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At least 1,387 records · Page 77Linked to original sources
USGS2017

Overview for geologic field-trip guides to volcanoes of the Cascades Arc in northern California

The California Cascades field trip is a loop beginning and ending in Portland, Oregon. The route of day 1 goes eastward across the Cascades just south of Mount Hood, travels south along the east side of the Cascades for an overview of the central Oregon volcanoes (including Three Sisters and Newberry Volcano), and ends at Klamath Falls, Oregon. Day 2 and much of day 3 focus on Medicine Lake Volcano. The latter part of day 3 consists of a drive south across the Pit River into the Hat Creek Valley and then clockwise around Lassen Volcanic Center to the town of Chester, California. Day 4 goes from south to north across Lassen Volcanic Center, ending at Burney, California. Day 5 and the first part of day 6 follow a clockwise route around Mount Shasta. The trip returns to Portland on the latter part of day 6, west of the Cascades through the Klamath Mountains and the Willamette Valley. Each of the three sections of this guidebook addresses one of the major volcanic regions: Lassen Volcanic Center (a volcanic field that spans the volcanic arc), Mount Shasta (a fore-arc stratocone), and Medicine Lake Volcano (a rear-arc, shield-shaped edifice). Each section of the guide provides (1) an overview of the extensive field and laboratory studies, (2) an introduction to the literature, and (3) directions to the most important and accessible field localities. The field-trip sections contain far more stops than can possibly be visited in the actual 6-day 2017 IAVCEI excursion from Portland. We have included extra stops in order to provide a field-trip guide that will have lasting utility for those who may have more time or may want to emphasize one particular volcanic area.

California↗
USGS1960

Geology and ground water in Napa and Sonoma Valleys, Napa and Sonoma Counties, California

Napa and Sonoma Valleys are adjacent alluvium-filled valleys about 40 miles northeast of San Francisco. They occupy alined and structurally controlled depressions in the northern Coast Ranges physiographic province and drain south into San Pablo Bay. The valleys are surrounded and underlain by unconsolidated marine and continental sediments and volcanic rocks of Pliocene and Pleistocene age, which are water bearing in large part and together make up relatively extensive ground-water basins. Napa Valley, the eastern valley, is the larger and has a valley-floor area of about 85 square miles. Sonoma Valley has a valley-floor area of about 35 square miles; in addition, about 10 square miles is unreclaimed tidal marsh. The rock units of Napa and Sonoma Valleys are divided into four classes on the basis of their distribution and relative capacity to yield water: (a) Consolidated virtually non-water-bearing chiefly sedimentary (some metamorphic) rocks that range in age from Jurassic ( ?) to Pliocene; (b) marine shale and sand of the Petaluma formation (Pliocene) and the Merced formation (Pliocene and Pleistocene) that do not crop out within Napa or Sonoma Valleys but perhaps are penetrated by some deep wells drilled in Sonoma Valley; (c) Sonoma volcanics of Pliocene age, parts of which are non-water-bearing and parts of which locally yield large quantities of water; and (d) unconsolidated alluvial deposits mainly of Quaternary age. The deposits of classes (c) and (d) contain the most important aquifers in the area. Most of the water used in these valleys is pumped from wells in the younger and older alluvium in the Huichica and Glen Ellen formations. and in the Sonoma volcanics. The principal aquifers are the younger and older alluvium. but appreciable quantities of water are pumped locally from the Sonoma volcanics. The Huichica and Glen Ellen formations yield water in small quantities and at most places supply water only for limited domestic uses. The younger alluvium COIM3ists of interbedded deposits of unconsolidated gravel. sand, silt. and. locally, peat. These deposits underlie the flood plains and channels of the Napa River. Sonoma Creek, and their tributaries, low alluvial fans or plains graded to these streams. and the tidal marshlands. The older alluvium of Napa and Sonoma Valleys is composed of lenticular deposits of unconsolidated and poorly sorted clay, silt. sand. and gravel. Where exposed, claypan or hardpan soil is characteristically developed at the surface. The Huichica formation is composed of deformed continental beds consisting mostly of yellow silt with some interbedded lenses of silt and gravel, and silt and boulders. At the base are beds of redeposited volcanic material, silt, clay, and lenses of coarse gravel and boulders. The Glen Ellen fcrmation consists of alluvial clay, silt, sand, and gravel in clearly stratified but generally lenticular beds. The Sonoma volcanics constitute a thick and highly variate series of continental volcanic rocks, including andesite, basalt, and minor rhyolite flows and interbedded coarse- to fine-grained pyroclastic tuff and breccia, redeposited tuff and pumice, and diatomaceous mud, silt, and sand. A prominent body of rhyolite flows and tuff with some obsidian and perlitic glass, called the St. Helena rhyolite member, occurs in the upper part. Estimated ground-water pumpage for all uses in the year 1949-50 was about 5,600 acre-feet in Napa Valley and about 2,400 acre-feet in Sonoma Valley. Of this quantity the amounts pumped for irrigation were about 2,900 and 1,900 acre-feet, respectively. Water levels in wells in the central parts of the valleys range from a few feet above the land surface to about 50 feet below, with an average of about 25 feet. The quality of the water in most wells is satisfactory for domestic use and irrigation. Locally at the southern end of the valley some contamination of the native waters is caused by the movement of salty wate

Water Supply Paper↗
USGS2021

Comment on ‘New insights on Franciscan Complex geology, architecture, depositional age, and provenance for the western Mt. Tamalpais area, Marin County, California’ by Bero et al. (2020)

Serious errors and inconsistencies in the article undermine many of its interpretations to the point that principal conclusions are not valid. Much dependence is placed on the maximum depositional age (Dmax) of sandstone units based on zircon analysis of 10 samples, but calculation of those Dmax values is flawed, and their use confuses maximum with actual depositional ages and makes age distinctions finer than the resolution of the data. Conclusions that are compromised include the concept of a westward/downward-younging tectonostratigraphic stack of accretionary units, comparison of mapped sandstones with other California Coast Ranges sandstones, comparison of timing of events recorded in the map area with regional events, identification of mélange only in a narrow band in the study area, and detrital provenance of some of the sandstone units.

California↗
USGS2014

A compilation of K-Ar-ages for southern California

The purpose of this report is to make available a large body of conventional K-Ar ages for granitic, volcanic, and metamorphic rocks collected in southern California. Although one interpretive map is included, the report consists primarily of a systematic listing, without discussion or interpretation, of published and unpublished ages that may be of value in future regional and other geologic studies. From 1973 to 1979, 468 rock samples from southern California were collected for conventional K-Ar dating under a regional geologic mapping project of Southern California (predecessor of the Southern California Areal Mapping Project). Most samples were collected and dated between 1974 and 1977. For 61 samples (13 percent of those collected), either they were discarded for varying reasons, or the original collection data were lost. For the remaining samples, 518 conventional K-Ar ages are reported here; coexisting mineral pairs were dated from many samples. Of these K-Ar ages, 225 are previously unpublished, and identified as such in table 1. All K-Ar ages are by conventional K-Ar analysis; no 40 Ar/ 39 Ar dating was done. Subsequent to the rock samples collected in the 1970s and reported here, 33 samples were collected and 38 conventional K-Ar ages determined under projects directed at (1) characterization of the Mesozoic and Cenozoic igneous rocks in and on both sides of the Transverse Ranges and (2) clarifying the Mesozoic and Cenozoic tectonics of the eastern Mojave Desert. Although previously published (Beckerman et al., 1982), another eight samples and 11 conventional K-Ar ages are included here, because they augment those completed under the previous two projects.

California↗
USGS1985

An investigation of ground-water recharge by injection in the Palo Alto Baylands, California: Hydraulic and chemical interactions — Final report

The U.S. Geological Survey, in cooperation with the Santa Clara Valley Water District, has completed a study of ground-water recharge by injection in the Palo Alto baylands along San Francisco Bay, California. Selected wells within the Water District 's injection-extraction network were monitored to determine hydraulic and chemical interactions affecting well-field operation. The well field was installed to prevent and eliminate saline contamination in the local shallow aquifer system. The primary focus of this study is on factors that affect injection efficiency, specifically well and aquifer clogging. Mixing and break-through curves for major chemical constituents indicate ion exchange, adsorption, and dissolution reactions. Freshwater breakthrough was detected in water-level data, which reflected fluid-density change as well as head buildup. Dissolution of calcium carbonate caused by dilution of saline ground water probably accounts for an apparent increase in specific capacity possibly related to improved aquifer permeability. Adsorption evidently removed trace elements during passage of injected water through the aquifer. In terms of hydraulic and chemical compatibility, the well field is a viable system for ground-water recharge. Aquifer heterogeneity and operational constraints reduce the efficiency of the system. Efficiency may be maximized by careful attention to extraction distribution and quantity and to injection distribution, quantity, and water quality. (USGS)

California↗
USGS2019

A revised continuous surface elevation model for modeling

A digital elevation model (DEM) is an essential component of any hydrodynamic model. The Delta Modeling Section (Section) has maintained a database of bathymetry soundings and levee surveys for decades and published a 10-meter (10m) DEM for the San Francisco Bay and Sacramento-San Joaquin Delta (Delta) (California Department of Water Resources 2012). In collaboration with the U.S. Geological Survey (USGS) Pacific Coastal and Marine Science Center, the California Department of Water Resources (DWR) has continued to upgrade these DEMs based on newer survey data and improved interpolation methodologies. An updated San Francisco Bay-Delta bathymetric/topographic digital elevation model was published by the USGS (Fregoso, Wang, Ateljevich, and Jaffe 2017). Both DWR and USGS continue to work on the elevation models for several reasons. First, high-resolution multibeam bathymetry data continues to become available. A good portion of the newer collections are performed at locations where bathymetry data is lacking, or of poor quality, or where model sensitivity to bathymetry is known to be high, so the effort has a high return on investment. Recent high-resolution multibeam datasets easily support the development of accurate 2-meter (2m) DEMs, although shallow water, turbidity, vegetation, and the gap between the multibeam data and terrestrial data from light detection and ranging (LiDAR) remain vexing issues that fuel development of enhanced techniques. In some locations, migration toward 2m resolution models is motivated by geographical structure even where there has been little improvement in the underlying data. DEMs at 10m resolution are insufficient to adequately describe small-scale terrain features, such as levee crests or the main conveyance channel through a narrow reach, such as Middle River. As a result, elevation modelers have traditionally needed to perform feature enforcement for 10m DEMs, but not for the Section’s 2m DEMs which do resolve these features (California Department of Resources 2012). There are several other problems associated with a coarse target resolution, including reduced conveyance and rough contours where channels run oblique to the elevation model. In places where the topography demands a finer elevation model, the Section and others have adopted improved interpolation techniques for single-beam data to produce reasonable 2m DEMs that preserve features on appropriate scales.

California↗
USGS2018

Soil moisture datasets at five sites in the central Sierra Nevada and northern Coast Ranges, California

In situ soil moisture datasets are important inputs used to calibrate and validate watershed, regional, or statewide modeled and satellite-based soil moisture estimates. The soil moisture dataset presented in this report includes hourly time series of the following: soil temperature, volumetric water content, water potential, and total soil water content. Data were collected by the U.S. Geological Survey at five locations in California: three sites in the central Sierra Nevada and two sites in the northern Coast Ranges. This report provides a description of each of the study areas, procedures and equipment used, processing steps, and time series data from each site in the form of comma-separated values (.csv) tables.

California↗
USGS2015

Holocene geologic slip rate for the Banning strand of the southern San Andreas Fault, southern California

Northwest directed slip from the southern San Andreas Fault is transferred to the Mission Creek, Banning, and Garnet Hill fault strands in the northwestern Coachella Valley. How slip is partitioned between these three faults is critical to southern California seismic hazard estimates but is poorly understood. In this paper, we report the first slip rate measured for the Banning fault strand. We constrain the depositional age of an alluvial fan offset 25 ± 5 m from its source by the Banning strand to between 5.1 ± 0.4 ka (95% confidence interval (CI)) and 6.4 + 3.7/−2.1 ka (95% CI) using U-series dating of pedogenic carbonate clast coatings and 10 Be cosmogenic nuclide exposure dating of surface clasts. We calculate a Holocene geologic slip rate for the Banning strand of 3.9 + 2.3/−1.6 mm/yr (median, 95% CI) to 4.9 + 1.0/−0.9 mm/yr (median, 95% CI). This rate represents only 25–35% of the total slip accommodated by this section of the southern San Andreas Fault, suggesting a model in which slip is less concentrated on the Banning strand than previously thought. In rejecting the possibility that the Banning strand is the dominant structure, our results highlight an even greater need for slip rate and paleoseismic measurements along faults in the northwestern Coachella Valley in order to test the validity of current earthquake hazard models. In addition, our comparison of ages measured with U-series and 10 Be exposure dating demonstrates the importance of using multiple geochronometers when estimating the depositional age of alluvial landforms.

Journal of Geophysical Research B: Solid Earth↗
USGS2016

California State Waters Map Series — Offshore of Monterey, 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 bathymetry 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 Monterey map area in central California is located on the Pacific Coast, about 120 km south of San Francisco. Incorporated cities in the map area include Seaside, Monterey, Marina, Pacific Grove, Carmel-by-the-Sea, and Sand City. The local economy receives significant resources from tourism, as well as from the Federal Government. Tourist attractions include the Monterey Bay Aquarium, Cannery Row, Fisherman’s Wharf, and the many golf courses near Pebble Beach, and the area serves as a gateway to the spectacular scenery and outdoor activities along the Big Sur coast to the south. Federal facilities include the Army’s Defense Language Institute, the Naval Postgraduate School, and the Fleet Numerical Meteorology and Oceanography Center (operated by the Navy). In 1994, Fort Ord army base, located between Seaside and Marina, was closed; much of former army base land now makes up the Fort Ord National Monument, managed by the U.S. Bureau of Land Management as part of the National Landscape Conservation System. In addition, part of the old Fort Ord is now occupied by California State University, Monterey Bay. The offshore part of the map area lies entirely within the Monterey Bay National Marine Sanctuary, one of the nation’s largest marine sanctuaries. State beaches and parks within the map area include Fort Ord Dunes State Park and the Marina, Monterey, and Asilomar State Beaches, as well as Carmel River State Beach, which includes the Carmel River Lagoon and Wetland Natural Preserve. The map area also includes all or part of several State Marine Protected Areas, including the Carmel Pinnacles, Asilomar, and Lovers Point–Julia Platt State Marine Reserves, as well as the Carmel Bay, Pacific Grove Marine Gardens, Edward F. Ricketts, and Portuguese Ledge State Marine Conservation Areas. The coastal zone in the map area is characterized by two distinct physiographies. From Marina to Monterey, sandy beaches are backed by a belt of sand dunes, as much as 30 to 40 m high and as wide as 8 km. The Salinas River supplies the sand for the beaches and dunes. Nearshore sediment transport is primarily to the south, in the southern Monterey littoral cell. Along the Monterey peninsula, which lies at the north end of the rugged Santa Lucia Range, coastal relief is very different. The peninsula is characterized largely by low marine terraces that formed mostly on hard and relatively stable granitic bedrock. Carmel Beach in Carmel-by-the-Sea is the longest continuous beach in this area; bedrock points and small pocket beaches characterize most of the rest of the peninsula. The Carmel River littoral cell extends along the coast from Point Pinos to Point Lobos (just south of the map area), including Carmel Beach; sediment transport is primarily to the south. The granitic rocks that crop out so prominently along the Monterey peninsula make up part of the Salinian block, a crustal terrane that in this area lies west of the San Andreas Fault and east of the San Gregorio Fault. The strike-slip San Andreas Fault Zone, which lies just 26 km east of the map area, is the most important structure within the Pacific–North American transform plate boundary. The San Gregorio Fault, a secondary fault within the distributed plate boundary, cuts through (and is roughly aligned with) Carmel Canyon, a submarine canyon in the southwest corner of the map area that is part of the Monterey Canyon system. The San Gregorio Fault Zone is part of a fault system that is present predominantly in the offshore for about 400 km, from Point Conception in the south (where it is known as the Hosgri Fault) to Bolinas and Point Reyes in the north. The offshore part of the map area primarily consists of relatively flat continental shelf, bounded on the west by the steep flanks of Carmel Canyon. Shelf width varies from 2 to 3 km in the southern part of the map area, near the mouth of Carmel Canyon, to 14 km in Monterey Bay. Bedrock beneath the shelf is overlain in many areas by variable amounts (0 to 16 m) of upper Quaternary shelf and nearshore sediments deposited as sea level fluctuated in the late Pleistocene. “Soft-induration,” unconsolidated sediment is the dominant (about 63 percent) habitat type on the continental shelf, followed by “hard-induration” rock and boulders (about 34 percent) and “mixed-induration” substrate (about 3 percent). At water depths of about 100 to 130 m, the shelf break approximates the shoreline during the sea-level lowstand of the Last Glacial Maximum, about 21,000 years ago. Carmel Canyon and other parts of the Monterey Canyon system in the map area extend from the shelf break to water depths that reach 1,600 m. Most of the extensive incision of the shelf break and canyon flanks probably occurred during repeated Quaternary sea-level lowstands. The relatively straight floor of Carmel Canyon notably is aligned with the San Gregorio Fault Zone. Mixed hard-soft substrate is the most common (about 51 percent) habitat type in Carmel Canyon; hard bedrock and soft, unconsolidated sediment cover about 40 percent and 9 percent of canyon habitat, respectively. This part of the central California coast is exposed to large North Pacific swells from the northwest throughout the year. Wave heights range from 2 to 10 m, the larger swells occurring from October to May. During El Niño–Southern Oscillation (ENSO) events, winter storms track farther south than they do in normal (non-ENSO) years, thereby impacting the map area more frequently and with waves of larger heights. Benthic species observed in the map area are natives of the cold-temperate biogeographic zone that is called either the “Oregonian province” or the “northern California ecoregion.” This biogeographic province is maintained by the long-term stability of the southward-flowing California Current, the eastern limb of the North Pacific subtropical gyre that flows from southern British Columbia to Baja California. Biological productivity resulting from coastal upwelling supports populations of Sooty Shearwater, Western Gull, Common Murre, Cassin’s Auklet, and many other less populous bird species. An observable recovery of Humpback and Blue Whales has occurred in the area; both species are dependent on coastal upwelling to provide nutrients. The large extent of exposed inner shelf bedrock supports large forests of “bull kelp,” which is well adapted for high-wave-energy environments. The kelp beds are well-known habitat for the population of southern sea otters. Common fish species found in the kelp beds and rocky reefs include lingcod and various species of rockfish and greenling.

California↗
USGS2022

Preliminary geologic map of early Miocene felsic eruptive centers in the Aquarius Mountains, west-central Arizona

The first author, Gary S. Fuis, conducted this mapping in the summer of 1967 in partial fulfillment of the entry requirements into the Ph.D program of the Division of Geological and Planetary Sciences of the California Institute of Technology, Pasadena, Calif. The area mapped lies wholly within the Fort Rock Ranch, a private ranch spanning ~50 square miles in Mohave and Yavapai Counties, Arizona. Access to the ranch is limited, and it is uncertain whether a detailed geologic map of the Aquarius Mountains can be recreated today. Therefore, we are making this map available to the public in this Open-File Report. The original mapping was compiled on an enlarged single aerial photograph at an approximate scale of 1:15,600. The second author, J. Luke Blair, photogrammetrically rectified the original map and added modern topography, which was not available at the time the original map was completed. Modern roads and drainages were also added, including I–40, built after the original map was completed. Both authors reformatted the original map using current USGS geologic map standards.

Arizona↗
USGS2016

Marine magnetic survey and onshore gravity and magnetic survey, San Pablo Bay, northern California

Introduction From November 2011 to August 2015, the U.S. Geological Survey (USGS) collected more than 1,000 line-kilometers (length of lines surveyed in kilometers) of marine magnetic data on San Pablo Bay, 98 onshore gravity stations, and over 27 line-kilometers of ground magnetic data in northern California. Combined magnetic and gravity investigations were undertaken to study subsurface geologic structures as an aid in understanding the geologic framework and earthquake hazard potential in the San Francisco Bay Area. Furthermore, marine magnetic data illuminate local subsurface geologic features in the shallow crust beneath San Pablo Bay where geologic exposure is absent. Magnetic and gravity methods, which reflect contrasting physical properties of the subsurface, are ideal for studying San Pablo Bay. Exposed rock units surrounding San Pablo Bay consist mainly of Jurassic Coast Range ophiolite, Great Valley sequence, Franciscan Complex rocks, Miocene sedimentary rocks, and unconsolidated alluvium (Graymer and others, 2006). The contrasting magnetic and density properties of these rocks enable us to map their subsurface extent.

California↗