USGS Science⌕ Search

SEARCH · USGS Science

Results for “Quaternary”

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

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

At least 1,693 records · Page 94Linked to original sources
USGS2002

Geological framework data from Long Island Sound, 1981-1990: A digital data release

Introduction Since 1980 the Coastal and Marine Geology Program of the U.S. Geological Survey and Connecticut Department of Environmental Protection have conducted a joint program of cooperative geologic research in Long Island Sound and its vicinity. As part of this program, a highly successful regional-scale study of the geologic framework was completed. Reconnaissance high-resolution seismic reflection data were collected and used to establish the basic stratigraphy within the Sound and to map the major geologic units; field verification of the geologic interpretations of the seismic profiles was primarily accomplished with vibratory cores. These interpretations were in turn used to produce basin-wide syntheses of the late Quaternary depositional history. Unfortunately, the original seismic records and core logs were generated only in analog form. These unique paper documents, which are still under demand for industrial applications and academic research, are fragile and have become ragged from frequent use. The purpose of this report is to preserve these data by converting the seismic profiles, core descriptions, and ancillary reports into digital form, and to organize these files into a product that can be more readily accessed and disseminated. Not all of the existing high-resolution seismic-reflection surveys, collected in Long Island Sound through cooperatives with the U.S. Geological Survey and the Connecticut Department of Environmental Protection, have been incorporated into this report. These surveys, whose records are still in need of preprocessing and annotation, generally cover smaller areas along the Connecticut coast and were originally intended to provide additional detail to the larger, more regional data sets presented herein. The digital release of the omitted data sets is planned as part of a future product.

Connecticut, New York↗
USGS2002

Soil chemistry and mineralogy of the Santa Cruz coastal terraces

Marine terraces in the central coast of California provide an opportunity to study a soil chronosequence in which similar materials (beach deposits) have been weathered under similar slope, climatic, and vegetation conditions during the Quaternary. The terraces between Santa Cruz and Año Nuevo, California, have been studied for decades and are thought to be one of the best example of marine terraces in California {Lawson (1893), Wilson (1907); Branner and others (1909), Rode (1930) Page and Holmes (1945), Alexander (1953), Bradley (1956, 1957, 1958, and 1965), Bradley and Addicott (1968), Clark (1966 and 1970), Jahns and Hamilton (1971), Lajoie and others (1972), Bradley and Griggs (1976). Hanks and others (1986), Aniku (1986), Fine and others (1988), Anderson (1990 and 1994), and Rosenbloom and Anderson (1994).} Here we report morphological, chemical, physical, and mineralogical data for the soils that were formed in deposits on the Santa Cruz marine terraces in order to examine soil characteristics as a function of increasing terrace age.

California↗
USGS2003

Structure of the Tucson Basin, Arizona from gravity and aeromagnetic data

Interpretation of gravity and high-resolution aeromagnetic data reveal the three-dimensional geometry of the Tuscson Basin, Arizona and the lithology of its basement. Limited drill hole and seismic data indicate that the maximum depth to the crystalline basement is approximately 3600 meters and that the sedimentary sequences in the upper ~2000 m of the basin were deposited during the most recent extensional episode that commenced about 13 Ma. The negative density contrasts between these upper Neogene and Quaternary sedimentary sequences and the adjacent country rock produce a Bouguer residual gravity low, whose steep gradients clearly define the lateral extent of the upper ~2000m of the basin. The aeromagnetic maps show large positive anomalies associated with deeply buried, late Cretaceous-early Tertiary and mid-Tertiary igneous rocks at and below the surface of the basin. These magnetic anomalies provide insight into the older (>13 Ma) and deeper structures of the basin. Simultaneous 2.5-dimensional modeling of both gravity and magnetic anomalies constrained by geologic and seismic data delineates the thickness of the basin and the dips of the buried faults that bound the basin. This geologic-based forward modeling approach to using geophysical data is shown to result in more information about the geologic and tectonic history of the basin as well as more accurate depth to basement determinations than using generalized geophysical inversion techniques.

Open-File Report↗
USGS2003

Preliminary metallogenic belt and mineral deposit maps for northeast Asia

The metallogenic belts and locations of major mineral deposits of Northeast Asia are portrayed on Sheets 1-4. Sheet 1 portrays the location of significant lode deposits and placer districts at a scale of 1:7,500,000. Sheets 2-4 portray the metallogenic belts of the region in a series of 12 time-slices from the Archean through the Quaternary at a scale of 1:15,000,000. For all four map sheets, a generalized geodynamics base map, derived from a more detailed map by Parfenov and others (2003), is used as an underlay for the metallogenic belt maps. This geodynamics map underlay permits depicts the major host geologic units and structures that host metallogenic belts. Four tables are included in this report. A hierarchial ranking of mineral deposit models is listed in Table 1. And summary features of lode deposits, placer districts, and metallogenic belts are described in Tables 2, 3, and 4, respectively. The metallogenic belts for Northeast Asia are synthesized, compiled, described, and interpreted with the use of modern concepts of plate tectonics, analysis of terranes and overlap assemblages, and synthesis of mineral deposit models. The data supporting the compilation are: (1) comprehensive descriptions of mineral deposits; (2) compilation and synthesis of a regional geodynamics map the region at 5 million scale with detailed explanations and cited references; and (3) compilation and synthesis of metallogenic belt maps at 15 million scale with detailed explanations and cited references. These studies are part of a major international collaborative study of the Mineral Resources, Metallogenesis, and Tectonics of Northeast Asia that is being conducted from 1997 through 2002 by geologists from earth science agencies and universities in Russia, Mongolia, Northeastern China, South Korea, Japan, and the USA. Companion studies and previous publications are: (1) a detailed geodynamics map of Northeast Asia (Parfenov and 2003); (2) a compilation of major mineral deposit models (Rodionov and Nokleberg, 2000; Rodionov and others, 2000; Obolenskiy and others, 2003); and (3) a database on significant metalliferous and selected nonmetalliferous lode deposits, and selected placer districts (Ariunbileg and others, 2003).

Open-File Report↗
USGS2003

Preliminary geologic map of the San Bernardino 30' x 60' quadrangle, California (includes preliminary GIS database)

The San Bernardino 30'x60' quadrangle, southern California, is diagonally bisected by the San Andreas Fault Zone, separating the San Gabriel and San Bernardino Mountains, major elements of California's east-oriented Transverse Ranges Province. Included in the southern part of the quadrangle is the northern part of the Peninsular Ranges Province and the northeastern part of the oil-producing Los Angeles basin. The northern part of the quadrangle includes the southern part of the Mojave Desert Province. Pre-Quaternary rocks within the San Bernardino quadrangle consist of three extensive, well-defined basement rock assemblages, the San Gabriel Mountains, San Bernardino Mountains, and the Peninsular Ranges assemblages, and a fourth assemblage restricted to a narrow block bounded by the active San Andreas Fault and the Mill Creek Fault. Each of these basement rock assemblages is characterized by a relatively unique suite of rocks that was amalgamated by the end of the Cretaceous and (or) early Cenozoic. Some Tertiary sedimentary and volcanic rocks are unique to specific assemblages, and some overlap adjacent assemblages. A few Miocene and Pliocene units cross the boundaries of adjacent assemblages, but are dominant in only one. Tectonic events directly and indirectly related to the San Andreas Fault system have partly dismembered the basement rocks during the Neogene, forming the modern-day physiographic provinces. Rocks of the four basement rock assemblages are divisible into an older suite of Late Cretaceous and older rocks and a younger suite of post-Late Cretaceous rocks. The age span of the older suite varies considerably from assemblage to assemblage, and the point in time that separates the two suites varies slightly. In the Peninsular Ranges, the older rocks were formed from the Paleozoic to the end of Late Cretaceous plutonism, and in the Transverse Ranges over a longer period of time extending from the Proterozoic to metamorphism at the end of the Cretaceous. Within the Peninsular Ranges a profound diachronous unconformity marks the pre-Late Cretaceous-post-Late Cretaceous subdivision, but within the Transverse Ranges the division appears to be slightly younger, perhaps coinciding with the end of the Cretaceous or extending into the early Cenozoic. Initial docking of Peninsular Ranges rocks with Transverse Ranges rocks appears to have occurred at the terminus of plutonism within the Peninsular Ranges. During the Paleogene there was apparently discontinuous but widespread deposition on the basement rocks and little tectonic disruption of the amalgamated older rocks. Dismemberment of these Paleogene and older rocks by strike-slip, thrust, and reverse faulting began in the Neogene and is ongoing. The Peninsular Ranges basement rock assemblage is made up of the Peninsular Ranges batholith and a variety of metasedimentary rocks. Most of the plutonic rocks of the batholith are granodiorite and tonalite in composition; primary foliation is common, mainly in the eastern part. Tertiary sedimentary rocks of the Los Angeles Basin crop out in the Puente and San Jose Hills along with the spatially associated Glendora Volcanics; both units span the boundary between the Peninsular Ranges and San Gabriel Mountains basement rock assemblages. The San Gabriel Mountains basement rock assemblage includes two discrete areas, the high standing San Gabriel Mountains and the relatively low San Bernardino basin east of the San Jacinto Fault. The basement rock assemblage is characterized by a unique suite of rocks that include anorthosite, Proterozoic and Paleozoic gneiss and schist, the Triassic

California↗
USGS2003

Geologic map and digital database of the Yucaipa 7.5’ quadrangle, San Bernardino and Riverside Counties, California

Introduction This geologic database of the Yucaipa 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 Yucaipa 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 Yucaipa 7.5' quadrangle contains materials and structures that provide unique insight into the Mesozoic and Cenozoic geologic evolution of southern California. Stratigraphic and structural elements include: (1) strands of the San Andreas Fault that bound far-traveled terranes of crystalline and sedimentary rock; (2) Mesozoic crystalline rocks that form lower and upper plates of the regionwide Vincent-Orocopia Thrust system; and (3) 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 geologic hazards and ground-water recharge and subsurface flow. Geologic information contained in the Yucaipa database is general-purpose data that is applicable to land-related investigations in the earth and biological sciences. The term "generalpurpose" 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.

California↗
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↗
USGS2003

Geology of Badlands National Park: A preliminary report

Badlands National Park is host to perhaps the most scenic geology and landscape features in the Western Interior region of the United States. Ongoing erosion that forms the "badlands" exposes ancient sedimentary strata of Late Cretaceous through Oligocene age. Quaternary erosional and depositional processes are responsible for most of the modern landscape features in the park and surrounding region. This report provides a basic overview of the park geology The discussions presented within include both well-established concepts and theories and new, preliminary data and interpretations. Much emphasis is placed on presenting information about the oldest and least studied rocks in the park (particularly the Late Cretaceous and earliest Tertiary deposits that underlie the White River beds throughout the park region). Rock formations and selected fossils they contain are described. Faults, folds, unconformities, and other geologic structures in the North Unit of the park are illustrated, including features associated with the Sage Creek anticline and fault system.

South Dakota↗
USGS2001

Thickness and geometry of Cenozoic deposits in California Wash area, Nevada, based on gravity and seismic-reflection data

Gravity and seismic-reflection data provide insights into the subsurface stratigraphy and structure of the California Wash area of southern Nevada. This area is part of the Lower Colorado flow system and stratigraphic and structural data are important inputs into developing the hydrogeologic framework. These data indicate that the basin beneath California Wash reaches depths of 2-3 km. The eastern margin of the basin coincides with a system of young (Quaternary and late Tertiary) faults, although both seismic and gravity data indicate that the major basin-bounding fault is 2-3 km west of the mapped young faults. Dry Lake Valley, the adjacent valley to the west, is characterized by thinner basin fill. The basin configuration beneath both California Wash and Dry Lake Valleys based on the inversion of gravity data is unconstrained because of the lack of gravity stations north of 36030?. Broad aeromagnetic anomalies beneath pre-Cenozoic basement in the Muddy Mountains and Arrow Canyon Range reflect Precambrian basement at depths of ~ 5 km. These rocks are probably barriers to ground-water flow,except where fractured.

Open-File Report↗
USGS2002

Preliminary geologic map of the Santa Barbara coastal plain area, Santa Barbara County, California

This report presents a new geologic digital map of the Santa Barbara coastal plain area at a compilation scale of 1:24,000 (one inch on the map = 2,000 feet on the ground) and with a horizontal positional accuracy of at least 20 m. This preliminary map depicts the distribution of bedrock units and surficial deposits and associated deformation underlying and adjacent to the coastal plain within the contiguous Santa Barbara and Goleta 7.5' quadrangles. A planned second version will extend the mapping westward into the adjoining Dos Pueblos Canyon quadrangle and eastward into the Carpinteria quadrangle. The mapping presented here results from the collaborative efforts of geologists with the U.S. Geological Survey Southern California Areal Mapping Project (SCAMP) (Minor, Kellogg, Stanley, Stone, and Powell) and the tectonic geomorphology research group at the University of California at Santa Barbara (Gurrola and Selting). C.L. Powell, II, performed all new fossil identifications and interpretations reported herein. T.R. Brandt designed and edited the GIS database,performed GIS database integration and created the digital cartography for the map layout. The Santa Barbara coastal plain is located in the western Transverse Ranges physiographic province along a west-trending segment of the southern California coastline about 100 km (62 mi) northwest of Los Angeles. The coastal plain region, which extends from the Santa Ynez Mountains on the north to the Santa Barbara Channel on the south, is underlain by numerous active and potentially active folds and partly buried thrust faults of the Santa Barbara fold and fault belt. Strong earthquakes that occurred in the region in 1925 (6.8 magnitude) and 1978 (5.1 magnitude) are evidence that such structures pose a significant earthquake hazard to the approximately 200,000 people living within the major coastal population centers of Santa Barbara and Goleta. Also, young landslide deposits along the steep lower flank of the Santa Ynez Mountains indicate the potential for continued slope failures and mass movements that may threaten urbanized parts of the coastal plain. Deformed sedimentary rocks in the subsurface of the coastal plain and the adjacent Santa Barbara Channel contain deposits of oil and gas, some of which are currently being extracted. Shallow, localized sedimentary aquifers underlying the coastal plain provide limited amounts of water for the urban areas, but the quality of some of this groundwater is compromised by coastal salt-water contamination. The present map compilation provides a set of uniform geologic digital coverages that can be used for analysis and prediction of these and other geologic hazards and resources in the coastal plain region. In the map area the oldest stratigraphic units consist of resistant Eocene to Oligocene marine and terrestrial sedimentary rocks that form a mostly southward-dipping and laterally continuous sequence along the south flank of the Santa Ynez Mountains. Less resistant, but more variably deformed, Miocene, Pliocene, and Pleistocene marine sedimentary rocks and deposits are exposed in the lower Santa Ynez foothills and in the coastal hills and sea cliffs farther south. Pleistocene and Holocene surficial alluvial, colluvial, estuarine, and marine-terrace deposits directly underlie much of the low-lying coastal plain area, and similar-aged alluvial and landslide deposits locally mantle the lower flanks of the Santa Ynez Mountains. Structurally, the Santa Barbara coastal plain area is dominated by the Santa Barbara fold and fault belt, an east-west-trending zone of Quaternary, partly active folds and blind and exposed reverse and thrust faults. The dominant trend of individual structures within the belt is west-northwest -- slightly oblique to the overall trend of the fold and fault belt. A conspicuous exception, however, is the More Ranch fault system, which strikes east-northeast across the fold and f

Open-File Report↗
USGS2004

Geology of the Ugashik-Mount Peulik Volcanic Center, Alaska

The Ugashik-Mount Peulik volcanic center, 550 km southwest of Anchorage on the Alaska Peninsula, consists of the late Quaternary 5-km-wide Ugashik caldera and the stratovolcano Mount Peulik built on the north flank of Ugashik. The center has been the site of explosive volcanism including a caldera-forming eruption and post-caldera dome-destructive activity. Mount Peulik has been formed entirely in Holocene time and erupted in 1814 and 1845. A large lava dome occupies the summit crater, which is breached to the west. A smaller dome is perched high on the southeast flank of the cone. Pyroclastic-flow deposits form aprons below both domes. One or more sector-collapse events occurred early in the formation of Mount Peulik volcano resulting in a large area of debris-avalanche deposits on the volcano's northwest flank. The Ugashik-Mount Peulik center is a calcalkaline suite of basalt, andesite, dacite, and rhyolite, ranging in SiO2 content from 51 to 72 percent. The Ugashik-Mount Peulik magmas appear to be co-genetic in a broad sense and their compositional variation has probably resulted from a combination of fractional crystallization and magma-mixing. The most likely scenario for a future eruption is that one or more of the summit domes on Mount Peulik are destroyed as new magma rises to the surface. Debris avalanches and pyroclastic flows may then move down the west and, less likely, east flanks of the volcano for distances of 10 km or more. A new lava dome or series of domes would be expected to form either during or within some few years after the explosive disruption of the previous dome. This cycle of dome disruption, pyroclastic flow generation, and new dome formation could be repeated several times in a single eruption. The volcano poses little direct threat to human population as the area is sparsely populated. The most serious hazard is the effect of airborne volcanic ash on aircraft since Mount Peulik sits astride heavily traveled air routes connecting the U.S. and Europe to Asia. Activity of the type described could produce eruption columns to heights of 15 km and result in significant amounts of ash 250-300 km downwind.

Alaska↗
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↗
USGS2004

Data collected from USGS drilling in Lafayette Park, Washington, D.C. in November-December, 1976

In 1976, the U.S. Geological Survey drilled four holes in Lafayette Park in Washington, D.C. These holes encountered two Coastal Plain units (Quaternary (undifferentiated) and the Lower Cretaceous Potomac Group), and then bottomed in Paleozoic metamorphic bedrock. The stratigraphic relations of the Coastal Plain formations indicate that the Potomac Group strata become abruptly thicker from west to east across the park.

Open-File Report↗
USGS2006

Geologic map of the Colonial Beach South 7.5-minute quadrangle, Virginia

The Open-File Report includes a geologic map with cross section, and composite stratigraphic section of the Tertiary stratigraphy and of the Quaternary stratigraphy. The Tertiary map units are presented and interpreted for erodability and derived surficial deposits. The map area contains the George Washington Birthplace National Monument. The map facilitates the interpretation of the natural history of the Park including processes such as bog (wetlands) formation and coastal erosion. Two cores of Holocene estuarine deposits are sited on the map. They present the transition from terrestrial to estuarine depositional environments.

Open-File Report↗
USGS2005

Surficial deposits in the Bear Lake Basin

Mapping and dating of surficial deposits in the Bear Lake drainage basin were undertaken to provide a geologic context for interpretation of cores taken from deposits beneath Bear Lake, which sometimes receives water and sediment from the glaciated Bear River and sometimes only from the small drainage basin of Bear Lake itself. Analyses of core sediments by others are directed at (1) constructing a high-resolution climate record for the Bear Lake area during the late Pleistocene and Holocene, and (2) investigating the sources and weathering history of sediments in the drainage basin. Surficial deposits in the upper Bear River and Bear Lake drainage basins are different in their overall compositions, although they do overlap. In the upper Bear River drainage, Quaternary deposits derived from glaciation of the Uinta Range contain abundant detritus weathered from Precambrian quartzite, whereas unglaciated tributaries downstream mainly contribute finer sediment weathered from much younger, more friable sedimentary rocks. In contrast, carbonate rocks capped by a carapace of Tertiary sediments dominate the Bear Lake drainage basin.

Open-File Report↗
USGS2005

Height changes along selected lines through the Death Valley region, California and Nevada, 1905-1984

Comparisons among repeated levelings along selected lines through the Death Valley region of California and adjacent parts of Nevada have disclosed surprisingly large vertical displacements. The vertical control data in this lightly populated area is sparse; moreover, as much as a third of the recovered data is so thoroughly contaminated by systematic error and survey blunders that no attempt was made to correct these data and they were simply discarded. In spite of these limitations, generally episodic, commonly large vertical displacements are disclosed along a number of lines. Displacements in excess of 0.4 m, with respect to our selected control point at Beatty, Nevada, and differential displacements of about 0.7 m apparently occurred during the earlier years of the 20th century and continued episodically through at least 1943. While this area contains abundant evidence of continuing tectonic activity through latest Quaternary time, it is virtually devoid of historic seismicity. We have detected no clear connection between the described vertical displacements and fault zones reportedly active during Holocene time, although we sense some association with several more broadly defined tectonic features.

Open-File Report↗
USGS2006

High-resolution geologic mapping of the inner continental shelf: Nahant to Gloucester, Massachusetts

This report presents high-resolution maps of the seafloor offshore of Massachusetts, from Nahant to Gloucester. Approximately 134 km² of the inner shelf were mapped with a focus on the nearshore region in water depths less than 40 m (fig. 1.1). The maps were prepared as part of a cooperative mapping program between the U.S. Geological Survey (USGS) and the Massachusetts Office of Coastal Zone Management (CZM). They are based on marine geophysical data, sediment sampling, and bottom photography obtained on two research cruises carried out in 2003 and 2004. The primary objective of this program is to develop a suite of seafloor maps that provide geologic information for management of coastal and marine resources. Accurate maps of seafloor geology are important first steps toward protecting fish habitat, delineating marine reserves, and assessing environmental changes due to natural or human impacts. The maps also provide a geologic framework for scientific research, industry and the public. The organization of this report is outlined in the navigation bar along the left-hand margin of the page. This is section 1, the introduction. Section 2 briefly describes the mapping products contained in this report and has links to large-format map sheets, that can be viewed on line or downloaded. Section 3 is a description of the data collection, processing, and analysis procedures used to create the map products. Section 4 examines the geologic framework and late Quaternary evolution of the region, and presents two different strategies for mapping the complex seafloor. This report also contains four appendices that include GIS layers of all data collected in this study, and copies of the sample and photographic data used to validate the interpretations.

Massachusetts↗
USGS2006

Preliminary isostatic gravity map of the Sonoma volcanic field and vicinity, Sonoma and Napa Counties, California

This isostatic residual gravity map is part of a three-dimensional mapping effort focused on the subsurface distribution of rocks of the Sonoma volcanic field in Napa and Sonoma counties, northern California. This map will serve as a basis for modeling the shapes of basins beneath the Santa Rosa Plain and Napa and Sonoma Valleys, and for determining the location and geometry of faults within the area. Local spatial variations in the Earth's gravity field (after accounting for variations caused by elevation, terrain, and deep crustal structure explained below) reflect the distribution of densities in the mid to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithologic boundaries. High-density basement rocks exposed within the northern San Francisco Bay area include those of the Mesozoic Franciscan Complex and Great Valley Sequence present in the mountainous areas of the quadrangle. Alluvial sediment and Tertiary sedimentary rocks are characterized by low densities. However, with increasing depth of burial and age, the densities of these rocks may become indistinguishable from those of basement rocks. Tertiary volcanic rocks are characterized by a wide range in densities, but, on average, are less dense than the Mesozoic basement rocks. Isostatic residual gravity values within the map area range from about -41 mGal over San Pablo Bay to about 11 mGal near Greeg Mountain 10 km east of St. Helena. Steep linear gravity gradients are coincident with the traces of several Quaternary strike-slip faults, most notably along the West Napa fault bounding the west side of Napa Valley, the projection of the Hayward fault in San Pablo Bay, the Maacama Fault, and the Rodgers Creek fault in the vicinity of Santa Rosa. These gradients result from juxtaposing dense basement rocks against thick Tertiary volcanic and sedimentary rocks.

Open-File Report↗