by Ronald K. Churchill
Radon is a naturally occurring odorless and colorless radioactive gas. It forms from the radioactive decay of small amounts of uranium naturally present in rocks and soils. Given the right circumstances, radon can move from the subsurface and concentrate in overlying homes and buildings. Breathing air with elevated radon gas increases one’s risk of developing lung cancer. While not everyone exposed to radon will develop lung cancer, the U.S. Environmental Protection Agency (U.S. EPA) estimates that 21,000 people in the United States die annually from lung cancer attributed to radon exposure. Indoor-radon concentrations are related to the uranium contents of local soils and rocks, soil permeability, climate, and building design, condition, and usage. Uranium data for rocks and soils provide information on where radon concentrations in the subsurface are higher or lower. Soil permeability data provide information on pathway availability for radon to move from the subsurface to a building’s foundation. Indoor-radon data represent the combined result of these factors at a specific location and can be used to develop radon potential maps. Radon potential maps identify areas where homes and other buildings are more likely, or less likely, to exceed the U.S. EPA’s recommended radon action level of 4 picocuries per liter (4 pCi/L). Radon potential maps may be used with population data to estimate the number of individuals exposed to 4 pCi/L or higher radon levels within the area of map coverage. In California, radon potential maps are informational, not regulatory.
The Department of Conservation, California Geological Survey (CGS) has completed a radon potential map and report for Amador, Calaveras, and Tuolumne Counties, California. The map identifies areas more likely, and areas less likely, to have indoor-radon measurements exceeding the U.S. EPA recommended action level of 4 pCi/L. The map also identifies areas where more data are needed to determine the radon potential. All radon potential areas, high, moderate, or low, contain some indoor-radon measurements above the U.S. EPA recommended action level and some below. This map cannot be used for determining the indoor-radon level of a particular building. Testing for radon is the only way to determine a building’s radon level, no matter where it is located. The Amador, Calaveras, and Tuolumne Counties radon potential map was developed using indoor-radon test data, geologic unit information from several geologic maps, uranium geochemistry data, and soil permeability data. Details about these data and maps, and the procedures used to develop the radon potential map, are included in the accompanying report. The report also estimates the number of Amador, Calaveras, and Tuolumne County residents potentially exposed to indoor-radon levels at or above the U.S. EPA recommended action level.
Special Report 242 and its associated plate (map) are available as free downloads or as printed products; prints are $35 each, plus $8 to cover shipping. (NOTE: Plate 1 measures 42 inches by 50 inches.) To purchase printed copies, contact our
Publications Sales Desk or visit the California Geological Survey Library in Sacramento.
Special Report 242 is not yet compatible with assistive technology, therefore it is not available for download at this time. Plate 1 is available for download below. Thank you for your patience while we work to make the report web accessible.
Plate 1 - Radon Potential Zone Map for Amador, Calaveras, and Tuolumne Counties, California (15 MB PDF)
by Anita Carney
The 2020 California Geological Survey calendar is available in two versions (see adjacent images). Click/tap one of the images to preview a full-size version of that image. Click/tap the hyperlink to download a printable version.
Printer-friendly version[poster, 12x19 inches horizontal, PDF]
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by W. Paul Burgess, Rachel A. Beard, Robert A. Wurgler, and Jeremy T. Lancaster
The nascent California “Recent Landslides” database compiled by the California Geological Survey (CGS) is a repository for the collection and communication of recent statewide landslide data. The repository is presented to the public as an online interactive ArcGIS Online map displaying landslide locations and other attributes to show varying scales of landslide processes affecting California's citizens, businesses, and infrastructure.
Landslide events are communicated with seven attribute fields including Landslide Date, Nearest Place, Info Source, Impacts, Damage Description, Latitude, and Longitude, and include (if available) a representative photograph to increase the educational impact of the landslide processes attributed to each event.
With the continued development of this database, the CGS endeavors to reach Californians and California governmental agencies with data useful for education and planning purposes. The development of the "Recent Landslides" database is considered vital to better describing the causes of storm-induced landslides. It is the aim of the CGS to eventually implement the database as a tool to provide statistical insights into frequency of given landslide types.
Explore the California Recent Reported Landslides Map
by Matt D. O'Neal and Fred W. Gius
California's Surface Mining and Reclamation Act of 1975 (SMARA) requires the State Geologist to classify land into Mineral Resource Zones (MRZs), based on the known or inferred mineral resource potential of that land. The process is based solely on geology, without regard to existing land use or land ownership. The primary goal of mineral land classification (MLC) is to help ensure, through appropriate local lead agency policies and procedures, that mineral resources will be available when needed and do not become inaccessible because of inadequate information during the land-use decision‑making process.
This report is the first MLC study of concrete aggregate resources to cover all lands within the newly defined Greater Sacramento Area Production-Consumption (P-C) Region. The region is 6,080 square miles in area, of which 2,580 square miles were classified for a variety of mineral commodities for different purposes between 1975 and 2010. The remaining 3,500 square miles of the P-C Region are newly classified for concrete aggregate resources in the present report.
Urban expansion in the P-C Region threatens to preclude mineral resource extraction. At present, the P-C Region contains sufficient concrete aggregate resources to meet the projected 50-year demand. However, there is a substantial and important disparity between the geographic distribution of mineral resources and population centers. Only a minor proportion of resources are located near population centers. Utilization of more distant resources results in a significant increase in cost to the aggregate consumer, road wear and tear, traffic congestion, greenhouse gas emissions, and air pollution. For example, each additional mile of aggregate transport costs 15 cents per ton, and one mile of a six-lane highway consumes more than 110,000 tons of aggregate.
In this update report, the following conclusions are reached:
Special Report 245 and its associated plates (maps) are available as free downloads or as printed products. (NOTE: The plates measure 36 inches by 48 inches each.) To purchase printed copies, contact our
Publications Sales Desk or visit the California Geological Survey Library in Sacramento.
Special Report 245: Mineral Land Classification: Concrete Aggregate in the Greater Sacramento Area Production-Consumption Region 2018 (2.6 MB PDF)
Plate 1: Mineral Land Classification Map (23 MB PDF)
Plate 2A: Resource Sector Map 1 of 2 (13 MB PDF)
Plate 2B: Resource Sector Map 2 of 2 (19 MB PDF)
California ranked fifth among the states in non-fuel mineral production, accounting for approximately 4.7% of the United States total. There were 1,042 active mines in the state, and of those, 663 reported the production of non-fuel minerals during 2017. The total market value of production was $3.6 billion. In terms of value, the top three non-fuel minerals produced in 2017 were construction sand and gravel, portland cement, and crushed stone.
To obtain the full report, visit
California's Non-Fuel Mineral Production web page.
by C.J. Wills, W.D. Haydon, B.J. Swanson, F.G. Perez, C.I. Gutierrez, and J.T. Lancaster
Caltrans has responsibility for over 1600 miles of landslide-prone highway corridors throughout California. The potential for landslide damage to highways in California is concentrated in areas where several aspects of the geology and geography converge to make landslide movement more likely. Landslide inventory maps are a key step supporting an analysis of the potential risks to highways from landslides.
This Phase 2 report extends Phase 1 work completed in 2006 and adds roughly 277 miles of landslide mapping, bringing the total for the Caltrans Highway Corridor Landslide Mapping project to 465 miles. Each highway corridor is divided into sections based on similarities in the bedrock geology, slopes, and size, type, and activity of landslides. The chapters summarize where a combination of factors lead to increased potential for landslides and provide information on the potential consequences to the roadway if a landside were to reactivate. These maps and descriptions of the factors leading to areas of high landslide potential will assist Caltrans in planning for long term landslide hazard mitigation and support slide-aware maintenance practices along these highway corridors.
This study was funded by the Caltrans Division of Research, Innovation and System Information. Cliff Roblee provided contract management and detailed product peer review as well as coordination with Caltrans geo-professionals through a project panel.
CGS Special Report 243 and its collection of forty-five plates (oversize maps) are available as free downloads from our
Highway Corridor Landslide Hazard Mapping page. We are not offering printed copies due to the prohibitive cost of production.
On April 4, 2019, the California Geological Survey (CGS) released five official maps of Seismic Hazard Zones affecting the cities of Antioch, Belmont, Brentwood, Burlingame, Concord, Half Moon Bay, Hillsborough, Millbrae, Oakley, Pacifica, Pittsburg, Redwood City, San Bruno, San Carlos, the towns of Portola Valley and Woodside, and the counties of Contra Costa and San Mateo. These maps were released under the authority of the Seismic Hazards Mapping Act that was passed following the 1989 Loma Prieta earthquake. The Seismic Hazards Mapping Act is a state law designed to reduce the hazards from soil liquefaction and landslides during an earthquake.
Seismic Hazard Zones are regulatory zones identifying areas that have a potential for future ground deformations caused by liquefaction or earthquake-induced landslides.
The maps are available as GeoPDF files, which can be viewed using Adobe Acrobat Reader; a GeoPDF file consists of multiple layers and gives the user greater flexibility in viewing and displaying the maps. The maps are also available as digital Geographic Information System (GIS) files. GIS files for both AP Earthquake Fault Zones and Seismic Hazard Zones released by CGS are considered Official Maps.
To obtain these maps, reports and GIS data, visit the
Regulatory Maps and Reports section of the CGS Information Warehouse. To view individual parcels affected by Seismic Hazard Zones and/or Earthquake Fault Zones, visit our
Earthquake Hazards Zone Application ("EQ Zapp").
The index maps below show the general areas in Contra Costa and San Mateo counties affected by this release.
by John P. Clinkenbeard and Fred W. Gius
Sand, gravel, and crushed stone are “construction materials.” These materials, collectively referred to as aggregate, provide bulk and strength to portland cement concrete, asphaltic concrete, Class II base, and other aggregate commodities such as subbase, drain rock, and fill. Aggregate normally provides 80 to 100 percent of the material volume in these uses.
The building and paving industries in California consume large quantities of aggregate and future demand for this commodity is expected to increase throughout California. Aggregate materials are essential to modern society, both to maintain the existing infrastructure and to provide for new construction. Because aggregate is a low unit-value, high-bulk-weight commodity, it must be obtained from nearby sources to minimize economic and environmental costs associated with transportation. These factors make information about the availability and demand for aggregate valuable to land-use planners and decision makers charged with planning for a sustainable future for California’s citizens.
Aggregate reserves and projected aggregate demand shown on Map Sheet 52 are updated from mineral land classification reports published by CGS between 1979 and 2017. The reports were prepared in response to California’s Surface Mining and Reclamation Act of 1975 (SMARA) that requires the State Geologist to classify land based on the known or inferred mineral resource potential of that land. The primary goal of mineral land classification is to ensure that the mineral resource potential of lands is recognized and considered in land-use planning.
Although the statewide and regional information presented on the map and in the accompanying report may be useful to decision-makers, it should not be used as a basis for local land-use decisions. The more detailed information contained in each of the aggregate studies employed in the compilation of Map Sheet 52 should be used for local land-use and decision-making purposes.
Map Sheet 52 is a statewide overview of projected future aggregate needs and currently permitted reserves. The purpose of the map is to compare projected aggregate demand for the next 50 years with currently permitted aggregate reserves in various regions of the state. The map also shows the projected years of permitted reserves remaining and highlights regions where less than 10 years of permitted aggregate supply remain. Map Sheet 52 was originally published in 2002 and subsequently updated in 2006 and 2012. Map Sheet 52 (2018) is an update of the version published in 2012. The estimates of permitted reserves, aggregate demand, and years of permitted reserves remaining are based on conditions as of January 1, 2017.
The report is divided into three parts:
Comparing regional needs to available reserves and resources demonstrates the important aggregate resource issues facing lead agencies in California. These issues include the need to plan carefully for the use of lands containing these resources and the need to consider the permitting of additional aggregate resources before currently permitted deposits are depleted.
The following conclusions can be drawn from Map Sheet 52 (2018) and the accompanying report:
Map Sheet 52 and its companion report are available as free downloads or as printed products; prints are $25 each, plus $8 to cover shipping. (NOTE: the map measures 36 inches by 42 inches.) To purchase printed copies, contact our
Publications Sales Desk.
Map Sheet 52: Aggregate Sustainability in California (4 MB PDF)
Map Sheet 52 companion report (270 KB PDF)
by James N. Falls, Gerald J. Marshall, Don R. Braun, and Shannon M.B. Utley
These are the first two maps in a series of adjacent geologic maps that will include Owl Creek, Iaqua Buttes, Mad River Buttes, and Yager Junction. The maps are available as free PDF downloads.
The Iaqua Buttes Quadrangle straddles the boundary of the Coastal and Central Belt of the Franciscan complex, and is underlain by two distinct northwest trending fault-bounded packages of sedimentary rocks. From west to east, rhythmically interbedded and sheared Eocene- to Paleocene(?)-aged sediments of the Yager Terrane (Coastal Belt) are faulted against Paleogene- to late Cretaceous-aged tectonic mélange of the Central Belt along the Freshwater Fault. The Freshwater fault is related to initial emplacement of Franciscan complex rocks along the western edge of North America and shows evidence of early Quaternary movement.
Map Sheet 65: Landslides, Geomorphology, and Geology of the Iaqua Buttes 7.5’ Quadrangle, Humboldt County, California (4 MB PDF)
The Owl Creek Quadrangle straddles the boundary of the Coastal and Central Belt portions of the Franciscan complex, and is underlain by three distinct northwest trending fault-bounded packages of sedimentary rocks. From west to east, late Pleistocene- to Miocene-aged marine and non-marine overlap deposits of the Wildcat Group are faulted against rhythmically interbedded Eocene- to Paleocene(?)-aged sediments of the Yager Terrane (Coastal Belt) along the Little Salmon fault. The Yager Terrane rocks are faulted against Paleogene- to late Cretaceous- aged tectonic mélange of the Central Belt along the Freshwater Fault. The faults are related to initial emplacement of Franciscan complex rocks along the western edge of North America, and more recent faulting related to northwest migration of the Mendocino Triple Junction. Age of faulting within the Owl Creek Quadrangle may be late Quaternary, however, faulting on the Little Salmon fault northwest in the adjacent Hydesville Quadrangle is considered Holocene based on relatively fresh scarps and topographic lineaments observed in recent alluvium.
Map Sheet 66: Landslides, Geomorphology, and Geology of the Owl Creek 7.5’ Quadrangle, Humboldt County, California (4 MB PDF)
by Fred W. Gius, Lawrence L. Busch, and Russell V. Miller.
This report updates the mineral land classification of western San Diego County, reevaluates the region's PCC-grade aggregate resources, and includes an updated 50‑year projection of construction aggregate demand for the P-C Region through the year 2065.
California’s Surface Mining and Reclamation Act of 1975 (SMARA) requires the State Geologist to classify land into Mineral Resource Zones (MRZs), based on the known or inferred mineral resource potential of that land. The process is based solely on geology, without regard to existing land use or land ownership. The primary goal of mineral land classification is to help ensure, through appropriate local lead agency policies and procedures, that mineral resources will be available when needed and do not become inaccessible because of inadequate information during the land-use decision-making process.
This report is the third in a series of regional mineral land classification reports for portland cement concrete (PCC)-grade aggregate for the Western San Diego County Production-Consumption Region (P-C Region). The original mineral land classification was published as Special Report (SR) 153 in 1982. The first update was published in 1996 as Open-File Report (OFR) 96-04. This current report updates the mineral land classification of the region, reevaluates the region’s PCC-grade aggregate resources, and includes an updated 50-year projection of construction aggregate demand for the P-C Region through the year 2065. This update report reevaluated the PCC-grade aggregate resources in areas originally designated by the State Mining and Geology Board and new areas identified in subsequent mineral land classification reports including this update report. This update report does not replace SR 153 or OFR 96-04.
Since the mid-1990s, local aggregate production has not been sufficient to meet local demand in the P-C Region. This shortfall has been met by importing construction aggregate, predominately sand, from neighboring aggregate producing regions. At various times, construction aggregate has been imported into the P-C Region from mines in Los Angeles, San Bernardino, Riverside, and Imperial counties, and Baja California, Mexico.
Special Report 240 and its associated plates (maps) are available as free downloads or as printed products; prints are $128 each, plus $8 to cover shipping. NOTE: Plate 1 measures 36 inches by 42 inches; Plates 2A and 2B measure 42 inches by 46 inches each. To purchase printed copies, contact our
Publications Sales Desk or visit the California Geological Survey Library in Sacramento.
Special Report 240: Update of Mineral Land Classification: Portland Cement Concrete-Grade Aggregate in the Western San Diego County Production-Consumption Region of California (1.3 MB PDF)
SR 240 Plate 1: Updated Mineral Land Classification Map for Portland Cement Concrete-Grade Aggregate in the Western San Diego County Production-Consumption Region, California (2.4 MB PDF)
SR 240 Plate 2A: Updated Aggregate Resource Sector Map [Northern Part] for Portland Cement Concrete-Grade Aggregate in the Western San Diego County Production-Consumption Region, California (4.8 MB PDF)
SR 240 Plate 2B: Updated Aggregate Resource Sector Map [Southern Part] for Portland Cement Concrete-Grade Aggregate in the Western San Diego County Production-Consumption Region, California (5.6 MB PDF)
On June 15, 2017 by the California Geological Survey (CGS) released three revised official maps of Alquist-Priolo Earthquake Fault Zones. Areas covered are within Los Angeles County and affect the cities of Arcadia, Los Angeles, Monrovia, Pasadena, San Marino, and South Pasadena. These maps are released under the authority of the Alquist-Priolo Earthquake Fault Zoning (AP) Act that was passed following the 1971 San Fernando earthquake. The
AP Act is a state law designed to reduce the hazard from surface fault rupture during an earthquake. Earthquake Fault Zones are regulatory zones that encompass surface traces of active faults that have a potential for future surface fault rupture. These revised maps show the location of AP Earthquake Fault Zones and Seismic Hazard Zones (if evaluated), and are collectively referred to as Earthquake Zones of Required Investigation.