SEARCH · Search USGS

Results for “Mountain Views”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources

USGS2010

Limited hydrologic response to Pleistocene climate change in deep vadose zones - Yucca Mountain, Nevada

Understanding the movement of water through thick vadose zones, especially on time scales encompassing long-term climate change, is increasingly important as societies utilize semi-arid environments for both water resources and sites viewed as favorable for long-term disposal or storage of hazardous waste. Hydrologic responses to Pleistocene climate change within a deep vadose zone in the eastern Mojave Desert at Yucca Mountain, Nevada, were evaluated by uranium-series dating of finely layered hyalitic opal using secondary ion mass spectrometry. Opal is present within cm-thick secondary hydrogenic mineral crusts coating floors of lithophysal cavities in fractured volcanic rocks at depths of 200 to 300 m below land surface. Uranium concentrations in opal fluctuate systematically between 5 and 550 μg/g. Age-calibrated profiles of uranium concentration correlate with regional climate records over the last 300,000 years and produce time-series spectral peaks that have distinct periodicities of 100- and 41-ka, consistent with planetary orbital parameters. These results indicate that the chemical compositions of percolating solutions varied in response to near-surface, climate-driven processes. However, slow (micrometers per thousand years), relatively uniform growth rates of secondary opal and calcite deposition spanning several glacial–interglacial climate cycles imply that water fluxes in the deep vadose zone remained low and generally buffered from the large fluctuations in available surface moisture during different climates.

Nevada↗

USGS2004

Map showing spatial and temporal relations of mountain and continental glaciations on the Northern Plains, primarily in northern Montana and northwestern North Dakota

This report is an overview of glacial limits and glacial history on the plains in northern Montana and northeastern North Dakota (long 102?-114?W.) and also in adjacent southern Alberta and Saskatchewan, Canada. In the Rocky Mountains and on the plains adjacent to the mountains in Montana, the map also depicts spatial relations of valley glaciers and piedmont ice lobes to continental ice sheets. Glacial limits east of 102?, in the United States and also in adjacent Canada, are depicted on published maps of the U.S. Geological Survey Quaternary Geologic Atlas of the United States (I-1420) map series. The limits shown here are from data compiled for the Lethbridge, Regina, Yellowstone, and Big Horn Mountains 4? x 6? quadrangles in the Quaternary Geologic Atlas series. This geospatial database has been prepared with a degree of detail appropriate for viewing at a scale of 1:1,000,000. Because of the degree of generalization required, the map is intended for regional analysis, rather than for detailed analysis in specific areas. It depicts the geographic positions of the limits of mountain and continental glaciations and the limits of selected glacial readvances. That information provides a foundation for reconstruction of geologic history and for reconstruction. The base map is simplified. Selected hydrographic features, selected towns and cities, selected physiographic features, and a grid of 1? x 2? topographic quadrangles are included to aid the reader in location of the glacial limits and other features that are depicted here on other maps at different scales. Most of the geologic data were compiled at 1:250,000 scale. The nominal reading scale of the digitized map data is 1:1,000,000. Enlargement will not restore resolution that was lost by simplification or generalization of data. Accompanying illustrations show regional directions of ice movement from Canada into the United States during maximum Illinoian glaciation, during maximum late Wisconsin glaciation, and during a later regional glacial readvance maximum

Scientific Investigations Map↗

USGS1966

Lake Bonneville: Geology and hydrology of the Weber Delta district, including Ogden, Utah

A cooperative investigation to determine the geology of the Weber Delta district, with emphasis on the occurrence and chemical quality of ground water, was made by the U.S. Geological Survey and the U.S. Bureau of Reclamation with the later assistance of the Utah State Engineer in the final preparation of the report. The Weber Delta district covers an area of almost 400 square miles between the Wasatch Range and the east shore of Great Salt Lake in north-central Utah. The district, which is about 30 miles long and 3-20 miles wide, is dominated by the Wasatch Range on the east. West of the mountains is a generally narrow foothill area, from which flatlands, interrupted by a few low sand ridges, slope gently westward to the shore of Great Salt Lake. Breaching the foothills and the flatlands near the center of the district is the Weber Delta, which is the largest of the deltas built in the Pleistocene Epoch by Lake Bonneville on an open plain. The Weber Delta, the smaller delta of the Ogden River to the north, and the alluvial fans of several small streams, coalesce to form a belt of plateau-like high-lands from 2 to 7 miles wide and about 10 miles long from north to south. Ten miles north of the city of Ogden the Pleasant View salient projects westward from the front of the Wasatch Range, and about 15 miles west of the mountain front, Little Mountain rises 450 feet above the surface of the nearly level plain.

Utah↗

USGS1997

Extensional reactivation of the Chocolate Mountains subduction thrust in the Gavilan Hills of southeastern California

The NE vergent Chocolate Mountains fault of south-eastern California has been interpreted as either a subduction thrust responsible for burial and prograde metamorphism of the ensimatic Orocopia Schist or as a normal fault involved in the exhumation of the schist. Our detailed structural analysis in the Gavilan Hills area provides new evidence to confirm the latter view. A zone of deformation is present at the top of the Orocopia Schist in which lineations are parallel to those in the upper plate of the Chocolate Mountains fault but oblique to ones at relatively deep levels in the schist. Both the Orocopia Schist and upper plate contain several generations of shear zones that show a transition from crystalloblastic through mylonitic to cataclastic textures. These structures formed during retrograde metamorphism and are considered to record the exhumation of the Orocopia Schist during early Tertiary time as a result of subduction return flow. The Gatuna fault, which places low-grade, supracrustal metasediments of the Winterhaven Formation above the gneisses of the upper plate, also seems to have been active at this time. Final unroofing of the Orocopia Schist occurred during early to middle Miocene regional extension and may have involved a second phase of movement on the Gatuna fault. Formation of the Chocolate Mountains fault during exhumation indicates that its top-to-the-NE sense of movement provides no constraint on the polarity of the Orocopia Schist subduction zone. This weakens the case for a previous model involving SW dipping subduction, while providing support for the view that the Orocopia Schist is a correlative of the Franciscan Complex.

California↗

USGS2002

Field-trip guide to the southeastern foothills of the Santa Cruz Mountains in Santa Clara County, California

This field trip is an introduction to the geology of the southeastern foothills of the Santa Cruz Mountains in southern Santa Clara County. Seven stops include four short hikes to access rock exposures and views of the foothills east of Loma Prieta Peak between Gilroy and San José. Field-trip destinations highlight the dominant rock types of the "Franciscan assemblage" including outcrops of serpentinite, basalt, limestone, ribbon chert, graywacke sandstone, and shale. General discussions include how the rocks formed, and how tectonism and stream erosion have changed the landscape through time. All field trip stops are on public land; most are near reservoir dams of the Santa Clara Valley Water District. In addition, stops include examination of an Ohlone Indian heritage site and the New Almaden Mining Museum.

California↗

USGS2022

Colorado and Landsat

Colorado’s geography seems designed to impress. Although the Rocky Mountains takes up only one-half of the State, more than 50 of its peaks rise at least 14,000 feet above sea level—far more “fourteeners” than any other State. Many of these mountains receive hundreds of inches of snow annually. The Rocky Mountains provide the Continental Divide, or watershed boundary, for North America. Three of the United States’ seven longest rivers originate in Colorado’s mountains: the Rio Grande, the Colorado, and the Arkansas Rivers. The mountains are also home to 11 national forests. Residents and tourists find many ways to appreciate the stunning views, from hiking and skiing to camping and birdwatching, in ecosystems that also include grasslands and shrublands.

Colorado↗

USGS2002

Sustainability of vegetation communities grazed by elk in Rocky Mountain National Park

Current management of the worlds' grazing lands in either based on changes in plant species composition or on other management evaluation programs that emphasize changes in net aboveground production. Management is based solely on changes in aboveground production has been criticized as too limited in view, because it ignores root production, nitrogen pools, nutrient processes, and the long-term sustainability of the ecosystem. The purpose of this study was to compare the effects of elk ( Cervus elaphus ) grazing on aboveground production, internal nitrogen (N) fluxes, N pools and inputs, and elk nutrient transfers across the landscape in different vegetation types in Rocky Mountain National Park (RMNP), Colorado. Nitrogen processes and possibly N pools were significantly reduced in the willow community, but not in the upland grass/shrub community. Nitrogen mineralization rates were lower in grazed versus ungrazed short willow sites (P = 0.07; n = 4 sites), as were nitrate (NO3) pools (P = 0.10), but not in tall willow sites (P > 1.10 n = 4 sites) after 4 years. There was about half the annual N inputs to the soil surface in grazed willow sites (5.79g N/m 2 /yr = annual herbaceous biomass a?? offtake + litterfall + elk urine and feces) compared to ungrazed sites (9.66 g N/m 2 /yr = annual herbaceous biomass + litterfall), suggesting elk herbivory and movement led to a net loss of N in the willow vegetation type. Elk substantially reduced the annual growth of willows (Salix spp.) by 98% after 35 years and 66% after 4 years of treatment. Thus, height and canopy and N yield of willows were reduced as well as willow litter biomass (65 g/m2/yr in ungrazed versus 33 g/m2/yr in grazed), and N yield of willows was 64% less in grazed plots. Elk grazing had no significant effect on other soil N pools (NH4) or litter decomposition rates in either of the two willow types, nor on any nitrogen process rates or pools in the upland grass/shrub type (P > 0.10). Nitrogen concentrations in plant tissue were not influenced for the most part by elk grazing (increased N concentration found in only 4 of 13 species). Elk apparently also transported N away from aspen at an even higher rate (N inputs were 1.65 g N/m2/yr in grazed sites vs. 3.79 g N/m 2 /yr ungrazed). CENTURY modeling supported these observations. This soil N model predicted almost no change (0.5$ - 2% less) in N or carbon (C) pools in 50 years in the upland grass/shrub vegetation type, but greater losses in the willow type. If elk population levels were increased to carrying capacity in the ecosystem (about 25% more consumption) projected losses after 50 years were greater, but still <4% for soil C and 1% for spoil N in the upland type, and 6% for soil C and 2% for soil N in the willow type. Total shrub C was projected to decline 10% in 50 years in the willow type at current elk densities. We recommend conservative management of elk numbers and grazing until additional years of measures are gathered on the lower mineralization rates in the short willow type and until the projected declines in N pools can be verified.

Report↗

USGS1992

Paired, facing monoclines in the Sanpete-Sevier Valley area, central Utah

Several major monoclines that trend northward through the Sanpete-Sevier Valley area of central Utah are paired and face one another. This pairing of monoclines may have occurred when near-horizontal sedimentary and volcanic strata subsided into voids created as salt was removed from a salt diapir concealed beneath valley fill. Removal was mostly by dissolution or extrusion during Neogene time. The paired monoclines, thus, are viewed as collapse features rather than as normal synclinal folds. -from Author

Mountain Geologist↗

USGS1980

Remote sensing data of SP Mountain and SP Lava flow in north-central Arizona

Multifrequency airborne radar image data of SP Mountain [Official name of feature (U.S. Geological Survey, 1970)] and SP flow (and vicinity) in north-central Arizona were obtained in diverse viewing directions and direct and cross-polarization, then compared with surface and aerial photography, LANDSAT multispectral scanner data, airborne thermal infrared imagery, surface geology, and surface roughness statistics. The extremely blocky, basaltic andesite of SP flow is significantly brighter on direct-polarization K-band (0.9-cm wavelength) images than on cross-polarized images taken simultaneously. Conversely, for the longer wavelength (25 cm) L-band radar images, the cross-polarization image returns from SP flow are brighter than the direct-polarized image. This effect is explained by multiple scattering and the strong wavelength dependence of polarization effects caused by the rectilinear basaltic andesite scatters. Two distinct types of surface relief on SP flow, one extremely blocky, the other subdued, are found to be clearly discriminated on the visible and thermal wavelength images but are separable only on the longer wavelength L-band radar image data. The inability of the K- and X- (3-cm wavelength) band radars to portray the differences in roughness between the two SP flow surface units is attributed to the radar frequency dependence of the surface-relief scale, which, described as the Rayleigh criterion, represents the transition between quasispecular and primarily diffuse backscatter.

Arizona↗

USGS2002

Evolution of the landscape along the Clear Creek Corridor, Colorado: Urbanization, aggregate mining and reclamation

Prime agricultural land along the Clear Creek floodplain, Colorado, attracted settlement in the 1850's but the demand for sand and gravel for 1900's construction initiated a sequence of events that exceeded previous interests and created the modified landscape and urban ecosystem that exists today. The Clear Creek valley corridor offers a landscape filled with a persistent visible and hidden reminder of it's past use. The map sheets illustrate the Clear Creek landscape as a series of compositions, both at the macro view (in the spatial context of urban structure and highways from aerial photographs) and micro view (from the civic scale where landscape features like trees, buildings, and sidewalks are included). The large-scale topographic features, such as mountains and terraces, appear 'changeless' (they do change over geologic time), while Clear Creek has changed from a wide braided stream to a narrow confined stream. Transportation networks (streets and highways) and spiraling population growth in adjacent cities (from approximately 38,000 people in 1880 to over a million in 1999) form two dominant landscape patterns. Mining and wetland/riparian occupy the smallest amount of land use acres compared to urban, transportation, or water reservoir activities in the Clear Creek aggregate reserve study area. Four types of reclaimed pits along Clear Creek were determined: water storage facilities, wildlife/greenbelt space, multiple-purpose reservoirs, and 'hidden scenery.' The latter involves infilling gravel pits (with earth backfill, concrete rubble, or sanitary landfill) and covering the site with light industry or residential housing making the landform hard to detect as a past mine site. Easier to recognize are the strong-edged, rectilinear water reservoirs, reclaimed from off-channel sand and gravel pits that reflect the land survey grid and property boundaries. The general public may not realize softly contoured linear wildlife corridors connecting urban, industrial, and natural space were once mine sites too. Multiple-use water projects from exhausted pits appear to be the new millennium parks, providing water storage, passive recreation, and habitat restoration for the Denver metropolitan area. The public objects to mining yet enjoys the reclaimed mine sites as recreation and wildlife space.

Colorado↗

USGS2005

American Fisheries Society 136th Annual Meeting Lake Placid, NY 10-14 September, 2006

The New York Chapter of the American Fisheries Society and the New York State Department of Environmental Conservation invite you to experience the beauty of New York's famous Adirondack Park as the American Fisheries Society (AFS) convenes its 136th Annual Meeting in the legendary Olympic Village of Lake Placid, NY, 10-14 September 2006. Our meeting theme "Fish in the Balance" will explore the interrelation between fish, aquatic habitats, and man, highlighting the challenges facing aquatic resource professionals and the methods that have been employed to resolve conflicts between those that use or have an interest in our aquatic resources. As fragile as it is beautiful, the Adirondack Region is the perfect location to explore this theme. Bordered by Mirror Lake and its namesake, Lake Placid, the Village of Lake Placid has small town charm, but all of the conveniences that a big city would provide. Whether its reliving the magic of the 1980 hockey team's "Miracle on Ice" at the Lake Placid Olympic Center, getting a panoramic view of the Adirondack high peaks from the top of the 90 meter ski jumps, fishing or kayaking in adjacent Mirror Lake, hiking a mountain trail, or enjoying a quiet dinner or shopping excursion in the various shops and restaurants that line Main Street, Lake Placid has something for everyone.

Conference Paper↗

USGS2021

Geologic and geophysical maps of the Newfoundland Mountains and part of the adjacent Wells 30' x 60' quadrangles, Box Elder County, Utah

The Newfoundland Mountains map area (Newfoundland Mountains and adjacent part of Wells 30' x 60' quadrangles) is located in Box Elder County, northwestern Utah. The map encompasses broad expanses of the Great Salt Lake Desert as well as several picturesque mountain ranges (figures 1, 2, and 3). The geology of the area was last mapped and summarized by Doelling (1980). Since that landmark study, much of the area has been mapped in greater detail and new paleontologic, geochronologic, and structural data provide for an updated view of the geology. In addition, new geophysical studies (Langenheim and others, 2013; Langenheim, 2016) provide key data for improved interpretation of subsurface geology. The geologic map (plate 1) was compiled from fifteen 7.5' quadrangles mapped at a scale of 1:24,000 (mostly in the western part of the area), one map covering the Newfoundland Mountains at a scale of 1:31,680 (Allmendinger and Jordan, 1989), unpublished geologic mapping at scales from 1:24,000 to 1:50,000 (most by Miller; Bovine Mountain by T.E. Jordan), and reconnaissance mapping and aerial photo interpretation in intervening areas by Miller. Some published maps were remapped or reinterpreted by the authors in light of more recent studies north of the map area. Geologic mapping conducted as part of several theses/dissertations and a few published papers also were used (plate 2, index to geologic mapping). Concealed faults under valley bottoms were interpreted from gravity and aeromagnetic data. Our approach for this map was to integrate across the main themes of the mapped geology by generalizing units, structures, and polygons. This has the aim of illustrating the principal tectonic and stratigraphic packages, as well as illustrating the patterns of surficial units and geomorphology. Cross sections (plate 2) were constructed to coincide with representative cross sections for several detailed geologic maps. This approach required large bends across valleys. Basin geometry shown in the cross sections was constrained by gravity data and a seismic line since few deep drill holes are available.

Utah↗

USGS2024

Precariously balanced rocks in northern New York and Vermont, U.S.A.: Ground-motion constraints and implications for fault sources

Precariously balanced rocks (PBRs) and other fragile geologic features have the potential to constrain the maximum intensity of earthquake ground shaking over millennia. Such constraints may be particularly useful in the eastern United States (U.S.), where few earthquake‐source faults are reliably identified, and moderate earthquakes can be felt at great distances due to low seismic attenuation. We describe five PBRs in northern New York and Vermont—a region of elevated seismic hazard associated with historical seismicity. These boulders appear to be among the most fragile PBRs in the region, based on reports from hobbyists. The PBRs are glacial erratics, best evidenced by glacial striations on bedrock pedestals. The pedestals themselves are locally high knobs, often situated on regionally high topography; this setting limits soil development and indicates that any outwash deposits were likely ephemeral. As a result, PBR ages can be reliably established by the retreat of the last continental ice sheet, ∼15–13 ka. To quantify the fragility of the PBRs, we surveyed them with ground‐based light detection and ranging and calculated geometric parameters from the point clouds, field observations, and seismic responses. Preliminary validation of the 2023 time‐independent U.S. National Seismic Hazard Model (NSHM) shows that the existence of PBRs is generally consistent with the median site‐specific hazard curves. Only the Blue Ridge Road site suggests a modest reduction in hazard. To visualize the ensemble of data, we mapped the minimum permissible distance to potential source faults around each PBR site as a function of source magnitude by using the ground‐motion models from the 2023 NSHM. Viewed in this manner, our data are consistent with potential M ∼6.5 earthquake‐source faults in many parts of the Lake Champlain Valley and northern Adirondack Mountains. Our work illustrates a potential pathway for better constraining earthquake‐source faults in regions of cryptic faults.

Bulletin of the Seismological Society of America↗

USGS2019

Oxygen isotopic investigation of silicic magmatism in the Stillwater caldera complex, Nevada: Generation of large-volume, low-δ18O rhyolitic tuffs and assessment of their regional context in the Great Basin of the western United States

Successive caldera-forming eruptions from ca. 30 to 25 Ma generated a large nested caldera complex in western Nevada that was subsequently dissected by Basin and Range extension, providing extraordinary cross-sectional views through diverse volcanic and plutonic rocks. A high-resolution oxygen isotopic study was conducted on units that represent all major parts of the Job Canyon, Louderback Mountains, Poco Canyon, and Elevenmile Canyon caldera cycles (29.2−25.1 Ma), and several Cretaceous plutons that flank the Stillwater caldera complex. We provide new oxygen and strontium isotope data for 12 additional caldera centers in the Great Basin, which are synthesized with >150 published oxygen and strontium isotope analyses for regional Mesozoic basement rocks. Stillwater zircons span a large isotopic range (δ 18 O zircon of 3.6‰−8.2‰), and all caldera cycles possess low-δ 18 O zircons. In some cases, they are a small proportion of the total populations, and in others, they dominate, such as in the low-δ 18 O rhyolitic tuffs of Job Canyon and Poco Canyon (δ 18 O zircon = 4.0‰−4.3‰; δ 18 O magma = 5.5‰−6‰). These are the first low-δ 18 O rhyolites documented in middle Cenozoic calderas of the Great Basin, adding to the global occurrence of these important magma types that fingerprint recycling of shallow crust altered by low-δ 18 O meteoric waters. The appearance of low-δ 18 O rhyolites in the Stillwater caldera complex is overprinted on a Great Basin−wide trend of miogeoclinal sediment contribution to silicic magmas that elevates δ 18 O compositions, making identification of 18 O depletions difficult. Though not a nominally low-δ 18 O rhyolite, the tuff of Elevenmile Canyon possesses both low-δ 18 O and high-δ 18 O zircon cores that are overgrown by homogenized zircon rims that approximate the bulk zircon average, pointing to batch assembly of isotopically diverse upper crustal melts to generate one of the most voluminous (2500−5000 km 3 ) tuff eruptions in the Great Basin. Despite overlapping in space and time, each caldera-forming cycle of the Stillwater complex has a unique oxygen isotope record as retained in single zircons. Most plutons that were spatially and temporally coincident with calderas have isotopic compositions that diverge from the caldera-forming tuffs and cannot be their cogenetic remnants.

Nevada↗

USGS2010

Earth as art three

For most of us, deserts, mountains, river valleys, coastlines even dry lakebeds are relatively familiar features of the Earth's terrestrial environment. For earth scientists, they are the focus of considerable scientific research. Viewed from a unique and unconventional perspective, Earth's geographic attributes can also be a surprising source of awe-inspiring art. That unique perspective is space. The artists for the Earth as Art Three exhibit are the Landsat 5 and Landsat 7 satellites, which orbit approximately 705 kilometers (438 miles) above the Earth's surface. While studying the images these satellites beam down daily, researchers are often struck by the sheer beauty of the scenes. Such images inspire the imagination and go beyond scientific value to remind us how stunning, intricate, and simply amazing our planet's features can be. Instead of paint, the medium for these works of art is light. But Landsat satellite sensors don't see light as human eyes do; instead, they see radiant energy reflected from Earth's surface in certain wavelengths, or bands, of red, green, blue, and infrared light. When these different bands are combined into a single image, remarkable patterns, colors, and shapes emerge. The Earth as Art Three exhibit provides fresh and inspiring glimpses of different parts of our planet's complex surface. The images in this collection were chosen solely based on their aesthetic appeal. Many of the images have been manipulated to enhance color variations or details. They are not intended for scientific interpretation only for your viewing pleasure. Enjoy!

General Information Product↗

USGS2020

Snow processes in mountain forests: Interception modeling for coarse-scale applications

Snow interception by the forest canopy controls the spatial heterogeneity of subcanopy snow accumulation leading to significant differences between forested and nonforested areas at a variety of scales. Snow intercepted by the forest canopy can also drastically change the surface albedo. As such, accurately modeling snow interception is of importance for various model applications such as hydrological, weather, and climate predictions. Due to difficulties in the direct measurements of snow interception, previous empirical snow interception models were developed at just the point scale. The lack of spatially extensive data sets has hindered the validation of snow interception models in different snow climates, forest types, and at various spatial scales and has reduced the accurate representation of snow interception in coarse-scale models. We present two novel empirical models for the spatial mean and one for the standard deviation of snow interception derived from an extensive snow interception data set collected in an evergreen coniferous forest in the Swiss Alps. Besides open-site snowfall, subgrid model input parameters include the standard deviation of the DSM (digital surface model) and/or the sky view factor, both of which can be easily precomputed. Validation of both models was performed with snow interception data sets acquired in geographically different locations under disparate weather conditions. Snow interception data sets from the Rocky Mountains, US, and the French Alps compared well to the modeled snow interception with a normalized root mean square error (NRMSE) for the spatial mean of ≤10 % for both models and NRMSE of the standard deviation of ≤13 %. Compared to a previous model for the spatial mean interception of snow water equivalent, the presented models show improved model performances. Our results indicate that the proposed snow interception models can be applied in coarse land surface model grid cells provided that a sufficiently fine-scale DSM is available to derive subgrid forest parameters.

Utah↗

USGS1991

Chloride cycling in two forested lake watersheds in the west-central Adirondack Mountains, New York, U.S.A.

The chemistry of precipitation, throughfall, soil water, ground water, and surface water was evaluated in two forested lake-watersheds over a 4-yr period to assess factors controlling C1- cycling. Results indicate that C1- cycling in these watersheds is more complex than the generally held view of the rapid transport of atmospherically derived C1- through the ecosystem. The annual throughfall Cl- flux for individual species in the northern hardwood forest was 2 to 5 times that of precipitation (56 eq ha-1), whereas the Na+ throughfall flux, in general, was similar to the precipitation flux. Concentrations of soil-water Cl- sampled from ceramic tension lysimeters at 20 cm below land surface generally exceeded the Na+ concentrations and averaged 31 ??eq L-1, the highest of any waters sampled in the watersheds, except throughfall under red spruce which averaged 34 ??eq L-1. Chloride was concentrated prior to storms and mobilized rapidly during storms as suggested by increases in streamwater Cl- concentrations with increasing flow. Major sources of Cl- in both watersheds are the forest floor and hornblende weathering in the soils and till. In the Panther Lake watershed, which contains mainly thick deposits of till( > 3 m), hornblende weathering results in a net Cl- flux 3 times greater than that in the Woods Lake watershed, which contains mainly thin deposits of till. The estimated accumulation rate of Cl- in the biomass of the two watersheds was comparable to the precipitation Cl- flux.The chemistry of precipitation, throughfall, soil water, ground water, and surface water was evaluated in two forested lake-watersheds over a 4-yr period to assess factors controlling Cl- cycling. Results indicate that Cl- cycling in these watersheds is more complex than the generally held view of the rapid transport of atmospherically derived Cl- through the excosystem. The annual throughfall Cl- flux for individual species in the northern hardwood forest was 2 to 5 times that of precipitation (56 eq ha-1), whereas the Na+ throughfall flux, in general, was similar to the precipitation flux. Concentrations of soil-water Cl- sampled from ceramic tension lysimeters at 20 cm below land surface generally exceeded the Na+ concentrations and averaged 31 ??eq L-1, the highest of any waters sampled in the watersheds, except throughfall under red spruce which averaged 34 ??eq L-1. Chloride was concentrated prior to storms and mobilized rapidly during storms as suggested by increases in streamwater Cl- concentrations with increasing flow. Major sources of Cl- in both watersheds are the forest floor and hornblende weathering in the soils and till. In the Panther Lake watershed, which contains mainly thick deposits of till (> 3 m), hornblende weathering results in a net Cl- flux 3 times greater than that in the Woods Lake watershed, which contains mainly thin deposits of till. The estimated accumulation rate of Cl- in the biomass of the two watersheds was comparable to the precipitation Cl- flux.

Water, Air, & Soil Pollution↗

USGS2002

Reconnaissance of alluvial fans as potential sources of gravel aggregate, Santa Cruz River valley, Southeast Arizona

This investigation was conducted to provide information on the aggregate potential of alluvial fan sediments in the Santa Cruz River valley. Pebble lithology, roundness, and particle size were determined in the field, and structures and textures of alluvial fan sediments were photographed and described. Additional measurements of particle size on digital photographs were made on a computer screen. Digital elevation models were acquired and compiled for viewing the areal extent of selected fans. Alluvial fan gravel in the Santa Cruz River valley reflects the lithology of its source. Gravel derived from granitic and gneissic terrane of the Tortolita, Santa Catalina, and Rincon Mountains weathers to grus and is generally inferior for use as aggregate. Gravel derived from the Tucson, Sierrita, and Tumacacori Mountains is composed mostly of angular particles of volcanic rock, much of it felsic in composition. This angular volcanic gravel should be suitable for use in asphalt but may require treatment for alkali-silica reaction prior to use in concrete. Gravel derived from the Santa Rita Mountains is of mixed plutonic (mostly granitic rocks), volcanic (mostly felsic rocks), and sedimentary (sandstone and carbonate rock) composition. The sedimentary component tends to make gravel derived from the Santa Rita Mountains slightly more rounded than other fan gravel. The coarsest (pebble, cobble, and boulder) gravel is found near the heads (proximal part) of alluvial fans. At the foot (distal part) of alluvial fans, most gravel is pebble-sized and interbedded with sand and silt. Some of the coarsest gravel was observed near the head of the Madera Canyon, Montosa Canyon, and Esperanza Wash fans. The large Cienega Creek fan, located immediately south and southeast of Tucson, consists entirely of distal-fan pebble gravel, sand, and silt.

Arizona↗