Bureau of Land Management

Abandoned Mine Land Inventory

Study for BLM-Managed Lands in

California, Nevada, and Utah:

Site and Feature Analysis

November 2014 
Production services provided by:

Bureau of Land Management 

National Operations Center 

Information and Publishing Services Section 

P.O. Box 25047 

Denver, CO 80225

Suggested citation:

Bureau of Land Management. 2014. Abandoned Mine Land Inventory Study for BLM-Managed Lands in 

California, Nevada, and Utah: Site and Feature Analysis. Department of the Interior, Bureau of Land 

Management, National Operations Center, Denver, CO.

BLM/OC/ST-15/001+3720
Bureau of Land Management

Abandoned Mine Land Inventory

Study for BLM-Managed Lands in

California, Nevada, and Utah:

Site and Feature Analysis

November 2014 

Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis iii

Table of Contents

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1. Background and Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 The BLM’s Progress in Inventorying AML Sites and Features . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Government Interest in the BLM’s AML Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3 Purpose of this Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4 States Covered by this Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5 Basis of Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2. Methods and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1 Estimating the Total Number of AML Sites and Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2 Calculating the Sites and Features that Remain to be Inventoried . . . . . . . . . . . . . . . . . . . . . 6

2.3 Results by State and BLM Field Office . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3. Estimating Time and Cost to Complete the AML Inventory

and Address the Remaining Physical Safety Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1 Estimated Time to Complete the AML Inventory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.2 Estimated Costs to Complete the AML Inventory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.3 Estimated Costs to Address Remaining Physical Safety Hazards . . . . . . . . . . . . . . . . . . . . . . 11

4. Refining the Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.1 Refining the California Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.2 Refining the Nevada Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.3 Refining the Utah Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6. Expanding the Study to Other States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis 1

Executive Summary

The Bureau of Land Management (BLM) manages 

more than 245 million acres of public land for 

multiple uses, including energy development, 

livestock grazing, recreation, mining, and timber 

harvesting. Historic mining activities have left 

thousands of abandoned hardrock mine sites 

scattered across the West on BLM-managed land. 

Under multiple authorities, the BLM Abandoned 

Mine Lands Program identifies and remediates 

physical safety and environmental hazards 

resultant from historic hardrock mining on or near 

public lands. Typical activities conducted by the 

Abandoned Mine Lands Program include: 

• Field validation of abandoned mine land (AML) 

sites (i.e., visiting the location of a mine site, 

characterizing and documenting the nature 

and type of features present, and maintaining 

an inventory database of sites and features).

• Environmental, cultural, historical, and 

wildlife studies required under the 

National Environmental Policy Act or the 

Comprehensive Environmental Response, 

Compensation, and Liability Act.

• Mitigation and remediation of physical safety 

and environmental hazards.

• Monitoring and maintenance of AML sites and 

implemented remedies.

Several government entities have issued 

reports over the last decade commenting on 

or requesting clarification of the status and 

management of AML sites on BLM-managed 

land. For example, the U.S. Senate Committee on 

Appropriations directed the Department of the 

Interior (DOI) Secretary to provide a report on 

the status of the AML inventory and to submit a 

completed inventory for review.1

 In addition, the 

Government Accountability Office reported and 

testified about the wide variation in estimates 

of abandoned hardrock mines owing to the 

lack of a generally accepted definition for an 

1

 111th Congress, Senate Report 111-38, “Department of the Interior, 

Environment, and Related Agencies Appropriations Bill, 2010” (Washington, DC: 

2009).

abandoned hardrock mine site among state 

and federal agencies in the West.2 Also, the DOI 

Office of Inspector General has issued several 

reports concerning AML programs and sites and 

recommended that the BLM:

• Assess its lands to identify hazardous sites in 

close proximity to populated places.

• Inspect these sites and take appropriate action 

to mitigate physical safety hazards.

• Validate existing inventory data and develop 

procedures for ongoing data collection to 

ensure that data in the inventory is complete, 

accurate, and consistent.3

In response to these critiques, the BLM has 

developed a nationwide approach to estimate the 

total number of AML sites and related features 

(i.e., single manmade disturbances associated with 

mining activity, such as shafts or waste rock piles) 

that remain to be inventoried on BLM-managed 

land. The approach used in this report expands a 

method developed by the California Department 

of Conservation’s Abandoned Mine Lands Unit 

(AMLU).4 The AMLU created a digital dataset of 

the mine symbols found on the U.S. Geological 

Survey (USGS) topographic quadrangle maps for 

California. The AMLU then visited the locations of 

a subset of these symbols in the field. The AMLU 

found that each USGS mine symbol represented 

one AML site and that, on average, 3.5 features 

occurred at or in close proximity to the mine 

symbol’s location. By adding the total number 

2

 Director of Natural Resources and Environment, “Hardrock Mining: Information 

on Abandoned Mines and Value and Coverage of Financial Assurances on BLM 

Land,” GAO-08-574T (Washington, DC: Government Accountability Office, March 

2008).

3

 DOI Office of Inspector General, “Public Safety Issues at the Saginaw Hill 

Property, Bureau of Land Management,” OIG Flash Report C-IN-BLM-0013-2005 

(U.S. Department of the Interior, Office of Inspector General, March 2005); and 

DOI Office of Inspector General, “Audit Report, Abandoned Mine Lands in the 

Department of the Interior,” C-IN-MOA-0004-2007 (U.S. Department of the 

Interior, Office of Inspector General, July 2008).

4 Douglas Craig, S. Reeves, J. Mistchenko, M. Tuffly, S. Hayashi, and N. Bergquist, 

“Abandoned Mine Lands Assessment of the North Yuba Watershed” (California: 

California Department of Conservation, Office of Mine Reclamation, 2003).
2 Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis

of mine symbols and then multiplying the sum 

by 3.5, the AMLU was able to estimate the total 

number of AML features in California.

The BLM, using this method, geographically 

filtered the USGS mine symbol datasets available 

for California, Nevada, and Utah to estimate the 

total number of AML sites and features on BLMmanaged land in these three states. From these 

estimates, the BLM then subtracted the number 

of AML sites and features already inventoried 

in these states to calculate the number of sites 

and features that remain to be inventoried. 

The BLM estimates that in these three states a 

total of approximately 93,000 sites containing 

approximately 368,000 features have not yet been 

inventoried. State by state, the BLM estimates that:

• In California, an estimated 22,730 sites 

containing 79,757 features have yet to be 

inventoried.

• In Nevada, an estimated 68,564 sites 

containing 273,239 features have yet to be 

inventoried.

• In Utah, an estimated 1,399 sites containing 

14,752 features have yet to be inventoried.

Based on these estimates, the BLM calculated the 

time required to validate these sites and features 

in the field. For California, Nevada, and Utah, 

the total time required to validate the estimated 

sites and features in the field is approximately 

2,625 work months (1 work month totals 4 work 

weeks), or 20 years of work for 10 two-person 

field crews. The BLM estimates that it will require 

approximately $212 million to complete the field 

validation of the sites in California, Nevada, and 

Utah.

Additionally, based on field validated AML 

inventory statistics in California, the BLM 

calculated the number of features that 

pose physical safety hazards and the cost to 

remediate those hazards. In California, there 

are an estimated 30,000 physical safety hazards 

requiring approximately $588 million to mitigate. 

The number of features that pose physical 

safety hazards in Nevada and Utah has yet to be 

estimated.

At present, the BLM does not have sufficient 

information to develop similar estimates of 

AML sites and features not yet inventoried in 

the remaining states where the BLM manages 

land. This report presents the methods used to 

develop estimates in California, Nevada, and Utah 

and outlines the requirements for completing 

estimates of the number of AML sites and features 

yet to be inventoried for the remaining BLM states. 
Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis 3

1. Background and Purpose

1.1 The BLM’s Progress in 

Inventorying AML Sites and Features

The Abandoned Mine Lands Program of the 

U.S. Department of the Interior (DOI), Bureau 

of Land Management (BLM), is responsible for 

addressing two broad categories of hazards 

associated with abandoned hardrock mine sites:5

(1) physical safety hazards, posed by features such 

as open adits (horizontal openings), open shafts 

(vertical openings), highwalls, and pits; and (2) 

environmental hazards, such as heavy metals in 

mine waste or mill tailings and acid mine drainage 

that can potentially impact water quality and 

human health. 

The Abandoned Mine Lands Program is also 

responsible for maintaining an inventory of 

abandoned mine land (AML) site and feature 

inventory data in the Abandoned Mine Site 

Cleanup Module (AMSCM) database. While the 

number of AML sites recorded in the AMSCM 

database (the “inventory”) has more than 

doubled from approximately 20,000 sites to 

47,000 sites since fiscal year (FY) 2010, the BLM 

is aware that the inventory is far from complete. 

Thus, the Abandoned Mine Lands Program is 

conducting a study to more efficiently calculate 

the number of AML sites and features that 

remain to be inventoried, or validated by field 

study and recorded in the AMSCM database. 

Another purpose of the study is to calculate the 

approximate time and costs to inventory these 

sites and mitigate their physical safety hazards.

5

 The BLM’s Abandoned Mine Land Program Policy, BLM Manual Section 

3720, defines an abandoned mine as follows: “An abandoned hard rock mine 

on, or affecting public lands administered by the BLM, at which exploration, 

development, mining, reclamation, maintenance, and inspection of facilities and 

equipment, and other operations ceased, and with no evidence demonstrating 

that the miner intends to resume mining as of January 1, 1981...Abandoned mines 

generally include a range of mining impacts, or features that may pose a threat to 

water quality, public safety, and/or the environment.”

1.2 Government Interest in the BLM’s 

AML Program

In recent years, there has been considerable 

government interest at the national level in the 

BLM Abandoned Mine Lands Program and in the 

AML inventory.

• The U.S. Senate Committee on Appropriations 

directed the DOI Secretary to provide a report 

on the status of the AML inventory and to 

submit a completed inventory for review.6

• The Government Accountability Office 

reported and testified about the wide variation 

in estimates of abandoned hardrock mines 

owing to the lack of a generally accepted 

definition for an AML hardrock mine site 

among state and federal agencies in the West.7

• The DOI Office of Inspector General (OIG) 

has issued several reports concerning AML 

programs and sites. In 2008, the OIG stated 

that the “BLM’s inventory was incomplete, 

inaccurate, and inconsistent.”8

 The OIG found 

that much of the data in the inventory was 

derived from the U.S. Bureau of Mines before 

its closure in 1996 and was never validated 

by field surveys. These reports recommended 

that the BLM validate existing inventory data 

and develop procedures for ongoing data 

collection to ensure that data in the inventory 

are complete, accurate, and consistent. 

6

 111th Congress, Senate Report 111-38, “Department of the Interior, Environment, 

and Related Agencies Appropriations Bill, 2010” (Washington, DC: 2009).

7 Director of Natural Resources and Environment, “Hardrock Mining: Information 

on Abandoned Mines and Value and Coverage of Financial Assurances on BLM 

Land,” GAO-08-574T (Washington, DC: Government Accountability Office, March 

2008).

8

 DOI Office of Inspector General, “Audit Report, Abandoned Mine Lands in the 

Department of the Interior,” C-IN-MOA-0004-2007 (U.S. Department of the 

Interior, Office of Inspector General, July 2008).
4 Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis

1.3 Purpose of this Report

This report presents the methods, status, and 

results of the ongoing study conducted by the 

BLM to estimate the number of AML sites and 

features that remain to be inventoried (i.e., field 

validated9 and recorded in the AMSCM database) 

in three states. It also presents time and cost 

estimates for field validating and remediating 

physical safety hazards at those sites in one 

state. This document does not, however, include 

estimated costs for environmental hazards.

1.4 States Covered by this Report

The results of the study for three states—

California, Nevada, and Utah—are presented in 

this report. These states were selected based on 

their existing and available high-quality datasets. 

The BLM plans to expand the study to other states 

as datasets are developed and become available.

1.5 Basis of Approach

The California Department of Conservation 

Abandoned Mine Lands Unit (AMLU) developed a 

method to estimate the total number of AML sites 

and features in California.10 The AMLU first created 

a geographic information dataset of each of the 

9 Field validation activities include visiting the location of a mine site and 

documenting the number and nature of mining-related features present and their 

hazards. Occasionally, temporary safety measures, such as constructing fences or 

posting signs, are performed during field validation.

10 Douglas Craig, S. Reeves, J. Mistchenko, M. Tuffly, S. Hayashi, and N. Bergquist, 

“Abandoned Mine Lands Assessment of the North Yuba Watershed” (California: 

California Department of Conservation, Office of Mine Reclamation, 2003).

topographically occurring mine symbols (TOMS) 

on the U.S. Geological Survey (USGS) 7.5 minute 

quadrangle maps for California. The AMLU then 

field validated the location of the TOMS and noted 

the number and type of AML features present. 

The AMLU found that an average of 3.5 AML 

features occurred at each symbol’s location. 

Although the original intent of the USGS map 

symbols were to display the location of a specific 

mine feature, the AMLU determined that a TOMS 

was more representative of an AML site because 

the location of the symbol may contain multiple 

features. Thus, the number of TOMS for an area 

is equal to the number of AML sites in that area. 

Then, by multiplying the total number of symbols 

in California by 3.5 (the average number of 

features present at a symbol), the AMLU estimated 

the number of AML features in California. During 

field validation of the mine symbols, the AMLU 

found that 84 percent of the sites posed physical 

safety hazards. Further, 38 percent of the features 

at those sites were hazardous openings (i.e., 

shafts, adits, or other openings that are large and 

deep enough to endanger human life).11

The BLM adapted the California AMLU approach 

for use in this study.

11 California Department of Conservation, “California’s Abandoned Mines: A 

Report on the Magnitude and Scope of the Issue in the State, Volume I” (California: 

California Department of Conservation, Office of Mine Reclamation, 2003); and 

California Department of Conservation, “California’s Abandoned Mine Lands 

Program Fact Sheet” (California: California Department of Conservation, Office of 

Mine Reclamation, January 2012). 
Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis 5

2. Methods and Results

The method used to calculate the number of AML 

sites and features on BLM-managed land that 

remain to be inventoried can be broken down into 

two parts:

• Estimate the total number of AML sites and 

features on BLM-managed land in a state using 

a mine symbol dataset, geographic filters, and 

BLM land boundary data.

• Reduce the total estimate of AML sites and 

features in a state by the known BLM inventory 

in the AMSCM database for that state.

2.1 Estimating the Total Number of 

AML Sites and Features 

Before an estimate of the number of AML sites and 

features on BLM-managed land (the “estimated 

total inventory”) for a state can be calculated, a 

high-quality mine symbol dataset must exist. In 

this study, high-quality mine symbol datasets 

are defined as those that are determined to 

adequately capture the number and location of 

each of the mine symbols from the USGS maps. 

Of the identified mine symbol datasets for each of 

the states where the BLM manages land, only the 

mine symbol datasets for California, Nevada, and 

Utah were determined to be of sufficient quality 

and available.

The first step in calculating the estimated total 

inventory is to geographically filter a statewide 

mine symbol dataset to smaller subsets containing 

only the symbols occurring on and/or near BLMmanaged land. Using a BLM land ownership 

dataset, a geographic information system was 

used to filter the mine symbol datasets into two 

BLM-focused subsets:

• TOMSr (robust): The TOMSr subset contains 

those mining symbols occurring on BLM land 

or within a certain distance12 of BLM land 

boundaries. The BLM has greater confidence 

that the estimates provided by this subset 

accurately represent the magnitude of the 

12 This distance was calculated based on location information for sites in the 

AMSCM database. The distance threshold was approximately 912 meters in 

Nevada, approximately 117 meters in Utah, and approximately 500 meters in 

California. 
6 Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis

number of AML sites and features on BLM land 

than the TOMSc subset.

• TOMSc (conservative): The TOMSc subset 

contains those mining symbols occurring only 

on BLM land. No additional search distance 

beyond the land boundary was used. The 

BLM has lesser confidence that the estimates 

provided by this subset accurately represent 

the magnitude of the number of AML sites and 

features on BLM land. 

For this assessment of AML data, an AML site 

and a mine symbol are assumed equivalent. The 

number of symbols in each subset was added for 

each state, resulting in the total number of AML 

sites on BLM-managed land in three states (Table 

1). Based on the robust subset (TOMSr), there is 

an estimated total of 84,930 AML sites in Nevada, 

5,932 AML sites in Utah, and 24,400 AML sites in 

California. 

The total number of mine symbols in each subset 

was multiplied by 3.5 (the average number 

of features, or single manmade disturbances 

associated with mining activity, including pits, 

adits, and shafts, that the AMLU found occurring 

at each symbol’s location during field validation in 

California) to calculate the number of estimated 

AML features (Table 1). Based on the robust subset 

(TOMSr), there is an estimated total of 297,255 

features in Nevada, 20,762 features in Utah, and 

85,400 features in California. 

Comprehensively, the number of AML sites and 

features estimated to exist on BLM-managed land 

in a state can be described by the robust (TOMSr) 

or the conservative (TOMSc) subsets. Using the 

robust subset, the BLM estimates that there a total 

of 115,262 sites containing 403,417 features in 

these three states. State by state, there are:

• In California, a total of 24,400 AML sites 

containing 85,400 features.

• In Nevada, a total of 84,930 sites containing 

297,255 features.

• In Utah, a total of 5,932 sites containing 20,762 

features.

Table 1. Number of AML sites and features inventoried in the AMSCM 

database and number of AML sites and features estimated to exist on or 

near BLM-managed land using the TOMS method (TOMSr, TOMSc) 

AMSCM1 TOMSr 

2 TOMSc3

Nevada

Sites 16,366 84,930 67,296

Features 24,016 297,255 235,536

Utah

Sites 4,533 5,932 4,629

Features 6,010 20,762 16,201

California

Sites 1,670 24,400 17,648

Features 5,643 85,400 61,768

1

AMSCM: Known and inventoried on BLM lands

2

TOMSr: Identified as occurring on or within 912 m of BLM lands

 in Nevada, 500 m in California, or 117 m in Utah (robust 

 estimate)

3

TOMSc: Identified as occurring on BLM lands (conservative estimate)

2.2 Calculating the Sites and Features 

that Remain to be Inventoried

After the estimated total inventory, or the total 

number of AML sites and features estimated 

to exist on BLM-managed land, for a state is 

calculated, the known inventory from the AMSCM 

database is subtracted from the estimated total 

inventory. This calculates the number of AML sites 

and features that remain to be inventoried by the 

BLM.

As of April 2014, the AMSCM database listed the 

following numbers in the BLM AML inventory:

• In California, there were 1,670 AML sites 

containing 5,643 features.

• In Nevada, there were 16,366 AML sites 

containing 24,016 features.

• In Utah, there were 4,533 AML sites containing 

6,010 features.

Both the robust (TOMSr) and conservative (TOMSc

) 

subsets were used as the estimated total inventory 

to calculate estimates of what remains to be 

inventoried (Remr, robust; Remc, conservative) 

(Table 2). After subtracting the known inventory 
Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis 7

from the robust estimated inventory, the BLM 

estimates that:

• In California, there are an estimated 22,730 

sites containing 79,757 features that remain to 

be inventoried.

• In Nevada, there are an estimated 68,564 sites 

containing 273,239 features that remain to be 

inventoried.

• In Utah, there are an estimated 1,399 sites 

containing 14,752 features that remain to be 

inventoried.

Table 2. Number of AML sites and features inventoried in the AMSCM 

database, number of AML sites and features estimated to exist on or near 

BLM-managed land using the TOMS method (TOMSr, TOMSc), and the 

number of estimated AML sites and features remaining to be inventoried 

(Remr, Remc) 

AMSCM1 TOMSr 

2 TOMSc3 Remr4 Remc5

Nevada

Sites 16,366 84,930 67,296 68,564 50,930

Features 24,016 297,255 235,536 273,239 211,520

Utah

Sites 4,533 5,932 4,629 1,399 96

Features 6,010 20,762 16,201 14,752 10,191

California

Sites 1,670 24,400 17,648 22,730 15,978

Features 5,643 85,400 61,768 79,757 56,125

 1

AMSCM: Known and inventoried on BLM lands

 2

TOMSr: Identified as occurring on or within 912 m of BLM lands in 

 Nevada, 500 m in California, or 117 m in Utah (robust estimate)

 3

TOMSc: Identified as occurring on BLM lands (conservative estimate)

 4

Remr: Robust estimate of sites and features remaining to be inventoried

 5

Remc: Conservative estimate of sites and features remaining to be 

 inventoried

2.3 Results by State and

BLM Field Office

Figures 1, 2, and 3 display the robust estimate 

of AML sites and features that have yet to be 

inventoried by the BLM, broken down by field 

office in each state. Figure 1 presents the number 

of AML sites in California, and Figures 2 and 3 

present the number of AML features13 in Nevada 

and Utah that have yet to be inventoried by the 

BLM.

13 The BLM has greater confidence that the number of features, rather than 

the number of sites, more accurately depicts the magnitude and scope of the 

remaining AML inventory in Nevada and Utah. This is discussed further in the 

“Refining the Estimates” section.
8 Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis

Figure 1. Robust estimate of remaining AML sites to be inventoried on BLM land in California, broken down by 

field office. 
Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis 9

Figure 2. Robust estimate of remaining AML features to be inventoried on BLM land in Nevada, broken down 

by field office. Features are used instead of sites for Nevada. For further details, see the section titled “Refining 

the Estimates.”
10 Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis

Figure 3. Robust estimate of remaining AML features to be inventoried on BLM land in Utah, broken down by field 

office. Features are used instead of sites for Utah. For further details, see the section titled “Refining the Estimates.”
Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis 11

3. Estimating Time and Cost to Complete the AML 

Inventory and Address the Remaining Physical 

Safety Hazards

3.1 Estimated Time to Complete the 

AML Inventory 

The number of estimated AML sites and features 

that remain to be inventoried provides a basis for 

calculating the amount of time it may take to field 

validate each of the symbols. The BLM estimates 

that 35 features (or 10 mine symbols) can be 

field validated in a week. Based on the robust 

estimate of AML sites and features that remain to 

be inventoried, it will take a field team of two AML 

specialists:

• In California, 568 work months to complete the 

estimated inventory by validating the mine 

symbols.14

• In Nevada, 1,952 work months to complete the 

estimated inventory by validating the mine 

symbols. 15

• In Utah, 105 work months to complete the 

estimated inventory by validating the mine 

symbols.16

Based on these estimates, it would require a 

total of 2,625 work months to validate the mine 

symbols in these three states. This workload 

distributed over 10 two-person field crews would 

require approximately 20 years to complete. 

3.2 Estimated Costs to Complete

the AML Inventory

In July 2013, the BLM Abandoned Mine Lands 

Program published the “Feasibility Study for AML 

Inventory Validation and Physical Safety Closures.” 

In this feasibility study, the Abandoned Mine 

14 22,730 sites divided by 10 sites per week = 2,273 weeks; 2,273 weeks divided 

by 4 weeks per work month

15 273,239 features divided by 35 features per week = 7,807 weeks; 7,807 weeks 

divided by 4 weeks per work month

16 14,752 features divided by 35 features per week = 421 weeks; 421 weeks 

divided by 4 weeks per work month

Lands Program estimated the costs for validating 

future AML sites in each state where the BLM 

manages land. In the report, the BLM presents the 

cost for field validating a mine site:

• In California, it will cost $5,200 to field validate 

a mine site.

• In Nevada, it will cost $1,100 to field validate a 

mine site.

• In Utah, it will cost $1,800 to field validate a 

mine site.

Using these cost values and the robust estimate 

of AML sites that remain to be inventoried, it 

will require approximately $212 million to field 

validate the estimated remaining AML sites in 

California, Nevada, and Utah. State by state, it will 

require:

• In California, approximately $118 million to 

field validate the estimated remaining AML 

sites.

• In Nevada, approximately $86 million to field 

validate the estimated remaining AML sites.17

• In Utah, approximately $8 million to field 

validate the estimated remaining AML sites.

3.3 Estimated Costs to Address 

Remaining Physical Safety Hazards

During field validation of the mine symbols, the 

California AMLU observed that approximately 84 

percent of the sites contain features that pose 

physical safety hazards. Further, 38 percent of the 

features present at the field validated sites were 

hazardous openings (i.e., shafts, adits, or other 

openings that are large and deep enough to 

17 Values of 78,068 sites (273,239 features divided by 3.5 features per site) in 

Nevada and 4,214 sites (14,752 features divided by 3.5 features per site) were 

used to calculate this amount. This concept is explained further in the section 

“Refining the Estimates.”

17
12 Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis

endanger human life).18 Based on these statistics 

and the robust subset, on BLM land in California 

there are approximately:

• 19,093 sites remaining to be inventoried that 

pose physical safety hazards. 

• 30,308 features that are hazardous openings. 

Similar field validated statistics concerning 

physical safety hazards do not currently exist for 

Nevada and Utah. Thus, physical safety hazard 

estimates are not calculated for Nevada or Utah.

18 Department of Conservation, “California’s Abandoned Mines: A Report on the 

Magnitude and Scope of the Issue in the State, Volume I” (California: California 

Department of Conservation, Office of Mine Reclamation, 2003); and California 

Department of Conservation, “California’s Abandoned Mine Lands Program 

Fact Sheet” (California: California Department of Conservation, Office of Mine 

Reclamation, January 2012). 

In the July 2013 publication, “Feasibility Study 

for AML Inventory Validation and Physical Safety 

Closures,” the BLM also estimated the future cost 

of remediating the physical safety hazards in 

California at $19,400 per physical safety hazard 

remediation. With an estimated total of 30,308 

remaining features in California that pose physical 

safety hazards, it will require approximately $588 

million to remediate them. 
Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis 13

4. Refining the Estimates

The BLM has confidence that the estimates of 

the total and remaining AML sites and features 

presented in this document adequately depict 

the scope and magnitude of the inventory work 

remaining to be performed by the Abandoned 

Mine Lands Program. However, the BLM believes 

that the actual values of the estimates presented 

in this document will become more refined as 

more sites (symbols) are field validated.

More than 3,000 of the mine symbols have been 

field validated by the California AMLU and used 

to record AML sites in their inventory database. 

However, field validation of mine symbols has not 

yet occurred in Nevada or Utah. As mine symbols 

are validated, the accuracy and confidence in 

the estimates will increase, especially for those in 

Nevada and Utah. 

4.1 Refining the California Estimates

Of the three states, the BLM has the most 

confidence in the estimates of the remaining 

AML sites and features for California based on the 

extensive field validation by the California AMLU. 

As more symbols are validated, the site to feature 

ratio may vary if there are differences in the site to 

feature ratio at the additional symbols.

4.2 Refining the Nevada Estimates

The BLM has not yet validated the mine symbols 

in Nevada. As such, the California metrics of 1 

symbol equaling 1 AML site and 3.5 AML features 

were used. The BLM has a reasonable degree of 

confidence that its application of the California 

statistics to the Nevada mine symbol data has 

adequately estimated the scope and magnitude 

of the AML sites and features that remain to be 

inventoried.

When 1 percent, or approximately 850, of the 

mine symbols are validated in Nevada, a Nevadaspecific features per mine symbol ratio can be 

used to calculate and refine the total amount of 

estimated AML sites and features (instead of the 

California ratio of 3.5 features per symbol). 

Further, the application of the term “site” can 

vary from state to state. Based on AMSCM data, 

Nevada reports that half of the sites contain only 

one feature. Because the application of the term 

“feature” is consistent between both the AMSCM 

data and the mining symbol statistics (i.e., a single 

manmade disturbance associated with mining 

activity), the BLM has confidence that the features 

more accurately depict the scope and magnitude 

of the total and remaining AML inventory work in 

this state. 

4.3 Refining the Utah Estimates

Like Nevada, the BLM has not yet validated the 

mine symbols in Utah. California metrics of 1 

symbol equaling 1 AML site and 3.5 AML features 

were used. The BLM has a reasonable degree of 

confidence that its application of the California 

statistics to the Utah mine symbol data has 

adequately estimated the scope and magnitude 

of the AML sites and features that remain to be 

inventoried. 

When 5 percent, or approximately 300, of the 

mine symbols are validated in Utah, a Utahspecific features per mine symbol ratio can be 

used to calculate and refine the total amount of 

estimated AML sites and features (instead of the 

California ratio of 3.5 features per symbol). 

The application of the term “site” can vary from 

state to state. Based on AMSCM data, Utah 

reports that two out of three sites contain only 

one feature. Because the application of the term 

“feature” is consistent between both the AMSCM 

data and the mining symbol statistics (i.e., a single 

manmade disturbance associated with mining 

activity), the BLM has confidence that the features 

more accurately depict the scope and magnitude 

of the total and remaining AML inventory work in 

this state. 
14 Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis

5. Limitations

While the mine symbols provide a good starting 

point for estimating the magnitude and scope of 

the estimated AML inventory at a state level, this 

approach can be less successful when analyzed at 

a local or field office level. For example, in Figure 

3 (the map of remaining AML features in Utah), 

some field offices exhibit a negative number of 

remaining features. This occurs when the number 

of features recorded in the AMSCM database 

exceeds the number of estimated AML features 

from mine symbols for that geographic area. 

Additionally, the mine symbols are not assumed 

to provide a comprehensive data source for all 

mining locations in a state. Other data sources 

(e.g., mining district mineral reports) and field 

investigations will be required to eventually 

document all AML sites and features on BLMmanaged land. However, the mine symbols 

provide locational data to potentially save time in 

field validation and improve the known BLM AML 

inventory.
Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis 15

6. Expanding the Study to Other States

In order to estimate the number of AML sites 

and features for the remaining states where the 

BLM manages land, a mining symbol dataset of 

sufficient quality must exist and be available. To 

date, the BLM has identified acceptable datasets 

for only California, Nevada, and Utah. However, 

the USGS, in partnership with the BLM and 

University of Wisconsin-Madison, began a project 

in 2012 to complete a mine symbol dataset for the 

nation.19 Upon completion of this project, AML site 

and feature estimates for the other states where 

the BLM manages land can be calculated.

19 Gregory Fernette (principal investigator), “Development of Enhanced Feature 

Recognition Software for the Extraction of Mine Features from USGS Topographic 

Maps” (project) (U.S. Geological Survey, Mineral Resource Program, 2013) http://

www.usgs.gov/cdi/year/2013.html.

BLM-managed lands
16 Abandoned Mine Land Inventory Study for BLM-Managed Lands in California, Nevada, and Utah: Site and Feature Analysis

7. Conclusion

Using the USGS symbol approach greatly 

improves the BLM’s ability to build a current, 

complete, and accurate database of AML sites 

and features. This is critical to measuring progress 

and reporting comprehensive results of program 

activities. Through field validation of the mine 

symbols, the BLM can inspect suspected AML sites 

and take appropriate action to mitigate hazards. 

The BLM currently estimates that the total cost 

of field validating and recording in the AMSCM 

database the estimated remaining 93,000 sites 

and 368,000 features in California, Nevada, and 

Utah to be approximately $212 million (see Table 3 

for overall summary). This would require 10 twoperson teams approximately 20 years to complete. 

In California alone, there are an estimated 

30,308 features that pose physical safety hazards 

requiring $588 million to remediate.

Table 3. Overall summary of the estimated number of sites and features remaining to be inventoried on 

BLM lands in California, Nevada, and Utah and the estimated time and cost to complete the inventory

Estimated Number 

of Sites

to be

Inventoried

Estimated Number 

of Features

to be

Inventoried

Estimated Time

to Complete 

Inventory

Estimated Cost to 

Complete Inventory

California 22,730 79,757 568 work months $118 million

Nevada 68,564 273,239 1,952 work months $86 million

Utah 1,399 14,752 105 work months $8 million

Total 92,693 367,748 20 years1 $212 million

1 This inventory time is based on 10 two-person work crews.