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At least 451 records · Page 25Linked to original sources
USGS2002

Early Holocene change in atmospheric circulation in the Northern Great Plains: An upstream view of the 8.2 ka cold event

Elk Lake, in northwestern Minnesota, contains numerous proxy records of climatic and environmental change contained in varved sediments with annual resolution for the last 10,000 years. These proxies show that about 8200 calendar years ago (8.2 cal. ka; 7300 radiocarbon years) Elk Lake went from a well-stratified lake that was wind-protected in a boreal forest to a well-mixed lake in open prairie savanna receiving northwesterly wind-blown dust, probably from the dry floor of Lake Agassiz. This change in climate marks the initiation of the widely recognized mid-Holocene “altithermal” in central North America. The coincidence of this change with the so-called 8.2 cal. ka cold event, recognized in ice-core and other records from the circum-North Atlantic, and thought by some to be caused by catastrophic discharge of freshwater from proglacial lakes Agassiz and Ojibway, suggests that the two “events” might be related. Our interpretation of the Elk Lake proxy records, and of other records from less accurately dated sites, suggests that change in climate over North America was the result of a fundamental change in atmospheric circulation in response to marked changes in the relative proportions of land, water, and, especially, glacial ice in North America during the early Holocene. This change in circulation probably post-dates the final drainage of proglacial lakes along the southern margin of the Laurentide ice sheet, and may have produced a minor perturbation in climate over Greenland that resulted in a brief cold pulse detected in ice cores.

Minnesota↗
USGS2003

Geologic map and digital database of the Redlands 7.5' quadrangle, San Bernardino and Riverside Counties, California

This geologic database of the Redlands 7.5' quadrangle was prepared by the Southern California Areal Mapping Project (SCAMP), a regional geologic-mapping project sponsored jointly by the U.S. Geological Survey and the California Geological Survey. The database was developed as a contribution to the National Cooperative Geologic Mapping Program's National Geologic Map Database, and is intended to provide a general geologic setting of the Redlands quadrangle. The database and map provide information about earth materials and geologic structures, including faults and folds that have developed in the quadrangle due to complexities in the San Andreas Fault system. The Redlands 7.5' quadrangle contains earth materials and structures that provide insight into the late Cenozoic geologic evolution of the southern California Inland Empire region. Important stratigraphic and structural elements include (1) the modern trace of the San Andreas and San Jacinto faults and (2) late Tertiary and Quaternary sedimentary materials and geologic structures that formed during the last million years or so and that record complex geologic interactions within the San Andreas Fault system. These materials and the structures that deform them provide the geologic framework for investigations of earthquake hazards and ground-water recharge and subsurface flow. Geologic information contained in the Redlands database is general-purpose data that is applicable to land-related investigations in the earth and biological sciences. The term "general-purpose" means that all geologic-feature classes have minimal information content adequate to characterize their general geologic characteristics and to interpret their general geologic history. However, no single feature class has enough information to definitively characterize its properties and origin. For this reason the database cannot be used for site-specific geologic evaluations, although it can be used to plan and guide investigations at the site-specific level. This summary pamphlet discusses major categories of surficial materials in the Redlands quadrangle, and provides a conceptual framework and basis for how geologicmap units containing such materials are recognized and correlated.

California↗
USGS1969

An analysis of gravity data in Area 12, Nevada Test Site

The gravity data available from Healey and Miller (1963a) were augmented by new observations along three profiles through two new drill holes in Area 12; UEI2t #1 and UEI2p #1. The data were interpreted to allow evaluation of the geologic structure prior to the planning and excavation of two proposed tunnel complexes, Ul2t and Ul2p. Density values for each of six rock units were determined to allow a two-dimensional analysis of the gravity data along the above-mentioned profiles. The surficial rocks of Quaternary and Tertiary age and the Tertiary volcanic rocks have a weighted average density of 1.86 gm/cc. The density of the caprock at Rainier and Aqueduct Mesas ranges from 2.17 gm/cc at UEI2p #1 to 2.27 gm/cc at UEI2t #1. The Gold Meadows stock and the associated Precambrian quartzite have an arithmetic average density of 2.60 gm/cc for all samples measured. The middle Paleozoic dolomite in Area 12 has an arithmetic average density of 2.75 gm/cc. The clastic rocks of Paleozoic age have an arithmetic average density of 2.60 gm/cc. Interpretation of the residual gravity data indicates a maximum thickness of about 2,800 feet for all Tertiary volcanic rocks. A normal fault striking N. 30 ? E. disrupts the pre-Cenozoic surface at UEI2p #1 and 0.4 mile east of UEI2t #1. The throw within rock of Paleozoic age is about 400-500 feet. Another normal fault that strikes about N. 20 ? E. is located about 1.5 miles east of UEI2p #1. The throw of this fault is at least 1,100 feet in rocks of pre-Cenozoic age. Elevation contours representing the pre-Cenozoic surface in Area 12 show a maximum relief of about 2,000 feet.

Nevada↗
USGS2000

Geophysical constraints on the Virgin River Depression, Nevada, Utah, and Arizona

Gravity and aeromagnetic data provide insights into the subsurface lithology and structure of the Virgin River Depression (VRD) of Nevada, Utah, and Arizona. The gravity data indicate that the Quaternary and Tertiary sedimentary deposits hide a complex pre-Cenozoic surface. A north-northwest-trending basement ridge separates the Mesquite and Mormon basins, as evidenced by seismic-reflection, gravity, and aeromagnetic data. The Mesquite basin is very deep, reaching depths of 8?10 km. The Mormon basin reaches thicknesses of 5 km. Its northern margin is very steep and may be characterized by right steps, although this interpretation could change with additional gravity stations. Most of the young (Quaternary), small-displacement faults trend within 10? of due north and occur within the deeper parts of the Mesquite basin north of the Virgin River. South of the Virgin River, only a few, young, small-displacement faults are mapped; the trend of these faults is more northeasterly and parallels the basement topography and is distinct from that of the faults to the north. The Virgin River appears to follow the margin of the basin as it emerges from the plateau. The high-resolution aeromagnetic data outline the extent of shallow volcanic rocks in the Mesquite basin. The north-northwest alignment of volcanic rocks east of Toquop Wash appear to be structurally controlled because of faults imaged on seismic-reflection profiles and because the alignment is nearly perpendicular to the direction of Cenozoic extension. More buried volcanics likely exist to the north and east of the high-resolution aeromagnetic survey. Broader aeromagnetic anomalies beneath pre-Cenozoic basement in the Mormon Mountains and Tule Springs Hills reflect either Precambrian basement or Tertiary intrusions. These rocks are probably barriers to groundwater flow, except where fractured.

Arizona, Nevada, Utah↗
USGS2006

Seismic constraints and Coulomb stress changes of a blind thrust fault system, 1: Coalinga and Kettleman Hills, California

This report reviews the seismicity and surface ruptures associated with the 1982-1985 earthquake sequence in the Coalinga region in California, and the role of Coulomb stress in triggering the mainshock sequence and aftershocks. The 1982-1985 New Idria, Coalinga, and Kettleman Hills earthquakes struck on a series of west-dipping, en echelon blind thrust faults. Each earthquake was accompanied by uplift of a Quaternary anticline atop the fault, and each was accompanied by a vigorous aftershock sequence. Aftershocks were widely dispersed, and are seen above and below the thrust fault, as well as along the up-dip and down-dip projection of the main thrust fault. For the Coalinga and Kettleman Hills earthquakes, high-angle reverse faults in the core of the anticlines are evident in seismic reflection profiles, and many of these faults are associated with small aftershocks. The shallowest aftershocks extended to within 3-4 km of the ground surface. There is no compelling evidence for aftershocks associated with flexural slip faulting. No secondary surface rupture was found on any of the anticlines. In contrast, the 1983 Nuñez rupture struck on a high-angle reverse fault 10 km west of the Coalinga epicenter, and over a 40-80-day period, up to 1 m of oblique surface slip occurred. The slip on this Holocene fault likely extended from the ground surface to a depth of 8-10 km. We argue that both the Nuñez and Kettleman earthquakes were triggered by stresses imparted by the Coalinga mainshock, which was the largest of the four events in the sequence.

California↗
USGS1979

Artificial-recharge investigation near Aurora, Nebraska: 2-year progress report

This report presents the results of the first 2 years of a 4-year investigation of potential for artificial recharge and recharge methods that might be used to mitigate excessive aquifer depletion in Nebraska. A Quaternary sand-and-gravel aquifer near Aurora, Nebr., was recharged by injecting water through a well at a rate of approximately 730 gallons per minute for nearly 6 months. Total recharge was 530 acre-feet. Recharge was intermittent during the first 2 months, but was virtually continuous during the last 4 months. Buildup of the water level in the recharge well was 17 feet. The rate of buildup indicates that the well could have accepted water by gravity flow at more than 3,000 gallons per minute for at least 1 year. The cause of a continuing slow rise in water levels in the recharge well in contrast to nearly stable water levels in observation wells as close as 10 feet from the recharge well is as yet uncertain. The recharge water and the native ground water appeared to be chemically compatible. Infiltration rates from 24-foot-diameter surface impoundments ranged from 0.04 to 0.66 feet per day. The higher rates may have resulted in part from leakage down incompletely sealed holes that were drilled to install monitoring equipment. The investigation, including a report on the entire project, is scheduled for completion by 1980.

Nebraska↗
USGS1981

Submarine topography and physiography of lower Cook Inlet, Alaska

The submarine topography of lower Cook Inlet, Alaska, is complex because the bathymetric aspects and water depths change rapidly over short distances. The folded upper Tertiary subbottom was eroded during the first of five major Quaternary glacial advances over the inlet, and later fluvial, fluvioglacial, glacial, and marine erosional and depositional processes shaped the bottom to its present configuration. Most of lower Cook Inlet has a relative smooth topography showing small local highs and lows, and slopes with gradients generally ranging from less than a degree to locally about 5°. Around the southwestern Kenai Peninsula and the Barren and Kodiak Islands, strong faulting with vertical movement has added to the complexity of bottom topography. Less complex, nonfaulted areas occur near Kalgin Island and south Kachemak Bay and around Augustine Island. To facilitate description of lower Cook Inlet the estuarine body is divided into three large regions, northern and central, southern, and eastern; and these regions are divided into smaller physiographic areas on the basis of submarine topographic characteristics and 20-m depth zonations. Each area is named by combining the geographic name of a nearby place or feature on land with a common term for a marine physiographic feature -- trough, platform, ramp, slope, plateau. Local highs and deeps having lees than 5-m relief, which can be important to fisheries and specific research or economic studies, are not named, mentioned in text, or shown on the figures.

Alaska↗
USGS1982

Availability and quality of water from the Dakota aquifer, northwest Iowa

The Dakota aquifer in northwest Iowa consists of sandstones in the Dakota Formation. It underlies most of the study area and is the most extensive source of ground water in the area. Individual sandstone beds are from less than 10 to more than 150 feet thick. The cumulative thickness of sandstone is more than 200 feet throughout much of the area. The aquifer is confined by overlying Cretaceous limestone and shale, Quaternary glacial deposits and loess. The underlying confining material is shale of the Dakota Formation, undifferentiated Paleozoic age rocks, or Precambrian crystalline rock. Water flows through the aquifer from the north-central part of the study area to the east, south and southwest. Recharge is dominantly by infiltration from the land surface through the confining materials. Discharge is to underlying Paleozoic aquifers and to the alluvium and glacial outwash deposits along the Missouri and Big Sioux Rivers in the southwest part of the area. Flow components toward bedrock valleys may reflect discharge to Quaternary sand and gravel deposits in these valleys. Pumping tests conducted in the study area indicate a narrow range of hydraulic conductivities of the Dakota aquifer, from 37 to 50 feet per day. Consequently, an average hydraulic conductivity of 40 feet per day was used to estimate the potential yield to wells completed in the aquifer. Yields of more than 250 gallons per minute can be expected throughout much of the study area and more than 1000 gallons per minute could be produced in some areas. The quality of water from the Dakota is a calcium, magnesium, sulfate type. It is generally suitable for irrigation purposes, based on comparisons of sodium adsorption ratios and electrical conductivities. In some areas the aquifer has water with high salinity hazard that may restrict its use to irrigation of only well drained types of soil. The concentration of radium226 and other radionuclides exceed recommended limits at several sites. The quality of water pumped from the aquifer may be altered by induced leakage from the underlying aquifers in Paleozoic age rocks if withdrawals reverse the pattern of natural flow from the Dakota into the Paleozoic aquifers. Evidence for such a reversal exists in the area around the city of LeMars.

Iowa↗
USGS1976

Submarine faults and slides that disrupt surficial sedimentary units, northern Gulf of Alaska

Faults and submarine slides or slumps of Quaternary age are potential environmental hazards on the outer continental shelf (OCS) of the northern Gulf of Alaska. Most of the faults that approach or reach the seafloor cut strata that may be equivalent to the upper Yakataga Formation (Pliocene-Pleistocene). Along several faults the seafloor is offset from 5 to 20 m. A few faults appear to cut Holocene sediments, but none of these show offset at the seafloor. Submarine slides or slumps have been found in two places in the OCS region: (1) seaward of the Malaspina Glacier and Icy Bay, an affected area of 1,770 km 2 with a slope of less than one-half degree, and (2) across the entire span of the Copper River prodelta, an area of 1,730 km 2 , having a slope of about one-half degree. Seismic profiles across these slide areas show disrupted reflectors and irregular topography commonly associated with submarine slides or slumps. Potential slide or slump areas have been delineated in areas of thick sediment accumulation and relatively steep slopes. These areas include (1) Kayak Trough, (2) parts of Hinchinbrook Entrance and Sea Valley, (3) parts of the outer shelf and upper slope between Kayak Island and Yakutat Bay and (4) Bering Trough.

Alaska↗
USGS2000

Preliminary maps of Quaternary deposits and liquefaction susceptibility, nine-county San Francisco Bay region, California: a digital database

This report presents a preliminary map and database of Quaternary deposits and liquefaction susceptibility for the nine-county San Francisco Bay region, together with a digital compendium of ground effects associated with past earthquakes in the region. The report consists of (1) a spatial database of fivedata layers (Quaternary deposits, quadrangle index, and three ground effects layers) and two text layers (a labels and leaders layer for Quaternary deposits and for ground effects), (2) two small-scale colored maps (Quaternary deposits and liquefaction susceptibility), (3) a text describing the Quaternary map, liquefaction interpretation, and the ground effects compendium, and (4) the databse description pamphlet. The nine counties surrounding San Francisco Bay straddle the San Andreas fault system, which exposes the region to serious earthquake hazard (Working Group on California Earthquake Probabilities, 1999). Much of the land adjacent to the Bay and the major rivers and streams is underlain by unconsolidated deposits that are particularly vulnerable to earthquake shaking and liquefaction of water-saturated granular sediment. This new map provides a modern and regionally consistent treatment of Quaternary surficial deposits that builds on the pioneering mapping of Helley and Lajoie (Helley and others, 1979) and such intervening work as Atwater (1982), Helley and others (1994), and Helley and Graymer (1997a and b). Like these earlier studies, the current mapping uses geomorphic expression, pedogenic soils, and inferred depositional environments to define and distinguish the map units. In contrast to the twelve map units of Helley and Lajoie, however, this new map uses a complex stratigraphy of some forty units, which permits a more realistic portrayal of the Quaternary depositional system. The two colored maps provide a regional summary of the new mapping at a scale of 1:275,000, a scale that is sufficient to show the general distribution and relationships of the map units but cannot distinguish the more detailed elements that are present in the database. The report is the product of years of cooperative work by the USGS National Earthquake Hazards Reduction Program (NEHRP) and National Cooperative Geologic Mapping Program, William Lettis and & Associates, Inc. (WLA) and, more recently, by the California Division of Mines and Geology as well. An earlier version was submitted to the Geological Survey by WLA as a final report for a NEHRP grant (Knudsen and others, 2000). The mapping has been carried out by WLA geologists under contract to the NEHRP Earthquake Program (Grants #14-08-0001-G2129, 1434-94-G-2499, 1434-HQ-97-GR-03121, and 99-HQ-GR-0095) and with other limited support from the County of Napa, and recently also by the California Division of Mines and Geology. The current map consists of this new mapping and revisions of previous USGS mapping.

Open-File Report↗
USGS2004

Geologic and bathymetric reconnaissance overview of the San Pedro shelf region, southern California

This report presents a series of maps that describe the bathymetry and late Quaternary geology of the San Pedro shelf area as interpreted from seismic-reflection profiles and 3.5-kHz and multibeam bathymetric data. Some of the seismic-reflection profiles were collected with Uniboom and 120-kJ sparker during surveys conducted by the U.S. Geological Survey (USGS) in 1973 (K-2-73-SC), 1978 (S-2-78-SC), and 1979 (S-2a-79-SC). The remaining seismic-reflection profiles were collected in 2000 using Geopulse boomer and minisparker during USGS cruise A-1-00-SC. The report consists of seven oversized sheets: 1. Map of 1978 and 1979 uniboom seismic-reflection and 3.5-kHz tracklines used to map faults and folds on San Pedro Shelf. 2. Maps of multibeam shaded bathymetric relief with faults and folds, and bathymetric contours. 3. Isopach map of unconsolidated sediment, seismic-reflection profile across the San Pedro shelf, seismic-reflection profile across San Gabriel paleo-valley. 4. Seismic-reflection profiles across the Palos Verdes Fault Zone. 5. Geologic map and samples of Uniboom and 120-kJ sparker seismic-reflection profiles used to make the map. 6. Map showing thickness of uppermost (Holocene?) sediment layer. 7. Map of San Gabriel Canyon paleo-valley and associated drainage basins.

California↗
USGS2019

Offshore shallow structure and sediment distribution, Point Sur to Point Arguello, central California

This publication consists of three map sheets that display shallow geologic structure, along with sediment distribution and thickness, for an about 225-km-long offshore section of the central California coast between Point Sur and Point Arguello. Each map sheet includes three maps, at scales of either 1:150,000 or 1:200,000, as well as a set of figures that contain representative high-resolution seismic-reflection profiles. The maps and seismic-reflection surveys cover most of the continental shelf in this region. In addition, the maps show the locations of the shelf break and the 3-nautical-mile limit of California’s State Waters. The seismic-reflection data, which are the primary dataset used to develop the maps, were collected to support the California Seafloor Mapping Program and U.S. Geological Survey Offshore Geologic Hazards projects. In addition to the three map sheets, this publication includes geographic information system data files of interpreted faults, folds, sediment thicknesses, and depths-to-base of sediment. The faults and folds shown on the maps have been locally simplified as appropriate for the map scales. The right-lateral San Gregorio–Hosgri Fault (SGHF) is the most significant structure in the map area. On a regional scale, the SGHF is part of a 400-km-long, right-lateral fault system that extends northwestward from Point Arguello to the area offshore of San Francisco, where it merges with the San Andreas Fault. From north to south in this part of central California, the SGHF lies offshore between the south flank of Point Sur and the north flank of Point Piedras Blancas, then comes onshore at Point Piedras Blancas, before heading offshore again between the south flank of Point Piedras Blancas and Point Arguello. Cumulative fault offset along the SGHF is as much as 150 to 160 km, decreasing to the south by transferring slip on to northwest-striking faults that converge with the SGHF both onland and offshore from the east. In the map area, the offshore-converging faults include the Los Osos Fault, the Shoreline–Point Buchon Fault, the Casmalia Fault, and the Lions Head Fault. Quaternary sediments and bedrock underlie the shelf. On the seismic-reflection profiles, we divide Quaternary shelf sediments into two units. Characterizing the younger, upper unit is a focus of this publication. This unit is inferred to have been deposited on the shelf in the last about 21,000 years during the sea-level rise that followed the last major lowstand and the Last Glacial Maximum (LGM). This upper unit overlies a transgressive surface of erosion, a commonly angular, wave-cut unconformity, and is generally characterized by low-amplitude, continuous to moderately continuous, diffuse, subparallel, generally flat reflections. Maps in this publication show both the thickness of this upper sediment unit and the depth to the base of the sediment unit. Within the map region, 11 different “domains” of post-LGM shelf sediment are delineated on the basis of sediment thickness and coastal geomorphology. Maximum sediment thickness is in the southern part of the region, offshore of the mouths of the Santa Ynez and Santa Maria Rivers. Minimum sediment thickness is found offshore of prominent rocky points, including Point Buchon and Piedras Blancas. Mean sediment thickness for the entire shelf in the map area between Point Sur and Point Arguello is 12.2 m, and total sediment volume is 24.7 million cubic meters.

California↗
USGS1973

Hydrology of the dunes area north of Coos Bay, Oregon

Hydrology of a 20-square-mile area of dunes along the central Oregon coast was studied. The area is underlain by 80 to 150 feet of Quaternary dune and marine sand which overlies Tertiary marine clay and shale. Ground water for industrial and municipal use is being withdrawn at a rate of 4 million gallons per day. Original plans to withdraw as much as 30 million gallons per day are evidently limited by the prospect of excessive lowering of levels in shallow lakes near the wells, and possibly sea-water intrusion, if water-level gradients are reversed. At the present stage of development there are 18 production wells, each capable of producing 200-300 gallons per minute from the lower part of the sand deposits. Except for thin layers of silt, clay, and organic matter, the deposits of sand are clean and uniform; horizontal permeability is two orders of magnitude times the vertical permeability. Because of the low vertical permeability, drawdown cones are not evident in the upper part of the aquifer adjacent to the wells. However, present pumping lowers general water levels in the lakes and the shallow ground-water zone as much as several feet. A two-layer electric analog model was built to analyze effects of present and projected development as well as any alternate plans. Model results were used to develop curves for short-term prediction of water levels.

Open-File Report↗
USGS2016

Statistical analysis of lake levels and field study of groundwater and surface-water exchanges in the northeast Twin Cities Metropolitan Area, Minnesota, 2002 through 2015: Chapter A of Water levels and groundwater and surface-water exchanges in lakes of the northeast Twin Cities Metropolitan Area, Minnesota, 2002 through 2015

Water levels declined from 2003 to 2011 in many lakes in Ramsey and Washington Counties in the northeast Twin Cities Metropolitan Area, Minnesota; however, water levels in other northeast Twin Cities Metropolitan Area lakes increased during the same period. Groundwater and surface-water exchanges can be important in determining lake levels where these exchanges are an important component of the water budget of a lake. An understanding of groundwater and surface-water exchanges in the northeast Twin Cities Metropolitan Area has been limited by the lack of hydrologic data. The U.S. Geological Survey, in cooperation with the Metropolitan Council and Minnesota Department of Health, completed a field and statistical study assessing lake-water levels and regional and local groundwater and surface-water exchanges near northeast Twin Cities Metropolitan Area lakes. This report documents the analysis of collected hydrologic, water-quality, and geophysical data; and existing hydrologic and geologic data to (1) assess the effect of physical setting and climate on lake-level fluctuations of selected lakes, (2) estimate potential percentages of surface-water contributions to well water across the northeast Twin Cities Metropolitan Area, (3) estimate general ages for waters extracted from the wells, and (4) assess groundwater inflow to lakes and lake-water outflow to aquifers downgradient from White Bear Lake. Statistical analyses of lake levels during short-term (2002–10) and long-term (1925–2014) periods were completed to help understand lake-level changes across the northeast Twin Cities Metropolitan Area. Comparison of 2002–10 lake levels to several landscape and geologic characteristics explained variability in lake-level changes for 96 northeast Twin Cities Metropolitan Area lakes. Application of several statistical methods determined that (1) closed-basin lakes (without an active outlet) had larger lake-level declines than flow-through lakes with an outlet; (2) closed-basin lake-level changes reflected groundwater-level changes in the Quaternary, Prairie du Chien, and Jordan aquifers; (3) the installation of outlet-control structures, such as culverts and weirs, resulted in smaller multiyear lake-level changes than lakes without outlet-control structures; (4) water levels in lakes primarily overlying Superior Lobe deposits were significantly more variable than lakes primarily overlying Des Moines Lobe deposits; (5) lake-level declines were larger with increasing mean lake-level elevation; and (6) the frequency of some of these characteristics varies by landscape position. Flow-through lakes and lakes with outlet-control structures were more common in watersheds with more than 50 percent urban development compared to watersheds with less than 50 percent urban development. A comparison of two 35-year periods during 1925–2014 revealed that variability of annual mean lake levels in flow-through lakes increased when annual precipitation totals were more variable, whereas variability of annual mean lake levels in closed-basin lakes had the opposite pattern, being more variable when annual precipitation totals were less variable. Oxygen-18/oxygen-16 and hydrogen-2/hydrogen-1 ratios for water samples from 40 wells indicated the well water was a mixture of surface water and groundwater in 31 wells, whereas ratios from water sampled from 9 other wells indicated that water from these wells receive no surface-water contribution. Of the 31 wells with a mixture of surface water and groundwater, 11 were downgradient from White Bear Lake, likely receiving water from deeper parts of the lake. Age dating of water samples from wells indicated that the age of water in the Prairie du Chien and Jordan aquifers can vary widely across the northeast Twin Cities Metropolitan Area. Estimated ages of recharge for 9 of the 40 wells sampled for chlorofluorocarbon concentrations ranged widely from the early 1940s to mid-1970s. The wide range in estimated ages of recharge may have resulted from the wide range in the open-interval lengths and depths for the wells. Results from stable isotope analyses of water samples, lake-sediment coring, continuous seismic-reflection profiling, and water-level and flow monitoring indicated that there is groundwater inflow from nearshore sites and lake-water outflow from deep-water sites in White Bear Lake. Continuous seismic-reflection profiling indicated that deep sections of White Bear, Pleasant, Turtle, and Big Marine Lakes have few trapped gases and little organic material, which indicates where groundwater and lake-water exchanges are more likely. Water-level differences between White Bear Lake and piezometer and seepage measurements in deep waters of the lake indicate that groundwater and lake-water exchange is happening in deep waters, predominantly downgradient from the lake and into the lake sediment. Seepage fluxes measured in the nearshore sites of White Bear Lake generally were higher than seepage fluxes measured in the deep-water sites, which indicates that groundwater-inflow rates at most of the nearshore sites are higher than lake-water outflow from the deep-water sites.

Minnesota↗
USGS2002

An update of Quaternary faults of central and eastern Oregon

This is the online version of a CD-ROM publication. We have updated the eastern portion of our previous active fault map of Oregon (Pezzopane, Nakata, and Weldon, 1992) as a contribution to the larger USGS effort to produce digital maps of active faults in the Pacific Northwest region. The 1992 fault map has seen wide distribution and has been reproduced in essentially all subsequent compilations of active faults of Oregon. The new map provides a substantial update of known active or suspected active faults east of the Cascades. Improvements in the new map include (1) many newly recognized active faults, (2) a linked ArcInfo map and reference database, (3) more precise locations for previously recognized faults on shaded relief quadrangles generated from USGS 30-m digital elevations models (DEM), (4) more uniform coverage resulting in more consistent grouping of the ages of active faults, and (5) a new category of 'possibly' active faults that share characteristics with known active faults, but have not been studied adequately to assess their activity. The distribution of active faults has not changed substantially from the original Pezzopane, Nakata and Weldon map. Most faults occur in the south-central Basin and Range tectonic province that is located in the backarc portion of the Cascadia subduction margin. These faults occur in zones consisting of numerous short faults with similar rates, ages, and styles of movement. Many active faults strongly correlate with the most active volcanic centers of Oregon, including Newberry Craters and Crater Lake.

Open-File Report↗
USGS1977

Geology of the Monterey Bay region

Geophysical data and sea floor samples collected from the continental shelf and slope between Ano Nuevo Point and Point Sur, California indicate that the Monterey Bay region has had a complex late Cenozoic tectonic history. Uplift and depression have produced a succession of regressive and transgressive sedimentary units, while contemporaneous right-slip along faults of the San Andreas system have offset major structural and lithologic elements. This deformation produced three regional and several local unconformities within upper Tertiary rocks and initiated development of a canyon system that today includes the Monterey, Ascension, Carmel, and other large submarine canyons. The Tertiary stratigraphy of the offshore Monterey Bay area is divided into two provinces by a major structural boundary, the north-trending Palo Colorado-San Gregorio fault zone. East of this zone in the offshore are four seismically distinct sequences that can be correlated with major sequences onshore. These sequences comprise (1) pre-Tertiary basement, and (2) middle Miocene, (3) upper Miocene to Pliocene, and (4) upper Pliocene to Holocene sedimentary intervals. Each of the latter three sequences is bounded by unconformities, as is its counterpart on land. Only Neogene sedimentary rocks are present offshore; Paleogene units, if originally present, have been removed completely by pre-middle Miocene erosion. An extensive erosional surface was cut during Zemorrian time into the late Mesozoic granitic basement rocks. Incised into this surface are the ancestral Monterey Canyon and an unnamed canyon. Marine sedimentary rocks of upper Miocene and Pliocene age overlie this unconformably and fill the unnamed canyon. Similar rocks also may have once filled Monterey Canyon. Near shore these strata are covered by terrestrial alluvial and eolian deposits, deltaic deposits, marine canyon fill, landslide and slump deposits, and unconsolidated sediments that range in age from upper Pliocene to Holocene. Monterey Canyon appears to have been filled and exhumed at least twice since its inception in Oligocene time, once in late Miocene and once in Pleistocene time. Three major seismic stratigraphic units are apparent in continuous seismic reflection profiles from the offshore area west of the Palo Colorado-San Gregorio fault zone. These are (1) acoustical basement, and (2) middle Tertiary and (3) late Tertiary to Quaternary sedimentary intervals. Acoustical basement comprises Cretaceous to early Tertiary sedimentary rocks, Mesozoic or older metamorphic rocks, and Cretaceous or Jurassic rocks of the Franciscan assemblage. The middle Tertiary sequence consists of sedimentary rocks of questionable Miocene age. The late Tertiary to Quaternary sequence is composed of Pliocene sedimentary rocks and unconsolidated marine sediments, and submarine landslide and slump deposits. Seismic reflection surveys indicate two major, intersecting, northwest-trending fault zones to be present in the offshore Monterey Bay area. The Palo Colorado-San Gregorio fault zone may be more than 200 km long; it is narrow (approximately 3 km wide) and is represented in most places by one or two faults. This zone appears to connect with faults mapped on land near Ano Nuevo Point and Point Sur. The Monterey Bay fault zone, located in the area between Santa Cruz and Monterey, is a diffuse zone, approximately 10 to 15 km wide, of en echelon faults. Faults within this zone appear to connect with faults on land near Monterey, and the zone appears to be truncated by the Palo Colorado-San Gregorio fault zone west of Santa Cruz. Locations of more than 110 earthquakes (1968-1976) show that the newly mapped fault zones in Monterey Bay are seismically active. Epicenters in the bay form two clusters, one at the intersection of the Monterey Bay and Palo Colorado-San Gregorio fault zones, and the other in a linear belt that trends northwest along the Palo Colorado-San Gregorio fault zone. Faults within th

California↗
USGS1998

Preliminary lithostratigraphy, interpreted geophysical logs and hydrogeologic characteristics of the 98th Street core hole, Albuquerque, New Mexico

Core samples, cuttings, and numerous geophysical logs obtained from the 1560 ft (475.5 m) core hole drilled at 98th Street on the west side of Albuquerque provide key stratigraphic and hydraulicproperty information for the upper clastic sediments of the Santa Fe Group, which form the principal aquifer in the region. The core hole and an adjacent water-level monitoring well were drilled cooperatively by the U.S. Geological Survey (USGS) and the City of Albuquerque and investigated in collaboration with the New Mexico Bureau of Mines and Mineral Resources and the New Mexico Office of the State Engineer to improve understanding of aquifer characteristics and controls on ground-water availability and quality. The 751.5 ft (229 m) of core samples recovered from the core hole are the only undisturbed samples of nonlithified sediments of the upper part of the Santa Fe Group that have been collected in this area. These samples have allowed us, for the first time, to directly observe and characterize the lithic and sedimentologic features of this part of the section, and to correlate the detailed geologic features with geophysical-log characteristics, magnetic susceptibility measurements, hydraulic variables, and trace-element geochemistry. The adjacent well was designed to be an areally representative ground-water level and water-quality monitoring well for the Santa Fe Group aquifer. This report chiefly addresses the lithologic, stratigraphic, and hydrogeologic features determined from the 98th Street core hole; other reports address related characteristics. Previous geologic studies predicted the stratigraphy at the site to be, from the land surface downward: 1) Quaternary alluvial and eolian valley-border sediments; 2) fluvial sand and gravel of the upper unit of the Santa Fe Group (Ceja Member of the Santa Fe Formation of Kelly, 1978; equivalent to the Sierra Ledrones Formation of Machette (1978a); 3) downward-fining basin-floor silty clay deposits and 4) fluvial sandy and silty facies of the middle unit of the Santa Fe Group (the Middle Red Member of Bryan and McCann, 1937, and Lambert, 1968). New geologic interpretations indicate that the drill site is in a fault block bounded by east-dipping normal faults and the oblique Atrisco-Rincon fault zone. Core-hole sampling recovered 760.6 ft (231.8 m) of core, in core segments 2.1-2.375 in. (5.3-6 cm) in diameter, and 0.2-10 ft (6.1 cm-3 m) long. The core hole was cased with centered 3-in. PVC casing, and is available for geophysical logging. The monitoring-well hole contains four piezometers at depths of 1544 ft (470.6 m), 1112 ft (338.9 m), 749 ft (228.3 m), and 458 ft (139.6 m). Sediments in the core are loose to weakly cemented gravel, sand, silt, and clay, and lithified sandstone. Laboratory analyses of particle-size distributions of 28 channel samples show that most silty sand samples are uniformly graded and poorly sorted; medium sand samples are moderately sorted. Six principal sediment types are used to describe the core; these sediment types are repeated in various combinations throughout the core and are used to define 22 lithologic units in the cored interval. The six principal sediment types contain sequences of beds having similar modal grain size and sedimentary structure, and are listed in decreasing abundance: 1) Silty fine sand, poorly sorted, containing a coarse silt matrix. Geophysical logs show highly variable baselines with deflections that are related to clay beds and sequences of silt, clay, and sorted fine sand. Density values of 2.12-2.25 g/cc and porosity values of 30-35 percent are typical. 2) Medium sand, moderately to poorly sorted. Geophysical logs show baselines of low variability with deflections that are related to clay beds and sequences of silt, clay, and sorted fine sand. Density values of 2.05-2.20 g/cc and porosity values of 30-35 percent are typical. 3) Clayey sandy silt, poorly sorted, locally microlaminated clay and silt, generally nonplastic. Geophysical logs show highly variable baselines with deflections that are related to sequences of clay and fine sand. Density values of 2.1-2.2 g/cc and porosity values of 30-40 percent are typical. 4) Silt and clay, characteristically red to reddish brown and medium to high plasticity, massive to indistinctly microlaminated. Geophysical logs show variable baselines with broad, high-amplitude compound spikes that are related to sequences of silt and fine sand. Density values of 2.12-2.25 g/cc and porosity values of >45 percent are typical. 5) Sand and gravel, poorly sorted. Geophysical logs show variable baselines with deflections that are related to sequences of silty and sorted fine sand. 6) Sandstone, fine-to-medium grained, poorly sorted, cemented chiefly by calcite, which fills the original pore space. Geophysical logs show density values >2.25 g/cc and porosity values <30 percent. The 22 lithologic units are correlated with recognized basin-floor fluvial lithofacies (Hawley, 1996), which include sand and gravel (lithofacies I), sand with lenses of pebbly sand, silt, and silty clay (lithofacies II), and interbedded sand, silt, and silty clay (modified lithofacies III, IV, IX). The sediments in the core hole are correlated with three informal lithostratigraphic units. The top unit, 0-19 ft (0-5.8 m) depth, consists of Quaternary eolian sand and valley-border alluvium. Coarsegrained deposits in the 19-97 ft (5.8-29.6 m) interval are correlated with the upper unit of the Santa Fe Group. The fine-grained section in the 97-787 ft (29.6-239.9 m) interval is correlated tentatively with the middle unit of the Santa Fe Group. This section contains thick sequences of laminated red and olivebrown clay and silt overbank deposits (441-787 ft) in the distinctive Atrisco member of Connell and others (1998). The Atrisco is correlated with fine-grained zones in numerous wells throughout the central Albuquerque metropolitan area, and is recognized as a zone that separates the upper Santa Fe aquifer from underlying middle Santa Fe deposits. The lower section of the middle unit of the Santa Fe, 787-1500 ft (239.9-457.2 m) depth, includes an upper sequence of moderately sorted channel-fill medium sand, and a lower sequence of sand, silt, and clay overbank deposits. The age of the cored interval is not known precisely. The upper Santa Fe gravel is related regionally to a through-flowing river system that was established in the Rio Grande rift valleys in Early Pliocene time, >4.5 MA. The middle Santa Fe unit is dated tentatively by correlation with a fossiliferous section, in which sandy beds that directly underlie the upper Santa Fe are Late Miocene (Hemphellian), 4.6- 8.9 MA. Further, the middle Santa Fe unit, with dominantly normal magnetic polarity, may have been deposited during closely spaced normal magnetic chrons 5.9-8.3 Ma. Four hydrostratigraphic units summarize the hydrogeologic framework for the 98th Street site: 1) Quaternary valley-border deposits, 2) upper Santa Fe sand and gravel deposits, 3) middle Santa Fe overbank deposits, and 4) middle Santa Fe channel-sand deposits. Empirical values of horizontal hydraulic conductivity estimated from core samples reveal a previously unknown contrast in hydraulic conductivity in the lowest two hydrostratigraphic units. Correlations among numerous wells show that the distinctively fine-grained Atrisco member, with estimated hydraulic conductivities (K) of <0.02-17 ft/day, is a laterally extensive barrier to vertical ground-water flow. The underlying unit that contains moderately sorted medium sand is a potential aquifer production zone that should be investigated further. Laboratory determination of vertical hydraulic conductivity values for fine-grained core samples range from 10 -2 to 10 -7 ft/day; recompacted sandy samples have K values of 1 to 10 -2 ft/day. Results of tests conducted with increasing effective stress show that K values of all samples decrease with decreasing porosity. Comparison of K values from laboratory, empirical, and calculated geophysical values shows discrepancies of 1-3 orders of magnitude (ft/day), indicating that additional analyses of core samples and geophysical data are necessary for future characterization of the Santa Fe Group aquifer.

New Mexico↗
USGS1979

A plan to study the aquifer system of the Central Valley of California

Unconsolidated Quaternary alluvial deposits comprise a large complex aquifer system in the Central Valley of California. Millions of acre-feet of water is pumped from the system annually to support a large and expanding agribusiness industry. Since the 1950's, water levels have been steadily declining in many areas of the valley and concern has been expressed about the ability of the entire ground-water system to support agribusiness at current levels, not to mention its ability to function at projected expansion levels. At current levels of ground-water use, an estimated 1.5 to 2 million acre-feet is withdrawn from storage each year; that is, 1.5 to 2 million acre-feet of water is pumped annually in excess of annual replenishment. The U.S. Geological Survey has initiated a 4-year study to develop geologic, hydrologic, and hydraulic information and to establish a valleywide ground-water data base that will be used to build computer models of the ground-water flow system. Subsequently, these models may be used to evaluate the system response to various ground-water management alternatives. This report describes current problems, objectives of the study, and outlines the general work to be accomplished in the study area. A bibliography of about 600 references is included. (Kosco-USGS)

California↗