Grant- Kohrs Ranch National Historic Site 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2007/004 

National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 
THIS PAGE: 

View of Grant-Kohrs Ranch NHS, MT 

ON THE COVER: 

Scenic vista of the ranch at Grant-Kohrs Ranch 

NHS, MT 

NPS Photos 
Grant- Kohrs Ranch National Historic Site 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2007/004 

Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, Colorado 80225 

June 2007 

U.S. Department of the Interior 

Washington, D.C.
The Natural Resource Publication series addresses natural resource topics that are of interest 

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Printed copies of reports in these series may be produced in a limited quantity and they are 

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gre_publications) on the internet, or by sending a request to the address on the back cover. 

Please cite this publication as: 

Thornberry- Ehrlich, T. 2007. Grant- Kohrs Ranch National Historic Site Geologic Resource 

Evaluation Report. Natural Resource Report NPS/NRPC/GRD/NRR—2007/004. National 

Park Service, Denver, Colorado. 

NPS D- 58, June 2007 
 GRKO Geologic Resource Evaluation Report iii

Table of Contents 

List of Figures .............................................................................................................. iv

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

Introduction ................................................................................................................... 2

Purpose of the Geologic Resource Evaluation Program ............................................................................................2

Geologic Setting .........................................................................................................................................................2

Geologic Issues............................................................................................................. 4

Introduction.................................................................................................................................................................4

Historic Mining Issues.................................................................................................................................................4

Geologic Features and Processes............................................................................. 10

Geology and history connections..............................................................................................................................10

Montana Lineament..................................................................................................................................................10

Map Unit Properties .................................................................................................... 11

Map Unit Properties Table........................................................................................................................................12

Geologic History.......................................................................................................... 15

Glossary....................................................................................................................... 22

References................................................................................................................... 24

Appendix A: Geologic Map Graphic .......................................................................... 26

Appendix B: Scoping Summary................................................................................. 29

Attachment 1: Geologic Resource Evaluation Products CD 
 NPS Geologic Resources Division iv 

List of Figures 

Figure 1: Map of Montana with physiographic features..................................................................................................3

Figure 2: Diagram of stream processes on the landscape at Grant-Kohrs Ranch National Historic Site .......................9

Figure 3: Geologic time scale.......................................................................................................................................18

Figure 4: Showing inferred Proterozoic structure of the Belt basin ..............................................................................19

Figure 5: Map of present day structural features..........................................................................................................20

Figure 6: Diagrammatic view of a retreating glacier .....................................................................................................21
 GRKO Geologic Resource Evaluation Report 1

Executive Summary 

This report has been developed to accompany the digital geologic map produced by Geologic 

Resource Evaluation staff for Grant- Kohrs Ranch National Historic Site in Montana. It 

contains information relevant to resource management and scientific research. 

Grant- Kohrs Ranch National Historic Site 

commemorates the western ranch lifestyle as part of a 

living museum. Simultaneously, the park protects a 

portion of the upper Clark Fork River drainage. GrantKohrs Ranch lies within the Northern Rocky Mountains 

Physiographic Province, which contains metamorphic, 

sedimentary, and igneous rocks of Precambrian to 

Tertiary age as well as recent alluvial and glacial deposits. 

The pre- Tertiary rocks are complex and were folded 

and deformed multiple times during the Sevier and 

Laramide orogenic events. 

Underlying geologic structure, past and present, defines 

every natural landscape. Geologic processes give rise to 

rock formations, mountains and valleys, mineral 

deposits, and broad river plains. The results of these 

processes played a prominent role in the history of the 

Clark Fork River Valley with regard to both mining 

activity and cattle ranching. Understanding Grant- Kohrs 

Ranch begins with the geology and with the processes 

from which today’s environments, history, and scenery 

arose. 

Geologic processes develop a landscape that influences 

human use patterns. The geology inspires wonder in 

visitors to Grant- Kohrs Ranch, and emphasizing it 

enhances the visitor experience. Rich geological, 

historical, and cultural resources impact land- use and 

visitor use planning in the park. Adding a detailed 

geologic map, wayside exhibits, a road or trail log, and a 

guidebook that ties Grant- Kohrs Ranch to the other 

parks in the Northern Rocky Mountains, and to the 

park’s existing portfolio of visitor information would 

enhance visitor appreciation of the geologic history and 

dynamic processes that created the natural landscape 

and could emphasize the long history showcased at the 

park. 

Humans have significantly modified the landscape and 

the geologic system surrounding Grant- Kohrs Ranch 

through mining and agriculture. Wastes from mining and 

smelting threaten ecosystem health, which is capable of 

noticeable change within a human life span. Acid mine 

drainage and heavy metal contamination are serious 

resource management concerns for Grant- Kohrs Ranch. 

The Clark Fork River is the lifeline of the vast Deer 

Lodge Valley. Intense seasonal precipitation and high 

runoff cause flooding along the upper reaches of the 

Clark Fork River. Grant- Kohrs Ranch is located 

downstream of many former mining operations in the 

upper Clark Fork River Drainage. Abandoned and 

inactive mines pose a threat to health, safety, and the 

environmental in the Grant- Kohrs Ranch area. 

Foremost among these is metal contamination of 

groundwater, surface water, and soils. Metal- rich floodplain deposits, derived from contaminated sediments 

dispersed during floods in the late 1800’s- early 1900’s, 

flank the Clark Fork River. The quality of the surface 

water system is threatened by the continuous reexposure to heavy metals eroded from floodplain 

deposits. Due to mining related contamination the 

Environmental Protection Agency (EPA) has designated 

the upper Clark Fork River as a superfund site. 

Erosion along the riverbanks in the area increases the 

overall sediment carried by the park’s streams and 

exposes aquatic ecosystems to further contamination 

once trapped in sediments. Heavy metal levels are 

elevated in the Clark Fork River sediments. Even 

changes in relatively clean sediment loads and 

distribution affect aquatic and riparian ecosystems. 

Sediment loading can change channel morphology and 

increase overbank- flooding frequency. 

The Clark Fork River with its associated hydrogeologic 

system is a primary resource at the park. Most working 

aquifers are at shallow levels in unconsolidated 

Quaternary and Tertiary deposits. Groundwater inflow is 

an important contributor to the water budget of the river 

in the park area. A working model of the hydrogeologic 

system within the park is needed to predict 

environmental responses to contaminants and to help 

remediate affected areas. 
 NPS Geologic Resources Division 2 

Introduction 

The following section briefly describes the regional geologic setting and the National 

Park Service Geologic Resource Evaluation program. 

Purpose of the Geologic Resource Evaluation Program 

The Geologic Resource Evaluation (GRE) Program is 

one of 12 inventories funded under the NPS Natural 

Resource Challenge designed to enhance baseline 

information available to park managers. The program 

carries out the geologic component of the inventory 

effort from the development of digital geologic maps to 

providing park staff with a geologic report tailored to a 

park’s specific geologic resource issues. The Geologic 

Resources Division of the Natural Resource Program 

Center administers this program. The GRE team relies 

heavily on partnerships with the U.S. Geological Survey, 

Colorado State University, state surveys, and others in 

developing GRE products. 

The goal of the GRE Program is to increase 

understanding of the geologic processes at work in parks 

and provide sound geologic information for use in park 

decision making. Sound park stewardship relies on 

understanding natural resources and their role in the 

ecosystem. Geology is the foundation of park 

ecosystems. The compilation and use of natural resource 

information by park managers is called for in section 204 

of the National Parks Omnibus Management Act of 1998 

and in NPS- 75, Natural Resources Inventory and 

Monitoring Guideline. 

To realize this goal, the GRE team is systematically 

working towards providing each of the identified 270 

natural area parks with a geologic scoping meeting, a 

digital geologic map, and a geologic report. During 

scoping meetings the GRE team brings together park 

staff and geologic experts to review available geologic 

maps and discuss specific geologic issues, features, and 

processes. Scoping meetings are usually held for 

individual parks and on occasion for an entire Vital Signs 

Monitoring Network. The GRE mapping team converts 

the geologic maps identified for park use at the scoping 

meeting into digital geologic data in accordance with 

their innovative Geographic Information Systems (GIS) 

Data Model. These digital data sets bring an exciting 

interactive dimension to traditional paper maps by 

providing geologic data for use in park GIS and 

facilitating the incorporation of geologic considerations 

into a wide range of resource management applications. 

The newest maps come complete with interactive help 

files. As a companion to the digital geologic maps, the 

GRE team prepares a park- specific geologic report that 

aids in use of the maps and provides park managers with 

an overview of park geology and geologic resource 

management issues. 

For additional information regarding the content of this 

report and up to date GRE contact information please 

refer to the Geologic Resource Evaluation web site 

(http://www2.nature.nps.gov/geology/inventory/). 

Geologic Setting 

Grant- Kohrs Ranch once encompassed 10 million acres 

of a cattle empire near Deer Lodge, Montana. Today this 

1,618- acre site is the only unit in the National Park 

Service commemorating the frontier ranch lifestyle. The 

historic site was designated an NPS unit on March 30, 

1971, and authorized August 25, 1972. John Francis Grant 

first developed the ranch in 1862. Grant sold the ranch to 

Conrad Kohrs in 1866. Kohrs expanded the ranch, taking 

advantage of the free range in western Montana. Today, 

the site contains 90 historic structures and maintains 

active cattle ranch operations in the Deer Lodge Valley. 

This living museum attracts 15,000+ visitors annually. 

Grant- Kohrs Ranch National Historic Site sits in the 

broad Deer Lodge Valley of the Clark Fork River in 

west- central Montana (figure 1). The valley includes 

approximately 775 square kilometers (300 square miles) 

in Powell, Deer Lodge, and Silver Bow counties 

(Konizeski et al. 1968). The headwaters of the Clark Fork 

River are located south of Grant- Kohrs Ranch where the 

Silver Bow and Warm Springs creeks merge. Structurally 

this valley is a half graben bounded on the western edge 

by normal faults at the range front. Mountains in this 

area include the Flint Creek, Anaconda, and Highland 

ranges. The eastern side of the Deer Lodge Valley lacks 

distinct fault boundaries, but is ultimately defined by the 

Boulder Mountains and further north, the Garnet 

Mountains. Mt. Haggin (3,250 m, 10,665 ft above sea 

level) is the highest point within the upper Clark Fork 

drainage area. These ranges are all part of the Northern 

Rocky Mountains physiographic province characterized 

by rugged mountains and intermontane valleys. 

Local geology varies greatly within the Grant- Kohrs 

Ranch area. In the eastern mountains, the Cretaceous 

Boulder Batholith granitic (monzogranite, granodiorite, 

and aplite) igneous intrusion is the predominant rock 

type. Several high- angle normal faults cut the area 

trending north, northwest, and northeast. Along the 

western side of the valley, the rocks are comprised of 

folded and faulted sedimentary units intruded by 

Cretaceous granitic to dioritic igneous dikes and stocks. 

Vast mineral deposits in the 16 different mining districts 

of the area are a result of this igneous activity (Madison 

et al. 1998). The upper Clark Fork River is the primary 

waterway in the area. Its basin covers more than 3,370 

square km (1,300 square miles). Local tributaries and 

small streams include Tin Cup Joe, Fred Burr, 

Cottonwood, Peterson, and Dempsey creeks (Nimick 

1993). Thick deposits of alluvium form terraces and 

rolling hills along the valley (Konizeski et al. 1968). 
 GRKO Geologic Resource Evaluation Report 3

Figure 1. Map of Montana with physiographic features surrounding Grant-Kohrs Ranch National Historic Site. Modified version of map 

from Perry-Castañeda Library Map Collection. 
 NPS Geologic Resources Division 4 

Geologic Issues 

A Geologic Resource Evaluation scoping session was held for Grant- Kohrs Ranch 

National Historic Site on August 19, 2002, to discuss geologic resources, address the 

status of geologic mapping, and assess resource management issues and needs. The 

following section synthesizes the scoping results, in particular, those issues that may 

require attention from resource managers. 

Introduction 

Recent human activity in the area has had some dramatic 

effects on the landscape. Early mining efforts released 

tailings and waste into the system. In addition, 

overgrazing by cattle (reducing the riparian buffer zone) 

has caused massive erosion. The combined result was the 

deposition of extensive floodplain deposits 

contaminated with heavy metals. Since the early 1900s, 

sediment management systems on the Clark Fork River 

and tributaries have lessened flooding, but regular stream 

migration and seasonal high flows are reworking 

contaminated sediments, reintroducing them to the 

environment at Grant- Kohrs Ranch National Historic 

Site (Nimick 1990). 

Geologic issues in this section are centered around 

historic mining issues with sub- categories relating 

primarily to that major issue. Potential research projects 

and topics of scientific interest are also presented at the 

end of the section. 

Historic Mining Issues 

Mining is not allowed in the park under existing federal 

law; however, the legacy of past mining in the area 

continues to affect the resources of Grant- Kohrs Ranch 

National Historic Site. According to the reclamation 

summary of abandoned mineral lands in the National 

Park Service conducted by the Disturbed Lands 

Restoration Program of the Geologic Resources 

Division, there is an abandoned mine feature at GrantKohrs Ranch. There are many more mine- related 

features beyond park boundaries. Abandoned and 

inactive mines create safety, environmental, and health 

concerns for the Grant- Kohrs Ranch area. Foremost 

among these is metal contamination of groundwater, 

surface water, and soils. Contamination is defined as the 

occurrence of metals exceeding baseline concentrations. 

Baseline concentrations are the probable concentration 

levels prior to mining activities (Moore and Woessner 

2000). In addition to water and soil contamination, air 

pollution results when dust blows from abandoned 

tailing piles. Further, tailing and other mill waste piles as 

well as mine openings and dilapidated structures have 

the potential for collapse and pose serious safety hazards 

(Madison et al. 1998). 

Metal concentrations in water, sediment, soils, and biota 

in the area are elevated due to historic mining practices, 

smelting, and natural mineralization (Smith et al. 1998). 

Between 1878 and 1925, over ten million tons of waste 

produced from smelting and milling activity in Butte 

alone were disposed of in Silver Bow Creek, near the 

headwaters of the Clark Fork River (Nimick 1990). 

Grant- Kohrs Ranch is located downstream from many 

mine operations in the upper Clark Fork River Drainage. 

Metal- rich flood- plain deposits flank the river from 

Warm Springs to Milltown Reservoir near Missoula, 

Montana (Smith et al. 1998). Due to the presence of 

hazardous substances related to mining activity 

throughout the region, the U.S. Environmental 

Protection Agency (EPA) designated the upper Clark 

Fork River as a superfund site, an operative unit of the 

Milltown Reservoir Superfund Site (Breuninger 2000). 

According to the historic site’s annual report for FY05, 

ongoing projects to install monitoring wells and lined 

irrigation ditches are a priority at Grant- Kohrs Ranch 

National Historic Site and financial negotiations between 

the Federal Government and responsible parties for 

superfund issues are still in progress (Rotegard 2006). 

The Montana Bureau of Mines and Geology (MBMG) 

and the U.S. Forest Service (USFS) studied this area 

regarding potential problems associated with abandoned 

and inactive mines. For the park, the study found that the 

potential for acid mine drainage is a serious resource 

management concern. 

Acid mine drainage is a condition resulting from sulfides 

reacting with water and lowering the pH by producing 

sulfuric acid (H2

SO4), sulfate (SO4

2- ), and reduced iron 

(Fe2+). This acidity increases the solubility of some 

potentially harmful metals. These metals are then 

dispersed from a mine source area by ground and surface 

water as dissolved ions, suspended sediment, or as part 

of the fluvial bedload (Madison et al. 1998). 

There are at least six components dictating the formation 

of acid mine drainage conditions (Trexler et al. 1975): 

1. availability of sulfides (including pyrite), 

2. presence of oxygen and iron- oxidizing bacteria, 

3. water in the atmosphere, 

4. availability of metals and minerals, 

5. availability of water to transport dissolved 

components, and 

6. mine and waste area characteristics. 

These components, present in mined areas upstream 

from Grant- Kohrs Ranch, have produced acid mine 

drainage. Once formed, the acidic water dissolves other 

minerals including sulfides such as arsenopyrite, 
 GRKO Geologic Resource Evaluation Report 5

chalcopyrite, tetrahedrite, galena, and sphalerite as well 

as aluminosilicate minerals. 

Metals such as manganese, silver, arsenic, copper, 

aluminum, cadmium, mercury, lead, zinc, and iron are 

present in the water as cations. When cation 

concentrations are high enough and pH rises (higher 

than 2.2) due to dilution, minerals containing these 

dissolved metals begin to precipitate ferric hydroxide 

(Fe[OH]3

) and other insoluble metal compounds 

(Madison et al. 1998; Schlumberger 2007). Precipitates 

cloud surface water, coat rocks, and deposit in layers in 

floodplain areas and along streambeds. 

Within the upper Clark Fork River drainage area, the 

MBMG and USFS study investigated 179 abandonedinactive mines and/or mills for potential environmental 

impacts. Many of these sites are upstream from GrantKohrs Ranch and may affect water and sediment quality 

within the park. These areas ranged from small hillslope 

prospects and adits to larger underground systems. 

Tailings from these mines have been, and continue to be, 

eroded, mixed with other sediments, transported 

downstream, and deposited in stream channels and 

floodplains as a result of fluvial processes such as a 

flattening of the gradient (Dodge et al. 2004). Because 

Grant- Kohrs Ranch sits in the downstream reaches of 

the upper Clark Fork River drainage (drainage area of 

2,600 square km, 1,005 square miles), environmental 

impacts from these upstream mines and tailings are a 

serious management concern (Madison et al. 1998). 

One of the closest mines to the ranch is the Champion 

mine and the accompanying mill about 19 km (12 miles) 

southeast of the town of Deer Lodge, Montana. The 

Dark Horse Mill sits west of the town of Racetrack, near 

Deer Lodge. The Ding Bat and Blue Eyed Maggie mines 

are 11 km (7 miles) east of Deer Lodge and Grant- Kohrs 

Ranch. Also nearby, are the Lower Hidden Hand, 

Racetrack, Sterrit, St Mary, and Rock Gulch mines. 

The Champion, Lower Hidden Hand, Racetrack, St. 

Mary, Sterrit, and Ding Bat mines show high levels of 

mercury in water tested by the MBMG and USFS study. 

Arsenic is concentrated in water at Ding Bat and Rocker 

Gulch mines; manganese is concentrated at Lower 

Hidden Hand mine; and lead, chlorine, and silver are 

concentrated in the water at Racetrack mine (Madison et 

al. 1998). 

Trace elements derived from mining, smelting, and 

milling activities in the area over the past 135 years 

(Nimick 1993), have contaminated broad land areas along 

the upper Clark Fork River drainage. Erosion of tailings 

deposits in the flood- plain is a major contributor of 

metals to the watershed (Smith et al. 1998). Elements of 

specific concern include arsenic, cadmium, copper, iron, 

lead, manganese, and zinc. Soil studies revealed high 

levels of arsenic, cadmium, copper, lead, and zinc at 

several mines upstream of Grant- Kohrs Ranch 

(Madison et al. 1998). Arsenic and cadmium have been 

identified in elevated concentrations in local 

groundwater supplies (Nimick 1993). 

Because continuous erosion of floodplain deposits and 

riverbanks redistributes (and slightly dilutes) heavy 

metals, the ecosystem is constantly re- exposed to 

contamination (Breuninger 2000). In situ remediation 

efforts to restore stable, healthy conditions within 

selected areas of the watershed such as the South Deer 

Lodge Improvement Project, the Governor’s 

Demonstration Project, and the Warm Springs 

Pond/Mill Willow Bypass cleanup showed no significant 

change to basin scale contaminant levels in 7 years 

between 1991 and 1998 (Breuninger 2000). 

Heavy metal contamination may impose chronic toxicity 

on biota of the upper Clark Fork River basin. In the 

reach of the river near Grant- Kohrs Ranch, flood- plain 

deposits and exposed tailing piles are extensive, as much 

as 0.3 m (1 ft) thick on terraces 2 m (6 ft) above the river 

(Nimick 1990; Smith et al. 1998; Breuninger 2000). 

Floodplain sediments are enriched in heavy metals as 

much as 1,800 times over background (Nimick 1990). 

Waste trapped in higher areas spread over the Clark Fork 

River valley during at least four large floods in the late 

1800’s and early 1900’s (Nimick 1990). Within local valley 

fill, an arsenic- rich flood deposit stands out as a yellow 

layer (Bruce Heise, personal communication 2005). 

Resource management needs to understand the nature of 

these potential threats to the ecosystem health. 

The toxicity of heavy metals is manifested by disrupting 

cellular enzymes, which run on nutritional minerals such 

as magnesium, zinc, and selenium. Heavy metals replace 

the nutrients and bind their receptor sites, causing 

diffuse symptoms by affecting nerves, hormones, 

digestion, and immune function. Threats to plant 

communities include loss in biodiversity, and toxicity, 

whereas in fish and aquatic life, toxicity and 

bioaccumulation threatens predatory species that 

consume them. In humans, heavy metal toxicity leads to 

myriad health problems ranging from memory loss, 

increased allergic reactions, high blood pressure, 

depression, mood swings, irritability, poor 

concentration, aggressive behavior, sleep disabilities, 

fatigue, speech disorders, high blood pressure, 

cholesterol, triglycerides, vascular occlusion, 

neuropathy, autoimmune diseases, and chronic fatigue 

(I.H. 2007). 

To better understand mining impacts and contamination 

transport processes, Grant- Kohrs Ranch National 

Historic Site had an in- depth environmental quality 

assessment done in cooperation with several universities. 

It is entitled "US Department of Interior Site 

Characterization and Natural Resource Damage 

Assessment Studies, Grant- Kohrs Ranch NHS and 

Bureau of Land Management, 2000- 2001; Clark Fork 

River Operable Unit of the Milltown Reservoir 

Sediments NPL Site; July 8, 2002". Other recent works by 

the Department of the Interior related to the Superfund 

site of the Clark Fork River Valley, including soil and 
 NPS Geologic Resources Division 6 

groundwater contamination studies, are available 

through the department. 

Geology and Biology 

Geology forms the basis of the ecosystem at GrantKohrs Ranch National Historic Site. Watersheds 

containing abandoned and inactive mines are continually 

at risk of heavy metal contamination through the 

processes of waste rock leaching, groundwater flow, 

redistribution of tailings, and particulate air- fall 

(Breuninger 2000; Butler 2003). 

Metals contained in riverine sediments are linked to 

decreases in the biodiversity of the associated ecosystems 

(Breuninger 2000). Heavy metal bearing minerals are 

often altered by mining, weathering, and fluvial 

processes in such a way that they become more 

bioavailable (Nimick 1990). The effect is stair step in 

nature with algae and other microorganisms 

incorporating the metals from the environment into their 

structures. Fish, such as trout and other aquatic life, feed 

on these organisms concentrating the contaminants. 

Birds and mammals, such as mink and otters, eventually 

feed on the toxic fish (Nimick 1990; Breuninger 2000). As 

mentioned above, heavy metals interrupt natural cellular 

processes in the body and cause myriad health problems, 

especially concerning the nervous system (I.H. 2007). 

As part of the historic site’s cattle herd management 

strategy, controlled stretches of the Clark Fork River 

stream bank are fenced to prevent cattle from 

overgrazing delicate and threatened riparian zones. The 

historic site has no control over what grazing practices 

are adopted by neighboring private landowners. Fenced 

reaches barring cattle from stream banks are shown to 

have better fish habitat and lower overall concentrations 

of heavy metals (Nimick 1990). 

Ongoing studies between 1993 and 2001 to determine if 

grazing affects biodiversity suggest plant community 

recovery is controlled by myriad factors beyond cattle 

grazing although degradations in stream bank stability 

were directly correlative with grazing areas (Bedunah 

and Jones 2001). In a study sampling riparian wetland 

species (e.g. cattails, Typha latifolia), elevated 

concentrations of copper, zinc, and lead were found in 

plant and root tissues (John 1994), in concentrations that 

could pose a health threat to grazing animals and in turn 

pose a threat to humans consuming meat or dairy from 

these cows. 

Surface Water Movement 

The upper Clark Fork River watershed covers 

approximately 3,370 square km (1,300 square miles). The 

downstream boundary of the upper Clark Fork is near 

the town of Drummond, Montana approximately 40 km 

(25 miles) northwest of Grant- Kohrs Ranch. The Clark 

Fork has a cobble- armored riverbed and in the Deer 

Lodge Valley, the river meanders through the 

unconsolidated valley fill from cut banks to point bars, 

constantly reworking the valley fill materials (figure 2) 

(Smith et al. 1998). 

Understanding the dynamics behind surface water 

movement in the area is essential for resource 

management since the transport of heavy metals and 

contaminants is controlled by the supply and input rates 

of the material, the association between metals and the 

sediment, and the downstream transport of water and 

sediment especially during peak flow (Smith et al. 1998). 

The average annual precipitation for the upper Clark 

Fork River ranges from 25 to 36 cm (10 to 14 inches) in 

the valleys to over 150 cm (60 inches) in the mountainous 

areas. Most of this precipitation occurs in late winter and 

early spring (Madison et al. 1998). Intense seasonal 

precipitation and/or high runoff events cause flooding 

along the upper Clark Fork River. Recent large 

mainstream peak flows occurred in 1908, 1948, 1964, 1975, 

1981 with the first being the largest recorded flood event. 

At Deer Lodge the peak discharge for a 100- year flood is 

170 m3

/sec (5,900 ft3/sec). 

Sediment Load and Channel Storage 

Massive amounts of contaminated sediment covers the 

Deer Lodge Valley floor. As much as 704,000 m3

(24,862,000 ft3

) of mine wastes are spread over 274 

hectares along a 10 km (6 miles) stretch of the river. As 

these sediments are transported back and forth between 

the river and floodplain, there is continual re- exposure 

and release of toxic metals to the environment (Nimick 

1990; Nimick and Moore 1994). 

Erosion of the landscape within the upper Clark Fork 

River watershed leads to increases in sediment carried by 

area streams. Bank erosion is a major factor leading to 

the introduction of heavy metals to the riverine 

environment. Land use appears to affect streambank 

erosion rates. Cattle grazing reduces the amount of 

buffering and stabilizing vegetation in the riparian zones 

along rivers and streams. Changes in sediment loads and 

distribution affect aquatic and riparian ecosystems, and 

sediment loading can result in changes to channel 

morphology and increase the frequency of overbank 

flooding. 

Elevated suspended sediment load is a resource 

management concern because it can contaminate 

drinking water sources and increase concentrations of 

toxic chemicals, including heavy metals and pesticides, 

formerly trapped in river bottom sediments. However, 

fine- grained sediments are also vital in the overall fluvial 

transport of contaminants in a water system. Thus, 

sediments act as contaminant sources and sinks 

(Breuninger 2000). 

Understanding the processes involved in sediment 

transport is vital for evaluating the movement of heavy 

metals attached to sediment particles. In the Clark Fork 

River, sediments are transported as bedload, rolling 

along the gravel streambed, or in suspension, as part of 

the water column (Smith et al. 1998). The amount of 

material moved by the river depends on flow conditions 

and overall hydrologic energy. During seasonal high 

flows, the river probably transports pebble and gravel 
 GRKO Geologic Resource Evaluation Report 7

size particles as bedload and sand and finer grained 

particles in suspension (Smith et al. 1998). 

These materials are typically deposited on downstream 

point bars. 

Channel storage of fine sediment and the contaminants 

contained therein follow a seasonal cycle. This cycle is 

subject to hydrologic variability with increased 

availability during the high flows of spring and decreased 

availability during the low flows of autumn. 

Fine- grained sediments do not travel downstream in a 

single pulse but are often resuspended bottom material 

(Miller et al. 1984). This intermittent transport of 

contaminants and fine- grained sediment increases the 

affected area. Heavy metals eroded from cut banks are 

transported in equilibrium with other sediments, mixed 

at point bars. The entire process results in a continuous 

downstream flux of metals (Smith et al. 1998). 

Groundwater Movement 

The broad Deer Lodge Valley of the upper Clark Fork 

River drainage is floored with thick Quaternary alluvium 

and glacial deposits, and unconsolidated Tertiary 

deposits. These mixed units in the Grant- Kohrs Ranch 

area have developed a number of shallow water aquifers. 

Groundwater flow responds to variations in seasonal 

precipitation and is drawn from upland areas around the 

baseline of the Clark Fork River (Nimick 1993). 

Groundwater flow generally follows the topographic 

surface, typically flowing towards the nearest stream or 

river. Fractured bedrock supplies some water to the 

system locally. 

The rate of groundwater inflow to the Clark Fork at 

2.5m3

/sec. (88 ft3/sec.) is significant between Racetrack 

and Garrison, Montana. This stretch corresponds with 

the location of Grant- Kohrs Ranch. Irrigation- return 

flow is likely responsible for this rate of inflow. 

Groundwater levels are highest during spring runoff and 

are highly influenced by local irrigation practices 

(Nimick 1993). 

Aquifers in Quaternary alluvium yield more water to 

wells than those in Tertiary deposits or fractured 

bedrock. Quaternary alluvium and Tertiary deposits are 

presumably connected hydraulically, thus some 

groundwater flows vertically downward from the 

alluvium into the older deposits (Nimick 1993). 

Depending on slope and hydraulic gradient, 

groundwater is thought to move laterally through 

adjacent aquifers as well. 

Tertiary units may be as much as 1,525 m (5,000 ft) thick 

beneath some reaches of the valley floor. Coarsergrained beds and lenses composed of sands and gravels 

develop permeable and productive aquifers. Finergrained beds of clay and silt sized particles do not 

develop groundwater yielding aquifers. Due to over 

irrigation with unlined ditches, sprinklers, and flood 

systems, water levels in these deeper aquifers are 

generally highest in the summer months. 

If the Tertiary deposits are part of a terrace structure, 

they typically discharge toward adjacent stream valleys 

into alluvium (Nimick 1993). 

Bedrock aquifers (primarily in Cretaceous sedimentary 

units) are water sources for human use when shallow 

alluvium and Tertiary deposit aquifers are unavailable, 

usually near the valley margins. The bedrock aquifers are 

productive enough for domestic use, however, these are 

not considered a significant water source for the park. 

Inflow to these aquifers is generally from precipitation. 

Discharge points include seeps, springs, other aquifers, 

and streams (Nimick 1993). Spring locations are generally 

associated with geologic structure, mostly occurring near 

faults and folds associated with the valley margins. 

Inventory, Monitoring, and Research Needs for Historic 

Mining Issues 

• Determine how contaminants are transported from 

upstream acid mine drainage. 

• Monitor biota (e.g., aquatic insects) for heavy metal 

contamination. 

• Use pH of saturation extracts of surface samples as a 

pollution index to map problem areas for spot 

remediation, providing a short- term solution to local 

contamination problems (Nimick 1990). 

• Spatially determine areas of non- point source runoff 

and study how this is affecting neighbors and the plant 

communities of the park. 

• Determine how surface water movement is affected by 

surficial deposits and soils. 

• Monitor discharge, pH, specific conductance, 

temperature, dissolved oxygen, and concentrations of 

cadmium, chromium, copper, lead, zinc, arsenic, iron, 

manganese, sulfate, and aluminum in surface waters 

(Duaime and Appleman 1990). 

• Monitor streamflow and timing and magnitude of 

storm events; supplement data from fixed river- level 

gauges with field data on submergence and exposure 

of key sites that can be correlated with ecosystem 

response to floods and droughts. 

• Investigate paleoflood hydrology. 

• Conduct hydrologic condition assessments to identify 

actual and potential “problem reaches” (near 

roadways, trails, and visitor and administrative 

facilities) for prioritized monitoring. 

• Increase monitoring of fine- sediment load in rivers 

and local tributaries affecting the park. 

• Relate surface water movement and surficial deposits 

to contaminant transport. 

• Measure morphologic change in stream channels 

related to sediment load. Reliable measurements 

generally require 3- 5 cross sections over several 

hundred meters of channel. 

• Promote cattle- free riparian zones along the river 

corridor to reduce streambank erosion of 

contaminated deposits. 
 NPS Geologic Resources Division 8 

• Use shallow (10- inch) and deeper core data to monitor 

rates of sediment accumulation and erosion and 

analyze changes in chemical constituents of sediments. 

• Cooperate with local agencies to determine amounts, 

types, and durations of exposure of the watershed to 

contaminants. 

• Correlate watershed disturbance with sediment load in 

streams and any aquatic biological productivity 

reductions. 

• Define the influences of bedrock and topography on 

local watersheds at Grant- Kohrs Ranch. 

• Map and quantify water subterranean recharge zones. 

• Install monitoring stations to measure atmospheric 

inputs of important chemical components (such as 

nitrogen, mercury, and pH), and outputs to 

groundwater. 

• Investigate additional methods to characterize 

groundwater recharge areas and flow directions 
 GRKO Geologic Resource Evaluation Report 9

Figure 2. Diagram of stream processes on the landscape at Grant-Kohrs Ranch National Historic Site. Note the inputs of floodplain 

runoff and bank erosion to the sediment load of the river. Note also the deposition of deposits in point bars and floodplains. Graphic 

by Trista L. Thornberry-Ehrlich (Colorado State University). 
 NPS Geologic Resources Division 10 

Geologic Features and Processes 

This section provides descriptions of the most prominent and distinctive geologic features 

and processes in Grant- Kohrs Ranch National Historic Site. 

Geology and history connections 

John Francis Grant came to the Deer Lodge Valley in 

1855 to take advantage of its rolling hills for pasture, a 

clean river, and open spaces. Seasonal water shortages 

made the landscape unattractive for intensive farming; 

however, cattle ranching flourished (Konizeski et al. 

1968). 

Early mineral interest in the Grant- Kohrs Ranch region 

stemmed from the discovery of gold in the southwestern 

corner of Powell County in 1852. Early placer strikes gave 

way to lode extraction in the early 1870s. The main 

period of mine production was between 1880 and 1907. 

By 1896, copper- bearing ores in the Anaconda- Butte 

mining district were the dominant resource in the upper 

Clark Fork River Valley (Johns 1994). Still, gold, silver, 

copper, lead, manganese, and zinc extraction operations 

were all active in the area during World War II with some 

renewed interest during the Korean War. Most of these 

operations closed as interest waned, prices dropped, and 

new environmental regulations were enacted in the 

1980s. By 1983, the Anaconda smelter shut down, 

eliminating the sell- to point for mined ore (Power 1996). 

As a result, many mines were abandoned and/or declared 

inactive. These sites continue to pose negative impacts to 

the environment (Madison et al. 1998). 

The U.S. Geological Survey defined sixteen mining 

districts in the upper Clark Fork River basin. These 

included: the Big Foot, Oro Fino, Pipestone, Homestake, 

Little Pipestone, Dunkleberg, Emery, Highland- Moose 

Creek, Pioneer (Gold Creek)- Rose Mountain, 

Racetrack, Red Lion, Silver Lake, Johnson Basin, Olson 

Gulch, Blue- Eyed Nellie, and Lost Creek districts 

(Madison et al. 1998). The estimated value of extracted 

minerals for these districts for combined gold, silver, 

copper, lead, and zinc totaled $15,106,170 at the time of 

production. 

By the time extensive mining operations were in full 

force in the upper Clark Fork River valley, riparian 

vegetation was disappearing from stream and river 

banks. The loss of this buffering vegetation made the 

impact of seasonal flooding more severe and widespread. 

Erodable materials such as mine tailings were placed 

near streams and easily carried away by rising waters and 

redeposited in the floodplains. The largest recorded 

flood in the system occurred in 1908. This single event 

resulted in a 0.3 m (1 ft) thick deposit along the river in 

the Deer Lodge Valley. Toxic deposits from this and 

even earlier floods are called “slickens” and are visible 

today throughout the Deer Lodge Valley. These 

unvegetated, exposed piles are extremely vulnerable to 

erosion today. 

Montana Lineament 

West of Grant- Kohrs Ranch, the Clark Fork River valley 

forms part of the Montana Lineament or Lewis and 

Clark Line (Nimick 1993; Loan 2001). This feature is 

defined by a complex assortment of roughly parallel 

faults, folds, and linear valleys. It extends from northern 

Idaho (Coeur d’Alene mining district) to an area east of 

Helena, Montana and has a locally anomalous northwest 

to west- northwest trend (Loan 2001). 

Despite some speculation on a Precambrian origin for 

the feature, most of the structures are late Cretaceous or 

younger and relate to the faulting associated with the late 

Laramide orogenic deformation (Loan 2001). Crustal 

movement along the Lewis and Clark line during the 

middle Eocene tilted the entire Garnet mountain range 

and changed the prevalent drainage system, leaving 

ancient stream gravels stranded hundreds of meters 

above the present Clark Fork River drainage (Reynolds 

and Sears 1989; Dundas 1990). 
 GRKO Geologic Resource Evaluation Report 11

Map Unit Properties 

This section provides a description for and identifies many characteristics of the map 

units that appear on the digital geologic map of Grant- Kohrs Ranch National Historic 

Site. The table is highly generalized and is provided for informational purposes only. 

Ground disturbing activities should not be permitted or denied on the basis of 

information contained in this table. More detailed unit descriptions can be found in the 

help files that accompany the digital geologic map or by contacting the NPS Geologic 

Resources Division. 

Precambrian age rocks underlie the Grant- Kohrs Ranch 

area almost entirely. These rocks are part of the Belt 

Supergroup that is Late Proterozoic in age. These were 

deposited in an ancient marine basin. In the Deer Lodge 

Valley, these units are exposed on the western side, 

juxtaposed against Mesozoic and Cenozoic age rocks by 

a large range- bounding fault. Individual formations 

recognized among these older rocks include the 

Snowslip, Shepard, Mt. Shields, Bonner, McNamara, and 

Garnet Range units (Loan 2001). 

The Jurassic Swift Formation and Cretaceous Golden 

Spike Formation are exposed north of the park. The 

Carter Creek and Kootenai formations are also present 

locally. These sedimentary units contain sandstone, 

mudstone, black shale, chert pebble conglomerate, rare 

limestone beds, and andesitic lava flows (Berg 2004). 

The locally present Cretaceous Blackleaf Formation is a 

mixed unit of shales, sands, volcanoclastics, and silts 

deposited during marine transgression (Dyman et al. 

1993). Many Cretaceous units were deposited during the 

regressions and transgressions of the Western Interior 

Seaway. 

On the eastern side of Deer Lodge Valley are the Elkhorn 

Mountain Volcanics and other Cretaceous to Tertiary 

age basaltic flow units. These volcanic rock units are 

exposed over large areas of the map coverage. 

The late Cretaceous to early Tertiary compressional 

Sevier–Laramide orogenic events caused huge blocks of 

buried rock to slide over younger rock in an easterly 

direction. These episodes caused the dramatic 

juxtaposition of rock ages found today at Grant- Kohrs 

Ranch. 

Tertiary age sediments cover the central portion of the 

valley and result from local basins filling with sediments 

when extension along normal faults followed mountain 

building. These sediments consist of lacustrine beds, 

fluvial deposits, and ash beds. Extensive volcanism also 

accompanied extension and produced rhyolite tuffs 

interbedded with limestones, some intrusive dikes, and 

extensive ash beds. These sediments are as thick as 

3,064 m (10,052 ft) 11 km (7 miles) south of Grant- Kohrs 

Ranch National Historic Site (Berg 2004). 

Pleistocene glaciation and other geomorphological 

agents such as streams and landslides have all left recent, 

Quaternary age deposits on the landscape of the Deer 

Lodge Valley. Extensive terraces flank both sides of the 

Clark Fork River. Poorly sorted glacial till and outwash 

as well as slope deposits (landslides) and alluvial fans are 

present along the sides of the valley. 

Large quantities of flood- deposited tailings are present 

throughout the Deer Lodge Valley. These deposits were 

derived from exposed and easily eroded mine and 

smelter waste and tailings. They are enriched in arsenic, 

cadmium, copper, iron, manganese, lead, and zinc (Smith 

et al. 1998). All of these contaminated deposits lie within 

the extensive 100- year floodplain of the upper Clark 

Fork River. 

The following table presents a view of the stratigraphic 

column and an itemized list of features for each map unit. 

The table includes properties specific to each unit 

present in the stratigraphic column including map 

symbol, name, description, resistance to erosion, 

suitability for development, hazards, potential 

paleontologic resources, cultural and mineral resources, 

potential karst issues, recreational use potential, habitat, 

global significance, and limits on restoration. 
Map Unit Properties Table 

Age Map Unit (Symbol) Features and Description Erosion Resistance Suitability for Development Hazards Paleontological Resources Potential Cultural Resources Potential for Karst M

Occ

QUATERNARY 

(Holocene)

Sand and gravel pit (sg); Alluvium (Qal); Alluvial terrace deposit, youngest (Qat1); Alluvial terrace deposit, 2nd

youngest (Qat2); Alluvial terrace deposit, 3rd

youngest (Qat3) 

Gravel, sand, silt, and clay along active river and creek channels; terrace deposits irregularly shaped, 1- 5 m (3- 6 ft) above current floodplain with poorly sorted clasts derived from Tertiary and older strata; older terraces contain similar clast deposits, but are higher above the floodplain; as much as 7- 10 m (20- 30 ft). 

Low 

Unconsolidated material underlies most valley areas of the park where buildings already exist and may heave with frost; high potential for groundwater and soil contamination in floodplain areas; should be avoided 

Heavy metals in floodplain deposits derived mine tailings could lead to contamination of groundwater, surface water, and soils; Unconsolidated deposits and tailing and other mill waste piles are associated with the potential for collapse and failure 

None documented 

Present land surface may contain Native American campsites and artifacts; history of landscape evolution related to ranching activities 

None 

Sand, acid mdrainprecip(heavand o

QUATERNARY 

(Pleistocene–Holocene) 

Alluvium and colluvium (Qac); Landslide deposit (Qls); Alluvial fan deposit (Qaf); Alluvial terrace deposit, 4thyoungest (Qat4); Alluvial terrace deposit, 5th youngest (Qat5) 

Mixed slope and fluvial deposits; landslide deposits occur on some steeper slopes of Tertiary sedimentary rocks; hummocky topography; contains poorly consolidated finegrained rock and soil; alluvial fans consist of small deposits of gravel, sand, silt and clay along tributaries’ boundary with the Clark Fork River floodplain; well developed on eastern shore. Poorly preserved terraces are moderately sorted and stratified above modern drainages, finer - grained than glacial deposits. 

Low 

Unconsolidated material flanking slopes along the valley edge may be too permeable for waste facilities and unstable for some building projects near slopes 

Unconsolidated deposits are associated with high erodability, and the potential for collapse and failure 

Some Pleistocene fossil assemblages present locally including shells, rodent bones, some larger mammal remains (Bison, Camelops, Equus, and Proboscidea) 

Higher present land terraces may contain Native American campsites and artifacts 

None San

QUATERNARY 

(Pleistocene – Holocene) 

Glacial outwash deposit (Qgo); Glacial till (Qgt); Glacial till, older (Qgto); Pediment gravel deposit (Qpg); Glacial outwash of Bull Lake Glaciation (Qgob); Glacial till of Bull Lake Glaciation (Qgtb) 

Poorly sorted, well rounded material ranging in size from sand and clay to boulders; outwash deposits primarily composed of volcanics on eastern side of valley; 80- 95% granitic clasts on western side. Percentage of quartzite clasts increases towards the Clark Fork River; till deposits mostly poorly sorted granitic material with little to no weathering noted; Scattered granite boulders are remnants of older till; pediment deposits are poorly stratified and range 0- 7 m (1- 20 ft) thk. with cobbles and pebbles ranging from east to west of volcanic rocks to metasedimentary rocks predominating; older glacial deposits and tills are poorly exposed, non- stratified or lithified, with a clay to sand matrix, and more weathered. 

Low 

Heterogeneous substrate may be unstable for building sites; dependent on abundance of clay; may be locally too permeable for waste facilities. 

Unconsolidated deposits are associated with high erodability, and the potential for collapse and failure, with higher clay contents in till; slumping and slope creep are possible. 

None 

documented 

Most recent glacial deposits may contain artifacts and campsites from Native Americans 

None 

Sand, and cunsordepos

TERTIARY Sedimentary rocks, undivided (Ts); Ash bed (Tsa) Massive deposits of sandy to silty mudstone with grayish- orange color; some sand, pebble conglomerate beds present locally with granite and quartzite clasts; some bentonite beds present locally; white ash beds form small resistant ledges 

1 to 2 m (3- 6 ft) thick with sand size fragments. 

Moderate 

Altered volcanic clays and poorly cemented rock layers render this unit rather unstable for development, especially for roads and foundations 

Resistant ledges may pose rockfall hazard, shrink and swell clays lead to instability 

None 

documented 

None 

documented None Vol
Age Map Unit (Symbol) Features and Description Erosion Resistance Suitability for Development Hazards Paleontological Resources Potential Cultural Resources Potential for Karst M

Occ

TERTIARY Mafic to intermediate intrusive bodies (Tmii) Dark- gray alkali basalt & andesite dikes intruding the Carter Creek Formation in the northwestern portion of the map coverage. Moderate to high Present only in local areas in limited extent More erodable if undercut; rockfall potential None None documented None Metal

minerassocalkali rocks 

TERTIARY Rhyolite tuff, tuffaceous sediments, and fossiliferous limestone (Trt) Tuffaceous rocks of white to buff- gray color containing sparse coarser grained tuff- breccia lenses and darker volcanic fragments; some interbedded fossiliferous limestone containing siliceous tuff in northwestern portion of map. Moderate 

Highly dissolvable limestone interbeds, if present, may render unit unstable for development, and too permeable for waste facilities 

High potential for slides and rockfalls if slope is present 

Fossils present in 

limestone 

None 

documented 

Some 

limestone 

dissolution 

possible 

Tuf

CRETACEOUS Golden Spike Formation (Kgs), Lava flow unit (informal) of the Golden Spike Formation (Kgsl) 

Andesitic lava flows with some interbedded sandstone, conglomerate, and volcaniclastic deposits; minor limestone and black shale; fragments include quartz, biotite, muscovite, plagioclase, volcanic glass and assorted lithic fragments. In lava flows, plagioclase phenocrysts 3 mm to 1 cm locally abundant; some pyroxene phenocrysts; tops of some flows marked by flow breccias; flow banding locally defined by phenocrysts. 

Moderate to 

high 

Strong bedding with contrasting rock types in sharp contact may present structural weakness; competent enough for most uses. 

Differing resistance to erosion increases possibility of rockfalls and slides 

Possible fossils in limestone interbeds 

None 

documented 

Minor 

limestone 

dissolution 

possible 

Hemadeposandeslimestconta

CRETACEOUS 

Basalt flows and flow breccia (Kba); Basalt flows and flow breccias, largepyroxene basalt (Kbpx); basalt flows and flow breccias, plagioclase basalt (Kbpl) 

Massive basalt beds, poorly exposed; some contain augite phenocrysts as large as 1 cm in a dark- green matrix; plagioclase phenocrysts common in some layers. 

Moderate 

Present only in local areas in limited extent 

Rough surface locally, could pose walking hazard 

None 

Phenocrysts may have been used as decorative elements 

None 

Au

pla

phe

CRETACEOUS 

Elkhorn Mountains Volcanics (Kem); Welded ash- flow tuff (Kemt); Andesitic lava flows (Kemf); Tuff and tuff breccia (Kemtb); Andesite flows, flow breccia and tuff breccia (Kemfb) 

Brownish- red tuff with abundant lithic fragments (mostly andesite), but sparse crystals; some dark green, fine- grained flows present; tuffs contain white plagioclase phenocrysts in dark gray- green groundmass; andesitic flows and tuffs are dark gray to purple with white, flattened plagioclase phenocrysts (“oatmeal andesite”). 

Moderate 

Good for most uses unless pervasive vesicles and fractures are present 

Rough surface locally, could pose walking hazard, differential erosion may lead to rockfall potential 

None 

Phenocrysts may have been used as decorative elements 

None 

“Oatmandesformeplagiopheno
Age Map Unit (Symbol) Features and Description Erosion Resistance Suitability for Development Hazards Paleontological Resources Potential Cultural Resources Potential for Karst M

Occ

CRETACEOUS Carter Creek Formation (Kcc) North part of map; consists of coarse- grained, cross- bedded sandstone with some light- colored tuffaceous interbeds and brownish- gray limestone lenses; locally more than 150 m (500 ft) thick. Moderate to high 

Good for most uses unless thin bedding is present, providing planes of weakness in the rock column; mostly exposed at higher elevations. 

Sandstone may be undercut leading to rockfall situations at the bases of slopes 

None described in limestones 

None 

documented 

Minor 

limestone beds 

possibly 

dissolved 

Sa

CRETACEOUS Kootenai Formation (Kk) Consists locally of four units; from bottom to top: calcareous, upper clastic, gastropod limestone, and upper quartzite members. Moderate to high Good for most uses unless pervasive dissolution is present and/or quartzite beds are undercut rendering them unstable Potential for rockfall where quartzite is undercut by dissolved limestone Gastropods found in middle to upper beds None documented Potential exists for small caves QJURASSIC Swift Formation (Jsw) Predominantly sandstone beds of light gray, tan and pink color; contains quartz veins that locally comprise more than 50% of the rock mass; chert clasts (up to 3 cm in diameter) and chert pebble conglomerate lenses also locally present. High 

Good for most uses unless highly fractured or jointed, providing planes of weakness in the rock column; mostly exposed at higher elevations 

If highly jointed or fractured and exposed on a slope, rockfall and slides possible 

None 

documented 

Large chert clasts may have provided tool material 

None 

Chert congland sa

MESOZOIC - 

PALEOZOIC Mesozoic and Paleozoic sedimentary beds (MPzs) Not exposed in Grant- Kohrs NHS; used only in cross section. NA NA NA NA NA NA 

PROTEROZOIC Belt Supergroup undivided (Ybe) Metasedimentary rocks including siltite, argillaceous quartzite, and quartzites present in northern areas of map coverage. Moderate to high 

Good for most uses unless thin bedding is present, providing planes of weakness in the rock column. Mostly exposed at higher elevations. 

If highly jointed or fractured and exposed on a slope, rockfall and slides possible 

Possible stromatolites in carbonate units 

None, unless igneous, orebearing veins are present 

Potential in 

carbonate units

Salt casome 
 GRKO Geologic Resource Evaluation Report 15

Geologic History 

This section highlights the map units (i.e., rocks and unconsolidated deposits) that occur 

in Grant- Kohrs Ranch National Historic Site and puts them in a geologic context in 

terms of the environment in which they were deposited and the timing of geologic events 

that created the present landscape. 

The known geologic history of Grant- Kohrs Ranch 

begins in the Proterozoic Eon (see figure 3). Little is 

known about this period of earth’s history. Most rocks 

on earth of Precambrian age are deformed and 

metamorphosed, losing most, if not all traces of their 

original structures. Western Montana, however, hosts 

one of the most well preserved Precambrian sedimentary 

records on earth. 

The Proterozoic rocks in the Deer Lodge Valley are part 

of the Belt Supergroup. This name refers to a stack of 

rocks formed in the ancient Belt basin that covered large 

parts of Montana, Idaho, Alberta, and Washington. The 

Belt basin formed in response to high angle faulting and 

subsidence of large continental basement blocks of rock, 

veneered by a discontinuous blanket of quartz sand. 

Dark quartzite, argillite, and carbonate of lower Belt 

formations mark the first and most extensive spread of 

the great Belt lake over basement crystalline rocks 

(Winston 1989b). 

Perhaps the most striking tectonic event during lower 

Belt deposition was block faulting along the Perry line, 

which uplifted the Dillon crustal block of the Archean 

Wyoming province to the south and downdropped 

crustal rocks to the north, forming the southern margin 

of the basin (figures 4 and 5). The resulting eastern 

indentation is called the Helena embayment and 

comprises an arm of the Belt basin. The basin extended 

across western Montana, northern Idaho, and into 

eastern Washington (Winston 1989b). 

From the relatively undisturbed, subaqueous, evenly 

layered deposits of the lower Belt formations, the 

upward transition into ripple- marked, mud- cracked 

redbeds indicates progradation of playas and alluvial 

aprons from the west across the Belt basin (Winston 

1989b). In other words, this transition shows the advance 

of continental environments, as opposed to marine, 

broadly across the basin. Sea level continued to fluctuate 

throughout the late Proterozoic. 

Many formations within the Belt Supergroup are 

widespread, extending from eastern Washington to east 

of Grant- Kohrs Ranch National Historic Site. This 

shows that, during its maximum spread, the Belt sea had 

a fetch of more than 300 km (186 mi), without including 

the western edge of the basin. This basin is inferred to be 

comparable in scale to the northern part of the modern 

Caspian Sea (Winston and Lyons 1993). 

The uppermost beds of the group record cyclic changes 

in sea level. During lowstand conditions, the variety of 

shoreline environments included: 1) braided flood 

channels filled with cross - bedded sand; 2) shallow sheet 

- flood tracks; 3) shallow ponds with mud layers and 

small- scale ripple marks; 4) exposed, desiccated 

mudflats, vulnerable to rip- ups during occasional floods; 

5) broad sand flats; and 6) beaches. These shoreline 

environments moved progressively basinward in periods 

of transgression and retreated from the basin towards 

the craton during periods of regression. 

Throughout the Paleozoic Era, Africa, and South 

America were approaching North America as the two 

great landmasses, Laurasia and Gondwana, collided. The 

ancient continent of Gondwana included Australia, 

Antarctica, Africa, South America, and India south of the 

Ganges River, plus smaller islands. Laurasia, located in 

the northern hemisphere contained the present northern 

continents. The union of Gondwana and Laurasia 

formed the supercontinent, Pangaea, which was centered 

on the equator. 

In the early Cambrian Period, the region again 

underwent uplift and erosion. Following the uplift, the 

region subsided and an ancient sea advanced bringing 

with it the depositional environments necessary to 

capture vast amounts of sediments. By Late Cambrian 

time, marine waters covered virtually all of Montana and 

Idaho. The equator ran through the length of Idaho, and 

carbonate muds accumulated under these warm- water 

conditions in much the same way as they do in the broad 

carbonate - mud shoal- bank area of the Bahaman Islands 

today (Hintze 1988). 

In the Early - Middle Devonian Period (about 401 Ma), 

the first compressive pulses of the Antler Orogeny in the 

west and the Acadian Orogeny in the east (part of the 

Appalachian Orogeny) began as landmasses accreted 

onto both the western and eastern borders of North 

America. 

To the west of Montana, a subduction zone formed and 

lithospheric plates collided against one another bending, 

buckling, folding, and faulting into a north- south 

trending mountain range that stretched from Nevada to 

Canada. 
 NPS Geologic Resources Division 16 

During orogenic events, great sheets of rocks measuring 

tens to hundreds of kilometers in width and length are 

stacked on top of one another. The weight of this rock 

depresses the land in front of the stack, or foreland area, 

and causes the foreland to subside into a foreland basin. 

As the highlands to the west were thrust above sea level 

at the beginning of the Mississippian, warm marine water 

flooded the foreland basin and spread over southeastern 

Idaho and western Montana giving rise to an extensive 

carbonate platform. 

The sea became shallower during the regression that 

followed the Antler Orogeny. The area transitioned into 

a broad karst plain of shallow- marine sandstone and 

micrite (carbonate mudstone), and by the end of the 

Mississippian, the area was again exposed to subaerial 

erosion (Poole and Sandberg 1991; Graham et al. 2002). 

Coincident with Pennsylvanian tectonics was a global 

climate shift from the warm humid environment of the 

Late Mississippian to a more arid environment in the 

region of Idaho during the Early Pennsylvanian (Rueger 

1996). 

As the Ancestral Rocky Mountains formed, the 

Ouachita- Marathon thrustbelt, the Anadarko Basin, and 

other Permian basins developed. From the 

Pennsylvanian to Middle Permian time, shallow stagnant 

seas persisted over most of the region (Baker and 

Crittenden 1961). Across the globe, the Permian Period 

appears to have been a time of dramatic environmental 

change. 

The Permian equator was oriented southwest- northeast 

through present- day Wyoming and eastern Utah. An 

arid climate prevailed in this western part of the 

supercontinent Pangaea and resulted in restricted marine 

evaporitic conditions over much of the cratonic shelf 

seaway (Peterson 1980; Graham et al. 2002). 

From rock deposits around the globe, geologists have 

documented the third, and most severe, major mass 

extinction of geologic time at the close of the Permian. 

Although not as well known as the extinction event that 

exterminated the dinosaurs at the end of the Mesozoic, 

the Permian extinction was much more extensive. 

Throughout the Triassic and Jurassic, periodic 

incursions from the north brought shallow seas flooding 

into Wyoming, Montana, and a northeast- southwest 

trending trough on the Utah and Idaho border. 

Volcanoes formed an arcuate north- south chain of 

mountains off the western coast in what is now central 

Nevada. To the south, the landmass that would become 

South America was splitting away from the Texas coast 

just as Africa and Great Britain were rifting away from 

the present East Coast and opening up the Atlantic 

Ocean. 

The Western Interior Basin was a broad, shallow, 

asymmetric basin on the southwest side of the North 

American craton during this time. The basin stretched 

northward from its southern margin in Arizona and New 

Mexico across the Canadian border. 

The next major tectonic event to leave its mark on the 

Grant- Kohrs Ranch area was regional compression. This 

resulted in the uplift of thousands of meters of 

sedimentary deposits buried in the basin covering 

western Montana. This event is known as the SevierLaramide orogeny. First, the Sevier orogeny was 

characterized by relatively thin slabs of older, upper 

Precambrian and lower Paleozoic sedimentary rocks 

being shoved eastward, over younger, upper Paleozoic 

and lower Mesozoic rocks. Later, the Laramide orogeny 

involved thick, basement- cored uplifts along shallowing 

downward thrust faults, and extensive folding. 

As the mountains rose in the west and the roughly 

north- south trending trough east of those highlands 

expanded, the Gulf of Mexico, separating North and 

South America, continued to rift open in the south. 

Marine water spilled northward into the basin. At the 

same time, marine water transgressed from the Arctic 

region. 

The seas advanced and retreated many times during the 

Cretaceous until the most extensive interior seaway ever 

recorded drowned much of western North America. The 

Western Interior Seaway was an elongate basin that 

extended from today’s Gulf of Mexico to the Arctic 

Ocean, a distance of about 4,827 km (3,000 mi) 

(Kauffman 1977). During periods of maximum 

transgression, the width of the basin was 1,600 km (1,000 

mi) from western Utah to western Iowa. The basin was 

relatively unrestricted at either end (Kauffman 1977).

For about 35 million years during the Laramide Orogeny, 

from roughly 70 Ma to 35 Ma, the collision of tectonic 

plates transformed the extensive basin of the Cretaceous 

Interior Seaway into smaller interior basins bordered by 

rugged mountains (anticlines and synclines on the scale 

of miles) (Ehrlich 1999; Graham et al. 2002). These 

mountains were the focus of intense erosion and 

weathering, resulting in basin infilling across the region 

during the Tertiary. 

Following extensive crustal thickening during the 

Laramide orogeny, melting of the lower crust occurred 

during decompression. This gave rise to the material of 

the Tertiary Boulder Batholith and the intrusions 

associated with mineral deposits found near GrantKohrs Ranch. The emplacement of these intrusions was 

facilitated by mantle upwelling and underplating of a hot 

lower crust during the regional crustal extension that 

followed decompression (Cunningham 1971; Vogel et al. 

1997). Near the end of the Laramide Orogeny, in early 

mid- Tertiary time, volcanic activity erupted across the 

area, depositing the volcanic rocks in the present Deer 

Lodge Valley (Baars 2000; Fillmore 2000). 

The deformational regime changed once again from 

compressional to extensional. The southwestern margin 

of North America underwent extensional deformation. 
 GRKO Geologic Resource Evaluation Report 17

As the crust was extended, movement along normal 

faults such as the Mount Powell fault accommodated 

crustal tension (Konizeski et al. 1968). When one block of 

rock falls relative to another, the resulting graben valley 

forms a substantial sediment sink. 

Accompanying the extension of the crust during the 

Tertiary, normal fault- bounded valleys filled with a 

variety of sediments shed from the newly exposed 

highlands. In the Grant- Kohrs area, during and after a 

period of intense regional erosion that probably 

occupied much of the Eocene and early Oligocene, 

pediments (erosion surfaces) formed throughout the 

valley (Konizeski et al. 1968). These surfaces are 

characterized by a variety of sediments ranging from 

sandstone, mudstone, limestone, and coal to volcanic ash 

deposits. This assortment reflects the tectonic and 

climatic variations during the Tertiary. 

The Quaternary Period is subdivided into two epochs: 1) 

the Pleistocene, which ranges from about 1.6 Ma to 

10,000 years before present (B.P.), and 2) the younger 

Holocene Epoch that extends from 10,000 years B.P. to 

the present. The Pleistocene Epoch is known as the Ice 

Age and is marked by multiple episodes of continental 

and alpine glaciation. 

During the Pleistocene great continental glaciers, 

thousands of feet thick, advanced and retreated in 

approximately 100,000- year cycles. Huge volumes of 

water were stored in the glaciers during glacial periods 

causing sea level to drop as much as 91 m (300 ft) 

(Fillmore 2000). Glacial deposits of till, outwash, and 

moraines are all present in the Deer Lodge Valley 

attesting to glacial conditions in the area (figure 6). 

The glacial deposits from the Pleistocene and Holocene 

and recent alluvial terrace, valley fill, and gravel deposits 

along the streams and rivers, represent Quaternary age 

processes at Grant- Kohrs Ranch National Historic Site 

(Konizeski et al. 1968). Landslide and slope deposits are 

also prevalent in recent sediments due to the relief along 

terraces. 
 NPS Geologic Resources Division 18 

Figure 3. Geologic time scale; adapted from the U.S. Geological Survey. Red lines indicate major unconformities between eras. Included are 

major events in life history and tectonic events occurring on the North American continent. Absolute ages shown are in millions of years. 
 GRKO Geologic Resource Evaluation Report 19

Figure 4. Showing inferred Proterozoic structure of the Belt basin during Late Belt Supergroup deposition. Note numerous faults providing 

means for uplift south of the basin (sediment source area). “U” indicates the uplifted side of the fault, and “D” indicates the downdropped 

side. Modified from Ackman 1988. 
 NPS Geologic Resources Division 20 

Figure 5. Map of present day structural features in the Grant-Kohrs Ranch area superimposed on Mid-Proterozoic fault lines (blue) with 

cratonic blocks labeled in green. Red lines indicate fold axes, black lines with teeth indicate thrust faults with teeth on overriding plate, 

black lines with bar and ball show normal faults with the symbol on the downthrown block. Adapted from Winston 1989. 
 GRKO Geologic Resource Evaluation Report 21

Figure 6. Diagrammatic view of a retreating glacier with a recent terminal moraine and a broad space between the moraine and the glacier 

front. Note the variety of deposits associated with glacial melt many of which exist on the landscape at Grant-Kohrs Ranch National Historic 

Site. 
 NPS Geologic Resources Division 22 

Glossary 

This glossary contains brief definitions of technical geologic terms used in this report. Not all 

geologic terms used are referenced. For more detailed definitions or to find terms not listed 

here please visit: http://wrgis.wr.usgs.gov/docs/parks/misc/glossarya.html. 

alluvium. Stream- deposited sediment that is generally 

rounded, sorted, and stratified. 

aquifer. Rock or sediment that are sufficiently porous, 

permeable, and saturated to be useful as a source of 

water. 

ash (volcanic). Fine pyroclastic material ejected from a 

volcano (also see tuff). 

basement. The undifferentiated rocks, commonly 

igneous and metamorphic, that underlie the rocks of 

interest. 

basin (structural). A doubly- plunging syncline in which 

rocks dip inward from all sides. 

basin (sedimentary). Any depression, from continental 

to local scales, into which sediments are deposited. 

batholith. A massive, discordant pluton, greater than 100 

km2

, (39.6 mi2) often formed from multiple intrusions. 

bed. The smallest sedimentary strata unit, commonly 

ranging in thickness from one centimeter to a meter or 

two and distinguishable from beds above. 

block (fault). A crustal unit bounded by faults, either 

completely or in part. 

cementation. Chemical precipitation of material into 

pores between grains that bind the grains into rock. 

clastic. Rock or sediment made of fragments or preexisting rocks. 

clay. Clay minerals or sedimentary fragments the size of 

clay minerals (<2 cm). 

conglomerate. A coarse- grained sedimentary rock with 

clasts larger than 2 mm in a fine- grained matrix. 

craton. The relatively old and geologically stable interior 

of a continent (also see continental shield). 

cross-bedding. Uniform to highly- varied sets of inclined 

sedimentary beds deposited by wind or water that 

indicate distinctive flow conditions. 

cross section. A graphical interpretation of geology, 

structure, and/or stratigraphy in the third (vertical) 

dimension based on mapped and measured geological 

extents and attitudes depicted in an oriented vertical 

plane. 

deformation. A general term for the process of faulting, 

folding, shearing, extension, or compression of rocks 

as a result of various Earth forces. 

dike. A tabular, discordant igneous intrusion. 

dip. The angle between a structural surface and a 

horizontal reference plane measured normal to their 

line of intersection. 

drainage basin. The total area from which a stream 

system receives or drains precipitation runoff. 

extrusive. Of or pertaining to the eruption of igneous 

material onto the surface of Earth. 

fault. A subplanar break in rock along which relative 

movement occurs between the two sides. 

formation. Fundamental rock- stratigraphic unit that is 

mappable and lithologically distinct from adjoining 

strata and has definable upper and lower contacts. 

fracture. Irregular breakage of a mineral; also any break 

in a rock (e.g., crack, joint, fault) 

graben. A down- dropped structural block bounded by 

steeply- dipping, normal faults (also see horst). 

horst. An uplifted structural block bounded by highangle normal faults. 

igneous. Refers to a rock or mineral that originated from 

molten material; one of the three main classes or rocks: 

igneous, metamorphic, and sedimentary. 

intrusion. A body of igneous rock that invades older 

rock. The invading rock may be a plastic solid or 

magma that pushes its way into the older rock. 

joint. A semi- planar break in rock without relative 

movement of rocks on either side of the fracture 

surface. 

lacustrine. Pertaining to, produced by, or inhabiting a 

lake or lakes. 

landslide. Any process or landform resulting from rapid 

mass movement under relatively dry conditions. 

levees. Raised ridges lining the banks of a stream; may be 

natural or artificial. 

lineament. Any relatively straight surface feature that can 

be identified via observation, mapping, or remote 

sensing, often representing tectonic features. 

lithology. The description of a rock or rock unit, 

especially the texture, composition, and structure of 

sedimentary rocks. 

lithosphere. The relatively rigid outmost shell of Earth’s 

structure, 50 to 100 km (31 to 62 mi) thick, that 

encompasses the crust and uppermost mantle. 

mantle. The zone of Earth’s interior between crust and 

core. 

matrix. The fine- grained interstitial material between 

coarse grains in porphyritic igneous rocks and poorly 

sorted clastic sediments or rocks. 

meanders. Sinuous lateral curves or bends in a stream’s 

channel. 

metamorphism. Literally, “change in form”. 

Metamorphism occurs in rocks with mineral 

alteration, genesis, and/or recrystallization from 

increased heat and pressure. 

mud cracks. Cracks formed in clay, silt, or mud by 

shrinkage during subaerial dehydration. 

nonconformity. An erosional surface preserved in strata 

in which crystalline igneous or metamorphic rocks 

underlie sedimentary rocks. 

normal fault. A dip- slip fault in which the hanging wall 

moves down relative to the footwall. 
 GRKO Geologic Resource Evaluation Report 23

orogeny. A mountain- building event, particularly a wellrecognized event in the geological past (e.g. the 

Laramide orogeny). 

outcrop. Any part of a rock mass or formation that is 

exposed or “crops out” at Earth’s surface. 

outwash. Glacial sediment transported and deposited by 

meltwater streams. 

overbank deposits. Alluvium deposited outside a stream 

channel during flooding. 

Pangaea. A theoretical, single supercontinent that 

existed during the Permian and Triassic Periods 

pebble. Generally, small, rounded, rock particles from 4 

to 64 mm in diameter. 

pediment. A gently sloping, erosional bedrock surface at 

the foot of mountains or plateau escarpments. 

permeability. A measure of the ease or rate that fluids 

move through rocks or sediments. 

plateau. A broad, flat- topped topographic high of great 

extent and elevation above the surrounding plains, 

canyons, or valleys (both land and marine landforms). 

plate tectonics. The theory that the lithosphere is broken 

up into a series of rigid plates that move over Earth’s 

surface above a more fluid aesthenosphere. 

point bar. A sand and gravel ridge deposited in a stream 

channel on the inside of a meander where flow 

velocity slows. 

porosity. The proportion of void space (cracks, 

interstices) in a volume of a rock or sediment. 

regression. A long- term seaward retreat of the shoreline 

or rrelative fall of sea level. 

reverse fault. A contractional, high angle (>45o), dip- slip 

fault in which the hanging wall moves up relative to the 

footwall (also see thrust fault). 

ripple marks. The undulating, subparallel, usually smallscale, ridge pattern formed on sediment by the flow of 

wind or water. 

sandstone. Clastic sedimentary rock of predominantly 

sand- sized grains. 

scarp. A steep cliff or topographic step resulting from 

vertical displacement on a fault or by mass movement. 

sediment. An eroded and deposited, unconsolidated 

accumulation of lithic and mineral fragments. 

sedimentary rock. A consolidated and lithified rock 

consisting of detrital and/or chemical sediment(s). 

shale. A clastic sedimentary rock made of clay- sized 

particles that exhibit parallel splitting properties. 

silt. Clastic sedimentary material intermediate in size 

between fine- grained sand and coarse clay (1/256- 1/16 

mm). 

siltstone. A variable- lithified sedimentary rock with siltsized grains. 

slump. A generally large, coherent mass movement with 

a concave- up failure surface and subsequent 

backward rotation relative to the slope. 

stratigraphy. The geologic study of the origin, 

occurrence, distribution, classification, correlation, 

age, etc. of rock layers, especially sedimentary rocks. 

strike. The compass direction of the line of intersection 

that an inclined surface makes with a horizontal plane. 

strike-slip fault. A fault with measurable offset where the 

relative movement is parallel to the strike of the fault. 

subsidence. The gradual sinking or depression of part of 

Earth’s surface. 

tectonic. Relating to large- scale movement and 

deformation of Earth’s crust. 

terraces. Step- like benches surrounding the present 

floodplain of a stream due to dissection of previous 

flood plain(s), stream bed(s), and/or valley floor(s). 

thrust fault. A contractional, dip- slip fault with a 

shallowly dipping fault surface (<45o

) where the 

hanging wall moves up and over relative to the 

footwall. 

transgression. Landward migration of the sea due to a 

relative rise in sea level. 

trend. The direction or azimuth of elongation or a linear 

geological feature. 

tuff. Generally fine- grained, igneous rock formed of 

consolidated volcanic ash. 

unconformity. A surface within sedimentary strata that 

marks a prolonged period of nondeposition or 

erosion. 

volcanic. Related to volcanoes; describes igneous rock 

crystallized at or near Earth’s surface (e.g., lava). 

water table. The upper surface of the saturated (phreatic) 

zone. 

weathering. The set of physical, chemical, and biological 

processes by which rock is broken down in place. 
 NPS Geologic Resources Division 24 

References 

This section provides a listing of references cited in this report. It also contains general 

references that may be of use to resource managers. A more complete geologic 

bibliography is available and can be obtained through the NPS Geologic Resources 

Division. 

Baars, D. L. 2000. The Colorado Plateau. Albuquerque, 

NM: University of New Mexico press. 

Baker, A.A., M.D. Crittenden, Jr. 1961. Geology of the 

Timpanogos Cave Quadrangle, Utah. U.S. Geological 

Survey, Geologic Quadrangle Map - Report: GQ- 0132. 

Bedunah, D., T. Jones. 2001. Flood Plain Vegetation 

Changes on the Grant- Kohrs Ranch National Historic 

Site Between 1993 and 2000.

http://www.nps.gov/archive/grko/Vegetation%20Cha

nges.pdf (accessed January 20, 2007). 

Berg, R.B. 2004. Geologic Map of the Deer Lodge and 

Conleys Lake 7 1⁄2’ Quadrangles, Powell County, 

Southwestern Montana. Montana Bureau of Mines and 

Geology Open File Report 509. 

Breuninger, A.B. 2000. Effects of floodplain remediation 

on bed sediment contamination in the Upper Clark Fork 

River basin, western Montana. Master’s thesis: 

University of Montana. 

Butler, J.A. 2003. Metal contamination of the Clark Fork 

River, western Montana; a comparative study of metal 

concentrations in fine- grained bed sediment and 

source material. Abstracts with Programs - Geological 

Society of America 35 (5): 7. 

Cunningham, F.F. 1971. The Silent City of Rocks, a 

bornhardt landscape in the Cotterrel Range, South 

Idaho, USA. Zeitschrift fuer Geomorphologie 15 (4): 

404- 429. 

Dodge, K.A., M.I. Hornberger, I.R. Lavigne. 2003. 

Water- quality, bed- sediment, and biological data 

(October 2001 through September 2002) and statistical 

summaries of data for streams in the upper Clark Fork 

Basin, Montana. U. S. Geological Survey, Open- File 

Report: OF 03- 0356. 

Dodge, K.A., M.I. Hornberger, I.R. Lavigne. 2004. 

Water- quality, bed- sediment and biological data 

(October 2002 through September 2003) and statistical 

summaries of data for streams in the upper Clark Fork 

Basin, Montana. U. S. Geological Survey, Open- File 

Report: OF 2004- 1340. 

Duaime, T.E., R.A. Appleman. 1990. Storm- event 

monitoring on the upper Clark Fork River basin, Silver 

Bow and Deer Lodge counties. MBMG Open- File 

Report: 228. 

Dundas, R.G. 1990. Paleontology and geology of the late 

Pleistocene Hoover Creek terrace, Granite and Powell 

counties, Montana. Northwest Geology 19: 31- 37. 

Dyman, T.S., R.G. Tysdal, C.A. Wallace, S.E. Lewis. 1993. 

Correlation chart of Lower and Lower- Upper 

Cretaceous Blackleaf Formation, eastern Pioneer 

Mountains, southwestern Montana, to Drummond, 

central- western Montana. AAPG Bulletin 77 (8): 1446. 

Ehrlich, T.K. 1999. Fault analysis and regional balancing 

of Cenozoic deformation in northwest Colorado and 

south- central Wyoming. Master’s thesis: Colorado 

State University. 

Fillmore, R. 2000. The Geology of the Parks, Monuments 

and Wildlands of Southern Utah. The University of 

Utah Press. 

Graham, J. P., T.L. Thornberry, S.A. O’Meara. 2002 

(unpublished). Geologic Resources Inventory for Mesa 

Verde National Park. National Park Service, Fort 

Collins, CO: Inventory and Monitoring Program. 

Hintze, L.F. 1988. Geologic history of Utah. Brigham 

Young University Geologic Studies, Special 

Publications: 7. 

Hornberger, M.I., J.H. Lambing, S.N. Luoma, E.V. 

Axtmann. 1997. Spatial and temporal trends of trace 

metals in surface water, bed sediment, and biota of the 

upper Clark Fork Basin, Montana, 1985- 95. U. S. 

Geological Survey - Open- File Report: OF 97- 0669. 

I.H. 2007. The Effects of Heavy Metal Toxicity. 

Incredible Horizons Digestive Problems Page, 

http://www.incrediblehorizons.com/toxicity%20&%2

0Autistic- symtoms.chelating.htm (accessed January 

20, 2007). 

Johns, C. 1995. Contamination of riparian wetlands from 

past copper mining and smelting in the headwaters 

region of the Clark Fork River, Montana, U.S.A. 

Journal of Geochemical Exploration 52, (1- 2): pp. 193-

203. 

Kauffman, E. G. 1977. Geological and biological 

overview: Western Interior Cretaceous Basin: 

Mountain Geologist 14: 75- 99. 
 GRKO Geologic Resource Evaluation Report 25

Konizeski, R.L., R.G. McMurtrey, A. Brietkrietz, A. 1968. 

Geology and ground- water resources of the Deer Lodge 

Valley, Montana. U. S. Geological Survey WaterSupply Paper: 1968. 

Lonn, J. 2001. Floater's guide to the belt rocks of 

Alberton Gorge, western Montana. Northwest Geology

20: 51- 61. 

Madison, J.P., J.D. Lonn, R.K. Marvin, J.J. Metesh, R. 

Wintergerst. 1998. Abandoned- inactive mines program, 

Deer Lodge National Forest; Volume IV, Upper Clark 

Fork River drainage. MBMG Open- File Report. 

Moore, J.N., W.W. Woessner. 2000. Geologic, Soil Water 

and Groundwater Report – 2000, Grant- Kohrs Ranch 

National Historic Site. Department of the Interior, U.S. 

National Park Service. 

Nimick, D.A. 1990. Stratigraphy and chemistry of metalcontaminated floodplain sediments, upper Clark Fork 

River valley, Montana. Master’s thesis: University of 

Montana, Master’s thesis. 

Nimick, D.A. 1993. Hydrology and water chemistry of 

shallow aquifers along the upper Clark Fork, western 

Montana. U. S. Geological Survey, Water- Resources 

Investigations: WRI 93- 4052. 

Nimick, D.A., J.N. Moore. 1994. Environmental 

chemistry of fluvially deposited mine tailings in the 

upper Clark Fork Valley, Montana. Eos, Transactions, 

American Geophysical Union 75 (44): 237. 

Nimick, D.A., J.N. Moore. 1994. Stratigraphy and 

chemistry of sulfidic flood- plain sediments in the 

upper Clark Fork Valley, Montana. ACS Symposium 

Series 550: 276- 288. 

Peterson, J. A. 1980. Permian paleogeography and 

sedimentary provinces, west central United States. In 

Thomas D. Fouch and Esther R. Magathan, eds., 

Paleozoic Paleogeography of the West- Central United 

States, eds. Fouch, T.D., E.R. Magathan, 271- 292. 

Rocky Mountain Section, SEPM (Society for 

Sedimentary Geology. 

Poole, F. G., C.A. Sandberg. 1991. Mississippian 

paleogeography and conodont biostratigraphy of the 

western United States. In Paleozoic Paleogeography of 

the Western United States – II, eds. Cooper, J.D., C.H. 

Stevens, 107- 136. Society of Economic Paleontologists 

and Mineralogists (SEPM), Pacific Section. 

Power, T.M. 1996. The Wealth of Nature. Issues in Science 

and Technology. 

http://www.findarticles.com/p/articles/mi_qa3622/is_1

99604/ai_n8743214/pg_1 (accessed January 21, 2007). 

Rasmussen, D.L., R.W. Fields. 1980. Road log No. 1; 

Missoula to Flint Creek via upper Clark Fork valley 

and Drummond. State of Montana Bureau of Mines and 

Geology, Special Publication (82): 1- 9. 

Reynolds, P.H., J.W. Sears. 1989. Pre- middle Eocene 

high- level gravel in the Garnet Range, west- central 

Montana. Abstracts with Programs - Geological Society 

of America 21 (5): 133. 

Rotegard, L. 2006. Annual Report – Grant- Kohrs Ranch 

National Historic Site, FY05. Department of the 

Interior, National Park Service. 

Rueger, B. F. 1996. Palynology and its relationship to 

climatically induced depositional cycles in the Middle 

Pennsylvanian (Desmoinesian) Paradox Formation of 

Southeastern Utah. U.S. Geological Survey, Bulletin: 

2000- K. 

Schlumberger. 2007. Oil Field Glossary – Precipitate. 

http://www.glossary.oilfield.slb.com/Display.cfm?Ter

m=precipitate (accessed January 21, 2007). 

Smith, D.J., J.H. Lambing, D.A. Nimick, C. Parrett, M. 

Ramey, W. Schafer, W. 1998. Geomorphology, floodplain tailings, and metal transport in the upper Clark 

Fork valley, Montana. U. S. Geological Survey, WaterResources Investigations: WRI 98- 4170. 

Swanson, B.J. 2002. Bank erosion and metal loading in a 

contaminated floodplain system, upper Clark Fork River 

valley, Montana. Master’s thesis: University of 

Montana. 

Trexler, B.D.Jr., D.A. Ralston, D.A. Reece, R.E. Williams. 

1975. Sources and causes of acid mine drainage. Idaho 

Bureau of Mines and Geology: Pamphlet 165. 

Vogel, T.A., F.W. Cambray, L. Feher, K.N. Constenius. 

1997. Petrochemistry and emplacement history of the 

Wasatch igneous belt, central Wasatch Mountains, 

Utah. Geological Society of America – Abstracts with 

Programs 29 (6): A- 282. 

Winston, D. 1989. Introduction to the Belt. In Volcanism 

and plutonism of western North America; Volume 2, 

Middle Proterozoic Belt Supergroup, western Montana, 

ed. Hanshaw, P.M, 1- 6. American Geophysical Union. 

Winston, D. 1989b. A Sedimentologic and tectonic 

interpretation of the Belt Supergroup. In Volcanism 

and plutonism of western North America; Volume 2, 

Middle Proterozoic Belt Supergroup, western Montana, 

ed. Hanshaw, P.M, 1- 6. American Geophysical Union. 

Winston, D., T. Lyons. 1997. Sedimentary cycles in the St. 

Regis, Empire and Helena Formations of the middle 

Proterozoic Belt Supergroup, northwestern Montana. 

In Geologic guidebook to the Belt- Purcell Supergroup, 

Glacier National Park and vicinity, Montana and 

adjacent Canada; field trip guidebook for Belt 

symposium III, ed. Link, P.K., 21- 51. 
 NPS Geologic Resources Division 26 

Appendix A: Geologic Map Graphic 

The following page provides a preview or “snapshot” of the geologic map for GrantKohrs Ranch National Historic Site. For a poster size PDF of this map or for digital 

geologic map data, please see the included CD or visit the GRE publications webpage: 

http://www2.nature.nps.gov/geology/inventory/gre_publications.cfm 


 GRKO Geologic Resource Evaluation Report 29

Appendix B: Scoping Summary 

The following excerpts are from the GRE scoping summary for Grant- Kohrs Ranch 

National Historic Site. The scoping meeting occurred August 19, 2002; therefore, the 

contact information and Web addresses referred to herein may be outdated. Please 

contact the Geologic Resources Division for current information. 

Executive Summary 

A geologic resources evaluation workshop was held for 

Grant- Kohrs Ranch NHS (GRKO) on August 19, 2002 to 

view and discuss the park’s geologic resources, to 

address the status of geologic mapping for compiling 

both paper and digital maps, and to assess resource 

management issues and needs. Cooperators from the 

NPS Geologic Resources Division (GRD), NPS GrantKohrs Ranch NHS, and the Montana Bureau of Mines 

and Technology were present for the workshop. 

This involved a field trip to view the geology of the 

Grant- Kohrs Ranch NHS area with the Montana Bureau 

of Mines and Geology and a scoping session to present 

overviews of the NPS Inventory and Monitoring (I&M) 

program, the Geologic Resources Division, and the ongoing Geologic Resources Evaluation (GRE). Round 

table discussions involving geologic issues for GrantKohrs Ranch NHS included interpretation, the status of 

geologic mapping efforts, sources of available data, and 

action items generated from this meeting. 

Because of the upstream impacts of mining in Butte, 

Montana, over the last 100 years, heavy metals have 

impacted the GRKO area negatively. On the field trip, 

the group was shown a deposit of arsenic that resulted 

from a large flood event in 1908 in stream banks flowing 

through the park. Considerable soil had been developed 

on top of the deposit in the last 94 years. Ben Bobowski is 

interested in expanding the existing two park 

quadrangles of interest (Deer Lodge and Conleys Lake) 

to include more quadrangles that take in the drainage 

basin of the surrounding area. 

Geologic Mapping 

Existing Geologic Maps and Publications 

The bounding coordinates for each map were noted and 

entered into a GIS to assemble an index geologic map. 

Separate coverage’s were developed based on scales 

(1:24,000, 1:100,000, etc.) available for the specific park. 

Numerous geologic maps at varying scales and vintages 

cover the area. Index maps were distributed to each 

workshop participant during the scoping session. 

Status 

At present, there are a few maps of various scales 

covering the GRKO area in published form. Currently 

the Montana Bureau of Mines and Geology are 

producing a geologic map of the Deer Lodge 15' 

quadrangle at 1:48,000 scale of the following 

quadrangles: Deer Lodge (one of two current GRKO 

quadrangles of interest); Baggs Creek, Orofino Creek, 

and Sugarloaf Mountain. They showed a draft that is 

very near completion and is also in ArcInfo format. 

There is a textual document with ancillary map 

information and map unit descriptions as well that will 

accompany this. They intend to publish it as an open file 

report in mid- 2003. 

The Conleys Lake quadrangle is not currently mapped at 

a scale suitable for park management needs and Dick 

Berg is interested in doing the mapping of the entire 

quadrangle at 1:24,000 scale. He anticipates that he could 

begin the work in 2003 upon completion of the Deer 

Lodge 15' geologic map. They would also deliver this map 

to the NPS in digital format like the Deer Lodge 

quadrangle. 

The Conley's lake quad is covered on Butte 250k and the 

62.5s and 63360s, but data are quite coarse and dated and 

probably more refined mapping would be desired. 

However, there is probably good textual information on 

these maps that might be able to be gleaned for the 

current project. 

Dick Berg is interested in mapping the Conleys Lake 7.5' 

quad in 2003 if NPS can assist financially or otherwise. 

MT GS would then open file it. We'll send them our 

template to them. 

Dick Berg suggested mapping the following quadrangles 

to get better coverage for the drainage basin of the 

GRKO area: Garrison, Conleys Lake, Deer Lodge, 

Racetrack, Orofino Creek, Warm Springs, Orofino 

Mountain, Opportunity, Ramose, Butte North, Elk Park 

Pass, Buxton, Butte South, Homestake, Tucker Creek 

As far as a geologic report for the park, GRE staff may be 

able to use portions of the Deer Lodge 15' map text and 

may also consult the 1:250,000 Butte sheet for its ancillary 

information. 

Digital Geologic Map Coverage 

The Montana Bureau of Mines has completed 

digitization of numerous 1:100,000 scale maps within the 

state of Montana. They are available to view as an index 

map for download from http://www.mbmg.mtech.edu. 

GRE staff needs to call their publication and sales office 

to get FTP access to the actual digital files. Karen Porter 

says to call Judy for digital and hardcopy and tell them 

we're a federal agency and they'll allow us to have them 

at no charge. 
 NPS Geologic Resources Division 30 

Miscellaneous Notes 

In a brainstorming session, GRKO staff says the main 

geologic issues at the park are as follows: 

• Ground- water movement; 

• surface water movement as affected by surficial 

deposits and soils and how they relate to contaminant 

transport from upstream acid mine drainage 

• Non- point source run- off and how it is affecting 

neighbors and the park plant communities. 

• Need to Define influences of bedrock and topography 

on watersheds 

To better understand these processes, GRKO has an indepth environmental quality assessment done in 

cooperation with several universities. It is entitled "US 

Department of Interior Site Characterization and 

Natural Resource Damage Assessment Studies, GrantKohrs Ranch NHS and Bureau of Land Management, 

2000- 2001; Clark Fork River Operable Unit of the 

Milltown Reservoir Sediments NPL Site; July 8, 2002" 

Dan Nottingham distributed CD- ROM copies of the 

above to a few of the meeting attendants, including GRE 

staff. 

Ben Bobowsky is interested in water rights in the area 

and needs NPS- WRD's Horizon reports. Folks to 

contact in Fort Collins are either Dan Kimball or Dean 

Tucker, who should be able to assist with both 

groundwater and surficial water issues. 

Ed Deal says the Montana Bureau of Mines and Geology 

is producing Ground- water assessments for the area that 

should be of great benefit to GRKO as well. It was also 

mentioned that Tom Patton has a database on water 

issues for the area at the Montana Bureau of Mines and 

Geology. 

GRKO GIS support has come from Theresa Ely's shop in 

the Intermountain Region GIS Support Office, but Ben 

Bobowsky said he is looking to hire a full- time GIS 

position into GRKO in the very near future. 

Other Desired Data Sets for GRKO 

Soils 

Soils maps are also of interest to GRKO staff. Tim 

Connors will check with Pete Biggam (NPS- Soil 

Scientist) on the status of soils mapping for the area; will 

require more follow- up. 

List of Attendees for Grant-Kohrs Ranch National Historic Site Workshop 

NAME AFFILIATION PHONE E- MAIL 

Dick Berg Montana Bureau of Mines 

and Geology dberg@mtech.edu 

Ben Bobowski NPS- GRKO (406)- 846- 2070 Ben_Bobowski@nps.gov 

Tim Connors NPS, Geologic Resources 

Division (303) 969- 2093 Tim_Connors@nps.gov 

Ed Deal Montana Bureau of Mines 

and Geology edeal@mtech.edu 

Bruce Heise NPS, Geologic Resources 

Division (303) 969- 2017 Bruce_Heise@nps.gov 

Greg Nottingham NPS- GRKO (406)- 846- 2070, ext. 

29 greg_nottingham@nps.gov 

Karen Porter Montana Bureau of Mines 

and Geology (406)- 496- 4327 kporter@mtech.edu 
The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific and other 

information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and affiliated Island 

Communities. 

Grant-Kohrs Ranch National Historic Site 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2007/004 

NPS D-58, June 2007 

National Park Service 

Director • Mary A. Bomar 

Natural Resource Stewardship and Science 

Associate Director • Michael A. Soukup 

Natural Resource Program Center 

The Natural Resource Program Center (NRPC) is the core of the NPS Natural Resource Stewardship and 

Science Directorate. The Center Director is located in Fort Collins, with staff located principally in 

Lakewood and Fort Collins, Colorado and in Washington, D.C. The NRPC has five divisions: Air 

Resources Division, Biological Resource Management Division, Environmental Quality Division, Geologic 

Resources Division, and Water Resources Division. NRPC also includes three offices: The Office of 

Education and Outreach, the Office of Inventory, Monitoring and Evaluation, and the Office of Natural 

Resource Information Systems. In addition, Natural Resource Web Management and Partnership 

Coordination are cross- cutting disciplines under the Center Director. The multidisciplinary staff of NRPC 

is dedicated to resolving park resource management challenges originating in and outside units of the 

national park system. 

Geologic Resources Division 

Chief • David B. Shaver 

Planning Evaluation and Permits Branch Chief • Carol McCoy 

Credits 

Author • Trista Thornberry- Ehrlich

Editing • Sid Covington and Melanie Ransmeier 

Digital Map Production • Georgia Hybels, Anne Poole and Montana Bureau of Mines and Geology 

Map Layout Design • Andrea Croskrey
Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, CO 80225 

http://www.nature.nps.gov/geology/inventory/ 

(303) 969-2090 

EXPERIENCE YOUR AMERICATM 

National Park Service 

U.S. Department of the Interior