124° W 122° W 120° W

118° W

116° W

114° W

118° W

120° W

34° N

36° N

122° W

38° N

124° W

40° N

42° N

38° N

42° N

40° N

114° W

34° N

36° N

116° W

IMPERIAL

SAN DIEGO

ORANGE

RIVERSIDE

SAN BERNARDINO

LOS ANGELES

VENTURA

SANTA BARBARA

SAN LUIS

OBISPO KERN

INYO

TULARE

KINGS

MONTEREY

SAN

BENITO

FRESNO

MADERA

MERCED

MARIPOSA

MONO

SANTA

CRUZ

SANTA

CLARA

STANISLAUS

ALAMEDA

MATEO

SAN

SAN

FRANCISCO

CONTRA

COSTA

SAN

JOAQUIN

MARIN

TUOLUMNE

CALAVERAS

ALPINE

AMADOR

SACRAMENTO

SOLANO

NAPA

SONOMA

YOLO

LAKE

PLACER

NEVADA

SIERRA

YUBA

SUTTER

COLUSA

GLENN BUTTE

MENDOCINO

PLUMAS

LASSEN

SHASTA

TEHAMA

MODOC

SISKIYOU

DEL

NORTE

TRINITY

HUMBOLDT

EL DORADO

NAPA

0 50 100 Miles

0 50 100 Kilometers

Projection: Lambert Conformal Conic

False Easting: 0.00000

False Northing: 0.000000

Central Meridian: -121.000000

Standard Parallel 1: 33.000000

Standard Parallel 2: 45.000000

Latitude of Origin: 0.000000

Datum: North American 1927

 EXPLANATION 

 Former asbestos mine (25 sites)

Former asbestos prospect (72 sites)

Reported asbestos occurrence (138 sites)

Asbestos-bearing talc deposit (55 sites)

Reported fibrous amphibole(s) (16 sites)

Ultramafic rock in outcrop

(from Krevor and others, 2009)

 

 

 

 

 

 

 

 County name

Reported Historic Asbestos Mines, Historic Asbestos Prospects, and 

Other Natural Occurrences of Asbestos in California

By

Bradley S. Van Gosen, U.S. Geological Survey, Denver, Colorado

and

John P. Clinkenbeard, California Geological Survey, Sacramento, California

2011

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Latitude 

The latitude of the site's location in decimal degrees, measured using the North American 

Datum of 1927. The number of significant figures following the decimal point indicates the believed 

accuracy of the location: (1) two significant figures (for example, 44.03) indicate an approximate 

location based on a general description; (2) three significant figures (for example, 44.094) indicate a 

fairly accurate location based on a detailed description or location shown on a small-scale map 

(1:50,000 scale or smaller); and (3) four significant figures (for example, 42.5586) indicate a precise 

location based on a detailed description or a location shown on a large-scale map (1:24,000 scale or 

larger).

Longitude

 Longitude was calculated in the same manner as latitude.Asbestiform mineral(s) 

reported 

 This field identifies the type of asbestos present as described in the source literature.

Associated minerals reported

Minerals mentioned in association with the asbestos, as they were described in the source 

literature. The order in which each mineral is listed does not necessarily indicate its relative 

abundance in the deposit, but rather its order of mention in the source report. 

Host rock(s) reported

The host rock type(s) for the asbestos is (are) listed when available as described in the source 

literature.

References

The references used to compile the site information are listed in this field. The full reference 

citations are provided in the accompanying digital files References.pdf and References.xls.

 A second dataset, Death_Valley_talc.xls, lists 55 talc deposits of the southern Death Valley 

region in which trace amounts of amphibole asbestos are likely to be intergrown with the talc. The 

data fields in this database—State, County, Historic site name as reported, Latitude, Longitude, and

References—are used in the same manner as those in the dataset asbestos_sites.xls. 

 A third dataset, fibrous_amphiboles.xls, lists 16 localities where fibrous amphiboles are 

described in the geologic literature. 

References Cited

Krevor, S.C., Graves, C.R., Van Gosen, B.S., and McCafferty, A.E., 2009, Mapping the mineral 

resource base for mineral carbon-dioxide sequestration in the conterminous United States: 

U.S. Geological Survey Data Series 414, 14 p., 1 plate, and digital GIS shapefiles, accessed 

December 27, 2010, at http://pubs.usgs.gov/ds/414/.

Van Gosen, B.S., 2005, Reported historic asbestos mines, historic asbestos prospects, and natural 

asbestos occurrences in the Eastern United States: U.S. Geological Survey Open-File Report 

2005-1189, accessed December 20, 2010, at http://pubs.usgs.gov/of/2005/1189/.

Van Gosen, B.S., 2006, Reported historic asbestos prospects and natural occurrences in the Central 

United States: U.S. Geological Survey Open-File Report 2006-1211, accessed December 20, 

2010, at http://pubs.usgs.gov/of/2006/1211/.

Van Gosen, B.S., 2007, Reported historic asbestos mines, historic asbestos prospects, and natural 

asbestos occurrences in the Rocky Mountain States of the United States (Colorado, Idaho, 

Montana, New Mexico, and Wyoming): U.S. Geological Survey Open-File Report 

2007-1182, accessed December 20, 2010, at http://pubs.usgs.gov/of/2007/1182/.

Van Gosen, B.S., 2008, Reported historic asbestos mines, historic asbestos prospects, and natural 

asbestos occurrences in the Southwestern United States (Arizona, Nevada, and Utah): U.S. 

Geological Survey Open-File Report 2008-1095, accessed December, 20, 2010, at 

http://pubs.usgs.gov/of/2008/1095/.

Van Gosen, B.S., 2010, Reported historic asbestos mines, historic asbestos prospects, and other 

natual occurrences of asbestos in Oregon and Washington: U.S. Geological Survey Open-File 

Report 2010-1041, accessed December 20, 2010, at http://pubs.usgs.gov/of/2010/1041/.

Introduction

 This map (Plate.pdf) and the accompanying digital datasets (asbestos_sites.xls and 

Death_Valley_talc.xls) provide information on 290 natural occurrences of asbestos in California, using 

descriptions found in the geologic literature. This report allows the user to examine the distribution 

and geologic characteristics of the reported asbestos occurrences in California. Data on location, 

mineralogy, geology, and relevant literature for each asbestos site are provided in the digital files. The 

reported natural occurrences of asbestos in California include 25 former asbestos mines, 72 former 

asbestos exploration prospects, 138 other sites with described asbestos mineralization, and 55 talc 

deposits in the southern Death Valley region (trace amounts of asbestos minerals are intergrown with 

the talc in these deposits, which are listed in Death_Valley_talc.xls). In addition, this report includes a 

dataset of sites where amphibole(s) was described as fibrous in the geologic literature 

(fibrous_amphiboles.xls). Although amphibole “asbestos” was not specifically mentioned at these 

sites, the occurrence of fibrous amphiboles indicates geologic settings with the potential to host 

asbestos. 

 This report is part of an ongoing study by the U.S. Geological Survey (USGS) to identify and 

map reported natural occurrences of asbestos in the United States, which thus far includes reports of 

similar format for the Eastern United States (Van Gosen, 2005), the Central United States (Van Gosen, 

2006), the Rocky Mountain States (Van Gosen, 2007), the Southwestern United States (Van Gosen, 

2008), and the Pacific Northwest States of Oregon and Washington (Van Gosen, 2010). These reports 

provide Federal, State, and local government agencies and other stakeholders with geologic 

information on natural occurrences of asbestos.

 The file asbestos_sites.xls was compiled through a systematic search of the published geologic 

literature. The search did not include unpublished documents, such as consulting or company reports. 

Although this asbestos dataset represents an extensive study of published literature, it should not be 

construed as the complete list. An asbestos site was included only when the literature specifically 

mentioned asbestos and (or) described the commonly recognized asbestos minerals as occurring in the 

asbestiform crystal habit. No attempt was made to infer the presence of asbestos if asbestos was not 

explicitly described. Only a small percentage of the sites were visited or sampled during this study. 

 For descriptions of the occurrences, the user should refer to references cited in 

asbestos_sites.xls for each asbestos-site entry. Asbestos occurrences were described from outcrop 

exposures or in rock exposed by exploration and mining operations. Note that these site descriptions 

related to the time of each report's publication. Sites may have been subsequently modified by human 

activities since their description. For example, site remediation may have occurred since the source 

literature description.

 In some instances, an occurrence of asbestos could not be included in the digital dataset, 

because the description of the site’s location was too vague. Examples are discussed in the 

accompanying report (Pamphlet.pdf). 

Note: The accompanying report (Pamphlet.pdf) contains discussion on these topics:

• What is Asbestos?

Defining Asbestos

Health Effects and Regulation of Asbestos

 

 

• Natural Occurrences of Asbestosin California

 California Asbestos Regulations

 California Asbestos Occurrences

• The Geology of Asbestos in California

• Asbestos-Bearing Talc Deposits of the Southern Death Valley Region

Fibrous Amphiboles in California

History of Asbestos Discovery and Mining in California

Studies by the California Geological Survey of Natural Occurrences of Asbestos in California

• 

• 

• 

Digital Datasets

 The report dataset asbestos_sites.xls summarizes information found in geologic references 

examined by the authors. The entries in the database are sorted by county and ascending order of 

latitude (south to north). The dataset includes these data fields:

State

 “CA” indicates that the site occurs in California.

County

 Name of the county in which the site is located.

Historic site name as reported 

 The name of the former asbestos mine, former asbestos prospect, or reported occurrence, 

matching the nomenclature used in the source literature.

Development

 This field indicates whether the asbestos site represents a former asbestos mine, former 

prospect, or an occurrence. "Past producer" indicates that the deposit was mined and produced 

asbestos ore for commercial uses sometime in the past. "Past prospect" indicates that the asbestos 

deposit was once prospected (evaluated) for possible commercial use, typically by trenching and (or) 

drilling, but the deposit was not further developed. "Occurrence" indicates that asbestos was reported 

at this site. The occurrence category includes (1) sites where asbestos-bearing rock is described in a 

geologic map or report; and (2) asbestos noted as an accessory mineral or vein deposit within another 

type of mineral deposit.

U.S. Geological Survey Open-File Report 2011-1188

California Geological Survey Map Sheet 59

Pamphlet accompanies map

cross-ber tremolite

sheared, altered dolomite

McIlroy tremolite asbestos mine, Inyo 

County, California. This mine shipped 

tremolite asbestos during 1940 and 1941. 

Photographs by B. Van Gosen, USGS. 

Upper photograph, vein of tremolite asbestos, about 6 

inches in width, in the ceiling of the McIlroy mine. 

Lower photograph, tremolite asbestos from the McIlroy 

mine.

Figure 1 of Report.pdf. Photograph taken in 1998 of KCAC mine, Joe Pit, in the Coalinga asbestos district of San Benito and 

Fresno Counties, west-central California. This large chrysotile mine was the last asbestos operation in the United States; the 

mine closed in 2002. Photograph by California Geological Survey.

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