Voyageurs National Park 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2007/007 

National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 
THIS PAGE: 

A geologist highlights a geologic contact during a Geologic 

Resource Evaluation scoping field trip at Voyageurs NP, MN 

ON THE COVER: 

Aerial view of Voyageurs NP, MN 

NPS Photos 
Voyageurs National Park 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2007/007 

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.
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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: 

Graham, J. 2007. Voyageurs National Park Geologic Resource Evaluation Report. Natural 

Resource Report NPS/NRPC/GRD/NRR—2007/007. National Park Service, Denver, 

Colorado. 

NPS D- 158, June 2007 
 VOYA Geologic Resource Evaluation Report iii

Table of Contents 

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

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

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

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

Park Setting and History.............................................................................................................................................2

Geologic Setting .........................................................................................................................................................3

Geologic Issues............................................................................................................. 7

Submerged Boating Hazards......................................................................................................................................7

Hydrogeology .............................................................................................................................................................7

Mineral Resources......................................................................................................................................................7

Abandoned Mine Hazards ..........................................................................................................................................8

Surficial Deposits......................................................................................................................................................10

Earthquake Potential ................................................................................................................................................10

Geologic Features and Processes............................................................................. 11

Precambrian Features and Processes .....................................................................................................................11

Quaternary Features and Processes........................................................................................................................12

Ellsworth Rock Garden.............................................................................................................................................13

Map Unit Properties .................................................................................................... 15

Map Unit Properties Table........................................................................................................................................16

Geologic History.......................................................................................................... 19

Precambrian .............................................................................................................................................................19

Quaternary................................................................................................................................................................20

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

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

Appendix A: Geologic Map Graphic .......................................................................... 25

Appendix B: Scoping Summary................................................................................. 27

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

List of Figures 

Figure 1. Map of Voyageurs National Park. ...................................................................................................................4

Figure 2. Geologic time scale.........................................................................................................................................5

Figure 3. Schematic drawing of subprovinces of the Superior Province. .......................................................................6

Figure 4. Photo of Precambrian rock exposure............................................................................................................14

Figure 5. Precambrian subduction and development of subprovinces.........................................................................21
 VOYA 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 Voyageurs National Park in Minnesota. It contains 

information relevant to resource management and scientific research. 

Located in the southern part of the Canadian Shield and 

sharing a common boundary with Canada, Voyageurs 

National Park contains some of the oldest rocks on the 

North American continent. The bedrock records 

evidence of mountain- building episodes that occurred 

approximately 2,500 million years ago as well as 

continental glaciation that affected the area as recently as 

10,000 years ago. Congress recognized Voyageurs 

geologic significance in the park’s 1971 enabling statute. 

A Geologic Resources Inventory (now Geologic 

Resources Evaluation) scoping meeting was held at 

Voyageurs National Park on June 1- 2, 2000, to discuss 

the status of geologic mapping in the park, to assess 

resource management issues and needs, and to evaluate 

the geologic resources (features and processes) of the 

park. 

The geologic issues identified at Voyageurs National 

Park fall into the following categories: 

• Submerged boating hazards 

• Surface water 

• Historic mining and abandoned mines 

• Geologic interpretation 

• Earthquake potential 

Islands of various shapes and sizes dot the lakes in 

Voyageurs National Park. Submerged rocks along their 

rocky shorelines pose hazards to boats and canoes. 

Shallow areas and narrow waterways connecting the 

lakes may conceal rocks just below the surface. 

Navigation charts identifying these hazards could help 

visitors avoid serious accidents and possible injuries. 

Voyageurs NP preserves and protects a hydrologically 

complex and sensitive environment. Impermeable 

bedrock impedes groundwater flow and thin soils allow 

relatively rapid surface runoff. The lakes comprising 

much of the park are controlled reservoirs and are a 

primary water source for both domestic and industrial 

use in the Voyageurs area. Surface runoff into the lakes 

may impact water quality by introducing heavy sediment 

loads, higher turbidity, and contamination from 

historical mining and milling activities. 

Northern Minnesota has experienced gold mining 

booms in the past. Several abandoned mines from the 

short lived gold boom of the late nineteenth century still 

can be found in the northwestern part of the park. Open 

adits and shafts associated with some of these mines may 

pose safety hazards, and liquid mercury from the milling 

process may have contaminated lake sediments. 

Interpretation of the complex metamorphic geology of 

Voyageurs is of great interest to the park natural 

resources staff. The metamorphic rocks at Voyageurs are 

the result of high pressures and elevated temperatures 

found at great depths in the crust. Siltstones and shales 

transformed into schists and gneisses; sandstones and 

conglomerates metamorphosed into quartzites and 

metaconglomerates; and oceanic sediments and basaltic 

lavas formed greenstone belts containing such distinct 

features as pillow lavas and metal deposits. 

The Pleistocene Ice Age left its mark on Voyageurs 

National Park. Glacial erratics, or ice- rafted rocks, are 

abundant in the park. These displaced blocks range in 

size from pebbles to blocks the size of automobiles. 

Ground moraine debris, interspersed with lakebed 

sediments, forms a distinctive undulating topography. 

Glacial striations and groove marks that were scratched 

and gouged into the bedrock by moving glaciers show 

the direction of ice movement. Striations in Voyageurs 

point south, south by southwest, and southwest. 

Thirty- two distinct rock units have been mapped in the 

vicinity of Voyageurs. The igneous and metamorphic 

units have a relatively high resistance to erosion and 

present few geologic hazards. Some rock units have 

provided sites for pictographs and petroglyphs. Most of 

the geologic units in Voyageurs have global significance 

because Archean rocks are relatively rare. 

The rocks exposed at Voyageurs National Park preserve 

windows into both the very distant past and the very 

recent past. The degree of metamorphism and 

deformation of Archean bedrock at Voyageurs records at 

least one mountain- building episode followed by 

millions of years of erosion. Few such exposures exist 

elsewhere on earth. The relatively recent Pleistocene ice 

age, also evident in Voyageurs, left a history recorded in 

the grooves and striations on bedrock, glacial erratics, 

and unconsolidated sediment. 

Although Minnesota has one of the lowest occurrence 

levels of earthquakes in the United States, participants at 

the 2000 scoping meeting recognized earthquakes as a 

potential hazard for Voyageurs. In the unlikely event of a 

severe earthquake, movement would likely occur along 

ancient fault planes that cut through the park. 
 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 Resources 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. These 

products support the stewardship of park resources and 

are designed for non- geoscientists. 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/). 

Park Setting and History 

Voyageurs National Park protects 218,200.17 acres in the 

lake country of northern Minnesota. Of these, 134,246 

acres are land and 83,808 acres are water. Roads end a 

short distance beyond the entry points into the park. 

Watercraft are necessary for access to the Kabetogama 

Peninsula, the islands, and most of the shoreline of the 

park. In the winter, access may be gained by crosscountry skis, snowshoes, or snowmobiles. The park 

includes 655 miles (1,054 km) of undeveloped shoreline 

and over 1,000 islands. Located about 15 miles (24 km) 

east of International Falls, Minnesota, Voyageurs 

National Park follows the international boundary 

between the US and Ontario, Canada for 55 miles (89 

km). The Boundary Waters Canoe Area Wilderness in 

Superior National Forest lies immediately east of the 

park (figure 1). 

The roadless Kabetogama Peninsula, south of Rainy 

Lake and north of Kabetogama Lake, is the main land 

area in Voyageurs. Water from the lakes drains to the 

northwest to Lake of the Woods and then to Lake 

Winnipeg in Canada, eventually flowing into Hudson 

Bay, the only U.S. park to do so(Kiver and Harris 1999). 

For over 8,000 years, Native Americans have lived in the 

Voyageurs area. The “Red Paint People” left clues of 

their Stone Age culture in the pictographs painted on 

rock cliffs with red ocher and in artifacts, such as slate 

knives and arrowheads. 

The Ojibwa (Chippewa in the U.S.) tribe was the largest 

and most powerful Native American tribe in an area 

extending as far west as Manitoba and Saskatchewan east 

to Quebec. In the United States their range extended 

northeast to Iroquois territory and west to the Great 

Plains and the Sioux. 

From the 1600s to the early 1800s, French- Canadian fur 

traders and canoe- men known as Voyageurs traveled in 

birch- bark canoes guided by the Ojibwa people who 

showed them the best water routes to follow from Grand 

Portage, east of the park on the northwest shores of Lake 

Superior, to the shores of Lake Athabasca in 

northwestern Saskatchewan. The Voyageurs canoed and 

portaged the 2,000- mile (3,220- km) journey from 

Grand Portage to Lake Athabasca trading furs and other 

goods. Their well established waterway between Lake 

Superior and Lake of the Woods was made the 
 VOYA Geologic Resource Evaluation Report 3

international boundary by the 1783 treaty ending the 

American Revolution. 

Within 50 years following the decline of the fur trade, 

practically all of the virgin north woods forest was 

logged. A short and unprofitable gold mining boom 

swept the Kabetogama Peninsula between 1893 and 1898. 

Rainy Lake City in the northwest corner of the park filled 

up with prospectors and miners but declined from a 

settlement of 500 people to a ghost town in five years. 

As early as 1891, the Minnesota legislature officially noted 

local interest in establishing a national park on the 

Kabetogama Peninsula. Public Law 91- 661 authorized 

Voyageurs National Park in 1971, and Voyageurs 

National Park was established in 1975 to preserve the 

scenery, geological conditions, and waterway system. 

Geologic Setting 

The park is at the southern end of the Canadian Shield, a 

large area of exposed basement rock containing some of 

the oldest Precambrian rocks in North America and 

forming the ancient core of the continent (Hemstad et al. 

2002). 

The Precambrian is divided into two eons: Archean 

(3,800+ to 2,500 million years) and the Proterozoic (2,500 

to 540 million years) Most of the rocks in Voyageurs NP 

are igneous and metamorphic rocks of Archean age. The 

metamorphic rocks, mostly schists and gneisses, are 

exposed in the west and central portions of Voyageurs 

and igneous granitic rocks are exposed in the east and 

southeast areas of the park. These units belong to the 

Quetico subprovince of the Superior Physiographic 

Province (Day 1990; Harris et al. 1995; Kiver and Harris 

1999; Davis et al. 1994). Voyageurs National Park 

straddles the transition from volcanogenic greywacke 

and granite of the Quetico subprovince to the 

metamorphosed sedimentary and volcanic rocks of the 

Wabigoon subprovince (figure 3) (Day 1990; Weeks and 

Andrascik 1998). 

Metamorphic rocks of the more northern Wabigoon 

subprovince form the islands in the extreme 

northwestern segment of the park and are part of a 

northeast trending greenstone belt. The Rainy Lake – 

Seine River fault zone, a major northeast- southwest 

trending right- lateral strike- slip fault zone, marks the 

contact between the two subprovinces. The rocks at 

Voyageurs have been deformed by at least three episodes 

of Precambrian folding and faulting. Each episode has 

resulted in a specific pattern of deformation. The 

metamorphic and igneous rocks reveal a history of 

moving lithospheric plates, ancient subduction zones, 

mountain building episodes, and extensive volcanic 

activity (Kiver and Harris 1999). 

During the Ice Age in the Pleistocene Epoch, which 

began about 190,000 years ago, the region experienced at 

least four periods of glaciation that shaped and carved 

the bedrock into the landscape seen by visitors today 

(Davis et al. 1994; Weeks and Andrascik 1998; Kiver and 

Harris 1999). The Precambrian was exposed during the 

most recent period of glaciation, the Wisconsin period, 

which lasted from 50,000 to 11,000 B.C. 

Glaciers scoured the region scooping- out dozens of lake 

basins while scratching and polishing rock surfaces by 

dragging loose rocks over the surface leaving lakes, 

outwash (mostly sand and gravel), and till deposits. 

Today the rugged and varied topography includes rolling 

hills interspersed with irregular slopes and outcrops of 

bedrock between bogs, beaver ponds, swamps, islands, 

small lakes, and the four large lakes. 

Lake elevations are about 1,100 feet (335 m) above mean 

sea level and land elevations in the west and north 

sections of the park rarely exceed the lake elevations by 

more than 100 feet (30 m) (Weeks and Andrascik, 1998). 

In the east section of the Kabetogama Peninsula and 

along the south shores of Kabetogama, Namakan, and 

Sand Point lakes, land elevations are commonly 100 to 

200 feet (30- 60 m) higher (Weeks and Andrascik 1998; 

NPS 1994). 

Biotite schist is the most widespread rock type in the 

park and forms the bedrock for most of the Kabetogama 

Peninsula (Day 1990; Hemstad et al. 2002). Outcrops of 

schist are relatively low and flat because the glaciers 

more easily eroded the schist than the surrounding 

granitic rocks. 

A broad belt of mixed gneiss trends through the middle 

of Kabetogama and Namakan Lakes. The gneiss lies 

between biotite schist to the north and massive granite to 

the south and consists of layers and irregular masses of 

biotite schist separated by sheets of granite. Most 

outcrops contain highly contorted folds. 

Granitic rocks compose the terrane south of 

Kabetogama Lake and Sullivan Bay. The mineral 

composition and texture vary greatly over short 

distances so that the rocks range from true granites to 

hornblende quartz diorite. Glaciers rounded and 

smoothed the granitic outcrops and marked them with 

glacial striations, chattermarks, and glacial polish. 

Mafic dikes, common in the area, are the youngest rocks 

at Voyageurs. The dikes are primarily composed of 

gabbro and diorite and cut through older granitic rocks. 
 NPS Geologic Resources Division 4 

Figure 1. Map of Voyageurs National Park. 
 VOYA Geologic Resource Evaluation Report 5

Figure 2. Geologic time scale; adapted from the U.S. Geological Survey and International Commission on Stratigraphy. 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. 
 NPS Geologic Resources Division 6 

Figure 3. A schematic drawing of subprovinces of the Superior Province. Contacts between subprovinces are fault zones. 
 VOYA Geologic Resource Evaluation Report 7

Geologic Issues 

A Geologic Resource Evaluation scoping session was held for Voyageurs National Park 

on June 1- 2, 2000, 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. 

This section addresses geologic issues as they affect the 

ecosystem and park management. 

Sharing a common boundary with Canada, Voyageurs 

National Park is part of a hydrologically complex and 

sensitive environment. Over the past several decades, 

numerous natural resource issues have arisen and almost 

all of these issues relate directly or indirectly to water 

(Weeks and Andrascik 1998). These issues are covered by 

Weeks and Andrascik (1998) in Technical Report 

NPS/NRWRS /NRTR- 98/201. In addition the following 

geologic issues have been identified by the park: 

• Submerged boating hazards 

• Hydrogeology 

• Mineral resources 

• Abandoned mine hazards 

• Surficial deposits 

• Earthquake potential 

Snowmobile use regulations and the preservation of 

petroglyphs are management issues beyond the scope of 

this report. While written for resource managers, this 

report may also provide information useful to the 

interpretive staff of Voyageurs, specifically the section on 

Geologic History. 

Submerged Boating Hazards 

As in any lake with rocky shorelines, the lakes in 

Voyageurs contain rocks that lie just below the surface. 

Motor boats and canoes may scrape their hulls or 

propellers on these rocks. Both large and small rocky 

islands lie within Rainy Lake, Kabetogama Lake, 

Namakan Lake, Sandy Point Lake, the bays within the 

lakes, and the narrows that connect the lakes and bays. 

Rocky reefs such as Ericksons Reef and Shortys Reef in 

Rainy Lake present hazards to boats. In addition to 

property damage, submerged boating hazards are a 

visitor and park safety concern. Much of the park can 

only be reached by boat and damaged boats may strand 

people creating difficult rescue situations. A map 

identifying near- surface, submerged rocks and reefs 

should help visitors avoid these hazards although 

bathymetric maps may serve the same purpose. 

Hydrogeology 

The bedrock at Voyageurs is relatively impermeable to 

groundwater flow and these units are not aquifers (Davis 

et al. 1994). Wells in this area typically yield less than five 

gallons per minute (Weeks and Andrascik 1998). 

Numerous fractures and faults, may provide some 

structural control for the limited groundwater resources. 

The bedrock is relatively impermeable and the soil is 

thin, resulting in rapid runoff of surface water. 

Voyageurs is part of the Rainy Lake basin, the 

headwaters of the Hudson Bay watershed. The Namakan 

River is the largest single source of inflow to the park, 

and water quality research has shown that the Namakan 

River is of higher quality and purity than Namakan Lake, 

Sand Point Lake, and Rainy Lake (Davis et al. 1994). 

Annual maximum flows usually occur in April or early 

May as a result of snowmelt. Due to minimal 

groundwater resources in the area, surface water is the 

primary water source for domestic and industrial use. 

Consequently, external upstream activities may impact 

Voyageurs with increased sediment loads, higher 

turbidity levels, and increased nutrient levels leading to 

increase algal growth. There is some potential of 

contamination from historical mining and milling 

activities (Davis et al. 1994; Weeks and Andrascik 1998). 

Mineral Resources 

The enabling statute for Voyageurs National Park 

contains a broad prohibition against all mining and 

mineral development activities within the unit. This 

prohibition encompasses mining on both federal and 

nonfederal lands within the park (see 16 U.S.C. § 160f(c)). 

In addition, Minnesota Statutes specifically exclude 

mining within Voyageurs National Park (Stat. 6132.2000, 

Subpart 2 B and Stat. 84B.03, Subdivision 1). The State 

also prohibits any mineral exploration or mining- related 

surface disturbances within 0.25 mile (0.4 km) of 

Voyageurs National Park (Stat. 6132.2000, Subpart 3 B). 

Historic Mining Activity 

During the gold- mining boom from 1893 to 1898, 

numerous prospects and small mines opened in northern 

Minnesota, mostly in greenstone belts. Greenstone belts 

are linear regions of rocks comprised of fine- grained 

metasedimentary rocks including silt- to sand- sized 

tuffaceous (volcanic ash derived) material and submarine 

basalt flows and pillow lavas. Minor amounts of gold 

associated with shear zones and fracture systems bearing 

quartz veins, gossans (deposits of hydrated oxides of 

iron), and iron formations were discovered in the 

northeast- tending Rainy Lake greenstone belt that 

passes through the northwestern corner of Voyageurs 

(Davis et al. 1994). 
 NPS Geologic Resources Division 8 

The Minnesota Geological Survey (MGS) evaluated the 

mineral potential of Voyageurs prior to its establishment 

as a national park (MGS 1969). Seven samples were 

collected from the Rainy Lake greenstone belt. Three of 

these samples contained “significant amounts of gold, 

silver, and copper” (MGS, 1969, p. 14) and one contained 

detectable amounts of platinum group metals. Because of 

these results and the productive gold mining operations 

on the Canadian side of the greenstone belt, the MGS 

recommended that this portion of the proposed park 

remain accessible for prospecting and possible mining. 

Congress did not agree with this recommendation, hence 

the inclusion of broad language prohibiting all mining in 

the park. 

For the first time since the 1930s, high gold prices in the 

late 1970s and early 1980s, as well as several major 

discoveries in Canada, led to further mineral exploration 

in the Voyageurs area outside the park. Exploration was 

primarily in the greenstone belt, 2 to 9 miles (3- 14 km) 

west of the park boundary, and to a lesser extent on the 

geophysical anomalies south and southwest of 

Voyageurs. Four exploration projects were completed in 

the area between 1984 and 1991. The only metal 

encountered in near economic concentrations was gold, 

and anomalous concentrations were largely in the range 

of 100 parts per billion (ppb) to 3.5 parts per million 

(ppm). The highest values encountered were about 10 

ppm (0.292 ounce/ton) and were from very thin (about 1 

foot) and very rare zones of mineralization. To justify any 

serious efforts at mineral reserve definition or mine 

development, grades on the order of 6 to 10 ppm would 

be necessary over intervals of several feet. These deposits 

would also have to show evidence of internal continuity 

(Davis et al. 1994). No such deposits were located during 

exploration. 

In 1993, the U.S. Bureau of Mines revisited the mineral 

potential of Voyageurs National Park (Davis et al. 1994). 

Their area of interest included not only Voyageurs but 

also a 30- mile (48 km) radius around the park. Their 

investigation included a literature search (including 

management response plans), fieldwork, petrologic and 

mineralogical studies, mine inspections, modeling 

studies of the mineral deposits, mines, and economic 

impacts, and GIS database processing and modeling. In 

addition, they addressed the probable effects of 

proposed changes to the existing mining rules by the 

State of Minnesota in order to “encourage mineral 

exploration and development” (Davis et al. 1994, p. 1). 

This comprehensive evaluation by the Bureau of Mines 

determined that gold mineralized areas were “simply 

mineral occurrences and do not constitute even 

subeconomic resources” (Davis et al., 1994, p. 1). Mine 

modeling studies conducted as part of this project 

indicated that any mine development that might occur 

within a 30- mile (48 km) radius of Voyageurs National 

Park would not pose a serious threat to the park 

management or diminish visitor enjoyment of the park 

(Davis et al. 1994). Additionally, the study showed that 

the Metallic Minerals Leasing Rules of the State of 

Minnesota and the proposed revisions to those rules 

would have minimal, if any, impact on foreseeable levels 

of mineral- related activities in the state as a whole, and 

particularly in the area of influence of Voyageurs 

National Park (Davis et al. 1994). 

The Tilson Creek banded iron formation is known to be 

an extensive area of carbonate- rich iron formation west 

of Voyageurs, and locally high gold concentrations have 

been documented within very restricted horizons of 

these same iron formations. However, commercial 

exploration has not encountered significant occurrences 

of economic gold concentrations in anywhere near the 

dimensions necessary to justify mining (Davis et al. 1994). 

Although magmatic nickel and copper mineralization 

occurs in nearby mafic gabbros in Canada, none have 

proven to be major resources, and no similar mafic hostrocks have been mapped in Voyageurs. Within the 30-

mile (48 km) radius of the park, a limited number of small 

mafic bodies have been recognized, but these contain a 

very low potential for magmatic nickel- copper deposits 

(Davis et al. 1994) 

In summary, the potential for establishing mining 

operations in the Voyageurs area, adjacent to the park, is 

very low. No evidence exists to indicate that the area 

might host massive, or disseminated, sulfides of base 

metals. Gold mineralization in the area does not 

approach the definition of an ore body, or even a 

subeconomic mineral resource. The better 

concentrations of gold appear very thin and highly 

discontinuous. (Davis et al. 1994). 

Abandoned Mine Hazards 

The gold rush of the Rainy Lake District in 1893 was 

sparked by the discovery gold in the extreme 

northwestern corner of the park on Little American 

Island. The Little American Mine, located in the park, is 

the only mine to have achieved even modest production 

in the United States portion of the Rainy Lake- Seine 

River mining district (Davis et al. 1994). 

Thirteen abandoned mines with 22 openings are present 

in Voyageurs National Park. All are located in the 

northwestern corner of the park along structures within 

the Rainy Lake greenstone belt. Some abandoned 

prospect pits, shafts, and open cuts are concealed by 

vegetation. These sites, including two of the “unnamed 

prospects” described below, have been examined by 

qualified park staff and do not pose major hazards (Chris 

Holbeck, Voyageurs NP Chief of Resource Management, 

personal communication, 2006). 

Although no obvious environmental hazards were 

observed during the field examinations for the 1994 

Bureau of Mines report, liquid mercury was used to 

recover gold in the amalgamation process for at least 

three sites now inside the park (Davis et al. 1994). The 

three historical sites were near Rainy Lake City, at the 

Lyle Mine site, and at the Little American Mine site. The 

mill at Rainy Lake City processed a significant tonnage of 
 VOYA Geologic Resource Evaluation Report 9

ore from 1894 through 1897. The other two sites were 

never very productive. 

When the mills at these three sites were disassembled for 

removal, liquid mercury may have contaminated the 

local surface and the adjacent waters of Rainy Lake. With 

a specific gravity of 13.5, mercury is essentially insoluble 

in water and sinks to the lowest sites in any body of water 

where it is incorporated into the sediment. Mercury 

tends to stay in bottom sediments unless remobilized by 

severe storm events, high winds, or disturbance by boat 

propellers. Mercury levels in Voyageur lake sediment 

have not been evaluated. Although core sampling and lab 

testing could determine the amount of mercury, it would 

also disturb and remobilize whatever mercury is present. 

Fish and wildlife in Voyageurs National Park show 

elevated levels of mercury even in comparison to those in 

the Superior National Forest (NPS 2001). The source of 

the mercury, however, is considered to be atmospheric, 

originating some distance away from the park. 

Little American Mine 

The Rainy Lake mining district is in the extreme 

northwestern part of the park. It encompasses Little 

American and Big American islands, Dryweed Island, 

Bushyhead Island and smaller islands between Dryweed 

Island and the Kabetogama Peninsula (figure 1). The only 

mine in the Rainy Lake district (USA) with recorded gold 

production, the Little American Mine was developed by 

two vertical shafts and an open cut along the vein 

structure. Most of the ore was taken from an open cut, 

which is west of the main shaft. The open cut strikes N 

80o E and is about 200 feet (61 m) long and 5 to 15 feet 

(1.5- 5 m) wide. All that remains of the 210- foot (64 m) 

main shaft is a collapse depression. In 1994, this mine 

opening posed a safety hazard, but since then, measures 

have been taken to make the mine safe (Chris Holbeck, 

Voyageurs NP Chief of Resource Management, personal 

communication, 2005). 

Lyle Mine 

The Lyle Mine, the second largest mine developed in the 

Rainy Lake district, began operations in 1894. The mine is 

located on a small island directly north of Dryweed 

Island (figure 1). By 1994, two 40- foot (12 m) deep shafts 

had been filled in and were unidentifiable, but the main 

Lyle shaft was flooded to within 10 feet (3 m) of the 

surface and had been fenced off and partially filled with 

miscellaneous debris (Davis et al. 1994). 

The mine was cared for by cabin residents for about 50 

years. When the park acquired the property the residents 

moved out leaving a water and trash filled open shaft 

accessible to visitors. The park has an unfunded PMIS 

proposal to close the shaft with polyurethane foam but as 

of April, 2007 it remains open and unsafe (NR Staff 

Voyageurs NP, personal communication, 2007). 

Big American Mine 

Located near the southwestern end of Big American 

Island (just west of Dryweed Island, figure 1) and about 

60 feet (18 m) above the level of Rainy Lake, the Big 

American Mine began operations in late 1894 or early 

1895. It saw only limited development until May of 1897 

when the Lyle Mining Company bought the property. 

Although extensive plans were designed for the mine, the 

main shaft was only sunk to a depth of 50 feet (15 m) 

before it was terminated. In 1994, the shaft was flooded 

to within 10 feet (3 m) of the surface and secured with a 

chain link and cable cover by the National Park Service 

(Davis et al. 1994). It is currently considered safe (Chris 

Holbeck, Voyageurs NP Chief of Resource Management, 

personal communication, 2005). 

Old Soldier Mine 

Another mine that began operations in 1894, the Old 

Soldier Mine, is located on a small peninsula off the 

north shore of Dryweed Island (figure 1). The vertical 

shaft was sunk to approximately 20 feet (6 m) below lake 

level (about 30 ft, 9 m, total depth). The shaft, located on 

private land inside the park, has been capped by a 10 x 10 

ft. (3 x 3 m) concrete slab. 

Bushyhead Mine 

The Bushyhead Mine is located near the center of 

Bushyhead Island, due south of Dryweed Island (figure 

1). It also began operations in 1894. Two vertical shafts, 

one 30 feet (9 m) deep and another 100 feet (30 m) deep, 

are now flooded and filled with sand and debris. 

Although the drifts have been filled, an adit remains 

open. It is partially flooded but remains accessible near 

the shore of Rainy Lake. The portal is stable and is now a 

habitat for bats (Chris Holbeck, Voyageurs NP Chief of 

Resource Management, personal communication, 2005). 

Hope-Still Mine and Little Chicago Mine 

Two other prospects with mine workings are the HopeStill Mine and the Little Chicago Mine, both located on 

small islands south of Dryweed Island (figure 1) in the 

park. The Hope- Still Mine is a relatively minor prospect 

probably dating to 1894. The shaft, less than 30 feet ( 9 m) 

is on private land and is flooded to within 7 feet (2 m) of 

the surface and covered by a small storage shed with a 

trap door for access. 

The Little Chicago Mine is a very modest prospect 

located on the southwest side of a small unnamed island 

lying directly south of Dryweed Island and east of Big 

American Island. The only identifiable workings are a 

shallow, 5 x 8 ft (1.5 x 2.4 m) prospect pit that is now 

debris filled and less than 3 feet (1 m) deep. 

Unnamed Prospects 

Many small prospect pits are located along the 

greenstone trend and southern Rainy Lake. Almost all of 

these prospects are in quartz veins and most are very 

limited. Two sites may pose a safety hazard. The first is 

located on the north side of a modest- sized, unnamed 

island directly northeast of Dove Bay and consists of a 
 NPS Geologic Resources Division 10 

shallow 8 x 12 ft (2.4 x 3.7 m) vertical shaft. The shaft is 

flooded to within 6 feet (1.8 m) of the surface but is easy 

to overlook. 

The second potentially hazardous unnamed prospect is 

located on a small unnamed island directly north of Dove 

Bay. The 8 x 10 ft (2.4 x 3 m) shaft is flooded to within 12 

feet (4 m) of the surface and somewhat debris filled. 

Surficial Deposits 

Surficial deposits in Voyageurs National Park are 

composed mostly of sandy tills, lake deposits, and 

localized glacial outwash deposits of sand and gravel 

produced from glacial scouring and prolonged erosion. 

Most of these surficial deposits and soils are shallow and 

relatively recent (<10,000 years) with low nutrient levels 

and high acidity, and are susceptible to erosion. At 

Voyageurs, the available water capacity of most soils in 

ranges from very low to moderate (Weeks and Andrascik 

1998). The underlying bedrock is nearly impermeable, 

presenting challenges to the development of septic 

systems and water wells. 

On level upland forested areas in the park sandy and silty 

tills derived from metamorphic rocks, such as schists and 

greenstones, are higher in nutrients, moderately acidic, 

and better able to hold water. Till deposits on the 

southwest end of the park have more limestone than 

those in the rest of the park (NPS 2001). Rivers that drain 

into Kabetogama Lake from these areas give the lake 

distinct water chemistry from the other large lakes in the 

park. 

Soils and surficial deposits have been impacted by a 

variety of activities in the park, such as; removal to build 

structures and facilities, and logging practices such as 

building logging roads and removal of tree roots. 

Recreational users have affected the soil by camping, 

boating, picnicking, and other activities at developed and 

undeveloped sites. Specific impacts include: compaction, 

trampling and destruction of vegetation, increased 

erosion, disturbance to wetlands, and reduction in 

porosity and infiltration rates. For information about 

soils please contact Pete Biggam, Soil Inventory Program 

Manager for the NPS Geologic Resources Division 

(303)- 987- 6948. 

It is estimated that there have been between 750 and 

1,000 temporary occupation sites in Voyageurs since the 

native Ojibwa and later the Voyageurs made camp on the 

islands. There were about 400 recreational cabins, 

mostly restored, and numerous camping sites, now 

limited to 250 (Chris Holbeck, Voyageurs NP Chief of 

Resource Management, personal communication, 2006). 

Earthquake Potential 

Participants at the scoping session in 2000 recognized 

the potential for earthquakes as a geologic hazard for 

Voyageurs National Park (Appendix B). However, 

Minnesota has one of the lowest occurrence levels of 

earthquakes in the United States (Chandler 1994). Since 

1860, a total of 19 small to moderate earthquakes have 

been documented in Minnesota and are attributed to 

minor reactivation of ancient faults in response to 

modern stresses. The largest well- documented 

earthquakes recorded magnitudes of 4.6 to 4.8, although 

a magnitude 5.0 earthquake shook nearly all of northern 

Minnesota in 1917. Epicenters of four of the five 

earthquakes with magnitudes greater than 4.0 were 

located in the west- central part of the state. The 

epicenter of the fifth earthquake with a magnitude larger 

than 4.0 was located in the southern part of the state near 

New Prague, MN. No epicenters have been recorded in 

the Voyageurs area in historical time. While weak to 

moderate earthquakes occasionally occur in Minnesota, 

a severe earthquake is very unlikely (Chandler 1994). 
 VOYA Geologic Resource Evaluation Report 11

Geologic Features and Processes 

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

and processes in Voyageurs National Park. 

Geologic features and processes in Voyageurs reflect the 

two widely separated time periods that formed the 

present landscape: the older, 2.5 billion year old 

Precambrian (Archean) and the Pleistocene Epoch ice 

age. The ancient rocks form part of a large area of 

basement rocks called the Canadian Shield, which is part 

of the North American craton (see Glossary). 

The Archean rocks at Voyageurs are associated with a 

mountain- building episode called the Kenoran 

(Algoman) orogeny. The Kenoran orogeny is the earliest 

datable orogeny in North America (Harris et al. 1995). 

Both igneous and metamorphic rocks are exposed in 

Voyageurs. Schists and gneisses, the products of 

metamorphism, are exposed in the west and central 

portions of the park (Rainy Lake and Kabetogama Lake) 

while granite, an igneous rock, is exposed on the east end 

at Namakan Lake and Sand Point Lake. Immediately 

south of the park and extending to the Vermillion Fault 

is a broad transition zone that contains bands of 

migmatite, a rock type that has characteristics of both 

igneous and metamorphic processes. 

The advance and retreat of Pleistocene glaciers as 

recently as 10,000 years ago left an indelible imprint on 

the rock in Voyageurs. Characteristic features of 

continental glaciation observed in Voyageurs range from 

scratches and grooves on bedrock to the chain- like 

pattern of lakes that formed from glacial scouring. 

Precambrian Features and Processes 

Voyageurs National Park is in the Superior 

physiographic province. The Superior physiographic in 

the Voyageurs area is divided into two subprovinces: the 

Quetico subprovince and the Wabigoon subprovince 

separated by the Rainy Lake- Seine River fault zone 

(figure 3). The park is mostly in the Quetico subprovince 

which is composed primarily of biotite schists and 

granitic rocks with only rare evidence of regional 

volcanic activity. The Wabigoon subprovince, however, 

is extremely variable. It contains numerous intrusive 

bodies and volcanically- derived greenstone belts. The 

Wawa subprovince also contains greenstone belts, but 

they are more localized and do not extend into 

Voyageurs. These rocks represent the juxtaposition of a 

sedimentary basin (Quetico subprovince) with a volcanic 

island arc (Wabigoon subprovince) (Davis et al. 1994). 

In Precambrian time deep crustal processes transformed 

sedimentary deposits into dense, recrystallized, and 

often foliated, metamorphic rocks. High pressures and 

temperatures at depth preferentially align mineral 

crystals, especially mica, in metamorphic rocks. 

Depending on the degree of pressure and temperature 

and the original composition of the sediments, this 

crystal alignment imparts a foliated or schistose 

character to the rocks. Submarine mudstones are 

converted to various schists. Siltstones, sandstones, and 

conglomerates are metamorphosed into metasiltstones, 

metasandstones (quartzites), and metaconglomerates. At 

Voyageurs a result of these metamorphic processes is the 

biotite schist that dominates the landscape. 

The Rainy Lake- Seine River fault zone, which separates 

the Quetico subprovince from the more northern 

Wabigoon subprovince, is a major, northeast- southwest 

trending strike- slip fault zone, trending N 80° E, that 

cuts through the northwestern part of Voyageurs and 

extends westward to International Falls. The fault has 

transported the rocks in the greenstone belt a 

considerable distance from their place of origin. The 

greenstone belt is 1.25- 2 miles (2- 3.2 km) wide and 

includes Big American Island, Dryweed Island, and the 

smaller islands between Dryweed Island and the 

Kabetogama Peninsula. At the Seven Sisters Islands 

further to the west, greenstone interfingers with pods of 

anorthositic gabbro (see Glossary). 

Greenstone belts are not as highly metamorphosed as the 

other Archean rocks in Voyageurs National Park. They 

are of special interest to economic geologists because 

greenstone belts are often host rocks for metallic mineral 

deposits. All of the known metallic mineral occurrences 

in Voyageurs National Park and the surrounding area 

have been found in the metasedimentary and 

metavolcanic rock units in the Rainy Lake greenstone 

belt. Greenstone belts form unique elongated 

downwarps of mixed metasedimentary and metavolcanic 

rocks. The green color comes from minerals such as 

chlorite, epidote, and actinolite that formed during 

metamorphism. 

Pillow lavas in the greenstone belts indicate that they 

were extruded in a marine seafloor environment. Most 

of the pillow structures in the Voyageurs area have been 

destroyed by metamorphism, but a few “pillows” up to 

three feet long (1 m) have been found on a small islet off 

Steamboat Island (north of Cranberry Bay). 

Some of the poorly sorted mixtures of clay, mica, and 

quartz (graywackes) are derived from the decomposition 

of pyroclastic debris (tuff and ash) suggesting that some 

explosive volcanic activity occurred in the area during 

Precambrian time. Lapilli tuff (see Glossary) can be 

found near Dog Island. Other clastic material has 

characteristics of rapid deposition by marine currents, 

possibly in an ocean trench (Harris et al. 1995). The finegrained sediments lithified into mudstones or siltstones 
 NPS Geologic Resources Division 12 

that later metamorphosed to chlorite- schist, a green, 

foliated rock. The coarse silt to sand- sized sedimentary 

part of the greenstone belt formed a feldspar- rich 

sandstone, or arkose, that metamorphosed to metaarkose. 

Interspersed with these rocks and the pillow basalts are 

seafloor hot- spring- derived chemical sedimentary 

layers high in silica and iron carbonate that may locally 

contain metallic sulfides and precious metals. These 

layers became banded iron formations, a principal source 

of iron in the Mesabi Range of northeastern Minnesota. 

Amorphous metallic sulfides and minor gold and silver 

are often found along with silica and iron in these 

banded iron formations. These minerals probably 

formed in the Precambrian by much the same geologic 

processes that are active on modern day seafloors. Hot 

spring vents on today’s seafloors often have chimneylike mineral walls built up around them. These vents are 

referred to as black smokers. Minerals associated with 

sediments deposited around black smokers include 

copper, zinc, lead, nickel, manganese, gold, and silver. 

The granitic rocks in Voyageurs are part of the 

Vermillion Granitic Complex and vary widely in 

composition. Rock types include granite, biotite granite, 

granodiorite, and quartz diorite (see the Map Unit 

Properties Table in the next section) (Davis et al. 1994). 

The Lac La Croix biotite granite batholith is the largest 

and youngest igneous intrusion in the area. It also 

comprises the principal rock type in the majority of the 

Boundary Waters Canoe Area Wilderness. Age dates on 

these granitic rocks show them to be almost as old as the 

schists, ranging in age from 2,690 million years before 

present (B.P.) to 2,640 million years B.P. 

During a period of very slow cooling in the late stage of 

granitic emplacement, numerous thin, tabular- to 

irregular- shaped bodies of very coarse- grained 

crystalline rocks solidified. These coarse- grained 

igneous rocks are pegmatites. Pegmatites are recognized 

by their coarse- grained texture, pink coloration 

(potassium feldspar), and a composition similar to 

granite but often with rare minerals, some of gem quality. 

Precambrian Fault Systems 

Three regional fault systems are present in Voyageurs: 1) 

a northwesterly- trending fault system that hosts the 

Kabetogama- Kenora Dike Swarm, 2) a set of regional 

structures that are almost perpendicular to the 

Kabetogama- Kenora Dike Swarm, and 3) a set of 

regional structures that lie wholly within the Lac La 

Croix biotite granite batholith in eastern Voyageurs 

National Park. 

The Kabetogama- Kenora Dike Swarm formed about 

2,200 to 2,100 million years B.P., in the Proterozoic Eon, 

when crustal bulging opened a northwest- trending 

fracture system in the area. Dark, intrusive rocks 

including gabbro, quartz diorite, and quartz diabase filled 

the fractures. The Kabetogama- Kenora Dike Swarm in 

Voyageurs is typical of the tabular dikes that formed in 

the long, linear fractures. They can be traced for several 

miles in length, while seldom exceeding 300 feet (91 m) in 

width. A mafic dike cuts the bedrock at the Kabetogama 

Visitor Center. Magnetite (magnetic iron oxide) is 

present in some of the dikes, allowing them to be 

mapped by means of surface or aerial magnetic surveys, 

even in areas of deep soil cover (Davis et al. 1994). 

The regional faults that cross almost perpendicular to the 

Kabetogama- Kenoran Dike Swarm are a secondary set 

of faults subparallel to the subprovince boundary 

structures. These faults cannot be traced for as great a 

distance and do not appear to have significantly 

displaced major rock units as those in the KabetogamaKenora Dike Swarm. The most notable segments of this 

fault system are the two faults within Voyageurs that are 

responsible for the two Chains of Lakes. The 

westernmost of these two faults controls the alignment 

of Locator, War Club, Quill, and Loiten Lakes while the 

second major structure is expressed by topographic lows 

containing Oslo, Brown, and Beast Lakes, and the 

western extension of Mica Bay (Davis et al. 1994). 

The third set of regional structures form a grid- like 

fracture network in the granite. There is a very strong 

north- south fracture set and a similar, linear, but 

somewhat less well- defined east- west fracture set. The 

fractures are probably related to the cooling of the 

batholith. 

Three phases of Precambrian deformation are recorded 

in the rocks at Voyageurs. The deformation folded the 

bedrock and can be recognized by the following (Day 

1990): 

• Phase 1: southwest- plunging en echelon (stacked) 

folds 

• Phase 2: small- scale folds, a strong schistosity in the 

rocks, mineral lineations, and a progressive transition 

in ductile deformation from the first phase 

• Phase 3: high- angle faults and shear zones 

Quaternary Features and Processes 

Glaciation 

Over the last 2 million years, glaciers have advanced and 

retreated in North America many times. As recently as 

10,000 years ago, the glaciers of late Wisconsin age 

covered Voyageurs National Park (Mikelson et al. 1983). 

Terminal moraines of Wisconsin age are primarily 

located south of the park in the southern Great Lakes 

area. In the more northern areas, where the ice was 

thicker and more erosive, glaciers scoured thousands of 

lake basins into the underlying bedrock. These lake 

basins were linked from west to east in southern Canada 

and the northern United States forming a remarkable 

waterway used for passage by Native Americans, 

voyageurs, explorers, and missionaries. 

Because the Voyageurs area is well within the major 

advance of the continental glaciers, very few morainal 

deposits exist. The prominent landforms are glacially 
 VOYA Geologic Resource Evaluation Report 13

scoured surfaces and extremely thin residual soils. Four 

types of glacial deposits are found in Voyageurs: lakebed 

sediments, outwash gravels, peat, and till. Glacial 

outwash and till (glacial debris) deposits are usually less 

than 100 feet (30 m) thick (Davis et al. 1994; Harris et al. 

1995). 

Glacial debris and outwash deposits left by retreating 

glaciers thicken westward to the extensive lake bed 

deposits of postglacial Lake Agassiz. Lake Agassiz was a 

vast, inland body of water that covered hundreds of 

square miles north and south of the international 

boundary for several thousand years (Teller and Clayton 

1983; Harris et al. 1995). Four of the five major phases of 

Lake Agassiz are recorded in the Voyageurs region 

(Teller and Clayton 1983; Davis et al. 1994). 

Holocene peat deposits formed in hollows or 

depressions such as old lake basins, bogs, and swamps. 

Deposits of unsorted glacial debris, or till, formed 

ground moraines and end moraines. Ground moraine 

debris was deposited under the ice sheet and 

interspersed with lakebed sediments forming an 

undulating surface known as “swell- and- swale” 

topography. End moraine till left hummocky ridges along 

the front of the ice sheet. One of these till deposits, left 

by the last, glacial retreat can be seen along the southwest 

shore of Rainy Lake. 

Glacial erratics are abundant in the Voyageurs area. 

These rocks of various compositions were transported 

from the north by glaciers and deposited randomly over 

the landscape when the glaciers melted. They range in 

size from pebbles to large boulders. For example, a large, 

light- colored granitic rock approximately 10 feet (3 m) in 

diameter is visible in Cranberry Bay where it rests on 

dark colored schist bedrock. Also, migmatite erratic sits 

on chlorite schist of the greenstone belt along the 

shoreline of Skipperrock Island in Rainy Lake. 

Glacial striations and glacial grooves appear as parallel, 

linear scratches or furrows on bedrock and erratics. 

Striations form from the scraping and scratching of 

quartz grains and hard, sharp rock fragments frozen into 

the bottom of the ice scratching across rock surfaces as 

glaciers move. Striations are generally oriented in the 

direction of glacial movement. In Voyageurs National 

Park, striations point south, south by southwest, and 

southwest (Harris et al. 1995). Cross- striations on some 

outcrops indicate more than one direction of ice 

movement. 

Repeated abrasion by glacial movement has smoothed 

and polished many of the bedrock exposures in the park. 

On highly resistant outcrops in Voyageurs, glacial polish 

still appears glossy and fresh or only slightly weathered. 

Ellsworth Rock Garden 

Although man- made, the Ellsworth Rock Garden is a 

unique feature in Voyageurs National Park constructed 

with local material. Built between 1944 and 1965, the rock 

garden was created by one man, retired Chicago building 

contractor Jack Ellsworth. The garden is located behind 

Cutover Island, near Clyde Creek on the northeast shore 

of Lake Kabetogama. Access to the garden is only by 

boat, or in the winter, by snowmobile, skis or snowshoes. 

Ellsworth was also a sculptor and, with his wife, collected 

thousands of rocks of all sizes from all over the area, 

often transporting them across the lake. The Ellsworths 

used the rocks to terrace the hillside near their home and 

within the terraces, they erected stone sculptures of a 

variety of forms. For example, a stone duck is perched on 

the side of a hill overlooking the lake, a deer stands 

behind a tree, a flat slab of rock supported by three 

triangular rocks forms a table, and stone monoliths stand 

in the woods. 

At its peak, the Ellsworth Rock Garden contained over 

200 sculptures. About 80 of these have been restored and 

in 2001, Lamp, Rynearson and Associates, Inc. worked 

with historical architects to retrace and locate as many 

features as possible using GIS. 
 NPS Geologic Resources Division 14 

Figure 4. Massive Precambrian rocks, like those pictured above, are exposed throughout Voyageurs National Park. 
 VOYA Geologic Resource Evaluation Report 15

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 Voyageurs National Park. 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. 

This section identifies the specific properties of the 

different geologic formations that may influence park 

management decisions. Geologic features and processes 

often occur in or can be restricted to a particular 

stratigraphic unit (group, formation, or member). This 

section ties together the geologic features with the 

formation properties, and also with the accompanying 

digital geologic map. 

The rocks exposed at Voyageurs National Park are 

primarily igneous and metamorphic. Igneous rocks 

record both intrusive and extrusive events. Metamorphic 

rocks include metamorphosed igneous and sedimentary 

units. 

The following table presents a view of the stratigraphic 

column and an itemized list of features for each rock 

unit. This table includes properties specific to each unit 

in the stratigraphic column including: map symbol, 

name, description, resistance to erosion, geologic 

hazards, suitability for development (e.g. trails, 

campgrounds, and/or buildings), mineral resources, and 

global significance. 

In general, the igneous and metamorphic units are 

resistant to weathering and erosion. Schistose rocks will 

erode more easily than granitic rocks or quartzite 

because the grains are bound more loosely and schist is 

composed of oriented micas that give the rock its 

characteristic schistosity. Water can enter between the 

mica sheets as well as decompose the mica thus 

loosening the grain structure. Schistose rocks will also 

fracture and split along these planes of weakness 

developed during metamorphism. Granite and quartzite 

are rich in quartz which is very resistant and the grains 

interlock more tightly preventing water to enter. 

Few geologic hazards are significant with regard to the 

specific units perhaps because of the low topographic 

relief and emphasis on water- related activities. Soil 

disturbance may be an issue for certain units that are 

exposed along the shoreline. If the Rainy Lake- Seine 

River fault was reactivated due to an extremely rare 

earthquake, some units might fracture and deform along 

previous fault planes. Many of the units comprise islands 

or parts of islands and shorelines. Near- shore 

submerged blocks of these units may pose a boating 

hazard. 

Some of the units, especially in the greenstone belt in the 

northwest part of Voyageurs, have limited exposures, 

and some comprise islands whose aerial extent may limit 

development. Those bedrock units that are more 

extensively distributed throughout the park and which 

have shoreline access are more suitable for development. 

This column primarily includes minerals that might be 

easily recognized in the unit as a whole and does not 

address economic mineral resources. Gold in the 

Schistose Tectonite (Ast) and Schistose Feldspathic 

Quartzite (Asq) is disseminated gold found in the 

greenstone belt. No economic deposits of gold have been 

found within Voyageurs National Park and it is not open 

to mineral entry (Davis et al. 1994). 

Rock units identified in the ‘other’ column occupy 

shorelines and thus, might be favorable units in which to 

find pictographs or petroglyphs. 

Most of the units have global significance because 

Precambrian rocks of this age have limited exposures on 

Earth. Voyageurs’ Archean rocks provide windows into 

the very distant past. 
Map Unit Properties Table 

Precambrian Age Map Unit (symbol) Unit Description Erosio

Resistan

Proterozoic 

(0.57- 2.5 

BA) Diabase (Pd) Fine- to coarse- grained, dark- brown to black; forms NW- trending dikes of Kenora- Kabetogama dike swarm; sharply discordant to structural grain of the enclosing Archean rocks; hornblende diorite in center of large dikes & hornblende gabbro toward margins. One dike had an U- Pb age of 2,067 +/- 5 Ma. High 

Proterozoic & Late 

Archean 

Schistose 

tectonite (Ast) 

Phyllitic & schistose, scaly to platy; composed principally of phyllosilicates, quartz, & carbonate minerals; tan to darkgreenish gray; variants include sericite- carbonate phyllite, biotite- rich phyllonite, & chlorite- rich phyllonite; found in & adjacent to major fault zones 

Limited to isin Rainy Lakzone 

QUETICO SUBPROVINCE OF THE SUPERIOR PROVINCE 

Pegmatite 

(Ap) 

Coarse- to very coarse- grained, light- pinkish gray; mostly potassium- feldspar, quartz, muscovite, & plagioclase. 

Mafic minerals are rare to absent; potassium feldspar crystals are euhedral & as long as 25 cm.; intrudes biotite schist 

south of the Rainy Lake- Seine River fault zone. 

High 

Leucogranite 

(Alg) 

Muscovite- & biotite- bearing, medium- to coarse- grained, strongly to moderately foliated granite; weathers very light- gray to almost white; forms predominantly lenticular intrusions, most of which are quasi- conformable to 

bedding & foliation in the wall rock, & numerous thin sills, dikes, & veinlets too small to show at map scale; related to the pegmatite (Ap) & is generally intruded by it. 

Not signif

Biotite Schist 

(Aqs) 

Fine- to medium grained, light- to dark- gray; derived from rhythmically bedded, texturally graded greywacke & shale. Composed mostly of plagioclase, quartz, biotite, & muscovite; minor garnet, sillimanite, kyanite, & hornblende; individual beds are typically 5- to 20- cm- thick; some sandy beds are as thick as 2 meters; characteristic & dominant rock type in the northern part of the Quetico subprovince, south of the Rainy Lake- Seine River fault zone. 

High: dominrock type in northern parthe park 

Lineated, 

mylonitized 

Granite (Avm) 

Part of Vermillion Granitic Complex. Mylonitic, equigranular, strongly lineated granite. Thought to have been granite of 

unit Avl or granite- rich migmatite of unit Avg prior to intense deformation. 

Probably lowthan surrounrocks due to deformation 

Lac LaCroix 

Granite (Avl) 

Part of Vermillion Granitic Complex. Biotite granite, massive to weakly foliated, medium- grained, somewhat porphyritic, light- gray to light- pink. Contains scattered inclusions of variably digested biotite schist, amphibolite, tonalite, trondhjemite, & leucogranite migmatite, typically less than about 5 percent; grades into granite- rich migmatite (Avg) as the proportion of inclusions increases. 

High: a majotype in southVoyageurs 

Granite –rich 

migmatite 

(Avg) 

Part of Vermillion Granitic Complex. Granite of the Lac LaCroix type that contains abundant inclusions (between 5 and 

25 %); inclusions may be several meters in size & consist of biotite schist, amphibolite, tonalite, trondhjemite, & leucogranite migmatite, as well as pale gray, ovoid to wispy inclusions of granitoid rock. 

High: a majotype in southVoyageurs 

Biotitehornblende 

quartz diorite 

(Avq) 

Part of Vermillion Granitic Complex. Massive, medium- grained, medium- to dark- gray. Extensively brecciated & invaded by pink granite of Lac LaCroix type (unit Avl); exposed south of Voyageurs, not in park. NA 

Leucograniterich migmatite 

(Avt) 

Part of Vermillion Granitic Complex. Layered migmatite within mostly biotite schist; comparable to unit Aqs; the 

injected rock is leucogranite comparable to unit Alg, together with leucotrondhjemite; granitic layers 1 m to 10s of meters thick, typically constituting about 50%- 90% of the bulk rock; contacts with units Alg & Avs are gradational. 

Schist layers resistant thagranitic laye

Migmatite 

(Ava) 

Part of Vermillion Granitic Complex. Country rock mostly amphibolite, hornblende gneiss, & biotite- hornblende 

gneiss; includes granite- rich & amphibolite- rich variants. 

Exposed weVoyageurs 

LATE ARCHEAN 

(2.5-3.0) 

Schist- rich 

leucogranite 

migmatite 

(Avs) 

Part of the Vermillion Granitic Complex. Layered migmatite of mostly biotite schist comparable to unit Aqs; country 

rock is leucogranite comparable to unit Alg, together with leucotrondhjemite; granitic layers range from 1 cm to several m. thick; typically constituting about 10%- 15% of bulk rock; contacts with units Aqs, Alg, & Avt are highly gradational. 

Schist layers resistant thagranitic laye
Precambrian Age Map Unit (symbol) Unit Description Erosio

Resistan

WABIGOON SUBPROVINCE OF THE SUPERIOR PROVINCE 

Granodiorite 

(Ag) 

Medium- to coarse- grained, light- gray to white with biotite & hornblende; exposed in the north part of map area & 

on Fransen and Susans Islands; moderately foliated w/ elongate mafic xenoliths oriented parallel to E- NE regional trend; may be correlative with granodiorite of the Ottertail Lake stock of NW Ontario, dated at 2,686.1 +1.5/- 1.4 Ma. 

Exposed NW Voyageurs oislands 

Lamprophyre 

(Al) 

Medium- to coarse- grained, dark- green schistose; composed mainly of chlorite, biotite, & pyroxene; west of Dryweed 

Island, lamprophyre dikes trend NW & E- NE; NW- trending dikes are biotite- hornblende- plagioclase & cutting regional foliation; 10 cm to greater than 50 meters thick; E- NE dikes are hornblende- pyroxene- biotite (Review Islands) with large phenocrysts (1 cm) of pyroxene, subparallel to regional foliation & as thick as 10 m.; an E- oriented dike cuts bedding on the south side of Dryweed Island & contains rounded fragments of quartz diorite 5 mm to 25 cm. in diameter. 

Dikes limitesmall islands of Dryweed 

Schistose 

rhyolite 

(Ar) 

Part of Seline Group. Reddish- gray, well- foliated; contains abundant rounded to angular rock fragments, interpreted as a clast- rich felsic flow; rock fragments decrease in abundance up- section from the contact with map units Ac1 and Ac2, sedimentary conglomerates; suite of rock types represented in the rock fragments identical to that in sedimentary clasts 

of underlying conglomerate; specular hematite locally occurs along joints. 

Exposed outVoyageurs in Tilson Bay/RLake fault zo

Schistose 

conglomerate 

2 (Ac2) 

Part of Seline Group. Polymictic, clast- supported, green to gray; differs from unit Ac1 in both stratigraphic position & clast composition; contains rounded pebbles, cobbles, & boulders of felsic plutonic rocks, mafic to felsic volcanic 

rocks, chert, biotite schist, & taconite; plutonic clasts are subspherical to elliptical; volcanic clasts tend to be moderatelyelongated in the regional lineation; schistose matrix composed of fine- to medium- grained biotite- or chlorite- rich lithic arenite with angular to subrounded granules of volcanic rock fragments, intrusive rock fragments, plagioclase, quartz, & chert; bedding crude to massive; subtle, fining- to coarsening- upward sequences common; dated at 2,686-2,695 Ma. 

Exposed o

Voyageu

Tilson Bay/

Lake fault 

Schistose 

feldspathic 

quartzite 

(Asq) 

Part of Seline Group. Medium- grained, light- gray to tan; quartz & feldspar grains, angular to subrounded, slightly 

flattened; matrix mostly fine- grained sericite, quartz, & chlorite; local biotite- & chlorite- rich beds; beds range 5 cm to 

1 m thick; subtle planar lamination & trough cross- stratification typical; cross- stratification indicates south & westerly transport directions; unit locally includes discontinuous lenses (10 cm to 1 m thick) of schistose conglomerate containing pebble- to cobble- sized clasts; green rip- up clasts composed of sericite- chlorite schist locally present. 

High. Dom

unit on Dry

Island 

Schistose 

conglomerate 1 

(Ac1) 

Part of Seline Group. Green to gray, rounded to angular pebbles, cobbles, & boulders of mafic to felsic volcanic rocks, 

pebbles of chert, & rare clasts of felsic plutonic rocks & iron- formation; numerous angular to rounded quartz pebbles common near top on the SW end of Dryweed Island; plutonic clasts subrounded to elliptical; volcanic clasts tend to be moderately to strongly elongated in the regional foliation; pebbles, cobbles, & boulders of rhyolite (unit Asr) with eyes of blue quartz are the dominant clast type; schistose matrix composed of fine- to medium- grained biotite- or chloriterich lithic arenite containing angular to subrounded grains of volcanic rock fragments, rare intrusive rock fragments, 

plagioclase, quartz, & chert; bedding is crude to massive with a subtle, overall fining upward; lenses of conglomerate 

interfinger with tuff beds of unit Aat. 

Very lim

exposure

Dryweed I

Schistose quartz- eye rhyolite (Aqr) 

Part of Seline Group. Medium- gray to light- green, well- foliated with euhedral phenocrysts of plagioclase & distinctive, 

double terminated crystals of blue quartz. 

Very lim

exposure

Dryweed I

Schistose mafic volcanic wacke and tuff (Ams) 

Meta- igneous Extrusive: Part of Seline Group. Dark green, strongly foliated chlorite schist; schistose, fine- to mediumgrained, containing angular to subrounded sand grains of dominantly mafic volcanic rocks, plagioclase, quartz & chert. Exposed out

Voyageurs in Lake fault zo

Schistose accretionary tuff and tuff breccia 

(Aat) 

Part of Seline Group. Gray to pink, consisting of abundant accretionary clasts in a schistose to phyllitic chloritedominated matrix; clasts are flattened & rotated & range from one to 10 cm in the longest dimension; internally, they are fine- grained & consist of a sugary pink rind that grades inward to a light- green inner rind & pink core; individual 

beds 10 cm to 2 m. thick, well graded, & with sequences predominately fining southward; scour- valleys are locally present implying younger rocks to the south. 

Limited to EDryweed Is; usually resiserosion 

Tonalite 

(At) 

Part of Seline Group. Fine- to medium- grained, light- gray to white, moderately to well foliated, biotite- rich; unit crosscuts diorite (unit Ad) & probably represents the latest phase of a shallow intrusion; similar rocks to the NE have been dated at about 2,729 to 2,736 Ma. 

Exposed outthe park in JBay fault zon

LATE ARCHEAN 

(2.5-3.0) 

Diorite 

(Ad) 

Part of Seline Group. Fine- to medium- grained, medium- to dark- gray, moderately to well foliated, biotite- & hornblende- bearing; cut by tonalite (unit At); locally forms angular brecciated fragments surrounded by the tonalite; 

unit occurs north of tonalite on Grassy Island & as thin sills within felsic & mafic metavolcanic rocks. 

Exposed outthe park in JBay fault zon
Precambrian Age Map Unit (symbol) Unit Description Erosio

Resistan

Leucogabbro 

(Alb) 

Part of Seline Group. Medium- grained, light- gray to white, moderately foliated plagioclase- rich, amphibole- bearing; exposed in the northern portion of the area on the Fox Islands. 

Compose 

Island

Schistose 

gabbro 

(Asg) 

Part of Seline Group. Medium- to coarse- grained, dark- green, texturally layered, strongly foliated metagabbro to 

diorite; forms small, glacially polished Whaleback Island just north of Steamboat Island in the northern part of the area; dominant mineral assemblage consists of plagioclase, pyroxene, amphibole, chlorite, & quartz; disseminated “brassy” sulfide blebs throughout; minor pyrite & chalcopyrite. 

High. Fo

Whaleback 

Schistose felsic 

rocks (Asf) 

Part of Seline Group. Very strongly foliated, light- green to gray; interpreted as metamorphosed dacite tuff interfingering with flows of map rhyolite and tuff (unit Asr) below. Outside th

Schistose 

rhyolite & 

dacite (Asr) 

Part of Seline Group. Light- to medium- gray, well- foliated; flows contain euhedral phenocrysts of plagioclase and distinctive, doubly terminated blue quartz. 

Small islands Rainy Lake fzone 

Volcanic 

conglomerate 

(Avc) 

Part of Seline Group.Bimodal, matrix- supported, gray to dark- green- gray; contains moderately to highly stretched 

felsic to mafic volcanic clasts that appear to have been originally rounded to subrounded; discontinuous beds as thick 

as one to 10 meters interstratified with felsic and mafic metavolcanic rocks; matrix is biotite- or chlorite- rich, finegrained tuffaceous meta- arenite; stretched rhyolite clasts that contain doubly terminated blue quartz phenocrysts probably derived from the schistose rhyolite and dacite unit (Asr) above; may represent subaerial debris flows. 

Exposed o

the par

Amphibolite 

schist 

(As) 

Part of Seline Group. Very strongly foliated; dark- green; composed of hornblende, biotite, and chlorite with thin, 

discontinuous lenses of brown iron- carbonate alteration, thin beds of magnetite- rich schist, and dark- gray cherty 

layers; occurs along the north side of the Rainy Lake- Seine River fault zone. 

Exposed o

the par

LATE ARCHEAN 

(2.5-3.0)

Mafic schist 

(Am) 

Part of Seline Group. Mostly chlorite schist, scaly to massive, dark green- gray, derived from mafic volcanic flows and interstratified tuff; less common sericite schist derived from felsic tuff; rock grades tectonically into the sheared rock of the schistose tectonite unit (Ast) with local thin interbeds of sulfide- rich iron formation and highly altered fragmental rocks along the fault (on the small island NE of Dryweed Island); metabasalt and interbedded tuffaceous sequences generally thin; metabasalts are fine- grained composed of chlorite, green hornblende and plagioclase with minor biotite, magnetite, and ilmenite, & relict vestiges of vesicular pillow basalts. 

Limited expon E. tip of Dryweed IslRainy Lake fzone. 

Unit descriptions are from Hemstad et al. 2002. 
 VOYA Geologic Resource Evaluation Report 19

Geologic History 

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

in Voyageurs National Park 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. 

Some of the oldest rocks in the world are exposed in 

Voyageurs National Park. About 2.5- 4.5 billion years ago 

(Ba), plate- tectonic processes generated a number of 

isolated areas of continental crust. In North America, 

rocks formed by these early tectonic events are found in 

Minnesota, Wyoming, parts of Canada, and Greenland. 

These bedrock units were shaped and carved by at least 

four periods of glaciation. The most recent continental 

glaciation in North America ended about 10,000 years 

ago. All evidence of the geologic history that has 

occurred between these two widely separated periods is 

missing from Voyageurs and most of the Canadian 

Shield. 

Precambrian 

Archean Eon (2.5-3.0 Ba) 

Relatively little is known about the early Precambrian 

since there were few fossils preserved and hard- bodied 

organisms are not found prior to about 550 million years 

ago at the beginning of the Cambrian Period (figure 2). 

However, excellent exposures of Archean rocks in 

northern Minnesota, including the Voyageurs area, 

reveal a protracted and complex structural evolution 

(Davis et al. 1994). The Archean basement complex of 

intensely metamorphosed rocks of sedimentary, 

volcanic, and intrusive igneous origin, dated at 2.6 Ba and 

older, is commonly referred to as pre- Kenoran. The 

earliest gneisses and schists, rich in mica, may have 

originally been sandstones (Harris et al. 1995). Following 

the emergence of the continental rocks of the Superior 

Province about 2.7- 3.0 Ba, structural deformation 

occurred over more than 100 million years. 

In late Archean time (2.8- 2.5 Ba), repeated episodes of 

continental collision and north- south directed 

compression and subduction generated a mountainbuilding episode known in North America as the 

Algoman Orogeny. This orogeny formed the gneisses, 

schists, and granites exposed today in Voyageurs 

National Park (Miller et al. 1987; Kiver and Harris 1999). 

Subduction of oceanic crust beneath the cratonic crust 

generated volcanic islands in the Precambrian sea. Zones 

of thick, basaltic lava accumulated in linear basins (backarc basins) formed between the less- dense continental 

crust and the volcanic islands. These lava- filled basins 

created today’s greenstone belts (Kiver and Harris 1999). 

The oldest known rock in Minnesota, the Ely 

greenstone, formed at this time. 

During the Algoman Orogeny, a great number of tectonic 

faulting and folding events deformed the rocks in the 

north- central Minnesota part of the Superior Province. 

Today, these event are seen in the three geologically 

distinct subprovinces, Wabigoon ,Quetico, and Wawa 

(figure 3). 

Major fault zones form the boundaries between the three 

subprovinces. The northeast- southwest trending Rainy 

Lake- Seine River fault zone separates the Quetico 

subprovince from the Wabigoon subprovince to the 

north. South of Voyageurs, the Vermillion fault zone 

marks the boundary between the Quetico subprovince 

and the Wawa subprovince (figure 3). The Quetico 

subprovince has been interpreted as a classical 

sedimentary basin (fore- arc or back- arc basin) 

developed between two active volcanic island chains 

(volcanic arcs) represented by the Wabigoon and Wawa 

subprovinces (figure 4) (Davis et al. 1994). 

These ancestral fault zones developed oblique, 

northwesterly components of movement that caused 

extensive strike- slip motion. Locally, segments on these 

faults were displaced by more than 20 miles (32 km), with 

the north side of faults displaced to the east (Davis et al. 

1994). 

At least three phases of deformation folded the bedrock 

of Voyageurs (Day 1990). The first episode produced 

southwest - plunging en echelon folds. The second phase 

of deformation was the most intense in the area and is 

recognized by small- scale folds, a strong schistosity in 

the rocks, mineral lineations, and a progressive transition 

in ductile deformation from the first phase to the second 

phase. The third phase produced high- angle faults and 

shear zones. Regional folding appears to have occurred 

prior to, concurrent with, and after regional 

metamorphism. 

Sedimentary units were complexly folded along eastwest axes and commonly have very steep to vertical dips. 

North- south directed compression generated regional, 

arch- like convex folds, or flexures, in sedimentary strata 

(antiformal syncline or anticlinoria) along eastnortheasterly trends. Regional metamorphism 

accompanied compressive north- south oriented 

thrusting and folding. 

Later in the orogeny, the granitic plutons found in 

Voyageurs intruded into the area. Mineral- rich fluids 

from these plutons produced dikes, pegmatites, and 
 NPS Geologic Resources Division 20 

quartz veins that concentrated metallic minerals in parts 

of the greenstone belts. 

Proterozoic Eon (2.5-0.5 Ba) 

The Proterozoic Eon represents about 40 percent of all 

geologic time. By 1.8 Ba, isolated regions had joined into a 

single large craton that included what we see today as 

Greenland, central Canada, and the north- central 

United States. The Midcontinent Rift that forms the axis 

of Lake Superior formed during this time and is likely the 

surface expression of a rising plume of hot mantle 

material (Hauser 1996). Faults and igneous dikes mark 

the northwest arm of this rift. Lava flows poured from 

long fissures to fill the axes of synclinal basins. Magma 

that did not breach the surface crystallized into granitic 

plutons that are now exposed in the park. 

Deformation in the Voyageurs area seems to have 

terminated by the time the northwest- trending diabase 

dike swarm was emplaced around 2.12 Ba (Day 1990). The 

Proterozoic diabase dikes of the Kabetogama- Kenora 

Dike Swarm in Voyageurs formed in long, linear 

fractures between 2.2 and 2.1 Ba. Proterozoic schistose 

tectonite (fault rock) intrude the older Archean rocks. 

Prolonged Erosion (570 Ma – 0.19 Ma) 

By the end of the Precambrian, the long series of tectonic 

events that created the basement complex of the 

Canadian Shield was over. Millions of years of erosion 

left only the roots of ancient mountains exposed (Harris 

et al. 1995). Extensive seaways covered much of the 

craton during the Early Paleozoic, but during the Late 

Paleozoic, Mesozoic, and Cenozoic, the province stood 

above sea level and was extensively eroded. The 

topography was reduced to a flat rolling plain even 

before the advance of the Pleistocene glaciers. The 

glaciers removed most of the Cenozoic deposits and all 

of the Paleozoic and Mesozoic record. When the first 

continental glaciers advanced into the Voyageurs area, 

the landscape was probably of low relief with a fairly 

uniform soil cover supporting extensive forests (Harris et 

al. 1995). 

Quaternary 

Pleistocene Epoch (1.6-0.01 Ma) 

Throughout the Ice Age, beginning perhaps 190,000 

years ago and extending intermittently in the Voyageurs 

region to approximately 11,400 years B.P., continental 

sheet glaciers covered north- central Minnesota, the 

Great Lakes Region, and most of Eastern Canada (Davis 

et al. 1994). The Illinoian stage (190,000 to 135,000 years 

B.P.) was the first glacial event and was followed by a 

warming period known as the Sangamonian Interglacial 

(135,000 to 119,000 years B.P.) The Wisconsin stage 

followed the Sangamonian Interglacial and advanced and 

retreated across the region from 135,000 years B.P. to 

10,000 years B.P. when the Holocene Epoch, or “Recent” 

geological time period began (figure 2). 

During the Pleistocene, glaciers scooped out Lake 

Superior’s basin along the trend of the Midcontinent 

Rift. At the east end of Lake Superior, the bottom of the 

lake is 1,302 feet (397 m) below the surface at an elevation 

of 700 feet (213 m) below sea level (Kiver and Harris 

1999). 

To the west of Voyageurs, Lake Agassiz formed during 

glacial retreat. Meltwater from the last continental 

glacier, backed- up because the north- flowing rivers that 

drained into Hudson Bay were blocked by ice. Water 

began to collect in the Red River valley in western 

Minnesota about 12,000 years ago and then spread over 

eastern North Dakota and adjacent Canadian Provinces. 

Lake Agassiz covered the Voyageurs area during glacial 

retreat from about 11,400 to 9,500 years B.P. (Davis et al. 

1994). 

Holocene Epoch 

Today unconsolidated sediments and thin soils have 

been superimposed on some of the oldest bedrock in 

North America. Streams have been reworking and 

sorting the glacial debris rather slowly due to the low 

relief in the area. Large basins are now occupied by lakes, 

ponds, bogs, wetlands, and interconnecting waterways. 

The tremendous weight of the ice sheet depressed the 

crust. When the ice melted, the crust rebounded and it is 

still rising today. Glacial rebound has caused some lakes 

to drain away and some lakes to become bogs and 

swamps. In the Boundary Waters region, the lakes 

occupy deeper parts of the basins once filled by Lake 

Agassiz. The land is rising at a rate of about 1 foot (0.3 m) 

per century (Kiver and Harris 1999).
 VOYA Geologic Resource Evaluation Report 21

Figure 5. Precambrian subduction and development of subprovinces. Modified from Davis et al. 1994. 
 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. 

anorthosite. An intrusive igneous rock composed almost 

entirely of calcium- rich plagioclase feldspar. 

aquifer. Rock or sediment that is sufficiently porous, 

permeable, and saturated to be useful as a source of 

water. 

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 (also see dome). 

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. 

bedrock. The underlying solid rock as it would appear 

with the sediment, soil, and vegetative cover stripped 

away. 

conglomerate. A coarse- grained sedimentary rock with 

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

continental crust. The type of crustal rocks underlying 

the continents and continental shelves; having a 

thickness of 25- 60 km (16- 37 mi) and a density of 

approximately 2.7 grams per cubic centimeter. 

craton. The relatively old and geologically stable interior 

of a continent (also see continental shield). 

crust. The outermost compositional shell of Earth, 10- 40 

km (6- 25 mi) thick, consisting predominantly of 

relatively low- density silicate minerals (also see 

oceanic crust and continental crust). 

crystalline. Describes the structure of a regular, orderly, 

repeating geometric arrangement of atoms; generally 

refers to igneous and metamorphic rocks. 

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, igneous intrusion that cuts across 

bedding. 

dip. The angle between a structural surface and a 

horizontal reference plane measured normal to their 

line of intersection. 

extrusive. Of or pertaining to the eruption of igneous 

material onto the surface of Earth. 

fault. A break or fracture 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) 

graywacke. A dark gray rock composed of poorly sorted 

grains of quartz, feldspar, clay and mineral fragments 

usually indicating rapid deposition. 

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. 

island arc. A line or arc of volcanic islands formed over 

and parallel to a subduction zone. 

lacustrine. Pertaining to, produced by, or inhabiting a 

lake or lakes. 

lapilli. Airborne volcanic (pyroclastic) fragments that 

range in size from 2- 64 mm. 

lapilli tuff. A pyroclastic rock composed mainly of lapilli. 

lava. Magma that has been extruded out onto Earth’s 

surface, both molten and solidified. 

left-lateral fault. A strike- slip fault on which the side 

opposite the observer has been displaced to the left. 

Also called a sinistral fault. 

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. 

mafic. A rock, magma, or mineral rich in magnesium and 

iron. 

magma. Molten rock generated within Earth that is the 

parent of igneous rocks. 

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. 

member. A stratigraphic unit with definable contacts that 

subdivides a formation. 

metamorphism. Literally, “change in form”. 

Metamorphism occurs in rocks with mineral 

alteration, genesis, and/or recrystallization from 

increased heat and pressure. 

migmatite. Literally, “mixed rock” with both igneous and 

metamorphic characteristics due to partial melting 

during metamorphism. 

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

moves down relative to the footwall. 

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. 

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

to 64 mm in diameter. 
 VOYA Geologic Resource Evaluation Report 23

phyllite. A metamorphic rock intermediate in grade 

between slate and mica schist. 

phyllonite. A rock formed by mechanical degradation 

(mylonization) of coarser rocks (e.g. granite or gneiss) 

pillow lavas. Lavas that extruded in a subaqueous 

environment characterized by discontinuous, often 

overlapping bun- shaped masses; usually composed of 

basalt or andesite. 

pluton. A body of intrusive igneous rock. 

porosity. The proportion of void space (cracks, 

interstices) in a volume of a rock or sediment. 

right-lateral fault. A strike- slip fault on which the side 

opposite the observer has been displaced to the right. 

Also called a dextral fault. 

sediment. An eroded and deposited, unconsolidated 

accumulation of rock and mineral fragments. 

sedimentary rock. A consolidated and lithified rock 

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

silt. Clastic sedimentary material intermediate in size 

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

mm). 

strata. Tabular or sheet- like masses or distinct layers 

(e.g., of rock). 

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. 

subduction zone. A convergent plate boundary where 

oceanic lithosphere descends beneath a continental or 

oceanic plate and is carried down into the mantle. 

tectonic. Relating to large- scale movement and 

deformation of Earth’s crust. 

terrane. A region or group of rocks with similar geology, 

age, or structural style. 

till. An unsorted, unstratified, and generally 

unconsolidated heterogeneous mixture of clay, silt, 

sand, gravel, and boulders deposited directly by and 

underneath a glacier. 

topography. The general morphology of Earth’s surface 

including relief and location of natural and 

anthropogenic features. 

tuff. Generally fine- grained, igneous rock formed of 

consolidated volcanic ash. 

volcanic ash. Fine pyroclastic material ejected from a 

volcano (also see tuff). 

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. A more complete geologic 

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

Division. 

Chandler, V.W., 1994, Earthquakes in Minnesota: 

Minnesota at a Glance, Minnesota Geological Survey, 

University of Minnesota, St. Paul, MN. 

Davis, S.R., Hite, A.G., and Larson, W.S., 1994, Mineral 

occurrences and development potential near 

Voyageurs National Park, Minnesota: U.S. 

Department of the Interior, Bureau of Mines, MLA 5-

94, Intermountain Field Operations Center, Denver, 

CO., 153 p. 

Day, W.C., 1990, Bedrock geologic map of the Rainy 

Lake area, northern Minnesota: USGS Map I- 1927, 

scale 1:50,000. 

Harris, A.G., Tuttle, E., Tuttle, S.D., 1995, Geology of 

National Parks: Kendall/Hunt Publishing Co., 

Dubuque, IA, p. 247- 258. 

Hauser, E.C., 1996, Midcontinent rifting in a Greenville 

embrace, in B.A. van der Pluijm, and P.A. Catacosinos, 

eds., Basement and Basins of Eastern North America: 

Geological Society of America Special Paper 308, p. 

67- 75. 

Hemstad, C.B., Southwick, D.L., and Ojakangas, R.W., 

2002, Bedrock geologic map of Yoyageurs National 

Park and Vicinity: Minnesota Geological Survey and 

University of Minnesota, Map M- 125, scale 1:50,000. 

Kiver, E.P., and Harris, D.V., 1999, Geology of U.S. 

Parklands: John Wiley & Sons, Inc., New York, p. 177-

189. 

Mikelson, D.M., Clayton, L., Fullerton, D.S., and Borns, 

H.W., Jr., 1983, The late Wisconsin glacial record of the 

Laurentide Ice Sheet in the United States, in S.C. 

Porter, ed., Late- Quaternary Environments of the 

United States: volume 1, The Late Pleistocene: 

University of Minnesota Press, Minneapolis, p. 3- 37. 

Miller, J.D., Jr., Morey, G.B., and Weiblen, P.W., 1987, 

Seagull Lake- Gunflint Lake area; A classical 

Precambrian stratigraphic sequence in northeastern 

Minnesota, in D.L. Biggs, ed., North- Central Section 

of the Geological Society of America: Geological 

Society of America, Centennial Field Guide, v. 3, p. 47-

51. 

Minnesota Geological Survey and University of 

Minnesota, 1969, An evaluation of the mineral 

potential of the proposed Voyageurs National Park, 

Minneapolis, MN., 16 p. 

NPS, 1994, Natural Resources Management Plan and 

Environmental Assessment, Voyageurs National Park, 

MN.: Department of the Interior, National Park 

Service, p. I- 3 – I- 38, II- 00- 1 – II- 00- 22, II- 03- 6 – II03- 12. 

NPS, 2001, General Management Plan/Environmental 

Impact Statement: Volume I: Department of the 

Interior, National Park Service, 426 p. 

Teller, J.T., and Clayton, L., 1983, Glacial Lake Agassiz: 

The Geological Association of Canada, Special Paper 

26, 451 p. 

Weeks, D.P., and Andrascik, R.J., 1998, Voyageurs 

National Park, Minnesota, Water Resources Scoping 

Report: National Park Service, Technical Report 

NPS/NRWRS/NRTR- 98/201, 51 p. 
 VOYA Geologic Resource Evaluation Report 25

Appendix A: Geologic Map Graphic 

The following page provides a preview or “snapshot” of the geologic map for Voyageurs 

National Park. 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. 

 VOYA Geologic Resource Evaluation Report 27

Appendix B: Scoping Summary 

The following excerpts are from the GRE scoping summary for Voyageurs National 

Park. The scoping meeting occurred June 1- 2, 2000; therefore, the contact information 

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

Resources Division for current information. 

Summary 

A geologic resources inventory workshop was held for 

Voyageurs National Park on June 1- 2, 2000 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 Voyageurs National 

Park, University of Minnesota and Minnesota Geological 

Survey staff were present for the workshop. 

This involved a very cold and wet one- day field trip to 

view the geology of the Voyageurs National Park area led 

by Chris Hemstad (University of Minnesota) and 

another one- day scoping session to present overviews of 

the NPS Inventory and Monitoring (I&M) program, the 

Geologic Resources Division, and the on- going Geologic 

Resouces Inventory (GRI). Round table discussions 

involving geologic issues for Voyageurs National Park 

included interpretation, the status of geologic mapping 

efforts, sources of available data, geologic hazards, and 

action items generated from this meeting. 

Items of discussion included the following: 

Geologic Mapping 

Chris Hemstad (University of Minnesota, Ph.D. 

candidate) is currently involved in a project to produce a 

compilation geologic map of Voyageurs National Park at 

1:50,000 scale. He will be using the existing USGS 

“I:50,000 scale metric topographic map of Voyageurs 

National Park, Minnesota (1979)” as the base map. 

He is using some of the existing unpublished “detailed 

reconnaissance” work of David Southwick (Minnesota 

GS) and Richard Ojakangas (University of Minnesota) 

and filling in where necessary. Southwick and Okakangas 

focused their efforts on shoreline mapping as part of 

mineral appraisal studies. Chris is mapping at 1:24,000 

scale using transects across various land areas of 

Voyageurs National Park. Chris is being funded through 

the EDMAP program and has received some funding 

from the NPS- GRI for his mapping activities. USGS 

funds cover 50 percent and the University of Minnesota 

covers the other 50 percent. He is in the second year of 

his EDMAP project. 

At the time of this meeting, Chris had completed 1:24,000 

scale detailed mapping of the Island View quadrangle 

(published by the MN GS) and is close to completion of 

the Cranberry Bay quadrangle. 

Previous work of Southwick and Ojakangas is also at 

1:24,000 scale (??). both will be compiling their existing 

work on mylars to be put in a final compilation by Chris. 

It is assumed that both edge- and unit- matching will be 

undertaken by all three authors prior to compilation. 

Chris sees the ultimate product of the compiled map as a 

1:50,000 scale map that could be sold in the Voyageurs 

visitor center. Funding for this cannot come from GRI, 

as we are not allowed to fund publication costs and will 

need to be sought elsewhere. 

As part of this mapping, it was suggested to work up the 

Kettle Falls and Ash River quadrangles (because of its 

high use) as detailed as possible as part of this project. 

Digital Geologic Map coverage 

At the time of this meeting, there was still confusion as to 

how to complete digital geologic coverage. By meetings 

end, it was suggested that the maps be digitized at the 

MN GS, so that the maps creator could oversee the 

digitization and answer any questions that may come up 

with regards to interpreting the maps. 

As of Fall 2000, GRI staff have allocated $5000 to cover 

digitization costs and will transfer the money to 

Voyageurs National Park to distribute to the MN GS or 

whoever will be digitizing the Voyageurs maps in Fall 

2000. 

If this were done at the MN GS, GRI staff would like to 

see the NPS Digital Geologic map model utilized (as 

demonstrated by GRI staff during the scoping session). A 

copy of the model can be supplied to the digitizing party. 

Contact Tim Connors for further information. 

Disturbed Lands and Abandoned Mineral Lands 

Voyageurs staff expressed interest in compiling data 

about disturbed land sites (gravel sites and old 

campgrounds and the Kettle Falls area), and other 

abandoned mineral lands (AML). It was suggested they 

contact GRD Disturbed Lands/ AML coordinator Dave 

Steensen (303- 969- 2014) with specific concerns on these 

matters. 

Additionally, the Bureau of Mines has published Mineral 

Occurrences and Development Potential near Voyageurs 

National Park, Minnesota (Mineral Land Assessment 

Open File Report 5- 94). 
 NPS Geologic Resources Division 28 

Interpretation 

Currently Kendall Dickinson (retired USGS) is working 

on Geology of Voyageurs National Park as an 

interpretive product for the general public. He is also 

seeking funding for this publication. It is not yet known if 

this publication would be suitable for the GRI needs of 

our geologic report and is currently under review by 

GRD staff. 

Southwich and Ojakangas would like the opportunity to 

critically review this report. 

Also mentioned were other geologic publications specific 

to Minnesota geology including a geology underfoot 

book and the Roadside Geology of Minnesota, both of 

which were likely to have sections on VOYA and other 

NPS areas in Minnesota. 

Geologic Report 

A comprehensive technical geologic report was 

discussed as a necessary component of the GRI. Again, at 

present, it is not known if Dickinson’s publication will 

fulfill this requirement. 

It was suggested that perhaps Chris Hemstad, Richard 

Ojakangas or David Southwick could be “coerced” into 

writing such a report in their copious free time for 

compensation. It they are interested, please let GRI staff 

know. 

Miscellaneous 

Geologic hazards include boats hitting rocks in the lake, 

the dangers of falling in the Little American Mine, and 

potential for earthquakes in the region. 

David Southwick mentioned he had done a cooperative 

report on Pipestone NM; GRI staff would be interested 

in obtaining this report from the Minnesota Geological 

Survey 

 

Scoping Session Attendees: 

Name Affiliation Phone E- Mail 

Roger Andrascik NPS, VOYA 218- 283- 9821 Roger_Andrascik@nps.gov 

Tim Connors NPS, GRD 303- 969- 2093 Tim_Connors@nps.gov 

Sid Covington NPS, GRD 303- 969- 2154 Sid_Covington@nps.gov 

Lee Grim NPS, VOYA 218- 283- 9821 Lee_Grim@nps.gov 

Bruce Heise NPS, GRD 303- 969- 2017 Bruce_Heise@nps.gov 

Chris Hemstad University of Minnesota 218- 286- 5560 Chemstad@d.umn.edu 

Richard Ojakangas University of Minnesota 218- 726- 7923 Rojakang@d.umn.edu 

JimSchaberl NPS, VOYA 218- 283- 9821 Jim_Schaberl@nps.gov 

David Southwick Minnesota Geological Survey 612- 627- 4780 x 224 South002@tc.umn.edu 

Barb West NPS, VOYA Superintendent 218- 283- 9821 Barbara_West@nps.gov 

Wayne Wold NPS, VOYA GIS 218- 283- 9821 Wayne_Wold@nps.gov 
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. 

Voyageurs National Park 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2007/007 

NPS D-158, 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 • Dr. John Graham

Editing • Sid Covington 

Layout • Melanie Ransmeier 

Digital Map Production • Victor DeWolfe, Stephanie O’Meara, and the Minnesota Geological Survey
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