and in the Cascade Mountains constitute the base on which rests a thick series of Tertiary lavas and associated lacustrine and fluviatile ediments. The core of the Olympic Mountains consists of greatly indurated but not metamorphosed sedimentary rocks, possibly late Mesozoic in age, which are bordered on the north, east, and south by 3,000 feet of Eocene volcanics and about 8,000 feet of later Tertiary marine sediments. Granites are absent in this area. The Coast Range from the Olympic Mountains southward to the Klamath Mountains is composed entirely of folded and locally faulted Tertiary lavas and sediments ranging from 10,000 to 20,000 feet thick. The basement rocks are unknown but the lower part of the Tertiary section everywhere consists of 3,000 to 5,000 feet of basic volcanics largely submarine in origin. Crustal movements of late Miocene age produced northwest-southeast folds in Washington, and north-south folds in the Coast Range of Oregon. Major north-south upwarps and downfolds at the close of the Pliocene were superimposed on the earlier structures with the resultant development of the Coast Range, Cascade Mountains, and the intervening trough. Indications of oil in the form of very small seepages occur in the Tertiary formations west of the Cascade Mountains. There is no conclusive evidence that commercial amounts of oil are present in these formations although drilling tests under geologic control are considered warranted. The metamorphic rocks, granites, lavas and continental sediments in eastern Oregon and Washington, and in the northern Cascade Mountains are considered as being unfavorable for the commercial occurrence of oil.

Birds of the Northern Cascade Mountains of Washington

Birds of the Northern Cascade Mountains of Washington