Late Quaternary Glacial and Vegetative 

History of the Glacier National Park 

Region, Montana 

U.S. GEOLOGICAL SURVEY BULLETIN 1902 
Cover. Agassiz Glacier and Kintla Peak (3,080 m) from the Boulder Pass area. Photograph by W.C. Alden (no. 705), 

August 5, 1913. U.S. Geological Survey Photo Library, Denver, CO 80225. 
LATE QUATERNARY GLACIAL AND VEGETATIVE HISTORY OF THE 

GLACIER NATIONAL PARK REGION, MONTANA 
Frontispiece. Agassiz Glacier and Kintla Peak (3,080 m) from the Boulder Pass area, August 17, 1981. 
Late Quaternary Glacial and Vegetative 

History of the Glacier National Park 

Region, Montana 

By PAUL E. CARRARA 

U.S. GEOLOGICAL SURVEY BULLETIN 1902 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government. 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1989 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Carrara, Paul E. 

Late quaternary glacial and vegetative history of the Glacier National Park 

region, Montana I by Paul E. Carrara. 

p. em. - (U.S. Geological Survey bulletin ; 1902) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3:1902 

1. Geology, Stratigraphic-Pleistocene. 2. Geology-Montana -Glacier 

National Park Region. 3. Paleobotany-Montana-Glacier National Park 

Region. 4. Paleobotany-Pleistocene. I. Title. II. Series. 

QE75.B9 no. 1902 

[QE697] 

557.3 s-dc20 89-600271 

[551.7'92'0978652] CIP 
CONTENTS 

Abstract 1 

Introduction 2 

Purpose and methods 2 

Geology and geography 2 

Climate 5 

Forests 6 

Acknowledgments 6 

Glacier National Park during the late Wisconsin glaciation 7 

Volcanic ashes in the Glacier National Park region 8 

Mazama ash 8 

Glacier Peak G ash 9 

Mount St. Helens Jy ash 9 

Identification of ashes in the Glacier National Park region 11 

Radiocarbon ages and volcanic ashes from bogs and exposures in the Glacier 

National Park region 13 

Bowman Lake area 14 

Cabin Creek exposure 14 

Bowman Lake bog 16 

Numa Ridge bog 16 

Discussion 18 

Lake McDonald area 20 

McGee bog 21 

East McGee bog 22 

Glacier Route 7 bog 22 

Howe Lake bog 25 

Ben Ryan bog 25 

Snyder Ridge bog 25 

Discussion 25 

Marias Pass area 27 

Marias Pass expo~ure 27 

Middle Fork bog 32 

Goat Lick exposure 32 

Guardipee Lake site 32 

Discussion 32 

Lower St. Mary Lake area 34 

Chewing Blackbones bog 34 

Discussion 34 

Kootenai Lakes area 36 

Mount Cleveland bog-hole #1 36 

Mount Cleveland bog-hole #4 37 

Discussion 37 

Deglaciation and revegetation elsewhere in the Rocky Mountains 37 

Moraines in the high areas of Glacier National Park 40 

Moraines of the older group 40 

Location and description 40 

Age 40 

Contents V 
Glaciers in Glacier National Park during the early to middle Holocene warm 

period 44 

Moraines of the younger group 45 

Location and description 45 

Age 45 

Climatic implications of the younger moraines 45 

Glacial fluctuations since the mid-19th century in Glacier National Park 46 

Conclusions 49 

Deglaciation 49 

Revegetation 53 

Moraines of the older group 54 

Moraines of the younger group 54 

Glacial fluctuations since the mid-19th century 55 

References cited 55 

Appendix A. Preparation and analysis of ashes by X-ray fluorescence 60 

Collecting and processing of ash samples 60 

Comparison of X-ray fluorescence data with electron-microprobe data 60 

Mazama ash 60 

Glacier Peak B and G ashes 61 

Mount St. Helens J ashes 63 

FIGURES 

1. General location and place name map of the Glacier National Park region, 

Montana 3 

2. General stratigraphic section in the Glacier National Park region 4 

3. Map of the Glacier National Park region showing late Wisconsin ice 

limits 7 

4. Map showing distribution pattern of the Mazama, Glacier Peak Band G, and 

Mount St. Helens Jy ashes 10 

5. Scanning electron micrographs of glass shards in the Mazama, Glacier Peak 

G, and Mount St. Helens Jy ashes 12 

6. Map of Bowman Lake area 18 

7. Diagram showing stratigraphy of the three bogs in Bowman Lake area 19 

8. Photograph of Cabin Creek exposure, showing the Glacier Peak G and 

Mount St. Helens Jy ashes 20 

9. Photograph of Numa Ridge bog 22 

10. Map of Lake McDonald area 23 

11. Diagram showing stratigraphy of the three bogs in the McGee Meadow 

area 24 

12. Diagram showing stratigraphy of Howe Lake, Ben Ryan, and Snyder Ridge 

bogs 26 

13. Map of Marias Pass area 28 

14. Diagram showing stratigraphy of Marias Pass exposure and Middle Fork 

bog 29 

15. Photograph of Glacier Peak G ash at Marias Pass exposure 30 

16. Percentage pollen diagram from Marias Pass exposure 31 

17. Photograph of Goat Lick exposure 33 

VI Contents 
18. Map of Lower St. Mary Lake area 35 

19. Stratigraphic section at Chewing Blackbones bog 36 

20. Map of Kootenai Lakes area 36 

21. Diagram showing stratigraphy of Mount Cleveland bog, holes #1 and 

#4 38 

22. Photograph of Sperry Glacier area showing moraines of both the older and 

younger groups 41 

23. Longitudinal profile of Agassiz Glacier area showing results of tree-ring 

studies 42 

24. Longitudinal profile of Jackson Glacier area showing results of tree-ring 

studies 43 

25. Map of mid-19th century Blackfoot Glacier showing disintegration of this 

glacier into the present-day Blackfoot and Jackson Glaciers 47 

26. Graphs of climatic data, Kalispell, Montana 48 

27. Map of former Logan and Red Eagle glacier areas showing moraines of both 

the older and younger groups, and Mazama ash sites 49 

28. Photograph of former Red Eagle glacier area showing moraines of both the 

older and younger groups 50 

29. Photograph of Agassiz Glacier area, showing mid-19th century extent and 

remnant snowfield 51 

30. Map of Sperry Glacier area, showing glacier shrinkage, moraines of the older 

and younger groups, and Mazama ash sites 52 

31. Photograph of Jackson Glacier area showing mid-19th century extent, and 

remnant glacier 53 

TABLES 

1. Climatic data from stations in the Glacier National Park region 6 

2. Major-element values of glass in the Mazama ash from bogs in the Glacier 

National Park region 15 

3. Major-element values of glass in the Mazama ash from soils in the Glacier 

National Park region 16 

4. Major-element values of glass in the Glacier Peak G ash from bogs and 

exposures in the Glacier National park region 17 

5. Major-element values of glass in the Mount St. Helens Jy ash from the 

Glacier National park region 18 

6. Radiocarbon age determinations from the Glacier National Park region 21 

7. Major-element values of glass in the Mazama ash, as reported by various 

investigators 61 

8. Major-element values of glass in the Glacier Peak B ash from the Trinity 

Mine, Washington, as reported by various investigators 62 

9. Major-element values of glass in the Glacier Peak Gash from the Trinity 

Mine, Washington, as reported by various investigators 62 

10. Major-element values of glass in the Glacier Peak G ash from Sun River 

Canyon, Montana, as reported by various investigators 63 

11. Major-element values of glass in the Mount St. Helens Jb, Jy, and Js 

ashes 64 

Contents VII · 

Late Quaternary Glacial and Vegetative History of the 

Glacier National Park Region, Montana 

By Paul E. Carrara 

Abstract 

Deglaciation was at least 90 percent complete in the 

Glacier National Park region by the time the Glacier Peak G 

(11 ,200 yr. BP) and Mount St. Helens Jy (11 ,400 yr. BP) 

ashes were deposited. The presence of these two ashes at 

Marias Pass, on the Continental Divide, indicates that the 

Marias Pass area was deglaciated before 11,400 yr. BP. The 

fact that the Two Medicine Glacier, a large piedmont glacier 

on the plains of Montana, was supplied by ice that flowed 

through Marias Pass indicates that this glacier retreated from 

the plains of Montana long before 11,400 yr. BP. Hence, by 

that time, former tributary glaciers along the eastern side of 

the Lewis Range in Glacier National Park no longer flowed 

east beyond the mountain front but were confined to their 

respective mountain valleys. 

On the west side of Glacier National Park, the large 

trunk glacier that filled the valley of the North Fork Flathead 

River had retreated at least 10 km north of the site of the 

present-day town of Polebridge by the time the Glacier Peak 

G and Mount St. Helens Jy ashes were deposited. Similarly, 

the valley of the Middle Fork Flathead River was ice-free by 

the time the Glacier Peak Gash was deposited. Furthermore, 

stratigraphic evidence in both valleys suggests that the large 

trunk glaciers that occupied these valleys may have retreated 

from these areas several hundred to several thousand years 

before the deposition of the Glacier Peak G and Mount St. 

Helens Jy ashes. 

By 11,200 yr. BP, glaciers in the Lewis, Livingston, 

Whitefish, and Flathead Ranges that were formerly tributary 

to the North and Middle Fork trunk glaciers were confined to 

their local mountain valleys. This conclusion is indicated by a 

radiocarbon age of 11,150±90 yr. BP (W-5043) from a bog 

on a moraine at the lower end of Bowman Lake and by the 

presence of the Glacier Peak Gash in a bog on a moraine 

deposited by the former McDonald glacier about 1 km 

southeast of the site of the present-day town of West Glacier. 

By 11,000 to 10,000 yr. BP, remaining glaciers in 

Glacier National Park were probably confined to the same 

cirques and well-shaded niches where present-day glaciers 

and snowfields lie. Although evidence was not found in the 

park, data from other areas in the Rocky Mountains suggest 

Manuscript approved for publication, June 30, 1989. 

that by as early as 11 ,000 yr. BP remaining glaciers may have 

been similar in size to present-day glaciers. Radiocarbon 

ages near present-day glaciers in Banff and Jasper National 

Parks, Alberta, and Yoho National Park, British Columbia, 

indicate that by 10,000 yr. BP, late Wisconsin glaciers had 

receded to positions close to those of present-day glaciers. A 

similar amount of deglaciation by these times is inferred for 

the Glacier National Park region. 

Initial revegetation of the Glacier National Park region 

had also occurred by the time the Glacier Peak G and Mount 

St. Helens Jy ashes were deposited. At Marias Pass, a 

conifer needle and an alder strobile were found beneath the 

Glacier Peak G ash, and several small willow fragments were 

found beneath the Mount St. Helens Jy ash. Pollen and 

insect macrofossils below the Mount St. Helens Jy ash at this 

site indicate that when this ash was deposited treeline was at 

least 500 m lower than present and possibly as much as 700 

m lower. 

Reforestation by at least 10,000 yr. BP is documented in 

several areas in Glacier National Park. In the McGee Meadow 

area, radiocarbon ages on lodgepole pine fragments indicate 

that this species was established by at least 10,000 yr. BP. 

Stratigraphic evidence from one bog in this area suggests 

that lodgepole pine may have been established as early as 

11 ,000 yr. BP. In the Howe Lake area, a radiocarbon age on 

a wood fragment indicates that either spruce or larch was 

growing in this area by at least 10,600 yr. BP. In the Kootenai 

Lakes area, a radiocarbon age on lodgepole pine fragments 

suggests that this species was growing there by about 

10,000 yr. BP. On Snyder Ridge, a radiocarbon age on gyttja 

containing coniferous wood fragments indicates the 

presence of conifers there by about 10,000 yr. BP. 

Two groups of moraines have been identified fronting 

the present-day glaciers and snowfields in the higher areas of 

Glacier National Park. Mazama ash in the soil overlying 

moraines of the older group establishes a minimum age of 

6,845 yr. BP for these moraines. Vegetative evidence and 

correlation with other moraines elsewhere in the Rocky 

Mountains suggest that the older moraines are latest Pleistocene in age. Whether these moraines were formed by the 

last advance or stillstand of Wisconsin glaciers or formed by 

a separate advance after the Wisconsin glaciation is not 

known. 

Abstract 
The younger group of moraines was formed by 

advances that culminated in the mid-19th century as 

indicated by tree-ring studies at several localities in the park. 

During that time, Glacier National Park contained more than 

150 glaciers. The climatic cooling of the mid-19th century that 

produced these moraines, although mild compared to fullglacial conditions, was the most severe climatic deterioration 

in the Glacier National Park region since the end of the 

Wisconsin glaciation. 

Since the mid-19th century, glaciers in Glacier National 

Park have shrunk dramatically. From the mid-19th century 

until about 1920 retreat rates were slow. From 1920 to the 

mid-1940's the Glacier National Park region experienced a 

period of above average summer temperatures and below 

average annual precipitation that caused the glaciers to 

retreat drastically; many disappeared altogether. After the 

mid-1940's, the overall retreat rates slowed. Between 1966 

and 1979, several of the larger glaciers in the Mount Jackson 

area advanced slightly. 

INTRODUCTION 

Purpose and Methods 

This report presents the late Quaternary glacial 

and vegetative history of the Glacier National Park 

region, northwestern Montana, based on field mapping, 

volcanic ash identification, radiocarbon age determinations, and tree-ring analysis. Field mapping was 

done during the summers of 1981 to 1985 as part of a 

U.S. Geological Survey project to update the geological 

knowledge of Glacier National Park. 

Three volcanic ashes erupted from volcanos in the 

Cascade Range of the Pacific Northwest have been 

identified in postglacial deposits in the Glacier National 

Park region. These ashes are the (1) Mazama, (2) 

Glacier Peak G, and (3) Mount St. Helens Jy. The 

Mazama ash, erupted in the middle Holocene, is a useful 

time-stratigraphic marker because it is commonly found 

in bogs and exposures throughout the Glacier National 

Park region. In addition, because this ash is also found in 

soils overlying glacial deposits in the higher areas of the 

park, it provides a minimum age for these deposits that 

could not be radiocarbon dated because of a lack of 

associated organic material (Osborn, 1985; Carrara, 

1987). 

The Glacier Peak G and Mount St. Helens Jy ashes 

were erupted in the late Pleistocene, when the Glacier 

National Park region was undergoing extensive deglaciation. Because these ashes would not be preserved if 

they had fallen on glacial ice, the presence of these ashes 

at a site provides information concerning the extent of 

deglaciation at the time they were deposited (Carrara, 

1986). Also, at sites where these ashes are associated 

with pollen, plant fossils, and insect macrofossils, 

information concerning environmental conditions during 

the late Pleistocene has been obtained (Carrara and 

others, 1986). Because of the problems associated with 

the radiocarbon dating of late Pleistocene events in the 

Glacier National Park region, the Glacier Peak G and 

Mount St. Helens Jy ashes are invaluable timestratigraphic markers. 

Thirteen radiocarbon ages were obtained from 

organic material collected from bogs and exposures in 

the Glacier National Park region. Radiocarbon dating of 

the lowermost organic material at these sites has yielded 

minimum ages for deglaciation and the beginning of 

organic sedimentation. Radiocarbon dating of wood 

fragments from some of these sites has yielded minimum 

ages for the establishment of shrubs and trees following 

deglaciation. 

Cores were taken from trees within the forest 

trimlines fronting the Agassiz and Jackson Glaciers and 

also from trees immediately beyond the fresh, bouldery 

moraines of several other glaciers in the park. These 

cores were analyzed to date the glacial advance of the 

mid-19th century. 

This report documents the presence of the three 

late Quaternary ashes in the Glacier National Park 

region and describes the stratigraphy at the sites of these 

ashes and (or) organic material on which radiocarbon 

age determinations were made. Next, this report 

discusses the implications of these ashes and radiocarbon 

ages to the late Quaternary history of the Glacier 

National Park region. The use of the Mazama ash to 

establish a minimum age for glacial deposits in the higher 

areas of the park is also discussed. In addition, this report 

documents the use of tree-ring analysis to date the minor 

glacial advance of the mid-19th century and subsequent 

recessiOn. 

Geology and Geography 

Glacier National Park, located in northwestern 

Montana adjacent to the Canadian border and 

comprising parts of Flathead and Glacier Counties, 

covers about 4,000 km2 (fig. 1). The park is an area of 

diverse topography underlain by rocks ranging in age 

from Precambrian to Tertiary (fig. 2), which are in many 

places mantled by surficial deposits of late Quaternary 

age (Carrara, 1989). 

On the west, trending northwest to southeast, are 

the valleys of the North and Middle Forks Flathead River 

(fig. 1) whose valley floors range in altitude from about 

1,280 to 975 m. These valleys have been down-dropped 

on the east and are underlain by about 5,000 m of the 

upper Paleogene Kishenehn Formation, consisting of 

lacustrine and fluvial sedimentary rocks (Constenius, 

2 Late Quaternary History, Glacier National Park Region, Montana 
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Figure 1. General location and place names in the Glacier National Park region, Montana. 
Surficial deposits ~ 

Kishenehn 

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Two 

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Medicine 

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Virgelle Sandstone 

Telegraph Creek Formation 

Marias River Shale 1.-- ~ 

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Formation 

Helena Formation 

Empire Formation 

Grinnell Formation 

Appekunny Formation ~ ~ ~ r--- A It~ Prichard ) Formation 

Formation ) Waterton 

Formation 

) Holocene 

) Pleistocene 

Belt Supergroup 

QUATERNARY 

TERTIARY 

CRETACEOUS 

JURASSIC 

LATE 

PROTEROZOIC 

MIDDLE 

PROTEROZOIC 

Figure 2. General stratigraphic section in the Glacier 

National Park region (modified from Ross, 1959; Mudge 

and Earhart, 1983; Raup and others, 1983; Whipple and 

others, 1984; J.W. Whipple, written commun., 1984; and 

Earhart and others, 1989). 

1981 ). In some places, these rocks have failed, resulting 

in large landslides, such as the one in the Halfmoon Lake 

area. In other areas the Kishenehn Formation is covered 

by late Wisconsin till as much as 30 m thick. Depressions 

within this till contain many bogs filled with peats, 

organic muds, and volcanic ashes. Valley glaciers 

emerging from the western flank of the Livingston Range 

carved large, U-shaped valleys in the underlying Kishenehn Formation. Many of these valleys now contain 

large, deep lakes (including Kintla, Bowman, Quartz, 

Logging, and McDonald Lakes). 

The central part of Glacier National Park is 

dominated by two rugged mountain ranges (fig. 1), 

trending northwest to southeast, that contain many small 

glaciers and snowfields. The Livingston Range on the 

west extends about 35 km from the Canadian border 

south to the Lake McDonald area. The Lewis Range on 

the east extends about 100 km from the border south 

through the park to Marias Pass. Large areas of these 

two ranges lie above timberline (about 2,000 m), and 

many peaks exceed 2,800 m in altitude. Mount Cleveland 

(3,191 m), about 8 km south of the border in the Lewis 

Range, is the highest peak in Glacier National Park. 

Local relief between many valleys and the surrounding 

summits is as much as 1,500 m. The Continental Divide 

follows the crest of the Lewis Range northward to about 

16 km south of the border, then swings westward and 

follows the crest of the Livingston Range to Canada. 

Both mountain ranges are underlain by Proterozoic sedimentary rocks of the Belt Supergroup (fig. 2) 

ranging from about 1,600 Ma to 800 Ma (Raup and 

others, 1983). These rocks consist of a sequence of 

argillites, siltites, and carbonates with a maximum stratigraphic thickness of about 5,200 m (Whipple and others, 

1984). Although these rocks have been affected by lowgrade regional metamorphism, many of their original 

sedimentary features (ripple marks, mud cracks, salt 

casts, and fossil algal stromatolites) are well preserved. In 

places, these rocks have been intruded by diabasic and 

gabbroic sills and dikes. Near the upper part of the 

section, mafic lava flows 10-60 m thick are present 

(McGimsey, 1985). In the Paleocene, this entire 

sequence of rocks was displaced about 65 km east over 

Cretaceous sedimentary rocks along the Lewis thrust 

(Raup and others, 1983). Today these rocks form a broad 

syncline whose axis closely parallels the Continental 

Divide (Ross, 1959). 

The Lewis and Livingston Ranges contain various 

surficial deposits (Carrara, 1989). A large block slide is 

present immediately west of Avalanche Lake and several 

block slides are also present in the area north of Glenn 

Lake. Steep valley sides, whose forest is scarred by snow 

avalanche tracks, are mantled by colluvium. Talus cones 

and sheets are common at the base of steep slopes and 

cliffs. Late Wisconsin till mantles the floors of many of 

the mountain valleys. In the higher areas of both ranges, 

two groups of moraines front the present-day glaciers 

and snowfields (Osborn, 1985; Carrara, 1987; Carrara 

and McGimsey, 1988). On the high, unglaciated upland 

surfaces, stone stripes, sorted polygons, and solifluction 

deposits have been formed on the regolith by severe frost 

action (Carrara, 1989). 

East of the Lewis thrust lies the western margin of 

the Montana plains. Here altitudes range from about 

1,370 to 2,000 m. This area consists of low, rounded hills 

mantled in places with a veneer of glacial till and 

underlain mainly by a dark-gray marine mudstone of the 

Upper Cretaceous Marias River Shale (Mudge and Earhart, 1983). In many places immediately east of the Lewis 

thrust, Pleistocene valley glaciers gouged deep, steepsided valley walls in these soft rocks as they emerged 

from the Lewis Range. These rocks have since failed and 

formed large landslides (Carrara, 1989). 

4 Late Quaternary History, Glacier National Park Region, Montana 
Two large rivers, the North and Middle Forks 

Flathead River (fig. 1), drain the west side of Glacier 

National Park. The North Fork Flathead River, one of 

the major rivers of northwestern Montana, heads in 

British Columbia and flows southeast about 120 km, 

draining an area of about 4,200 km2 (Erdmann, 1947). 

Streams draining the eastern flank of the Whitefish 

Range and the western flank of the Livingston Range in 

Glacier National Park (Kintla, Akokala, Bowman, 

Quartz, Logging, Anaconda, Dutch, and Camas Creeks) 

are tributary to this river. The Middle Fork Flathead 

River heads in the Lewis and Clark Range, south of 

Glacier National Park in the Great Bear Wilderness, and 

flows northwest about 100 km to the town of West 

Glacier, draining an area of about 2,900 km2 (Erdmann, 

1947). Streams draining the eastern flank of the Flathead 

Range and the western flank of the Lewis Range in 

Glacier National Park south of Lake McDonald 

(Lincoln, Harrison, Nyack, Coal, Park, and Ole Cree~s) 

are tributary to this river. Near the town of West Glacier 

the Middle Fork Flathead River is joined by McDonald 

Creek, which drains a large area in the north-central part 

of the park enclosed by the Livingston Range on the west 

and the Lewis Range on the east. About 7 km southwest 

of the town of West Glacier, the North and Middle Forks 

Flathead River join and flow south 10 km to the town of 

Hungry Horse, where they are joined by the northwestflowing South Fork Flathead River. This river, which 

heads in the Swan Range and the Lewis and Clark Range 

about 140 km southeast in the Bob Marshall Wilderness, 

drains an area of about 4,450 km2 (Erdmann, 1947). The 

combined Flathead River then flows west about 3 km 

through Bad Rock Gap, where it turns south and flows 

about 65 km to Flathead Lake. The Flathead River is a 

tributary of the Clark Fork of the Columbia River. 

The east side of Glacier Park is drained by several 

rivers that head along the Continental Divide (fig. 1 ). The 

Waterton, Belly, and St. Mary Rivers drain the northern 

and northeastern areas of Glacier National Park. These 

rivers flow north and northeast into Canada and are part 

of the Hudson Bay drainage system. The Two Medicine, 

Cutbank, and Milk Rivers drain valleys along the east 

flank of the Lewis Range south of St. Mary Lake. The 

Two Medicine and Cutbank Rivers flow east about 100 

km to the Marias River. The Milk River flows northeast 

into Canada, then southeast and east back into the 

United States about 400 km to the Missouri River. 

Climate 

The Continental Divide separates the Glacier 

National Park region into two areas dominated by 

different climatic systems. The area west of the 

Continental Divide, which is the wettest part of Montana, 

is dominated mainly by Pacific air masses. However, 

during the winter, cold continental polar air masses from 

Canada sometimes pour over the mountains into this 

area. Also, in the spring and summer, air masses from the 

Gulf of Mexico sometimes invade this area (Cunningham, 1982). In this area, winter is the wettest season and 

snowfalls are quite heavy. However, both the towns of 

Polebridge and West Glacier record significant 

precipitation during May and June (U.S. Dept. of 

Commerce, 1982), reflecting the effect of the invasion of 

warm moist air masses from the Gulf of Mexico. The 

period of minimum precipitation on both sides of the 

park is July and August (Finklin, 1986). 

The area east of the Continental Divide is 

dominated by cold, dry continental-polar air masses 

during the winter. Here winter precipitation is slight. 

From October to March, the towns of Babb and 

Browning receive only 28 percent and 33 percent, 

respectively, of their annual precipitation (U.S. Dept. of 

Commerce, 1982). During the winter, strong Chinook 

winds can occur when Pacific air masses invade this area. 

These air masses, which lose their moisture as they 

ascend the western slopes, warm adiabatically as they 

descend the eastern slopes, producing winds that may 

exceed 160 km/hr (Cunningham, 1982; Finklin, 1986). In 

this area, the wet season is from April through June and 

is caused by the incursion of air masses from the Gulf of 

Mexico after the northward retreat of the polar front in 

the spring (Cunningham, 1982). 

These air masses from the Gulf of Mexico can 

cause extensive flooding when heavy rains from them fall 

on late-lying snowpack. For instance, in June 1964 as 

much as 37 em of rain fell over a 30-hour period in the 

central region of Glacier National Park (U.S. Dept. of 

Commerce, 1964). The towns of Browning, East Glacier 

Park, and Summit (fig. 1) received about 20 em of rain 

during this period. Record floods resulting from heavy 

rain on snowpack occurred in northwestern Montana on 

both sides of the Continental Divide. The floods were so 

severe that several dams were destroyed, including the 

Two Medicine Dam at Lower Two Medicine Lake (U.S. 

Dept. of Commerce, 1964). 

Climatic data from several stations in the Glacier 

National Park region are presented in table 1. Some 

climatic data also exist for the higher areas of the park. 

Annual precipitation near the Grinnell Glacier (fig. 1) 

(2,135 m altitude) averaged 265 em between 1950 and 

1966. Annual precipitation in the Grinnell valley below 

the glacier averaged 375 em between 1956 and 1966 

(Dightman, 1961, 1967). A storage precipitation gage on 

Flattop Mountain (fig. 1 ), at an altitude of 1,920 m, 

indicates an average annual precipitation of 200 em 

(Finklin, 1986), most of which falls a~ snow. ~now may 

fall in the higher areas of the park dunng any time of the 

year, and will often linger there until mid-summer. 

Introduction 5 
Table 1. Climatic data (1951-1980) from stations in the Glacier National Park region1 

[n.a., data not available] 

Average annual Average Average 

Station A1 ti tude ( m) precipitation (em) Jan. temperature (oC) July temperature (oC) 

Kalispell 903 39.0 -5.5 19.1 

West Glacier 962 76.0 -6.3 17.3 

Polebridge 1125 59.3 -8.3 15.8 

Babb 1311 47.6 n.a. n.a. 

Browning 1328 39.4 -8.4 16.8 

1united States Department of Commerce (1982). 

Forests 

Forests in Glacier National Park reflect the two 

different climatic systems that affect this region. Because 

of the influence of Pacific air masses west of the 

Continental Divide, many trees common in the Pacific 

Northwest reach their eastern limits in the western part 

of Glacier National Park (Hansen, 1948). These trees 

include western hemlock (Tsuga heterophylla), western 

red cedar (Thuja plicata), western white pine (Pinus 

monticola), and Pacific yew (Taxtls brevifolia). Grand fir 

(Abies grandis), also common in the Pacific Northwest, 

extends into Glacier National Park and areas farther to 

the southeast (Hansen, 1948). These trees, along with 

western larch (Larix occidentalis), Douglas fir (Pseudotsuga menziesii), western paper birch (Betula papyifera ), 

and quaking aspen (Populus tremuloides) form dense 

forests in moist sites at lower altitudes. Douglas fir and 

Rocky Mountain juniper (Juniperus scopulorum) can also 

be found at dry sites along the valley of the North Fork 

Flathead River. Lodgepole pine (Pinus contorta) and 

ponderosa pine (Pinus ponderosa) are common at lower 

altitudes along the west side of the park, and usually grow 

in drier, open areas. Trees in the subalpine zone on the 

west side of the park include subalpine fir (Abies /asiocarpa), Engelmann spruce (Picea engelmannii), subalpine larch (Larix lyalli), and whitebark pine (Pinus a/bicaulis). 

Forests in Glacier National Park east of the 

Continental Divide contain species also found in the 

southern Rocky Mountains of Colorado and New 

Mexico. These forests are more open and drier than 

those on the west side of the park. Trees here include 

lodgepole pine, quaking aspen, Douglas fir, limber pine 

(Pinus flexilis), subalpine fir, and Engelmann spruce. 

Lodgepole pine inhabit low and mid-altitudes and form 

almost pure stands in some areas. Aspen is found at 

lower altitudes in moisl sites and also on the many 

landslide deposits east ~f the Lewis thrust. Douglas fir 

inhabit low, dry sites in t is area. Limber pine is found at 

dry, windy sites at low . r altitudes, such as along the 

shores of St. Mary and Uower St. Mary Lakes, as well as 

near upper timberline. ~ngelmann spruce and subalpine 

fir are found from higher altitudes to treeline. 

Timberline in Glacier National Park is at an 

altitude of about 2,000 m. Above this altitude, thickets of 

dwarf, windswept (krummholz) subalpine fir and 

occasional Engelmann spruce extend upward to treeline, 

where they give way to tundra vegetation, at an altitude of 

about 2,050 m. Studies indicate that treeline in Glacier 

National Park is migrating upward (Habeck, 1969). 

Thickets of thinleaf alder (Alnus sp.) and willow 

(Salix sp.) are found on both sides of the park. These 

shrubs commonly inhabit moist sites, such as stream 

banks and the margins of bogs. 

Acknowledgments 

I thank D.S. Fullerton, W.R. Hansen, W.D. 

Johnson, R.F. Madole, D.R. Mullineaux, K.L. Pierce, 

G.M. Richmond, A.M. Sarna-Wojcicki, R.R. Shroba, 

C.A. Wallace, and R.E. Wilcox (U.S. Geological Survey) 

whose knowledge and ideas contributed to this report. 

D.R. Mullineaux and R.E. Wilcox also helped identify 

some of the ash samples reported in this study. J.A. Cary, 

P.L. Lewis, R.G. McGimsey, S.P. Schilling, and G.A. 

Swayze ably assisted the author in the field. D.J. 

6 Late Quaternary History, Glacier National Park Region, Montana 
113° 111° 

--r-----

St Mary Glacier 

Sun River Glacier 

0 Great Falls 

'1. e 

c 

0 Missoula 

50 100 KILOMETERS 

Figure 3. The Glacier National Park region showing late Wisconsin ice limits (modified from Alden, 1932, 1953; Calhoun, 

1906; Colton and others, 1961; Mickelson and others, 1983; Richmond, 1986; and Waitt and Thorson, 1983). 

Christensen and J.T. Quirk (Center for Wood Anatomy 

Research, Madison, Wisconsin) kindly identified wood 

fragments found in the various bogs and exposures. 

Emmett Evanoff (University of Colorado Museum) 

identified the fossil mollusks recovered from several of 

the bogs reported in this study. S.C. Porter (Quaternary 

Research Center, University of Washington) kindly 

provided samples of the Glacier Peak B and G ashes 

from the Trinity Mine site, Washington. D.M. Cheney 

and J.E. Jenness (U.S. Geological Survey) prepared the 

ash samples for chemical analysis; D.M. Cheney also 

provided the grain-size analyses. A.J. Bartel (U.S. 

Geological Survey) performed the X-ray fluorescence 

analyses. A.M. Sarna-Wojcicki analyzed the ash samples 

from Guardipee Lake. S.A. Elias and S.K. Short 

(Institute of Arctic and Alpine Research, University of 

Colorado) identified the fossil insects and pollen 

respectively from the Marias Pass exposure. This 

manuscript, or parts of it, benefited substantially from 

reviews by L.M. Carter, A.J. Donatich, W.R. Hansen, 

R.F. Madole, G.M. Richmond, V.S. Williams (U.S. 

Geological Survey), P.T. Davis (Bentley College), P.J. 

Mehringer, Jr. (Washington State University), and J.E. 

Beget (University of Alaska). 

GLACIER NATIONAL PARK DURING THE 

LATE WISCONSIN GLACIATION 

During the height of the late Wisconsin glaciation, 

much of northwestern Montana, including Glacier 

National Park, was covered by glacial ice (fig. 3). West of 

Glacier National Park lay the Cordilleran ice sheet, 

whose southern margin stretched from the Puget Sound 

area of Washington eastward to western Montana. This 

large ice sheet formed from the coalescence of large 

valley glaciers within the mountains of British Columbia. 

It then flowed south, overriding low mountain ranges in 

Washington, Idaho, and Montana, and sending ice lobes 

into the major valleys. The easternmost lobe of this ice 

sheet, the Flathead lobe, flowed south into the presentday Flathead Lake area (Alden, 1953; Richmond and 

others, 1965; Waitt and Thorson, 1983; Richmond, 

1986a). 

On the plains of Montana east of Glacier National 

Park lay the southwestern lobe of the Laurentide ice 

sheet. This ice sheet covered most of Canada, and its 

southern margin stretched from Montana east to the 

Glacier National Park During the Late Wisconsin Glaciation 7 
Atlantic Ocean. The southwestern lobe of this ice sheet, 

the Shelby lobe, advanced south from Canada onto the 

plains of Montana (fig. 3) (Alden, 1932; Mickelson and 

others, 1983). 

Between these two large ice sheets, in the 

mountains along the Continental Divide, valley glaciers 

and icefields covered the Glacier National Park region 

beneath hundreds of meters of ice (Alden, 1953; 

Richmond, 1986a). Only the higher peaks protruded 

above this ice cover as nunataks. Radiocarbon age 

determinations from the Colorado Rockies suggest that 

late Wisconsin valley glaciers reached their maximum 

extent in that area about 23,000 to 22,000 yr. BP (Rosenbaum and Larson, 1983; Madole, 1986). Obsidian 

hydration dating from the Yellowstone region suggests 

that late Wisconsin ice reached its maximum extent there 

as early as 30,000 yr. BP (Pierce and others, 1976; Pierce, 

1979). 

West of the Continental Divide in the Glacier 

National Park region, a large trunk glacier flowing 

southeast down the valley of the North Fork Flathead 

River was fed by glaciers flowing from valleys along the 

western flank of the Livingston Range and from valleys 

along the eastern flank of the Whitefish Range. Many of 

these tributary glaciers were 10-20 km long and several 

hundred meters thick. This large trunk glacier headed 

about 30 km north of the U.S.-Canadian border and 

filled the valley of the North Fork Flathead River with at 

least 1,000 m of ice. This ice thickness is indicated by 

striations and erratics along the crest of the Apgar 

Mountains and Demers Ridge (Alden, 1953), and by 

many sinuous meltwater channels, trending northwestsoutheast, on the interfluves on the west side of the 

Livingston Range, such as Adair Ridge (Carrara, 1989). 

This ice · overrode the Apgar Mountains, flowed 

southwest, and merged with the Flathead lobe of the 

Cordilleran ice sheet. 

Another large trunk glacier filled the valley of the 

Middle Fork Flathead River. This glacier was fed by 

glaciers flowing from valleys along the western flank of 

the Lewis Range and from valleys along the eastern flank 

of the Flathead Range. This trunk glacier, which headed 

in the Lewis and Clark Range about 100 km to the 

southeast in the present-day Great Bear Wilderness, 

formed a local ice field west of Marias Pass. Some of this 

ice flowed northwest and joined the Lake McDonald 

glacier (which drained the Flattop Mountain area) and 

the large trunk glacier flowing down the valley of the 

North Fork Flathead River. This combined ice body then 

flowed south-southwest and merged with the Flathead 

lobe of the Cordilleran ice sheet. Still other ice from the 

ice field west of Marias Pass flowed east across the 

Continental Divide as a major tributary of the Two 

Medicine glacier. 

East of the Continental Divide in the Glacier 

National Park region, some glaciers advanced beyond the 

mountain front onto the adjoining plains, where they 

formed large piedmont glaciers. The largest of these 

piedmont glaciers was the Two Medicine glacier (fig. 3). 

Glaciers along a 60-km length of the mountain front 

merged to form this glacier, including glaciers from Two 

Medicine valley and from the ice field west of Marias 

Pass. The Two Medicine glacier had a maximum width of 

about 50 km, extended about 55 km beyond the 

mountain front, and left a scattered veneer of hummocky 

till over an area of 2,000 km2 (Calhoun, 1906; Alden, 

1932). 

To the north, other glaciers heading in Glacier 

National Park extended beyond the mountain front onto 

the plains. Glaciers in the valleys of Lake and Cutbank 

Creeks flowed east and merged on the plains into a small 

piedmont lobe that extended about 15 km beyond the 

mountain front (Calhoun, 1906; Alden, 1953). Farther 

north, a large glacier in the St. Mary River valley flowed 

beyond the mountain front and into Canada (fig. 3), 

where its terminal deposits lie beneath till of a 

subsequent advance of the Laurentide ice sheet (Calhoun, 1906; Alden, 1932; Horberg, 1954). The St. Mary 

glacier was fed by tributary glaciers flowing from the 

valleys of Divide, Red Eagle, Boulder, Swiftcurrent, 

Kennedy, and Otatso Creeks in Glacier National Park. 

At Lower St. Mary Lake this glacier was about 370 m 

thick (Alden, 1932). In the interior of the park, in the 

valleys of the Belly and Waterton Rivers, large glaciers 

about 400 m thick flowed north into Canada. 

VOLCANIC ASHES IN THE GLACIER 

NATIONAL PARK REGION 

The Mazama, Glacier Peak G, and Mount St. 

Helens Jy volcanic ashes (from youngest to oldest) have 

been found in the Glacier National Park region. These 

late Quaternary ashes were identified on the basis of (1) 

stratigraphic position, (2) radiocarbon dating, (3) maf:~ 

mineral assemblage, and ( 4) various properties of their 

glass fraction including shard morphology, refractive 

index, and major element values. Because these ashes 

were used to establish a chronology for late Quaternary 

events in the Glacier National Park region, a brief 

summary discussion of each ash follows. 

Mazama Ash 

The Mazama ash is the most widespread late 

Quaternary ash in the western United States and 

southwestern Canada. It has been found in Oregon, 

8 Late Quaternary History, Glacier National Park Region, Montana 
Washington, Idaho, northern California, northern 

Nevada, northern Utah, western Montana, western 

Wyoming, southern British Columbia, and southern 

Alberta (fig. 4 ). After some initial confusion this ash was 

identified as having originated from the great eruption of 

Mount Mazama (present site of Crater Lake, southcentral Oregon) (Powers and Wilcox, 1964), a former 

volcano about 900 km southwest of Glacier National 

Park. This volcano was a complex assemblage of 

overlapping shield and stratovolcanic deposits whose 

climatic eruption about 6,845±50 yr. BP produced the 

Mazama ash (Bacon, 1983). This ash has been identified 

in about 25 bogs or exposures in the Glacier National 

Park region (Carrara, 1989). 

Glacier Peak G Ash 

Glacier Peak is a stratovolcano in north-central 

Washington, about 550 km west of Glacier National Park 

(fig. 4). Powers and Wilcox (1964) identified a 

widespread late Pleistocene ash as originating from this 

volcano, and subsequent work has shown that Glacier 

Peak has erupted many times since the late Pleistocene 

(Porter, 1978; Beget, 1982a, 1982b ). Porter (1978) 

identified at least nine ashes erupted from Glacier Peak 

since the late Pleistocene. However, only two ashes, 

designated B (youngest) and G, have been identified as 

far east as Montana; of these only the G ash was found in 

the Glacier National Park region. These two ashes were 

deposited from distinct plumes by closely spaced 

eruptions about 11,200 yr. BP (Mehringer and others, 

1984). Layer B spread southeast from Glacier Peak (fig. 

4) and has been reported as far east as Lost Trail Pass 

bog in the Lemhi Range on the Idaho-Montana border 

(Mehringer, Arno, and Petersen, 1977; Mehringer, BEnman, and Petersen, 1977; Mehringer and others, 1984 ), 

and Cub Creek Pond in Yellowstone National Park 

(Waddington and Wright, 1974; Westgate and Evans, 

1978). 

Layer G spread east from Glacier Peak and has 

been reported as far as southern Alberta (Westgate and 

Evans, 1978). Layer G has also been found in the 

Kootenai River area, Montana (Mierendorf, 1984 ); 

Sheep Mountain bog, about 18 km northeast of Missoula, Mont. (Mehringer and others, 1984); the Sun 

River Canyon area, Montana (Lemke and others, 1975; 

Carrara and others, 1986); and the Glacier National Park 

region (Carrara, 1986; Carrara and others, 1986). In the 

Glacier National Park region the Glacier Peak Gash has 

now been identified at 10 sites (Carrara, 1989). 

Mount St. Helens Jy Ash 

Mount St. Helens, a stratovolcano in southern 

Washington about 700 km west-southwest of Glacier 

National Park (fig. 4), erupted many times during the late 

Quaternary (Mullineaux and Crandell, 1981; Mullineaux, 1986). Most ashes produced by these eruptions are 

of only local extent, but several have been found far to 

the east. 

Ash layers of the Mount St. Helens set J were the 

product of explosive eruptions between about 11,500 and 

10,800 yr. BP (D.R. Mullineaux, written commun.,1986). 

East of Mount St. Helens, three ash layers have been 

recognized in set J. From youngest to oldest these ash 

layers are the Jb, Jy, and Js. In addition, west of Mount 

St. Helens, another layer, Jg, thought to be the youngest 

set J ash, is present (Mullineaux, 1986). The Jy ash 

consists of at least two voluminous, overlapping beds 

without known evidence of a significant time lapse 

between them (Mullineaux, 1986). This ash, which has 

been found in the Glacier National Park region stratigraphically below the Glacier Peak G ash, was estimated 

by Carrara and others (1986) to date from about 11,400 

yr. BP. 

Both layers Jb and Jy are extensive enough to be 

useful marker beds far from Mount St. Helens. The Jb 

ash spread southeast as a narrow plume, whereas the Jy 

ash covered a broader area from northeast to southwest 

of Mount St. Helens (fig. 4) (D .R. Mullineaux, oral 

commun., 1986). Set J ashes have been reported 

previously from two localities in Montana. An ash of set 

J (probably Jy, based on the K:Fe ratio) has been 

reported in the Kootenai River valley, about 150 km west 

of Glacier National Park (Mierendorf, 1984). In addition, 

the Jy ash has been reported near Marias Pass 

immediately south of Glacier National Park (Carrara and 

others, 1986). In the Glacier National Park region the 

Mount St. Helens Jy ash has been identified at three sites 

(Carrara, 1989), including the Marias Pass site. At these 

three sites it is stratigraphically below the Glacier Peak 

Gash. 

Although the Glacier Peak G and Mount St. 

Helens Jy ashes were not identified in many of the bogs 

inspected in this study and were not found in soils in the 

high areas of the park, their absence cannot be taken as 

conclusive evidence that the underlying deposits postdate 

these ashes. Where found, the Glacier Peak G and 

Mount St. Helens Jy ashes are usually less than 2 em 

thick. As the majority of these ash localities are in bogs, 

the ashes were recovered by angering several meters 

below the surface. Thus, it is possible that in some bogs 

these ashes were present but not identified. In addition, 

the likelihood of preservation of these ashes on a deposit 

in the higher areas of the park would be minimal in a 

sparsely vegetated, recently deglaciated landscape. In 

support of the idea that ash preservation would be 

minimal in a recently deglaciated terrain, Jackson and 

others (1982) found that the early postglacial period was 

a time of active geomorphic processes not conducive to 

Volcanic Ashes in the Glacier National Park Region 9 
\ 

\ \ 

\ 

\ 

MAZAMA ASH 

\ 

\ 

\ r~ \ J 

\ I 

\] 

\ 

) ,.. 

) 

I 

) 

200 

I 

I 

! 

I 

I 

I _______ __J_ 

400 KILOMETERS 

-..fANADA I UNJT~:--L -D S1AT£s -

I 

I 

I 

I 

I 

I 

NEW MEXICO 

Figure 4. Distribution pattern of the Mazama, Glacier Peak Band G, and Mount St. Helens Jy ashes 

(modified from Porter, 1978; Westgate and Gorton, 1981; Sarna-Wojcicki and others, 1983; and 

Mullineaux, 1986). 

10 Late Quaternary History, Glacier National Park Region, Montana 
ash preservation. Hence, the absence of the Glacier Peak 

G or Mount St. Helens Jy ashes in a bog, in an exposure, 

or in a soil does not prove that a given deposit postdates 

these ashes. 

Identification of Ashes in the Glacier 

National Park Region 

In the field the middle Holocene Mazama ash may 

tentatively be distinguished from the late Pleistocene 

Glacier Peak G and Mount St. Helens Jy ashes by 

stratigraphic position and the amount of mafic crystals. 

Stratigraphically, in bogs or exposures, the 

Mazama ash is usually within 0.5 to 2m of the surface in 

the highly organic, dark-brown (10 YR 3/3) to black 

(10 YR 2!1),1 fine-grained sediment characteristic of the 

middle Holocene in the Glacier National Park region. 

The ash consists of a silty layer ranging in thickness from 

3 em to as much as 100 em. Grain-size analyses of several 

samples of this ash yielded an average sand:silt:clay ratio 

of 13:63:24. Where thick and containing little organic 

matter, the ash is light gray (10 YR 7!1); where thin and 

contaminated with detrital sediment and organic matter, 

the ash is pale brown (10 YR 6/3) to dark yellowish brown 

(10 YR 316). However, because of its gritty feel, caused by 

its sand-sized fraction, and because of its lighter color, 

which contrasts with the darker surrounding organic 

sediment, the Mazama ash is easily recognized even 

when highly contaminated. 

Stratigraphically, in bogs or exposures, the Glacier 

Peak G and Mount St. Helens Jy ashes are usually within 

the lowermost organic sediments, or in the underlying 

inorganic sediments deposited soon after deglaciation. 

The Glacier Peak G ash ranges in thickness from 3 mm 

to 3 em, whereas the Mount St. Helens Jy ash is from 1 

mm to 1 em thick. Grain-size analyses of several samples 

of the Glacier Peak G ash yielded an average sand:silt: 

clay ratio of 18:57:25. Grain-size analysis of the Mount 

St. Helens Jy ash from the Marias Pass exposure (Carrara and others, 1986) yielded a sand:silt:clay ratio of 

9:69:22. Both ashes are white (10YR 8/1) to light gray 

(10YR 7!1) in color. 

The Mazama ash has also been identified in soil in 

many places in Glacier National Park, and is common in 

areas above treeline (Osborn, 1985; Carrara, 1987). In 

these places, the ash is a light-yellowish-brown (10 YR 

6/4) to reddish-brown (2.5 YR 5!6) (due to mafic mineral 

oxidation) silt, 5-10 em thick in small depressions at a 

depth of 10-20 em. Grain-size analyses of two samples 

yielded an average sand:silt:clay ratio of 8:67:25. 

1

All colors given in this report are for moist or wet sediment. 

Mafic crystals, easily seen with a hand lens, are 

relatively abundant in the Glacier Peak G ash compared 

with the Mazama and Mount St. Helens Jy ashes (Powers 

and Wilcox, 1964; Lemke and others, 1975). In the 

Glacier National Park region, mafic crystals compose 

about 15-20 percent by volume of the Glacier Peak G 

ash. In contrast, mafic crystals make up only about 5 

percent of the Mazama and Mount St. Helens Jy ashes. 

Microscopically, the Mazama ash is also easily 

distinguished from the Glacier Peak G and Mount St. 

Helens Jy ashes. Although all three ashes contain crystals 

of plagioclase, hornblende, hypersthene, and opaque 

oxides, the Mazama ash also contains crystals of augite 

and apatite (Lemke and others, 1975, table 1; and 

Sarna-Wojcicki and others, 1983, table 5-2). Numerous 

elongate frothy glass shards containing tubular voids 

separated by thin glass walls are characteristic of 

Mazama ash (fig. SA). In addition, the refractive index of 

the glass is > 1.502, higher than any other Holocene or 

late Pleistocene ash reported in Montana (Wilcox, 1965, 

fig. 2). Glass shards within the Glacier Peak G ash 

contain small crystals, are vesicular, and relatively equidimensional in comparison to shards in the Mazama ash 

(fig. 5 B). Glass shards within the Mount St. Helens Jy 

ash are similar in appearance to those of the Glacier 

Peak G ash but are relatively free of crystals (fig. 5 C). 

Chemically, glass from the Mazama ash can also be 

distinguished from that of other common Holocene and 

late Pleistocene ashes, including the Glacier Peak G and 

Mount St. Helens Jy ashes. Mazama glass has less silica 

and more iron and titanium than these other ashes. For 

instance, Mazama glass commonly is about 73 percent 

Si02, 2 percent FeO, and 0.4 percent Ti02, whereas 

common values for glass within the Glacier Peak B, G, 

and Mount St. Helens Jy ashes are 76-77 percent, 76-77 

percent, 75-76 percent Si02; 1.2 percent, 1 percent, 1.3 

percent FeO; and 0.2 percent, 0.2 percent, 0.2 percent 

Ti02 respectively (Lemke and others, 1975; Westgate 

and Evans, 1978; Westgate and Gorton, 1981; SarnaWojcicki and others, 1983; Mehringer and others, 1984). 

The higher iron content of glass within the Mazama ash 

compared to Glacier Peak B and G, and Mount St. 

Helens Jy ashes is also shown by K:Fe ratios. In this 

study, K:Fe ratios determined by wavelength dispersive 

X-ray fluorescence for 11 samples of Mazama ash from 

bogs in the Glacier National Park region ranged from 

1.37:1 to 1.51:1 and averaged 1.46:1 (table 2). K:Fe ratios 

also determined by X-ray fluorescence for five samples of 

Mazama ash from soils in the high areas of Glacier 

National Park ranged from 1.46:1 to 1.51:1 and averaged 

1.49:1 (table 3). As will become apparent in the following 

discussion, these K:Fe values for the Mazama ash are 

significantly lower than K:Fe values of the Glacier Peak 

B, and G, and Mount St. Helens Jy ashes. 

Volcanic Ashes in the Glacier National Park Region 11 
Figure 5 (above and following pages). Scanning electron micrographs of glass shards. A, Mazama ash. 

Although the Glacier Peak Bash was not found in 

the Glacier National Park region, at the start of this study 

its presence could not be ruled out. Hence, its mineral 

and chemical characteristics are discussed and contrasted 

with the Glacier Peak G and Mount St. Helens Jy ashes 

that are present in the region. 

The Glacier Peak B and G and Mount St. Helens 

Jy ashes all contain crystals of hornblende, hypersthene, 

plagioclase, and opaque oxides. The refractive index of 

the glass shards of all these ashes is about 1.498. Hence, 

these ashes cannot be distinguished from one another 

under a microscope. Because these ashes are very close 

in age, they could be considered as a single timestratigraphic marker in order to establish a chronology 

for upper Quaternary deposits in the northwestern 

United States and southwestern Canada. However, their 

specific identifications are important in gaining a better 

understanding of their distribution and age relationships. 

Fortunately, these ashes can be distinguished by 

chemical analysis of their glass fractions. The Glacier 

Peak B ash contains more calcium and iron and less 

potassium than the G ash (Westgate and Evans, 1978). 

Glass within the Glacier Peak B ash commonly contains 

about 1.3-1.4 percent CaO, 1.2 percent FeO, and 3 

percent K20, whereas glass within the Glacier Peak G 

ash contains about 1.2-1.3 percent CaO, 1 percent FeO, 

and 3.5 percent K20 (Lemke and others, 1975; Westgate 

and Evans, 1978; Sarna-Wojcicki and others, 1983; 

Mehringer and others, 1984). These seemingly small 

chemical differences are readily apparent in the K:Fe 

ratios. Smith and others (1977) found that K:Fe ratios of 

7 samples of B ash ranged from 2.7:1 to 2.9:1 and 

averaged 2.8:1, and that K:Fe ratios of 10 samples of G 

ash ranged from 3.1:1 to 3.7:1 and averaged 3.4:1. 

In this study, K:Fe ratios, determined by X-ray 

fluorescence for nine samples of Glacier Peak G ash 

from the Glacier National Park region, ranged from 

3.05:1 to 3.41:1 and averaged 3.23:1 (table 4). The ratio 

for the Guardipee Lake sample determined by electron 

microprobe was 3.69:1. 

The Mount St. Helens J ashes contain more iron 

(except the Js layer), aluminum and sodium, and less 

12 Late Quaternary History, Glacier National Park Region, Montana 
Figure 5-Continued. Glass shards in 8, Glacier Peak G ash. 

potassium, than the Glacier Peak B and Gashes (Westgate and Evans, 1978). The two widespread ashes of set 

J, Jb and Jy, can be distinguished from one another in 

that Jb contains more iron, magnesium, and calcium than 

does the Jy ash. Glass in the Mount St. Helens Jb ash is 

about 2 percent FeO, 0.75 percent MgO, and 2 percent 

CaO, whereas glass in the Jy ash is about 1.35 percent 

FeO, 0.35 percent MgO, and 1.35 percent CaO (Westgate and Evans, 1978, table 3; D.R. Mullineaux, oral 

commun., 1984). Because of their different iron contents, 

these two ash layers can also be distinguished by their 

K:Fe ratios. Samples UA 482 and UA 483 (Westgate and 

Evans, 1978, table 3) are from layers Jb and Jy 

respectively (D.R. Mullineaux, oral commun., 1984). 

Layer Jb has a K:Fe ratio of 1.23:1; layer Jy has a ratio of 

1.96:1. A sample of set J ash, probably Jy (D.R. Mullineaux, oral commun., 1984) analyzed by Smith and others 

(1977) yielded a K:Fe ratio of 1.9:1. 

In this study, K:Fe ratios determined by X-ray 

fluorescence for the two samples of Mount St. Helens Jy 

ash from the Glacier National Park region were both 

1.91:1 (table 5). The ratio for the Guardipee Lake 

sample determined by electron microprobe was 2.14:1. 

RADIOCARBON AGES AND VOLCANIC 

ASHES FROM BOGS AND EXPOSURES 

IN THE GLACIER NATIONAL PARK 

REGION 

In this report, the bogs and exposures from which 

radiocarbon ages were obtained and volcanic ashes were 

identified have been placed into five groups based upon 

their geographical location or related glacial history. 

Most of these sites are on the west side of Glacier 

National Park because bogs are abundant in this area, 

especially in the valley of the North Fork Flathead River 

and in the Lake McDonald area, whereas they are sparse 

in the Livingston and Lewis Ranges and the eastern areas 

of the park. Not all bogs and exposures inspected in this 

study are described in this report; only those that yielded 

information pertaining to the late Quaternary history of 

the Glacier National Park region are discussed. Areas 

containing important bogs and (or) exposures are (1) 

Bowman Lake, three sites; (2) Lake McDonald, six sites; 

(3) Marias Pass, four sites; ( 4) Lower St. Mary Lake, 

one site; and (5) Kootenai Lakes, two sites. Stratigraphy 

at these sites is described from youngest to oldest. 

Radiocarbon Ages and Volcanic Ashes from Bogs and Exposures 13 
Figure 5-Continued. Glass shards in C, Mount St. Helens Jy ash. 

Bowman Lake Area 

Bowman Lake is in the northwestern corner of 

Glacier National Park (fig. 1). It is a deep lake, 10.4 km 

long, occupying a glacial valley and dammed by a 

hummocky end moraine of late Wisconsin age deposited 

by the former Bowman glacier (Carrara, 1989). The 

moraine contains several bogs. During late Wisconsin 

time, a large glacier that headed along the Continental 

Divide on the west side of the Livingston Range flowed 

down the Bowman valley for about 20 km and joined the 

large trunk glacier occupying the valley of the North Fork 

Flathead River. This trunk glacier was about 120 km long 

and 1,000 m thick. Three sites were investigated in the 

Bowman Lake area: (1) Cabin Creek exposure, (2) 

Bowman Lake bog, and (3) Numa Ridge bog (fig. 6). 

Cabin Creek Exposure 

The Cabin Creek exposure is in the valley of the 

North Fork Flathead River at an altitude of 1,122 m, 

about 9 km north of the Polebridge Ranger Station (fig. 

6). The exposure is about 0.3 km east of the river and 

about 20m above it in a former bog along the east side of 

Glacier Route 7. The former bog is drained and incised 

by a small north-flowing stream, which has exposed 

stratigraphic sections along its banks. The area is 

underlain by late Wisconsin till deposited by the trunk 

glacier that filled the valley of the North Fork Flathead 

River. This till in places exceeds 30 m in thickness, and it 

overlies the Kishenehn Formation. Forests in this area 

consist primarily of ponderosa and lodgepole pine, 

Engelmann spruce, and subalpine fir. 

The Cabin Creek exposure, which is almost 4 m 

high, lies in a stream cut at the north end of the former 

bog (fig. 7). In addition, the stratigraphy was extended 

another 2.3 m by auger. Although the stratigraphic 

section at this exposure does not extend from the late 

Pleistocene to the most recent sediments, younger 

sediments including the Mazama ash were found in the 

stream bank farther upstream (south). Hence, a 

complete stratigraphic section spanning the last 12,000 

years is represented by the various sections exposed 

along the stream bank. 

At the Cabin Creek exposure the Glacier Peak G 

and Mount St. Helens Jy ashes were identified in a 

massive, inorganic, dark-grayish-brown (2.5 Y 4/2), 

clayey-silt lake sediment (tables 4 and 5; fig. 8). This lake 

sediment has a sand:silt:clay ratio of 1:56:43. The Glacier 

Peak Gash is a white (10 YR 8/1) silty layer 3-6 mm thick. 

The Mount St. Helens Jy ash, about 25 em below the 

14 Late Quaternary History, Glacier National Park Region, Montana 
:xJ 

I» 

0. 

c;· 

(') 

I» 

a0 

::s 

)> 

co 

CD 

Ul 

I» 

::s 

0. 

~ n 

I» 

::s 

c;· 

)> 

Ul 

::J' 

CD 

Ul 

-

0 

3 

t'D 

0 

co 

Ul 

I» 

::s 

0. 

tr 

"0 

0 

0 

c 

c; 

0 

.... 

(II 

Table 2. Major-element values of glass in the Mazama ash from bogs in the Glacier National Park region 1 

Site-- Dry2 Bowman Mud McGee Glacier Ben 

Lake Lake3 Meadow Route 7 Ryan 

Sio2 72.8 72.8 72.5 72.9 71.9 72.4 

Al 2o3 14.6 14.6 14.7 14.8 15.7 14.8 

6Fe0 1.97 2.01 2.10 2.02 1. 92 1. 99 

MgO .54 .53 .61 .58 .56 .51 

CaO 1. 83 1. 75 1.94 1.83 1. 91 2.07 

Na2o s.oo 5.05 5.04 4.78 4.90 5.08 

K20 2.79 2.81 2.70 2.68 2.69 2.68 

Ti02 .41 .42 .45 .43 .44 .43 

Total--- 99.94 99.97 100.07 100.02 100.02 99.96 

K:Fe 1.51:1 1.49:1 1.37:1 1.42:1 1.49:1 1.43:1 

1Weight percent, without water, recalculated to 100 percent. 

2Located 150m south of the Cabin Gulch exposure (see fig. 6). 

3Located 5 km south-southeast of Polebridge (see fig. 1). 

4Located 0.5 km southwest of Marias Pass. 

sLocated in upper St. Mary River drainage area (see fig. 18). 

6Total iron as FeO. 

Snyder Marias Middle Chewing 

Ridge Pass4 Fork Black bones 

7 3.1 73.6 72.6 73.0 

14.5 13.9 14.7 14.5 

1. 99 2.15 1. 98 2.01 

.56 .53 .52 .52 

1.77 1.69 1.94 1.74 

4.91 4.69 5.15 5.07 

2.72 2.82 2.71 2.79 

.45 .40 .44 .43 ---

100.00 100.05 100.04 100.06 

1.46:1 1.40:1 1.46:1 1.49:1 

Analysis by A.J. Bartel, U.S. Geological Survey. 

Mirror 

Pond5 Average 

72.9 72.8 

14.5 14.6 

2.01 2.01 

.52 .54 

1.80 1.84 

5.09 4.99 

2.78 2.75 

.41 .43 

100.01 99.96 

1.48:1 1.46:1 
Table 3. Major-element values of glass in the Mazama ash from soils in the Glacier National Park region1 

Site--

SiOz 

MgO 

CaO 

Na2o 

Total--

K:Fe 

Sperry 

Glacier 

72.6 

14.7 

1.94 

.50 

1.95 

5.16 

2.71 

.41 

99.97 

1.49:1 

Comeau 

Pass2 

72.0 

15.1 

1.86 

.44 

2.31 

5.26 

2.54 

.41 

99.92 

1.46:1 

Red Eagle 

Glacier 

73.7 

13.9 

2.06 

.46 

1. 49 

5.09 

2.91 

.39 

100.00 

1.51:1 

Grinnell 

Glacier 

72.5 

14.8 

1.98 

.51 

1. 81 

5.19 

2.74 

.43 

99.96 

147:1 

Clements 

Glacier 

72.7 

14.7 

1. 93 

.50 

1. 89 

5.13 

2.73 

.41 

99.99 

1.51:1 

Average 

72.7 

14.6 

1.95 

.48 

1.89 

5.17 

2.73 

.41 

99.93 

1.49:1 

1Weight percent, without water, recalculated to 100 percent. Analysis 

by A.J. Bartel, U.S. Geological Survey. 

2Located 0.8 km west of Sperry Glacier (see fig. 30). 

3rotal iron as FeO. 

Glacier Peak G ash (fig. 7), is a white (10 YR 8!1) silty 

layer, 1 mm thick. The Mount St. Helens Jy ash is 

underlain by 3.4 m of fine-grained sediment that overlies 

till or outwash. 

Bowman Lake Bog 

The Bowman Lake bog is at an altitude of 1,238 m, 

about 0.6 km southwest of the outlet of Bowman Lake 

(fig. 6). Forest surrounding this bog consists mostly of 

lodgepole pine with some Engelmann spruce and subalpine fir. The bog is on the hummocky end moraine of late 

Wisconsin age (Carrara, 1989) deposited by the former 

Bowman glacier after it separated from the large trunk 

glacier in the valley of the North Fork Flathead River and 

retreated upvalley. 

At the Bowman Lake bog a hole was angered 280 

em into the underlying sediments (fig. 7). The Mazama 

ash (table 2) forms as a dark-yellowish-brown (10 YR 3/6) 

layer 10 em thick at a depth from 140 to 150 em. 

Grain-size analysis of the ash from this bog gave a 

sand:silt:clay ratio of 12:66:22. Below the Mazama ash, at 

a depth from 260 to 275 em, near the base of the hole, a 

sample of gray (5 Y 6/1) clay was obtained. Although this 

sample had a low organic content, its organic matter was 

concentrated in the laboratory (Kihl, 1975) and yielded a 

radiocarbon age of 11,150± 90 yr. BP (W-5043) (table 6). 

Numa Ridge Bog 

Numa Ridge bog, at an altitude of 1,535 m, is on 

Numa Ridge about 1 km northwest of Bowman Lake (fig. 

6). The bog borders a small lake (fig. 9) and is 

surrounded by forest containing lodgepole pine, Engelmann spruce, and subalpine fir. The bog is underlain by 

late Wisconsin till deposited by the large trunk glacier 

that filled the valley of the North Fork Flathead River. 

At Numa Ridge bog a hole was angered 430 em 

into the underlying sediments (fig. 7). Here the Mazama 

ash is a light-gray (10 YR 7/1) layer 15 em thick at a depth 

from 275 to 290 em. Grain-size analysis of this ash gave 

a sand:silt:clay ratio of 11:62:27. The ash is in a dark16 Late Quaternary History, Glacier National Park Region, Montana 
:c 

Table 4. Major-element values of glass in the Glacier Peak Gash from bogs and exposures in the Glacier National Park region1 

Site--

Si02 

Al 2o3 

4Fe0 

MgO 

GaO 

Cabin 

Gulch 

74.9 

14.1 

1.08 

.47 

2.10 

Glacier 

Route 7 

76.2 

13.3 

1.05 

.39 

2.10 

Howe Ben 

Lake Ryan 

75.6 73.9 

13.5 14.6 

1.06 1.07 

.45 .39 

2.17 2.41 

Snyder Marias Middle Goat Chewing 

Ridge Pass Fork Lick Black bones 

75.9 76.5 75.7 75.4 76.6 

13.4 13.3 13.7 14.0 12.6 

1.08 1.06 1.06 1.06 1.05 

.45 .40 .40 .42 .42 

1. 87 1.53 1.90 1.91 1.90 

Guardipee 

Lake2 

78.5 

12.0 

.95 

.23 

1.21 

~ Na2o 4.05 3.70 3.75 4.17 3.96 3.63 3.88 3.87 3.97 3.58 

cs· 

() 

I» 

a0 

:::s 

l> 

co 

Cl) 

en 

I» 

:::s 

a. 

~ c; 

I» 

:::s 

c;· 

l> 

en 

:::J" 

Cl) 

• -

0 

3 

m 

K20 3.09 3.11 3.30 3.28 3.16 3.39 3.19 3.22 3.26 3.29 

Ti02 .17 .20 .19 .17 -- .19 .19 .18 .18 .17 .21 

Total-- 99.96 100.05 100.02 99.99 100.01 100.00 100.01 100.06 99.97 99.97 

K:Fe 3.05:1 3.16:1 3.32:1 3.27:1 3.12:1 3.41:1 3.21:1 3.24:1 3.31:1 3.69:1 

1weight percent, without water, recalculated to 100 percent. Analysis by A.J. Bartel, U.S. Geological Survey. 

2Analysis by A.M. Sarna-Wojcicki, U.S. Geological Survey, using electron microprobe (written commun., 1985) • 

3rncludes only those samples (9) collected by author and analyzed by XRF. 

~ 4rotal iron as FeO • • I» 

a 

~ ~ 

0 • c 

G • 

... 

..... 

Average 3 

75.6 

13.6 

1.06 

.42 

1. 99 

3.89 

3.22 

.18 

99.96 

3.23:1 
Table 5. Major-element values of glass in the Mount St. 

Helens Jy ash from the Glacier National Park region1 

Site-- Cabin Marias Guardipee 

Gulch Pass Lake2 

Si02 75.6 75.9 78.4 

Al2o3 13.7 13.8 12.3 

3Fe0 1.29 1. 32 1.12 

MgO .40 .41 .26 

CaO 1.88 1.68 1.40 

Na2o 4.56 4.40 4.15 

K2o 2.31 2.36 2.25 

Tio2 .18 .20 .18 

Total-- 99.92 100.07 100.06 

K:Fe 1.91:1 1.91:1 2.14:1 

1

Weight percent, without water, recalculated 

to 100 percent. Analysis by A.J. Bartel, U.S. 

Geological Survey. 

2Analysis by A.M. Sarna-Wojcicki, U.S. 

Geological Survey, using electron microprobe 

(written commun., 1985). 

3Total iron as FeO. 

brown (10 YR 313) organic clay. Below the Mazama ash at 

a depth of 410 to 430 em, near the base of the hole, an 

olive-gray (5 Y 4/2) gyttja was sampled. This material 

yielded a radiocarbon ageof10,090± 130yr. BP (Y'/-5185) 

(table 6). 

Discussion 

The presence of the Glacier Peak G and Mount St. 

Helens Jy ashes at the Cabin Creek exposure indicates 

that this part of the valley of the North Fork Flathead 

River was deglaciated before 11,400 yr. BP. Hence, the 

large trunk glacier that filled this valley during late 

Wisconsin time had retreated substantially and lay 

somewhere to the north of the Cabin Creek exposure by 

11,400 yr. BP. This date (the estimated age of the Mount 

St. Helens Jy ash, Carrara and others, 1986), which 

represents a minimum date of deglaciation, may be 

minimum by several hundred or thousand years because 

the Mount St. Helens Jy ash at this exposure is underlain 

48° 

52' 

30" 

1W15' 

EXPlANATION 

~ Prominent ridge 

Figure 6. The Bowman Lake area. 

~ M?Custer~ 2.707 • ~ 

Boulder , , \ IV7: 

Pass· ~~l 

/ 

(___, 

l Jefferson 

Mt Carter Pass) 

3.000 m ?\'c . O;V;. 

Rainbow~~ 

3.016m \ 

10 KILOMETERS 

by 340 em of fine-grained sediment (fig. 7). Because the 

Glacier Peak G ash (11,200 yr. BP) and the Mount St. 

Helens Jy ash (11,400 yr. BP) are both present at this 

exposure, a rate of sedimentation can be calculated 

between these two ashes and then extrapolated down to 

the base of the massive lake sediment unit in which these 

two ashes occur. In this way, an age of about 13,700 yr. 

BP is obtained for the base of the lake sediment at a 

depth of 570 em (fig. 7). This age is of course only an 

estimate, but it suggests that the age of the Mount St. 

Helens Jy ash may be a very minimum date of deglaciation for this section of the valley of the North Fork 

Flathead River. 

Theradiocarbonageof11,150±90yr.BP(W-5043) 

from the Bowman Lake bog is a minimum age for the 

hummocky end moraine on which this bog lies and is a 

minimum date for the withdrawal of ice from this section 

of Bowman Creek valley. This date indicates that by 

11,150 yr. BP the Bowman glacier had shrunk drastically 

from its maximum late Wisconsin extent and was 

confined to its own valley in the Livingston Range, if it 

still existed at all. 

Although the radiocarbon age of 10,090± 130 yr. BP 

(W-5185) from the Numa Ridge bog is not as old as the 

radiocarbon age from Bowman Lake bog or the volcanic 

ashes from the Cabin Creek exposure, the date from 

Numa Ridge is important in that it provides a minimum 

date for revegetation following deglaciation at a site 300 

m above Bowman Lake. Note that, as the bottom of the 

Numa Ridge bog was not reached by auger, the 

radiocarbon age from this bog is not thought to represent 

a close limiting date. 

18 Late Quaternary History, Glacier National Park Region, Montana 
CJ) 

cc: 

w 

1--

w 

~ 

0 

100 

200 

f= 300 z 

w 

u 

z 

:i 

h: 

w 

0 

400 

500 

600 

Cabin Creek 

exposure 

Duff ( 1 OYR 3/3) 

Massive clayey silt 

(10YR 8/4) 

mollusks abundant 

thin peat at 80 em 

Laminated silty clay 

(2.5Y 6/4) 

p...... ............ ...j Glacier Peak G ash 

(10YR 8/1) 

~~~~ Mount St Helens Jy ash 

(10YR 8/1) 

Sand (1 OYR 4/1) 

Gravel 

Bowman Lake 

bog 

Peat (10YR 2/2) 

Organic clay 

(10YR 2/1) 

11,1 50±90 yr BP 

(W-5043) 

Gravel 

Numa Ridge 

bog 

Peat (7.5YR 3/4) 

Organic clay 

(10YR 3/3) 

Mazama ash 

(10YR 7/1) 

Gyttja (5Y 4/2) 

1 ."'-'· ·-"'· ·.1'.1• 10,090±130 yr BP 

(W-5185) 

Figure 7. Stratigraphy of the three bogs investigated in the Bowman Lake area. 

Radiocarbon Ages and Volcanic Ashes from Bogs and Exposures 19 
Figure 8. The Cabin Creek exposure, showing the Glacier Peak G and Mount St. 

Helens Jy ashes; shovel handle is 50 em long. 

Lake McDonald Area 

Lake McDonald is in the west-central part of 

Glacier National Park. It is a deep lake, 15 km long, 

occupying the lower end of McDonald Valley (figs. 1 and 

10) and dammed by till and outwash. During late 

Wisconsin time, a large glacier in the McDonald Valley 

headed in cirques along the western side of the 

Continental Divide in the Logan Pass and Flattop 

Mountain area. The McDonald glacier was tributary to 

the large trunk glaciers that filled the valleys of the North 

and Middle Forks Flathead River. To the south, Snyder 

Ridge was overrun by ice from the trunk glacier of the 

valley of the Middle Fork Flathead River. To the north, 

the McGee Meadow area and Howe Ridge were overrun 

by ice from the trunk glacier in the valley of the North 

Fork Flathead River. The Apgar Mountains, west of 

McGee Meadow, were also overridden by this glacier, 

indicating that in the vicinity of McGee Meadow this 

glacier was at least 800 m thick. 

20 Late Quaternary History, Glacier National Park Region, Montana 
Table 6. Radiocarbon age determinations from the Glacier National Park region 

14c age Lab. No. Material Site 

780+70 W-5169 wood1 Halfmoon Lake area. 

7,940.:!:_200 W-5572 Salix Snyder Ridge bog. 

8,730_:1:80 W-5041 McGee bog. 

9,510.:!:_350 W-5571 Mount Cleveland bog #1. 

9,650.:!:_250 W-5575 

9,850.:!:_260 W-5577 

9, 910.:!:_1 00 W-5191 

gyttja, contained conifer fragments 2 

gyttja, contained Salix fragments 3 

Pinus2 

Snyder Ridge bog. 

Mount Cleveland bog #4. 

East McGee bog. 

9 ,920.:!:_120 W-5187 peat, contained Pinus contorta cone 2 Glacier Route 7 bog. 

10,090_:1:130 

10,630.:!:_250 

W-5185 

W-5348 

gyttja3 Numa Ridge bog. 

Picea or Larix2 Howe Lake bog. 

11, 150_:1:90 W-5043 

)27,000 W-5166 

)40,000 W-5213 

organic material ((0.125 mm) 3 

organic material ((0.125 mm) 4 

organic material ((0.125 mm) 4 

Bowman Lake bog. 

Marias Pass exposure. 

Marias Pass exposure. 

1wood at base of landslide exposed in section along Middle Fork Flathead River 

(see Carrara, 1989). 

2Minimum date of reforestation following deglaciation. 

3Minimum date of organic sedimentation following deglaciation. 

4samples associated with the Glacier Peak G and Mount St. Helens Jy ashes; samples 

contaminated by old carbon (see discussion in text). 

Six sites were investigated in the Lake McDonald 

area: (1) McGee bog, (2) East McGee bog, (3) Glacier 

Route 7 bog, (4) Howe Lake bog, (5) Ben Ryan bog, and 

(6) Snyder Ridge bog (fig. 10). 

McGee Bog 

The McGee bog, at an altitude of 1,177 m, is about 

12 km north-northwest of the town of West Glacier, in 

McGee Meadow near the headwaters of McGee Creek 

(fig. 10). Forest in the McGee Meadow area includes 

lodgepole pine, Engelmann spruce, subalpine fir, western 

larch, paper birch, and black cottonwood. The area is 

underlain by late Wisconsin till that in places exceeds 30 

m in thickness (Carrara, 1989), and that overlies the 

Kishenehn Formation. 

At the McGee bog a hole was augered 290 em into 

the underlying sediments (fig. 11). The Mazama ash 

(table 2) was found near the surface, indicating a slow 

sedimentation rate since its deposition. The ash is a 

light-gray (10 YR 7/2) layer 60 em thick. Grain-size 

analysis of the ash indicated a sand:silt:clay ratio of 

16:61:23. 

Several small wood fragments were recovered 

below the Mazama ash, at a depth between 130 and 140 

em at the base of a brown (10 YR 4/3), organic, silty clay 

(fig. 11). These fragments were identified as ''yellow 

pine" (D.J. Christensen, written commun., 1981) and are 

probably lodgepole pine. These fragments yielded a 

radiocarbon age of 8,730± 80 yr. BP (W-5041) (table 6). 

Radiocarbon Ages and Volcanic Ashes from Bogs and Exposures 21 
Figure 9. Numa Ridge bog; view is to the east; Rainbow Peak (3,016 m) and Square Peak (2,676 m), left and right 

respectively, are in the background. 

East McGee Bog 

The East McGee bog, at an altitude of 1,180 m, is 

about 1 km southeast of the McGee bog (fig. 10). At the 

East McGee bog a hole was angered 520 em into the 

underlying sediments (fig. 11). Here the Mazama ash is a 

light-brownish-gray (10 YR 612) layer, 35 em thick at a 

depth between 135 and 170 em. Grain-size analysis of 

this ash yielded a sand:silt:clay ratio of 14:63:23. 

Several coniferous wood fragments were recovered 

below the Mazama ash at a depth between 500 and 520 

em, in a very dark brown (10 YR 212) gyttja. These 

fragments, also identified as "yellow pine" (D.J. Christensen, written commun., 1983), are probably lodgepole 

pine and yielded a radiocarbon age of 9,910± 100 yr. BP 

(W-5191) (table 6). 

Glacier Route 7 Bog 

The Glacier Route 7 bog, at an altitude of 1,192 m, 

is about 100m west of the Glacier Route 7 road, about 1 

km south of the East McGee bog (fig. 10). At the Glacier 

Route 7 bog a hole was angered to a depth of 450 em (fig. 

11). Here the Mazama ash (table 2) is a dark-yellowishbrown (10 YR 4/4) layer 20 em thick at a depth from 82 

to 102 em, overlying a black (5 Y 2.5/3) peat. Grain-size 

analysis of the ash yielded a sand:silt:clay ratio of 

11:66:23. 

Abundant fossil mollusks were found in a very pale 

brown (10 YR 7/3), organic (10 percent), silty-clay unit at 

a depth from 315 to 415 em, containing thin lenses of 

peat. Two species of aquatic snails, Gyraulus pa1VUs and 

Planorbella trivolvis, and two species of freshwater clams, 

Pisidium compressum and Pisidium variable, were 

identified (Emmett Evanoff, written commun., 1985). 

These species are very widespread today in North 

America, ranging from the central United States to the 

northern limit of boreal forest in Canada; hence, these 

mollusks provide no information concerning past 

climates. However, they do indicate that this bog was a 

perennial pond rich in aquatic vegetation at the time this 

unit was deposited (Emmett Evanoff, written commun., 

1985). 

A lodgepole pine cone was recovered at a depth of 

400 em in the mollusk-bearing unit. Unfortunately, the 

cone was too small for a conventional radiocarbon age 

22 Late Quaternary History, Glacier National Park Region, Montana 
EXPlANATION 

~- Prominent ridge 

48°45' 

48°30' 

Figure 10. The Lake McDonald area. 

114"00' 113°45' 

/' ~ /-------~ 

r r- ) ----_( \__/~r - Ahern Pk 

"--~ L / 2·

666 m ~'-) Ahern Pass \1 / m J/2 

rapper Pk ( 

2~7 1 

- Flattop Mtn ~ / 

\ , <.P - \-Swiftcurrent 

\.___Pass 

~ ~'() 

~owe Lake bog 

Heavens Pk 

2,739 m 

Avalanche 

Lake 

(/) ~ 

'6\ 

?_\ 

~>--­ ~1'~ 

::0 

Logan Pass ~ ,.------::>:; 

(>;> 

Reynolds Mt~ 2J87 m / 

)z 

I 

) G) 

) 

) 

) 

I 

A ');: ht 

Lincoln Pk ss 0/~ ~ 7~ I()~ 

'&D ~'lJ 

-<-0 

ast McGee bog 

0 Snyder Ridge bog 

If 

-1 Itt 

10 KILOMETERS G ~ 

Radiocarbon Ages and Volcanic Ashes from Bogs and Exposures 23 
(/l 

a: 

w 

1-

w 

~ 

i= 

z 

0 

100 

200 

~ 300 

z 

I 

1-

a.. 

w 

0 

400 

500 

600 

McGee 

bog 

Organic silty clay 

(1 OYR 2/1) 

Mazama ash 

(10YR 7/2) 

Organic silty clay 

(10YR 4/3) 

conifer fragments present 

8,730±80 yr BP 

!=':=:::::::::.=:~ (W-5041) 

Clayey silt 

(10YR 6/1) 

Clayey silt 

(5YR 5/2) 

East McGee 

bog 

Organic silty clay 

(10 YR 2/2) 

Mazama ash 

(10YR 6/2) 

Peat (5Y 3/3) 

Gyttja ( 1 OYR 2/2) 

conifer fragments present 

, ........ ,.., ... Ail_ 9,910±100 yr BP 

(W-5191) 

Figure 11. Stratigraphy of the three bogs investigated in the McGee Meadow area. 

24 Late Quaternary History, Glacier National Park Region, Montana 

Glacier Route 7 

bog 

Organic silty clay 

(10YR 3/2) 

Mazama ash 

(10YR 4/4) 

Peat (5Y 2.5/3) 

Organic silty clay 

(10YR 7/3) 

mollusks abundant 

contains peat lenses 

9,920±120 yr BP 

(W-5187) 
determination, so it was combined with the peat from the 

lenses in this unit and yielded a radiocarbon age of 

9,920± 120 yr. BP (W-5187) (table 6). 

The Glacier Peak G ash (table 4) was found at a 

depth of 410 em near the bottom of the mollusk-bearing 

unit. The ash forms a light-gray (10 YR 7/1) layer about 

1 em thick. Grain-size analysis of this ash indicated a 

sand:silt:clay ratio of 12:54:34. The mollusk-bearing unit 

overlies a light-gray (10 YR 6/1) pebbly sand, silt, and clay 

unit, that could only be penetrated about 35 em by the 

auger. 

Howe Lake Bog 

The Howe Lake bog, at an altitude of 1,256 m, is on 

Howe Ridge north of Lake McDonald about 13 km north 

of the town of West Glacier (fig. 10). The area is 

underlain by late Wisconsin till that overlies the Kishenehn Formation. A nearby exposure in a landslide scarp 

indicates that the till is more than 30 m thick in this area. 

Forest surrounding this bog consists of lodgepole pine, 

Engelmann spruce, subalpine fir, and western larch. 

The Howe Lake bog lies immediately northwest of 

Howe Lake. Here, a hole was augered to a depth of 355 

em (fig. 12). The upper 300 em of sediment consisted of 

a black (10 YR 2/1) gyttja that contained abundant wood 

fragments. One fragment from a depth of 270 em, 

identified as either spruce or larch (D .J. Christensen, 

written commun., 1983), yielded a radiocarbon age of 

10,630±250 yr. BP (W-5348) (table 6). 

Fossil mollusks were also recovered at the Howe 

Lake bog. Aquatic snails ( Gyraulus pmvus) and 

freshwater clams (Pisidium vmiable) were found at a 

depth of 300 to 310 em (Emmett Evanoff, written commun., 1985). Because these mollusks are overlain by the 

wood fragment that yielded a radiocarbon age of 

10,630±250 yr. BP and underlain by the Glacier Peak G 

ash, they indicate that this bog was a perennial pond rich 

in aquatic vegetation about 11,000 yr. BP. 

The Mazama ash was not found in this bog. 

However, the Glacier Peak G ash was identified at a 

depth of355 em (table 4; fig.12). The ash occurs in a very 

dark grayish brown (10 YR 3/2) gyttja as a light-gray 

(10 YR 7/1) sandy-silt layer about 1 em thick. Grain-size 

analysis of this ash yielded a sand:silt:clay ratio of 

35:46:19. 

Ben Ryan Bog 

Ben Ryan bog, at an altitude of 1,107 m, is about 2 

km south-southeast of the town of West Glacier (fig.10). 

Forest around the bog includes western white pine, 

lodgepole pine, Engelmann spruce, subalpine fir, western 

larch, and paper birch. The surrounding area is underlain 

by a hummocky end moraine deposited by the late 

Wisconsin McDonald glacier that contains many ponds 

and bogs. 

At the Ben Ryan bog a hole was angered 260 em 

into the underlying sediments (fig. 12). Here the 

Mazama ash (table 2; fig. 12) is a yellowish-brown (10 YR 

5/4) silty layer, about 5 em thick, at a depth from 100 to 

105 em at the base of a black (10 YR 2/1) peat. The 

Glacier Peak G ash (table 4; fig. 12)) was found at a 

depth of 255 em. This ash is a white (10 YR 8/l) layer 1 

em thick in a grayish-brown (10 YR 5/2) organic clayey 

silt. 

Snyder Ridge Bog 

Snyder Ridge bog, at an altitude of 1,351 m, is on 

Snyder Ridge south of Lake McDonald and about 12 km 

northeast of the town of West Glacier (fig. 10). The bog 

is underlain by late Wisconsin till that overlies the 

Kishenehn Formation. Till in this area locally exceeds 30 

m in thickness. Forest surrounding this bog consists of 

lodgepole pine, Engelmann spruce, subalpine fir, 

Douglas fir, and western larch. 

At the Snyder Ridge bog a hole was angered to a 

depth of 410 em (fig. 12). Here the Mazama ash (table 2) 

is a yellowish-brown (10 YR 5/4) layer, 15 em thick at a 

depth between 50 and 65 em. Grain-size analysis of this 

ash yielded a sand:silt:clay ratio of 11:66:23. 

Two radiocarbon ages were obtained on samples 

below the Mazama ash (fig.12). An age of7,940±200 yr. 

BP (W-5572) was obtained on wood fragments from a 

depth of 110 em in a black (10 YR 2/1) peat (table 6). 

These wood fragments were identified as willow (J .T. 

Quirk, written commun., 1984). An age of 9,650±250 yr. 

BP (W-5575) was obtained on yellowish-brown (10 YR 

5/4) gyttja that contained coniferous wood fragments 

from a depth from 185 to 195 em. The lower part of this 

gyttja contained the Glacier Peak Gash (table 4; fig. 12). 

Here the ash consisted of a white (10 YR 8/1) silty layer 

about 1 em thick at a depth of 235 em. This gyttja unit is 

underlain by 150 em of a light-gray (10 YR 7/1) clay. 

Discussion 

The presence of the Glacier Peak G ash at four 

sites in the Lake McDonald area (Glacier Route 7, Howe 

Lake, Ben Ryan, and Snyder Ridge bogs) indicates 

extensive deglaciation of this area before 11,200 yr. BP. 

The fact that the Glacier Peak Gash at Snyder Ridge bog 

is underlain by 25 em of gyttja and 150 em of clay 

suggests that this site may have been ice free for some 

time before the deposition of the ash, and indicates that 

the glacier that filled the valley of the Middle Fork 

Flathead River no longer overtopped Snyder Ridge. In 

fact, because both the radiocarbon age of 9,650±250 yr. 

Radiocarbon Ages and Volcanic Ashes from Bogs and Exposures 25 
U) 

a: 

w 

1-

w 

~ 

i= 

z 

0 

100 

~ 200 

z 

:i 

h: 

w 

0 

Howe Lake 

bog 

Ben Ryan 

bog 

Peat ( 1 OYR 2/1) 

Snyder Ridge 

bog 

. Organic silty clay 

(1 OYR 3/2) 

Mazama ash 

(10YR 5/4) 

·''' Peat ( 1 OYR 2/1) 

wood fragments abundant 

7,940±200 yr BP 

(W-5572) 

Gyttja (1 OYR 5/4) 

conifer fragments present 

9,650±250 yr BP 

(W-5575) 

~~~ Glacier Peak G ash 

(1 OYR 8/1) 

jieiiiiiiiiii;;.,;;;;;;;~ Glacier Peak G ash 

(10YR 8/1) 

1 0,630±250 yr BP 

(W-5348) 

~o-A,~/"<:A~ Gravel 

300 

Clay (1 OYR 7/1) 

-~- Glacier Peak G ash 

(10YR 7/1) 

400 

Gravel 

Figure 12. Stratigraphy of the Howe Lake, Ben Ryan, and Snyder Ridge bogs. 

BP and the Glacier Peak G ash occur in the yellowishbrown gyttja (fig. 12), a rate of sedimentation was 

calculated between them and then extrapolated down to 

the base of the gyttja. In this way, an estimated age of 

about 12,000 yr. BP was obtained for the base of the 

gyttja at a depth of 260 em. This age, determined by a 

sedimentation rate, is of course only an estimate, but 

does suggest that the area around the Snyder Ridge bog 

may have been ice free for some time before the 

deposition of the Glacier Peak G ash. 

The presence of the Glacier Peak G ash at Ben 

Ryan bog provides a minimum age for the hummocky 

end moraine that this bog overlies and a minimum date 

for the withdrawal of ice from this section of the McDonald valley. Richmond (1986a) has suggested that this 

hummocky till, which he referred to as the Five Lakes 

moraine, marks the outer limit of a significant readvance 

of local mountain glaciers about 12,000 to 11,500 yr. BP. 

However, instead of representing a significant advance, 

this moraine could also have been formed by a stillstand 

26 Late Quaternary History, Glacier National Park Region, Montana 
during a general retreat. Whatever the Five Lakes 

moraine represents, the McDonald glacier had shrunk 

drastically from its late Wisconsin maximum by 11,200 

yr. BP, and if it still existed was confined solely to its 

valley. This moraine is correlative with the hummocky 

end moraine at the lower end of Bowman Lake from 

which a minimum radiocarbon age of 11,150±90 yr. BP 

(W-5043) was obtained. 

Minimum dates of revegetation in the Lake 

McDonald area are indicated by stratigraphic 

relationships and several radiocarbon ages of coniferous 

wood fragments from the bogs inspected in this area. 

That a lodgepole pine cone overlay the Glacier Peak G 

ash by about 10 em at the Glacier Route 7 bog suggests 

that reforestation by that species may have taken place 

about 11,000 yr. BP. As previously mentioned, this cone 

was too small for a conventional radiocarbon age 

determination; it was combined with peat from overlying 

lenses within the mollusk-bearing unit and yielded an age 

of 9,920±120 yr. BP (W-5187). Hence, this age 

represents a very minimum date of reforestation. The 

radiocarbon age of 9,910± 100 yr. BP (W-5191) of pine 

fragments from East McGee bog also is a minimum date 

of reforestation because the bottom of the dark-brown 

gyttja containing these coniferous wood fragments was 

not reached. Hence, the radiocarbon ages from both the 

Glacier Route 7 and East McGee bogs suggest the 

reintroduction of lodgepole pine into the Lake McDonald area before 10,000 yr. BP. In addition, the age of 

10,630±250 (W-5348) on a spruce or larch fragment at 

Howe Lake bog provides a minimum age for the reintroduction of either of these species into this area. 

Although the coniferous fragments from Snyder 

Ridge bog could not be identified to genus, their 

radiocarbon age of 9,650±250 yr. BP (W-5575) is a 

minimum date for the return of conifers to Snyder Ridge, 

the highest bog investigated in the Lake McDonald area. 

Based on sedimentation rates, an estimated age of about 

12,000 yr. BP represents the beginning of organic 

sedimentation at this bog. 

Marias Pass Area 

Marias Pass, at an altitude of 1,595 m, is on the 

Continental Divide immediately south of Glacier 

National Park, about 15 km west of the mountain front 

(figs. 1 and 13). The area around the pass has a broad 

rolling topography and is mantled with thin scattered 

deposits of till and glaciofluvial sediments (Carrara, 

1989), underlain mainly by gray and dark-gray 

Cretaceous marine mudstone (Mudge and Earhart, 

1983). During late Wisconsin time, the Marias Pass area 

was a major accumulation area and thoroughfare for ice 

flowing east across the divide to the Two Medicine 

piedmont glacier. Calhoun (1906) indicated that the ice 

was about 550 m thick in the Marias Pass area at that 

time. 

A local ice field west of Marias Pass supplied much 

of the ice to the Two Medicine glacier. This ice field may 

have been substantially thickened by the Flathead lobe of 

the Cordilleran ice sheet, which effectively blocked local 

mountain ice west of the divide, causing this ice field to 

thicken and spill east over Marias Pass (Richmond, 

1986a). The Two Medicine glacier, fed by glaciers along 

a 60-km length of the mountain front, flowed east onto 

the plains to form the largest piedmont glacier in 

Montana: it extended about 55 km beyond the mountain 

front, had a maximum width of 50 km, and covered about 

2,000 km2 (fig. 13) (Calhoun, 1906; Alden, 1932). 

Three sites were investigated in the Marias Pass 

area. In addition, a fourth site was investigated by C.W. 

Barnosky (Barnosky and others, 1987). Although widely 

separated, these sites provide information regarding the 

former Two Medicine glacier. They are (1) Marias Pass 

exposure, (2) Middle Fork bog, (3) Goat Lick exposure, 

and (4) Guardipee Lake (fig. 13). 

Marias Pass Exposure 

The Marias Pass exposure, at an altitude of 1,550 

m, is about 2 km southwest of Marias Pass in a road cut 

along the south side of U.S. Highway 2. Forest 

surrounding this exposure includes lodgepole pine, 

Engelmann spruce, and .subalpine fir. Here, a Glacier 

Peak ash was found in a section of postglacial laminated 

clayey-silt lake sediment (Richmond, 1972). Actually, the 

lake sediment contains two ashes, as the Glacier Peak G 

ash is underlain by the Mount St. Helens Jy ash (tables 4 

and 5; fig. 14) (Carrara and others, 1986). 

An exposure about 5 m high was excavated at the 

Marias Pass site (fig. 14). Most of the deposits consist of 

finely laminated (varves?), brown (10 YR 4/3) clayey-silt 

lake sediments. Grain-size analysis of these sediments 

indicated a sand:silt:clay ratio of 5:59:36. The laminae 

(940 were counted) consist of thin (1-3 mm) alternating 

fine and coarse layers. Several layers of brown (10 YR 

4/3) fluvial gravelly sand 5-10 em thick are present. Due 

to postglacial stream erosion and highway construction, it 

is not clear how the former lake was dammed. However, 

a nearby deposit of till suggests that the lake was 

dammed either by till or by a landslide of till shortly after 

deglaciation. 

The upper ash, identified as the Glacier Peak G 

(Carrara and others, 1986), is 3 em thick and consists of 

two layers. Its basal layer, 1 em thick, is light gray (2.5 Y 

7/1) and contains noticeably more mafic crystals and 

coarser glass shards than does the overlying fine-grained 

white (2.5 Y8/2) layer. A combined grain-size analysis of 

these two layers indicated a sand:silt:clay ratio of 

Radiocarbon Ages and Volcanic Ashes from Bogs and Exposures 27 
113°30' 113° 00 ' 112°30' 

48° DO' ~--------------L-----------------------------~------------------------------~----~ 

Figure 13. The Marias Pass area. 

15:69:16. Above the ash is a layer of ash-rich, wavyrippled clayey-silt lake sediment 2 em thick (figs. 14 and 

15). This layer of rippled sediment may be a turbidite 

(Bouma, 1962), and its presence suggests that the 

deposition of the Glacier Peak G ash interrupted normal 

sedimentation in the small lake. Above the wavy-rippled 

sediment is a zone of light-gray (10 YR 6!2), ash-rich, 

laminated lake sediment 13 em thick. 

The lower ash, a white (10 YR 8/1) layer 1 em thick, 

identified as the Mount St. Helens Jy (Carrara and 

others, 1986), was found about 1 m below the Glacier 

Peak G ash near the bottom of the exposure (fig. 14). 

Grain-size analysis of this ash yielded a sand:silt:clay 

ratio of 9:69:22. Overlying this ash is a pale-brown 

(10 YR 6!3), ash-rich, laminated clayey-silt lake 

sediment, 10 em thick, that grades upward into 

laminated, brown (10 YR 4/3) lake sediment. 

Five samples of lake sediment from the Marias 

Pass exposure were examined for pollen. These samples 

were collected at about 30 em intervals from immediately 

below the Glacier Peak G ash to immediately below the 

Mount St. Helens Jy ash. The pollen of these samples 

(samples 1 to 5, fig. 16) is compared to those of two 

modern surface samples (samples 0 and 00, fig. 16) from 

nearby forest duff. Pollen concentration values were 

generally low in the fossil samples. For samples 2 and 3, 

two slides were needed to count > 100 grains. 

The two modern samples (0 and 00) are dominated 

by pine pollen (82 and 88 percent) (fig. 16). Fir, alder, 

sagebrush (Artemisia), grass (Gramineae), spruce, and 

Douglas fir/larch percentages are low ( < 5 percent). 

Other pollen types were rare or absent in these samples. 

The fossil pollen samples are also dominated by 

pine pollen (68 to 74 percent) (fig. 16). However, several 

differences distinguish the fossil pollen spectra from the 

modern pollen spectra: (1) the fossil samples contain 

more haploxylon pine pollen (whitebark pine type) than 

the modern samples, although diploxylon pine pollen 

(lodgepole pine type) still predominates; (2) spruce is 

more abundant in the fossil samples (reaching a high of 9 

percent in sample 5); (3) sagebrush, grass, and other 

nonarboreal pollens are also more abundant in the fossil 

28 Late Quaternary History, Glacier National Park Region, Montana 
0 

100 

200 

en 

a: 

w 

1-

w 

~ 

i= 

z 

w 

u 

~ 

:i 

1-

a.. 

w 

0 

300 

400 

500 

Marias Pass 

exposure 

Laminated clayey silt ( 1 OYR 4/3) 

Contorted bedding ( 1 OYR 4/3) 

~~~~ Rippled clayey silt ( 1 OYR 4/3) 

f;: Ash-rich laminated clayey silt ( 1 OYR 6/2) 

:=---=.:...~ Ash-rich wavy-rippled clayey silt ( 1 OYR 4/3) 

Glacier Peak G ash (2.5Y 8/2) 

>27,000 yr BP (W-5166) 

Laminated clayey silt ( 1 OYR 4/3) 

Ash-rich laminated clayey silt ( 1 OYR 6/3) . _ . Mount St Helens Jy ash ( 1 OYR 8/1) 

. --;-. _'_ >40,000 yr BP (W-52 1 3) 

Middle Fork 

bog 

Peat ( 1 OYR 2/2) 

Mazama ash (1 OYR 5/4) 

Gyttja (10YR 3/4) 

Sand, silt, clay ( 1 OYR 5/2) 

Gravel 

Figure 14. Stratigraphy of the Marias Pass exposure and Middle Fork bog. 

Radiocarbon Ages and Volcanic Ashes from Bogs and Exposures 29 
Figure 15. Glacier Peak Gash at the Marias Pass exposure. 

samples; ( 4) fir pollen is rare and Douglas fir/larch pollen 

is absent in the fossil samples; and (5) several spore 

types, ferns (Filicales ), stiff clubmoss (Lycopodium 

annotinum), and rock selaginella (Selaginella densa), that 

are typical of subalpine areas are present only in the fossil 

samples. 

Plant macrofossils were found in the lake sediment 

below both ashes at the Marias Pass exposure. These 

macrofossils were recovered by washing the sediment 

through a 125 ~m sieve. Although insufficient in quantity 

for conventional radiocarbon dating, these macrofossils 

indicate environmental conditions in the Marias Pass 

area at the time the Glacier Peak G and Mount St. 

Helens Jy ashes were deposited. 

A conifer needle, an alder strobilus, and an 

unidentifiable wood fragment were found in the 

sediment immediately below the Glacier Peak G ash. The 

sediment immediately below the Mount St. Helens Jy ash 

contained most of the macrofossils. Several small woody 

fragments were identified as either Salix (willow) or 

30 Late Quaternary History, Glacier National Park Region, Montana 
::0 

Q) 

Q. 

c;· 

(') 

Q) 

... 

C" 

0 

:s 

)> 

(Q 

(I) 

en 

Q) 

:s 

Q. 

~ c; 

Q) 

:s 

c;· 

)> 

en 

:T 

(I) 

cn 

::::r 

0 

3 

m 

SAMPLE SCALE 

NO. 

5 PERCENT 10 20 30 40 50 60 70 80 PERCENT 5 PERCENT 5 PERCENT CHANGE 50 1 00 PCT 

0 

00 

2 

3 

4 

5 

L-l__~~~~--~~~--~~~--~~~~--~~~~ ~ ~ 

rr-

~ ~--------------------------------------------

f---

f---

"S'6."S'/. & "i- · "~..r ?yo.!' ~~...:: ?~ C'~Q Q ~ .... 

<-..r 

.0. 

-Q 

<-..r 

Sample 

No. 

0 

00 

1 

2 

3 

4 

5 

.0 '-t "S'...,.-: o.l'~<:-: ~-i- ~~ C CQ (..O~&V.C-<'<':15' -'5<9 o~ ~ ~ o<"~ O,s- Q_...0 ".f :f;o /~· :£-00 ~~ "o ~0 '?,.. v~. ?~. Ql('(!) 06 "'o ~ ..... Ql 0

<il/. ;;oo \9,-~ 

~ (!)(!)IS' 

%<"': ".J>Q o.l'~ 

~ 

~0 IS'/;_. "(!)Ql ~ ~ Ql(!) Q<'\ ~.., ('(!) (!)IS' ~· ~-% 0/,;~ <il<9, <9 OIS'Ql % <-..r Ql<9 v~ QQ: 

(!)Ql ~ ~ ~ Q? ~? Q">-i- ~ ~. ~~ ~~ '/~ 

EXPlANATION 

Location No. of 

grains counted 

Surface sample 300 

Surface sample 300 

Immediately below Glacier Peak G ash 198 

23 em below sample No. 1 134 

58 em below sample No. 1 144 

88 em below sample No. 1 200 

Immediately below Mount St. Helens Jy ash 200 

~(5) y~ 

} 

r 

& -Y. ~..... <9,...6 

v6.r IS' 

c& Figure 16. Percentage pollen diagram from the Marias Pass exposure. cn 

Q) 

:s 

Q. 

, 

~ 

0 

cn 

c 

... 

CD 

cn 

w 

.... 
Populus (aspen, cottonwood, and poplar) (D.J. Christensen, written commun., 1983). As Populus does not 

presently inhabit the area, these woody fragments are 

probably willow. 

Fossil insects were also identified in the sediment 

immediately below the Mount St. Helens Jy ash (Elias, 

1988). Insects provide environmental information, 

especially those that are predaceous or scavengers: 

because they can respond quickly to changing 

environments, predators and scavengers can exploit 

newly deglaciated regions before revegetation, which 

may take several hundred or possibly several thousand 

years. Insects identified include; (1) Tachyponls ntlomus, 

(2) Bembidion sulcipenne hyperboroides, (3) Amara discars, (4) Thanatophilus trituberculatus, and (5) Fonnica 

neorufibarbis. 

T. rulomus, a staphylinid beetle, commonly is found 

across boreo-arctic and montane North America. This 

species lives in wet habitats including damp leaf litter, 

mosses, and the borders of lakes and marshes, and is the 

most common arctic Tachyponts (Elias, 1988). B. sulcipenne hyperboroides, a riparian ground beetle, commonly 

inhabits the gravel banks of streams. This species is 

known only from northern British Columbia, the Yukon 

Territory, and Alaska (Lindroth, 1963, 1969). A. discors, 

a ground beetle, lives in sandy, open habitats (Lindroth, 

1968) within the boreo-montane regions of North 

America. This species has been reported from three 

alpine sites in Glacier National Park (Edwards, 1975). T. 

trituberculatus, a beetle associated with carrion, reaches 

the arctic tundra in Canada and is not known from the 

lower 48 States (Elias, 1988). F. neorufibarbis, an ant, 

commonly is found in the upper subalpine and just above 

treeline in the Rocky Mountains and as far north as the 

arctic treeline. It is the most cold-adapted species of 

North American Formica (Francoeur, 1973). 

Middle Fork Bog 

The Middle Fork bog, at an altitude of 1,317 m, is 

near the southwest corner of Glacier National Park 

about 6 km south of the Walton Ranger Station (fig. 13). 

The area around this bog is underlain by rock of the Belt 

Supergroup covered in places with a veneer of late 

Wisconsin glacial and fluvial deposits. Forests 

surrounding this bog consist of western white pine, 

lodgepole pine, Engelmann spruce, subalpine fir, and 

western larch. 

The bog is in a small depression near the summit of 

a hill about 0.5 km southeast of the confluence of the 

Middle Fork Flathead River and Bear Creek. Here, a 

hole was augered to a depth of 400 em (fig. 14). The 

Mazama ash (table 2) is a yellowish-brown (10 YR 5!4) 

layer 10 em thick, at a depth from 160 to 170 em at the 

base of a very dark brown (10 YR 2/2) peat. Grain-size 

analysis of the Mazama ash yielded a sand:silt:clay ratio 

of 8:67:25. The Glacier Peak Gash (table 4) was found at 

a depth of 352 em in the upper part of a grayish-brown 

(10 YR 512) sand-silt-clay unit. This ash is a white (10 YR 

8/1) silty layer about 1 em thick. The ash is underlain by 

about 50 em of fine-grained sediment that overlies gravel. 

Goat Lick Exposure 

The Goat Lick exposure is in the southwest corner 

of Glacier National Park at an altitude of 1,195 m, about 

2 km south of the Walton Ranger Station (fig. 13). This 

exposure is about 200 m north of the Goat Lick 

Viewpoint along U.S. Highway 2. The exposure is in the 

fac ..) of a gravel terrace about 30 m thick that overlies 

bedrock of the Belt Supergroup. During the late 

Wisconsin, this site, like the Middle Fork bog, was 

covered by hundreds of meters of ice by the glacier that 

occupied the valley of the Middle Fork Flathead River. 

The Glacier Peak G ash (table 4) is in the terrace 

face about 30 m above the Middle Fork Flathead River 

(fig. 17). The ash forms a light-gray (10 YR 7/1) silty layer 

2-4 em thick in a sand and gravel layer about 1.5 to 2 m 

below the terrace surface (fig. 17). 

Guardipee Lake Site 

Guardipee Lake is a shallow lake, about 0.5 km2 in 

area, on the plains east of Glacier National Park, at an 

altitude of 1,235 m, about 21 km east of the town of 

Browning (fig. 13). The lake is situated in broad rolling 

topography, underlain by thin, scattered deposits of late 

Wisconsin till deposited by the former Two Medicine 

glacier. Cretaceous sedimentary rock underlies this area 

(Mudge and Earhart, 1983). 

Guardipee Lake was cored by C.W. Barnosky for 

pollen analysis in August 1984 (Barnosky and others, 

1987, fig. 3). The core was more than 6 m long and 

consisted of gray clays, gray silty clays, interbedded marls 

and clays, and interbedded silts and sands. Two white 

(10 YR 8/1) ashes about 1 em thick and 18 em apart, the 

Glacier Peak G and Mount St. Helens Jy (tables 4 and 5), 

were identified in the lower meter of the core (Barnosky 

and others, 1987). 

Discussion 

The presence of the Mount St. Helens Jy ash at two 

of the sites in the Marias Pass area (Marias Pass 

exposure and Guardipee Lake) and the Glacier Peak G 

ash at all four sites in this area indicates extensive 

deglaciation of the area occupied by the former Two 

Medicine glacier before 11,400 and 11,200 yr. BP. 

32 Late Quaternary History, Glacier National Park Region, Montana 
Figure 17. The Goat Lick exposure; Middle Fork Flathead River in foreground. 

The presence of the Glacier Peak G and Mount St. 

Helens Jy ashes at the Marias Pass exposure indicates 

that the Continental Divide in this area was deglaciated 

before 11,400 yr. BP (Carrara and others, 1986). The 

presence of the Glacier Peak G ash at the Middle Fork 

bog and Goat Lick exposure indicates that the large 

trunk glacier that filled the valley of the Middle Fork 

Flathead River had retreated from this part of the valley 

by 11,200 yr. BP. Hence, by that time former tributary 

glaciers heading along the western flank of the Lewis 

Range and the eastern flank of the Flathead Range, if 

they still existed, were confined to their own valleys. 

Furthermore, the stratigraphy at the Middle Fork bog 

and Goat Lick exposure suggests that the age of the 

Glacier Peak Gash (11,200 yr. BP) may represent only a 

very minimum date of deglaciation. At the Middle Fork 

bog, this ash is underlain by 50 em of fine-grained 

sediment (fig. 14). At the Goat Lick exposure the ash is 

underlain by at least 30 m of fluvial gravels. Hence, the 

stratigraphy at both sites suggests that they were deglaciated several hundred or possibly several thousand years 

before the Glacier Peak G ash was deposited. The 

stratigraphic position of the Glacier Peak G ash at the 

Middle Fork bog indicates that organic material 

colonized this area shortly after the deposition of this ash. 

Plant macrofossils, pollen, and spores from the 

Marias Pass exposure suggest that the local vegetation in 

this area consisted of an open landscape with shrubs, 

herbs, and scattered conifers when the Glacier Peak G 

and Mount St. Helens Jy ashes were deposited. At that 

time there was a larger proportion of spruce and whitebark pine than at present (Carrara and others, 1986). 

These vegetative data are characteristic of the tundra/ 

subalpine forest boundary (treeline). As the Marias Pass 

exposure is at an altitude of 1,550 m, whereas presentday treeline is at about 2,050 m, these data indicate that 

treeline at the time these ashes were deposited was about 

500 m lower than present. 

The fossil insect data suggest that this 500 m 

lowering of treeline may be a minimum estimate. Elias 

(1988) noted the lack of any insect species associated 

with coniferous forest among the fossil insect 

assemblage. Insect assemblages from other sites at or 

above treeline have generally contained considerable 

Radiocarbon Ages and Volcanic Ashes from Bogs and Exposures 33 
numbers of coniferous-bark beetles because of the 

tendency for these insects to be blown upslope (Elias, 

1988). Hence, Elias suggested that the lack of any such 

insect species in the fossil insect assemblage below the 

Mount St. Helens Jy ash could be interpreted as 

indicating that treeline could have been as much as 200m 

below the Marias Pass exposure. Therefore, at about 

11,400 yr. BP, treeline was probably at least 500 m lower 

than present, and may have been as much as 700 m lower. 

Pollen data from Guardipee Lake indicate that the 

area around this site has been treeless for the past 12,000 

years. During glacial times, conifers may have survived in 

small populations along the lower mountain slopes 

bounded by tundra or steppe vegetation at both higher 

and lower altitudes (Barnosky and others, 1987). The 

ratio between sagebrush pollen and grass pollen suggests 

that the area was a grassland before 11,400 yr. BP, as 

opposed to a sagebrush steppe (Barnosky and others, 

1987). 

Problems with radiocarbon age determinations in 

the Glacier National Park region are demonstrated by an 

attempt to date both the Glacier Peak G and Mount St. 

Helens Jy ashes at the Marias Pass exposure. Blocks of 

lake sediment about 10 em thick were collected from 

under both ashes. Although the amount of organic 

matter in these sediments was quite low ( < 5 percent-lost 

on ignition), it was concentrated in the laboratory using a 

technique modified from Kihl (1975), and the < 125-J.Lm 

fraction was submitted for radiocarbon age 

determination. Ages obtained for the sediments 

underlying the Glacier Peak G and Mount St. Helens Jy 

ashes were > 27,000 yr. BP (W-5166) and > 40,000 yr. 

BP (W-5213), respectively (fig. 14). These ages are 

obviously older than the true age of the sediment. Much 

of the fine organic material in these lake sediments was 

probably derived from the Cretaceous mudstones in the 

area. 

These radiocarbon ages underscore the problems 

of contamination of organic material with older radiometrically inactive carbon in the Glacier National Park 

region. Other possible sources of error include the 

presence of reworked lignite from the Kishenehn 

Formation in the valleys of the North and Middle Forks 

Flathead River and reworked organic material from 

black Cretaceous shales on the east side of the 

Continental Divide beyond the mountain front. These 

sources of error highlight the importance of the Mazama, 

Glacier Peak G, and Mount St. Helens Jy ashes in this 

region, because the ashes are reliable time-stratigraphic 

markers of known age. 

Lower St. Mary Lake Area 

Lower St. Mary Lake lies to the east of Glacier 

National Park on the adjacent Blackfoot Indian 

Reservation (figs. 1 and 18). The lake is 9 km long and 

occupies a former glacial valley that is dammed by a large 

alluvial fan deposited by Swiftcurrent Creek. During the 

late Wisconsin, this valley was occupied by the St. Mary 

glacier, that headed on the eastern side of the Lewis 

Range along the Continental Divide, from the Logan 

Pass area south to the Blackfoot Mountain area. This 

glacier flowed down the St. Mary valley, past the 

mountain front and north across the U.S.-Canada 

border, where . its terminal deposits lie beneath till of a 

subsequent advance of the Laurentide ice sheet. 

Tributary glaciers flowed from the valleys of Divide, Red 

Eagle, Boulder, Swiftcurrent, Kennedy, and Otatso 

Creeks in Glacier National Park. One site was 

investigated in this area, the Chewing Blackbones bog 

(fig. 18). 

Chewing Blackbones Bog 

The Chewing Blackbones bog is along the eastern 

side of Lower St. Mary Lake at an altitude of 1,448 m 

(fig. 18). The bog is in a small valley trending north to 

south ·between two late Wisconsin lateral moraines 

deposited by the former St. Mary glacier. Thick clusters 

of small aspen containing an occasional Douglas fir dot 

the surrounding hillsides. The site is underlain by a 

veneer of late Wisconsin till (deposited by the former St. 

Mary glacier), which overlies the Two Medicine 

Formation, an Upper Cretaceous nonmarine mudstone 

(Mudge and Earhart, 1983). 

At the Chewing Blackbones bog a hole was 

augered to a depth of 350 em (fig. 19). The Mazama ash 

(table 2) is 25 em thick at this site and forms a lightbrownish-gray (2.5 Y 6/2) layer at a depth from 105 to 

130 em. Grain-size analysis of this ash yielded a sand:silt: 

clay ratio of 8:70:22. The Glacier Peak G ash (table 4) 

was found at a depth of 240 em in an inorganic greenishgray (5 GY 5/1) silty clay. The ash is a light-gray (10 YR 

7/2) silty layer 1 em thick and is underlain by 110 em of 

fine-grained sediments. 

Discussion 

The presence of the Glacier Peak G ash at the 

Chewing Blackbones site indicates that the former St. 

Mary glacier had retreated substantially from its late 

Wisconsin position before 11,200 yr. BP. Although the 

Chewing Blackbones bog is beyond the mountain front, 

the presence of the Glacier Peak Gash indicates that the 

St. Mary glacier was confined to its own valley by 11,200 

yr. BP and no longer merged with the other glaciers to 

the north flowing from the valleys of Boulder, Swiftcurrent, Kennedy, and Otatso Creeks; however, it could still 

have been receiving contributions of ice from glaciers in 

34 Late Quaternary History, Glacier National Park Region, Montana 
EXPLANATION 

~ Prominent ridge 

"-

dlceberg Pk 

/ 

\ 

\ 

/ 2. 788m 

'*-Swiftcurrent 

'-f'ass 

~() 

\~ 

~ ~ 

~':..<! ~MtGould \2_972 m 

) 

\ Pollock Mtn 

2.807 m 

J ~y_ 1- Logan Pass 

~~ 

~ ~ 

Reynolds Mtrl)L> 

2.787 m/ 

GLACIER 

PARK 

) Mirror Pond o 

( 

~ ?2.635 m 

) 

( 

""' ~ 

\ Mt Jackson 

-4..!!!_64m J -------~"'--- "----/ 

\ 

\ BLACKFOOT 

INDIAN 

RESERVATION 0 Babb 

L, Blackfoot Mtn \ ( \_ / ~ \ 

2.9 7 9 m '----\'( "'---- , 

10 KILOMETERS Red Eagle Pass ""'--l:$Triple Divide Pk 

\ 2.254 m ~~--~--~~--~--------------~ 

Figure 18. The Lower St. Mary Lake area. 

0 

Chewing 

Blackbones 

bog 

\ 

\ 

Radiocarbon Ages and Volcanic Ashes from Bogs and Exposures 35 
(/) 

a: 

UJ 

1--

UJ 

~ 

i= 

z 

Ghewing Blackbones 

bog 

0 

Peat ( 1 OYR 2/2) 

100 Clayey silt (5Y 5/1) 

Mazama ash (2.5Y 6/2) 

Silty clay (5GY 5/1) 

~ 200 

~ 

I 

b: 

UJ 

0 

300 

400 

Gravel (5GY 5/1) 

Figure 19. Stratigraphic section at Chewing 

Blackbones bog. 

Divide and Red Eagle valleys. The fact that the Glacier 

Peak Gash is underlain by 110 em of silty clay at this bog 

suggests that the age of this ash may represent only a very 

minimum date of deglaciation for the Chewing Blackbones area. Because the base of the Mazama ash rests 

upon this silty-clay unit in which the Glacier Peak G ash 

occurs (fig. 19), a rate of sedimentation was calculated 

between these two ashes and extrapolated down to the 

base of this unit at 350 em. The extrapolated 

sedimentation rate yielded an age of about 15,500 yr. BP. 

This age is of course only an estimate, but indicates that 

the age of the Glacier Peak G ash is a very minimum date 

of deglaciation for the area around the Chewing Blackbones bog. 

Kootenai Lakes Area 

The Kootenai Lakes area lies in the north-central 

section of Glacier National Park (figs. 1 and 20). The 

area is underlain by till, in turn overlying rocks of the Belt 

Supergroup. Forest surrounding this area contains lodgepole pine, Engelmann spruce, and subalpine fir. During 

the late Wisconsin, this area was overlain by a large 

glacier several hundred meters thick that headed along 

the eastern flank of the Livingston Range and the 

western flank of the Lewis Range. This glacier flowed 

north down the Waterton valley into Canada. Two sites 

from the same bog (Mount Cleveland bog) were 

investigated in this area (fig. 20). 

Mount Cleveland Bog-Hole #1 

The Mount Cleveland bog, at an altitude of 1,341 

m, lies in theW aterton valley about 3 km north-northeast 

of Kootenai Lakes and northwest of Mount Cleveland 

(fig. 20). At this bog, hole #1 was augered 540 em into 

the underlying sediments (fig. 21 ). The Mazama ash 

lWOO' CANADA 

~--------- ~- ('~ownPa~ 

( 

~ 

Olson 

MtCieveland ) 3190m 

~ ~ : Kootena1 

he Guardhouse Lakes 

2,846 m 1 . Creek 

/ \)o\e~'~ttne 

rc;:, ~\::Jefferson Col\t Pass ~l"(~ 

~~ \>;-

'\ ~Redhorn Pk 

\478m E 

~ 

Nahsukin Mtnl ,,o.\e~tofl if'~ / 2

A 98 mcf;V. ....... -.. "' «.fJ E';a;LANATION "-.(j__D~ \l'J~ '\_,_~ _/ ~ Prominent ridge 

5 KILOMETERS 

Figure 20. The Kootenai Lakes area. 

36 Late Quaternary History, Glacier National Park Region, Montana 
forms a grayish-brown (10 YR 512) layer 3 em thick at a 

depth between 200 and 203 em, in a very dark brown 

(10 YR 2/2) peat. Grain-size analysis of this ash yielded a 

sand:silt:clay ratio of 10:60:30. Wood fragments, 

collected from a depth of 250 to 290 em and identified as 

pine (J.T. Quirk, written commun., 1984), yielded a 

radiocarbon age of 9,510±350 yr. BP (W-5571) 

(table 6). 

Mount Cleveland Bog-Hole #4 

Hole #4lies about 100m west of hole #1. Hole #4 

was augered to a depth of 380 em (fig. 21 ). The Mazama 

ash forms a brown (10 YR 5/3) layer 10 em thick at a 

depth from 145 to 155 em in a dark-reddish-brown (5 YR 

3/3) peat. Grain-size analysis of this ash yielded a sand: 

silt:clay ratio of 8:67:25. Organic material, containing 

willow fragments (J.T. Quirk, written commun., 1984) 

were recovered from an olive (5 Y 4/3) gyttja at a depth of 

330 to 380 em. A radiocarbon age of 9,850±260 yr. BP 

(W-5577) was obtained on this material (table 6). 

Discussion 

The radiocarbon ages from the two holes augered 

in the Mount Cleveland bog provide both minimum dates 

of revegetation and reforestation and very minimum 

dates of deglaciation for the Kootenai Lakes area. The 

age of 9,510±350 yr. BP of pine fragments from hole #1 

indicates a minimum date for the reintroduction of 

lodgepole pine into this area. The fact that these wood 

fragments are underlain by 160 em of organic sediment 

(fig. 21) suggests that revegetation occurred at least 

several hundred or possibly several thousand years 

before this date. That this organic sediment is underlain 

by 90 em of pale-red (2.5 YR 512) laminated clayey silt 

also suggests that a significant amount of time may have 

elapsed between deglaciation of this site and revegetation. In support of this suggestion, a sedimentation rate 

was calculated for the interval between the Mazama ash 

and the radiocarbon age of 9,510±350 yr. BP and then 

extrapolated down to the base of the organic silty clay at 

a depth of 450 em (fig. 21). In this way an age of about 

16,600 yr. BP was obtained for the base of the silty clay. 

Although this age is only a crude estimate, it does suggest 

that deglaciation of the Kootenai Lakes area may be 

much older than the radiocarbon age of pine fragments 

from the bog. 

The age of 9,850±260 yr. BP for organic sediment 

containing willow fragments in hole #4 (fig. 21) is a 

minimum date for the reintroduction of willow following 

deglaciation of the Kootenai Lakes area. This 

radiocarbon age is of material obtained from the lower 

50 em of this hole, but the organic material in the 

lowermost several centimeters is probably much older 

than the radiocarbon age, which represents the average 

age of organic material in this 50-cm interval. 

The radiocarbon ages and associated stratigraphy 

at the Mount Cleveland bog suggest that revegetation in 

the Kootenai Lakes area was underway before 10,000 yr. 

BP. Lodgepole pine was reestablished by at least 9,500 

yr. BP. Both radiocarbon ages from this area are 

minimum dates for the reintroduction of lodgepole pine 

and willow. However, the associated stratigraphy 

suggests that some time elapsed between deglaciation 

and revegetation, and therefore deglaciation is tentatively 

suggested at about 11,000 yr. BP. Hence, this study 

suggests that by 11,000 yr. BP the glacier that once filled 

the W aterton valley no longer extended more than about 

10 km from its headwall, if it still existed at all. 

DEGLACIATION AND REVEGETATION 

ELSEWHERE IN THE ROCKY 

MOUNTAINS 

The dates of deglaciation and revegetation from 

the Glacier National Park region are similar to other 

dates elsewhere in the Rocky Mountains. In the upper 

Elk River valley of British Columbia, a radiocarbon age 

of 13,430±450 yr. BP (GX-5599) was obtained from 

Weary bog (Ferguson and Osborn, 1981). This bog, at an 

altitude of 1,582 m, is 29 km south of the Mount Joffre 

Ice Field. This radiocarbon age was determined from 

gastropod shells and may have been older than the true 

age of the shells, due to the incorporation of older 

carbonate (Ferguson and Osborn, 1981). Ages of 

11,900±100 yr. BP (GSC-2142) and 12,200±160 yr. BP 

(GSC-2275) were obtained on material containing wood 

and unidentifiable organic matter collected along a 

terrace scarp about 30 km downvalley from Weary bog 

(Harrison, 1976). During the late Wisconsin, the Elk 

River valley was filled by a large glacier about 100 km in 

length; this glacier was tributary to Cordilleran ice in the 

Rocky Mountain trench that flowed further south into 

the Flathead Lake area of Montana (Waitt and Thorson, 

1983). Hence, the radiocarbon ages from the Elk River 

valley indicate extensive deglaciation of that valley and 

also the Rocky Mountain trench by about 12,000 yr. BP 

and possibly as early as 13,500 yr. BP. In addition, 

because the Mount Joffre Ice Field lies on the 

Continental Divide between the Elk River and Kananaskis River valleys, and therefore also supplied ice to the 

glacier in the Kananaskis River valley, the radiocarbon 

ages also indicate extensive deglaciation of that valley. 

In the Sun River Canyon area of Montana, about 

100 km south of Glacier National Park, extensive 

Deglaciation and Revegetation Elsewhere In the Rocky Mountains 37 
(/) 

a: 

w 

1--

w 

~ 

i= 

0 

100 

200 

~ 300 u 

z 

I 

li: 

w 

0 

400 

500 

600 

Hole# 1 

Peat ( 1 OYR 2/2) 

wood fragments present 

9,510±350 yr BP 

(W-5571) 

Organic silty clay ( 1 OYR 4/2) 

mollusks present 

wood fragments present in 

upper part of unit 

Laminated clayey silt (2.5 YR 5/2) 

Hole# 4 

Peat (5YR 3/3) 

Mazama ash ( 1 OYR 5/3) 

Gyttja (5Y 4/3) 

wood fragments present 

9,850±260 yr BP (W-5577) 

Figure 21. Stratigraphy of the Mount Cleveland bog, holes #1 and #4. 

38 Late Quaternary History, Glacier National Park Region, Montana 
deglaciation occurred before the deposition of the 

Glacier Peak G ash, 11,200 yr. ago (Lemke and others, 

1975; Carrara and others, 1986). This canyon was 

occupied by a large glacier that flowed beyond the canyon 

mouth and formed a piedmont glacier 550 km2 in area on 

the plains (Calhoun, 1906; Alden, 1932). The presence of 

the Glacier Peak G ash at several sites in the canyon, 

including a site 11 km upstream from the canyon mouth, 

indicates extensive deglaciation of this area before 11,200 

yr. BP. Furthermore, stratigraphic relationships suggest 

that deposition of the Glacier Peak G ash in the Sun 

River Canyon may postdate deglaciation by several 

thousand years (Carrara and others, 1986). 

In Yellowstone National Park, Wyo., radiocarbon 

age determinations indicate that deglaciation of the 

Pinedale ice cap of the Yellowstone Plateau was largely 

completed by 14,000 to 13,000 yr. BP (Pierce, 1979). This 

large ice cap covered about 3,400 km2

, averaged more 

than 700 min thickness, and produced an outlet glacier 

that flowed 60 km down the Yellowstone valley (Pierce, 

1979). 

In Colorado, a radiocarbon age of 13,680± 110 yr. 

BP (W-5028) was obtained from a bog on the 

Continental Divide in the southern Park Range (Madole, 

1986). This area had been covered by a broad ice cap 

from which large valley glaciers descended. An icefield in 

the northwestern San Juan Mountains of Colorado, the 

largest glacier in the southern Rocky Mountains, no 

longer existed by 15,000 radiocarbon years ago (Carrara 

and others, 1984). 

In the western United States, deglaciation may 

have been essentially complete by about 11,000 yr. BP. In 

the North Cascade Range of Washington, cirques were 

deglaciated before the Glacier Peak ash eruptions, 

11,200 yr. ago (Beget, 1984). Beget (1984) further 

concluded that the glacier cover in the North Cascade 

Range was similar to that of the present by that time. 

Pollen records from the western United States can be 

interpreted as indicating that by about 11,500 yr. BP, 

Pinedale glaciers had probably disappeared or were 

about as small as subsequent late Holocene glaciers 

(Porter and others, 1983). 

Similar conclusions regarding the timing of deglaciation have been reached for the Canadian Rockies. In 

Jasper National Park, Alberta, late Wisconsin ice 

receded from Tonquin Pass, on the Continental Divide, 

before 10,000 yr. BP (Luckman and Osborn, 1979; Kearney and Luckman, 1983a). Luckman and Osborn (1979) 

also concluded that by 10,000 yr. BP glaciers in the 

middle Canadian Rocky Mountains had receded to 

positions close to present-day glacial limits. Organic 

sedimentation began before 9,500 yr. BP in an alpine bog 

close to its headwall in Watchtower basin, in Jasper 

National Park (Luckman and Kearney, 1986). In Yoho 

National Park, British Columbia, late Wisconsin ice 

receded from the Lake O'Hara basin before 10,060±160 

yr. BP (RIDDL-511) (Reasoner and Rutter, 1988). This 

radiocarbon age determination indicates that the Bow 

Valley glacier had receded to cirques adjacent to the 

Continental Divide before 10,000 yr. BP. Because pollen 

and macrofossil data indicate that a pine-fir forest was 

also established in this basin by that time, the 

radiocarbon age is a minimum date of deglaciation. 

Evidence from the Rocky Mountains also indicates 

that revegetation was underway by the time the Glacier 

Peak ash was erupted 11,200 yr. ago. In the Kootenai 

River valley, about 150 km west of Glacier National Park, 

a sediment core from Tepee Lake was collected by Mack 

and others (1983). This lake is at an altitude of 1,270 m, 

and the surrounding forest contains grand fir, lodgepole 

pine, western white pine, ponderosa pine, western larch, 

Engelmann spruce, and Douglas fir. Five pollen zones 

were recognized in the sediment core from Tepee Lake. 

The basal zone (pollen zone 1) contains the Glacier Peak 

G ash and is dominated by pine pollen (56 percent 

haploxylon). Other important arboreal pollen includes 

spruce, fir, alder, and willow. The nonarboreal pollen 

contribution is relatively small and consists mostly of 

sagebrush and grass (both s 7 percent). The sunflower 

family (Compositae) and goosefoot family (Chenopodiaceae) are also represented (Mack and others, 1983). 

These pollen spectra, similar to those from the Marias 

Pass exposure (fig. 16), are thought to represent a cool, 

moist climate. The closest modern pollen rain analog is 

within stands of whitebark pine and subalpine fir that 

presently grow at higher altitudes (Mack and 

others, 1983). 

At Sheep Mountain bog, about 150 km south of 

Glacier National Park, Glacier Peak ash is dominated by 

pine pollen (about 55 percent) consisting of about equal 

amounts of haploxylon and diploxylon pine pollens 

(Mehringer, 1985). This bog is at an altitude of 1,920 m 

and is presently surrounded by forest containing ponderosa pine, lodgepole pine, whitebark pine, western 

larch, Douglas fir, subalpine fir, and Engelmann spruce. 

The distribution of fossil needles and cones in the 

sampled section indicates that Douglas fir has grown 

near this site since at least 10,000 yr. BP. 

At Lost Trail Pass bog, on the Continental Divide, 

about 300 km south of Glacier National Park, a core was 

obtained for pollen analysis (Mehringer, Arno, and 

Petersen, 1977). This bog lies at an altitude of 2,152 m, 

and the surrounding forest contains lodgepole pine, 

whitebark pine, Engelmann spruce, and subalpine fir. 

Pollen zone 2, containing the Glacier Peak ash, has 

percentages of pine, spruce, alder, grass, sagebrush, and 

sedge ( Cyperaceae) pollen similar to those of the Marias 

Deglaciation and Revegetation Elsewhere In the Rocky Mountains 39 
Pass exposure. Hence, at about 11,200 yr. BP Lost Trail 

Pass bog was probably surrounded by an open forest 

similar to the mixed whitebark pine/lodgepole pine forest 

currently found at higher altitudes, indicating a climate 

slightly cooler than present (Mehringer, Arno, and 

Petersen, 1977). 

At Cub Creek Pond, in Yellowstone National Park, 

about 450 km south-southeast of Glacier National Park, 

a core was taken for pollen analysis (Waddington and 

Wright, 1974). The pond lies at an altitude of 2,485 m, 

surrounded by forest containing lodgepole pine, with 

some stands of spruce and fir. Pollen zone 1, which 

immediately overlies the Glacier Peak B ash (Westgate 

and Evans, 1978), contains relatively high percentages of 

sagebrush, spruce, juniper, birch, willow, grass, and 

sedge pollen. This pollen data was interpreted to suggest 

that upper treeline was about 500 m lower than present 

(Waddington and Wright, 1974). This estimate of treeline lowering agrees well with that of 500 to 700 m from 

the Marias Pass exposure. 

In the Front Range of Colorado, Benedict (1973) 

obtained a radiocarbon age of 9,200± 135 yr. BP 

(I-6520) for wood from a bog near Satanta Peak. Basal 

muck and peat samples from two nearby bogs, in the 

present krummholz zone, contained spruce cones and 

wood fragments that gave weighted average ages of 

9,590±130 yr. BP (I-12,198 A,B) and 8,885±120 yr. BP 

(I-12,787 A,B) (J.B. Benedict, written commun., 1983). 

These radiocarbon ages indicate that treeline in the 

Front Range had risen to at least its present -day altitude 

by 9,500 yr. BP. 

In the San Juan Mountains of southwest Colorado, 

22 radiocarbon ages of coniferous wood (spruce and fir) 

fragments were obtained from the Lake Emma site, 

above the present-day krummholz limit (Carrara and 

others, 1984). These radiocarbon ages indicate that treeline in this mountain range was at least 80 m higher than 

present by 9,600 yr. BP. 

MORAINES IN THE HIGH AREAS OF 

GLACIER NATIONAL PARK 

Moraines of two different age groups have been 

identified in the high areas of Glacier National Park 

(Osborn, 1985; Carrara, 1987; Carrara and McGimsey, 

1988). Most of these moraines lie at altitudes between 

1,900 and 2,400 m and are generally found within a 

kilometer or two of their cirque headwalls. Both agegroups of moraines lie in front of the present -day glaciers 

and snowfields, indicating that glacier fluctuations since 

the late Wisconsin have been small. 

Moraines of the Older Group 

Location and Description 

Moraines of the older group have been identified at 

25 sites in Glacier National Park. Many of these sites are 

in the central part of the Lewis Range, from the Sperry 

Glacier area east to the Triple Divide Pass area (fig. 1). 

In the Livingston Range, moraines of this group have 

been identified at only two sites-one near the former 

Agassiz Glacier, the other in the Boulder Pass area. 

These moraines are commonly well vegetated, 

supporting a dense cover of alpine tundra and krummholz (dwarf, windswept trees above timberline) of subalpine fir and Engelmann spruce. These moraines are 

rarely more than 10m high (fig. 22) and generally extend 

only short distances downvalley from moraines of the 

younger group (Carrara and McGimsey, 1981, 1988; 

Carrara, 1987). However, in the Upper Two Medicine 

Lake area, several snowfields are fronted only by 

moraines of the older group; moraines of the younger 

group are not present. 

Age 

Mazama ash has been identified in the soils of the 

older moraines at several localities in Glacier National 

Park (Osborn, 1985; Carrara, 1987; Carrara and 

McGimsey, 1988). The ash usually forms a lightyellowish-brown (10 YR 6/4) to reddish-brown (2.5 YR 

5/6) silt, 5-10 em thick at a depth of 10 to 20 em in small 

depressions. 

In this study the Mazama ash was found in the soils 

at the following sites: (1) on moraines of the older group 

fronting the Sperry Glacier, (2) on moraines of the older 

group fronting the site of the former Red Eagle glacier, 

(3) immediately downvalley from a moraine of the 

younger group fronting the Grinnell Glacier, and ( 4) 

immediately downvalley from a terminal moraine of the 

younger group fronting the site of the former Clements 

glacier (table 3). At the latter two sites, moraines of the 

older group are not present. 

Osborn (1985) also identified Mazama ash on 

moraines of the older group at several sites in Glacier 

National Park and adjacent Waterton National Park in 

Alberta. Those sites in Glacier National Park include (1) 

immediately downvalley from two small glaciers 

northwest of Triple Divide Pass, (2) the Iceberg Lake 

area, (3) the Rose Basin area, and ( 4) the Ptarmigan 

Lake area. 

Mazama ash, dated at 6,845±50 yr. BP (Bacon, 

1983), establishes a minimum age for moraines of the 

older group. Because organic material has not been 

found to date these moraines, their actual age has not 

been determined by radiocarbon dating. 

40 Late Quaternary History, Glacier National Park Region, Montana 
Figure 22. The Sperry Glacier area showing moraines of both the older and younger groups; view is to the 

south-southeast. 

A worldwide early Holocene glacial advance 

between 8,500 and 7,500 yr. BP has been suggested by 

Beget (1983). No evidence suggests that moraines of the 

older group in Glacier National Park date from that 

period. In fact, evidence elsewhere in the Rocky 

Mountains suggests that cirque moraines thought to be 

correlative with moraines of the older group in Glacier 

National Park are late Pleistocene in age. 

In Jasper National Park, Alberta, Crowfoot 

moraines, also overlain by Mazama ash, are thought to be 

correlative with moraines of the older group in Glacier 

National Park (Carrara and McGimsey, 1981; Osborn, 

1985; Carrara, 1987). Crowfoot moraines are thought to 

date from either the period between 9,200 and 8,500 yr. 

BP or before 9,700 yr. BP (Kearney and Luckman, 1981 ). 

The dates of 9,200 to 8,500 yr. BP correspond to a poiien 

zone in a sediment core from Tonquin Pass, Alberta, 

thought to represent a cool period. The age of 9,700 yr. 

BP is the core's basal age. Later studies, including 

fir:pine poiien ratios and radiocarbon ages of coniferous 

wood above present-day timberline, indicate that 

timberline in the Jasper National Park region was at least 

100 m higher than present (hence, the climate was 

correspondingly warmer) by 8,800 yr. BP and generaiiy 

remained higher until about 5,200 yr. BP (Kearney and 

Luckman, 1983b; Luckman and Kearney, 1986). During 

this warm period, glaciers in this region were smaller 

than present. Wood fragments recovered from the snout 

of the Athabasca Glacier, Alberta, yielded radiocarbon 

ages of 8,230±80 (Beta-17373) and 8,000±90 (Beta20047), indicating that at these times, this glacier was less 

extensive than at present (Luckman, 1988a). From this 

evidence, it can be inferred that Crowfoot moraines must 

predate this warm period and therefore are at least older 

than 8,800 yr. BP. 

In the Wind River Range of Wyoming, a 

radiocarbon age of 11,770±710 yr. BP (GX-11,772) is 

thought to closely date the type Temple Lake moraines 

(Zielinski and Davis, 1986). This age was obtained from 

Rapid Lake, 1 km downvaiiey from the Temple Lake 

moraines, and dates the abrupt transition from clastic to 

organic sediment. This transition was interpreted as 

dating the retreat of the former Temple Lake glacier 

upvalley and deposition of clastic sediment in the basin 

now occupied by Miller Lake (Zielinski and Davis, 1986). 

A subsequent radiocarbon age of 11,400±630 yr. BP 

Moraines in the High Areas of Glacier National Park 41 
~ 

N 

I; 

CD 

c 

c 

I» 

CD 

3 

I» 

-< 

::::1: 

0 

C) 

~ 

C) 

iii 

0 

~-

z 

! 

c;· 

::J 

!.. 

"'tt 

I» 

;. 

:a 

CD 

CQ 

c;· 

~::J 

3: 

0 

::J 

S' 

::J 

I» 

EXPlANATION 

4 Tree-ring station number 

1 908 Date of glacier withdrawal 

0 

1 5 Rate of glacier retreat (m/yr) * Alden (1914) estimated that in 1913 the Agassiz Glacier was 1.8 miles 

(2.9 km) in length 

+ As station 6 yielded the same date of deglaciation as station 7 it was 

disregarded in this analysis and the rate of retreat given represents that 

between stations 5 and 7 

1884 

9 lateral moraine 

t 

1872 

7 

200 400 600 800 1000 1200 1400 1600 

DISTANCE FROM TRIMLINE POSITION, IN METERS 

~ 

/ I 23oo 

1942 

1979 12000 

(/) 

2100 ffi I90 

w 

~ 

2000 ~-z 

0 

f= 

<( 

1900 ~ _J 

w 

2000 

~1800 

2200 1700 1800 2400 

Figure 23. Profile along the central flow axis of the mid-19th century Agassiz Glacier. Profile shows dates of deglaciation, and rates of glacial retreat as determined 

by tree-ring studies and historical records (Carrara and McGimsey, 1981). Stations 8 and 9 were located above the valley floor on the western margin of the forest 

trimline and western lateral moraine respectively, associated with the maximum mid-19th century Agassiz Glacier. These stations have been projected over the flow 

axis, hence their height above the profile (shown by a dagger) represents the ice thickness of the Agassiz Glacier at that time. 
s: 

0 

.. I» 

S" 

CD 

fn 

s· 

-:::r 

CD 

:::1: 

ca· 

:::r 

> ; 

I» 

fn 

2. 

G) 

ii" 

n 

i" 

.. 

z 

f 

:::. 

!. 

.. 

~ 

~ 

t 

II 

3 

1911 

7 

* 

4,5,10 5.5 

1860 

EXPlANATION 

Tree-ring station number 

Date of glacier withdrawal 

Rate of glacier retreat (m/yr) 

Alden (1914) estimated that in August 1913 the, 

Jackson Glacier was about 1,000 ft (305.m) back 

from its • recent maximum' 

1863 

8 lateral moraine 

t 

6 13.8 

1926 

5\ooe 1932 

112 

f00o.(a'!-'4-

10 

National 

1.3 

1979 

1944 

f---------Tree-ring data Inferred SPar_k --l erv1ce 

records 

2100 

2000 

(f) 

a: 

LJJ 

1--

1900 :g 

z 

;i 

0 

t= 

1800:;; 

1700 

LU 

_J 

LJJ 

L_------------~-------------L------------~------------~--------------L-------------~------------~------------~1600 

0 200 400 600 800 1000 1200 1400 1600 

DISTANCE FROM TRIMLINE POSITION, IN METERS 

Figure 24. Profile along the central flow axis of the mid-19th century Jackson Glacier. Profile shows dates of deglaciation, and rates of glacial retreat as 

determined by tree-ring studies and historical records (Carrara and McGimsey, 1981). Station 8 was located on the western lateral moraine, deposited by the 

Jackson Glacier during its mid-19th century maximum position. This station has been projected over the flow axis, hence its height above the profile (shown 

by a dagger) represents the ice thickness of the Jackson Glacier at that time. 
(GX-12,719) was obtained from a core from Temple 

Lake, that is inside the inner Temple Lake moraine. 

Hence, this latter date is a minimum age for the type 

Temple Lake moraines (Zielinski and Davis, 1987). 

In Colorado, minimum ages are also available for 

cirque moraines similar to the older moraines in Glacier 

National Park. In the Front Range, a radiocarbon age of 

9,915±165 yr. BP provides a minimum age for the 

Satanta Peak moraine, which is thought to have been 

deposited between 12,000 and 10,000 yr. BP (Benedict, 

1973, 1985). In the San Juan Mountains, spruce:pine 

pollen ratios and 22 radiocarbon age determinations of 

coniferous wood fragments from above present -day treeline indicate that by at least 9,600 yr. BP treeline in this 

mountain range was higher than present and that the 

climate from 9,600 to 3,000 yr. BP was generally warmer 

than present (Carrara and others, 1984). Hence, the 

Yankee Boy and Grenadier cirque moraines in this 

mountain range must predate 9,600 yr. BP. 

As previously discussed, the Glacier Peak G ash 

has been identified at 10 sites in the Glacier National 

Park region. Although this ash has not been found in the 

higher areas of the park, the lack of it on moraines of the 

older group is difficult to interpret. These moraines may 

postdate this ash, which dates from about 11,200 yr. BP 

(Mehringer and others, 1984). However, if the older 

moraines were already formed by the time this ash was 

erupted, the likelihood of its preservation would be 

minimal on a recently deglaciated landscape with sparse 

vegetation subject to paraglacial processes (Jackson and 

others, 1982). Furthermore, in the Glacier National Park 

region, the Glacier Peak G ash is thin compared to the 

commonly found Mazama ash. The Mazama ash, which 

has been identified in more than 25 bogs in the Glacier 

National Park region, is usually 5-20 em thick; and in 

some bogs it is more than 50 em thick. The Glacier Peak 

Gash is usually only 1-2 em thick. Hence, the absence of 

the Glacier Peak G ash on moraines of the older group 

cannot be taken as conclusive proof that these moraines 

postdate 11,200 yr. BP. 

In summary, although the moraines of the older 

group are known to predate the Mazama ash ( 6,845 yr. 

BP), their actual age is presently unknown. These 

moraines probably do not represent the early Holocene 

advance (8,500 to 7,500 yr. BP) suggested by Beget 

(1983). Moreover, Davis (1984) and Davis and Osborn 

(1987) have questioned many of the arguments used by 

Beget to support this proposed early Holocene advance. 

Moraines of the older group in Glacier National Park are 

thought to be correlative with other high-altitude cirque 

moraines elsewhere in the Rocky Mountains. These 

moraines were probably deposited in the latest Pleistocene. After Osborn and Davis (1985) and Davis and 

Osborn (1987) reviewed the published radiocarbon ages 

and paleoclimatic records, they concluded that many of 

the older, well-vegetated cirque moraines in the 

American and southern Canadian Cordillera were 

produced during a roughly synchronous advance around 

or before 10,000 yr. BP. 

Whether moraines of the older group are the 

product of a separate advance after the end of the late 

Wisconsin glaciation or are simply the product of the last 

advance or stillstand of late Wisconsin glaciers before 

final deglaciation is not known. Because Crowfoot 

moraines in Banff and Jasper National Parks, Alberta, 

which are thought to be correlative with the older 

moraines in Glacier National Park, are found in virtually 

the same sites as Cavell moraines, which date from the 

last several centuries, the Crowfoot moraines are thought 

to represent a separate advance after the end of the late 

Wisconsin glaciation (Luckman and Osborn, 1979). 

However, because late Wisconsin glaciers would 

probably have retreated to those same cirques and wellshaded niches where present -day glaciers and snowfields 

lie, it seems just as possible that moraines of the older 

group could simply have been formed during a stillstand 

or minor advance of late Wisconsin glaciers before final 

deglaciation. 

Moraines of the older group in Glacier National 

Park are thought to correlate with other cirque moraines 

elsewhere in the Rocky Mountains: (1) Crowfoot 

moraines in the middle Canadian Rockies (Luckman and 

Osborn, 1979); (2) Temple Lake moraines in the Wind 

River Range of Wyoming (Currey, 1974; Zielinski and 

Davis, 1986, 1987); (3) Satanta Peak moraines in the 

Front Range of Colorado (Benedict, 1973, 1985); and ( 4) 

Yankee Boy moraines in the San Juan Mountains of 

Colorado (Carrara and others, 1984). 

Glaciers in Glacier National Park during 

the Early to Middle Holocene Warm 

Period 

During the early to middle Holocene warm period 

there were probably even fewer glaciers in the park than 

at present. Several of the larger glaciers in Glacier 

National Park may have survived this warm period, 

although many of the park's glaciers probably did not 

exist at this time. Oxygen-isotope ratios determined by 

B.H. Luckman on fir fragments from Jasper National 

Park suggest that the mean annual temperature at 5,900 

yr. BP was about 1.9 oc warmer than present (Osborn, 

1982). Although a similar amount of warming would 

certainly eliminate many of the smaller, marginal glaciers 

in Glacier National Park, the larger, higher glaciers such 

as the Blackfoot, Harrison, Sperry, Rainbow, Grinnell, 

and Jackson probably survived the early to middle 

Holocene warm period. It is interesting to note that as 

44 Late Quaternary History, Glacier National Park Region, Montana 
early as 1942, Matthes stated that most of the presentday glaciers in the park were not the shrunken remnants 

of late Wisconsin glaciers but were new glaciers that 

probably formed when the climate cooled after the 

middle Holocene (Matthes, 1942). 

Moraines of the Younger Group 

Location and Description 

Moraines of the younger group have been 

identified at more than 150 sites throughout Glacier 

National Park and are commonly the only moraines 

fronting the many present-day glaciers and snowfields 

(Osborn, 1985; Carrara, 1987; Carrara and McGimsey, 

1988). These moraines lack soils or ash layers, and are 

generally devoid of vegetation, although pioneering 

vegetation including scattered krummholz conifers is 

locally present. They are typified by sharp-crested rubbly 

moraines, are as much as 50 m high, and slope at the 

angle of repose (fig. 22). These moraines may contain ice 

cores. 

Some glaciers did not form terminal moraines. 

During the mid-19th century the Agassiz and Jackson 

Glaciers extended about 2 km from their cirque headwalls into forested areas. Although the maximum 

positions of these glaciers are well marked by forest 

trimlines that merge with fresh, prominent lateral 

moraines of the younger group, terminal moraines were 

not formed (Carrara and McGimsey, 1981). 

Age 

Most of the moraines of the younger group in 

Glacier National Park are thought to date from advances 

that culminated in the mid-19th century. Tree-ring 

studies within the trimlines fronting the Agassiz and 

Jackson Glaciers (the only glaciers in the park that 

advanced into well-forested areas during the last several 

centuries) indicate that retreat began about A.D. 1860 

(figs. 23 and 24) (Carrara and McGimsey, 1981). Hence, 

the glacial advances probably occurred shortly before this 

time during the mid-19th century. In support of this 

interpretation, several trees cored just beyond the 

outermost moraine of the younger group fronting the 

Sperry Glacier contained very narrow tree rings for the 

years between A.D. 1840 and 1850, suggesting that this 

glacier was near its maximum extent during that decade. 

In addition, Luckman (1988b) dated the maximum Little 

Ice Age advance of the Athabasca and Dome Glaciers in 

Jasper National Park, Alberta, at 1843/44 and 1846 

respectively. 

Some of the moraines of the younger group date 

from advances other than the mid-19th century. 

Historical records indicate that several small recessional 

moraines fronting various ice bodies in the park were 

deposited in the early 20th century (Carrara and McGimsey, 1988). For instance, two small moraines east of 

Comeau Pass were deposited in the early 20th century by 

a western remnant of the Sperry Glacier that no longer 

exists. Richmond (1986b ), who studied glacial deposits in 

Glacier National Park and the adjacent Blackfoot Indian 

Reservation during the late 1950's and early 1960's, 

recognized two ages of moraines within the younger 

group, both of which he referred to as the Mount Jackson 

moraines. He thought that the greater amount of 

vegetation and stability of boulders on the outer of the 

two moraines present in some cirques suggested that 

some of them may be "earlier late neoglacial" in age. 

In the middle Canadian Rockies, Cavell moraines 

have been deposited in front of many of the present-day 

glaciers and snowfields. These moraines have been dated 

between the 16th and early 20th centuries by dendrochronology, lichenometry, and historical records (Luckman and Osborn, 1979). 

In the Wind River Range of Wyoming, moraines in 

front of present-day glaciers were deposited during the 

Gannett Peak stade. These bouldery, unvegetated 

moraines are thought to have been deposited by advances 

between the 16th and 19th centuries, with the advance of 

A.D. 1850 being in general the most extensive 

(Richmond, 1965). 

In the Front Range of Colorado, bouldery, unvegetated, ice-cored moraines in front of present -day 

glaciers and snowfields were deposited by the Arapahoe 

Peak advance. Lichen measurements suggest that the 

oldest of these moraines may have been deposited about 

A.D. 1650, whereas historic records indicate that the 

youngest of these moraines were deposited by the 

beginning of the 20th century (Benedict, 1968). 

In summary, moraines of the younger group in 

Glacier National Park are thought to correlate with other 

"Little Ice Age" moraines elsewhere in the Rocky 

Mountains: (1) Cavell moraines of the middle Canadian 

Rockies (Luckman and Osborn, 1979); (2) Gannett Peak 

moraines in the Wind River Range of Wyoming 

(Richmond, 1965); and (3) Arapahoe Peak moraines in 

the Front Range of Colorado (Benedict, 1968, 1973, 

1981, 1985). 

Climatic Implications of the Younger Moraines 

At most sites ( > 80 percent) in Glacier National 

Park, only a single moraine of the younger group fronts 

the present-day glaciers and snowfields. Moraines of the 

older group are rarely present. Thus, at most sites the 

climatic cooling of the mid-19th century produced 

Moraines in the High Areas of Glacier National Park 45 
glaciers that probably overran and destroyed moraines of 

the older group. Hence, the climatic cooling of the 

mid-19th century, although mild compared to full-glacial 

conditions, was the most severe in the Glacier National 

Park region since the end of the late Wisconsin 

glaciation. 

The severity of the mid-19th century climate and 

the corresponding glacial advance are also indicated by 

the presence of Mazama ash in the soil immediately 

downvalley from moraines of the younger group fronting 

the Grinnell Glacier and the site of the former Clements 

glacier. Any earlier more extensive glacial advances 

would have scraped the ash away from these sites; 

therefore, the presence of this ash indicates that the 

mid-19th century advances of these two glaciers were 

their most extensive since the Mazama ash was deposited 

6,845 yr. ago. 

Similar conclusions regarding the mid-19th century 

glacial expansion have been reached in the Canadian 

Rockies. In Jasper National Park, the Cavell advance was 

generally more extensive than the older Crowfoot 

advance (Luckman and Osborn, 1979; Osborn, 1982). 

Based on the relative extent of the Cavell and Crowfoot 

moraines, Kearney and Luckman (1981) concluded that 

the most favorable climatic conditions for Holocene 

glacier development occurred in the last 500 years. In 

addition, fir:pine pollen ratios from Watchtower basin in 

Jasper National Park indicate that Holocene timberline 

reached its lowest altitude (hence the climate was the 

coolest) in the last 500 years (Kearney and Luckman, 

1983). 

GLACIAL FLUCTUATIONS SINCE THE 

MID-19TH CENTURY IN GLACIER 

NATIONAL PARK 

Since their mid-19th century culmination, glaciers 

in Glacier National Park have shrunk drastically (Alden, 

1914; Dyson, 1940, 1948, 1952; Johnson, 1980; Carrara 

and McGimsey, 1981, 1988; and Carrara, 1987). Field 

and airphoto inspection of moraines of the younger 

group indicate that during the mid-19th century there 

were more than 150 glaciers in Glacier National Park. 

These glaciers ranged in size from small ice bodies of 

only a few hectares to the Blackfoot Glacier, which 

covered about 7.6 km2 and encompassed the area of the 

present-day Blackfoot and Jackson Glaciers (fig. 25). 

During that time the Mount Jackson area of Glacier 

National Park contained 27 glaciers totaling about 21.6 

km2 (Carrara and McGimsey, 1988). 

Observations and photographs from between A.D. 

1900 and 1914 indicate that although many glaciers in 

Glacier National Park had downwasted since the mid19th century, most still extended to or near to their 

terminal moraines (Alden, 1914). On the basis of treering studies and historical records, Carrara and McGimsey (1981) concluded that the retreat rates of the Agassiz 

and Jackson Glaciers were generally modest before 

about A.D. 1920, but after that time both glaciers began 

to retreat rapidly (figs. 23, 24). This period of rapid 

retreat continued until the mid-1940's. This conclusion is 

supported by climatic records from Kalispell, Mont., that 

indicate that above average summer temperatures and 

below average annual precipitation occurred from about 

A.D. 1918 to 1943 (Carrara and McGimsey, 1981) (fig. 

26). Glacier retreat rates slowed markedly after this 

period (Dyson, 1952; Johnson, 1980; Carrara and 

McGimsey, 1981 ). 

During the warm, dry period from about A.D. 1918 

to 1943, many glaciers in Glacier National Park 

disappeared. Of the more than 150 glaciers in the park 

during the mid-19th century, only 50 to 70 remained by 

1950 (Dyson, 1952). Only 53 glaciers, comprising 13.8 

km2

, remained in 1958 (Meier, 1961). 

In 1979, 17 of the 27 glaciers present in the Mount 

Jackson area during the mid-19th century no longer 

existed. The remaining glaciers comprised a total area of 

only about 7.4 km2

, compared with the 21.6 km2 

contained in the 27 glaciers in this area during the 

mid-19th century (Carrara and McGimsey, 1988). 

Most of the 17 former glaciers in the Mount 

Jackson area were either small or unfavorably oriented 

with respect to solar radiation. The two largest of these 

former glaciers, the Logan and Red Eagle glaciers, faced 

due east and were 0.93 and 0.5 km2 in size, respectively, 

during the mid-19th century (fig. 27). These two glaciers 

probably disappeared by A.D. 1950 (Dyson, 1952). In 

August 1983, the site of the former Red Eagle glacier 

was occupied by a freshly striated bedrock surface 

covered with a veneer of bouldery rubble. A small 

snowfield lay against the headwall, in several places 

pierced by bedrock (fig. 28). 

The most drastic shrinkage of an ice body during 

this century in Glacier National Park is that of the 

Agassiz Glacier, in the northwest corner of the park in 

the Livingston Range. This glacier occupied a shallow 

cirque between Kintla Peak (3,080 m) and Mount Peabody (2,808 m) (fig. 29). During the mid-19th century the 

Agassiz Glacier was one of the largest ice bodies in the 

park. At that time, it flowed northeast down a bedrock 

dip slope for 2.4 km before spilling over a small cliff, then 

advanced across relatively flat forested terrain for 

another 0.7 km. This glacier had a surface area of 3.38 

km2 and a terminus altitude of 1,793 m (Carrara and 

McGimsey, 1981). 

Retreat of the Agassiz Glacier from its maximum 

mid-19th century downvalley extent, as shown by its 

associated forest trimline, began about A.D. 1859 

46 Late Quaternary History, Glacier National Park Region, Montana 
Mount 

Jackson 

3, 065 m 

~ 

~ 

~ 

"" 

2 KILOMETERS 

48 °35' L__ ______ _____l _ _ _ ______________________ _j___ ______ _ __j 

EXPLANATION 

Extent of glaciers in 1979 Moraines of the younger group 

-1 91 3- Extent of glaciers in specific year prior to 1979 Moraines of the older group 

--- Extent of Blackfoot glacier during the mid-19th century 

Figure 25. The mid-19th century Blackfoot Glacier showing the disintegration of this glacier into the present-day Blackfoot 

and Jackson Glaciers. Moraines of the older and younger groups are also shown (modified from Carrara and McGimsey, 

1988). 

Carrara and McGimsey, 1981 ). Eleven tree-ring stations 

within the forest trimline, from the maximum downvalley 

extent to the base of the bedrock dip slope, indicate that 

the glacier retreat rates were modest (2.4 to 15 m/yr) 

until1917, after which they became quite rapid (>40 

m/yr) (fig. 23). By the mid-to-late 1920's this glacier had 

retreated back onto the bedrock dip slope. 

During the next several decades retreat was rapid. 

From 1932 to 1942 retreat of the Agassiz Glacier was 

measured by the National Park Service (Matthes, 1944). 

Retreat was greatly accelerated because the bedrock dip 

slope under the glacier at that time was 15°. Matthes 

(1944) stated that recession was caused not only by 

melting but also by the avalanching of ice down the dip 

slope. During the period from 1932 to 1942, the Agassiz 

Glacier retreated nearly 0.9 km. In 1939, Dyson (1941) 

reported that the Agassiz Glacier had almost separated 

into two parts, one along the eastern flank of Kintla Peak, 

the other along the northwest side of Mount Peabody. By 

1940, this separation was complete, and although the 

eastern ice body had a distinct tongue, this tongue 

disappeared shortly after 1941. At that time Dyson 

(1941) estimated that these two remnants had a 

combined surface area of 0.75 km2

• 

In 1979, patches of blue ice and projections of 

bedrock were observed in the western ice body, which 

had a surface area of 0.75 km2

, but only firn was observed 

on the eastern ice body, and it is doubtful that either is 

still a glacier. Volume shrinkage has been drastic due to 

the tremendous lowering of the ice surface. Field 

inspection and map interpretation revealed that in places 

now devoid of ice, the Agassiz Glacier had been 200 m 

thick. In 1979, ice in the western ice body did not exceed 

10 or 15 m in thickness. This western ice body represents 

less than 3 percent of the volume of the Agassiz Glacier 

at the time of its culmination in the mid-19th century. 

Glacial Fluctuations Since The Mid-19th Century 47 
(/) 

~ 18 _J 

L.I.J 

u 

(/) 

L.I.J 

L.I.J 

a: 

~ 

L.I.J 

0 

z 

~ 17 ::::> 

~ a: 

L.I.J 

a.. 

~ 

L.I.J 

1--

a: 

L.I.J 

~ 

3 16 (/) 

15 

47 

45 

(/) 

a: 

L.I.J 

IL.I.J 

~ 

i= 

z 

L.I.J 

u 40 ~ 

z 

0 

i= 

<( 

Ia: 

u 

L.I.J 

a: 

a.. 

_J 

<( 35 ::::> 

z 

z 

<( 

Average A~ summer M temperature 1896-1986 

A 

Figure 26. Climatic data, Kalispell, Mont. A, Average summer (June, July, August) temperatures; 5-year 

running mean, 1897-1984. 8, Average yearly precipitation; 5-year running mean, 1898-1984. 

48 Late Quaternary History, Glacier National Park Region, Montana 
48 °35' 

Mt Logan 

2,816m 

I 

I 

/ 

11 3°37'30" 

EXPLANATION 

-1 914- Extent of glacier in specific year 

--- Extent of former Logan and Red Eagle glaciers 

during the mid-19th century 

Moraines of the younger group 

Moraines of the older group 

Mazama ash site 

Figure 27. The former Logan and Red Eagle glacier areas, 

showing moraines of both the older and younger groups and 

Mazama ash sites (modified from Carrara and McGimsey, 

1988). 

The Sperry Glacier provides another welldocumented example of an ice body that has retreated 

drastically from its mid-19th century position (Johnson, 

1980; Carrara, 1987; Carrara and McGimsey, 1988). 

During the mid-19th century, this glacier was about 3.87 

km2 in area (fig. 30). By 1927, it had separated into one 

large and two smaller glaciers (Dyson, 1948). The two 

smaller glaciers lay against the northeast face of Edwards 

Mountain and the area southeast of Comeau Pass, and 

they probably disappeared sometime during the warm, 

dry period between 1920 and the mid-1940's. In 1979, the 

Sperry Glacier consisted of a single ice body of about 

1.06 km2

, lying against the northern flank of Gunsight 

Mountain. 

Other glaciers have divided into several smaller ice 

bodies. For example, the Blackfoot Glacier, in the Lewis 

Range along the Continental Divide between Mount 

Jackson (3,065 m) and Mount Logan (2,817 m), had two 

ice lobes and covered about 7.6 km2 during the mid-19th 

century. By 1979, this glacier was divided into seven 

smaller glaciers with a total area of about 3 km2 (fig. 25). 

Again, most of this retreat occurred during the warm, dry 

period between about 1918 and 1943. 

During the mid-19th century the western ice lobe 

of the Blackfoot Glacier (the present-day Jackson 

Glacier) extended 2.2 km down its steep (15°) bedrock 

dip slope and another 0.6 km across a relatively flat 

forested terrain to an altitude of 1,695 m. Tree-ring 

studies at the downvalley limit of the forest trimline 

fronting the Jackson Glacier indicate that retreat began 

about A.D. 1860 (figs. 24, 31). Ten tree-ring stations 

within the forest trimline indicate that the rate of retreat 

was modest ( < 7 m/yr) until about 1911, after which the 

rate increased. Like the Agassiz Glacier, the Jackson 

Glacier retreated to its steep bedrock dip slope in the 

mid- to late-1920's; at that time retreat became rapid. By 

1939, the Jackson Glacier had separated from the Blackfoot Glacier by 0.8 km and its terminus was at an altitude 

of 1,965 m (Dyson, 1941). 

Between 1966 and 1979, several of the larger 

glaciers in the Mount Jackson area advanced slightly 

(Carrara and McGimsey, 1988). A comparison of 1966 

and 1979 airphotos revealed that the ice tongues of the 

Harrison and Jackson Glaciers (fig. 25) advanced about 

100 m during that time. The Blackfoot Glacier also 

advanced as much as 100 m along its broad western 

margin at that time, but its eastern margin remained 

stationary. However, the Sperry Glacier continued a 

pattern of overall retreat (fig. 30). Climatic records from 

Kalispell, Mont., suggest that these small advances 

correspond to an increase in annual precipitation and a 

decrease in summer temperatures beginning about 1975 

(fig. 26). 

In 1979, the largest ice body in Glacier National 

Park, the Blackfoot Glacier, had an area of about 1.74 

km2

• Other relatively large glaciers in the park include 

the Harrison (1.49 km2

), Sperry (1.06 km2), Rainbow 

(1.06 km2), Grinnell (1.03 km2), and Jackson (1.02 km2

) 

(Carrara and McGimsey, 1988). 

CONCLUSIONS 

Deglaciation 

This study indicates that large areas of the Glacier 

National Park region were deglaciated before the 

deposition of the Glacier Peak G and Mount St. Helens 

Jy ashes 11,200 and 11,400 yr. BP. Any remaining 

glaciers at that time were confined to local mountain 

valleys. 

Conclusions 49 
Figure 28. The former Red Eagle glacier area, showing moraines of both the older and younger groups. 

Deglaciation was extensive before 11,400 yr. BP in 

the Marias Pass area. The presence of the Glacier Peak 

G and Mount St. Helens Jy ashes at the Marias Pass 

exposure clearly indicates deglaciation of this area before 

11,400 yr. BP. As ice flowing east through Marias Pass 

supplied much of the ice to the Two Medicine piedmont 

glacier, the disappearance of this glacier from the plains 

of Montana probably predates the deglaciation of the 

Marias Pass area by at least several hundred, if not 

several thousand years. 

Extensive retreat of the St. Mary glacier before 

11,200 yr. BP is indicated by the presence of the Glacier 

Peak G ash at the Chewing Blackbones bog. During late 

Wisconsin time this glacier flowed at least 50 km from its 

source area along the Continental Divide in the Logan 

Pass area north into southwestern Alberta. The presence 

of the Glacier Peak G ash at the Chewing Blackbones 

bog indicates that by 11,200 yr. BP the St. Mary glacier 

had retreated at least 20 km from its maximum late 

Wisconsin position. Because the Glacier Peak G ash is 

underlain by 110 em of silty clay at this site, the age of the 

ash is thought to represent a very minimum date of 

deglaciation for this area. 

On the west side of the park, the valleys of the 

North and Middle Forks Flathead River, which had 

contained large trunk glaciers, were extensively, if not 

completely deglaciated by the time the Glacier Peak G 

and Mount St. Helens Jy ashes were deposited. The 

presence of these ashes at the Cabin Creek exposure 

indicates that by 11,400 yr. BP, the trunk glacier that had 

filled the valley of the North Fork Flathead River had 

retreated upvalley from the Cabin Creek exposure. 

Because at this site the Mount St. Helens Jy ash is 

underlain by 340 em of fine-grained sediment that may 

have required several hundred or thousand years to 

accumulate, the age of the ash is probably a very 

minimum date of deglaciation. 

Deglaciation of the valley of the Middle Fork 

Flathead River by 11,200 yr. BP is indicated by the 

presence of the Glacier Peak Gash at the Middle Fork 

bog and Goat Lick exposure in the southwestern corner 

of Glacier National Park. At the Middle Fork bog, this 

ash is underlain by 50 em of fine-grained sediment. At 

the Goat Lick exposure, the Glacier Peak G ash is 

underlain by about 30 m of gravel. Hence, the stratigraphy at both sites suggests that they may have been 

50 Late Quaternary History, Glacier National Park Region, Montana 
Figure 29. The Agassiz Glacier area, showing forest trimline marking the mid-19th century extent of this glacier and remnant 

snowfield on eastern flank of Kintla Peak. Numbers within forest trimline represent those tree-ring study sites shown on figure 

23 (modified from Carrara and McGimsey, 1981). View is towards the southwest. Photograph by Austin Post, U.S. Geological 

Survey, Aug. 7, 1961. 

deglaciated several hundred or possibly several thousand 

years before the deposition of the Glacier Peak G ash. 

Therefore, the large trunk glacier that filled the valley of 

the Middle Fork Flathead River with hundreds of meters 

of ice probably had retreated far upvalley into the Lewis 

and Clark Range by the time the Glacier Peak Gash was 

deposited. 

The former Bowman and McDonald glaciers, 

which were tributary to the large trunk glaciers in the 

valleys of the North and Middle Forks Flathead River, 

were confined solely to their respective valleys before 

11,200 yr. BP. This is indicated by the radiocarbon age of 

11,150±90 yr. BP from Bowman Lake bog and by the 

presence of the Glacier Peak G ash at Ben Ryan bog in 

the Lake McDonald area. Other tributary glaciers along 

the western flank of the Livingston Range and eastern 

flank of the Whitefish Range probably were also confined 

to their valleys by that time. How much farther upvalley 

from the Bowman Lake and Ben Ryan bogs the Bowman 

and McDonald glaciers actually lay is unknown. 

However,· data elsewhere in the Rocky Mountains 

suggest that by as early as about 11,500 yr. BP remaining 

glaciers may have been as small as subsequent late 

Holocene glaciers (Porter and others, 1983). 

Conclusions 51 
EXPLANATION 

Extent of glacier in 1979 

-1946- Extent of glacier in specific year 

prior to 1979-Dashed where uncertain 

----Extent of glacier during mid-19th century 

Moraines of the younger group 

Moraines of the older group 

• Mazama ash site 

Edwards 

Mountain 

2,166m 

1 KILOMETER 

I 

/ 

/ 

( 

\ 

) 

I 

( 

\ 

I 

& 

I~ 

I~ 

\8 

\ 

\ 

2,635 ~ 

I 

f:y<v 

I§ 

;cs 

)Z698m 

Figure 30. The Sperry Glacier area, showing shrinkage of this glacier from the mid-19th century to 1979, 

moraines of the older and younger groups, and Mazama ash sites (modified from Carrara and McGimsey, 1988). 

The Kootenai Lakes area was also probably deglaciated before 11,000 yr. BP. Although neither the Glacier 

Peak G nor Mount St. Helens Jy ashes were found in this 

area, stratigraphic evidence suggests that the time of 

deglaciation may be older than the radiocarbon ages 

obtained from the Mount Cleveland bog by several 

thousand years. This suggestion is based on the fact that 

pine fragments from hole #1, dated at 9,510±350 yr. BP, 

were underlain by 250 em of sediment. The radiocarbon 

age of 9,850±350 yr. BP on willow fragments from hole 

#4 is an average radiocarbon age of the lower 50 em of 

organic material from this bog. The lower several 

centimeters of organic material from this hole are probably 

much older than this date. Hence, the radiocarbon ages 

from the Mount Cleveland bog are thought to be very 

minimum dates of deglaciation for the Kootenai Lakes 

area. 

By 10,000 yr. BP, glaciers in Glacier National Park 

were probably confined to the same cirques and wellshaded niches that shelter the present-day glaciers and 

snowfields. Radiocarbon ages from sites near presentday glaciers in Banff and Jasper National Parks, Alberta, 

and Yoho National Park, British Columbia, indicate that 

by 10,000 yr. BP late Wisconsin glaciers had receded to 

positions close to those of present -day glaciers (Luckman 

and Osborn, 1979; Reasoner and Rutter, 1988). 

Although evidence of that limited glacier extent by 

10,000 yr. BP was not found in the Glacier National Park 

region, a similar amount of deglaciation by that time is 

suggested. 

52 Late Quaternary History, Glacier National Park Region, Montana 
Figure 31. The Jackson Glacier area, showing forest trimline marking the mid-19th century extent of this glacier and 

remaining glacier. View is toward the south-southwest. Numbers within forest trimline represent those tree-ring study sites 

shown on figure 24 (modified from Carrara and McGimsey, 1981). Photograph by Austin Post, U.S. Geological Survey, Sept. 

8, 1969. 

Revegetation 

Timberline in the northern Rocky Mountains may 

have been about 1,000 m lower than at present, during the 

Wisconsin glaciation (Baker, 1983). Conifers expanded 

their range rapidly throughout the Rocky Mountains 

between 11,000 and 9,000 yr. BP (Barnosky and others, 

1987). The distribution of conifers during the late 

Wisconsin is not known with certainty, but they may have 

survived in small groups along the mountain slopes 

(Barnosky and others, 1987). With deglaciation, these 

small groups could have rapidly expanded their range. 

Revegetation of deglaciated areas by trees and 

shrubs was underway by the time the Glacier Peak G and 

Mount St. Helens Jy ashes were deposited. This is 

indicated by the macrofossils and pollen found in 

association with these ashes at the Marias Pass exposure. 

A conifer needle and alder strobilus found there 

immediately below the Glacier Peak G ash, and several 

small willow fragments found below the Mount St. 

Conclusions 53 
Helens Jy ash indicate that revegetation of this area was 

underway between 11,200 and 11,400 yr. BP. From these 

macrofossils and an analysis of pollen found in the 

sediment at this exposure, Carrara and others (1986) 

concluded that at the time the Glacier Peak G and Mount 

St. Helens Jy ashes were deposited, vegetation in the 

Marias Pass area consisted of an open landscape of 

shrubs, herbs, and scattered conifers. At that time there 

was a larger proportion of spruce and whitebark pine 

than at present. Because such an assemblage is 

characteristic of the tundra/subalpine forest boundary 

(treeline) (presently at an altitude of about 2,050 m), 

whereas the Marias Pass exposure is at an altitude of 

1,550 m, these data may be interpreted as indicating a 

treeline about 500 m lower than present 11,400 years 

ago. However, the fossil insect data suggest that a 500-m 

lowering of treeline may be a minimum estimate. The 

lack of any tree-related fossil insect species in the 

sediment immediately below the Mount St. Helens Jy ash 

led Elias (1988) to suggest that treeline may have been 

below the Marias Pass exposure by an additional several 

hundred meters. Therefore, at about 11,400 yr. BP 

treeline was at least 500 m lower than present and may 

have been as much as 700 m lower. At that time, the area 

around Guardipee Lake, on the plains about 60 km 

northeast of Marias Pass, probably was a grassland 

(Barnosky and others, 1987). 

Evidence of extensive reforestation was obtained 

from the Lake McDonald area. Radiocarbon ages of 

wood or peat containing wood fragments of 9,920± 120 

yr. BP, 9,910± 100 yr. BP, and 8,730±80 yr. BP from 

Glacier Route 7, East McGee, and McGee bogs, 

respectively, clearly indicate reforestation of the McGee 

Meadow area by lodgepole pine by about 10,000 yr. BP. 

In addition, the stratigraphy of the Glacier Route 7 bog 

suggests that the reforestation of this area by lodgepole 

pine may have occurred soon after the deposition of the 

Glacier Peak Gash. The radiocarbon age of 10,630±250 

yr. BP of a wood fragment from the Howe Lake bog is a 

minimum date of reforestation by either spruce or larch 

in the Lake McDonald area. In addition, the age of 

9,650±250 yr. BP of gyttja containing coniferous 

fragments at the Snyder Ridge bog indicates 

reforestation of the area surrounding that relatively high 

altitude (1,351 m) bog by that time. Hence, by as early as 

11,000 yr. BP, and certainly by 10,000 yr. BP, the Lake 

McDonald area supported a forest containing lodgepole 

pine and probably Engelmann spruce. This forest was 

probably well established throughout the valleys of the 

North and Middle Forks Flathead River. 

A similar time of reforestation is indicated for the 

Kootenai Lakes area of Waterton Valley by the 

radiocarbon ages from the Mount Cleveland bog. A 

radiocarbon age of 9,510±350 yr. BP from hole #1 is a 

minimum date for the return of lodgepole pine to this 

area. The radiocarbon age of 9,850±260 yr. BP from 

hole #4 is a minimum date for the return of willow. As 

the major angering effort was concentrated in the valley 

of the North Fork Flathead River and only a short trip 

was made into the Waterton Valley, there is no reason to 

believe that the time of reforestation in W aterton Valley 

was much different than that of the better documented 

North Fork. Hence, a forest containing lodgepole pine 

was probably also well established in the Kootenai Lakes 

area by 10,000 yr. BP. 

Moraines of the Older Group 

Mazama ash, which was found to overlie several 

moraines of the older group in Glacier National Park, 

provides a minimum age of 6,845 yr. BP for these 

moraines. This older group of moraines probably do not 

date from the early Holocene advance (8,500 to 7,500 yr. 

BP) suggested by Beget (1983). Vegetative evidence as 

well as correlation with other moraines elsewhere in the 

Rocky Mountains suggests that these moraines are late 

Pleistocene in age. Whether these moraines are the 

product of a separate post-Wisconsin glacial advance or 

are simply the product of the last advance or stillstand of 

late Wisconsin glaciers before final deglaciation is not 

known. 

Moraines of the Younger Group 

Most of the moraines of the younger group in 

Glacier National Park were deposited by advances that 

culminated in the mid-19th century. This is indicated by 

tree-ring studies in the forest trimlines fronting the 

Agassiz and Jackson Glaciers (Carrara and McGimsey, 

1981) and in the area just beyond the outermost moraine 

of the younger group fronting the Sperry Glacier. 

Historical records indicate that several small recessional 

moraines fronting various ice bodies in the park were 

deposited in the early 20th century. Richmond (1986b) 

thought that some moraines of the younger group in 

Glacier National Park might be "early late neoglacial" in 

age. Cavell moraines in the middle Canadian Rockies, 

which are correlative with moraines of the younger group 

in the park (Carrara and McGimsey, 1981; Osborn, 1985; 

Carrara, 1987), have been dated between the 16th and 

early 20th centuries (Luckman and Osborn, 1979). 

Most of the present-day glaciers and snowfields in 

Glacier National Park are fronted only by a single 

moraine of the younger group. Moraines of the older 

group are rarely present. Hence, at most sites, the 

climatic cooling that culminated in the mid-19th century 

produced glaciers that probably overran and destroyed 

moraines of the older group. Although mild compared to 

54 Late Quaternary History, Glacier National Park Region, Montana 
full-glacial conditions, the climatic cooling of the mid19th century was the most severe in the Glacier National 

Park region since the end of the late Wisconsin 

glaciation. 

Glacial Fluctuations since the 

Mid-19th Century 

Glaciers in Glacier National Park have shrunk 

drastically since the mid-19th century when the park 

contained more than 150 glaciers. From the mid-19th 

century until about 1920, glacier retreat rates were slow. 

However, from about 1920 to the mid-1940's, the Glacier 

National Park region had above average summer 

temperatures and below average annual precipitation. 

During this time the glaciers retreated drastically or 

disappeared altogether. After the mid-1940's, the overall 

retreat rates slowed. Between 1966 and 1979, several of 

the larger glaciers in the Mount Jackson area advanced 

slightly (Carrara and McGimsey, 1988). By 1979, more 

than half the glaciers present in Glacier National Park 

during the mid-19th century no longer existed. 

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environments of the United States, volume 1, The late 

Pleistocene: Minneapolis, Minn., University of 

Minnesota Press, p. 71-111. 

Powers, H.A., and Wilcox, R.E., 1964, Volcanic ash from 

Mount Mazama (Crater Lake) and from Glacier Peak: 

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Raup, O.B., Earhart, R.L., Whipple, J.W., and Carrara, P.E., 

1983, Geology along Going-to-the-Sun Road, Glacier 

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Reasoner, M.A., and Rutter, N.W., 1988, Late Quaternary 

history of the Lake O'Hara region, British ColumbiaAn evaluation of sedimentation rates and bulk amino 

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___ 1972, Appraisal of the future climate of the Holocene in 

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315-322. 

___ 1986a, Tentative correlation of deposits of the Cordilleran Ice Sheet in the northern Rocky Mountains: 

Quaternary Science Reviews, v. 5, p. 129-144. 

References Cited 57 
___ 1986b, Stratigraphy and correlation of glacial deposits 

of the Rocky Mountains, the Colorado Plateau, and the 

ranges of the Great Basin: Quaternary Science Reviews, 

v. 5, p. 99-127. 

Richmond, G.M., Fryxell, Roald, Neff, G.E., and Weis, P.L., 

1965, The Cordilleran Ice Sheet of the northern Rocky 

Mountains, and related Quaternary history of the 

Columbia Plateaus, in Wright, H.E., Jr., and Frey, D.G., 

eds., The Quaternary of the United States: Princeton, 

N.J., Princeton University Press, p. 231-242. 

Rosenbaum, J.G., and Larson, E.E., 1983, Paleomagnetism of 

two late Pleistocene lake basins in Colorado-An 

evaluation of detrital remanent magnetism as a recorder 

of the geomagnetic field: Journal of Geophysical 

Research, v. 88, no. B12, p. 10611-10624. 

Ross, C.P., 1959, Geology of Glacier National Park and the 

Flathead region, northwestern Montana: U.S. Geological 

Smvey Professional Paper 296, 125 p. 

Sarna-Wojcicki, A.M., Champion, D.E., and Davis, J.O., 1983, 

Holocene volcanism in the conterminous United States 

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Smith, H.W., Okazaki, R., and Knowles, C.R., 1977, Electron 

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materials by wavelength dispersive X-ray fluorescence 

spectrometry, in Baedecker, P.A., ed., Methods for geochemical analysis: U.S. Geological Survey Bulletin 1770, 

p. E1-E19. 

U.S. Department of Commerce, 1964, General summary of 

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p. 292-300. 

___ 1982, Monthly normals of temperature, precipitation, 

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(Montana): Climatology of the United States, no. 81, 

24p. 

Waddington, J.C.B., and Wright, H.E., Jr., 1974, Late 

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Waitt, R.B., Jr., and Thorson, R.M., 1983, The Cordilleran Ice 

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adjacent Canada: Montana Geological Society 

Guidebook 1984 Field Conference and Symposium, 

p. 33-50. 

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States: Princeton, N.J., Princeton University Press, 

p. 807-816. 

Zielinski, G.A., and Davis, P.T., 1986, Probable late Pleistocene age for the type Temple Lake moraine, Wind 

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58 Late Quaternary History, Glacier National Park Region, Montana 
APPENDIX A 
APPENDIX A. PREPARATION AND 

ANALYSIS OF ASHES BY X-RAY 

FLUORESCENCE 

Collecting and Processing of Ash 

Samples 

Most of the ash samples discussed in this paper 

were obtained with a bucket auger from bogs, at depths 

ranging from 0.3 to 4 m. Some samples of Mazama ash 

were collected from soils. Hence, in many cases, these 

ash samples were heavily contaminated with detrital 

sand, silt, clay, and organic material. Several relatively 

clean ash samples were collected directly from exposures, 

although these samples also contained small amounts of 

detrital material. Because of this contamination, all 

samples were pretreated before microscopic examination 

and chemical analysis. 

Ash samples collected in this study commonly 

contained about 80-90 percent silt and clay. Because the 

silt- and clay-size fraction of the ash samples could not be 

separated from the contaminating detrital silt and clay, 

the entire silt- and clay-size fraction was discarded 

leaving only the sand-size fraction. Hence, all analyses 

were performed on the sand-size fraction, which 

commonly comprised only about 10-20 percent of the 

ash samples. Therefore, when collecting ash samples, a 

relatively large amount (300-500 g) was needed to assure 

that after elimination of the silt- and clay-size fraction, 

enough would be left for analyses. 

In order to obtain a relatively clean sample of the 

glass fraction, the ash samples were initially put in a weak 

solution of dispersing agent (commercial laboratory 

detergent) and agitated for about 5 minutes daily with an 

ultrasonic probe to disperse any clay and organic 

material present in the sample. After several days, 

organic material would rise to the surface of the liquid 

and could then be decanted off. The samples were then 

placed on a 270-mesh sieve and washed with water to 

remove the silt and clay. If the sample was heavily 

contaminated with silt and clay, it was again put into a 

weak dispersing solution for several days and the 

procedure was repeated. Next, the samples were 

centrifuged in heavy liquid (specific gravity of 2.42) to 

separate out the glass fraction (specific gravity < 2.42). 

Although the > 2.42 specific gravity fraction contained 

some detrital rock fragments, it also contained the 

various accessory minerals used to help identify the ash; 

hence, it was also saved. Finally, the glass fraction was 

passed through a magnetic separator to eliminate those 

glass shards that contained mafic crystals. The remaining 

glass fraction, at least 0.8 g, was then analyzed for major 

elements by wavelength-dispersive X-ray fluorescence. A 

complete explanation of the principles of wavelengthdispersive X-ray fluorescence spectrometry, sample 

preparation, instrumentation, and precision is given in 

Taggart and others (1981, 1987). 

Comparison of X-ray Fluorescence Data 

with Electron-microprobe Data 

It has been suggested that major-element values 

determined on bulk samples may be affected by 

contamination and weathering (Lemke and others, 1975; 

Smith and others, 1977). Because of the~'e concerns, the 

use of the electron microprobe has been favored to 

obtain chemical data from the various ash fractions 

commonly analyzed. However, Cormie and Nelson 

(1983) used energy-dispersive X-ray fluorescence on 

glass separates to obtain trace-element data that allowed 

them to distinguish between the Mazama, Bridge River, 

and Mount St. Helens Yn ashes. Results from this study 

indicate that most major-element values on glass 

separates determined by wavelength-dispersive X-ray 

fluorescence for the Mazama, Glacier Peak Band G, and 

Mount St. Helens Jy ashes are comparable to values of 

other investigators using electron microprobes. 

Mazama Ash 

Major-element values of Mazama ash determined 

by X-ray fluorescence in this study are compared to 

values determined by electron microprobe by different 

investigators (table 7). As can be seen, values obtained by 

X-ray fluorescence for samples of Mazama ash from 

both bogs and soils in the Glacier National Park region 

are comparable to those obtained by electron microprobe. In fact, except for the Si02 values, which are lower 

than the other Si02 values listed in table 7 by less than 1 

percent, all other major-element values determined by 

X-ray fluorescence are intermediate to values in table 7 

that were determined by electron microprobe. This 

comparability is also demonstrated by the K:Fe ratios. 

Ratios determined for 11 samples of Mazama ash from 

bogs in the Glacier National Park region (table 2) 

averaged 1.46:1, whereas ratios determined for 5 samples 

of Mazama ash from soil samples (table 3) averaged 

1.49:1. Both ratios are intermediate between those 

derived from the major-element values of Westgate and 

Gorton (1981), 1.37:1; Sarna-Wojcicki and others 

(1983), 1.55:1; and Lemke and others (1975), 1.61:1, 

determined by electron microprobe. In fact, table 7 

suggests that individual preparation and operation 

procedures may be more significant than the type of 

equipment used to obtain the major-element values for 

the Mazama ash. 

60 Late Quaternary History, Glacier National Park Region, Montana 
Table 7. Major-element values of glass in the Mazama ash, as reported by various 

investigators 

Reference-- S and W and G2 L and c4 c5 

others 1 others3 

Sio2 73.6 72.6 73.0 72.8 72.7 

Al203 14.4 14.4 15.7 14.6 14.6 

6Fe0 1.98 2.11 1. 85 2.01 1. 95 

MgO .37 .56 .46 .54 .48 

CaO 1.56 1.66 1. 91 1.84 1. 89 

Na2o 4.70 5.18 4.17 4.99 5.17 

K2o 2.87 2.70 2.79 2.75 2.73 

Tio2 .44 .48 .38 .43 .41 

Total-- 99.92 99.69 100.26 99.96 99.93 

K:Fe 1.55:1 1.37:1 1.61:1 1.46:1 1. 49:1 

1Modified from Sarna-Wojcicki and others (1983' table 5-2); values 

determined by electron microprobe. 

2From Westgate and Gorton (1981, table 2); values determined by 

electron microprobe. 

3From Lemke and others (197 5' 

determined by electron microprobe. 

4carrara, this study, average 

determined by X-ray fluorescence. 

5carrara, this study, average 

determined by X-ray fluorescence. 

6Total iron as FeO. 

Glacier Peak B and G Ashes 

Major-element values determined on samples of 

Glacier Peak B and G ashes collected at the Trinity Mine 

site in Washington (Porter, 1978) are presented in tables 

8 and 9. This site is the type locality for ashes erupted 

from Glacier Peak about 11,200 yr. BP. These tables 

compare major-element values determined by electron 

microprobe by various investigators to major-element 

values determined by X-ray fluorescence in this study. 

Results indicate that several of the major-element 

values determined by X-ray fluorescence differ 

significantly from values determined for those same 

elements by electron microprobe. For the Glacier Peak B 

table 2, sample 60-7-29R); values 

of values in table 2. 

' values 

of values in table 3; values 

ash, values obtained by X-ray fluorescence were 

significantly lower than values obtained by electron 

microprobe for Si02, K20, and Ti02, whereas 

significantly higher values were obtained for Ah03, 

MgO, and CaO (table 8). For the Glacier Peak G ash, 

values determined by X-ray fluorescence were 

significantly lower than those determined by electron 

microprobe for Si02, whereas significantly higher values 

were determined for MgO and CaO (table 9). Although 

the FeO value of 1.09 determined by X-ray fluorescence 

for the Glacier Peak G ash is the highest value on table 9, 

it is close to the values of 1.04 and 1.07 determined by 

electron microprobe by Westgate and Evans (1978) and 

Appendix A. Preparation and Analysis of Ashes by X-Ray Fluorescence 61 
Table 8. Major-element values of glass in the Glacier Peak 

B ash from the Trinity Mine, Washington, as reported by 

various investigators 

References- W and E1 S and M and c4 

others 2 others3 

Sio2 77.2 77.8 77.1 74.3 

Al203 12.6 13.1 13.2 15.0 

5Fe0 1.14 1.12 1.21 1.20 

MgO .38 .26 .30 .43 

Cao 1.37 1.33 1.38 2.30 

Na2o 3.97 3.00 3.26 3.92 

K2o 2.91 3.08 2-96 2-69 

Ti02 .23 .27 .23 .20 

Total-- 99.80 99.96 99.64 100.04 

K:Fe 2.72:1 2.93:1 2.61:1 2.39:1 

1From Westgate and Evans (1978, table 2, 

sample UA 147); values determined by electron 

microprobe. 

2Modified from Sarna-Wojcicki and others 

(1983, table 5-2); values determined by electron 

mic.roprobe. 

3Modified from Mehringer and others (1984, 

table 1); values determined by electron microprobe. 

4carrara, this study; values determined by 

X-ray fluorescence. 

5Total iron as FeO. 

Mehringer and others (1984). In fact, these three values 

of FeO are significantly different from those values of 

Sarna-Wojcicki and others (1983) and Lemke and others 

(1975), 0.93 and 0.95 respectively. Reasons for this 

difference in FeO values are not readily apparent, but 

they may result from different preparation procedures. 

In addition, values reported for Na20 in both the Glacier 

Peak B and G ashes vary among the different 

investigators (tables 8, 9). Those for the Glacier Peak B 

Table 9. Major-element values of glass in the Glacier Peak 

G ash from the Trinity Mine, Washington, as reported by 

various investigators 

Reference-- L and W and S and M and cs 

others 1 E2 Others 3 others4 

SiOz 77.1 77.2 77.4 77.7 75.7 

Alzo3 13.7 12.7 12.8 13.1 13.7 

6Fe0 .95 1.04 .93 1.07 1.09 

MgO .29 .33 .zo .27 .40 

CaO 1.15 1.17 loll 1.21 1.69 

Na2o 3.21 3.89 3.81 3.04 3.94 

KzO 3.40 3.36 3.50 3.17 3.27 

TiOz .17 .zz .21 .19 .19 

Total-- 99.97 99.91 99.96 99.75 99.98 

K:Fe 3.82:1 3.45:1 4.02:1 3.16:1 3.20:1 

1From Lemke and others (1975, table 2, sample 

68W48); values determined by electron microprobe. 

2From Westgate and Evans (1978, table 2, sample 

UA 148); values determined by electron microprobe. 

3Modified from Sarna-Wojcicki and others (1983, 

table 5-2); values determined by electron microprobe. 

4Modified from Mehringer and others (1984, table 

1); values determined by electron microprobe· 

5carrara, this study; values determined by Xray fluorescence. 

6Total iron as FeO. 

ash range from 3.00 to 3.97, and those for the Glacier 

Peak Gash range from 3.04 to 3.94. 

The differences in major-element values between 

those determined by X-ray fluorescence and those 

determined by electron microprobe for the Glacier Peak 

B and G ashes from the Trinity Mine site may be due to 

the proximity of the site to Glacier Peak, and the cleaning 

procedure used in this study. The Trinity Mine is only 

about 20 km from Glacier Peak (Porter, 1978). These 

ash samples contained a large nonglass fraction that the 

cleaning procedure used in this study may not have 

adequately removed. In the process of preparing the 

Glacier Peak B and G samples from the Trinity Mine site 

for analysis, it was found that the < 2.42 specific-gravity 

62 Late Quaternary History, Glacier National Park Region, Montana 
fraction comprised only 7.6 percent and 12.2 percent 

respectively of the sample weight. This same specificgravity fraction in samples of the Glacier Peak G ash 

from the Glacier National Park region comprised about 

40-45 percent. 

With increasing distance from the volcano, the ash 

became increasingly lighter as the heavier minerals and 

rock fragments settled out. Hence, about 40-45 percent 

of samples of the Glacier Peak Gash in Glacier National 

Park had a specific gravity < 2.42. Therefore, majorelement values determined by X-ray fluorescence may 

become increasingly accurate and hence more 

comparable to values determined by electron microprobe, with increasing sample distance from the volcano. 

At Sun River Canyon, Mont., a site containing the 

Glacier Peak G ash has been sampled and analyzed 

(table 10) by several investigators (Lemke and others, 

1975; Westgate and Evans, 1978; and Carrara and others, 

1986). Most major-element values determined by X-ray 

fluorescence (Carrara and others, 1986) are similar to 

those values determined by electron microprobe (Lemke 

and others, 1975; Westgate and Evans, 1978) (table 10). 

However, the CaO value determined by X-ray 

fluorescence (1.49) is significantly higher than those CaO 

values determined by electron microprobe (table 10). 

Also, the Na20 value determined by X-ray fluorescence 

is somewhat low compared to those determined by 

electron microprobe. Inasmuch as Na20 values on tables 

8 and 9 range widely, this difference is not considered 

significant. Moreover, some of the electron microprobe 

data seem suspect. For example, the MgO value (0.22) of 

Lemke and others (1975) is quite low compared to the 

other MgO values in table 10. Also, the K20 value (3.40) 

of Westgate and Evans (1978) is somewhat low 

compared to the other K20 values in table 10. Hence, it 

appears that as the Glacier Peak G ash becomes more 

glass-rich with increasing distance from the source, 

major-element values determined by X-ray fluorescence 

become more comparable to values determined by 

electron microprobe, except for CaO values. 

CaO values determined for the Glacier Peak B and 

G, and Mount St. Helens Jy ashes by X-ray fluorescence 

were significantly higher than values determined by 

electron microprobe. In addition, CaO values 

determined for the Glacier Peak G ash by X-ray 

fluorescence on the nine samples listed in table 4 range 

rather widely, from 1.53 to 2.41. Many of the glass shards 

in the Glacier Peak ashes contain small nonmagnetic 

inclusions. The cleaning procedures used in this study to 

obtain bulk samples of the glass fraction may not have 

eliminated all those glass shards containing these 

inclusions. 

Table 10. Major-element values of glass in the Glacier Peak 

G ash from Sun River Canyon, Montana, as reported by 

various investigators 

Reference-- L and Wand C and 

others 1 E2 others 3 

Si02 76.6 77.0 76.6 

Al2o3 13.2 12.7 13.0 

4Fe0 .99 1.06 1.03 

MgO .22 .39 .38 

CaO 1.26 1.18 1.49 

Na2o 3.94 3.94 3.66 

K20 3.62 3.40 3.63 

Ti02 .18 .22 .19 

Total-- 100.01 99.89 99.98 

K:Fe 3.90:1 3.42:1 3.76:1 

1From Lemke and others (1975, table 2, 

sample HS-87); values determined by electron 

microprobe. 

2From Westgate and Evans (1978, table 2, 

sample UA 647); values determined by electron 

microprobe. 

3From Carrara and others (1986, table 

1); values determined by X-ray fluorescence. 

4Total iron as FeO. 

Comparison of major-element values for Glacier 

Peak ashes found in the Glacier National Park region 

(table 4) to values obtained for the Glacier Peak Band G 

ashes collected from the Trinity Mine site, Washington 

(tables 8 and 9), indicate that the Glacier Peak ash 

present in the Glacier National Park region is the G 

layer. This correlation is based primarily on the FeO and 

K20 values and is also reflected in the K:Fe ratios, which 

are also characteristic of the G ash. 

Mount St. Helens J Ashes 

The ash of Mount St. Helens set J, at the three sites 

in the Glacier National Park region, is believed to be the 

Appendix A. Preparation and Analysis of Ashes by X-Ray Fluorescence 63 
Table 11. Major-element values of glass in the Mount St. 

Helens Jb, Jy, and Js ashes (from Westgate and Evans, 

1978) 

Ash-- Jb1 JY2 JS3 JY4 

Si02 72.4 75.7 77.3 75.8 

Al2o3 14.8 13.8 13.5 13.8 

5Fe0 1.97 1.31 .92 1.31 

MgO • 75 .33 .14 .41 

CaO 2.02 1.36 .97 1.78 

Na2o 5.40 4.88 4.34 4.48 

K2o 2.27 2.41 2.60 2.34 

Ti02 .33 -20 .20 .19 

Total-- 99.94 99.99 99.97 100.11 

K:Fe 1.2 3:1 1.96:1 3.02:1 1.91:1 

1From Westgate and Evans (1978, table 3, sample 

UA 482); values determined by electron microprobe. 

2From Westgate and Evans (1978, table 3, sample 

UA 483); values determined by electron microprobe. 

3From Westgate and Evans (1978, table 3, sample UA 

484); values determined by electron microprobe. 

4carrara, this study, average of the Marias Pass 

and Cabin Gulch samples (table 5); values determined 

by X-ray fluorescence. 

5Total iron as FeO. 

Jy layer. Westgate and Evans (1978) analyzed the glass 

fraction of various set J ashes collected by D.R. Mullineaux. Samples UA 482, UA 483, and UA 484 (Westgate 

and Evans, 1978, table 3) are from layers Jb, Jy, and Js, 

respectively (D.R. Mullineaux, oral commun., 1984). 

Comparison of major-element values of glass in these 

three set J layers (table 11) with values of the ashes from 

the three sites in the Glacier National Park region (table 

5) indicate that the Mount St. Helens ash in the Glacier 

National Park region is Jy. 

Mount St. Helens J ashes from the Marias Pass and 

Cabin Creek exposures were analyzed by X-ray 

fluorescence. Values of the eight major elements 

analyzed for the Marias Pass ash are similar to the Jy ash 

analyses of Westgate and Evans (1978) except for NazO, 

whose value of 4.40 is closer to that of Js (4.34). Values 

determined for the Mount St. Helens J ash at the Cabin 

Creek exposure are also most similar to values given for 

the Jy ash by Westgate and Evans (1978), although the 

CaO and KzO values (1.88 and 2.31) are closer to those 

of the Jb ash. Some of the major-element values 

determined for the Mount St. Helens J ash from Guardipee Lake are similar to values given by Westgate and 

Evans (1978) for the Js ash (SiOz, Ah03, and NazO). 

However, considering that the Js layer is of limited 

extent, the ash from Guardipee Lake is also probably the 

Jy ash. In addition, all three J ashes from the Glacier 

National Park region have K:Fe ratios (Marias Pass 

1.91:1; Cabin Creek 1.91:1; Guardipee Lake 2.14:1) 

similar to that of the Jy (1.96:1) ash analyzed by Westgate 

and Evans (1978) (tables 5 and 11). 

64 Late Quaternary History, Glacier National Park Region, Montana 

t:f U.S. GOVERNMENT PRINTING OFFICE: 1989-773-047/06,026 REGION NO. 8