U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005–3148

January 2006 Printed on recycled paper

The Boulder River watershed in Montana is one of many 

watersheds in the western United States where historical mining 

has left a legacy of acid mine drainage and elevated concentrations of potentially toxic trace elements in surface streams. U.S. 

Geological Survey (USGS) scientists recently completed a major 

assessment of the environmental effects of historical mining in the 

Boulder River watershed. The study demonstrated how the watershed approach can be used to assess and rank mining-affected sites 

for possible cleanup. The study was conducted in collaboration 

with State and Federal land-management agencies, which have the 

responsibility to clean up many historical mine sites.

Results of the study have been published in USGS Professional 

Paper 1652. This report describes the geology and geochemistry of 

rocks and sediment, the hydrology and water chemistry of streams 

and ground water, and the diversity and health of aquatic organisms. Most importantly, the report defines the major sources of 

trace elements in the watershed and describes many techniques that 

can be used to identify these sources and determine their environmental effects. Maps and data collected for the study are included 

on a CD that accompanies the report.

The Historical Mining Era

The Boulder River watershed study area encompasses the 

Boulder and Basin mining districts. Mining of ore deposits containing copper, lead, and zinc, as well as silver and some gold, 

started in the early 1860s and ended in the 1970s. The main period 

of mining was from about 1880 to 1907, and peak production 

occurred during 1895–1903.

During the mining era, mine waste and mill tailings were 

discharged with little regard for potential effect on the landscape or 

streams. Although most mining in the watershed occurred nearly 

a century or more ago, effects on the environment are still present 

today. Physical manifestations of these effects are evident as land 

disturbances, unvegetated areas, and colorful mine drainage near 

mine and mill sites (fig. 1). Ecological impairment is reflected 

through reduced abundance and diversity of aquatic organisms and, 

in some stream reaches, total absence of a viable fish community.

In some mining districts, trace-element concentrations in 

streambed sediment and water were elevated long before any 

mining occurred because mineralized rocks were weathering and 

contributing acid and trace elements to streams. This was not the 

case in the Boulder River watershed. Acidic and trace-element-rich 

water in the study area is associated with 

• mine adits that opened and exposed vein deposits and channeled ground water to the land surface, or

• dumps containing mineralized mine waste or mill tailings.

Environmental Effects

Environmental effects from historical mining in the Boulder River 

watershed are most noticeable in streams. In many stream reaches, 

concentrations of toxic trace elements were elevated in the stream 

water, in the sediment forming the streambed, and in the aquatic 

organisms that inhabit the streams. The major tributaries of the 

Boulder River as well as the Boulder River downstream from Basin 

Creek had elevated concentrations of copper, lead, and zinc (fig. 2). 

These effects were observed for a distance of 55 miles downstream 

to the confluence of the Boulder River with the Jefferson River.

The major environmental effect of historical mining in the 

watershed has been impairment of aquatic life in streams. All species 

of fish were absent in stream reaches downstream from a few large 

mines because of the high trace-element concentrations caused by 

acid mine drainage. Farther downstream, trout were found in less 

contaminated reaches, but exposure to high trace-element concentrations affected the health of these fish. The effects on the fish were 

shown to result from the trace elements in water through exposure of 

the gills and in diet through the consumption of aquatic insects. 

Environmental Effects of Historical Mining in the

Boulder River Watershed, Southwestern Montana

The U.S. Geological Survey recently completed an environmental study of historical mining in the Boulder 

River watershed. Results of the study have been used by 

State and Federal agencies to plan and implement cleanup.

The Watershed Approach provides an effective means to 

evaluate the environmental impacts of historical mining and 

helps to focus cleanup efforts at sites where the most benefit 

will be gained in the watershed. The watershed approach is 

based on the premise that contaminated sites that have the 

most profound effect on water and ecosystem quality within 

an entire watershed can be identified, characterized, and 

ranked for cleanup.

Figure 1. Mill tailings in the High Ore Creek valley before large-scale 

cleanup activities at the Comet mine site, October 1996.
Mine Cleanup and Monitoring

Many of the historical mine sites identified as 

contributors of trace elements in the watershed 

have been targeted for cleanup. Large-scale cleanup 

efforts have been undertaken at the Comet mine in 

High Ore Creek (fig. 1), the Buckeye and Enterprise 

mine site (fig. 3), and the Bullion mine, both of 

which are in the Basin Creek drainage. 

Monitoring is an important tool for evaluating 

the effectiveness of cleanup efforts and assessing 

the extent of ecological restoration. When comprehensive monitoring data have been collected 

and analyzed, land managers can more objectively 

evaluate the success of a cleanup action and whether 

cleanup goals have been met. Monitoring data for 

water, streambed sediment, and biology have been 

collected downstream from each cleanup project.

Figure 2. Map showing concentration of zinc in streambed 

sediment. The highest concentrations of zinc were in stream 

reaches downstream from the Comet, Crystal, Bullion, and, 

to a lesser extent, the Buckeye and Enterprise mines. This 

pattern of concentrations indicates that these five mines are 

the main sources of zinc in the Boulder River watershed.

Figure 3. Buckeye mill site, upper Basin Creek, before (left) and after (right) cleanup.

For further information contact: David Nimick, USGS, Helena, MT (406-457-5900) 

For the complete report see: Nimick, D.A., Church, S.E., and Finger, S.E., eds., 2004, Integrated investigations of environmental 

effects of historical mining in the Basin and Boulder mining districts, Boulder River watershed, Jefferson County, Montana: U.S. 

Geological Survey Professional Paper 1652, 524 p. URL: http://pubs.usgs.gov/pp/2004/1652/.

This Fact Sheet is available online at: http://pubs.usgs.gov/fs/2005/3148/

112o22'30''

46o

22'

30''

46o15'

R6W

R5W

T8N

T7N

T6N

R4W

112o15'

Base from U.S. Geological Survey

Digital line graphs, 1:100,000

0

0 1

1 2 MILES

2 KILOMETERS

Hoodoo

River

CONTINENTAL

DIVIDE

Basin

Weasel Gulch

Joe Bowers

Cr

Jimmys

Cr

Jack

Creek

Nellie Grant

Cr

Overland Cr

Snow drift

Creek

Creek

Cataract

Creek

Deer

Creek

Basin

Creek

Limber

Gulch

Bishop

Creek

High

Boomerang

Gulch

Galena

Gulch

Little Galena Gulch

Kleinsmith

Gulch

POWELL CO

LEWIS AND CLARK CO

 Three

 Brothers

 Jack

Mountain

Clear Creek

Grub

Gulch

Rocker

Creek

Ore

Creek

Peters

Gulch

Big

Saul Haggerty Gu cl h

JEFFERSON CO

EXPLANATION

NATIONAL FOREST BOUNDARY

Zinc, ppm

> 1,500

750–1,500

375–750

225–375

< 225

Ribbon

BULLION

BUCKEYE AND

ENTERPRISE

CRYSTAL

COMET

Uncle Sam Gulch

Boulder

Inactive mine

Boulder River

 watershed 

 study area

Boulder River

Boulder

Little

River

Boulder River

 watershed