Surficial Geology 

Of 

Mount Rainier National Park 

Washington 
AVALANCHE DEPOSIT of yellowish-orange clay and rock debris lies on 

top of Tahoma Glacier on the west side of Mount Rainier. The avalanche 

originated in rockfalls at the cliffs at the upper left and slid down to 

the end of the glacier. The cliffs form the headwall of Sunset Amphitheater; Point Success is the peak at the right. The front of the glacier, 

in the foreground, is about 200 feet high. 
{ ,yv-v) 

Surficial Geology of 

Mount Rainier National Park 

Washington 

By 

Dwight R. Crandell 

- , -: GEOLOGICAL SURVEY BULLETIN 1288 
UNITED STATES 

DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary 

GEOLOGICAL SURVEY 

William T. Pecora, Director 

Library of Congress Catalog-Card No. 77-601776 

U.S. GOVERNMENT PRINTING OFFICE • 1969 

For sale by the Superintendent of Documents, U.S. Government 

Printing Office, Washington, D.C. 20402 
contents 

Page 

Surficial deposits record recent geological events. . . . . . . 1 

How surficial deposits are formed. . . . . . . . . . . . . . . . . . . . 2 

Landslides, mudflows, and Mount Rainier's shape. . . . . . 3 

Recent pumice deposits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

Surficial deposits shown on the geologic map. . . . . . . . . . 11 

Old drift. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Hayden Creek Drift. . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

Evans Creek Drift. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

Mudflow at Van Trump Park .................... 18 

MeN eeley Drift. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Rock-glacier deposits. . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Protalus ramparts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

Mudflow at Paradise Park ...................... 23 

Osceola Mudflow ............................... 25 

Interbedded mudflows and alluvium. . . . . . . . . . . . . . 27 

Burroughs Mountain Drift. . . . . . . . . . . . . . . . . . . . . . 28 

Garda Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 

Bomb-bearing deposit in South Puyallup River 

valley ...................................... 32 

Mudflows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 

Taluses ...................................... 35 

Block-field deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 

Landslide deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 

Travertine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 

Alluvial cones. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 

Alluvium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

Avalanche deposits from Little Tahoma Peak ..... 38 

Perspective ....................................... 40 

Further reading ................................... 41 

v 
Surficial geology of 

Mount Rainier National Park 

Washington 

By DwiGHT R. CRANDELL 

Surficial. Deposits Record 

Recent Geological Events 

Much of the ground surface around Mount Rainier volcano is directly underlain by loose geologic deposits that 

veneer the hard rock formations. Examples of these deposits 

are sand and gravel bars along the rivers, ridges of loose 

rock debris beside the glaciers, and sloping aprons of rock 

fragments beneath almost every cliff. Even though they are 

generally thin and inconspicuous when compared with the 

rock formations, these surficial deposits are clues to geologic 

events that have profoundly influenced the shape of the 

park's landscape. Thus, from the character and extent of 

glacial deposits one can judge the age and size of former 

glaciers that carved the cirques and deep canyons of the 

park; from the mudflows which streamed down nearly every 

valley one can infer the age and size of huge landslides of 

the past that helped determine Mount Rainier's present 

shape; and from the pumice deposits some of the volcano's 

recent eruptive activity can be reconstructed. 

1 
The map (plate 1, in pocket) that accompanies this description of the surficial deposits of Mount Rainier National 

Park shows the location of the various geologic formations, 

and the explanation shows the formations arranged in order 

of their relative age, with the oldest at the bottom. The 

text describes the surficial deposits in sequence from older 

to younger. A discussion of the pumice deposits of the park, 

which were not mapped, is followed by a description of the 

formations shown on the geologic map. 

Inspection of the geologic map may lead the viewer to 

question why the surficial deposits are shown in more detail 

in a zone several miles wide around the base of the volcano 

than elsewhere. This is partly because the zone is largely 

near or above timberline, relatively accessible, and the surficial deposits there can be readily recognized, differentiated, 

and mapped. In contrast, access is more difficult in the 

heavily timbered parts of the park, and surficial deposits 

there are generally blanketed by a dense virgin forest and 

are rarely exposed. Geologic investigations in such areas of 

the park were of a reconnaissance nature. 

How Surficial Deposits Are Formed 

Most of the surficial deposits were formed by geologic 

processes that occurred over and over again, and some of 

these processes are still going on today. One kind of geologic 

process is the erosion of rock by glaciers, the transportation 

of the resulting debris downvalley by the ice, and the 

eventual deposition of the debris at and beyond the glacier 

margins. The resulting surficial deposits are referred to 

collectively as glacial drift. They include rock debris deposited by glacier ice as well as sand and gravel formed by 

melt water from glaciers. The term till refers to an unsorted 

mixture of rock debris formed directly by a glacier. Moraines 

are ridges of till that have been deposited along the sides 

of a glacier (lateral moraines) or at its front (end moraines). 

A second geologic process responsible for many surficial deposits in the park is landsliding. Some large slides 

of the past became mixed with water as they moved 

downslope into valleys and formed mudflows. Mudflows are 

mixtures of water and rock debris of many sizes and during 

movement resemble wet concrete. Falls of masses of rock 

from cliffs are also a type of landslide; they range in size 

2 
from small pieces that accumulate at the base of the cliff 

and form a sloping talus of angular rock fragments to falls 

of whole sections of a cliff. Rockfalls that become broken 

into material of many sizes sometimes move rapidly far 

downvalley as avalanches of rock debris. 

A geologic process that is going on today just as it did 

in the past is the erosion, transportation, and deposition of 

rock debris by streams and rivers. The sand and gravel deposits in river bars and terraces that result from this process 

are called alluvium. 

Still another geologic process that has resulted in some 

widespread but thin surficial deposits is volcanism. Within 

the last 10,000 years or so, Mount Rainier has repeatedly 

erupted clouds of pumice that have settled to the ground 

over much of the eastern part of the park. Pumice is a type 

of lava that is so full of gas bubbles that it is light enough 

to float on water. Because of its light weight, pumice can be 

transported great distances by wind. 

Some geologic processes other than those mentioned are 

responsible for a few of the surficial deposits in the park; 

these will be discussed as the specific deposits are described. 

landslides, Mudflows, and 

Mount Rainier's Shape 

Landslides have played an unusually important role at 

Mount Rainier, both in determining the volcano's shape and 

in forming some of the park's surficial deposits. Although 

landslides are common features elsewhere, those at Mount 

Rainier are exceptionally large. The largest one destroyed 

much of the volcano's former summit about 5,700 years ago. 

The top of Mount Rainier today is the crest of a small lava 

cone that perhaps is only about 2,000 years old. The cone 

occupies a broad depression whose broken rim is represented 

by Gibraltar Rock, Point Success, and the ridge between 

Liberty Cap and Russell Cliff (fig. 1). The broad depression 

resulted from great landslides of rock from the former 

summit of the volcano, which had become decomposed to clay 

and weakened by hot volcanic gases and solutions over many 

centuries. These slides of wet clayey rock formed a truly 

spectacular mudflow that streamed downvalley from the volcano at least 70 miles. 

3 
Point Columbia 

Success Crest Liberty Cap 

... _,--..c-~_....,-. 

· _ ,& Summjt Cone h;i''L_ . Gibraltar " · 

///~ J~r :r -, . , ,~~ .. - ~ IJI'~ " /.-7 ~ .... ''"- ft -.:~ Little Tahi>rna ' " 

' " - -~~ ~ ~.,r ./' _;If.( llfl" Peak- "' 

~- ~ :,P. '>t: <!"' / /if Je· '· Ingraha-m /-0 ~ t ~ -... Glacier ?f ~7::::: -.. /" 

EAST SIDE OF MOUNT RAINIER. The summit cone lies within a broad 

depression whose rim is represented by Point Success, Gibraltar Rock, 

and the ridge between Liberty Cap and Russell Cliff. The depression 

was formed when the former top of the volcano, which consisted of 

rock that had been partly altered to clay, slid off to the east and 

descended Emmons Glacier in a tremendous avalanche that produced 

the Osceola Mudflow 5,700 years ago. The distance from Point Success 

to Liberty Cap is 11/4 miles, and the summit crater is about 1,300 feet 

across. (Fig. 1) 

Similar but smaller slides of clayey rock have occurred 

repeatedly on other parts of the volcano during the last 

10,000 years and have also resulted in clayey mudflows. 

These mudfl9ws contain clays that originated from longcontinued steaming and chemical breakdown of volcanic 

rocks. Decomposed and altered rocks of this kind at Sunset 

Amphitheater on the west side of Mount Rainier are part of 

a central plug of lava that cooled and solidified in a former 

throat of the volcano. Although its shape is similar to that 

of depressions carved wholly by glacial erosion, Sunset 

Amphitheater was probably formed in large part by repeated landslides and is analogous in origin to the former 

broad depression at the summit of the volcano. Several clayey 

mudflows in the valleys on the west side of the volcano 

originated in these slides at Sunset Amphitheater, and the 

landslide of yellowish-orange clay and altered rock from the 

same source that lies at the end of Tahoma Glacier (frontispiece) is no more than a few decades old. 

4 
Recent Pumice Deposits 

Thin layers of pumice erupted by Mount Rainier and by 

other volcanoes in the Cascade Range are the most widespread surficial deposits in the park. Although these deposits are not represented on the geologic map because of 

their thinness, the distribution of five layers erupted by 

Mount Rainier is shown in figure 2. 

The ages of most of the pumice deposits are known 

within a few hundred years because wood buried with them 

can be dated by determining the proportion of radioactive 

carbon the wood contains. Other surficial deposits that are 

interbedded with pumice layers of known age can be dated 

approximately. Elsewhere, the age of a surficial deposit, 

such as a moraine, can be limited by the presence or absence 

of a certain pumice layer on top of it (see sketches at the 

bottom of the map explanation [plate 1]) -if the pumice 

is present, the deposit must be older; if the pumice layer is 

not on top, the deposit is younger than the pumice. This 

method of dating surficial deposits, of course, can be used 

only in areas covered by the pumice layer in question. 

The most distinctive and widespread pumice deposits at 

Mount Rainier-and those most useful for purposes of dating other surficial deposits-were erupted by two other 

volcanoes and brought to the park by southwesterly winds. 

Layer 0 (table 1) is about 2 inches thick and blankets the 

entire park and adjoining region. It can be readily recognized by a distinctive yellowish-orange color (fig. 3) and 

a flourlike texture. When it is studied under the microscope, 

its characteristics are found to correspond precisely to those 

of the pumice that was erupted by Mount Mazama volcano 

at the site of Crater Lake, Oreg., about 6,600 years ago. 

The extreme fineness of layer 0 can be attributed to the 

distance of 250 miles that separates Mount Rainier from 

Crater Lake. 

5 
M 

s 

p 

y 

w 

Layer X 

T 

0 

(Between llO and 150 years old) 

0 

Layer C 

(Between 2,150 and 2,500 years old) 

5 10 MILES 

DISTRIBUTION OF PUMICE DEPOSITS in Mount Rainier National Park. 

6 

Only the pumice layers erupted by Mount Rainier within the last 10,000 

years are shown. The extent of layer X is based on the recognition of 

the pumice at certain localities, regardless of its thickness; other layers 

are shown wherever they are at least 1 inch thick. Letters represent the 

following localities: C, Cougar Rock campground; I, lpsut Creek campground; L, Longmire; M, Mowich Lake; 0, Ohanapecosh campground; 

P, Paradise Park; S, summit crater; T, Tipsoo Lake; W, White River 

campground; andY, Yakima Park. Based on studies by D. R. Mullineaux. 

(Fig. 2) 
M M 

Layer D Layer L 

(Between 5,800 and 6,600 years old) (Between 5,800 and 6,600 years old) 

N 

Layer R 

(More than 8,750 years old) 

7 
RECENT PUMICE DEPOSITS on the floor of a cirque a quarter of a mile 

southeast of Sluiskin Falls. The yellow bed at the bottom is layer 0, 

which was erupted at the site of Crater Lake, Ore., about 6,600 years 

ago. The yellowish-brown pumice a few inches above layer 0 is layer D, 

which was erupted by Mount Rainier more than 5,800 years ago, and the 

light-yellowish-brown pumice bed at the top of the outcrop is layer Y, 

which originated at Mount St. Helens volcano between 3,300 and 4,000 

years ago. (Fig. 3) 

8 
Pumice layers Y and W originated at Mount St. Helens 

volcano, which is about 50 miles southwest of Mount Rainier. 

Both layers cover lobate areas that extend far northeastward from their source. The centerline of the lobe of layer Y 

lies near the west edge of the park, where the pumice is 

commonly as much as 18 inches thick. The thickness of 

layer Y decreases to the east, and the layer is thin or absent 

in the southeast corner of the park. Layer Y is light yellowish brown (fig. 3), which helps to distinguish it from layer 

W, which is white. The center of the lobe of layer W lies 

near the east boundary of the park, where the pumice is 

about 2 inches thick. 

The thickest and most widespread pumice from Mount 

Rainier is layer C, which is found throughout the eastern 

and northeastern parts of the park. Layer X, which represents Mount Rainier's most recent known eruption, was 

formed about the middle of the last century. It is found 

only in a small area close to the volcano. 

0 

Seattle 

WASHINGTON 

x Mount Rainier 

x Mount St Helens 

0 R E G 0 N 

0 Crater Lake 

100 200 MILES 

9 
TABLE !.-Characteristics, sources, and ages of pumice layers in 

Mount Rainier National Park 

[Based on studies by D. R. Mullineaux] 

Common range 

of thickness Range in in park (inches) diameter -------- of pumice 

Pumice 

layer West East fragments side side (inches) 

X ........... Absent 

W .......... 0-1 1-3 Medium 

sand. 

C ........... Absent 1-8 1,4-8 

Y. .......... 5-20 1-5 Coarse 

~and. 

D ........... Absent 0-6 1,4-6 

L ........... Absent 0-8 1,4-2 

0....... ... 1-3 1-3 Silt and 

very 

fine 

sand. 

R. .......... Absent 0-5 Vs-1 

Color 

Light 

olive 

gray. 

Source 

Mount 

Rainier. 

White ............ Mount St. 

Helens. 

Brown ........... Mount 

Rainier. 

Yellow ........... Mount St. 

Helens. 

Brown ........... Mount 

Rainier. 

Brown ........... Mount 

Rainier. 

Yellowish Mount 

orange. Mazama. 

Reddish Mount 

brown. Rainier. 

Approximate 

age in 1968, or limiting 

dates (years ago) 

100-150 

2450 

2,150-2,500 

3,300-4,000 

5,800-6,600 

5,800-6,600 

About 6,600 

8,750-11,000? 

Pfhe X pumice occurs as scattered fragments and does not form a continuous layer. 

2Ages of more than 150 and less than 6,000 years cited in this report are based on radiocarbon determinations which have been corrected by the use of a C14 half life of 5,730 years and for variations in atmospheric C14 (H. E. Suess, written communi~ 

cation to Meyer Rubin, 1968). 

10 
Surficial Deposits Shown on the 

Geologic Map 

OLD DRIFT 

The age and extent of the glaciers responsible for the 

old drift are not known, but glaciers evidently covered this 

part of the Cascade Range very early in the development of 

Mount Rainier, perhaps even before the volcano first appeared. The old drift consists mostly of glacial deposits overlying bedrock formations that are older than Mount Rainier 

and underlying lava flows from the volcano. The lava flows 

are of a rock known as andesite, 1 and they form many of the 

ridges that radiate from the base of the volcano, such as 

Mazama and Rampart Ridges and Burroughs Mountain. 

Each old drift deposit shown on the geologic map contains 

compact till, but some also include mudflows and rubbles 

of volcanic origin. 

Old drift exposed in a roadcut upslope from Narada Falls 

lies on a surface of glacially smoothed and scratched bedrock 

(fig. 4, locality 1). The till at this locality is overlain by 

a pumice-bearing deposit of sand and fine gravel that is 

interbedded with mudflows. This deposit, together with the 

till, is about 100 feet thick and is overlain by a lava flow 

from Mount Rainier that forms Mazama Ridge. 

Old drift at the west end of Burroughs Mountain (fig. 4, 

locality 2) consists of about 800 feet of compact bouldery 

gray till and beds of sand and fine gravel. It is overlain, 

consecutively, by a deposit of loose gray and red volcanic 

rubble about 300 feet thick and by a lava flow from Mount 

Rainier. In Glacier Basin (fig. 4, locality 3) old till lies on 

top of compact mudflows and hard bedrock (fig. 5). The 

till is very compact and bouldery (fig. 6) and is several 

hundred feet thick. Banked against it is an old lava flow 

from Mount Rainier, and both the till and the flow are overlain, in turn, by a red volcanic rubble and a younger lava 

flow from Mount Rainier. The red rubble probably is part 

of the deposit that overlies the old drift at the west end 

of Burroughs Mountain. The old mudflows, the till, and the 

red rubble have been intruded by a wall-like andesite dike 

that forms a prominent ridge along the north side of Glacier 

Basin. 

lRock formations in Mount Rainier National Park are described in some of the reports listed at the end of the text. 

11 
12 

121·50· _ __ _ _____ _ __ _ __ _ T __ 

o;,~' 

.. Tyee Peak 

Point 

0 2 4 MILES 

~"' 

Sluiskin 

Falls 

MAP OF MOUNT RAINIER NATIONAL PARK, showing 
121°40' 

; 

The 

Palisades 

@) ~ Hidden Lake .;; ( o.."' "' 

I ~ t)~ 

-, \ 

I 

I 

) Panhandle 

. _, Gap 

Frytngpan 

Glaci~ 

' ' ' ' 

'i!i'"" Cowlitz ;. Glacier 

,_1 

' , ___ 

\ 

\ 

\ 

I 

I 

I 

' I 

I 

I 

I 

I 

I 

J r/ 

~~f'P-'" _, 

Box Canyon 

__l_ __ _ 

'$ ~ J .... ~'l.l """" ~ J c,'> <> 

localities mentioned in text (numbered). (Fig. 4) 

121°30' 

147"00' 

) . L----. 

/ 

\ 

13 
OLD DRIFT on the north side of Glacier Basin. The geologic formations, 

in order of decreasing geologic age, are: 1, Bedrock much older than 

Mount Rainier; 2, mudflows which came from an old Mount Rainier 

volcano; 3, old drift, which consists mostly of very bouldery till; 4, an 

old andesite lava flow from Mount Rainier; 5, a red volcanic rubble 

from Mount Rainier; 6, a younger andesite lava flow from Mount Rainier; 

and 7, an andesite dike. The age relation of the dike to the younger 

lava flow is not known. The yellow deposit in the right foreground is 

a Garda moraine of Inter Glacier; it is about 200 feet high and consists 

almost wholly of Osceola Mudflow, which was eroded from the floor 

of the basin and redeposited by the glacier. The de_posits in the left 

foreground and middle distance are alluvium younger than the moraine. 

(Fig. 5) 

14 
BOULDERY TILL exposed in a gully on the north side of Glacier Basin 

is part of the old drift. The boulders and smaller stones of various 

colors in the till are derived from the bedrock that underlies the volcano. The stones are contained in a very hard and compact (Tlatrix of 

brownish-gray silt and sand. (Fig. 6) 

15 
HAYDEN CREEK DRIFT 

The Hayden Creek Drift is here named for a stony till 

that is intermittently exposed in cuts along the Mowich 

Lake Road (fig. 7) from a point near the mouth of Hayden 

Creek (fig. 4, locality 4) westward beyond the park boundary. 

The distribution of Hayden Creek Drift outside the park, 

as well as the drift's presence on some high ridges within 

the park, indicates deposition during a glaciation of icecap 

HAYDEN CREEK TILL along the Mowich Lake Road. The thick brown 

oxidized zone at the top of the till is typical of the Hayden Creek Drift. 

Bedrock at the right is much older than Mount Rainier volcano. (Fig. 7) 

16 
proportions, when glaciers west of Mount Rainier locally 

reached the western front of the Cascade Range. The entire 

park was covered by ice at that time. The Hayden Creek 

Drift probably was formed during a glacial episode that 

occurred between 35,000 and 50,000 years ago. 

Extensive weathering in the Hayden Creek Drift shows 

it to be older than the Evans Creek Drift (described next), 

which was formed during the most recent major glaciation. 

Although initially brownish gray, the Hayden Creek till has 

been weathered to dark yellowish brown to a depth of 

6-8 feet below the ground surface. Stones in the upper few 

feet of the till have been partly decomposed; these stones 

have weathered rinds or shells 1-3 mm thick (fig. 8). Hayden Creek Drift was found at the summits of Iron and 

Copper Mountains and at the top of a ridge that extends 

eastward from Tyee Peak. A brown bouldery till at least 

100 feet thick on a ridge northwest of The Palisades probably is also Hayden Creek Drift. 

Hayden Creek Drift underlies a thick deposit of Mount 

Rainier pumice on the north valley wall of the White River 

about 2 miles southeast of Yakima Park (fig. 4, locality 5). 

YELLOWISH-ORANGE RINDS on these stones of dark-gray volcanic rocks 

are the result of weathering over a long period of time. Weathered rinds 

like these, but about half as thick, are present on stones near the surface of the Hayden Creek Drift. (Fig. 8) 

17 
The pumice can be seen in a roadcut a short distance west 

of Yakima Creek where it is overlain by an old talus deposit 

and Evans Creek till. Wood in the pumice is more than 

38,000 years old, as determined by radiocarbon dating. More 

than 50 feet of Hayden Creek till is exposed beneath the 

pumice in a steep bank downslope from the highway. 

EVANS CREEK DRIFT 

Between about 25,000 and 15,000 years ago Mount 

Rainier and the adjacent mountains were again buried by 

large glaciers ; these glaciers formed the Evans Creek Drift, 

which consists of till as well as stream-deposited sand and 

gravel. These glaciers developed during an early part of the 

last major glaciation of the Pleistocene (Ice Age) ; at that 

time lateral moraines were deposited along the margins of 

glacier§! high on the sides of some valleys and even along 

the crests of some divides, as at Ricksecker Point (fig. 4, 

locality 6) and Rampart Ridge. Till in the moraines is 

generally very coarse, loose or slightly compacted, and as 

much as 50 feet thick. The till is mostly gray or purplish 

gray, but it has a yellowish-brown oxidized zone in the 

upper 2 or 3 feet that has been formed by weathering processes since the till was deposited. Stones in this oxidized 

zone rarely have weathered rinds. Evans Creek till is especially well exposed in roadcuts along the north side of the 

White River valley east of Yakima Park (fig. 4, locality 7). 

At the time the Evans Creek Drift was deposited, icefields and glaciers mantled the slopes of the volcano above 

an altitude of about 5,000 feet. Each major valley was occupied by a glacier 1,000-1,500 feet thick which extended from 

5-35 miles beyond the park boundaries (fig. 9). 

MUDFLOW AT VAN TRUMP PARK 

Between 11,000 and 15,000 years ago a large landslide of 

rock from the summit of Mount Rainier swept down the 

south flank of the volcano and spread as a mudflow over 

Van Trump Park. There it deposited a yellowish-orange 

unsorted mixture of clay, sand, and rock debris which is as 

much as 6 feet thick on the ridgetop at Van Trump Park 

(fig. 4, locality 8) and is 20 feet thick in the valley of Van 

18 
Trump Creek northeast of Comet Falls. The mudflow 

is widespread in areas beyond an end moraine of Van Trump 

Glacier that probably was formed about 11,000 years ago, 

but it does not overlie the moraine itself and thus is older. 

0 5 10 15 MILES 

EXTENT OF GLACIERS at Mount Rainier and in the adjacent mountains 

during the most recent major glaciation is shown by stipple pattern. 

The heavy black line at the upper left marks the boundary between the 

Puget Sound lowland and the Cascade Range. This line also represents 

the southeast edge of a massive glacier in the lowland which originated 

in southwestern Canada and reached this part of the lowland about 

14,000 years ago. The arrows show the direction of glacier movement. 

Black areas are covered by glaciers today. (Fig. 9) 

19 
McNEELEY DRIFT 

McNeeley Drift, named in this report, consists of till in 

moraines formed during the latest part of the most recent 

major glaciation, probably about 11,000 years ago. The 

name of the drift is taken from McNeeley Peak, which is 

north of Yakima Park. A typical moraine lies within a 

north-facing cirque half a mile south of the peak (fig. 4, 

locality 9). Weathering extends to a depth of 15 inches or 

less in the till, and stones in the till that have been decomposed by weathering processes are rare. McNeeley moraines 

are found adjacent to some large active valley glaciers on 

Mount Rainier and in some cirques at altitudes between 

5,500 and 6,700 feet. Areas in front of cirque moraines generally consist of either glacier-scoured bedrock or featureless Evans Creek Drift. McNeeley moraines are sharp 

crested and little modified by erosion. They range from 

single low narrow ridges of till to accumulations as much 

as 1,000 feet wide that are distinguished by multiple ridges. 

One of the largest MeN eeley moraines dams Mystic Lake on 

the north side of the park, and the Wonderland Trail 

crosses another at the south end of Berkeley Park (fig. 4, 

locality 10). A small McNeeley cirque moraine can be seen 

along the highway between Tipsoo Lake and Chinook Pass 

(fig. 4, locality 11). 

ROCK-GLACIER DEPOSITS 

Rock-glacier deposits are thick flat-lying or gently sloping accumulations of coarse angular rock debris that have a 

lobate form and a surface marked by pits and by ridges and 

furrows. Angular blocks several tens of feet in maximum 

dimension are generally strewn over the surface. A depression separates the upslope margin of most rock-glacier deposits from nearby talus (fig. 10). The fronts of rockglacier deposits are abrupt, steep, and from 25 to 100 feet 

high. Rock-glacier deposits owe their shape and size to 

flowage of accumulations of rock debris that contain ice. 

20 
Active rock glaciers differ from true glaciers chiefly in 

having a very high proportion of rock debris to ice. All of 

those in the park were formed during a late part of the 

most recent major glaciation and are inactive now. 

Most rock-glacier deposits occupy north- or east-facing 

cirques within an altitude range of 5,500 to 6,600 feet. Many 

are closely associated with McNeeley Drift, and in some 

cirques they merge with McNeeley moraines. All are about 

the same age as the MeN eeley Drift. 

A trail just east of Mount Fremont crosses a representative rock-glacier deposit (fig. 4, locality 12), and one 

of the largest in the park occupies an east-facin~ cirque 

between the Palisades and Hidden Lake (fig. 10; fig. 4, 

locality 13) . 

ROCK-GLACIER DEPOSIT in the foreground is an accumulation of lightcolored rock debris derived from the cliffs of The Palisades in the 

northeastern section of the park. The deposit covers an area of about 

100 acres and is 100-300 feet thick. The steeply sloping deposit of rock 

debris just below the cliffs is a talus. (Fig. 10) 

21 
PROT ALUS RAMPARTS 

Protalus ramparts are ridges of loose angular rock fragments that lie a few tens of feet beyond the toes of taluses 

(fig. 11). Blocks larger than 3 feet in diameter are rare, and 

most ramparts seem to consist chiefly of fragments 6 inches 

to 2 feet in diameter. The ridges are generally 10-30 feet 

PROTALUS RAMPART on the north side of Sunrise Ridge is separated 

from the partly vegetated talus on the left by a depression 5-6 feet 

deep and 20--30 feet wide. A thick wedge-shaped snowbank blanketed 

the talus and the depression when the arcuate rampart was formed. 

(Fig. 11) 

22 
wide and 5-15 feet high on the side next to the talus. In 

ground plan they range from straight to sinuous ; many are 

arcuate and are convex in a direction away from the talus. 

Their distribution, shape, and nearness to taluses indicate 

that they were formed at some time when thick persistent 

snowbanks buried the toes of some cliffs and parts of 

taluses. Rock debris falling from a cliff and sliding down 

the snowbank accumulated at the toe of the snowbank as 

a ridge or rampart; a subsequent change in climatic conditions prevented such a large snowbank from forming, 

so that the falling rock debris then became part of the main 

talus and building of the rampart ceased. 

Most protalus ramparts are the same age as the McNeeley Drift. The close association of protalus ramparts 

with McNeeley moraines in some cirques suggests that the 

glacier responsible for the moraine dwindled until only a 

perennial snowbank remained, at the toe of which the 

rampart was formed. 

The trail to White River Park crosses a typical and 

readily accessible protalus rampart at the base of Sunrise 

Ridge (fig. 4, locality 14), and there are several other ramparts associated with McNeeley moraines along the north 

side of Sunrise Ridge a little to the west. 

MUDFLOW AT PARADISE PARK 

A very large landslide of clayey altered rock avalanched 

down the south side of Mount Rainier between 5,800 and 

6,600 years ago. Upon reaching the lower slopes of the volcano, the avalanche became a mudflow that spread over the 

Paradise area. Here the mudflow deposited a plastic yellowish-orange mixture of unsorted clay, sand, and rock fragments a few inches to more than 15 feet thick. Blocks in the 

deposit are as large as 6 feet in diameter. The presence 

of thin remnants on top of Mazama Ridge indicates that the 

mudflow must have been 600 feet deep in the adjacent 

23 
Paradise River valley. Farther downvalley, at Ricksecker 

Point, the mudflow was temporarily at least 800 feet deep. 

The mudflow lies on top of pumice layer 0 (fig. 12). 

PUMICE LAYER 0 from Mount Mazama (Crater Lake) forms a thin yellow 

band at the base of the yellowish-orange mudflow that blankets Paradise Park. This outcrop is at Ricksecker Point, and its height above 

the floor of the adjacent Paradise River valley indicates that the mudflow was temporarily at least 800 feet deep here. (Fig. 12) 

24 
OSCEOLA MUDFLOW 

The Osceola Mudflow is the largest mudflow that has 

originated at Mount Rainier and is one of the largest volcanic mudflows in the world. It originally covered an area 

of more than 100 square miles in the Cascade Range and 

the Puget Sound lowland, and its volume probably was 

more than half a cubic mile. Radiocarbon determinations of 

logs in the mudflow indicate an age of about 5,700 years. 

The mudflow is an unsorted mixture of plastic clay, sand, 

and rock debris that includes boulders as large as 15 feet 

in diameter (fig. 13). It is purplish gray where fresh and 

weathers to yellowish orange. Remnants of the mudflow 

high on the sides of the White River and West Fork valleys 

show that both valleys were temporarily filled with streams 

of mud more than 500 feet deep. After the crest of the mudflow passed a given point, most of the material drained 

away downvalley, leaving veneers a few feet to a few tens 

of feet thick on the valley walls. Much of the flowing mud 

finally came to rest in the Puget Sound lowland, 40-70 

miles away. 

The presence of the Osceola Mudflow on ridgetops above 

Glacier Basin and at the top of Steamboat Prow indicates 

that it originated even higher on the volcano. This distribution and a large clay content suggest that the mudflow was 

caused by huge slides of altered rock material from a former 

summit of the volcano. These slides probably were triggered 

by volcanic explosions, and they produced the large craterlike depression at the top of the volcano that contains the 

present summit lava cone. 

Roadcuts expose the mudflow at the White River Ranger 

Station (fig. 4, locality 16), and one of the best outcrops is 

in the valley of Inter Fork about 1.5 miles west of White 

River campground (fig. 13; fig. 4, locality 17). 

25 
OSCEOLA MUDFLOW is exposed on the south bank of Inter Fork. Slope 

wash from the bouldery yellow mudflow has nearly hidden the underlying gray Evans Creek till, which can be seen at the lower left. {Fig. 13) 

26 
INTERBEDDED MUDFLOWS 

AND ALLUVIUM 

Mudflows are interbedded with alluvium in terraces or 

benches along the sides of nearly every major valley in the 

park. Individual mudflows are from about 1 to 15 feet thick 

and typically are unsorted mixtures of sand, clay, and stones 

of many sizes. Individual mudflows lack bedding, although 

a succession of several mudflows, or an alternation of mudflows and alluvium, may give an outcrop a layered appearance. Most mudflows are purplish gray where unweathered, 

and yellowish orange or yellowish brown where weathered. 

Many of these mudflows resulted from floods caused by 

eruptions. The volcano has repeatedly erupted hot rock 

debris and lava flows which melted snow and ice. The resulting floods that cascaded down the flanks of the cone 

became mudflows by scouring loose alluvium and moraines 

on the valley floors. Other mudflows, however, probably 

originated during periods of unusually heavy rainfall, when 

parts of recent moraines became saturated and slid and 

flowed downvalley. 

Alluvium that is interlayered with the mudflows was 

formed mainly by streams and rivers like those of today. 

It generally consists of sand and gravel in which some 

boulders are as large as 6 feet in maximum diameter, and 

it ranges in thickness from a few inches to at least 50 feet. 

Alluvium can be distinguished from mudflows mainly by 

the presence of bedding and by lenses and layers of wellsorted material. 

Pumice layers that locally lie between deposits of alluvium and mudflows are commonly interbedded with rooted 

stumps, logs, and other organic matter formed on forest 

floors that have since been buried. As many as four successive buried forest layers can be seen in the steep banks of 

Kautz Creek near the Wonderland Trail (fig. 4, locality 18), 

and the north bank of Tahoma Creek shows a similar sequence about a mile upstream from Tahoma Creek campground (fig. 4, locality 19). Some pumice layers, whose age 

is known, permit age bracketing of interbedded deposits, 

27 
and the presence or absence of other layers on top of the 

deposits permits subdivision of the mudflows and alluvium 

into map units of four ages. (See explanation for the geologic 

map.) Unit A includes deposits older than pumice layer 0; 

unit B contains the deposits younger than layer 0 and older 

than layer Y; unit C represents the deposits younger than 

layer Y but older than layer W; and unit D includes the 

deposits younger than layer W. The surface deposit represented on the map commonly is underlain by mudflows and 

alluvium of older units. 

BURROUGHS MOUNTAIN DRIFT 

The Burroughs Mountain Drift was formed during a 

period of glacier expansion that occurred between about 

2,500 and 3,000 years ago. Although the glaciers of the park 

became only a little larger than they are today, this was a 

significant change, for during the time since the end of the 

last major glaciation they had been smaller. Burroughs 

Mountain moraines can be recognized by the fact that they 

are older than pumice layer C (fig. 14), and younger than 

layer Y. 

Till in the Burroughs Mountain moraines is gray, generally loose, and not appreciably weathered. The moraines 

below timberline are densely forested with trees several 

generations younger than the first forest that became established on the moraines after their formation. Most of the 

Burroughs Mountain moraines are only a few yards beyond 

moraines formed within the last 700 or 800 years, although 

those of Winthrop Glacier represent a glacier 300 feet 

thicker than at any subsequent time. The largest Burroughs 

Mountain moraines occur in the areas adjacent to Winthrop 

Glacier and between Winthrop and Carbon Glaciers, and 

smaller ones have been identified at a few other places 

in the park. The Wonderland Trail crosses a Burroughs 

Mountain moraine of Winthrop Glacier on the west slope of 

Burroughs Mountain (fig. 4, locality 20). 

28 
PUMICE LAYER C forms a thin brown veneer on the drift in the foreground and on the Burroughs Mountain moraine in the center of the 

photograph. This pumice was erupted by Mount Rainier between 2,150 

and 2,500 years .ago. The Garda moraine of Fryingpan Glacier at the left 

has no pumice on it, and thus is younger. The large boulder in the 

middle foreground is about 6 feet long. This locality is at an altitude 

of 7,500 feet about a mile southwest of Panhandle Gap. (Fig. 14) 

29 
GARDA DRIFT 

Moraines formed since the eruption of pumice layer C 

are included in the Garda Drift (fig. 14) ; contemporaneous 

glacial melt-water deposits, however, are represented' on the 

geologic map only as alluvium. The till consists of a gray 

unsorted mixture of pebbles, cobbles, and boulders in a silt 

and sand matrix and is unweathered. The presence or absence of pumice layer W divides Garda moraines into groups 

that are older or younger, respectively, than about 450 years. 

Trees growing on some Garda moraines are at least 750 

years old. Moraines younger than layer W include stable, 

forested deposits decades or a few centuries old as well as 

subsiding masses of rock debris that still bury blocks of 

slowly melting ice. Younger Garda moraines are especially 

unstable on steep valley sides in areas from which glaciers 

have receded within the last half century. Boulders in the 

moraines become dislodged from time to time and roll and 

bound down to the valley floor at high speed. During periods 

of heavy rainfall or rapid snowmelt, saturated masses of 

drift sometimes move from the moraines onto the valley 

floors as mudflows. 

Moraines of Garda Drift range in size from ridges only 

a few feet high and a few tens of feet wide to massive complex end moraines such as the one that was formed in the 

White River valley by Emmons Glacier between the 17th 

century and about 1910 (fig. 15; fig. 4, locality 21). Dates 

shown on individual moraines on the geologic map are based 

on the earliest growth ring of the oldest known living tree 

on the moraine ; the moraine is older than the tree by an 

unknown number of years, perhaps as much as several 

decades. One of the most readily accessible Garda moraines 

in the park lies at the west end of the bridge across the 

Nisqually River (fig. 4, locality 22), 3.5 miles northeast of 

Longmire. This moraine is conspicuous because trees on it 

are much younger and smaller than those in the adjacent 

older forest. When this moraine was formed in 1840, Nisqually Glacier covered the site of the present highway and 

reached to a point about 750 feet downvalley from the bridge. 

30 
END MORAINE of Garda Drift formed by Emmons Glacier is a hummocky 

accumulation of bare rock debris in the center of the White River 

valley. When the ice front stood at the moraine, the upper surface of 

the glacier coincided with the conspicuous sloping trimline in the 

trees on the opposite valley wall. The exposure in the center foreground is that shown in figure 13. (Fig. 15) 

31 
BOMB-BEARING DEPOSIT IN 

SOUTH PUYALLUP RIVER VALLEY 

A deposit of unsorted and unstratified rock debris that 

contains many light-olive-gray breadcrust bombs is exposed 

along the highway in the South Puyallup River valley (fig. 

4, locality 23). Breadcrust bombs are formed when blobs of 

lava are thrown from a volcano; as the bomb cools, a solid 

skin forms, which then ruptures as gas pressure in the lava 

causes it to expand slightly. The bomb's exterior is a network of fissures and segments that resemble those on a loaf 

of hard-crusted bread; inside, most bombs are very porous 

because of the gas bubbles that formed in the lava (fig. 16). 

Many bombs have one flat side, which was formed when 

still-plastic blobs of hot lava struck the ground after flying 

through the air. Bombs in the South Puyallup River valley 

are 6 inches to 4 feet in diameter. 

BREADCRUST BOMB on the left shows a typical cracked and segmented 

surface formed during cooling; the other bomb is broken open to show 

the black bubbly interior. The bombs are about 10 inches in diameter. 

(Fig. 16) 

32 
The bombs are contained in a deposit of loose purplishgray sand. Although the bombs are the most conspicuous 

part of the deposit, fragments of dense glassy dark-gray 

andesite as much as several inches in diameter are also 

abundant. The deposit is at least 200 feet thick in places, 

and it overlies very coarse mudflows and alluvium in which 

no bombs were seen. On top of the deposit are two thin 

clayey mudflows which probably were formed about 1,000 

and 600 years ago, respectively. A carbonized log 4 feet 

long that was found just above the base of the bomb-bearing 

deposit had a radiocarbon age of about 2,500 years. Streams 

have eroded the bomb-bearing deposit to form ridges that 

greatly resemble lateral moraines near the West Side Road. 

The deposit originated when hot rock rubble, ash, and 

bombs avalanched from the top of the volcano during an 

eruption. Even though the rock debris flowed down the 

South Puyallup River valley in a fluid manner, the magnetic 

properties of rock fragments indicate temperatures of hundreds of degrees above the boiling point of water when 

movement stopped. Thus, the rock debris must have flowed 

in a dry condition, and it probably was "lubricated" by 

steam, hot air, and other gases. 

MUDFLOWS 

As many as five mudflows, each of which is from a few 

feet to several tens of feet thick, lie on low terraces, valley 

sides, and some ridgetops in and adjacent to the valleys of 

Tahoma Creek and the North and South Puyallup Rivers 

(fig. 17). All have been formed within the last 4,000 years, 

and one is only about 440 years old. The mudflows are unsorted mixtures of boulders of many sizes in a yellowishorange matrix of sand, silt, and clay. One, exposed in roadcuts at Round Pass (fig. 4, locality 24), can be traced along 

a trail to Lake George to a height of about 350 feet vertically 

higher than the pass, which indicates that the Tahoma 

Creek valley temporarily must have had at least 1,000 feet 

of mud flowing in it. Remnants of the deposit on the sides 

of the South Puyallup River valley indicate a comparable 

thickness or depth there. At Indian Henry's Hunting 

Ground, on the divide between the Tahoma Creek and Kautz 

Creek valleys, the southwest margin of the mudflow forms 

an abrupt front about 17 feet high where it is crossed by 

33 
the Wonderland Trail (fig. 4, locality 25). The boundary 

there between the mudflow and the adjacent surface is conspicuous because pumice layer Y abruptly disappears as one 

passes from the older surface onto the mudflow. 

The approximate maximum height or the deepest mudflows in the valleys west of the volcano, shown by a heavy 

dashed line on the geologic map, is reconstructed from the 

highest known remnants of the deposits ; this line probably 

represents the height attained by a single mudflow that 

occurred about 2,800 years ago. Another mudflow temporarily reached almost as high on the valley sides about 600 

years ago. It had enough volume to move 25 miles downvalley 

and to extend an additional 15 miles into the Puget Sound 

lowland. All the mudflows originated in avalanches of clay 

and altered rock from the west side of the volcano at Sunset 

Amphitheater (frontispiece). 

MUDFLOW from Mount Rainier is the dark-brown deposit above the head 

of the pick; it lies on top of yellow pumice (layer Y) from Mount St. 

Helens which is between 3,250 and 4,000 years old. This locality is on 

the north side of the North Puyallup River valley a mile west of the 

park boundary. Its height of about 240 feet above the valley floor indicates that the mudflow was temporarily at least 240 feet deep here. 

The pumice is unusually thick. (Fig. 17) 

34 
TALUSES 

Taluses are loose accumulations of coarse rock fragments 

that lie beneath cliffs (fig. 10). Their surfaces slope at angles 

ranging from about 30° to 35°. Rock fragments in a talus 

are generally fresh and angular and range in size from 

pieces a few inches across to blocks that are several tens of 

feet in maximum diameter. Some taluses have bulbous toes 

that suggest movement by flowage, perhaps caused by ice 

within the rock debris. Taluses that are wholly forested are 

not shown on the geologic map. 

BLOCK-FIELD DEPOSITS 

Block-field deposits consist of angular rock fragments 

that lie on both sloping and horizontal surfaces. The rock 

fragments are pried from the underlying solid rock formations by the repeated freezing and expansion of moisture in 

cracks. Some block fields resemble taluses in that they have 

slopes of as much as 35°, but they differ in that they are 

not littered with very lanie blocks and do not have a cliff at 

their head. Downslope-trending bands of vegetated and 

unvegetated rock debris a few feet to a few tens of feet 

wide give some sloping block fields a distinctly striped appearance. Other fields end downslope in elongate lobes of 

rock debris a few feet to several tens of feet wide and 1-4 

feet thick. The shape of these lobes suggests that they 

originated from flowage of the rock debris, perhaps caused 

by saturation from rain or melting snow. Block fields are not 

common where rock debris produced by frost action consists 

mostly of fragments smaller than 3 inches in diameter. 

Some block fields probably date from the last major glaciation, and others may be of more recent age. 

Especially well developed and easily accessible block fields 

are crossed by the trail to the Mount Fremont fire lookout 

(fig. 4, locality 26). 

35 
LANDSLIDE DEPOSITS 

Landslides consist of chaotic mixtures of loose rock 

debris, or several very large blocks of rock, that have broken 

away from the bedrock and have moved downslope. They 

include those which seem to be inactive and those in which 

there was evidence of movement during the period of field 

study (1960-67). An example of an inactive slide is one that 

originated in west-dipping bedrock just north of Ohanapecosh campground (fig. 4, locality 27). Cuts in this landslide 

along State Highway 143 expose a jumbled mixture more 

than 100 feet thick of rock fragments of many sizes in which 

some layers or zones have a plastic purplish-gray clay 

matrix. The surface of the slide deposit is hummocky, includes closed depressions, and is strewn with angular blocks 

as much as 15 feet across. Another inactive slide is crossed 

by the Mather Memorial Parkway (U.S. Highway 410) half 

a mile north of Cayuse Pass (fig. 4, locality 28). The slide 

originated in west-sloping bedrock and descended into the 

valley of Klickitat Creek, where it now impounds Ghost 

Lake. Highway cuts through the slide deposit show a loose 

mixture of rock fragments of many sizes, some as large as 

20 feet across. 

An active landslide is slowly moving down the west 

slope of Backbone Ridge (fig. 4, locality 29). It consists of a 

jumbled mass of sandstone and claystone, probably only 

about 25 feet thick. From 1962 to 1966 the slide moved at 

an average rate of about 6 inches per year. 

An active slide on the west side of the Nisqually River 

valley west of Paradise Park involves lava flows from the 

volcano as well as the underlying bedrock. The slide block 

seems to be dropping eastward toward the center of the 

valley and rotating, so that the north side of the block is 

moving more than the south side. The slide is broken into 

several smaller blocks by cracks that parallel the 1,000-footlong main crack at the slide's head. Photographs taken in 

1912 show the fresh scarp at the head of the slide, so it 

evidently began to move at some earlier time. The slide can 

be seen from various viewpoints along the trail from the 

Paradise visitor center to Panorama Point. 

36 
TRAVERTINE 

Travertine is a calcium carbonate mineral that has been 

deposited by the water of warm or hot springs. Deposits of 

yellowish-orange to white travertine of unknown thickness 

that underlie parts of a meadow at Longmire and a small area 

near Ohanapecosh campground have been formed by warm 

spring water that still issues from the ground at both 

localities. Pumice layer W is interbedded with the travertine 

near Ohanapecosh campground. 

ALLUVIAL CONES 

Alluvial cones are steeply sloping, poorly sorted stream 

deposits of loose rock debris which lie beneath cliffs and are 

wedge shaped in ground plan (fig. 18). Their surfaces are 

ALLUVIAL CONE at the east base of Mount Wow. The largest blocks in 

the deposit are about 20 feet in diameter. (Fig. 18) 

37 
scarred by one or more gullies, the sides of which are paralleled by low bouldery ridges 5-25 feet wide and 3-10 feet 

high. Some cones seem to consist chiefly of rock fragments 

larger than 6 inches in diameter, but others are rich in 

debris of sand and pebble sizes. Very large blocks lie on the 

surface of some cones. Alluvial cones are distinguished from 

taluses by less steep slopes, by a markedly decreasing slope 

toward the toe, and by stream-gullied surfaces. Most cones 

head at the mouths of steep rock-walled gullies and have 

been formed by small streams and mudflows that descend 

the gullies during rainstorms. From Ricksecker Point, a 

typical alluvial cone can be seen on the opposite side of the 

Paradise River valley (fig. 4, locality 30), and the West Side 

Road crosses one at the base of Mount Wow (fig. 4, locality 

31). 

ALLUVIUM 

Alluvium includes both unvegetated sand and pebble-toboulder gravel deposited by modern streams and rivers and 

the same type material underlying forested terraces or 

benches as much as 15 feet higher than the stream channels. 

Some low terraces contain poorly sorted bouldery deposits 

that may be mudflows or alluvium transported by floods. 

Near the ends of present glaciers, alluvium locally includes 

lenticular mudflows a few feet thick that came from 

moraines or from rock debris on the glaciers ; boulders 

larger than 5 feet in diameter in the alluvium probably were 

carried by these mudflows. Nearly all the alluvium shown 

on the geologic map has been formed within the last 500 

years. 

AVALANCHE DEPOSITS FROM 

LITTLE TAHOMA PEAK 

Seven or more rockfalls from the steep north face of 

Little Tahoma Peak in December 1963 resulted in a series 

of large avalanches that rushed as far as 4.3 miles downvalley. Although these avalanches were a form of landslide, 

they differed from most other landslides of the park in 

their speed. An extremely high velocity, probably exceeding 

100 miles per hour, is indicated by the height to which some 

avalanches rose onto the sides of obstacles in their paths. 

38 
Such a velocity is also suggested by the way some avalanches caromed from one side of the valley to the other 

during movement, by their distance of movement, and by 

the presence of rock fragments embedded in the trunks 

of trees along the south margin of the avalanches a quarter 

of a mile upvalley from White River campground. 

The avalanche deposits are jumbled mixtures of angular 

rock debris of many sizes in a loose reddish-gray matrix of 

sand (fig. 19). Scattered blocks of andesite breccia in the 

deposits are as large as 60 by 130 by 160 feet. The surface 

of the avalanche deposits is hummocky in most areas, but in 

some places there are ridges and furrows in the debris. Some 

AVALANCHE DEPOSIT of rock debris in the foreground originated in 

rockfalls from Little Tahoma Peak. The deposit buried the former floor 

of the White River valley to depths as great as 100 feet. The boulder 

on the ridge at the left has dimensions of about 24 by 30 by 46 feet. 

(Fig. 19) 

39 
ridges and furrows parallel the trend of the valley, and 

others are transverse to it. The deposits have a maximum 

thickness of about 100 feet, and they originally covered an 

area of about 2 square miles, including the part on the 

surface of Emmons Glacier. The total volume is estimated 

to be at least 14 million cubic yards. 

The long distance some avalanches moved is attributed 

to the development of cushions of compressed air beneath 

the avalanches as they hurtled off the steep front of Emmons Glacier. These air cushions buoyed up the swiftly 

moving avalanches for long distances and prevented them 

from striking the ground. 

Perspective 

The surficial deposits of Mount Rainier National Park 

record a complex series of events that have occurred within 

the recent geological past. Glaciers formed the oldest deposits very early in the history of Mount Rainier, perhaps 

even before the volcano as we know it today began to develop. Huge glaciers again blanketed almost the entire park 

twice during the last 40,000-50,000 years. The last of these 

major glaciations ended only about 10,000 years ago, but 

within just the last few thousand years the glaciers of the 

park have experienced renewed growth at least twice. 

Mount Rainier has erupted repeatedly since the end of 

the last major glaciation, but most of this activity has been 

on a feeble scale in comparison with the cataclysmic eruptions that built the main cone. The production of new lava 

and pumice, some as recently as the mid-1800's, has not 

kept pace with the piecemeal destruction of the volcano by 

glacial erosion and repeated landslides. Some of these slides 

have had wide-reaching effects, for at least two mudflows 

generated by them were large enough to reach far down 

valleys and to bury parts of the adjacent Puget Sound lowland. 

Although all the surficial deposits were created by geologic events of the past, when viewed in the immense perspective of geologic time-measured in hundreds of millions 

of years-these events occurred only yesterday or early 

this morning; in all probability they will recur tomorrow. 

40 
Further Reading 

Crandell, D. R., and Fahnestock, R. K., 1965, Rockfalls and 

avalanches from Little Tahoma Peak on Mount Rainier, 

Washington: U. S. Geological Survey Bulletin 1221-A, 

30 pages. A description of the seven successive landslides of December 1963 that buried the upper White 

River valley under thick deposits of rock debris. 

Crandell, D. R., and Mullineaux, D. R., 1967, Volcanic hazards at Mount Rainier, Washington: U.S. Geological 

Survey Bulletin 1238, 26 pages. A discussion of the 

eruptive history of the volcano during the last 10,000 

years and the anticipated effects of similar future 

eruptions. 

Fiske, R. S., Hopson, C. A., and Waters, A. C., 1963, Geology 

of Mount Rainier National Park, Washington: U. S. 

Geological Survey Professional Paper 444, 93 pages. A 

technical description of the rock formations of the park. 

Fiske, R. S., Hopson, C. A., and Waters, A. C., 1964, Geologic 

map and section of Mount Rainier National Park, Washington: U.S. Geological Survey Miscellaneous Geologic 

Investigations Map 1-432. A relatively nontechnical discussion of the geological evolution of the park as recorded by the rock formations. 

Sigafoos, R.S., and Hendricks, E. L., 1961, Botanical evidence 

of the modern history of Nisqually Glacier, Washington: 

U. S. Geological Survey Professional Paper 387-A, 20 

pages. A description of the recent moraines of several 

glaciers and an explanation of how they are dated by 

counting the growth rings of trees growing on them. 

41 tr 1).5. GOVERNMENT PRINTING OFFICE : 1969 0-360-688