Unified Interior Regions

California

The Southwest Region includes California, Nevada, and Arizona. The Regional Office, headquartered in Sacramento, provides Center oversight and support, facilitates internal and external collaborations, and works to further USGS strategic science directions.

States L2 Landing Page Tabs

Filter Total Items: 421
Date published: June 7, 2018
Status: Active

2013 Springs Fire, Ventura County, California

The Springs Fire burned many steep basins in the Santa Monica Mountains east of Oxnard, CA in May, 2013. The USGS has installed a telemetered rain gage to monitor the rainfall conditions in the Springs Fire burn area.

Contacts: Dennis Staley, Jason Kean, National Oceanic and Atmospheric Association
Date published: June 6, 2018
Status: Active

U.S. Highway 50, California - Report

Mark E. Reid, and Richard G. LaHusen, 1998, Real-time Monitoring of Active Landslides Along Highway 50, El Dorado County: adapted from: California Geology, v.51, n.3, p.17-20

Date published: June 6, 2018
Status: Active

U.S. Highway 50, California

The Highway 50 landslide monitoring system uses data acquisition systems and radio telemetry developed by the USGS Volcano Hazards Program to operate in remote, hazardous sites with limited power. In many landslides, infiltration of rainfall or rapid snowmelt increases groundwater pressures. These elevated pressures can, in turn, trigger landslide movement.

 

Contacts: Mark Reid
Date published: June 6, 2018
Status: Active

2009 Station Fire, Dunsmore Canyon, Glendale, California

In 2009, the Station Fire burned 160,000 acres in the San Gabriel Mountains. Vegetation has started to return, but it can take many years for a basin to fully recover from the effects of fire.

Date published: June 6, 2018
Status: Active

2009 Station Fire, Arroyo Seco, Pasadena, California

In 2009, the Station Fire burned 160,000 acres in the San Gabriel Mountains. Vegetation has started to return, but it can take many years for a basin to fully recover from the effects of fire.

Date published: June 5, 2018
Status: Active

Post-Fire Flooding and Debris Flow

Fast-moving, highly destructive debris flows triggered by intense rainfall are one of the most dangerous post-fire hazards. The risk of floods and debris flows after fires increases due to vegetation loss and soil exposure. Cases of sudden and deadly debris flow are well documented along the western United States, particularly in ...

Date published: June 5, 2018
Status: Active

Water Quality after a Wildfire

About half of the water supply in the southwestern United States is supplied by water from forests, which generally yield higher quality water than any other source. Approximately 80 percent of the freshwater resources in the U.S. originate on forested land, and more than 3,400 public drinking-water systems are located in watersheds containing national forest lands (USDA, 2006). More than 12...

Date published: May 23, 2018
Status: Active

Rangeland Ecosystem Services

The Rangeland Ecosystem Services research described below is conducted and managed under the USGS Applied Landscape Ecology and Remote Sensing project and partners.

Date published: May 23, 2018
Status: Active

Applied Landscape Ecology and Remote Sensing

We focus on landscape studies of natural and working lands, in particular coastal and inland wetlands and rangelands. We quantify ecosystem benefits, find areas vulnerable to future change, and identify potential for climate mitigation and resilience. We conduct research by scaling field measurements to the regional, state and national scale with remote sensing, geospatial analysis, and...

Date published: May 10, 2018
Status: Active

Land Treatment Exploration Tool

The Land Treatment Exploration Tool provides a practical resource for managers who are planning restoration and rehabilitation actions on public lands. The tool generates a variety of spatial products while being user friendly for all levels of GIS expertise, even to those with little or no experience.

Date published: May 8, 2018
Status: Completed

Rare Earth Element Deposits in the Southeast Mojave Desert

In an effort to better understand domestic resource potential, the USGS is investigating the genetic relationship between rare earth element deposits at Mountain Pass, California and Music Valley (Pinto Mountains, California) and extend these studies across a 130-km long belt of alkaline Proterozoic rocks in the southeast Mojave Desert. Such a combined study would significantly improve our...

Contacts: David Ponce
Date published: April 30, 2018
Status: Completed

Untangling Faults at Depth – What Lies Beneath Panamint Valley, California?

Release Date: APRIL 30, 2018

The eastern edge of Panamint Valley,CA has two types of faults that can be seen in the near-surface geology. 150 geophones and a seismic source will help reveal the subsurface picture.

Filter Total Items: 583
Date published: January 1, 2019

Hydrodynamic and sediment transport data from San Pablo Bay (northern San Francisco Bay), 2011-2012

The U.S. Geological Survey Pacific Coastal and Marine Science Center collected data to investigate sediment dynamics in the shallows of San Pablo Bay in two deployments: February to March 2011 (ITX11) and May to June 2012 (ITX12). This data release includes time-series data and grain-size distributions from sediment grabs collected during the deployments. During each deployment, time

Date published: January 1, 2019

Transgressive Contours--Punta Gorda to Point Arena, California

This part of DS 781 presents data for the transgressive contours of the Punta Gorda to Point Arena, California, region. The vector data file is included in the "TransgressiveContours_PuntaGordaToPointArena.zip," which is accessible from https://doi.org/10.5066/P9PNNI9H.
As part of the USGS's California State Waters Mapping Project, a 50-m...

Date published: January 1, 2019

CoSMoS (Coastal Storm Modeling System) Central California v3.1 water-level projections: 1-year storm in San Francisco County

This data contains model-derived total water levels (in meters) for the sea-level rise (SLR) and storm condition indicated.
The Coastal Storm Modeling System (CoSMoS) makes detailed predictions (meter-scale) over large geographic scales (100s of kilometers) of storm-induced coastal flooding and erosion for both current and future sea-level rise (SLR) scenarios. Projecti

Date published: January 1, 2019

CoSMoS (Coastal Storm Modeling System) Central California v3.1 ocean-currents projections: 1-year storm in Santa Barbara County

This data contains maximum model-derived ocean currents (in meters per second) for the sea-level rise (SLR) and storm condition indicated.
The Coastal Storm Modeling System (CoSMoS) makes detailed predictions (meter-scale) over large geographic scales (100s of kilometers) of storm-induced coastal flooding and erosion for both current and future sea-level rise (SLR) scen

Date published: January 1, 2019

CoSMoS (Coastal Storm Modeling System) Central California v3.1 flood-hazard projections: 100-year storm in San Francisco County

This data contains geographic extents of projected coastal flooding, low-lying vulnerable areas, and maximum/minimum flood potential (flood uncertainty) associated with the sea-level rise (SLR) and storm condition indicated.
The Coastal Storm Modeling System (CoSMoS) makes detailed predictions (meter-scale) over large geographic scales (100s of kilometers) of storm-ind

Date published: January 1, 2019

CoSMoS (Coastal Storm Modeling System) Central California v3.1 ocean-currents projections: 1-year storm in San Mateo County

This data contains maximum model-derived ocean currents (in meters per second) for the sea-level rise (SLR) and storm condition indicated.
The Coastal Storm Modeling System (CoSMoS) makes detailed predictions (meter-scale) over large geographic scales (100s of kilometers) of storm-induced coastal flooding and erosion for both current and future sea-level rise (SLR) scen

Date published: January 1, 2019

Structure-from-motion point cloud of Mud Creek, Big Sur, California, 1967-10-18

Presented here is a point cloud produced by the U.S. Geological Survey (USGS) from historical U.S. Air Force vertical aerial imagery, covering the area of the Mud Creek landslide on California State Route 1 (SR1), Mud Creek, Big Sur, California. The point cloud is referenced to previously published lidar data and contains RGB information as well as XYZ. Point cloud coordinates are

Date published: January 1, 2019

Isopachs--Punta Gorda to Point Arena, California

This part of DS 781 presents data for the isopachs of the Punta Gorda to Point Arena, California, region. The vector data file is included in the "Isopachs_PuntaGordaToPointArena.zip," which is accessible from https://doi.org/10.5066/P9PNNI9H.
As part of the USGS's California State Waters Mapping Project, a 50-m grid of sediment thickness...

Date published: January 1, 2019

CoSMoS (Coastal Storm Modeling System) Central California v3.1 ocean-currents projections: average conditions in San Francisco County

This data contains maximum model-derived ocean currents (in meters per second) for the sea-level rise (SLR) and storm condition indicated.
The Coastal Storm Modeling System (CoSMoS) makes detailed predictions (meter-scale) over large geographic scales (100s of kilometers) of storm-induced coastal flooding and erosion for both current and future sea-level rise (SLR) scen

Date published: January 1, 2019

CoSMoS (Coastal Storm Modeling System) Central California v3.1 water-level projections: 20-year storm in Santa Barbara County

This data contains model-derived total water levels (in meters) for the sea-level rise (SLR) and storm condition indicated.
The Coastal Storm Modeling System (CoSMoS) makes detailed predictions (meter-scale) over large geographic scales (100s of kilometers) of storm-induced coastal flooding and erosion for both current and future sea-level rise (SLR) scenarios. Projecti

Date published: January 1, 2019

CoSMoS (Coastal Storm Modeling System) Central California v3.1 flood-hazard projections: average conditions in San Luis Obispo County

This data contains geographic extents of projected coastal flooding, low-lying vulnerable areas, and maximum/minimum flood potential (flood uncertainty) associated with the sea-level rise (SLR) and storm condition indicated.
The Coastal Storm Modeling System (CoSMoS) makes detailed predictions (meter-scale) over large geographic scales (100s of kilometers) of storm-ind

Date published: January 1, 2019

Magnetotelluric data from Mountain Pass, CA, 2015

This dataset consists of 65 magnetotelluric (MT) stations collected in 2015 near Mountain Pass, California. The U.S. Geological Survey acquired these data to create a regional conductivity model near the Mountain Pass mine. This work is in support of characterizing mineral deposits.

Filter Total Items: 481
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Year Published: 2010

Estuarine sedimentation, sediment character, and foraminiferal distribution in central San Francisco Bay, California

Central San Francisco Bay is the deepest subembayment in the San Francisco Bay estuary and hence has the largest water volume of any of the subembayments. It also has the strongest tidal currents and the coarsest sediment within the estuary. Tidal currents are strongest over the west-central part of central bay and, correspondingly, this area is...

Chin, John L.; Woodrow, Donald L.; McGann, Mary; Wong, Florence L.; Fregoso, Theresa A.; Jaffe, Bruce E.
Estuarine sedimentation, sediment character, and foraminiferal distribution in central San Francisco Bay, California; 2010; OFR; 2010-1130; Chin, John L.; Woodrow, Donald L.; McGann, Mary; Wong, Florence L.; Fregoso, Theresa; Jaffe, Bruce E.

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Year Published: 2010

Emergency assessments of postfire debris-flow hazards for the 2009 La Brea, Jesusita, Guiberson, Morris, Sheep, Oak Glen, Pendleton, and Cottonwood fires in southern California

This report presents an emergency assessment of potential debris-flow hazards from basins burned by the 2009 La Brea and Jesusita fires in Santa Barbara County, the Guiberson fire in Ventura County, the Morris fire in Los Angeles County, the Sheep, Oak Glen, and Pendleton fires in San Bernardino County, and the Cottonwood fire in Riverside County...

Cannon, Susan H.; Gartner, Joseph E.; Rupert, Michael G.; Michael, John A.
Emergency assessments of postfire debris-flow hazards for the 2009 La Brea, Jesusita, Guiberson, Morris, Sheep, Oak Glen, Pendleton, and Cottonwood fires in southern California; 2010; OFR; 2010-1186; Cannon, Susan H.; Gartner, Joseph E.; Rupert, Michael G.; Michael, John A.

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Year Published: 2010

The 2007 M5.4 Alum Rock, California, earthquake: Implications for future earthquakes on the central and southern Calaveras Fault

[1] The similarity of seismograms recorded by two seismic stations demonstrate that the 31 October 2007 moment magnitude M5.4 Alum Rock earthquake is a repeat of a 1955 ML5.5 earthquake. Both occurred on Oppenheimer et al.'s (1990) Zone V “stuck patch” on the central Calaveras fault, providing new support for their model of...

Oppenheimer, David H.; Bakun, William H.; Parsons, Tom; Simpson, Robert W.; Boatwright, John; Uhrhammer, R. A.

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Year Published: 2010

Reconnaissance geologic map of the Hyampom 15' quadrangle, Trinity County, California

The Hyampom 15' quadrangle lies west of the Hayfork 15' quadrangle in the southern part of the Klamath Mountains geologic province of northern California. It spans parts of four generally northwest-trending tectono- stratigraphic terranes of the Klamath Mountains, the Eastern Hayfork, Western Hayfork, Rattlesnake Creek, and Western Jurassic...

Irwin, William P.
Reconnaissance geologic map of the Hyampom 15' quadrangle, Trinity County, California; 2010; SIM; 3129; Irwin, William P.

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Year Published: 2010

Reconnaissance Geologic Map of the Hayfork 15' Quadrangle, Trinity County, California

The Hayfork 15' quadrangle is located just west of the Weaverville 15' quadrangle in the southern part of the Klamath Mountains geologic province of northern California. It spans parts of six generally north-northwest-trending tectonostratigraphic terranes that are, from east to west, the Eastern Klamath, Central Metamorphic, North Fork, Eastern...

Irwin, William P.
Reconnaissance Geologic Map of the Hayfork 15' Quadrangle, Trinity County, California; 2010; SIM; 3119; Irwin, William P.

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Year Published: 2010

Final Report: Baseline Selenium Monitoring of Agricultural Drains Operated by the Imperial Irrigation District in the Salton Sea Basin, California

This report summarizes comprehensive findings from a 4-year-long field investigation to document baseline environmental conditions in 29 agricultural drains and ponds operated by the Imperial Irrigation District along the southern border of the Salton Sea. Routine water-quality collections and fish community assessments were conducted on as many...

Saiki, Michael K.; Martin, Barbara A.; May, Thomas W.
Final Report: Baseline Selenium Monitoring of Agricultural Drains Operated by the Imperial Irrigation District in the Salton Sea Basin, California ; 2010; OFR; 2010-1064; Saiki, Michael K.; Martin, Barbara A.; May, Thomas W.

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Year Published: 2010

Relations Between Rainfall and Postfire Debris-Flow and Flood Magnitudes for Emergency-Response Planning, San Gabriel Mountains, Southern California

Following wildfires, emergency-response and public-safety agencies are faced often with making evacuation decisions and deploying resources both well in advance of each coming winter storm and during storms themselves. Information critical to this process is provided for recently burned areas in the San Gabriel Mountains of southern California....

Cannon, Susan H.; Boldt, Eric M.; Kean, Jason W.; Laber, Jayme; Staley, Dennis M.
Relations Between Rainfall and Postfire Debris-Flow and Flood Magnitudes for Emergency-Response Planning, San Gabriel Mountains, Southern California; 2010; OFR; 2010-1039; Cannon, Susan H.; Boldt, Eric M.; Kean, Jason W.; Laber, Jayme; Staley, Dennis M.

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Year Published: 2010

Mercury concentrations in fish from a Sierra Nevada foothill reservoir located downstream from historic gold-mining operations

This study examined mercury concentrations in whole fish from Camp Far West Reservoir, an 830-ha reservoir in northern California, USA, located downstream from lands mined for gold during and following the Gold Rush of 1848–1864. Total mercury (reported as dry weight concentrations) was highest in spotted bass (mean, 0.93 μg/g; range, 0.16–4....

Saiki, Michael K.; Martin, Barbara A.; May, Thomas W.; Alpers, Charles N.

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Year Published: 2009

Data from theodolite measurements of creep rates on San Francisco Bay region faults, California, 1979-2012

IntroductionOur purpose is to annually update our creep-data archive on San Francisco Bay region active faults for use by the scientific research community. Earlier data (1979-2001) were reported in Galehouse (2002) and were analyzed and described in detail in a summary report (Galehouse and Lienkaemper, 2003). A complete analysis of our earlier...

McFarland, Forrest S.; Lienkaemper, James J.; Caskey, S. John
McFarland, F.S., Lienkaemper, J.J., and Caskey, S.J., 2016, Data from theodolite measurements of creep rates on San Francisco Bay Region faults, California (ver. 1.8, March 2016): U.S. Geological Survey Open-File Report 2009–1119, 21 p. and data files, https://doi.org/10.3133/ofr20091119.

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Year Published: 2009

Summary of survival data from juvenile coho salmon in the Klamath River, northern California, 2009

A study of the effects of the discharge from Iron Gate Dam on the Klamath River on juvenile coho salmon during their seaward migration began in 2005. Estimates of fish survival through various reaches of the river downstream of the dam were completed in 2006, 2007, 2008, and 2009. This report describes the estimates of survival during 2009, and is...

Beeman, John W.; Juhnke, Steven D.
Beeman, J.W., and Juhnke, S.D., 2009, Summary of survival data from juvenile coho salmon in the Klamath River, northern California, 2009: U.S. Geological Survey Open-File Report 2009-1270, 8 p.

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Year Published: 2009

Total selenium in irrigation drain inflows to the Salton Sea, California, April 2009

This report presents the results for the final sampling period (April 2009) of a 4-year monitoring program to characterize selenium concentrations in selected irrigation drains flowing into the Salton Sea, California. Total selenium and total suspended solids were determined in water samples. Total selenium, percent total organic carbon, and...

May, Thomas W.; Walther, Michael J.; Saiki, Michael K.; Brumbaugh, William G.
Total Selenium in Irrigation Drain Inflows to the Salton Sea, California, April 2009; 2009; OFR; 2009-1230; May, Thomas W.; Walther, Michael J.; Saiki, Michael K.; Brumbaugh, William G.

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Year Published: 2009

Geologic Map of the Weaverville 15' Quadrangle, Trinity County, California

The Weaverville 15' quadrangle spans parts of five generally north-northwest-trending accreted terranes. From east to west, these are the Eastern Klamath, Central Metamorphic, North Fork, Eastern Hayfork, and Western Hayfork terranes. The Eastern Klamath terrane was thrust westward over the Central Metamorphic terrane during early Paleozoic (...

Irwin, William P.
Geologic Map of the Weaverville 15' Quadrangle, Trinity County, California; 2009; SIM; 3095; Irwin, William P.

Filter Total Items: 1,116
Map highlighting sampling locations of 339 Northern Spotted Owls used in Miller, et al, 2018
August 2, 2018

Figure 1 from Miller, et al, 2018

Map highlighting sampling locations of 339 Northern Spotted Owls used in Miller, et al, 2018

July 26, 2018

PubTalk 7/2018— Extreme acid mine drainage at Iron Mountain California

Title: Iron Mountain, California: An Extreme Acid Mine Drainage Environment

  • "The world's most acid water" — explaining negative pH
  • Colorful mineral salts that store metals and acidity in underground mine workings
  • Microbial iron oxidation and formation of pipe scale in the water treatment system
  • Challenges and successes of
View from the sky of a jagged coastline with many roads, houses, a park, and other buildings nearby.
July 25, 2018

Natural Bridges

Natural Bridges State Beach, shown here in the middle of the photo, is nestled amongst coastal neighborhoods in the southwestern part of Santa Cruz, California. View is looking south. The offices of the USGS Pacific Coastal and Marine Science Center are just a few hundred feet north, outside the bottom portion of the photograph.

View from the sky of a large estuary with large and small waterways surrounded by villages and agriculture, hills in background.
July 25, 2018

Elkhorn Slough

Elkhorn Slough is a tidal river delta, salt marsh, and estuary in Monterey County, California. It is near the community of Moss Landing and is fed by Carneros Creek.

Photographs looking at a coastal cliff with a road covered by a landslide, then debris is cleared and road is repaired.
July 18, 2018

Mud Creek landslide changes March 2017-June 2018

USGS scientists produced an animated GIF in coordination with the California Department of Transportation (Caltrans) re-opening of State Highway 1 through Big Sur on July 18, 2018. In 2017, the massive Mud Creek landslide buried a quarter-mile of the famous coastal route with rocks and dirt more than 65 feet deep. As part of a new research project to monitor erosion along

...
adult male harrier
July 13, 2018

Adult Male Northern Harrier (Circus cyaneus)

An adult male Northern Harrier (Circus cyaneus) surveys Suisun Marsh, CA. Males are known for their beautiful, steel-gray plumage.

Salt marsh harvest mouse
July 13, 2018

Endangered Salt Marsh Harvest Mouse (Reithrodontomys raviventris)

A Federally endangered salt marsh harvest mouse (Reithrodontomys raviventris) climbs a branch.

Female northern harrier
July 13, 2018

Adult Female Northern Harrier (Circus cyaneus)

An adult, female northern harrier (Circus cyaneus) flies overhead in Suisun Marsh, CA. Before habitat loss drove declines in the bird's populations, Suisun Marsh hosted the state's largest population of northern harriers.

Northern harrier nestlings
July 13, 2018

Northern Harrier (Circus cyaneus) Nestlings

Northern harrier (Circus cyaneus) nestlings in Suisun Marsh, CA. Northern harriers are considered a "species of concern" by the U.S. Fish and Wildlife Service, due to their declining populations.

View from the sky looking at mouth of river with lots of sediment deposited at a beach.
July 8, 2018

Estero de San Antonio

Aerial view of Estero de San Antonio on Bodega Bay, near Dillon Beach, California.

A metal boat sits on a towing trailer in a parking lot.
July 3, 2018

PCMSC vessel Jewell on its towing trailer

USGS PCMSC vessel Jewell, shown on its towing trailer in the wareyard of MarFac in Santa Cruz, CA.

View from the air across a tidal march, mudflat, and channels with bay water to the right and a city in the background.
June 26, 2018

Bair Island, Redwood City

After 100 years of restricted tidal activity to support agricultural use and salt harvesting, the tidal marshes around San Francisco Bay, like this one at Bair Island, are steadily rebuilding, returning to a stunning mosaic of marsh, mudflat, and channels.

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Image: Baby Spider Monkey Snacking While Clinging to Mom
August 20, 2015

In a paper released today in Science, a new model presents a common mathematical structure that underlies the full range of feeding strategies of plants and animals: from familiar parasites, predators, and scavengers to more obscure parasitic castrators and decomposers. Now ecologists can view all food-web interactions through the same lens using a common language to understand the natural world.

Image: Elevation Field Work at Bandon Marsh
August 14, 2015

The U.S. Geological Survey and Oregon State University released a report this week examining Pacific Northwest tidal wetland vulnerability to sea level rise. Scientists found that, while vulnerability varies from marsh to marsh, most wetlands would likely be resilient to rising sea levels over the next 50-70 years.

Image: Nearshore Algae
August 12, 2015

The U.S. Geological Survey and the University of Nevada, Reno, will study the cause of eutrophication, or increased algae growth, along the nearshore of Lake Tahoe. Supported by California’s Lahontan Water Quality Control Board, the investigation is in response to widespread concerns with water quality and ecological degradation of the lake’s nearshore environment.

USGS
August 4, 2015

A new study now underway by the U.S. Geological Survey is exploring the groundwater resources and geothermal energy potential in drought-stricken areas of eastern Oregon and nearby parts of California, Idaho and Nevada.

USGS science for a changing world logo
July 30, 2015

RESTON, Va.— The U.S. Geological Survey has awarded approximately $4 million this week to four universities – California Institute of Technology, University of California, Berkeley, University of Washington and University of Oregon – to support transitioning the “ShakeAlert” earthquake early warning system toward a production stage.

USGS
July 27, 2015

One winter's night in the year 1700, a mysterious tsunami flooded fields and washed away houses in Japan. It arrived without the warning that a nearby earthquake usually provides.

Image: U.S. Fish and Wildlife Service Vessel Seen Through Bird Flock
July 16, 2015

The U.S. Geological Survey today released the North Pacific Pelagic Seabird Database — a massive online resource compiling the results of 40 years of surveys by biologists from the United States, Canada, Japan and Russia. The database documents the abundance and distribution of 160 seabird and 41 marine mammal species over a 10 million-square-mile region of the North Pacific.

Issue3.5May2015Thumb
June 5, 2015

The Delta – Developing Models to Understand Fish Passage and Survival In a Complex System

Drought effects at Trinity Lake
May 28, 2015

Although record low precipitation has been the main driver of one of the worst droughts in California history, abnormally high temperatures have also played an important role in amplifying its adverse effects, according to a recent study by the U.S. Geological Survey and university partners.

USGS science for a changing world logo
May 26, 2015

Recently, U.S. Geological Survey researchers and partners working in California’s Channel Islands National Park discovered mammoth remains in uplifted marine deposits that date to about 80,000 years ago, confirming a long-held but never proven hypothesis that mammoths may have been on the Channel Islands long before the last glacial period 25,000 to 12,000 years ago.

Map of sediment thickness in state waters offshore of San Francisco.
May 21, 2015

Three new sets of maps detail the offshore bathymetry, habitats, geology and submarine environment of the seafloor off the coast of San Francisco, Drakes Bay, and Tomales Point.

Lassen Volcanic National Park, California. Northeast side of Lassen Peak, showing the area devastated by mudflows and a lateral
May 19, 2015

2015 marks the centennial of the May 22, 1915 explosive eruption of Lassen Peak.