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At least 1,405 records · Page 78Linked to original sources
USGS1984

Reconnaissance geology of the Al'Awshaziyah Quadrangle, sheet 26/41 B, Kingdom of Saudi Arabia

The Al 'Awshaziyah quadrangle (26/41 B) is located between lat 26°30' and 27°00 f N. and long 41°30' and 42°00' E. in the northeastern part of the Arabian Shield. The quadrangle contains surficial Quaternary deposits and locally exposed underlying upper Proterozoic intrusive, volcanic, and volcaniclastic rocks. The oldest rocks, gabbro and pyroxenite, are tentatively correlated with the Ha'il mafic-ultramafic complex to the north of the quadrangle. Two younger volcanic sequences, structurally more or less distinct but compositionally transitional, have been identified. The Aqab formation (about 640-610 Ma old) consists of slightly metamorphosed, moderately to strongly folded flows and tuffs of basalt, dacite, and minor rhyolite. An interlayered subaerial conglomerate and a lack of deep-marine sediments distinguish the Aqab from the older and distinctly oceanic Nuf formation. The.Aqab formation is overlain by felsic ash-flow tuffs and related fragmental rocks of the Al 'Awshaziyah formation whose major source is a large caldera in the western part of the quadrangle. Plutonic rocks include granites that predate and postdate both the Aqab and Al 'Awshaziyah formations. The youngest granites, dated at about 580 Ma, are the Salma and Ar Rumman batholiths and are more -alkaline and more silicic than the older granites. The Ar Rumman granite is peralkaline. Even the youngest intrusive rocks have been cut by faults that are probably related to the northwest-trending Najd fault system. No metallic mineralization has been recognized in the quadrangle. A small quarry near the western boundary of the quadrangle produces crushed rock.

Open-File Report↗
USGS1968

The age of the Puerto Rico Trench

The Puerto Rico Trench is parallel to and north of Puerto Rico and the Virgin Islands and reaches depths of more than 8000 meters. Puerto Rico, the closest land area, has a central longitudinal core of Cretaceous and early Tertiary volcanic rocks, some serpentinite of undetermined age, and numerous small intrusions. These rocks were folded into an anticlinorium and intensely faulted into hundreds of fault blocks in an orogeny that lasted from Late Cretaceous until middle Eocene time. Most fold axes and the major fault zones trend approximately west-northwest at an angle of about 15° to the general trend of the island and to the Puerto Rico Trench. Near the north coast, late Oligocene rocks rest on a truncated surface of Cretaceous and early Tertiary volcanic rocks. The Oligocene and overlying Miocene sedimentary rocks strike approximately east, parallel to the Puerto Rico Trench. Apparently the trench is not related to the tectonic movements that folded and faulted the Cretaceous and early Tertiary rocks, but it is closely related tectonically to the Oligocene and Miocene rocks. The trench probably first appeared in Oligocene or possibly late Eocene time and may have reached its maximum depth in late Miocene or Pliocene time.

Puerto Rico↗
USGS1997

Mid-crustal flow during Tertiary extension in the Ruby Mountains core complex, Nevada

Structural analysis and geochronologic data indicate a nearly orthogonal, late Eocene–Oligocene flow pattern in migmatitic infrastructure immediately beneath the kilometer-thick, extensional, mylonitic shear zone of the Ruby Mountains metamorphic core complex, Nevada. New U-Pb radiometric dating indicates that the development of a northward-trending lineation in the infrastructure is partly coeval with the development of a pervasive, west-northwest–trending lineation in the mylonitic shear zone. U-Pb monazite data from the leucogranite orthogneiss of Thorpe Creek indicate a crystallization age of ca. 36–39 Ma. Zircon fractions from a biotite monzogranite dike yield an age of ca. 29 Ma. The three dated samples from these units exhibit a penetrative, approximately north-south–trending elongation lineation. This lineation is commonly defined by oriented bundles of sillimanite and/or elongated aggregates of quartz and feldspar, indicating a synmetamorphic and syndeformational origin. The elongation lineation can be interpreted as a slip line in the flow plane of the migmatitic, nonmylonitic infrastructural core of the northern Ruby Mountains. A portion of this midcrustal flow is coeval with the well-documented, west-northwest sense of slip in the structurally overlying kilometer-thick, mid-Tertiary mylonitic shear zone. Lineations in the mylonitic zone are orthogonal to those in the deeper infrastructure, suggesting fundamental plastic decoupling between structural levels in this core complex. Furthermore, the infrastructure is characterized by overlapping, oppositely verging fold nappes, which are rooted to the east and west. One of the nappes may be synkinematic with the intrusion of the late Eocene orthogneiss of Thorpe Creek. In addition, the penetrative, elongation lineation in the infrastructure is subparallel to hinge lines of parasitic folds developed synchronous with the fold nappes, suggesting a kinematically related evolution.

Nevada, Utah↗
USGS2026

Long-term monotonic trends in water budget components in the contiguous United States: Insights from two hydrologic models

Characterizing changes to water availability for domestic, industrial, agricultural, and other uses is essential to support water management. To better quantify these changes, the U.S. Geological Survey and National Science Foundation National Center for Atmospheric Research produced two hydrologic models simulating water budget components from 1980 to 2021 over the contiguous United States (CONUS). Both hydrologic models were driven by a common atmospheric forcing dataset and aggregated to common spatial and temporal scales, which enables a novel evaluation of congruency between the models. We present annual and seasonal trends in six water budget components (precipitation, evapotranspiration, streamflow, groundwater recharge, soil saturation, and snow water equivalent) based on the Mann–Kendall test for monotonic trend and Theil-Sen slope estimate for the water year 1983–2021 period for ~86,000 catchments in CONUS. Additional components and metrics from our analysis pipeline are available in an associated published dataset, which contains more than 46 million trend results. The water budget trends showed broad agreement with prior observational and modeling studies that indicate increasing trends in the northeast and decreasing trends in southwestern CONUS. We found the seasonal variability in water budget trends was greatest in the southern, central, and northwest CONUS. These findings support integrated trend assessments when coupled with trends in water quality and use.

Contiguous United States↗
USGS1972

Reconnaissance geology of the Precambrian rocks in the Ayn Qunay quadrangle, Kingdom of Saudi Arabia

The Aya Qunay quadrangle covers an area of 2833 sq km in central Saudi Arabia, Only the western edge of the quadrangle is underlain by Precambrian rocks, which were the subject of this investigation. Toward the east the Precambrian rocks are unconformably overlain by Permian and younger sedimentary rocks. The Permian rocks at the west edge of the Ayn Qunay quadrangle consist mainly of a granitic intrusive complex of batholithic dimensions. Parts of the eastern edge of the granitic complex are exposed just west of the overlying Khuff Formation of Permian age, where biotite-hornblende granite of the complex intrudes chlorite-sericite schist of the Precambrian Bi'r Khountina Group. The biotite-hornblende granite of the complex also intrudes plutons of diorite, gabbro, and pyroxenite and is itself intruded by granite porphyry, thereby indicating some difference in age between the granitic rocks in the complex. A sequence of metamorphosed volcanic rocks composed mainly of andesite, rhyolite, and kindred rocks, and called the Halaban Group, is older than the Bi'r Khountina Group. Relations between the Halaban and a gray hornblende-biotite granite gneiss are uncertain, but the gneiss may be older than the Halaban. The few observed contacts disclosed parallel foliation in the two units, but the foliation may have been imposed after the Halaban was deposited on the granite gneiss. Two major left-lateral faults extend west-northwest across the Precambrian rocks but are not in the Permian rocks. These faults parallel to the Najd fault zone found farther south. Seemingly they correlate in time with early movements on the Najd fault zone, but not with the latest. Saprolitic material-of variable thickness is present on the upper surface of the Precambrian rocks beneath the Khuff Formation at many places. Where the Khuff Formation has been removed by erosion, the saprolite is also stripped away. The weathering probably took place in pre-Khuff time. No ancient mines or prospects were seen in the Precambrian rocks; however, a notable positive anomaly for tungsten in concentrates is associated with a small prominence of granite porphyry 35 km southwest of Ayn Qunay. Further investigation of the porphyry should be undertaken to learn the amount of scheelite at this locality.

Open-File Report↗
USGS1995

Geologic framework and hydrogeologic characteristics of the Edwards Aquifer recharge zone, Bexar County, Texas

In Bexar County, residential and commercial development on the Edwards aquifer recharge zone is increasing. The aquifer possibly can be contaminated by spills, leakage of hazardous materials, or runoff from the rapidly developing urban areas that surround, or are built on, the intensely faulted and fractured, karstic limestone outcrops characteristic of the recharge zone. Furthermore, some of the hydrogeologic subdivisions that compose the Edwards aquifer have greater effective porosity than others. The areas where the most porous subdivisions crop out might provide efficient avenues for contaminants to enter the aquifer. The Edwards aquifer recharge zone has relatively large permeability resulting, in part, from the development or redistribution of secondary porosity. Lithology, stratigraphy, diagenesis, and karstification account for the effective porosity and permeability in the Edwards aquifer outcrop. Karst features that greatly enhance effective porosity in the outcrop area include sinkholes and caves. Hydrogeologic subdivision VI, the Kirschberg evaporite member, appears to be the most porous and permeable subdivision within the Kainer Formation. Hydrogeologic subdivision HI, the leached and collapsed members, undivided, is the most porous and permeable subdivision within the Person Formation. Hydrogeologic subdivision II, the cyclic and marine members, undivided, is moderately permeable, with both fabric- and not-fabric-selective porosity. The faults in northern Bexar County are part of the Balcones fault zone. Although most of the faults in this area trend northeast, a smaller set of cross-faults trend northwest. Generally, the faults are en echelon and normal, with the downthrown blocks typically toward the coast.

Texas↗
USGS1985

Characteristics of the aftershock sequence of the Borah Peak, Idaho, earthquake determined from digital recordings of the events

The U.S. Geological Survey, Menlo Park, deployed and maintained a network of twelve digital instruments over the 2 weeks following the 28 October 1983 Borah Peak, Idaho, earthquake. The network recorded 45 events with M ≧ 3.0, and 6 events with M ≦ 4.0. The epicenters are located in a narrow band which parallels the trace of the surface fauiting up to the Willow Creek summit; the depths of the events range from 5 to 16 km. In the south, the distribution of hypocenters delineate a plane which dips to the southwest at 50°; to the north, the hypocenters dip steeply to the east. Composite focal mechanisms for three groups of events show normal faulting mechanisms; the mechanism of the aftershocks in the north appear rotated in both strike and dip from the aftershocks in the south. The seismic moments of the aftershocks increase with increasing hypocentral depth below 12 km. The dynamic stress drops of the events do not show any systematic variation with depth, however. Most of the events with large stress drops are clustered in the northwest limb of the aftershock distribution; the average stress drop of the southern events is 31 ± 16 bars, while the average stress drop of the events in the northwest limb is 77 ± 52 bars. This clustering of events with large stress drops marks an apparent stress concentration, possibly associated with the arrest of the main shock rupture propagation by a fracture barrier at depth.

Idaho↗
USGS1975

Effects of sediment control on sediment transport in the northwest branch Anacostia River basin, Montgomery County, Maryland

Streamflow and sediment were monitored in an urbanizing drainage basin in southeastern Montgomery County, Md., from 1962 to 1972. During this period, urban construction areas averaged about 3 percent of the 21.1 mi 2 (54.6 km 2 ) basin. Urban land increased from 3.5 percent in 1959 to 20 percent in 1971. Virtually all the suspended sediment was transported during storms; three-fourths of it, during large storms. High sediment yields were observed in February, March, June, and August; and low yields, generally from September through January. The decrease in sediment discharge in the latter half of the study period is attributed to a sediment-control program. Sediment discharge decreased 35 percent between 1967 and 1972, when effective control measures were installed on about half the construction sites.

Maryland↗
USGS2011

Borehole geophysical investigation of a formerly used defense site, Machiasport, Maine, 2003-2006

The U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, collected borehole geophysical logs in 18 boreholes and interpreted the data along with logs from 19 additional boreholes as part of an ongoing, collaborative investigation at three environmental restoration sites in Machiasport, Maine. These sites, located on hilltops overlooking the seacoast, formerly were used for military defense. At each of the sites, chlorinated solvents, used as part of defense-site operations, have contaminated the fractured-rock aquifer. Borehole geophysical techniques and hydraulic methods were used to characterize bedrock lithology, fractures, and hydraulic properties. In addition, each geophysical method was evaluated for effectiveness for site characterization and for potential application for further aquifer characterization and (or) evaluation of remediation efforts. Results of borehole geophysical logging indicate the subsurface is highly fractured, metavolcanic, intrusive, metasedimentary bedrock. Selected geophysical logs were cross-plotted to assess correlations between rock properties. These plots included combinations of gamma, acoustic reflectivity, electromagnetic induction conductivity, normal resistivity, and single-point resistance. The combined use of acoustic televiewer (ATV) imaging and natural gamma logs proved to be effective for delineating rock types. Each of the rock units in the study area could be mapped in the boreholes, on the basis of the gamma and ATV reflectivity signatures. The gamma and mean ATV reflectivity data were used along with the other geophysical logs for an integrated interpretation, yielding a determination of quartz monzonite, rhyolite, metasedimentary units, or diabase/gabbro rock types. The interpretation of rock types on the basis of the geophysical logs compared well to drilling logs and geologic mapping. These results may be helpful for refining the geologic framework at depth. A stereoplot of all fractures intersecting the boreholes indicates numerous fractures, a high proportion of steeply dipping fractures, and considerable variation in fracture orientation. Low-dip-angle fractures associated with unloading and exfoliation are also present, especially at a depth of less than 100 feet below the top of casing. These sub-horizontal fractures help to connect the steeply dipping fractures, making this a highly connected fracture network. The high variability in the fracture orientations also increases the connectivity of the fracture network. A preliminary comparison of all fracture data from all the boreholes suggests fracturing decreases with depth. Because all the boreholes were not drilled to the same depth, however, there is a clear sampling bias. Hence, the deepest boreholes are analyzed separately for fracture density. For the deepest boreholes in the study, the intensity of fracturing does not decline significantly with depth. It is possible the fractures observed in these boreholes become progressively tighter or closed with depth, but this is difficult to verify with the borehole methods used in this investigation. The fact that there are more sealed fractures at depth (observed in optical televiewer logs in some of the boreholes) may indicate less opening of the sealed fractures, less water moving through the rock, and less weathering of the fracture infilling minerals. Although the fracture orientation remained fairly constant with depth, differences in the fracture patterns for the three restoration sites indicate the orientation of fractures varies across the study area. The fractures in boreholes on Miller Mountain predominantly strike northwest-southeast, and to a lesser degree they strike northeast. The fractures on or near the summit of Howard Mountain strike predominantly east-west and dip north and south, and the fractures near the Transmitter Site strike northeast-southwest and dip northwest and southeast. The fracture populations for the boreholes on or near the summit of Howard Mountain show more variation than at the other two sites. This variation may be related to the proximity of the fault, which is northeast of the summit of Howard Mountain. In a side-by-side comparison of stereoplots from selected boreholes, there was no clear correspondence between fracture orientation and proximity to the fault. There is, however, a difference in the total populations of fractures for the boreholes on or near the summit of Howard Mountain and the boreholes near the Transmitter Site. Further to the southwest and further away from the fault, the fractures at the Transmitter Site predominantly strike northeast-southwest and northwest-southeast.Heat-pulse flowmeter (HPFM) logging was used to identify transmissive fractures and to estimate the hydraulic properties along the boreholes. Ambient downflow was measured in 13 boreholes and ambient upflow was measured in 9 boreholes. In nine other bedrock boreholes, the HPFM did not detect measurable vertical flow. The observed direction of vertical flow in the boreholes generally was consistent with the conceptual flow model of downward movement in recharge locations and upward flow in discharge locations or at breaks in the slope of land surface. Under low-rate pumping or injection rates [0.25 to 1 gallon per minute (gal/min)], one to three inflow zones were identified in each borehole. Two limitations of HPFM methods are (1) the HPFM can only identify zones within 1.5 to 2 orders of magnitude of the most transmissive zone in each borehole, and (2) the HPFM cannot detect flow rates less than 0.010 + or - 0.005 gal/min, which corresponds to a transmissivity of about 1 foot squared per day (ft2/d). Consequently, the HPFM is considered an effective tool for identifying the most transmissive fractures in a borehole, down to its detection level. Transmissivities below that cut-off must be measured with another method, such as packer testing or fluid-replacement logging. Where sufficient water-level and flowmeter data were available, HPFM results were numerically modeled. For each borehole model, the fracture location and measured flow rates were specified, and the head and transmissivity of each fracture zone were adjusted until a model fit was achieved with the interpreted ambient and stressed flow profiles. The transmissivities calculated by this method are similar to the results of an open-hole slug test; with the added information from the flowmeter, however, the head and transmissivity of discrete zones also can be determined. The discrete-interval transmissivities ranged from 0.16 to 330 ft2/d. The flowmeter-derived open-hole transmissivity, which is the combined total of each of the transmissive zones, ranged from 1 to 511 ft2/d. The whole-well open-hole transmissivity values determined with HPFM methods were compared to the results of open-hole hydraulic tests. Despite the fact that the flowmeter-derived transmissivities consistently were lower than the estimates derived from open-hole hydraulic tests alone, the correlation was very strong (with a coefficient of determination, R2, of 0.9866), indicating the HPFM method provides a reasonable estimate of transmissivities for the most transmissive fractures in the borehole. Geologic framework, fracture characterization, and estimates of hydraulic properties were interpreted together to characterize the fracture network. The data and interpretation presented in this report should provide information useful for site investigators as the conceptual site groundwater flow model is refined. Collectively, the results and the conceptual site model are important for evaluating remediation options and planning or implementing the design of a well field and borehole completions that will be adequate for monitoring flow, remediation efforts, groundwater levels, and (or) water quality. Similar kinds of borehole geophysical logging (specifically the borehole imaging, gamma, fluid logs, and HPFM) should be conducted in any newly installed boreholes and integrated with interpretations of any nearby boreholes. If boreholes are installed close to existing or other new boreholes, cross-hole flowmeter surveys may be appropriate and may help characterize the aquifer properties and connections between the boreholes.

Maine↗
USGS2005

Hydrogeologic framework, ground-water quality, and simulation of ground-water flow at the Fair Lawn Well Field Superfund site, Bergen County, New Jersey

Production wells in the Westmoreland well field, Fair Lawn, Bergen County, New Jersey (the 'Fair Lawn well field Superfund site'), are contaminated with volatile organic compounds, particularly trichloroethylene, tetrachloroethylene, and 1,1,1-trichloroethane. In 1983, the U.S. Environmental Protection Agency (USEPA) placed the Westmoreland well field on its National Priority List of Superfund sites. In an effort to determine ground-water flow directions, contaminant-plume boundaries, and contributing areas to production wells in Fair Lawn, and to evaluate the effect of present pump-and-treat systems on flowpaths of contaminated ground water, the U.S. Geological Survey (USGS), in cooperation with the USEPA, developed a conceptual hydrogeologic framework and ground-water flow model of the study area. MODFLOW-2000, the USGS three-dimensional finite-difference model, was used to delineate contributing areas to production wells in Fair Lawn and to compute flowpaths of contaminated ground water from three potential contaminant sources to the Westmoreland well field. Straddle-packer tests were used to determine the hydrologic framework of, distribution of contaminants in, and hydrologic properties of water-bearing and confining units that make up the fractured-rock aquifer underlying the study area. The study area consists of about 15 square miles in and near Fair Lawn. The area is underlain by 6 to 100 feet of glacial deposits and alluvium that, in turn, are underlain by the Passaic Formation. In the study area, the Passaic Formation consists of brownish-red pebble conglomerate, medium- to coarse-grained feldspathic sandstone, and micaceous siltstone. The bedrock strata strike N. 9o E. and dip 6.5o to the northwest. The bedrock consists of alternating layers of densely fractured rocks and sparsely fractured rocks, forming a fractured-rock aquifer. Ground-water flow in the fractured-rock aquifer is anisotropic as a result of the interlayering of dipping water-bearing and confining units. Wells of similar depth aligned along the strike of the bedding intersect the same water-bearing units, but wells aligned along the dip of the bedding may intersect different water-bearing units. Consequently, wells aligned along strike are in greater hydraulic connection than wells aligned along dip. The Borough of Fair Lawn pumps approximately 770 million gallons per year from 13 production wells. Hydrographs from six observation wells ranging in depth from 162 to 505 feet in Fair Lawn show that water levels in much of the study area are affected by pumping. Straddle packers were used to isolate discrete intervals within six open-hole observation wells owned by the Fair Lawn Water Department. Transmissivity, water-quality, and static-water-level data were obtained from the isolated intervals. Measured transmissivity ranged from near 0 to 8,900 feet squared per day. The broad range in measured transmissivity is a result of the heterogeneity of the fractured-rock aquifer. Eight water-bearing units and eight confining units were identified in the study area on the basis of transmissivity. The water-bearing units range in thickness from 21 to 95 feet; the mean thickness is 50 feet. The confining units range in thickness from 22 to 248 feet; the mean thickness is 83 feet. Water-level and water-quality data indicate effective separation of water-bearing units by the confining units. Water-quality samples were collected from the six observation wells at 16 depth intervals isolated by the straddle packers in 2000 and 2001. Concentrations of volatile organic compounds generally were low in samples from four of the wells, but were higher in samples from a well in Fair Lawn Industrial Park and in a well in the Westmoreland well field. The digital ground-water flow model was used to simulate steady-state scenarios representing conditions in the study area in 1991 and 2000. These years were chosen because during the intervening period,

Scientific Investigations Report↗
USGS1976

Large sand waves on the Atlantic Outer Continental Shelf around Wilmington Canyon, off Eastern United States

New seismic-reflection data show that large sand waves near the head of Wilmington Canyon on the Atlantic Outer Continental Shelf have a spacing of 100-650 m and a relief of 2-9 m. The bedforms trend northwest and are asymmetrical, the steeper slopes being toward the south or west. Vibracore sediments indicate that the waves apparently have formed on a substrate of relict nearshore sediments. Although the age of the original bedforms is unknown, the asymmetry is consistent with the dominant westerly to southerly drift in this area which has been determined by other methods; the asymmetry, therefore, is probably modern. Observations in the sand-wave area from a submersible during August 1975, revealed weak bottom currents, sediment bioturbation, unrippled microtopography, and lack of scour. Thus, the asymmetry may be maintained by periodic water motion, possibly associated with storms or perhaps with flow in the canyon head.

Wilmington Canyon↗
USGS2015

California State Waters Map Series — Offshore of Bodega Head, California

Introduction In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow subsurface geology. The Offshore of Bodega Head map area is located in northern California, about 70 km north of San Francisco and about 80 km south of Point Arena. The onshore part of the map area is largely undeveloped, used primarily for recreation, farms and ranches, and a few wineries. The small town of Bodega Bay, located on the east side of Bodega Harbor, is the largest cultural center. Bodega Harbor is an important commercial fishing base and, in season, an active sport fishing and recreation harbor. Much of the coastline from Bodega Head north to about 6 km north of the Russian River is part of Sonoma Coast State Park. The Offshore of Bodega Head map area includes two California Marine Protected Areas, the Bodega Head State Marine Reserve and the northern part of the Bodega Head State Marine Conservation Area. Additionally, the inland parts of two large estuaries in the map area, Estero Americano and Estero de San Antonio, have been designated as State Marine Recreational Management Areas. The map area is cut by the northwest-striking San Andreas Fault, the right-lateral transform boundary between the North American and Pacific plates. This fault juxtaposes rocks of the Jurassic and Cretaceous Franciscan Complex on the northeast with Cretaceous granitic rocks on the southwest, and it has an estimated slip rate of about 17 to 25 mm/yr in this area. The devastating great 1906 California earthquake (M7.8) is thought to have nucleated on the San Andreas Fault offshore of San Francisco, about 80 km south of Bodega Head, with the rupture extending northward through the Offshore of Bodega Head map area and an additional 220 km to the south flank of Cape Mendocino. North of the mouth of Salmon Creek, the coast and shoreline are rugged and scenic, characterized by flights of uplifted marine terraces, rocky promontories, nearshore sea stacks, kelp-rich coves, and both pocket beaches and longer beach strands, the latter of which include Wrights Beach and Portuguese Beach. The coast has lower relief between the mouth of Salmon Creek and Mussel Point, where South Salmon Creek Beach is backed by a large (about 4 km 2 ) complex of coastal sand dunes. The enormous volume of sand on the beach and in the dune field is derived by southward littoral drift from the Russian River, Salmon Creek, and smaller coastal watersheds. The sediment is trapped by protruding bedrock at Mussel Point, which represents the south end of the Russian River littoral cell. Bodega Head is underlain by Cretaceous granitic rocks, and its shoreline is variously characterized by relatively low-lying terraces, steep and high bluffs, and a few pocket beaches. East of Bodega Head, Doran Beach (part of Doran Regional Park) is a 1.7-km-long sand spit that forms the north boundary of Bodega Bay and the south boundary of Bodega Harbor. The coast south of Doran Beach on the east flank of Bodega Bay is composed of rocky bluffs, hummocky marine terraces, and a few small pocket beaches. The bluffs are underlain by sheared rocks of the Franciscan Complex and are highly susceptible to landslides. This section of coast includes two prominent watersheds, Estero Americano and Estero de San Antonio, which drain westward into Bodega Bay. The offshore part of the Offshore of Bodega Head map area is characterized by an extensive, rugged and rocky shelf underlain by Cretaceous granitic rocks. This rocky terrain, centered offshore of Bodega Head, extends northwestward for about 15 km, from the south edge of the map area (where it forms the west boundary of Bodega Bay) to the northern-central part of the map area offshore of the mouth of Salmon Creek. This rocky seafloor reaches water depths of 40 to 80 m and is overlain by young sediment. Circulation over the shelf and seafloor in the map area (and in the broader central California region) is dominated by the southward-flowing California Current, the eastern boundary current of the North Pacific Gyre. Associated upwelling brings cool, nutrient-rich waters to the surface, resulting in high biological productivity. Persistent northwest winds are sometimes weak or absent during the fall and winter, causing the California Current to move farther offshore so that the shelf is affected by the Davidson Current, a weaker northward-flowing countercurrent. As a result, net flow over the continental shelf is commonly southeastward during the spring and summer and northwestward during the fall and winter. Throughout the year, this part of the northern California coast is exposed to four wave climate regimes: the north Pacific swell, the southern swell, northwest wind waves, and local wind waves. The north Pacific swell dominates in winter months (typically November through March). During summer months, the largest waves come from the southern swell, generated by storms in the south Pacific and offshore of Central America. Northwest wind waves affect the coast throughout the year, whereas local wind waves are most common from October to April. Potential marine benthic habitats in the Offshore of Bodega Head map area include unconsolidated continental-shelf sediments, mixed continental-shelf substrate, and hard continental-shelf substrate. Rocky-shelf outcrops and rubble are considered to be promising potential habitats for rockfish and lingcod, both of which are recreationally and commercially important species.

California↗
USGS2003

Biostratigraphy and structure of paleozoic host rocks and their relationship to Carlin-type gold deposits in the Jerritt Canyon mining district, Nevada

The Jerritt Canyon mining district in the northern Independence Range, northern Nevada, contains multiple, nearly horizontal, thrust masses of platform carbonate rocks that are exposed in a series of north- to northeast-elongated, tectonic windows through rocks of the Roberts Mountains allochthon. The Roberts Mountains allochthon was emplaced during the Late Devonian to Early Mississippian Antler orogeny. These thrust masses contain structurally and stratigraphically controlled Carlin-type gold deposits. The gold deposits are hosted in tectonically truncated units of the Silurian to Devonian Hanson Creek and Roberts Mountains Formations that lie within structural slices of an Eastern assemblage of Cambrian to Devonian carbonate rocks. In addition, these multiply thrust-faulted and folded host rocks are structurally interleaved with Mississippian siliciclastic rocks and are overlain structurally by Cambrian to Devonian siliciclastic units of the Roberts Mountains allochthon. All sedimentary rocks were involved in thrusting, high-angle faulting, and folding, and some of these events indicate substantial late Paleozoic and/or Mesozoic regional shortening. Early Pennsylvanian and late Eocene dikes also intrude the sedimentary rocks. These rocks all were uplifted into a northeast-trending range by subsequent late Cenozoic Basin and Range faulting. Eocene sedimentary and volcanic rocks flank part of the range. Pathways of hydrothermal fluid flow and locations of Carlin-type gold orebodies in the Jerritt Canyon mining district were controlled by structural and host-rock geometries within specific lithologies of the stacked thrust masses of Eastern assemblage rocks. The gold deposits are most common proximal to intersections of northeast-striking faults, northwest-striking dikes, and thrust planes that lie adjacent to permeable stratigraphic horizons. The host stratigraphic units include carbonate sequences that contained primary intercrystalline permeability, which provided initial pathways for fluid flow and later served as precipitation sites for ore minerals. Alteration, during, and perhaps prior to mineralization, enhanced primary permeability by dissolution, by removal of calcite, and by formation of dolomite. Ore-stage sulfide minerals and alteration minerals commonly precipitated in pore spaces among dolomite grains. Microveinlets and microbrecciation in zones of intense alteration also provided networks of secondary permeability that further enhanced fluid flux and produced additional sites for ore deposition.

Economic Geology↗
USGS2004

Revisiting the 23 February 1892 Laguna Salada earthquake

According to some compilations, the Laguna Salada, Baja California, earthquake of 23 February 1892 ranks among the largest earthquakes in California and Baja California in historic times. Although surface rupture was not documented at the time of the earthquake, recent geologic investigations have identified and mapped a rupture on the Laguna Salada fault that can be associated with high probability with the 1892 event (Mueller and Rockwell, 1995). The only intensity-based magnitude estimate for the earthquake, M 7.8, was made by Strand (1980) based on an interpretation of macroseismic effects and a comparison of isoseismal areas with those from instrumentally recorded earthquakes. In this study we reinterpret original accounts of the Laguna Salada earthquake. We assign modified Mercalli intensity (MMI) values in keeping with current practice, focusing on objective descriptions of damage rather than subjective human response and not assigning MMI values to effects that are now known to be poor indicators of shaking level, such as liquefaction and rockfalls. The reinterpreted isoseismal contours and the estimated magnitude are both significantly smaller than those obtained earlier. Using the method of Bakun and Wentworth (1997) we obtain a magnitude estimate of M 7.2 and an optimal epicenter less than 15 km from the center of the mapped Laguna Salada rupture. The isoseismal contours are elongated toward the northwest, which is qualitatively consistent with a directivity effect, assuming that the fault ruptured from southeast to northwest. We suggest that the elongation may also thus reflect wave propagation effects, with more efficient propagation of crustal surface (Lg) waves in the direction of the overall regional tectonic fabric.

Bulletin of the Seismological Society of America↗
USGS1975

Application of ERTS images and image processing to regional geologic problems and geologic mapping in northern Arizona

The purpose of this study was to apply the techniques of computer image processing to ERTS images as an aid to the solution of some regional geologic problems of significant interest. ERTS-1 images were applied to studies in the Shivwits Plateau, Coconino Plateau, and north-central Arizona regions. Unprocessed ERTS images revealed a wealth of new structural information and enabled a broad regional study to be made of the tectonic history of the southwestern Colorado Plateau. Spectral information from ERTS-1 was shown to be compatible with ground spectral reflectance measurements made with a portable field instrument developed during this investigation, provided that allowance was made for atmospheric effects. Computer image processing yielded lithologic boundary information within the Coconino Plateau region not obtainable from unprocessed images. Various enhancement techniques were compared in the three areas of study, and some simple rules were developed to guide the processing of images in unknown areas. A new hypothesis was developed for the history of the Colorado River. An ancestral and relatively old Upper Colorado Drainage followed approximately its present course as far as the western side of the Kaibab Uplift, where it diverged from the present course by following a strike valley trending north-northwest. This drainage was captured relatively recently by a much younger Lower Colorado Drainage, which developed by headward erosion after the opening of the Gulf of California. A byproduct of the regional studies in each of the three areas was the identification of areas favorable for the localization of shallow and deep ground waters. On the Shivwits Plateau water trapped in the axis of the old strike valley underlying the Shivwits lavas is a potential source. On the Coconino Plateau sandstone lenses, underlain by clays, within the otherwise permeable Kaibab Limestone are potential perched aquifers. These can be identified on computer-enhanced images. Lineaments detected first on ERTS-1 frames and later verified on aerial photographs were used south of Flagstaff, Arizona, to identify maximum fracturing along the Oak Creek fault in the Woody Mountain well field; a site for a new deep well has been selected and is being drilled by the city of Flagstaff.

Arizona↗
USGS1998

Hydrology, water quality, and phosphorus loading of Kirby Lake, Barron County, Wisconsin

In 1992, residents near Kirby Lake, located about five miles northwest of Cumberland, in Barron County, Wisconsin, formed the Kirby Lake Management District. The Lake District immediately began to gather information needed for the preparation of a comprehensive lake-management plan that would be used to protect the natural and recreational assets of the lake. The Lake District completed a land-use inventory of the watershed and an evaluation of available lake water-quality data. The land-use data were used to assess the potential contribution of nutrients to the lake from the watershed. The evaluation of lake water-quality data, which were collected as part of the Wisconsin Department of Natural Resources (WDNR) Self-Help Monitoring Program, indicated the lake has relatively good water quality. Before a comprehensive lake-management plan could be prepared, however, a better understanding of several aspects of the lake and its surroundings was needed. To address those aspects including the definition of the lake's hydrology and the principal sources of nutrients, and the relation of the lake's water quality to nutrient loading the U.S. Geological Survey, in cooperation with the Lake District and the WDNR (through a Lake Management Planning Grant), conducted a study of Kirby Lake and its watershed. This Fact Sheet presents the results of that study.

Wisconsin↗
USGS1986

Precambrian basement geology of North and South Dakota

Combined analysis of drill-hole, gravity, and magnetic data indicates that the buried Precambrian basement rocks of the Dakotas can be divided into several lithotectonic terranes. Eastern North Dakota and northeastern South Dakota are underlain by Archean gneiss. Except for the Black Hills region of South Dakota, where Archean rocks are also exposed, the western third of both Dakotas is underlain mainly by Early Proterozoic gneiss and metasedimentary rocks. Part of this region is underlain by Archean crust with an Early Proterozoic tectonic overprint. A broad transition zone of strongly overprinted Archean crust occurs between the Proterozoic rocks to the west and the Archean rocks to the east. South central South Dakota is underlain by an Early Proterozoic batholith. Early Proterozoic felsic volcanic rocks occur in southeast South Dakota. The bootheel portion of South Dakota contains a diverse assemblage of basement rocks that are partly Archean in age.Churchill Province rocks of the Trans-Hudson foldbelt project into the western Dakotas. The Thompson nickel belt and the Pickwitonei gneiss belt correlate with the western and eastern halves, respectively, of the transition between Archean and Proterozoic crust, and the Archean Glennie – Hanson Lake microcontinent of the Churchill Province likely extends into western North Dakota. Archean rocks of Minnesota extend into the eastern Dakotas, and the Wyoming craton extends to the Black Hills region. The Cheyenne foldbelt projects into southwest South Dakota. The Penokean foldbelt of Michigan and Wisconsin does not extend into the Dakotas, but it most likely extends into northwest Iowa.Tectonic evolution of the Early Proterozoic terrane in the Dakotas was most likely similar to plate tectonic models for the evolution of the Trans-Hudson foldbelt in the Churchill Province. As in the Churchill Province, the western Dakotas are underlain by Early Proterozoic rocks, but it is not known whether these rocks formed as a result of rifting and subsequent closure of a once extensive Archean crust or as a result of collision of once widely separated blocks of Archean crust.

North Dakota, South Dakota↗
USGS2018

California State Waters Map Series — Offshore of Gaviota, California

Introduction In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow subsurface geology. The map area is in the southern part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland. Significant clockwise rotation—at least 90°—since the early Miocene has been proposed for the Western Transverse Ranges province, and the region is presently undergoing north-south shortening. The offshore part of the map area lies south of the steep south flank of the Santa Ynez M ountains . The crest of the range , which has a maximum elevation of about 760 m in the map area , lies about 4 km north of the shoreline. Gaviota is an unincorporated community that has a sparse population (less than 100), and the coastal zone is largely open space that is locally used for cattle grazing. The Union Pacific railroad tracks extend westward along the coast through the entire map area, within a few hundred meters of the shoreline. Highway 101 crosses the eastern part of the map area, also along the coast, then turns north (inland) and travels through Cañada de la Gaviota and Gaviota Pass en route to Buellton. Gaviota State Park lies at the mouth of Cañada de la Gaviota. West of Gaviota, the onland coastal zone is occupied by the Hollister Ranch, a privately owned, gated community that has no public access. The map area has a long history of petroleum exploration and development. Several offshore gas fields were discovered and were developed by onshore directional drilling in the 1950s and 1960s. Three offshore petroleum platforms were installed in adjacent federal waters in 1976 (platform “Honda”) and 1989 (platforms “Heritage” and “Harmony”). Local offshore and onshore operations were serviced for more than a century by the Gaviota marine terminal, which is currently being decommissioned and will be abandoned in an intended transition to public open space. The Offshore of Gaviota map area lies within the western Santa Barbara Channel region of the Southern California Bight, and it is somewhat protected from large Pacific swells from the north and northwest by Point Conception and from south and southwest swells by offshore islands and banks. Much of the shoreline in the map area is characterized by narrow beaches that have thin sediment cover, backed by low (10- to 20-m-high) cliffs that are capped by a narrow coastal terrace. Beaches are subject to wave erosion during winter storms, followed by gradual sediment recovery or accretion in the late spring, summer, and fall months during the gentler wave climate. The map area lies in the western-central part of the Santa Barbara littoral cell, which is characterized by west-to-east transport of sediment from Point Arguello on the northwest to Hueneme and Mugu Canyons on the southeast. Sediment supply to the western and central part of the littoral cell is mainly from relatively small coastal watersheds. In the map area, sediment sources include Cañada de la Gaviota (52 km 2 ), as well as Cañada de la Llegua, Arroyo el Bulito, Cañada de Santa Anita, Cañada de Alegria, Cañada del Agua Caliente, Cañada del Barro, Cañada del Leon, Cañada San Onofre, and many others. Coastal-watershed discharge and sediment load are highly variable, characterized by brief large events during major winter storms and long periods of low (or no) flow and minimal sediment load between storms. In recent (recorded) history, the majority of high-discharge, high-sediment-flux events have been associated with El Niño phases of the El Niño–Southern Oscillation climatic pattern. Shelf width in the Offshore of Gaviota map area ranges from about 4.3 to 4.7 km, and shelf slopes average about 1.0° to 1.2° but are highly variable because of the presence of the large Gaviota sediment bar. This bar extends southwestward for about 9 km from the mouth of Cañada de la Gaviota to the shelf break, is as wide as 2 km, and is by far the largest shore-attached sediment bar in the Santa Barbara Channel. The shelf is underlain by bedrock and variable amounts (0 to as much as 36 m in the Gaviota bar) of upper Quaternary sediments deposited as sea level fluctuated in the late Pleistocene. The trend of the shelf break changes from about 276° to 236° azimuth over a distance of about 12 km, and it ranges in depth from about 91 m to as shallow as 62 to 73 m where significant shelf-break and upper-slope failure and landsliding has apparently occurred. The shelf break in the western part of the map area is notably embayed by the heads of three large (150- to 300-m-wide) channels that have been referred to as “the Gaviota Canyons” or as “Drake Canyon,” “Sacate Canyon,” and “Alegria Canyon.” Seafloor habitats in the broad Santa Barbara Channel region consist of significant amounts of soft, unconsolidated sediment interspersed with isolated areas of rocky habitat that support kelp-forest communities in the nearshore and rocky-reef communities in deeper water. The potential marine benthic habitat types mapped in the Offshore of Gaviota map area are directly related to its Quaternary geologic history, geomorphology, and active sedimentary processes. These potential habitats lie primarily within the Shelf (continental shelf) but also partly within the Flank (basin flank or continental slope) megahabitats. The fairly homogeneous seafloor of sediment and low-relief bedrock provides characteristic habitat for rockfish, groundfish, crabs, shrimp, and other marine benthic organisms. Several areas of smooth sediment form nearshore terraces that have relatively steep, smooth fronts, which may be attractive to groundfish. Below the steep shelf break, soft, unconsolidated sediment is interrupted by the heads of several submarine canyons and rills, some bedrock exposures, and small carbonate mounds associated with asphalt mounds and pockmarks, also good potential habitat for rockfish. The map area includes the relatively small (5.2 km 2 ) Kashtayit State Marine Conservation Area, which largely occupies the inner part of the Gaviota sediment bar.

California↗