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Research about California, Oregon

Source-linked reports with geographic coverage including California, Oregon.

At least 109 records · Page 6Linked to original sources
USGS1999

Plutons and accretionary episodes of the Klamath Mountains, California and Oregon

The Klamath Mountains consist of various accreted terranes and include many plutons that range in composition from gabbro to granodiorite. Some of the plutons (preaccretionary plutons) were parts of terranes before the terranes accreted; others (accretionary plutons) intruded during or after the accretion of their host terrane(s). This report attempts to (1) graphically illustrate how the Klamath Mountains grew by the accretion of allochthonous oceanic terranes during early Paleozoic to Cretaceous times, (2) identify the plutons as either preaccretionary or accretionary, and (3) genetically relate the plutonic intrusions to specific accretionary episodes. The eight accretionary episodes portrayed in this report are similar to those shown by Irwin and Mankinen (1998) who briefly described the basis for the timing of the episodes and who illustrated the ~110 degrees of clockwise rotation of the Klamath Mountains since Early Devonian time. Each episode is named for the accreting terrane. In all episodes (Figs. 1-8), the heavy black line represents a fault that separates the accreting oceanic rocks on the left from earlier accreted terranes on the right. The preaccretionary plutons are shown within the accreting oceanic crustal rocks to the left of the heavy black line, and the accretionary plutons in most instances are shown intruding previously accreted terranes to the right. Episodes earlier than the Central Metamorphic episode (Fig. 1), and that may have been important in the formation of the early Paleozoic nucleous of the province (the Eastern Klamath terrane), are not known. The 'Present Time' distribution of the accreted terranes and plutons is shown at a large scale in Figure 9. The schematic vertical section (Fig. 10) depicts the terranes as a stack of horizontal slabs that include or are intruded by vertical plutons. Note that at their base the ~170 Ma preaccretionary plutons of the Western Hayfork subterrane are truncated by the ~164 Ma Salt Creek accretionary fault, the ~160 Ma accretionary plutons are truncated by the ~150 Ma Bear Wallow accretionary fault, and the ~150 Ma accretionary plutons (and questionably the Grants Pass ~139 Ma accretionary pluton) are truncated by the ~120 Ma South Fork fault.

California, Oregon↗
USGS1999

Klamath-Siskiyou herpetofauna: Biogeographic patterns and conservation strategies

The Klamath-Siskiyou region of southwest Oregon and northwest California (USA) has some of the most complex landscape mosaics and plant communities in western North America, reflecting its marked diversity of precipitation and topography. With 38 native species of amphibians and reptiles, the Klamath-Siskiyou region has the most species-rich herpetofauna of any similarly sized mountain range in the Pacific Northwest. Although it is a biodiversity 'hot spot,' there are only two endemic species, both salamanders, in the Klamath-Siskiyou region. High diversity is due to the overlap of two major biogeographic groups: the Arcto- (= northern) and Madro- (= southern) Tertiary herpetofaunas. Many of the amphibians in the Klamath-Siskiyou region are restricted to specialized habitats. Much of our knowledge about the biology of the regional fauna is based on studies elsewhere. Distributional surveys and ecological research are needed to address how the herpetofauna responds to timber harvest and other human activities that may reduce populations and increase fragmentation of suitable habitats. Conservation of the region's diverse herpetofauna should emphasize strategies directed at habitat specialists and species at the latitudinal limits of their ranges.

California, Oregon↗
USGS1998

Wide-angle seismic constraints on the evolution of the deep San Andreas plate boundary by Mendocino triple junction migration

Recent, wide-angle seismic observations that constrain the existence and structure of a mafic layer in the lower crust place strong constraints on the evolution of the San Andreas plate boundary system in northern and central California. Northward migration of the Mendocino Triple Junction and the subducted Juan de Fuca lithospheric slab creates a gap under the continent in the new strike-slip system. This gap must be filled by either asthenospheric upwelling or a northward migrating slab attached to the Pacific plate. Both processes emplace a mafic layer, either magmatic underplating or oceanic crust, beneath the California Coast Ranges. A slab of oceanic lithosphere attached to the Pacific plate is inconsistent with the seismic observation that the strike-slip faults cut through the mafic layer to the mantle, detaching the layer from the Pacific plate. The layer could only be attached to the Pacific plate if large vertical offsets and other complex structures observed beneath several strike-slip faults are original oceanic structures that are not caused by the faults. Otherwise, if oceanic slabs exist beneath California, they do not migrate north to fill the growing slab gap. The extreme heat pulse created by asthenospheric upwelling is inconsistent with several constraints from the seismic data, including a shallower depth to the slab gap than is predicted by heat flow models, seismic velocity and structure that are inconsistent with melting or metamorphism of the overlying silicic crust, and a high seismic velocity in the upper mantle. Yet either the Pacific slab model or the asthenospheric upwelling model must be correct. While the mafic material in the lower crust could have been emplaced prior to triple junction migration, the deeper slab gap must still be filled. A preexisting mafic layer does not reduce the inconsistencies of the Pacific slab model. Such material could, however, compensate for the decrease in mafic magma that would be produced if asthenospheric upwelling occurred at a lower temperature. These low temperatures, however, may be inconsistent with asthenospheric rheology.

California, Oregon↗
USGS1998

Valve morphology and systematic position of Navicula walkeri (Bacillariophyceae), a diatom endemic to Oregon and California (USA)

Variation in valve size and ultrastructure is documented for Navicula walkeri, a freshwater diatom species endemic to Oregon and central California (USA). In LM, this large diatom has longitudinal lines on either side of the axial area, as well as lineolate striae. External proximal raphe ends recurve toward the same side as the deflected distal ends. A large central nodule and bulbous areas at the terminus of each raphe branch are visible internally. The edges of an axial plate form the image of longitudinal lines. The suite of features present in N. walkeri suggests it is part of Navicula sensu stricto but occupies an isolated position within the group. Navicula sensu stricto is not an entirely homogeneous assemblage, and further refinements of the systematic affinities of its members may be warranted.

California, Oregon↗
USGS1998

Rotational and accretionary evolution of the Klamath Mountains, California and Oregon, from Devonian to present time

The purpose of this report is to show graphically how the Klamath Mountains grew from a relatively small nucleus in Early Devonian time to its present size while rotating clockwise approximately 110°. This growth occurred by the addition of large tectonic slices of oceanic lithosphere, volcanic arcs, and melange during a sequence of accretionary episodes. The Klamath Mountains province consists of eight lithotectonoic units called terranes, some of which are divided into subterranes. The Eastern Klamath terrane, which was the early Paleozoic nucleus of the province, is divided into the Yreka, Trinity, and Redding subterranes. Through tectonic plate motion, usually involving subduction, the other terranes joined the early Paleozoic nucleus during seven accretionary episodes ranging in age from Early Devonian to Late Jurassic. The active terrane suture is shown for each episode by a bold black line. Much of the western boundary of the Klamath Mountains is marked by the South Fork and correlative faults along which the Klamath terranes overrode the Coast Range rocks during an eighth accretionary episode, forming the South Fork Mountain Schist in Early Cretaceous time.

California, Oregon↗
USGS1996

Source and tectonic implications of tonalite-trondhjemite magmatism in the Klamath Mountains

In the Klamath Mountains, voluminous tonalite-trondhjemite magmatism was characteristic of a short period of time from about 144 to 136 Ma (Early Cretaceous). It occurred about 5 to 10 m.y. after the ∼165 to 159 Ma Josephine ophiolite was thrust beneath older parts of the province during the Nevadan orogeny (thrusting from ∼155 to 148 Ma). The magmatism also corresponds to a period of slow or no subduction. Most of the plutons crop out in the south-central Klamath Mountains in California, but one occurs in Oregon at the northern end of the province. Compositionally extended members of the suite consist of precursor gabbroic to dioritic rocks followed by later, more voluminous tonalitic and trondhjemitic intrusions. Most plutons consist almost entirely of tonalite and trondhjemite. Poorly-defined concentric zoning is common. Tonalitic rocks are typically of the low-Al type but trondhjemites are generally of the high-Al type, even those that occur in the same pluton as low-Al tonalite. The suite is characterized by low abundances of K 2 O, Rb, Zr, and heavy rare earth elements. Sr contents are generally moderate (∼450 ppm) by comparison with Sr-rich arc lavas interpreted to be slab melts (up to 2000 ppm). Initial 87 Sr/ 86 Sr, δ 18 O, and ɛ Nd are typical of mantle-derived magmas or of crustally-derived magmas with a metabasic source. Compositional variation within plutons can be modeled by variable degrees of partial melting of a heterogeneous metabasaltic source (transitional mid-ocean ridge to island arc basalt), but not by fractional crystallyzation of a basaltic parent. Melting models require a residual assemblage of clinopyroxene+garnet±plagioclase±amphibole; residual plagioclase suggests a deep crustal origin rather than melting of a subducted slab. Such models are consistent with the metabasic part of the Josephine ophiolite as the source. Because the Josephine ophiolite was at low T during Nevadan thrusting, an external heat source was probably necessary to achieve significant degrees of melting; heat was probably extracted from mantle-derived basaltic melts, which were parental to the mafic precursors of the tonalite-trondhjemite suite. Thus, under appropriate tectonic and thermal conditions, heterogeneous mafic crustal rocks can melt to form both low- and high-Al tonalitic and trondhjemitic magmas; slab melting is not necessary.

California, Oregon↗
USGS1996

Detailed study of water quality, bottom sediment, and biota associated with irrigation drainage in the Klamath Basin, California and Oregon, 1990-92

The effect of irrigation drainage on the water quality and wildlife of the Klamath Basin in California and Oregon was evaluated during 1990-92 as part of the National Irrigation Water Quality Program of the U.S. Department of the Interior. The study focused on land serviced by the Bureau of Reclamation Klamath Project, which supplies irrigation water to agricultural land in the Klamath Basin and the Lost River Basin. The Tule Lake and Lower Klamath National Wildlife Refuges, managed by the U.S. Fish and Wildlife Service, are in the study area. These refuges provide critical resting and breeding habitat for waterfowl on the Pacific flyway and are dependent on irrigation drainwater from upstream agriculture for most of their water supply. Water-quality characteristics throughout the study area were typical of highly eutrophic systems during the summer months of 1991 and 1992. Dissolved-oxygen concentrations and pH tended to fluctuate each day in response to diurnal patterns of photosynthesis, and frequently exceeded criteria for protection of aquatic organisms. Nitrogen and phosphorus concentrations were generally at or above threshold levels characteristic of eutrophic lakes and streams. At most sites the bulk of dissolved nitrogen was organically bound. Elevated ammonia concentrations were common in the study area, especially downstream of drain inputs. High pH of water increased the toxicity of ammonia, and concentrations exceeded criteria at sites upstream and downstream of irrigated land. Concentrations of ammonia in samples from small drains on the Tule Lake refuge leaseland were higher than those measured in the larger, integrating drains at primary monitoring sites. The mean ammonia concentration in leaseland drains [1.21 milligrams per liter (mg/L)] was significantly higher than the mean concentration in canals delivering water to the leaseland fields (0.065 mg/L) and higher than concentrations reported to be lethal to Daphnia magna (median lethal concentration of 0.66 mg/L). Dissolved-oxygen concentrations also were lower, and Daphnia survivability measured during in situ bioassays was correspondingly lower in the leaseland drains than in water delivery canals. In static laboratory bioassays, water samples collected at the primary monitoring sites caused toxicity in up to 78 percent of Lemna minor tests, in up to 49 percent of Xenopus laevis tests, in 17 percent and 8 percent of Hyalella azteca and Pimephales promelas tests, respectively, and 0 percent in Daphnia magna tests. In situ exposure at the sites caused mortality in more than 83 percent of Pimephales tests and in more than 41 percent of Daphnia and Hyalella tests. Much of the observed toxicity appears to have been caused by low dissolved oxygen, high pH, and ammonia. Although water in the study area was toxic to a variety of organisms, no statistically significant differences in the degree of toxicity between sites were observed above or below irrigated agricultural land in any of the bioassays. Pesticides were frequently detected in water samples collected at the monitoring sites during the 1991 and 1992 irrigation seasons. Among the most frequently detected compounds were the herbicides simazine, metribuzin, EPTC, and metolachlor and the insecticide terbufos. All the insecticides detected were at concentrations substantially below acute toxicity values reported for aquatic organisms. The herbicide acrolein has been used extensively in the basin to manage aquatic plant growth in irrigation canals and drains. The concentration of acrolein was monitored in a canal near Tule Lake after an application in order to evaluate the potential for the pesticide to be transported to refuge waters. Although acrolein concentrations were toxic to fish in the channels adjacent to Tule Lake, very little of the canal water entered the refuge during the monitoring period. Organochlorine pesticide concentrations in 25 surficial sediment samples collected in 1990 were below baseline levels commonly found in soils and sediment. Seventeen sediment samples were analyzed for chlorophenoxy acid herbicides and two samples were analyzed for organophosphorus and carbamate insecticides in 1992. No pesticides were detected in any of these samples. Residues of the trace elements selenium, mercury, and arsenic in algae, invertebrates, fish, and avian eggs revealed no bioaccumulation problems. Concentrations of organochlorine compounds, especially of p,p' DDE, were associated with a mean 11-percent eggshell thinning in white-faced ibis. However, ibis populations appear to be increasing, and some eggs of ibis were relatively low in DDE concentration. DDE concentrations in eggs of western grebes were not as high as in the eggs of ibis. Concentrations and types of organochlorine compounds detected in grebe and ibis eggs were highly variable, indicating that the birds were exposed to these compounds outside the basin. Fish and invertebrates inhabiting drainwater were representative of pollution-tolerant species assemblages. The aquatic communities retained little of their historic ecological structure. Extensive hydrologic modifications and hypereutrophic conditions in Klamath Basin waterways have degraded the quality of aquatic habitat and altered aquatic communities.

California, Oregon↗
USGS1995

Alteration of basalt hyaloclastite at the off-axis Sea Cliff hydrothermal field, Gorda Ridge

The Sea Cliff hydrothermal field on the northern segment of the Gorda Ridge is situated along a rift-bounding normal fault about 2.6 km east of the neovolcanic zone and approximately 300 m above the spreading axis. The structural setting of this hydrothermal field differs from that of most other active seafloor hydrothermal sites investigated to date, which are typically situated in the neovolcanic zone. Mineralization occurs in basaltic talus covering a large normal-fault scarp. Hydrothermal crusts cover much of the seafloor in the area of the active hydrothermal field. These crusts form by extensive alteration of basaltic hyaloclastite in a zone of mixing between ascending hydrothermal fluid and entrained seawater. The initial stage of alteration is magnesian metasomatism of both crystalline basalt and basaltic glass, converting the rock to Mg-rich smectite and smectite/chlorite. Further alteration removes nearly all cations and ultimately leads to silicification. Preservation of basaltic texture in the silicified rocks provides evidence that even such sparingly soluble elements as A1 and Ti have been removed. Oxygen-isotopic ratios of the altered rocks constrain initial alteration to temperatures near 220°C, close to the maximum measured vent temperatures of 247°C. Silicification proceeded to much lower temperatures, and most amorphous silica deposition occurred at temperatures below 100°C. Sulfur-, strontium-, and lead-isotopic data all indicate a predominantly basaltic source, with important contributions from seawater but no significant contribution from sedimentary sources. Comparison with ophiolite-hosted massive sulfide deposits shows that the structural setting, alteration sequence, and depositional environment are all similar and suggests that mineralization and replacement of basaltic breccia in the Sea Cliff hydrothermal field likely occur in the subsurface beneath a capping layer of silicified hyaloclastite.

California, Oregon↗
USGS1993

Family stability in greater white-fronted geese

I investigated the stability of parent-offspring bonds, and sibling-sibling bonds of neck-banded Greater White-fronted Geese ( Anser albifrons frontalis ) during winters (September-May) in California and southern Oregon from 1979 to 1989. Geese captured at feeding sites were more likely to be in social groups than those captured at roosting sites. Offspring remained associated with their parents longer than reported for other geese, as 69% of yearlings, 39% of two-year-olds, and 38% of three-year-olds and older were observed with their parents during winter. The proportion of time offspring spent with their parents declined as they grew older, being 76% for juveniles, 32% for yearlings, and 15% for two-year-olds and older. The prevalence of extended family groups was corroborated by counts of landing groups of unmarked geese. Sibling bonds also persisted after the first year of life, with 74%, 50%, and 39% of siblings maintaining some degree of social contact at ages of one, two and three years or older, respectively. Older offspring were more likely to associate with brood mates than with parents. Intensive observations ended when the oldest known-age geese were 34 months old. Incidental sightings in subsequent years revealed that some offspring up to eight years of age still associated with their parents and/or siblings. The benefits of maintaining long-term family bonds were not readily apparent, as there was no difference in the reproductive success of parents with and without attendant offspring, and yearlings that associated with parents were not more likely to survive than yearlings that did not associate with parents. However, older offspring and their parents may benefit by remaining together if extended families are more dominant and have better access to limited food and safe roost sites. Parents benefit if their fitness is enhanced due to nest defense provided by older offspring, and subadults probably benefit from staying with their parents by learning foraging and predator avoidance strategies from parents and older siblings.

California, Oregon↗
USGS1990

Microbial control of silver mineralization at a sea-floor hydrothermal site on the northern Gorda Ridge

THE Sea Cliff hydrothermal field, on the northern Gorda Ridge, contains mounds and chimneys of hydrothermally precipitated sulphide and sulphate minerals typical of sea-floor hydrothermal vent sites 1 . In addition, large areas of the sea floor are covered by subhorizontal hydrothermal crusts. Samples of the crust recovered by submersible are composed of intensely altered fragments of basalt and basaltic hyaloclastite cemented by amorphous silica and chalcedony with less abundant barite, and minor amounts of base-metal sulphide minerals 2 . Some surfaces of the crust were formerly colonized by bacterial mats, which are locally preserved by replacement and overgrowth of the bacterial filaments by metal sulphide minerals and amorphous silica. The bacterial filaments are selectively replaced by prousite (Ag 3 AsS 3 ), pearceite 3 (Ag 14.7–x Cu 1.3+x As 2 S 11 ), chalcopyrite (CuFeS 2 ) and rarely by galena (PbS). Our observations suggest that bacterially mediated processes selectively precipitate silver, arsenic and copper, and that biological processes may contribute to precious-metal enrichment in some sea-floor hydrothermal base-metal sulphide deposits.

California, Oregon↗
USGS1990

Geochemistry and intrusive history of the Ashland pluton, Klamath Mountains, California and Oregon

The Ashland pluton is a calc-alkaline plutonic complex that intruded the western Paleozoic and Triassic belt of the Klamath Mountains in late Middle Jurassic time. The pluton comprises a series of compositionally distinct magma pulses. The oldest rocks are hornblende gabbro and two-pyroxene quartz gabbro with initial 87 Sr/ 86 Sr = 0˙7044, δ 18 O = 8˙7%, and REE patterns with chondrite normalized La/Lu = 7. These units were followed by a suite of tonalitic rocks (La N /Lu N = 7) and then by a suite of K 2 O- and P 2 O 5 rocks of quartz monzodioritic affinity (La N /Lu N = 13–21; La N /Sm N = 2˙4–3˙) The quartz monzodioritic rocks were then intruded by biotite granodiorite and granite with lower REE abundances but more fractionated LREE(La N /Lu N = 13–19; La N /Sm N = 4˙3–6 and they, in turn, were host to dikes and bosses of hornblende diorite. The latest intrusive activity consisted of aplitic and granitic dikes. Combined phase equilibria and mineral composition data, indicate emplacement conditions of approximately P total = 2˙3kb, P H2O between 1˙5 and 2˙2 kb, and f O2 between the nickel-nickel oxide and hematite-magnetite buffers. Successive pulses of magma display increasing SiO 2 together with increasing δ 18 O and decreasing initial 87 Sr/ 86 Sr. The isotopic data are consistent with either (1) combined fractional crystallization of andesitic magma and concurrent assimilation of crustal material characterized by low Sr 1 and high (δ 18 O or, more probably, (2) a series of partial melting events in which sources were successively less radiogenic but richer in 18 O Each intrusive stage displays evidence for some degree of crystal accumulation and/or fractional crystallization but neither process adequately accounts for their compositional differences. Consequently, each stage appears to represent a distinct partial melting or assimilation event. The P 2 O 5 -rich nature of the quartz monzodiorite suite suggests accumulation of apatite. However, the suite contains abundant mafic microgranitoid enclaves and most apatite in the suite is acicular. These observations suggest that magma mixing affected the compositional variation of the quartz monzodiorite suite. Mass balance calculations are consistent with a simple mixing process in which P 2 O 5 -rich alkalic basalt magma (represented by the mafic microgranitoid enclaves) was combined with a crystal-poor felsic magma (represented by the tonalite suite), yielding a quartz monzodioritic magma that then underwent differentiation by crystal fractionation and accumulation.

California, Oregon↗
USGS1989

Cryptic tectonic domains of the Klamath Mountains, California and Oregon

Numerous fragments of oceanic crust and island arcs make up the Klamath Mountains province. These fragments were joined together (amalgamated) in an oceanic setting during Paleozoic and Mesozoic collisional events and were accreted to North America as a composite unit during latest Jurassic or earliest Cretaceous time. The roughly arcuate and concentric distribution of the terranes of the Klamath Mountains does not now seem to be a result of simple oroclinal bending as earlier believed. Although commonly described as a west-facing arcuate structure, the province is cut diagonally by a vaguely defined NW-trending zone of discontinuity, or hinge line, that divides the province into NE and SW tectonic domains. The zone of discontinuity is marked by a number of lithic and structural anomalies, and particularly by the distribution of a remarkable series of belts of plutonic rocks. The terranes, regional structures, and plutonic belts of the NE domain trend NE and are generally wider and more coherent than the narrow NW-trending terranes and plutonic belts of the SW domain. Most plutonic belts of the NE domain do not have equivalents in the SW domain. Paleomagnetic evidence suggests that all the plutonic belts, except possibly the youngest (the earliest Cretaceous Shasta Bally belt), were emplaced before the Klamath Mountains terranes finally accreted to North America.

California, Oregon↗
USGS1989

Body composition and weight dynamics of wintering greater white-fronted geese

Adult greater white-fronted geese ( Anser albifrons frontalis ) wintering in southern Oregon and California increased or maintained body weight in autumn, lost weight from autumn through winter, and rapidly increased in weight before spring migration in late April. We documented significant annual differences in body weights for both sexes. We related seasonal changes in body weight to changes in lipid levels, which were lowest (12-13% of wet wt in M and F) in mid-March and highest in late April (24% in F). Greater white-fronted geese maintained lipid levels during winter similar to those reported for large subspecies of Canada geese ( Branta canadensis ), and greater than those reported for small subspecies of Canada geese and other small species of geese. Protein content of carcasses varied significantly in females; i.e., lowest in early October and highest in late October and late April. Differences among species in patterns of weight change and body composition during winter seem to be related to social organization, body size, food type, and foraging behavior. Females left spring staging areas weighing relatively less than most other species of geese and may have benefited from foraging opportunities on the nesting grounds.

California, Oregon↗
USGS1989

Presumed drowning of Aleutian Canada geese on the Pacific coast of California and Oregon

Carcasses of 42 and 17 Aleutian Canada geese ( Branta canadensis leucopareia ), a federally listed endangered species, were found on ocean beaches near Crescent City, California, and near Pacific City, Oregon, respectively, following severe storms. Necropsies and other information suggest that the birds were flushed during the storms and somehow entered the water where they were washed into the surf and drowned.

California, Oregon↗