This dissertation has been mlcroillmed exactly as received 6 9 -2 2 ,2 i0

SMITH, Geoffrey Wayne, 1939- SURF1CIAL GEOLOGY OF THE SHUSWAP RIVER DRAINAGE, BRITISH COLUMBIA.

The Ohio State University, Ph.D., 1969 Geology

University Microfilms, Inc., Ann Arbor, Michigan SURFICIAL GEOLOGY OF THE SHUSWAP RIVER

DRAINAGE, BRITISH COLUMBIA

DISSERTATION

Presented In Partial Fulfillm ent of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State University

By

Geoffrey W. Smith, B.S., M.S.

The Ohio State University

1969

Approved by q j j Q cM Jr Adviser Department of Geology ACKNOWLEDGMENTS

The present study was undertaken as an outgrowth of the region al mapping program of the G eological Survey of Canada for

1966 and 1967. The author i s most g ra tefu l to the G eological

Survey for financial and logistical support during the field season and for permission to use the results of the study for this disser­ tation. Special thanks are due Dr. Robert J. Fulton of the

Geological Survey who suggested the problem, introduced this investigator to the area, and gave generously of his time and counsel in the planning and execution of the project.

It is a pleasure to acknowledge the advice and guidance of Dr.

Richard P. Goldthwait of the Department of Geology at the Ohio State

University. Hia help in the several problems encountered during the field work and preparation of the manuscript is most appreciated.

Able assistance in the field was provided by Messrs. Greg

Smith, Andr£ Lemay, and P eter Jensens in 1966, and by Messrs.

Ronald Nielsen and Roland Proctor in 1967.

Finally, grateful appreciation is expressed to Drs. R. P.

Goldthwait, A. LaRocque, G. E. Moore, and S. E. White for c r it ic a l reading of the manuscript and for the constructive suggestions which served to improve its effectiveness.

i i VITA

September 29, 1939 Born - Boston, Massachusetts 1961 ...... B .S., Tufts University, Medford, Massachusetts 1961-1964 .... Teaching a ssista n t, Department of Geology, University of Maine, Orono, Maine 1964 ...... M.S., University of Maine, Orono, Maine 1964-1968 .... Teaching a ssista n t, Department of Geology, The Ohio State University, Columbus, Ohio 1965-1967 .... Technical officer, Geological Survey of Canada, Ottawa, Ontario 1968-1969 .... Instructor, Colby College, Waterville, Maine

PUBLICATIONS

With R. P. Goldthwait (1969); Glacial Geology; in Encyclopedia of Geomorphology (R. W. Fairbridge, editor): Reinhold Publishing Co., New York, pp. 431-439. With R. P. Goldthwait and T, Lewis (In press); Recent radiocarbon dates from Lake W hittlesey and Lake Warren beaches in northern Ohio.

FIELDS OF STUDY

Major Field: Geology StudleB in Glacial Geology. Professor Richard P. Goldthwait Studies in Quaternary Stratigraphy. Professor Richard P. Goldthwait Studies in Geomorphology. Professor Sidney E. White Studies in Paleontology. Professor Aurele LaRocque Studies in Petrography. Professor George E. Moore, Jr.

i i i TABLE OF CONTENTS

INTRODUCTION ..... I Location and Extent of Area ...... I Nature of Investigation . . 3 Previous Investigations ...... , . 5 Bedrock Geology ...... 6

PHYSIOGRAPHY...... 12 Monashee Mountains ...... „ ...... , 12 Shuswap and Okanagan Highlands ...... 15 Drainage . , , . 18 Shuswap River . . . 19 Eagle River . . ... 23 Preglacial Physiography . , 26 Effects of Glacial Erosion 32 Glacial Movement Associated with the Last Glaciation ...... 36

GLACIAL STRATIGRAPHY - TERMINOLOGY .... 42

GLACIAL STRATIGRAPHY - OLYMPIA INTERGLACIAL DEPOSITS . . - . 45 Bessette Sediments ...... 45 Definition . . 45 Nature of Deposits ... . , 49 Latewlios Creek . , 49 Bessette Creek ...... 51 Cherryville . . . , ...... 56 Origin of Bessette Sediments ...... 56 Probable Correlative Deposits . .59 Age and Significance of Deposits ...... 61

GLACIAL STRATIGRAPHY - FRASER GLACIAL DEPOSITS ...... 66 Lumby T ill ...... 66 Definition ...... 66 Nature of Deposits ...... 66 Valley Tills ...... 68 Upland T ills . , ...... 76

IV TABLE OF CONTENTS (continued)

Monashee S edim ents ...... , . 78 Definition 78 Nature and Distribution of Deposits ...... 80 Monashee-Pass Cherryville Area ...... 80 Sugar Lake V a lle y ...... 87 Creighton Valley ...... 94 Lumby-Bessette Creek Lowland ...... 97 Mabel Lake V a lle y ...... 98 Trinity Creek Valley . 104 Eagle River Valley , . „ ...... 106 Age of Monashee S edim ents ...... 112

GLACIAL STRATIGRAPHY - POSTGLACIAL DEPOSITS ...... 114 Eagle Valley Sediments 114 Nature of Deposits , . . . „ ...... 114 Historical Significance of Eagle Valley Sediments ...... 124

OUTLINE OF DEGLACIATION AND DRAINAGE CHANGES ...... 126 Introduction ...... , ...... 126 Ice Regimen . . . „ . 127 Deglaciation and Drainage Development ...... 129 Map-Are a 1 . 129 Map-Area 2 ...... 135 Lumby-Bessette Creek Lowland ...... 135 Mabel Lake Valley ...... 140 Map-Area 3 . 146

HISTORICAL SUMMARY ...... 152

REFERENCES ...... 155

v TABLES

Table Page

1. Petrographlc Properties of Olympia Interglacial Volcanic Ash ...... 55

2. Radiocarbon Dates from Bessette Sediments and Correlative D eposits ...... , 62

3. Pebble Counts of Lumby T ills within the Shuswap River Drainage ...... 73

4. Pebble Counts of Monashee and Eagle Valley Sediments within the Shuswap RiverDrainage .... 89

5. Outline of Major Late-Glacial Events in the Shuswap River Drainage and Adjacent Areas ...... 121

v i ILLUSTRATIONS

Index map showing location and extent of study area . . 1 Generalized geologic map of the Shuswap River drainage and adjacent areas (after Jones, 1.959 ) . . 7 Physiographic subdivisions of southern British Columbia ,, ...... 13 Monashee Mountains. View west from Revelstoke to Mount Begbie ...... , ...... 14 Monashee Mountains View east from summit; of (jueest Mountain to Gold Range ...... 16 Okanagan Highland, View south from Lumby to upland surface of; Okanagan Highland ...... 17 Shuswap River View east along Shuswap River Valley between Cherryville and Shuswap Falls . . . 20 Shuswap River. View west across Mabel Lake to Dolly Varden Beach ...... 22 Kngle River.. Fast end of Lagle River Valley looking southeast to valley of Wap Creek ...... 24 Lagle River. WesL end of Fagle River Valley looking norLheasL iram Yard Creek to Malakwa . . , 25 Inferred pattern of preglacial drainage ...... 28 Orientation of cn.jues in Monashee Mountains .... 35 Stratigraphic and environmental chart ...... 43 Bessette Sediments exposed at the mouth of Latewhos Creek ...... 46 Distribution of surface exposures of Bessette Sediments ...... 48 Bessette Sediments exposed at Bessette Creek two miles west of Shuswap Falls ...... 52 Location of exposed sections of Bessette Sediments and probable equivalent deposits outside of the study area that have provided radiocarbon dates . . 60

vii ILLUSTRATIONS (continued)

Figure

18. Mechanical analyses of the <2 mm. size fraction of Lumby t i l l s ..... 69 19. Gravelly till exposed at Shuswap Falls ...... 71 20. liouldery till exposed in the valley of Tsuius Creek . . . . 74 21„ Beach and delta terraces in Cherry Creek Valley . . 82 22. Internal structure of delta terrace ...... 83 23. Top of succession of varved lacustrine s i l t s in valley of Cherry C reek ...... 85 24. Slumped lacustrine s i l t s at the west end of Creighton V alley ...... 96 25. D istribution of raised d eltaic and flu v ial features in Mabel Lake V a l l e y ...... 100 26. Exposure of Monashee Sediments on Kingfisher Creek four miles north of H u p ei ...... 102 27 Prominent delta terrace at southern end of Wap Creek V alley ...... 105 28. Kame terrace at Three Valley ...... 108 29. Exposure in kame terrace on Highway 1 approximately three miles east of Three V alley ...... 110 30. Delta terrace on Highway 1, one mile east of Eagle Pass ...... Ill 31. Talus apron at foot of bedrock slope in Eagle River V alley ...... 118 32. Deglaciation of Map-Area 1 ...... 131 33. Deglaciation of Map-Area 1 ...... 132 34. Deglaciation of Map-Area 1 ...... 134 35. Deglaciation of Map-Area 1 ...... 136 36. Deglaciation of Map-Area 1 ...... 137

viii ILLUSTRATIONS (continued)

Figure

37. Deglaciation of Map-Area 1.Extension ofLake Lumby into Coldstream Valley at1800-foot level . . . 139 38. Deglaciation of Map-Area 2 ...... 141 39. Deglaciation of Map-Area 2 ...... 142 40. Deglaciation of Map-Area 2 ...... 145 41. Successive positions of ice margin during deglaciation of Map-Area 3 ...... 147

Plate

IA Surficial Geology, Shuswap River Drainage, B ritish Columbia ...... (in pocket) IB Surficial Geology, Shuswap River Drainage, B ritish Columbia ...... (in pocket) II Direction of Glacifil Movement Associated with the Last Regional Glaciation (in pocket)

lx INTRODUCTION

Surficial deposits within the valleys of the Shuswap River and Its tributaries include a wide variety of glacial and non­ glacial sediments that are of both economic and academic interest.

The present report involves the definition, description, and delineation of these deposits and the determination of their stratigraphic relationships to one another. In addition, the report presents a coordinated account of the progression of events during and following the disappearance of glacial ice within the valleys of the Shuswap River drainage.

Location and Extent of Area

The area of study comprises an irregular tract, approximately

1200 square miles in exten t, on the eastern margin of the Interior

Plateau of south-central B ritish Columbia. It encompasses portions of the Shuswap and Okanagan Highlands and Monashee Mountains physiographic subprovinces (Holland, 1964), and is roughly defined by latltud s 50“00' and 51°00' north and by longitudes 118°30' and

119°00' west. The location and extent of the study area are shown in Figure 1. Mapping of the surficial deposits was concentrated

1 m m

P v n r t T f M

STAT E S U,N IT EO

Figure 1. Index map showing location and extent of study area*

K) 3 largely in the valleys of the Shuswap and Eagle Rivers and their major tributaries and in the adjacent lowlands. Uplands were mapped in reconnaissance where access permitted.

Nature of Investigation

Field work for the present report was conducted during the summers of 1966 and 1967; a to ta l of seven months was spent in the field. Considerations of access and thorough coverage of the area required that map units be established on features that were easily distinguishable on aerial photographs and readily traceable in the field. A descriptive classification employing geomorphic form as the baBls of differentiation has been successfully utilized by

Fulton in the mapping of surficial deposits in the Kamloops region

(1963, 1967) and in the Okanagan Valley (in press). A similar approach was followed in the present study. Thus, the map of surficial deposits (Plates IA, IB) presented herein is based primarily on morphology. It should be noted, however, that certain genetic implications are necessarily inherent in any such distinc­ tion of morphologic units.

Original mapping of the surficial deposits of the area was done on aerial photographs at scales of approximately 1 inch to

1 mile and 2 inches to 1 mile. This information was then trans­ ferred to topographic mapB with a scale of 2 inches to 1 mile and a contour interval of 50 feet, from which Plates IA and IB were prepared. Where additional detail seemed necessary, geologic 4

boundaries were mapped directly on topographic maps with a scale of 1 inch to 1000 feet and a contour interval of 20 feet. Eleva­ tions in the field were determined by the use of a Wallace and

Tleman altimeter model no. FA 181. By recognition of the contrasting soil and vegetation types, and of the distinctive topo­ graphic expression of certain sediments, it was possible to maintain close horizontal control in mapping the distribution of the various sediments. Vertical control was more difficult, but contacts are believed to be correct within an interval of approximately twenty fe e t.

Till fabric analyses were made in exposures of till within the valleys where outcrops of bedrock were scarce. In determining the till-fabric orientations, the azimuth of the long axes of 100 pebbles between 1 and 2 inches in length was measured to the near­ est 5 degrees with a Brunton compass. The direction of dip of the pebbles was recorded, but the magnitude of dip was not. Only rod­ shaped pebbles in which the length of the greatest axis was at least twice that of the shortest axis were used for fabric analysis.

The pebble orientations thus determined were plotted on rose diagrams, and the orientation of the modal peak was considered to represent the preferred pebble orientation. In several cases, oriented till samples were collected and the fabric orientations were determined In the laboratory by measuring the azimuth of the long axes of 100 to 200 pebbles greater than 2mm in length (see

Dreimanis, 1959). Fabric orientations determined in this fashion 5

were checked against fabric analyses made in the field at four lo c a litie s . The two methods provide results that are consistent within ± 5 degrees.

Each pebble count presented in this report represents approximately 100 pebbles between 1 and 3 inches in length collected at random from exposures of t i l l or gravel and grouped according to rock type.

Previous Investigations

The earliest recorded observations on the geology of the study area are those of G. M. Dawson (1878, 1890) and R. A. Daly

(1912). With the exception of brief notes by Dawson, these

reports deal primarily with the broad aspects of the bedrock geology and the physiographic development of the region, and give but passing attention to the surficial deposits of the immediate

study area. Recent work on the bedrock geology of the area has been summarized by A. G. Jones (1959).

Soils surveys of the North Okanagan Valley (Sprout and

Kelley, 1960) and the Eagle River Valley (Dawson and Kelley, 1964)

afford information on surficial deposits in portions of the study area, and offer brief discussions of the origin of the soil-forming m aterials.

The late-glacial history and the surficial deposits of the

Okanagan Valley, immediately west of the present study area have

been studied by Nasmith (1962). This valley and the valleys of the Thompson River system have been mapped in detail by Fulton

(1963, 1967, in press) as part of the regional mapping program of the Geological Survey of Canada. The Columbia River Valley, immediately east of the present study area, is currently being studied under th is same program. The present report provides information pertinent to the understanding of the glaciation and deglaciation of the adjacent Columbia and Okanagan Valley systems.

Bedrock Geology

Most of the study area is underlain by regionally meta­ morphosed rocks of the Shuswap terrane (Jones, 1959), though younger rocks of the Cache Creek Group underlie much of the south­ ern portion of the area (Figure 2). Small granitic Intrusions and irregular bodies of Tertiary volcanic and sedimentary rocks are exposed locally. A thorough treatment of the bedrock geology of

the study area was published by A. G. Jones (1959). Much of the following discussion is drawn from that report.

The Shuswap terrane comprises three stratlgraphic groups

of which only the Monashee Group is widespread within the area of

the present study. Rocks of the Monashee Group are predominantly

gn eisses, though quartzite, schiBt, and marble are common and

lo ca lly important components of the assemblage. These rockB are

derived from sedimentary progenitors that have undergone regional metamorphism. The complex structural aspect of the rocks and the Figure 2. Generalized geologic map of the ShuBwap River drainage and adjacent areas (after Jones, 1959).

EXPLANATION

Fault (dashed where inferred)

QUATERNARY Unconsolidated surficial (Pleistocene & Recent) sediments

TERTIARY Kamloops Group (volcanic (Oligocene or Miocene) and sedimentary rocks)

JURASSIC and/or '*4*1 < V A Coast Intrusions V- V ▼ V T 1“ CRETACEOUS t 4 y m r- < (granitic intrusives)

CARBONIFEROUS (?) Cache Creek Group and PERMIAN Upper unit - mainly limestone

Middle unit - mainly andesitic lava

Lower unit - mainly a r g illite

ARCHEAN(?) SHUSWAP TERRANE

Mount Ida Group (occurs I west of study area) Monashee Group High metamorphic grade

Low metamorphic grade 8

t

d

V«rnen Ui»fcrS 9

general uniform appearance of the strata has not allowed for stratl-

graphlc subdivision of the group. Although the temporal relation­

ships of the Monashee Group are not clearly established, Jones

(1959) considers the rocks to be Archean in age.

Three suites of pre-Permian Intrusive rocks, confined to the

Shuswap terrane, have been distinguished in the study area. These

rocks include small gabbroic and dioritic sills and dikes (Three

Valley intrusions), granitic bodies (Silver Star intrusions), and

serpentlnlzed ultramafic dikes (Old Dave intrusions).

Carboniferous (?) and Permian rocks of the Cache Creek

Group are exposed in the southern portion of the study area.

These rocks are thought to represent a continuous conformable

succession, overlying rocks of the Shuswap terrane with erosional

unconformity, or occurring as block-faulted inliers within the

Shuswap rocks. The Cache Creek Group has been subdivided into

three units on the basis of the dominant lith o lo g ies of the rocks

(Jones, 1959). The lowermost unit is mostly argillite. The

middle unit is mostly andesitlc lava and tuff with subordinate

amounts of argillite, quartzite, and limestone. The upper unit

is mostly limestone with minor amounts of argillite, quartzite,

and andesitic lava, breccia, and tuff.

Granitic rocks of Late Mesozoic age within the area have been

ascribed to the Coast Intrusions. These intrusions are generally

rare in the Monashee rockB, but granitic bodies north of Sugar Lake

and along the southern margin of the Btudy area belong to this 10

group. The intrusive rocks display a wide range of composition, and include true granite, quartz monzanite, granodiorite, and quartz diorite. More basic varieties are rare. Pegmatites occur in proximity to the larger intrusive bodies and as scattered Bills and dikes throughout the Monashee Group.

The youngest rocks exposed in the study area include basaltic lava and flow breccia and Intercalated units of sandstone, shale, and conglomerate. These rocks comprise the Kamloops Group of

Oligocene or Miocene age and are important elements of the terrain in the southern portion of the study area, and in the Trinity Hills west of Mabel Lake.

The e ffe c ts of two major periods of deformation have been recognized in the rocks of the Shuswap terrane; structures of the younger deformation have been superimposed upon those of the older.

Structures resulting from the "Older" deformation (Jones, 1959) con sist of extensive is o c lin a l, recumbent folds and zones of

Intense shearing. Fold axes and lineation are parallel and trend northeas te rly-southwes terly.

Structures of the "Younger" deformation are typified by faults, gentle warps, and folds that are generally upright in contrast to those of the "Older" deformation. The regional tectonic axis of the "Younger" deformation trends northwest-

Boutheast, parallel with the trend of the Cordillera in general.

The network of block faults that has resulted from the last stages of deformation are the most prominent of the "Younger" structures. The principal effect of the regional faulting 1b believed to have been a general uplift of the Shuawap terrane.

The major Vernon-Sicamous fau lt and the Columbia River fault system bound the central block of the Monashee Group massif on the west and east, respectively. Jones (1959, p. 124) contends that the alpine topography of the Monashee massif as contrasted to the low relief of the adjacent Interior Plateau is probably more closely related to this uplift than to the character of the rocks underlying the two physiographic divisions. 12

PHYSIOGRAPHY

The area of study includes portions of the Interior Plateau

and Columbia Mountains physiographic provinces (Holland, 1964).

The boundary between these two provinces coincides with that between the Shuswap and Okanagan Highlands on the one hand, and

the Monashee Mountains on the other. This divides the area into

two contrasting physiographic elements (Figure 3).

Monashee Mountains

The Monashee Mountains occupy an irregular tract up to 25

miles in width along the eastern margin of the study area. The

mountains comprise several smaller ranges of which the Gold,

Sawtooth, and Mabel Ranges lie within the present study area

(Plates IA, IB).

Summit elevations of the Monashee Mountains within the area

are mostly between 6000 feet and 8000 feet above sea lev el, though

several peaks in the Gold Range attain elevations just under

10,000 feet (Figure 4). North of the study area, summit elevations

are generally higher, whereas to the south, peaks are progressively

lower. Most of these mountain summits extend above tim berllne,

which is at an elevation of approximately 6500 feet. Consequently,

uplands in the northern and eastern portions of the area are )\,M tu

1\ Vernon - r

S

20 A-

Figure 3. Physiographic subdivisions of southern British Columbia. Area of study indicated by cross-hatched pattern. Figure 4. Monashee Mountains. Looking west from Revelstoke to Mt. Begbie (8963 feet) in the northeastern corner of the study area. Small glaciers occupy cirques on north- and northeast- facing slopes. 15 generally open and meadowed or rugged and rocky (Figure 5). The high mountains of the Gold Range support a number of small glaciers and perennial snowflelds, nearly all of which are in north- or eaat-faclng cirques. All peaks of the Monashee Mountains display the effects of Intense mountain glaciation. 'I

Shuswap and Okanagan Highlands

The Shuswap and Okanagan Highlands constitute a tran sition al belt of terrain up to 50 miles wide that separates the Monashee

Mountains from the gen tly -ro llin g upland of the Thompson Plateau

(Figure 3). Elevations of most of the highland area are generally between 5000 feet and 7000 feet above se a le v e l, though high points on the upland surface attain altitudes ranging from 7200 feet In

the north to 6500 feet In the southern portion of the study area.

In contrast to the mountains of the eastern part of the area,

the Shuswap and Okanagan Highlands are characterized by a relatively smooth, gen tly-rollin g upland surface. Mountains and h ills are

rounded, with gentle open slopes which are set back from the valley bottoms, producing an average relief of 3500 feet to 5000 feet.

Tertiary lavas cap much of the upland In the southern portion of the

area, and h ills are comnonly flat-topped and poorly drained

(Figure 6).

Pleistocene ice covered the highland area, but the effects of

glaciation were largely to reduce upland relief while accentuating

total relief by steepening and deepening major valleys. Small Figure 5. Monashee Mountains. Looking east to Gold Range from summit of Queest Mountain (6846 feet) north of Slcamous. Shuswap Erosion Surface in foreground. Figure 6. Okanagan Highland. Looking south to upland surface of Okanagan Highland east of Lumby. Broad flat area In foreground la low gradient fan complex b u ilt by Creighton Creek, which enters main valley from left middle distance. 18 cirques are common in the higher elevations of the Hunters Range and a ttest to a former period of mountain glaciation in that area.

Drainage

The area of study is drained by the Shuswap and Eagle Rivers and their tributaries. The major valleys of this drainage system range in elevation from approximately 1100 feet to 3000 feet above sea level. Local relief is about 7000 feet in the northeastern sector of the area, and decreases gradually to about 2200 feet in the southwestern comer of the area.

Major valleys trend north-south or east-west in an almost rectangular system. North-south valleys, notably those occupied by

Sugar and Mabel Lakes, parallel the general direction of Pleistocene ice movement and display steep valleys and U-shaped cross-profiles.

These valleys are partially filled with glacial and postglacial sediments, and the valley floors are generally flat. East-west valleys, on the other hand, are transverse to the_direction of ice movement over the area and display little evidence of profound glacial modification. Interstream drainage on the uplands is poorly developed, and small ponds dot the upland surface. Most tributary streams meet trunk streams at grade, flowing over broad gravelly a llu v ia l fans.

Some tributaries bear a hanging relationship to the trunk streams; the valleys of these tributaries can often be traced headward to cirque basins. This relationship is particularly evident in the

Shuswap Valley north of Sugar Lake. 19

Shuswap River

Several aspects of the present Shuswap River drainage are of interest and deserve brief mention. The Shuswap River rises on the western flanks of the Gold Range Immediately southwest of

Revelstoke (Plate IB). From its point of origin, the river flows southward In a narrow, steep-walled valley for a distance of 27 m iles to Sugar Lake. Major tribu taries Join the Shuswap Valley from the east and flow in distinctly U-shaped valleys.

At the southern end of Sugar Lake, the Shuswap River spills over a bedrock threshold (Brenda F alls) and flows in a narrow valley deeply Incised into unconsolidated Pleistocene sediments.

Broad alluvial fans fill the Shuswap Valley north of Cherryville and have displaced the river westward in its valley against the steep bedrock slopes of the Silver Hills.

The Shuswap River turns westward at Cherryville, and for a distance of 9 miles cuts across the grain of the topography.

Approximately seven miles west of Cherryville, the river swings northwestward in a course of shallows and rapids over a thinly- veneered bedrock floor (Figure 7). This section culminates in a spectacular chute through a narrow bedrock gorge (Shuswap Falls).

Here the river drops approximately 210 feet in a distance of less

than a quarter of a mile, and changes its aspect totally. The

section of rapids and falls marks the postglacial connection between

the preglacial Shuswap River draining the eastern portion of the

area and the preglacial Shuswap River draining southward from Mabel

Lake (Figure 11), 20

Figure 7. Shuswap River. Looking east toward Cherryville along the valley of the Shuswap River between Cherryville and Shuswap Falls. Note rapids in foreground and middle distance. Upland of Shuswap Erosion Surface in background. 21

Bessette Creek, which joins the Shuswa;,. River immediately below Shuswap Falls, originates at Lumby wheve Harris, Duteau, and

Creighton Creeks merge to form a single stream. Approximately three miles north of Lumby, Bessette Creek enters a narrow, steep- walled valley incised some 200 feet into a drift-filled lowland area two to three m iles w ide. To i t s ju n ctio n w ith the Shuswap

River, a distance of five miles, Bessette Creek meanders in a deep valley never more than three-quarters of e mile wide and generally f less than one-quarter of a mile wide. By co-.’i arison with other streams in the area, Bessette Creek is cleariv underfit. The broad lowland into which the creek is incised marki< the preglacial course of the Shuswap R iver, which flowed southward and westward through

Lumby and thence westward down the Coldstream Valley to Vernon

(Figure 11).

From i t s confluence w ith B essette Creek, the Shuswap River flows northward today for a distance of ten miles to Mabel Lake.

This lake is the water-filled portion of a deep through-valley extending from Three V alley on the north to Shuswap F a lls on the south. Presently, Mabel Lake drains to the west through a narrow outlet at Dolly Varden Beach (Figure 8). The outlet has been cut through more than 100 feet of deltaic deposits at the mouth of

Kingfisher Creek, and is presently superimposed on bedrock at

Skookumchuck Rapids. From these rapids, the Shuswap River flows

18 miles west to the town of Enderby in the Okanagan Valley. Figure 8. Shuswap R iver, Looking w est across Mabel Lake to Dolly Varden Beach. The present outlet of Mabel Lake i s v is ib le in cen ter o f photograph above the beach. The clearing is located on the lowest of a series of deltas constructed by King­ fish e r Creek, which jo in s the Shuswap R iver from the north (right center of photograph). Valley of Shuswap River i s seen in middle d ista n c e . Upland of Shuswap Erosion Surface in background. 23

Eagle River

The Eagle River flows westward across the northern margin of the study area, and across the general grain of topography and structure. It originates in a series of small lakes immediately west of Eagle Pass at an elevation of approximately 1800 feet above sealevel. Hie length of the river is 36 miles, and the total area drained by the river and its tributaries is approximately 450 square m iles.

Above its junction with the Perry River, the Eagle River is steep and the flow is fast. The valley in this section is narrow and is bordered by precipitous bedrock slopes (Figure 9).

Tributaries enter the main valley across coarse gravelly fans; the interstream areas are commonly marked by small landslides.

In this upper part of Its course, the gradient of the Eagle River is approximately 35 feet per mile and the bedload is predominantly coarse sand and gravel.

In marked contrast to the eastern end of the valley, thick accumulations of unconsolidated deposits f ill the western section of the valley and blanket the lower slopes of the valley sides

(Figure 10), In the lower part of its course, the gradient of the Eagle River is between five and six feet per mile and the bedload Is largely silt and sand. At Slcamous, the river enters

Shuswap Lake. Here i t has constructed a d e lta two and a h a lf m iles w ide, sep aratin g Mara Lake from the main body of Shuswap Lake. 24

If*

Figure 9. Eagle River. East end of Eagle River Valley looking southeast across Griffin Lake to the valley of Wap Creek, The hummocky forested area in middle distance is a landslide that blocks the Eagle River Valley and contains Three Valley Lake. Mount English in left distance. 25

Figure 10. Eagle River. West end of Eagle River Valley looking northeast from Yard Creek to Malakwa. The Eagle R iver flow s w est ( l e f t , beyond highway) to Slcamous. North Queest Mountain In left middle distance. Perry River Valley In right distance. Monashee Mountains In background. 26

Preglaclal Physiography

The major physiographic features of the area are genetically related to bedrock structure and preglaclal fluvial erosion. These elements have been modified by glacial and post-glacial erosion and d ep o sitio n .

Prior to uplift, the land surface of the Shuswap and

Okanagan Highlands (Figure 3) was one of moderately low relief that transected a wide variety and age of rocks (Holland, 1964).

This is abundantly clear in the rolling upland of the Park Range above the 5500-foot contour or of the Hunters Range, Silver H ills,

Cherry Ridge, and Grizzly Hills above 4500 feet. These upland surfaces crosscut most of the rock types shown in Figure 2 and display the hip-roof cross-profile of raised and dissected old erosion surfaces. This upland surface is here called the Shuswap

Erosion Surface.

Elevation of the Monashee Mountains to their present position relative to the lowlands, and the dissection of the mountains by narrow valleys was contemporaneous with uplift and dissection of the adjacent highlands. Holland (1964, p .75) suggests that this uplift occurred during the mid-Pllocene. The mountains were uplifted higher and were more deeply incised by rejuvenated streams than were the highlands. In addition, most peaks above 8000 feet have been deeply sculptured by mountain glaciers, and mountain valleys display profound modification of their longitudinal and transverse profiles by both continental and mountain glaciation. 27

Major streams have developed coincident with major north- south fa u lt and jo in t p attern s (see Figure 2 ), and fo r the moBt part seem to have resulted from differential erosion along these zones of structural weakness. Tributary streams, and drainage normal to the grain of the topography, appear to have developed parallel to the east-west trend of fold axes of the "Older" deformation.

Streams were rejuvenated during differential uplift of the region, probably in mid-Pliocene. Drainage lines remained essen­ tially unaltered, though streams flowing west, perpendicular to the axis of uplift would have had steeper gradients and should have experienced more active degradation of their valleys. Erosion following uplift, therefore, tended to deepen and accentuate e a s t- and w est-flo w in g stream s, whereas major north- and south- flowing streams were affected by uplift only in response to the active downcutting of their tributaries.

At the end of the Tertiary, with the advent of glaciation, the land stood comparatively high, and the pattern of major valleys was essentially as it is today (Figure 11). Drainage directions within these valleys, however, were markedly altered during glaciation and immediately thereafter.

The fact that there has been significant alteration of pre­ glaclal drainage is apparent upon close examination of the configuration of major valleys within the area (see Plates XA and

IB). The gross aspect of the major stream valleys is one of a Figure 11. Inferred pattern of preglacial drainage as suggested by configuration of present topography, location of bedrock gorges, and geology of surficial deposits within valleys. 29

C. I. > 2 0 0 0 ft.

O 9 m llM

C*. ------

r i J BICAMOUS*

Zz

&

a 30

well-integrated dendritic system draining to the southwest. The pre­ glacial Mabel Lake Valley was the trunk valley within the study area, but was Itself tributary to a south-flowing trunk system which occupied the Okanagan Valley, immediately west of the study area (Figure 11).

Minor diversions of streams within the area are recorded by the presence of bedrock gorges and by the surficial deposits of the valleys. Dawson (1879) recognized that the valley of Cherry Creek, east of Cherryville, had been shifted from its preglaclal course.

Placer accumulations of gold within this valley were extracted from

"Tertiary" gravels that conformed to the pattern of preglaclal drain­ age. Thus, Dawson suggested that the lower portion of Cherry Creek formerly flowed in a valley somewhat south of the valley which it presently occupies. Monaehee Creek, which joins Cherry Creek from the south and flows in a deep, narrow bedrock gorge east of Hilton, likewise has been displaced from its preglacial course. In the words of Dawson:

When the glacier ice . . . retreated, leaving the valley blocked with moraine material and boulder- clay . . . , the stream again taking its way down the valley began anew to excavate its bed. The soft materials were rapidly removed, the stream at first changing its bed frequently, but at last subsiding into the deep narrow valley in which it now flow s. In some p la ces th is would appear to be identical with the original valley, while in others it is probable that a new course has been cut out in the rocky floor of the wide valley, leaving the old channel yet buried with drift on one side of the present. The canyons with steep rocky sides may represent such places, in which the stream has aban­ doned the pre-glacial channel, and cut itself a more d ir e c t course across some p ro jectin g rocky point (Dawson, G. M., 1879, pp. 1588-159B). The preglaclal confluence of Cherry and Monashee Creeks appearB to have been at a position approximately half a mile southwest of the present junction, and in a part of the valley now filled with more than 200 feet of Pleistocene deposits. Similar diver­ sions, the result of superposition from a thick cover of Pleisto­ cene sediments, have been recognized within the valleys of Ferry,

Harris, and Ireland Creeks, Undoubtedly others exist.

Major drainage rev ersa ls w ith in the Shuswap system have occurred in the Coldstream Valley immediately west of the study area, in the Shuswap Valley weBt of Mabel Lake, and in the Eagle

River Valley west of Three Valley. Perhaps the most conspicuous a lte r a tio n of p r e g la c la l drainage w ith in the Shuswap system is that which reversed the general southwestward drainage through

Lumby and Vernon to a northward drainage into Mabel Lake. Drain­ age through Lumby and the Coldstream V alley was m aintained during early stageB of deglaciation of the area (see p. 138). However, during later stages of deglaciation, Coldstream Creek constructed an extensive alluvial fan across the Coldstream Valley, forming a new divide, and diverting the drainage to its present course northward from Shuswap F a lls to Mabel Lake.

West o f Mabel Lake, the course of the Shuswap River for a distance of approximately seven miles is marked by rapids and shallows; exposures of bedrock are common along the floor of the valley. Five miles west of the lake, the valley narrows abruptly, and for a d ista n ce o f two m iles the Shuswap River flow s in a 32 narrow bedrock valley leas than half a mile wide. Tributary streams enter this portion of the valley over steep cascades and waterfalls.

West of the narrows the river begins to meander over a floodplain as much as one mile in width. The inner valley widens east of the narrows and, though shallow, is bordered by a wide floodplain and low terraces. It is postulated that this narrow portion of the valley west of Mabel Lake was the preglacial divide separating westward drainage to the Okanagan Valley through Enderby from southward drainage through Lumby to Vernon. This inference is supported by the observations of the configuration of the valley, the distribution of bedrock within the valley, and the nature of the angular relationship between tributary and trunk valley. Gla­ c ia l ero sio n and la t e - g la c ia l and p o s tg la c ia l stream ero sio n have lowered the divide and permitted westward drainage from Mabel Lake.

Similar evidence suggests that a preglacial divide within the present valley of the Eagle River between Three Valley and

Taft has been lowered by glacial and fluvial erosion to allow drainage westward from the present headwaters of the Eagle River to Slcamous.

Effects of Glacial Erosion

The surface of the Cordilleran ice sheet during the last glaciation reached a maximum elevation in excess of 8000 feet over the southern interior of British Columbia (Holland, 1964; Prest, et a l., 1968). In the study area, ice appears to have overridden 33

uplands below an elevation of between 7500 and 8000 feet above sea- level, but the exact limit Is obscure. Glacial striae and grooves, and polished bedrock surfaces, are widespread on uplands throughout the area, and have been recorded at elevations of approximately

6800 feet on the summit of Queest Mountain and 7000 feet on the upland e a st of Mount Mara. Above t h is e le v a tio n , although bedrock outcrops are commonly rounded and smooth, p o s itiv e evidence of glacial cover was not found. The sharp and rugged alpine topography of the mountains in the eastern portion of the area stand in marked contrast to the more subdued erosion surface of the central and western highlands, and is in accord with the inference that most of the summits of these mountains projected as nunataks through or east of the dome of continental ice. Concurrent and subsequent undercutting by flanking cirque glaciers haB accentuated this con­ tr a s t between mountain and highland.

On a very broad scale, glacial erosion does not appear to have altered the preglacial landscape very much outside of the Monashee

Mountains. Major valleys that nearly paralleled the spread of continental ice were deepened and widened, and valley sides were oversteepened by glacial erosion. Upland areas and transverse valleys, on the other hand, seem to have been modified little by the overrid in g ic e . Rounded and p o lish ed bedrock su rfaces at obtuse angles to the general ice motion bear out universal small-scale glacial sculpture, but valleys are not U-shaped. In the uplands of the southern portion of the area, glacial erosion was not severe 34

enough to reshape significantly even the relatively thin and vulner­ able Tertiary basalt that caps the upland. As in many other places, this suggests that the ice was not very thick (1000 ± feet) over the upland surface.

Perhaps the most Btrlking features produced by glacial erosion are the numerous cirques in the northern and eastern sections of the study area. Cirques occur on most upland areas with sunmit eleva­ tions above 7000 feet, but are absent on highlands with summits below

6000 feet, and are sparse or poorly-developed on uplands with

Bummits between 6500 and 7000 fe e t in e le v a tio n . Most cirq u es are between a quarter of a mile and three-quarters of a mile in diameter, between 500 and 1000 feet deep, and occupy positions generally on the north- and east-facing mountain slopes (Figure 12).

The cirques that occupy high positions on the mountain slopes, particularly those of the Monashee Mountains in the northeastern portion of the study area, differ conspicuously in their degree of preservation from those cirques at lower elevations and from those in the western highlands. In general, there appear to be two distinct groups of cirques. Cirques of the higher group are characterized by their clear definition, fretted walla, the presence in some of alpine moraines, and the presence in most of abundant accumulations of lichen-free rock debris; several contain small glaciers or permanent snowfields today. These cirque basins

range in elevation from approximately 6500 feet to 7000 feet

above sealevel. Sawtooth - Mahal Tha Ranges Pin

(160)

Sugar Mtn.~ Mt. MacPh*rson> Mt. Fosthall Mt. Bagbl*

(100) (6 0 )

Figure 12. Orientation of cirques in Monashee Mountains. Each rose diagram Is divided into 36 directions, each with an area of 10 degrees. Number in parentheses is to^al number of cirques counted. Inner circle represents 10 per cent of cirques counted. 36

Cirque9 of the lower group are subdued and poorly-defined with gentle bowl-shaped walls and no lateral or looped moraines.

Moralnal material, if present, is generally covered with a thick overgrowth of forest. Cirque floors and walls and adjacent slopes and ridges display the marks of scouring and rounding by over­ riding ice. The floors of most of these cirques range in eleva­

tion from 5000 feet to 6000 feet.

It seems very evident from topographic study of more than

400 of these cirques that the higher sharp cirques have been occu­ pied and enlarged since continental glaciation, if not also during it. It is almost as evident by contrast and lack of local moraines

that the subdued lower cirques date from an earlier glacial epi­

sode preceding the climax of the last continental glaciation.

G la c ia l Movement A ssociated VJith The Last Glaciation

The d ir e c tio n of ic e movement has been in fer red wherever possible by careful examination of striae, grooves, stoss-and-lee

surfaces, and crag-and-tail forms.. The orientations of large-

scale directional features have been determined in many cases

directly from aerial photographs and have been utilized primarily

In upland areas where information on direction of ice movement

could not be obtained otherwise In addition, till fabrics have

been measured in the valleys and lowlands where drift is deeper

and exposures of bedrock are rare or absent. This data is 37

illustrated in Plate II.

I t i s assumed that most of the g la c ia l markings shown in

Plate II are related to the last (Fraser) glaciation, since pro­ tection by covering drift for the duration of the Fraser Glaciation is doubtful, physically and glaciologically. This inference is supported by the observation th at the d ir e c tio n of the ic e movement determined from stones in the Lumby T ill, wherever such determina­ tions have been possible, are parallel to the nearby striae, grooves, etc. Moreover, glacial movements associated with earlier glaciations may well have been similar to those associated with the Lumby glaciation. Thus, inclusion of some directional indica­

tors of earlier glaciations with those of the last would probably not lead to radical inconsistencies. Such a conclusion is supported by the measurement of the trends of striae on bedrock beneath Bessette Sediments at ShuBwap Falls. These striae clearly

relate to an earlier glaciation. The average of twenty readings

at this locality is N25°W, which is, in fact, essentially parallel

to the orientation of pebbles within the overlying Lumby T ill at

th is lo c a lit y , which trend N20°W, ThiB re la tio n sh ip has been

recorded elsewhere in the study area.

Glacial flow markings over the uplands of the area all

appear to have been made by ice moving uniformly south to south­

east. On the ridge crests of the Hunters Range, striae and

grooves trend predominantly south and southeast. Deviations from

this trend can be explained in all caBes by local topographic control. Stoss-and-lee profiles and crag-and-tall forms on the ridge crestB clearly indicate southward glacial flow. As dis­ cussed previously, glacial ice appears to have overridden all upland surfaces below an elevation of between 7500 and 8000 feet.

Cirques and cirque-headed valleys facing northward or northeastward in the Hunters Range and in the vicinity of Sugar

Mountain provide evidence of up-valley glacial movements in the same general direction aB the ice flow recorded on nearby ridges.

Southward up-valley glacial movement in these valleys is recorded by stoss-and-lee profiles and crag-and-tail forms on the valley floors and walls. The cirques were sculptured by local glaciers that moved north or northwest down the valleys; therefore, the up- valley movements clearly took place after this sculpture. Logi­ cally, the flow of ice up the valleys occurred during the climax of glaciation while the ice stood above the ridge crests at the valley heads.

Glacial ice moved southward and southwestward in the passes and valleys through the northern uplands and southeastward in the valleys of the southern uplands. In the Trinity Hills and across the upland west of Mabel Lake, drumlins and striated surfaces indicate that the ice bifurcated in the vicinity of Trinity Valley.

Ice entering the mouth of the Trinity Creek Valley was channeled up the valley and thence into the valley of Christian Creek Just south of Bobby Bums Mountain. Directional markings on the adjacent valley sides and upland surfaces Indicate that ice over 39 the uplands maintained Its southeasterly flow, and glacial markings

In the valley south of Trinity Valley show that ice flow here was likewise toward the southeast.

Ice that entered the northern part of the Mabel Lake Valley flowed in a general southerly direction parallel to the axis of the valley, as did Ice In the Sugar Lake Valley. Striated and p o lish ed bedrock su rfa ces in the v ic in it y of Shuswap F a lls and

B esse tte Creek and in the Shuswap V alley e a st of the F a lls suggeBt that ice flowing from the upland surface to the north was sharply diverted there to a nearly east-west direction. Striae and grooves throughout the Shuswap V alley e a s t of Shuswap F a lls and in the Blue Springs Valley trend consistently between east-west and N70°W. Although other directional features are rare, a few stoss-and-lee profiles and crag-and-tail forms do suggest that

Ice movement was from the w est. Drumllns in the Shuswap V alley e a st o f Shuswap F a lls and over the upland north o f Echo Lake indicate that ice In this area flowed to the east-southeast and southeast. Southeastward movement is also recorded along the southern slopes of the Hilton Upland south of Cherryville.

One Inharmonious area of t ill fabrics needs interpretation.

In the low valley areas of the Shuswap. drainage south and east of

Cherryville, till fabric orientations trend east-west, and the plunge of the long axes of pebbles la toward the east. This

suggests that ice in this area flowed toward the west. T ill

fabrics and flute casts in lake silts near the center of the 40

Bessette Creek Valley likewise suggest westward-flowing ice in these low valleys. The evidence from the Bessette Creek Valley is ambiguous, because westward-flowing ice could have entered the v a lle y from the Mabel Lake V alley or from the Shuswap V alley e a st of Shuswap F a lls . However, in the C h erryville area, westward-

flowing ice could have originated only in the mountains along the eastern margin of the study area. Pebble counts for the tills in

the vicinity of Cherryville (Table 3) show a high percentage of

granitic rocks. The nearest reasonable source for these rocks is

the large granitic intrusion north of Sugar Lake. Thus, although

the available evidence is far from conclusive, It seems reasonable

to suggest that at some time, probably during the Initial stages of

continental glaciation, small alpine glaciers occupied the valleys

of the eastern part of the area. These glaciers would have origin­

ated in the Monashee Mountains and spread westward in the low

valleyB, possibly as far west as the Bessette Creek Valley.

The e a st-w est v a lle y s th at jo in the Shuswap system w ith the

Okanagan V alley ( i . e . , Coldstream V a lley , Shuswap R iver V alley

between Enderby and Mabel Lake) contain glacial markings that

demonstrate glacial flow both east and west. Ice flowing from the

uplands between Mabel Lake and the Hunters Range entered the east-

w est v a lle y of the Shuswap R iver w est of Mabel Lake and was

diverted to a southwesterly course. Abundant large- and small-scale

directional features in this area attest to the local control

exerted by the valley topography on the southward-flowing ice. 41

West of Hidden Lake, grooves and miniature crag-and-tall forms record Ice movement to the southw est (S30°W) and p a r a lle l to the v a lle y of the Shuswap R iver. Evidence fo r westward movement of

Ice In this valley occurs as far west as Ashton Creek. But at

Enderby, just west of the area, glacial markings suggest that Ice flowed eastward Into this valley, at least for this short distance

(Fulton, In press).

Drumllns and various small-scale glacial llneatlons at the mouth of the Coldstream Valley, and as far east as Lavlngton,

Indicate clearly that Ice entered the west end of the valley

(Fulton, In press). This Ice flowed eastward In the valley, merged with Ice moving from the uplands north of Lumby, and spread across the uplands In the vicinity of Harris Creek. GLACIAL STRATIGRAPHY - TERMINOLOGY

The s u r f ic la l m a teria ls w ith in the Shuswap drainage system consist of a thick succession of Interglacial sediments (Bessette

Sediments), glacial deposits of the last stage of regional glaciation (Lumby T ill), and varied late-glacial (Monashee Sedi­ ments) and postglacial (Eagle Valley Sediments) fluvial and lacustrine sediments. This cover of unconsolidated Pleistocene sediments Is amenable to treatment by the traditional methods of stratigraphy. Distinctive sedimentary bodies occur as units of mappable extent that can be placed in a loose tlme-stratigraphlc framework so that major divisions possess implications both of time and of spatial relation with glacial ice. In the absence of a formal stratlgraphlc terminology, the glacial deposits and each group of non-glacial deposits have been set apart as separate

Btratlgraphlc units. Each stratlgraphlc unit is given an informal name and each consists of lithologlc or morphologic units that are either facies equivalents or fit together as a distinctive part of the stratlgraphlc succession (Figure 13).

The terms " g la c ia l" , " la te -g la c ia l" , and " p o stg la cia l" are used informally in the present report to describe the Pleisto­ cene events and surficlal deposits. The term "glacial" refers to events occurring during glacial advance and occupation or to the

42 GLACIO- GLACIO- TIMECROUP GLACIAL ALLUVIAL SLOPE FLUVIAL LACl’STRINE FLUVIAL DELTAIC LACUSTRINE FAN DEPOSITS

EAGLE VALLEY F Loodpla In Delta Lacustrine A1Luvial RECENT Landslide SEDIMENTS a 1iuvium a 1luviun alluvium fan deposits

Talus Te rraccd V 1 -i : tn Laces trine a ilu u ia l Lerr... 11 rr.-no dopes i ls fan MONASliSE lato - [ SEDIMENTS g lacial K* ^-,1 Kar.e

L l- rrac*' de i ta Earte fan Ceil arse.: < Chanr.c L Ucvdtrir.c dtl-pos 1:5 5 LL'pv'S i L>

n C- •■■ —d s -ora ir«> s.LT-niV z l-^ i si\ t Dru-i ir.oid

. ..i

C jarii’ Col Iuviuir, ± ■'■ 3ESSETTE rcue ' and s i l l and accret ion k ?i T zV.- . ¥ and s i n d; ash. Riev, as!i s-LACl ...... J peut.r.ueUs

^ f. ra t i ^raphi ^Lid t-uvj r rh^r: ,

toJS deposits formed under such conditions. "Late-glacial" relates more specifically to the time of deglaciation of the area or to deposits whose character was influenced by the proximity of wasting glacial

Ice during their formation. It includes the interval during final withdrawal of the ice from the major valleys and prior to establish­ ment of present baselevel. Recent and postglacial time are here considered to be synonymous. Recent time constitutes the time since tne establishment of present baselevel. It describes events

that have occurred in an environment Indistinguishable from that in the area today. Clearly these terms define time-transgresslve events, and are therefore applicable only to geographically

restricted areas. Stratlgraphlc units have thus been distinguished

on the basis of the Inferred local conditions of climate and sedi­ mentation at the time of their formation. GLACIAL STRATIGRAPHY - OLYMPIA INTERGLACIAL DEPOSITS

Bessette Sediments

D e fin itio n

Materials which pre-date the last regional glaciation are here namud the Bessette Sediments. They are considered to be of non-glacial origin and consist of (1) a lower unit of coarse gravel; (2) a middle unit of sand and silt containing shells of mollusks, lenses of peat, and a thin layer of volcanic ash; and

(3) an upper unit of gravel and sand. Exposures of these sediments are found widely distributed in the major valleys of the area and are inferred to underlie considerable parts of the lowlands south o f C h erryvllle and ea st and north of Lumby. S ectio n s exposed a t the mouth of Latewhos Creek (Figure 14) and in the v a lle y of

Bessette Creek (Figure 16) are considered to be type localities for the Bessette Sediments as defined and used in this report. The distribution of exposures of the Bessette Sediments Is shown in

Figure 15.

45 Figure 14. Bessette Sediments exposed at the mouth of Latewhos Creek. (Top) Sandy till overlying upper sand and gravel unit which has been faulted and locally Incorporated Into till. (Bottom) Lower gravel unit and middle silt unit of Bessette Sediments. S3

•4 ISO

119 * 0 0 ' l i t 30

*0 .40

130

35 LUMBY *o 3 0 TO to

75

Figure 15. Map shoving distribution of surface exposures of Bessette Sediments within study area. Small open circles mark locations of exposures; numbers indicate approximate minimum thickness of exposed strata in feet. 49

Nature of Deposits

Latewhos Creek

At the mouth of Latewhos Creek, and In Iso la ted exposures within the Shuswap Valley south of Mabel Lake, gravel beds as much as 25 fe e t th ick underlie the middle and upper u n its o f the

Bessette Sediments. Although the base of the beds has not been seen in any of the exposures, the absence of nearby bedrock outcrops suggests that thick unconsolidated deposits may lie below those that are exposed.

The lower unit at Latewhos Creek is a poorly-sorted pebble and cobble gravel that d isplays no apparent stru ctu re and i s oxidized to a yellowish brown (Munsell soil color 10YR 5/8) color.

Clasts range from half an inch to more than six inches in diameter; the medium- to coarse-grained sand matrix has a median grain diameter of 0.32 mm. The clasts are predominantly of local origin, consisting of 19 per cent granitic rocks, 13 per cent high-grade metamorphic rocks, 24 per cent volcanic rocks, and 44 per cent various low-grade metamorphlc rocks.

A small borrow pit two miles south of Latewhos Creek exposes approximately 35 feet of moderately well-sorted medium to coarse pebble gravel with lenses and beds of medium-grained well-sorted light brownish gray (10YR 6/2) sand. Unlike that at the Latewhos

Creek section, the gravel unit here is unoxidized and pebbles are generally fresher and little decomposed. Scattered Irregular pods of silt and till are found near the base of the gravel. The sandy 50

lenses and Interbeds, which are thick and Irregular near the base of the exposure, become thinner and more abundant upward In the section. In neither of the exposures Is there any evidence of deformation of the sediments. The stratlgraphlc relationship between the gravels at the two localities is not certain, though they may be equivalent.

The lower gravel unit at Latewhos Creek is overlain with sharp contact by a unit that Is mostly gray (5Y 6/1) laminated slit. Near the base, this unit consists of layers a fraction of an inch to one Inch thick of silt, clayey silt, and fine sandy clayey silt. Individual layers are graded and are themselves composed of numerous laminae. The thickness of the laminae and the graded units varies widely, and nowhere does the silt have the regular laminated appearance of true varves. Near the top of the unit, the silt layers thicken to nearly one foot, and coarser silt and sand replace the finer materials seen near the base. Approximately 70 feet above the base, the silt grades Into sandy sediments that are horizontally-bedded and display small-scale cross-stratlficatlon.

The silt, where It grades Into the upper sand, is dark gray

(5Y 4/1) in color, finely-laminated, and Intercalated with thin layers of strongly-oxidized coarse sand. The upper sand is 40 feet thick in the exposed section and is comprised predominantly of muscovite and angular to sub-angular grains of quartz and feldspar. The sand is overlain unconformably by dense gray

(10YR 5/1) sandy till. The contact between the till and the sand 51

Is Irregular and marked by relief of as much as ten feet. Bodies

of sand have been Incorporated into the till, and below the till

the sand has been deformed.

Bessette Creek

Stream banks on Bessette Creek two and a half miles west of

Shuswap Falls provide excellent exposures of the middle and upper

units of the Bessette Sediments (Figure 16). The thickness of the

exposed sediments here ranges from 150 to 200 feet. In the lower

35 feet of this succession, alternate layers of dark gray (10YR 4/1)

and grayish brown (10YR 5/2) silt and clayey silt are intercalated with beds of fine to coarse sand that is generally highly oxidized

and displays Bmall-scale cross-bedding. Silt layers near the base

of the succession contain scattered shells of mollusks. The shells

are broken so that identification of most speclrens is impossible.

The list of identifiable genera includes Oxyloma, Succinea,

Vertigo, and Fossarla; specimens of Plsidium sp. are present but

not common. The silty strata also contain finely disseminated

bits of charcoal and thin dark reddish brown (5YR 3/3) seams of

p ea t.

A layer of volcanic ash approximately one-half inch thick

occurs within this succession of interbedded silt and sand, The

ash is white (10YR tt/1) in color and consists of glass shards and

whole and broken euhedral crystals of plagioclase, hornblende,

orthopyroxene, m agn etite, and minor amounts o f garnet and zircon Figure 16. Bessette Sediments exposed at Bessette Creek two miles west of Shuswap Falls. Detail of stratigraphy Illustrated In diagram. Lacualrlna vanaar

,rr^n. Till

Oraval

Croii-baddad tand

lamlnafad silt

Sill and •and

aih 54

(Table 1), The Index of refraction of the glass ranges between

1.515 and 1.517, which indicates a rock of dacitic composition

(George, 1924).

Approximately 35 feet above the base of the exposed sediments, the silt-sand sequence grades into a succession of regularly-* laminated gray (5Y 6/1) silt. Plant material collected from this transitional zone has provided a radiocarbon date of 19,100 ± 240 years B.P. (GSC-913).

The thickness of the laminated silt varies between 45 and 60 feet in the Bessette Creek sections. These sediments are compact, generally well-sorted, and form horizontal beds one to three Inches thick. They are gray (7.SYR N5/) to dark gray (7.SYR N4/) in color when wet and light gray (7.SYR N7/) when dry. Mechanical analyses of the s ilt show a range of median grain diameter between

0.008 mm. and 0.012 mm., and so r tin g c o e f f ic ie n t s between 1.92 and

2.34. Concretions and concretionary layers are common along bedding planes, notably in exposures of dry, light-colored silt.

An eroslonal contact of minor relief separates the silt from overlying beds of sand and gravel. Immediately above the silt is approxim ately 30 fe e t of interbedded medium to coarse sand and cobble and pebble gravel that displays large- and small-scale current-bedding. This u n it grades upward in to 40 fe e t of p o o rly - sorted cobble gravel and coarse sand. Pebble counts in the upper gravel show 24 to 28 per cent granitic rocks, 21 to 33 per cent high-grade metamorphlc rocks, and 11 to 20 per cent volcanic rocks, 55

TABLE 1

PETROGRAPHIC PROPERTIES OP OLYMPIA INTERGLACIAL VOLCANIC ASH

B essette Meadow Creek Cherryville Creek

Per cent light m inerals 99% 99* 99* G lass 73* 72* 69* Plagioclase 23 25 28 Quartz 4 3 3

Per cent heavy m inerals trace 1* 1* Hornblende 38** 42* 34* Orthopyroxene 16 14 19 M agnetite 42 38 43 Zircon 2 2 3 Garnet 1 0 1 Other 1 0 0

Range of index of refraction of glass 1.515- 1 .5 1 5 - 1 .5 1 7 - 1.517 1.517 1.522

Per cent of mineral in heavy mineral assemblage 56 with the remaining percentage comprised of various low-grade metamorphlc rocks.

Cherr/vllle

Exposures of the Bessette Sediments elsewhere In the area

display much the same character as those deposits already described.

Variations In thickness, texture, and llthology of the materials

reflect local conditions of the sedimentary environment. One other

locality, however, is noteworthy for the presence there of volcanic

ash. Shallow roadcuts on Highway 6, one mile west of Cherryvllle,

expose colluvlal deposits of fine sand and silty sand that consti­

tute the materials of an accretion-gley. Volcanic ash in this soil

is petrographlcally similar to the ash at Bessette Creek (Table 1),

so the period of time represented by the soil is considered to be

contemporaneous with the time of accumulation of the lower silts

at Bessette Creek.

Origin of Bessette Sediments

Most of the Bessette Sediments possess characteristics of

river floodplain and lacustrine deposits; colluvial material con­

stitutes a subordinate element of the exposed sediments. The

lower gravel exposed at Latewhos Creek and in the Shuewap Valley

south of Mabel Lake is of uncertain origin, although the presence

of local bodies of silt and till within this unit suggests that the

gravel may be glacial outwash. The coarseness of the gravel, the 57

poor sorting, and the presence of cut-and-fill structures support the Inference that these sediments were deposited by glacial melt- water streams.

The basal peat-bearing beds at Bessette Creek appear to have formed on a poorly-drained alluvial floodplain. The lenses and layers of peat, which in part represent in place organic growth, record the presence of shallow ponds or swampy ground. The mollusk8 collected from the lower silt unit at Bessette Creek all represent modern forms. All can be found presently in south-central

British Columbia, which indicates that climatic conditions during accumulation of the silt were not significantly different from conditions In the area today. The assemblage includes both fresh­ water and land individuals and is in accord with the suggestion that the basal succession at Bessette Creek accumulated in a flood- plain environment.

The overlying laminated s ilt contains no organic matter; neither is there any clastic sedimentary material in this unit coarser than silt. The contact with the underlying sand-silt unit is gradational and records a gradual change in the sedimentary environment. Information necessary to deduce the cause of the change from fluvial to lacustrine conditions is not provided by

the available exposures.

The upper surface of the laminated silt is eroded, so that direct measurement of the initial thickness of the unit is not possible. The silt below the erosion surface is oxidized to a 58 depth of as much as three fee:. This oxidation may simply reflect the presence of a perched water table on top of the Impermeable silt. Alternatively, it may represent the lower portion of a sub- aerlally produced soil. However, the absence of organic remains, root tubes, and disturbed bedding within or below the oxidized zone suggests the unlikelihood of a subaerial soil.

The upper sand and gravel unit at Bessette Creek le horizon­ ta lly -b ed d ed near I t s b a se, but grades upward in to str a ta d isp la y in g la r g e - and sm a ll-sc a le cross-b ed d in g. The sedim ents increase in coarseness from bottom to top of the unit. Current- bedding and imbrication of pebbles within the travel indicate streams flowing toward the southwest during deposition of the unit.

Although pebble lithologles do not provide conclusive evidence of provenance, they are not inconsistent with the suggested southward drainage. Foreset beds of equivalent deltaic sand exposed at

Shuswap Falls were likewise constructed by streams flowing to the southw est.

Deposition of the sand and gravel probably occurred under climatic conditions that were cooler or more temperate than they are today. The presence of fresh grains of readily weathered minerals in the sediments indicates that chemical weathering was slow relative to both the rate of erosion in the source areas and the rate of deposition of the sand and gravel. These materials may have accumulated slowly under temperate or cool conditions concom­ itant with gradual drainage of the lake. However, they may have accumulated more rapidly in response to glacial activity in the 59

mountains, or B till more rapidly as advance outwash from glaciers spreading into the lowlands.

Probable Correlative Deposits

Non-glacial sediments broadly similar in character to the

Bessette Sediments have been described by Fulton (1963, 1967, in p ress) in the Okanagan and South Thompson R iver System s. For the most part, these deposits are unnamed, and reference is made simply to "sub-till sediments", or in some cases to "pre-Fraser sediments".

Fulton (in Dyck and Fyles, 1963) has suggested the tentative corre­ lation of sub-till sediments in the vicinity of Kamloops with Quadra sediments of the Georgia Depression (Fyles, 1963). Wheeler (in Dyck,

Fyles, and Blake, 1965) has referred laminated blue-gray micaceous sandy silt beneath t ill at the settlement of Boat Encampment

(Figure 17) to an interstadlal or interglacial period prior to the last glaciation. In the Purcell Trench, to the east of the present study area, Fulton (1968) has recorded the occurrence of Olympia

Interglacial deposits between two tillB . Volcanic ash at three localities outside the present study area (Figure 17) may be equivalent to that found in the study area, though such equivalence has as yet been demonstrated petrographically only with the Purcell

Trench locality. 122 5 0

Ar*o of ttvdy

r « h a-M C'cwh Vernon

Figure 17. Map shaving location of exposed sections of Bessette Sediments and probable equivalent deposits outside of the study area that have provided radiocarbon dates. Numbers refer to localities and dates listed in Table 2. Locations of exposures in which volcanic ash has been observed are indicated by the word "ashM. Age and Significance of Deposits

Radiocarbon dates from south-central British Columbia assign

the Bessette Sediments to the Olympia Interglacial episode of

southwestern British Columbia and northwestern Washington (Armstrong et al. , 1965), These dates (Table 2) comprise two distinct groups

those that range between 20,000 years B.F. and 26,000 years B.P.,

and those that are greater than 30,000 years B.P. The date of

19,100 ± 240 years B.P. for peat from the Bessette Sediments is

clearly consistent with the first group of dates.

The group of older dates indicates that the nonglacial

interval represented by the Bessette Sediments began more than

43,800 years ago. Wood from a sequence of silt, sand, and gravel

at the Meadow Creek site In the Purcell Trench has provided radio­

carbon dates of 32,710 ± 800 years B.P. (GSC-493) and 33,700 ± 330

years B.P. (GSC-542) (Fulton, 1968). Volcanic ash within this

succession is petrographically similar to that found at the two

localities within the present study area (Table 1). Finite dates

as great as 43,800 ± 800 years B.P. (GSC-740) have been obtained

at the Meadow Creek locality from sediments at least in part equi­

valent to those that provided the dates of 32,710 and 33,700 years

B.P. It is therefore reasonable to suggest that deposition of the

Bessette Sediments began prior to 33,700 years B.P., and possibly

before 43,800 years B.P. Deposition of these sediments ended some­

time after 19,100 years B.P. TABLE 2

RADIOCARBON DAZES FROM BESSETTE SEDIMENTS AND CORRELATIVE DEPOSITS

Sample No. Radiocarbon Date Location M aterials C o llecto r

1. GSC-913 19,100 ± 240 B.P. B e sse tte Creek Peat within G. W. Smith alluvial silt and sand.

2. GSC-194 20,230 ± 270 B.P, Shuswap Lake Bark and twigs R. J . Fulton within lacustrine sand and slit.

3. GSC-173 21,500 ± 300 B.P. Boat Encamp- Plant detritus H. W. Nasmith ment within laminated sandy silt.

4. GSC-79* 25,200 ± 460 B.P. Kamloops, Freshwater shells R. J. Fulton GSC-79-2* 24,200 ± 290 B.P. Mission Flats within clayey silty sand.

5. GSC-479 >22,200 B.P. Salmon River Charcoal from R. J. Fulton s o i l on ta lu s and colluvium . (ash in soil)

6. GSC-477 21,630 ± 870 B.P. Gardom Lake Wood fragments G. W. Smith within silt. for R. J. Fulton TABLE 2 (continued)

Sample No. Radiocarbon Date Location Materials C o lle c to r

7. GSC-715 25,840 ± 320 B.P. Meadow Creek Wood fragments R. J . Fulton from gravel.

8. GSC-493 32,710 ± 800 B.P. Meadow Creek Wood w ith in R. J . Fulton silt, sand, and gravel-soil and ash.

9. GSC-542 33,700 ± 330 B.P. Meadow Creek Same R. J . Fulton

10. GSC-275 >32,700 B.P. Kamloops, Wood fragments R, J . Fulton Peterson Creek w ith in s i l t and sand.

11. GSC-258 >37,200 B.P. Merritt Fresh water shells R. J. Fulton within alluvial sand, s i l t , and g ra v el.

12. GSC-219 >39,700 B.P. Meadow Creek Peat within silt H. W. Nasmith, and sand. R. C. Thurber, and Associates.

13. GSC-716 41,800 ± 600 B.P. Meadow Creek Stump in F. J. Fulton p a le o so l. TABLE 2 (continued)

Sample No. Radiocarbon Date Location M aterials C o llecto r

14. GSC-733 41,900 ± 600 B.P. Meadow Creek Roots within R. J. Fulton p a le o so l.

15. GSC-720 42,300 ± 700 B.P. Meadow Creek Peat within R. J. Fulton silt and gravel.

16. GSC-740 43,800 ± 800 B.P. Meadow Creek Root within R. J . Fulton s i l t .

■k GSC-79-2 is a re-run of GSC-79. This date is anomalously younger than GSC-413 (>35,500 B.P.) which occurs stratigraphically higher in the same exposure. Fulton suggests that the discrepancy may result from secondary deposition of modern carbon. Armstrong and others (1965) define the Olympia Interglacla-

tlon as extending from at least 36,000 years B.P. to the beginning of the Fraser Glaciation, between 15,000 years B.P. and 24,500 years B.P, The general correspondence of these dates with those

from the present study area and adjacent areas permits the conclu­ sion that the Bessette Sediments represent the same non-glacial

interval as do the Olympia Interglacial sediments of southwestern

British Columbia and northwestern Washington. GLACIAL STRATIGRAPHY - FRASER GLACIAL DEPOSITS

Lumby T i l l

D e fin itio n

The name Lumby T ill Is applied to deposits of the last

(Fraser) stage of regional glaciation. Typical Lumby deposits occur throughout the area, but are best exposed in the Bessette Creek

Valley north of Lumby. The tills comprising the ground moraine of the area have yielded no evidence of large differences of age or of distinct substages of glacial advance or retreat; they are thus considered to relate to a single stage of glacial advance and retreat. As here defined, the Lumby T ill constitutes only those materials deposited by glacial ice and do not include materials related to late stages of glacial occupation and retreat. This latter group of deposits comprises the Monashee Sediments and w ill be discussed In a subsequent section of the report.

Nature of Deposits

The Lumby T ill Is a very compact unsorted and unstratlfled mixture of pebbleB and cobbles In a matrix of silt and sand. Most of the Included stones are of pebble and cobble size; boulders are

66 67 p resen t but not conmon. The t i l l ranges In th ick n ess from a few feet to as much as 40 feet, but is generally five to ten feet thick within the valleys. On the uplands and hlllslopes it is generally thinner and less continuous, ranging from a patchy veneer to approximately 10 feet in thickness. Dry till near the surface is o liv e gray (5Y 5 /2 ) to grayish brown (10YR 5 /2 ) , and commonly breaks into horizontal plates. Moist till at greater depths is dark gray (5Y 4/1) and somewhat softer, but nonetheless w ill main-* tain vertical faces. Compositionally and texturally the till closely reflects the underlying bedrock and unconsolidated deposits.

The till is generally calcareous and effervesces freely in dilute hydrochloric acid. The depth at which free carbonates occur is seldom less than three feet, and In many exposures leaching of carbonates extends to depths of about six feet. In the deeply- leached tills an horizon of secondary calcium carbonate concentra­ tio n i s commonly present at depths o f 30 to 40 in ch es.

Much of the morainic material displays no distinctive topo­ graphy but merely fills irregularities on the surface of the under­ lying bedrock or unconsolidated materials. Nonetheless, fairly extensive areas of drumllnized ground moraine occur on the uplands of the T r in ity H ills and south of the Shuswap R iver between Cherry- vllle and Shuswap Falls. No end moraines were seen in the area stu d ied . 68

Valley Tills

The Lumby T ill Is Inferred to form a continuous sheet within

the valleys of the Shuswap drainage. It Is generally mantled by

younger fluvial and lacustrine deposits or by extensive aprons of

alluvial fan debris, and Is exposed only where the overlying mater­

ial has been removed by erosion or artificial excavation.

Tex;turally, the tills within the major valleys form two

distinct groups (Figure 18) - sandy tills containing more than 48

per cent sand, and silty tills containing over 52 per cent silt and

clay. These two groups presumably reflect the nature of the under­

lying materials, though such cannot always be demonstrated. Lumby

tills at Harris Creek and Yard Creek, where the till overlies lacus­

tr in e B ilt and very fin e sand, are g ra v e lly loams and fin e sandy

loams containing abnormally little pebble- and boulder-size material.

Grainslze analyses of these tills reveal a concentration of material

In the silt and very fine sand sizes with a single mode at 0.032 mm.

Larger stones in the valley tills are typically subrounded,

whereas p eb b le- and sa n d -size m a teria l is commonly angular to sub-

angular. The subrounded nature of most large stones suggests

derivation from fluvial gravels rather than directly from bedrock.

This relationship Is particularly evident in the case of tills from

B e sse tte Creek and Shuswap F a lls (Figure 1 9 ). Samples o f t i l l from

these localities contain 25 to 40 per cent of gravel and boulders,

and grain-slze analyses reveal a large concentration of material In

the medium to coarse sand range. Some of the gravelly tills are Figure 18. Mechanical analyses of the <2 nua. size fraction of Lumby tills. Sand, silt, and clay are defined in terms of the Wentworth grade scale. O Silty valley tills • Sandy volley tills x Upland tills

•Illy

silty /\ '»* " A ll!

Sand Silt Figure 19. G ravelly t i l l exposed at Shuswap Falls. The till overlies the upper unit of the Bessette Sediments and contains as much as 40 per cent of gravel from the underlying sediments. 72

bimodal with concentrations at 0.1 to 0.5 ran. and 10 to 20 ran., which implies that sand and gravel from the upper unit of the

Bessette Sediments has been incorporated into the till.

By way of contrast, samples of tills from major tributary v a lle y s are commonly bouldery, and the la rg er ston es are angular to subangular. T ill in the valley of Tsuius Creek (Figure 20) contains 30 to 40 per cent of boulders that are angular to sub- angular and commonly s tr ia te d . There i s l i t t l e evidence th at any of the coarser material of the till here has been derived from water-laid sediments.

Pebble counts have been made on valley tills throughout the study area (Table 3). Their value in determining provenance of the tills is limited, however, because the bedrock geology is com­ plex and is as yet only roughly mapped. For the most part, the t pebble counts reflect the lithology of the underlying bedrock.

However, in some cases, the presence of volcanic rocks (Kamloops

Group) or granitic rocks (Coast Intrusions) in the till was used to determine the provenance of the till and the probable direction of ice movement.

The Lumby T i l l commonly d isp la y s le n se s of p o o rly -so rted sand, silt, and pebble gravel. In most places the lenses are a fraction of an inch to a few Inches thick, and are considered to be of only local extent. Exposures of till near the mouth of Ireland

Creek and in one exposure on Bessette Creek show lenses and beds of till intercalated with sand, gravel, and silt several feet thick. 73

TABLE 3

PEBBLE COUNTS OF LUMBY TILLS WITHIN THE SHUSWAP RIVER DRAINAGE

Location Percentage of Rock Types

G ranite Gneiss S c h ist Basalt & R h y o lite AndesIte A r g illit e Q u artzite Limestone Other

Sugar Lake 61 0 14 4 0 6 5 0 10 Cherryville 57 9 11 3 2 8 4 3 3 Monashee Creek Valley 14 0 5 16 21 17 2 25 0 Cherry Creek Valley 13 3 5 21 0 52 4 1 1 Relswig 45 24 6 9 5 2 7 1 1 Shuswap F a lls 56 14 4 7 2 8 1 5 3 Bessette Creek 32 3 2 10 1 26 4 16 6 (upper till) Bessette Creek 33 2 2 9 4 28 5 17 0 (lower till) Lumby 38 6 7 19 2 20 2 6 0 Creighton Valley 20 8 5 29 14 11 11 0 0 (e a st end) Creighton Valley 22 21 11 12 6 10 18 0 0 (w est end) Blue Springs Valley 56 0 4 14 3 2 6 14 2 Harris Creek 57 0 3 22 4 8 0 6 0 Trinity Creek Valley 14 6 3 13 0 61 1 0 2 Putnam Creek Valley 58 4 14 3 2 10 7 0 2 Figure 20. Bouldery till exposed In the valley of Tsuius Creek. Angular and subangular boulders and cobbles c o n s ti­ tute 30 per cent of the till at this lo c a lit y . 75

Two tills at Ireland Creek are separated by a sequence of

Interbedded sand and gravel and silty till. The thickness of the intertill succession is 25 to 35 feet; sand and gravel is as much as 15 feet thick, and individual layers of till are as much as four feet thick. Pebble counts and fabric analyses of the two bracket­ ing tills are similar, and there is no clear indication of any significant lapse of time between deposition of the two tillB .

The interbeds of sand and gravel probably represent materials washed in from adjacent hillslopes during oscillations of an advanc­ ing ice front. On the other hand, they may have been produced as a result of basal melting of glacial ice.

At Bessette Creek, two sheets of loamy till are separated by as much as 40 feet of intensely sheared silt and sand that contains lenses and beds of coarse sand and till. The lower till overlies gravel of the upper unit of the Bessette Sediments. Pebble counts of the two tills are nearly identical (Table 3), and the fabrics of pebbles in both tills trend southeast.

The significance of this intertill succession at the

Bessette Creek locality is not entirely clear. Similar relation­ ships are not exposed elsewhere in the Bessette Creek Valley, and the thick "glacial" sequence here is in marked contrast with generally thin accumulations of till throughout the eastern end of the valley. A water well drilled at the west end of the Bessette

Valley Indicates a similar till sandwich and shows that the upper till is 30 feet thick. The relationship between the tills and the 76

intervening silt-till-sand succession suggests that ice advancing across the western end of the valley blocked drainage, creating an

ice-marginal lake. Minor fluctuations of the advancing ice front

into this lake are recorded by the presence of lenses of till and

coarse sand within the lacustrine silt and sand. Eventually the

ice advanced over the site of the lake and spread eastward in the valley and southward over the adjacent uplands. The presence of

the local lake and the buoying effect that it would have had on the

advancing ice might afford at least partial explanation for the

unusually thin till sheet in the eastern part of the Bessette Creek

V a lley .

The till-in tertlll relationships recorded in the valley of

Bessette Creek might alternatively be explained in termB of retreat­

ing ice. However, the conditions required to create the ice-marginal

lake in th is p o s itio n , and the nature and d istr ib u tio n of t i l l s

within the valley do not seem as reasonably explained by this

alternative.

Upland TIII b

Lumby T ill constitutes the major part of the surficial deposits

of the uplandB. The morainic materials range from isolated patches

several inches in thickness to extensive valley fillings a few tens

of feet thick. Texturally, the tills are extremely variable (from

stony, sandy tills to heavy-textured, clayey boulder tills) and

closely reflect the character of the underlying bedrock. Most 77 commonly the upland t i l l s occur In d ep ression s and v a lle y bottoms and on the lower p ortion s of mountain s lo p e s . On the Shuswap

Erosion Surface north of Mount Mara and south of Creighton Valley, the till occurs as a relatively uniform blanket of drift generally less than ten feet thick. In local hlllslope positions, as on the southern slopes of the Silver Hills west of Cherryville, and extensively on the high valley sides of Harris Creek, till overlies thick deposits of unconsolidated material. In many of the upland valleys and lower valley slopes, till is mixed with colluvlal material very similar in appearance to the till itself, and very difficult in most cases to distinguish from the till.

Most deposits of upland till do not display any distinctive constructional topography. However, a broad belt of hummocky till extends across the narrow upland surface north of Creighton Valley eastward to Echo Lake. Isolated drumllnold ridges occur along the southern slopes of the Hilton Upland south of Cherryville. On the

Trinity Hills upland west of Mabel Lake the till surface is marked by numerous drumllnold ridges averaging half a mile in length, a quarter of a mile in width, and 100 to 200 feet in height.

The tills of the uplands are mostly Btony sandy loams

(Figure 1 8 ), but some are loams and sandy clay loams. The sandy nature of most of these tills is reasonably attributed to their derivation from a mlxed-metamorphlc terrane. Local variations in the texture of the upland tills can be clearly related to the lithology of the adjacent or underlying bedrock. For example, till from the uplands north of Lumby is generally very dark gray 78

(7.5YR 3/) silty clay loam with abundant fragments of very dark gray phylllte derived from the highlands Immediately west of the study area. This till Is markedly different from the till on the upland north of Echo Lake, which Is a sandy clay loam and contains numerous pebbles and cobbles of granitic and gneisslc rocks.

The upland tills contain a higher percentage of pebbles and boulders than do the valley tills, and the sandy upland tills are generally more stony than the more heavy-textured tills. Most stones In the upland tills are angular fragments of the local bed­ rock, though subangular to rounded erratic stones are found in most samples.

Monaahee Sediments

D e fin itio n

The Monashee Sediments constitute those deposits that accu­ mulated during late stages of glacial occupation and glacial with­ drawal. These deposits are separated from those of the Lumby T ill because they reflect an Important change in the character of the deposltional environment. The Lumby T ill was deposited by actively- moving glacial ice, whereas the Monashee Sediments reflect condi­ tions of stagnant or dead glacial ice. Any ice motion that may have occurred during accumulation of these sediments Involved only secondary spreading of Bteeply-sloping residual ice masses. During deposition of the Monashee Sediments, the ice was largely confined 79

to the individual valleys, the uplands were ice-free, and meltwater exerted an increasingly important role in the sedimentary environ­ ment.

The Monashee Sediments include materials that were deposited in streams and lakes surrounded by glacial ice, confined between ice and higher ground, or controlled by the presence of ice within the drainage system. Locally it can be demonstrated that these sediments accumulated on top of stagnant or dead ice that was sub­ merged beneath water of an ice-dammed lake, Some of the Monaehee deposits display distinctive ice-contact topography, whereas others are perched on hillsides in such positions that the streams or lakes in which they accumulated must have been confined by glacial ice. Lateral drainage channels (Mannerfelt, 1949) and indistinct shorelines were also formed in proximity to glacial ice and are some of the most useful indicators of the pattern of deglaclatlon

(Kujansuu, 1967).

Deposits formed In contact with glacial ice are commonly gradational into sediments that were deposited away from the direct influence of the ice. These latter deposits generally occur as terraced or perched sediments and record higher positions of base- level, which were controlled in most cases by the presence of ice within the major valleys. Any attempt to separate these two groupB of deposits on a temporal basis involves the establishment of arbi­ trary boundaries that are, at best, difficult to define and con­ fusing to utilize. For this reason, deposits of the "ice/water" 80 environment (Fulton, 1963) and deposits of the "water" environ­ ment are here considered to be a continuum reflecting the gradual change from glacial to non-glacial conditions.

Nature and Distribution of Deposits

MonaBhee P a ss-C h erry v ille Area

During deglaciation of the study area, uplands were the first areas to become ice-free, and the ice margin down-wasted toward the valley bottoms. The ice sheet disappeared from the area in a northerly direction, so that the southern uplands were the first to emerge from beneath the ice. When the ice front had retreated to the position of the drainage divide bordering the southern margin of the area, meltwater escaped southward through cols at successively lower elevations. The lowest of these Is Monashee

Pass at an elevation of 3935 feet above sealevel. Lateral drainage channels on the valley sides south of Monashee Pass outline the pattern of ice withdrawal northward and toward the valley bottom.

As the Ice continued to retreat, drainage became Impounded, blocked on the north by Ice and on the south by the higher ground of the d iv id e.

At the confluence of Monashee Pass Creek and Monashee Creek, kame deltas record the levels of three major pro-glacial lakes that formed in the lowland south and east of Cherryville (see p. 133).

Beaches associated with these lake levels can be traced into the 81

valley of Cherry Creek (Figure 21), and small deltas perched at the mouths of tributary streams have been found throughout the

Cherryvllle-Hllton area and In the valleys of Cherry and Monashee

Creeks. The most prominent beach occurs at an elevation of 2690 feet (Lake Cherryville - Hilton Stage), approximately 250 feet above the present valley floor. The two lower lake levels at 2580 feet (Lake Cherryville - Cherry Creek Stage) and 2500 feet (Lake

Cherryville - Currie Creek Stage) are less well-defined. These lower lakes were probably either of shorter duration or were less extensive and without adequate fetch to produce distinct beaches.

The perched deltas associated with these lakes are similar in form to modern deltas. They are extremely variable In outline, and range from a few hundred feet to a mile across their front margin.

The top surfaces of the deltas are horizontal or slope very gently toward the center of the valley. The deltas are bordered on their frontal margins by clearly-defined scarps which are 10 feet to 200 feet high and slope away from the front of the delta at an angle of between 5 and 30 d egrees. The su rfa ces of some of the higher d e lta s are marked by k e ttle h o le s , and the fr o n ta l scarps of th ese higher deltas are scalloped or poorly-defined.

All but the thinnest deltaic deposits display an Internal

"delta structure" (Figure 22). The topset beds are 1 to 10 feet

thick and generally show prominent horizontal stratification. In most instances the topset sediments truncate the underlying foreset beds, although in a few places individual topset strata are 82

Figure 21, Beach and delta terraces In Cherry Creek Valley. Looking southeast Into valley o£ Currie Creek. Beach visible on hillside at right of photograph records stand of lake level at 2690 f e e t . Figure 22. Internal structure of delta terrace. Foresets and bottomsets clearly visible in foreground; topsets are exposed at back of pit. 84

traceable downward Into the foreset beds. The foreset beds dip at 10 to 25 degrees and range up to 50 feet In thickness.

The deltaic materials are variable In texture, but generally consist of Interbedded coarse and fine sand and silt. Some deltas are composed entirely of well-sorted fine micaceous sand, while others are predominantly coarse sand and gravel. Cross-bedding and ripple marks are common in the finer deltaic sediments. There is generally no slumped or contorted bedding In these sediments, though a Bmall delta one mile southeast of Hilton is pitted with several closed depressions, and the poorly-sorted delta sediments are highly disturbed.

Both kettled and undisturbed silts associated with the Ice- dammed lakes are widespread In the southeastern sector of the area.

These silts are at least 200 feet thick In the Cherry Creek Valley

and throughout the lowland southeast of Cherryville. Generally, however, the silts range in thickness between 30 and 50 feet, and

commonly occur as a veneer less than 10 feet thick over bedrock

and till. In the Cherry Creek Valley the silts are regularly-

laminated; clay-rich bands alternate with bands rich In silt-size material (Figure 23). The base of each clay band Is well-defined

in that the dark-colored clay contrasts sharply with the lighter-

colored silt below. The upper contact, on the other hand, is

indefinite with the upper portion of the clay band grading upward

into silt. Nowhere do these rhythmltes, or varves, display Ice-

contact deformation. Wherever they occur, the rhythmltes increase 85

Figure 23. Top of succession of varved lacus­ trine silts in valley of Cherry Creek. Thickness of varves above pick is approximately one inch. 86

in thickness from the top to the bottom of an exposed section.

Stream banks on the north side of Cherry Creek, approximately five miles northeast of Cherryville, expose at least 225 feet of lacustrine sediments. These sediments are predominantly silt and clayey silt, Analyzed samples contain less than 25 per cent clay and between 5 and 12 per cent sand-size material. Silt bands near the top of the section are considerably finer-grained than those near the base, and the individual varves range in thickness from half an inch to two feet near the middle of the section. The base of the exposed section is comprised of massive sandy silt which contains scattered angular boulders and lenses of coarse sand.

The nature of the lacustrine materials within the Cherry Creek

Valley is markedly different from that of the silts which cover the upland in the vicinity of Hilton. These latter sediments consist of irregularly alternating layers of silt and fine to medium sand more than 30 feet thick. Shallow roadcuts expose the internal structure of these sediments and reveal that at least locally they are slumped and con torted . S cattered sm all k e t t le h o les mark the general f l a t surface of the lake deposits.

The lacustrine deposits described above are confined largely to the lowlands north of the confluence of Monashee and Heckman

Creeks and e a s t of the ju n ctio n of Ferry Creek and the Shuswap R iver.

Lacustrine sediments mixed with colluvlal material and till occur as a discontinuous veneer along the south w a ll of the Shuswap V a lley west of Ferry Creek. The patchy distribution of the lacustrine 87

sediments may indicate that lakes in the Cherryville-Hilton lowland were continuous along the ic e margin to Shuswap F a lls , though more

likely these sediments record deposition of sediment in small dis­

connected ice-marginal ponds. The lacustrine sediments have not

been found along the Shuswap V alley south of Sugar Lake, in d ic a tin g

that ice blocked this valley during the existence of the lakes in

the vicinity of Cherryville.

The v a lle y between Ferry Creek and Shuswap F a lls contains only

scattered and poorly-defined glacio-fluvial and glacio-lacustrine

d e p o sits. Numerous la te r a l drainage channels mark the north w all

of the valley, and several larger overflow channels are cut into

the southern valley side. The latter group of channels were outlets

for the various levels of the lakes impounded in the vicinity of

Cherryville (see p. 133). Narrow kame terraces and small irregular

gravel h ills occur along the southern wall of the valley between 150

and 300 feet above the present valley floor. Because of their

perched position, they were most likely deposited by streams flowing

between the valley side and the stagnant ice. The original extent

and configuration of the kame terraces have been partly altered by

subsequent alluvial fan deposition and recent stream erosion.

Sugar Lake V alley

Kame terrace deposits form a thick fill within the valley of

the Shuswap River for a d ista n ce of approxim ately four m iles south

of Sugar Lake. These deposits consist predominantly of pebble and 88 cobble gravel, but Include beds of silt and sand. Most of the terrace deposits are horizontally stratified, although some expo­ sures display slumped and contorted bedding. Fifty-two per cent of the pebbles in the terrace gravels are granite (Table A), reflecting the proximity of the Sugar Lake granitic intrusive and indicating that the gravels were deposited by southward-flowing streams. The gravels decrease in grain-size toward the south, grading from cobble and pebble gravel to pebbly sand. The surface of the kame terrace slopes southward with a gradient that is steeper at the head of the terrace and varies between 50 and 70 feet per mile.

The kame terrace is undercut at its downstream end by younger gravel terraces which stand from 5 to 70 feet above the present floodplain, and can be traced to Shuswap Falls where they merge with terraced deltaic deposits. The stream terraces appear to be remnants of at least five constructional surfaces that sloped at about the same gradient as the present valley floor.

The stream terraces consist principally of well-rounded pebble and cobble g r a v e l, sandy g r a v e l, and sand con tain in g l i t t l e interstitial silt or clay, but in many places they contain or are covered by beds of clay, silt, and stony sandy silt. Pebble counts o f the terrace m a teria ls between Sugar Lake and Shuswap F a lls

(Table A) show a general decrease in the amount of granitic consti­ tuents and an increase in the percentage of mixed metamorphic rocks in a downstream direction. The pebble lithologies of modern 89

TABLE 4

PEBBLE COUNTS OF MONASHEE AND EAGLE VALLEY SEDIMENTS WITHIN THE SHUSWAP RIVER DRAINAGE

Location Percentage of Rock Types

(0 CO (b -H TJ 0) Q) 0)0)0) a 3 <-cj w

o2 |ss a o mm -5353 < <; s i O' s hj os

A. Monashee Sediments

Shuswap R iver V alley 18 0 26 20 0 0 9 15 12 (12 mi. north of Sugar Lake) Shuswap R iver V alley 68 0 17 10 2 2 0 1 0 (5 ml. north of Sugar Lake) Sugar Lake 52 0 2 6 14 3 8 8 0 7 Cherryville 45 0 5 16 7 3 10 9 5 0 Monashee Pass 2 0 12 2 15 13 8 10 34 4 Monashee Creek Valley 5 0 3 2 28 9 48 2 3 0 Shuswap R iver V alley 42 0 11 19 8 4 7 4 2 3 (3 ml. west of Cherryville) Shuswap F a lls 55 0 6 8 4 4 8 2 6 7 Vance Creek V alley 55 0 3 0 15 1 16 2 4 4 Blue Springs Valley 22 0 0 0 45 5 10 7 10 1 Creighton Valley 32 0 3 4 25 9 4 7 9 7 (e a st end) Creighton Valley 20 0 0 5 49 12 4 2 1 7 (w est end) Putnam Creek V alley 15 0 6 3 14 0 59 1 0 2 90

TABLE 4 (continued)

Location Percentage of Rock Types

to to 0 •H •o 0) a) 01 4 -1 to 4-» ij a 0) s to Si tI •H 4-1 H to +J •H iH *4 r-t o m q d 0) 0) « i*.. 0) n U J3 1 3 Q S) 4-* a 3 o W o V) « 3 I O'

Trinity Creek Valley 34 0 0 2 7 0 50 5 0 2 Wap Creek Valley 21 13 59 0 3 0 0 4 0 0 (south end) Wap Creek Valley 20 17 55 1 4 0 0 1 0 2 (north end) Eagle Pass 17 7 64 0 5 0 0 3 0 4 Three Valley 27 4 54 2 1 0 2 2 0 8 Perry River Valley 18 12 51 2 4 0 0 4 0 9 Eagle River Valley 17 10 52 2 10 0 1 3 0 5 (a t Camble)

B. Eagle V alley Sediments

Shuswap R iver V alley 67 0 11 3 3 4 0 1 2 9 (5 mi. north of Sugar Lake) Shuswap River V alley 23 0 9 5 18 9 14 4 16 2 (at Shunter Creek) Cherryville 57 0 1 13 2 5 15 3 2 2 Monashee Creek Valley 8 0 9 4 35 4 36 1 2 1

Shuswap FbII b 49 0 9 17 9 3 4 2 1 6 Trinity Creek Valley 28 0 3 5 4 4 43 8 3 2 Wap Creek Valley 15 16 56 0 6 0 3 2 0 2 (south end) 91

TABLE 4 (continued)

Location Percentage of Rock Types

<0 to 01 *H ♦a o) <11 0! ill V n w U H (I W U H nH H N 4J •H ,£) i-j (-1 O Q H O O ) i-i U CO U 9 « s ji s S I ! * * * * o

Hap Creek Valley 16 14 63 1 0 0 0 4 0 2 (north end) Eagle Pass 14 11 57 4 8 0 0 4 0 2 Three Valley 25 8 47 4 3 0 0 1 0 12 Eagle River Valley 19 13 57 0 6 0 0 1 0 4 (a t Malakwa) 92

floodplain sediments (Table 4) are similar to those of the stream terraces, suggesting that late-glacial drainage between Sugar Lake and Shuswap F a lls was e s s e n t ia lly as i t i s today.

R eiter Creek jo in s the Shuswap R iver approxim ately three m iles south of Sugar Lake. The kame terrace d ep o sits o f the Shuswap

Valley merge here with similar gravel deposits built at the mouth of Reiter Creek. Kame deltas and kame fans occupy successively higher levels above the terrace gravels within the Reiter Creek

Valley. The highest of these alluvial features occurs at an eleva­ tion of 2060 feet, approximately 800 feet above the present valley floor. The kame deltas and fans consist of poorly-sorted angular to subround gravel and sand. They are bordered on their distal edgeB by scalloped, irregular faces, and the higher kame deltas display pitted surfaces.

An abandoned channel, floored with thin and irregular deposits of sand and gravel, extends from the head of the Reiter Creek

Valley to the margin of the depression occupied by Sugar Lake. The floor of this channel lies at an elevation of 3400 feet. The channel and the fan and delta features in the Reiter Creek Valley appear to have formed when sloping ice filled the valley occupied by Sugar Lake and stagnant ice masses remained in the valley south of Sugar Lake. Meltwater streams draining through the channel deposited the series of deltas in ice-marginal lakes impounded by the ice that occupied the Shuswap River Valley. As the ice retreated toward the valley bottom, the channel into the Reiter 93

Creek Valley was abandoned and meltwater escaped directly down the valley south of Sugar Lake. Meltwater streams carrying large

volumes of gravel and sand flowed southward along the margins of

the stagnant ice that occupied the floor of the valley.

Prominent kame terraces occur along both sides of the Shuswap

River Valley north of Sugar Lake. The upper surfaces of these

terraces lie between 75 and 150 feet above the level of the Shuswap

River. Smaller kame terraces occur high on the valley sides, as

much as 700 feet above the valley floor.

Exposures in the kame terraces are generally few and poor;

at no place was a section sufficiently well-exposed to show collapsed

features In the stratified sediments. However, the geographic distri­

bution of the deposits and their surficial morphology indicate an

ice-contact origin. Although some erratic boulders up to 3 or 4

feet in diameter are present in the terraces, sediments generally

range in size from fine sand to small boulders 18 Inches in diameter.

Well-rounded cobbles 4 to 6 inches in diameter are most common.

Pebble counts (Table 4) of the kame terrace gravel show that the

sediments closely reflect the composition of the local bedrock and

substantiate the Inference that during glacier recession in the

Sugar Lake area, meltwater streams drained southward along the

ice margins. 94

Creighton Valley

Narrow kame terraces occupy valley-side positions along the northern margin of Echo Lake at the east end of Creighton Valley.

These terraces stand approximately 200 feet above the floor of the valley and have a gentle surface slope toward the west. A broad triangular bench at the head of the valley is rimmed with gravel

terraces that appear to have formed contemporaneously with those

in the Creighton Valley. The gravel benches extend for some dis­

tance southward up the valley of Ferry Creek and can be traced to a series of ice-marginal channels that slope westward along the hillslopes south of Hilton.

The highest kame terraces block the Creighton Valley west

of Echo Lake where Creighton Creek enters the valley from the southern uplands. Here the terraces extend into the valley of

Creighton Creek and merge on the opposite side of Creighton Valley with a hummocky bench that fills a narrow col and extends into the head of the Blue Springs Creek Valley. West of the valley-filling

bench, the terraces can be traced unbroken for a distance of about

two miles. S till further west they are covered and dissected by

several large alluvial fans and can be traced only as diconnected

terrace segments. At the west end of the valley, poorly-defined

benches of sand and gravel are overlain by laminated silt.

A low divide at the west end of Creighton Valley extends

southwestward from Creighton Valley to the valley of Harris Creek.

During deglaciation, a Bmall tongue of ice melted back through 95

this divide into Creighton Valley, and meltwater was discharged southward into the valley of Harris Creek. Small poorly-defined benches are perched along the walls of the divide, and the floor

of the valley is filled with silt and fine sand. A broad hummocky

sand and gravel bench extends across the southern end of the valley

and appears to have been built against stagnant ice that occupied

the valley of Harris Creek. A similar low-divide channel breaches

the upland between Creighton Valley and Blue Springs Valley. Ice

in this case withdrew into Blue Springs Valley and meltwater

drained into Creighton Valley.

Ice disappeared from Creighton Valley largely by stagnation.

The kame terrace gravels at the east end of the valley contain

32 per cent granitic pebbles and 25 per cent volcanic pebbles,

whereas the terraces at the west end of the valley contain 20 per

cent granitic pebbles and 49 per cent volcanic pebbles (Table 4).

The marked in crea se of v o lca n ic pebbles and the decrease of

granitic pebbles from east to west in the valley indicate that the

kame terraces were constructed by meltwater streams flowing west­

ward along the margins of the stagnant ice.

Throughout the eastern and central portions of Creighton

Valley, the terrace gravels are overlain by highly contorted,

massively-bedded silts that contain irregular bodies and lenses

of gravel and coarse Band (Figure 24). It appears, then, that as

ice receded from the valley, an ice-marginal lake formed at the

e a st end of the v a lle y and expanded in the wake of the ic e u n til 96

Figure 24. Slumped lacustrine silts at the west end of Creighton Valley. 97

it could drain first through the low divide into Harris Creek, and ultimately into the lowland south of Lumby.

Lumby-Bessette Creek Lowland

Late-glacial features in the Lumby-Bessette Creek lowland

include ice-marginal drainage channels and channel deposits, perched deltas and fans, and an extensive veneer of laminated lacuBtrine

s i l t .

Terraced deltas and alluvial fans at the mouths of Vance

and DeafieB CreekB, four miles north of Lumby, range in elevation

from 1640 feet to 2050 feet. The higher terraces are kame deltas

that were constructed into ice-marginal lakes at 1950 feet and

2050 feet. The lower terraces, ranging from 1640 to approximately

1800 feet in elevation, were built to grade with successive positions of a lowering local baselevel. Similar terraces at the mouths of Albers and Beaverjack Creeks occur at elevations as

high as 2600 feet; here the lowest kettled features are at an

elevation of 1850 feet.

Lateral drainage channels, channel deposits, and patchy

accumulations of lacustrine sediments are widely distributed

along the hillsides bordering the Lumby-Bessette Creek lowland.

These features are important since their distribution delineates

the pattern of ice withdrawal from the lowland (see Plate IA),

As ice retreated from the uplands, it separated into two long 98 valley tongues in the vicinity of Lumby. One tongue receded northward into the Mabel Lake Valley, the other withdrew westward into the Coldstream Valley.

A veneer of laminated silt, generally less than ten feet thick, covers most of the lowland below an elevation of 1800 feet. The silt is generally horizontally bedded and free of stones. Locally, however, these sediments are contorted, and in one field a boulder more than five feet in diameter has been removed from the silt.

The s ilt accumulated in an extensive ice-dammed lake, impounded by

the disappearing ice masses in the Mabel Lake and Coldstream

Valleys. The highest levels of this lake were controlled by out­

lets along the ice margin at the west end of the Coldstream Valley

(Fulton, in press). Continued ice retreat opened lower outlets

until the lake became part of the Okanagan Valley lake system

(see p. 138).

Mabel Lake V alley

Glacial retreat in the Mabel Lake Valley was mostly by

downwastlng of a narrow ice mass. Surficial deposits within the

re-entrant formed by Bigg Creek and Ireland Creek record a sequence

of events that is typical for most tributaries entering the Mabel

Lake Valley. The head of the Ireland Creek Valley Is floored with

mixed glacio-lacustrine sediments, till, and poorly-sorted gravel.

These sediments vary from horizontally-laminated lacustrine silt

to boulder clay comprised of angular boulders and cobbles in a 99

matrix of poorly-sorted sand, silt, and clay. This complex of sediments records deposition of material in shallow pro-glacial lakes formed around the margin of the retreating ice front. Perched deltas near the head of Ireland Creek Valley occur at elevations between 2300 and 2400 feet. One of these indicates that Taylor

Creek drained southward into the Ireland Creek Valley over the

2500-foot threshold before it assumed its present course northward toward Latewhos Creek.

Deltas at the mouths of Ireland and Bigg Creeks range in elevation from 1520 feet to 1690 feet. Deltas at elevations of

1660 feet and 1690 feet are believed to be equivalent to deltas at similar levels in the Lumby-Bessette Creek lowland and in the

Coldstream Valley. It is therefore inferred that the Coldstream

Valley lake extended at least this far into the Mabel Lake Valley during early stages of deglaciation. The absence of deltaic features above the 1690-foot level in the Mabel Lake Valley suggests that ice blocked the southern end of this valley while higher-level lakes existed in the Lumby-Bessette Creek lowland.

Kame deltas occur at the mouths of most tributaries entering the Mabel Lake Valley. TheBe features range in elevation between approximately 1700 feet and 2600 feet, though there is generally no correspondence between the elevations of delta terraces from one valley to the next. The altitudinal distribution of these features is shown schematically in Figure 25.

The head of Sowsap Creek and the v a lle y s o f Noisy Creek, Cr.

MA B “ ^

Dally Vardan c»- SaacK

Seal*: lin. = 4mi.

1700

Figure 25. Distribution of raised deltaic and fluvial features in Matel Lake Valley. Each dot represents the elevation of a raised feature constructed into higher levels of Mabel Lake. Dashed lines connect features built into the same lake level. Small open circles indicate positions of lake outlets. 1 0 1

K in gfish er Creek, and Cooke Creek were u t iliz e d as o u tle t channels by meltwater streams during stagnation of the ice tongue in the

Mabel Lake Valley. Numerous smaller channels in this vicinity record the progressive withdrawal of ice from the uplands toward the valley and the general northward retreat of the valley ice tongue. Deposits of the Monashee Sediments in the valley of King­ fisher Creek are indicative of the deposits found in many of the outlet channels.

Exposures on Kingfisher Creek, approximately four miles north of Hupei, reveal a succession of lacustrine sediments overlain un- conformably by fluvial deposits (Figure 26). The lacustrine sedi­ ments consist of regularly-laminated silt and fine sand which grade upward in to w e ll-so r te d micaceous fin e sand. The upper sand d isp la y s low-energy current-bedding and r ip p le marks and contains thin beds of coarse sand and fine pebble gravel. These sediments were deposited in a proglacial lake that formed when ice at the mouth of the valley impounded meltwater streams entering the head of the valley. During this time, ice occupied the Mabel Lake

Valley and a small tongue of stagnant ice remained in the ShuBwap

River Valley east of Cooke Creek.

When ice withdrew from the mouth of Kingfisher Creek Valley, the lake drained and a Beries of deltas were constructed by melt­ water streams at the mouth of the valley. An erosion surface with as much as ten feet of local relief separates the fine sand of the lacustrine succession from eight to ten feet of poorly sorted Graval and tand

Mlcaceout tand

Figure 26, Exposure of Monashee Sediments on Kingfisher Creek four miles north of Hupei. Detail of stratigraphy illustrated in diagram. 103 cobble and pebble gravel and coarse sand. The surface of the gravel forms a prominent bench that can be traced northward to a narrow gorge at the head of the valley and southward to a broad kame delta at the mouth of the valley. The kame delta stands at an elevation of approximately 1600 feet, and is the lowest ice- contact feature at the mouth of the creek. Lower delta terraces at the mouth of Kingfisher Creek are not kettled and range in elevation between 1300 feet and 1480 feet.

Organic material from the bottom of a small bog immediately north of Dolly Varden Beach has provided a radiocarbon date of

9280 ± 160 years B.P. (GSC-923). The bog sediments are underlain by lacustrine silt which was deposited in a small ice-marginal lake formed in the valley of Kingfisher Creek when ice s till occu­ p ied the Shuswap V alley w est of Mabel Lake. The date i s a minimum age fo r the withdrawal of ic e from the mouth of K in gfish er Creek.

Glacial retreat north of Mabel Lake is recorded by isolated kame terraces and ice marginal channels on the valley sides. At

the head of the valley, a broad kettled terrace was constructed

against ice that occupied the Eagle River Valley while meltwater

drainage from this valley was s till southward through the valley

of Wap Creek into the Mabel Lake depression. This terrace merges

downstream in the Wap Creek Valley with fluvial terrace deposits

that are not kettled. This highest terrace is undercut by younger

gravel terraces that stand from 10 to 60 feet above the present

floodplain and merge with terraced deltaic deposits north of Mabel 104

Lake (Figure 2 7 ). The stream terra ces are remnantB of four major constructional surfaces that sloped at about the same gradient as the present valley floor and were built to grade with the falling water level of Mabel Lake.

Trinity Creek Valley

Monashee Sediments in the Trinity Creek Valley consist of deposits of poorly-sorted gravel and sand that accumulated on and around the margins of bodies of stagnant ice that occupied the center of the valley. The sediments were deposited by streams draining the adjacent uplands, and they closely reflect the lithology of the local bedrock. Terraced alluvial fans and kame terraces occur along the valley sides and at the mouths of most tributaries entering the Trinity Creek Valley. Numerous kettle holes in the vicinity of Trinity Valley contain thick accumulations of silty clay, marl, and peat. Bog-bottom organic matter from one of these kettle holes has provided a radiocarbon date of 15,000 ± 300 years

B.P. (GSC-946), indicating that this portion of the study area was ice-free at least that long ago.

Streams draining the Trinity Creek Valley constructed kettled delta terraces at the mouthB of Sowsap and Christian Creeks while ice still occupied the Mabel Lake Valley. Therefore, retreat of the ice from the Trinity Valley area predates the events des­ cribed for the valley b of Ireland and Bigg Creeks. Likewise, kame deltas in the vicinity of Vance Creek appear to have been constructed Figure 27. Prominent delta terrace at southern end of Wap Creek Valley. Streams flowing southward in the Wap Creek Valley constructed the delta into a higher late-glacial level of Mabel Lake. Present elevation of the top of the delta is 1613 feet. 106 in part by streams draining the Trinity Valley area while ice s till occupied the Lumby-Bessette Creek lowland. It therefore appears that deglaciation of the Trinity Valley area also predates ice withdrawal from the Lumby-Bessette Creek lowland.

Eagle River Valley

Monashee Sediments within the Eagle River Valley record the disappearance of a tongue of ice by separation and stagnation. A body of ic e stagnated between Malakwa and the Shuswap Lake basin; a second ice mass melted from the vicinity of Clanwilllam eastward into the Columbia River Valley. A tongue of ice appears to have retreated into the Perry River Valley at Taft, and a large mass of ice stagnated between Endiver and Clanwilllam.

The highest ice-marginal channels at the west end of the

Eagle River Valley indicate that early meltwater drainage was toward the west. However, marginal channels and kame terraces below an elevation of approximately 2600 feet indicate that during later stages of deglaclatlon meltwater drainage was eastward. Kettled f lu v ia l and d e lta ic terra ces and is o la te d accum ulations of g la c io - lacuatrine sediments on the valley sides range in elevation between

1600 feet and 2700 feet. The stream and delta terraces below 1600 feet are not kettled and record deposition in an environment free of ic e .

Kame terraces at the mouth of Craigellachie Creek occur at elevations between 1700 and 2700 feet. Most of these features have 107

a surface slope toward the west and record meltwater drainage in that direction. In this portion of the valley there 1 b no indication of a reversal of meltwater drainage during deglaciation; it appears always to have been toward the weBt.

Meltwater channels at elevations between 3500 feet and 2500 feet slope southward along the sides of the valley south of Three

Valley Lake. A large kettled terrace fills the valley south of

Three Valley Lake (Figure 28). The terrace stands at an elevation of 1800 feet, 160 feet above the level of Three Valley Lake, and slopes southward with a gradient of approximately 35 feet per mile.

The terrace materials consist predominantly of rounded to subangular cobble gravel and fine to coarse moderately well-sorted sand, which is slumped and contorted. Irregular bodies of till and sheared lacustrine silt are Intercalated with the fluvial materials. The

terrace was constructed against ice that occupied the present site of Three Valley Lake when meltwater from the east end of the

Eagle River Valley drained southward through the Wap Creek Valley

rather than westward in to Shuswap Lake.

Organic material from the bottom of a kettlehole-bog on the

surface of the terrace at Three Valley has been radiocarbon dated

at 7640 ± 150 years B.P. (GSC-947). This date is a minimum date

for the disappearance of ice from Three Valley Lake.

East of Three Valley Lake the Eagle River is confined to a

narrow steep-walled valley, for the most part without significant

accumulations of Burficial materials. Landslide and taluB deposits Figure 28. Kame terrace at Three Valley. Looking southeast across Three Valley Lake to head of Wap Creek Valley. Mt. English in background. 109

are, however, particularly common In this part of the valley. Some appear to have been associated with the retreat of glaciers; some seem to have formed at the same time as adjoining fans, river terraces, etc.; others are clearly modem features. Many of them are not readily assignable to one or another of the units employed

In this report. The materials range from collections of loose angular blocks of rock to mudflow materials very similar to till or alluvial fan deposits. Locally these materials attain a thick­ ness of several hundred feet.

Isolated exposures of kame terraces consist of little more than a rubble of angular boulders and coarse, poorly-sorted gravel and sand (Figure 29). Approximately one mile east of Eagle Pass

(elevation - 1799 feet) a large flat-topped delta terrace forms a prominent bench projecting into the valley. The top of the delta stands at an elevation of 1950 feet. Coarse sand and gravel comprise the delta materials, which are evenly-bedded and dip between 15 and

20 degrees to the east (Figure 30). A series of lower terraces at elevations of 1900 feet, 1770 feet, and 1680 feet can be traced eastward into the Columbia River Valley. The 1950-foot delta terrace appears to have been built by meltwater streams issuing from ice

In the Eagle River Valley while ice in the Columbia River Valley

Impounded eastward drainage and created a sm all ice-m argin al la k e.

The lower terraces are not kettled and have gradients essentially the same as that of Tonkawatla Creek, which drains the eastern part of the Eagle River Valley. They probably relate to positions 110

Figure 29. Exposure In kame terrace on Highway 1 approximately three miles east of Three Valley. Boulder on lip of exposure in background is roughly 15 feet in diam eter. Figure 30. Delta terrace on Highway 1, one mile east of Eagle Pass. Foreset bedding dips between 15 and 20 degrees toward the east (right of photograph). 112

of higher baselevel within the Columbia River Valley during and following the disappearance of glacial ice.

Age of Monashee Sediments

Accumulation of the Monashee Sediments occurred after glacial ice had begun a general retreat from the position of its maximum stand. This phase of the glaciation of the area was a time-trans- gressive event, beginning first on the uplands and in the southern part of the study area, and ending when the last ice had disappeared from the northern valleys.

The glacial ice that deposited sediments of the Lumby and

Monashee units clearly extended far beyond the limits of the present study area. This ice covered the entire Interior Plateau, advancing as far southward as the State of Washington. It seems reasonable, therefore, to correlate the glacial deposits of the present study area w ith those in the Okanagan and Thompson drainage system s, and with due reservation to suggest the probable equivalence of these deposits with those in southwestern British Columbia and northwestern Washington.

Radiocarbon dates from bog-bottom samples collected within the study area indicate the following: (1) uplands and highest valleyB in the central portion of the area were free of ice by at least

15,000 years ago (GSC-946); (2) ice had receded from the mouth of

Blue Springs Creek prior to 10,200 years ago (GSC-905); (3) the ice 113

tongue that blocked the Shuswap R iver V alley w est of Mabel Lake had withdrawn from the mouth of Kingfisher Creek by 9280 years ago (GSC-923); and (4) ice had retreated from the head of the Wap

Creek Valley prior to 7640 years ago (GSC-947). Published dates on the withdrawal of ice from the Okanagan-Thompson drainage system

(Lowdon, J. A., et a l., 1967, 1968; Dyck, W., et a l., 1965, 1966) range from 8900 ± 150 years B.P. (GSC-193) to 9750 ± 170 years

B.P. (GSC-526), which is in good agreement with the dates cited for the present study area.

The late-Pleistocene chronology in southwestern British

Columbia and northwestern Washington has been well-documented on the basis of numerous radiocarbon determinations (Armstrong, J. E., et a l., 1965). The last major glaciation in this area has been named the Fraser Glaciation. Limiting dates on this episode indi­ cate that it was initiated after 25,000 years B.P. in the northern part of the Georgia Depression and as late as 15,000 years B.P.

In the Puget Lowland. The major pulse of this glacial episode ended approximately 13,000 years B.P., though valley glaciers appear to have remained in the area as late as 9000 years B.P.

It seems reasonable to propose that the glacial events in the present study area and those of southwestern British Columbia re­

late to the same climatic episode, and that there is a general aynchroneity between the initiation and conclusion of the glacial events in the two areas. GLACIAL STRATIGRAPHY - POSTGLACIAL DEPOSITS

Eagle Valley Sediments

Nature of Deposits

The Eagle Valley Sediments relate to present river and lake levels and are represented In this area by floodplain and alluvial fan deposits along the rivers and deltaic deposits where there are lakes. Colluvlal deposits and swamp sediments include equivalents of both the Eagle Valley and Monashee Sediments, but have been assigned, for the most part, to the Mabel Lake deposits, since in most cases it can be demonstrated that such materials are s till accumulating. Lowland swamp deposits in river floodplalns and lakeshore lagoons are considered to be part of the fluvial or lacustrine deposits with which they are associated.

The floodplain deposits on the floors of the river valleys consist largely of gravel and sand, though they are covered in some places by a few Inches or feet of silt, clay, or peat. These flood- plain sediments are, for the most part, less than 15 feet thick, and in many places consist of less than 5 feet of bouldery or

cobbly gravel. By way of contrast, parts of the floor of the Shu­ swap R iver V alley south of Mabel Lake and the flo o r o f the west

114 115

end of the Eagle River Valley are inferred to be underlain by several tens of feet of gravel, sand, and silt.

Major deltas within the area Include those of the Shuswap

River at Mabel Lake and the Eagle River at Sicamous. These deltas

range in width from 1.5 miles to 2.5 miles, and probably average

several tens of feet in thickness. Little is known of their

internal structure or of the nature of the component materials at

depth, but they are probably similar in both respects to the delta

terraces described in the preceding chapter (p. fll)•

Alluvial fanB are formed where streams leave the confines of

a trunk stream channel, spread laterally, and deposit their en­

trained sediment (Bull, 1964, p. 17). Within the study area fans

occur at the mouths of most narrow mountain valleys, and are

generally best developed on the north slopes of east-west valleys

and on the east slopes of north-south valleys. The fan deposits

are commonly sev e r a l tens of f e e t th ick and c o n sist predominantly

of poorly-sorted angular gravel, much of which contains intersti­

t i a l s i l t and c la y . The gravel i s c o a r se st, and commonly bouldery,

at the apex of the fan, and becomes progressively finer toward the

toe of the fan. Gradients of both the fan surface and the bedding

vary between 5 and 15 degrees. On the other hand, the fan complex

built at the mouths of Creighton, Harris, Blue Springs, and Duteau

Creeks (Figure 6) is notable both for the fine texture of the fan

materials and the unusually low gradient of the fan surface. The

surface gradient of the fan complex is less than one degree from the apices to the point at which the complex merges with the

floodplain of Bessette Creek at Lumby. The fan material at this

low angle consists predominantly of medium to fine sand and silt w ith le n se s of gra v el and coarse sand.

Many of the alluvial fans show no evidence of recent growth.

Others, notably in the northern valleys of the area, are presently

undergoing active construction. Deposition of material was

observed during the summers of 1965-1967 on several fans in the

Eagle River and Perry River Valleys. This deposition of fan mater­

ial occurred entirely during the spring runoff; in some cases,

deposition occurred during two consecutive years. The deposits

of recent fan material are poorly-sorted, consisting of large

amounts of very coarse material and an abundance of interstitial

silt and sand. Alluvial fan deposition, in the cases observed,

appears to have been primarily from debriB flows, rather than from

water flows (Bull, 1968, p. 102).

Owing to a combination of great relief, steep cliffs of well-

jointed bedrock, and an alpine climate, many mountain Blopes in

the study area are characterized by appreciable accumulations of

sllderock. Although usually present on all but the steepest slopes

sliderock has been mapped only where sufficiently thick and exten­

sive to form a conspicuous talus. Sliderock is particularly plentl

ful in the cirques and high valleys of the Monashee Mountains, but

significant accumulations of sliderock are also found within the

Eagle River Valley. 117

Moat accumulations of recent allderock on the uplands rest at steep angles, between 30 and 36 degrees, and are very unstable.

They consist of a loose rubble of angular rock fragments a fraction of an Inch to several feet in diameter (Figure 31). Most of this recent sliderock shows no evidence of weathering and is generally free of lichens or patches of vegetation. However, at the base of slopes within the Eagle River Valley, stable sliderock generally l i e s downslope from u n stable rubble, and commonly forms slo p es of lesB than 30 degrees. The rock appears more weathered than fresh sliderock upslope, and a semi-continuous mat of vegetation covers the surface. These deposits may have accumulated at a time when the climate favored the production of more sliderock than it does today.

Accumulations of sliderock are generally in the form of coalescing talus cones, or talus aprons, at the foot of steep valley walls; isolated talus cones are uncommon. Typically the finest sliderock is found near the apex of the talus, and frag­ ments Increase in size toward the toe of the talus slope. In most cases the sliderock increases in size from the surface of the talus to the slope beneath the talus.

Examination of several widely separated sliderock accumula­ tions indicates that different llthologies produce very different shapes of sliderock material; thus, blotite gneiss produces

tabular or platy material, whereas quartzose gneiss and basalt produce blocky fragments of sliderock. The size of sliderock material produced from different llthologieB, however, does not Figure 31, Talus apron at foot of bedrock slope in Eagle River Valley. Largest blocks at toe of apron are approximately ten feet in diameter. appear to vary in any predictable way, though in a number of caseB talus derived from volcanic rocks appears to contain a higher per­ centage of interstitial fines than does that produced from other llthologies.

Debris avalanches (Sharpe, 1938) occur throughout the mount­ ainous parts of the area; fine examples can be seen in the eastern part of the Eagle River Valley. These features appear as long and narrow unvegetated tracks trending down the valley sides and ter­ minating in an irregularly-shaped accumulation of loose rubble at

the foot of the slope. Commonly the pathB of the avalanches are marked by sub-linear channels up to 4 feet deep and 6 feet wide.

Many have natural levees that rise from 1 to 3 feet above the general surface of the avalanche path.

During the early summer of 1968 a large debris avalanche swept across the Trans-Canada Highway 20 miles west of Revelstoke, leaving a mound of debris up to 600 feet wide and 20 feet deep across the highway. The avalanche moved down the valley of Camp

Creek, which was swollen by runoff and heavy weekend rains. It was probably Initiated by the heavy rainfall and the undermining of unconsolidated material near the head of the valley.

A large landslide has blocked the Eagle River Valley at the west end of Three Valley Lake (Plate IB). A large scar marks the site of the slide. Both the scar and the slide debris at the base of the Blope are heavily vegetated, indicating that the

slide has not been active in recent time. 120

The slide mass descended a total of 2000 feet down the mount­ ain slope, moved across the valley, and rose approximately 200 feet up the opposite side of the valley. The dam thus formed was about

150 feet high and 1.5 miles wide. The bulk of the landslide debris consists of angular boulders of mica schist and granitic gneiss, heavily Btained and partially cemented by limonite. Interstitial gravel, sand, and silt appears to have been derived in part from stream terrace materials which were overridden by the slide.

The upper surface of the slide debris is hummocky and resembles morainal topography. This surface morphology, the character of the slide debris, and the inferred movement (without backward rotation) indicates that the slide should be designated a "rock slide" in the terminology of Sharpe (1938).

A veneer of colluvium a few inches to several feet thick covers most hillslopes of the area. The materials are extremely varied, but generally consist of mixtures of till, gravel, sand, clay, etc. Although the colluvium forms a distinctive layer in most placeB, it usually differs little from the material beneath i t and has not been shown as a sep arate unit on the g e o lo g ic map.

Swamp deposits occupy poorly-drained depressions on the surface of the unconsolidated sediments and bedrock of the area.

These deposits consist largely of undecomposed or partially decomposed plant material, but also contain significant amounts of fine inorganic colluvium. The most extensive swamp deposits TABLE 5

OUTLINE OF MAJOR LATE-GLACIAL EVENTS IN THE SHUSWAP RIVER DRAINAGE AND ADJACENT AREAS

Radiocarbon Shuswap River A Figure Dace Drainage Okanagan Basin Shuswap Basin

32 Ice sheet retreated to vicinity of Monashee Pass; drainage still south into Kettle River. 33 Valley north of Monashee Pass free of ice; small ice-dammed lakes at heads of valleys. 34 Hilton area ice-free; Lake Cherryville occupies lowland south of Cherryville; outlet channel west of Ferry Creek at 2700 feet. 15,000 yrs. B.P, Ice retreated from Trinity Valley prior to formation of Lake Cherryville by 15,000 years B.P. 35 Ice retreated into Mabel Lake and Sugar Lake Valleys; Lake Cherryville drained into Blue Springs Valley. 10,200 yrs. B.P. Ice withdrew from mouth of Blue Springs Valley prior to estab­ lishment of outlets at Reiswig and Bessette Creek Valley, approximately 10,200 years ago. TABLE 5 (continued)

Radiocarbon Shuswap River Figure Date Drainage Okanagan Basin Shuswap Basin

37 Lumby-Bessette Creek low- Coldstream Lake formed; land ice-free; area occupied ice-margin outlet by Lake Lumby, continuous above 1800 feet, with lake in Coldstream V a lle y . Lake Lumby stages at 1800, Ice withdrew from 1690, and 1650 feet con­ Coldstream Valley; lakes trolled by outlets at mouth at 1800, 1690, and 1660 of Coldstream Valley. f e e t . Lower levels extended into Mabel Lake Valley 39 Lake Lumby separated from Lake Penticton, Long Coldstream Valley lake; lake Lake Stage; Lake Pent­ level in Mabel Lake Valley icton expanded into falls to 1570 feet. Coldstream Valley. 9,280 yrs. B.P. Ice withdrew from valley Lake Penticton, Grandview Lake Thompson, west of Mabel Lake causing F la ts Stage; m arginal to South Thompson lake to fall to 1570 level. ice in Okanagan Lake basin; Stage, marginal Mabel Lake extended into lake level temporarily to ice. Wap Valley, but not contin­ stabilized at 1600 feet. uous with Lake Penticton. Lakes *in Mabel Lake basin at levels of 1520, 1490, and 1430 feet extended into valley west of Mabel Lake, but not continuous with Lake P e n tic to n . TABLE 5 (continued)

Radiocarbon Shuswap R iver * Figure Date Drainage Okanagan Basin Shuswap Basin

40 Lake level fell to 1390 Lake Penticton, B.X. Lake Shuswap, feet; Mabel Lake contin­ Stage; lake level Rocky P t . and uous w ith la k es in Okanagan temporarily stabilized Magna Bay S ta g es. and Shuswap basins. at 1400 feet. Lakes a t 1600 and 1300 f e e t . Mabel Lake assumed present Lake Penticton, level Shuswap Lake, configuration at 1300 feet; gradually falling. Magna Bay Stage; lake at 1300 feet in valley basin free of ice, west of Mabel Lake contin­ uous with lake in Okanagan and Eagle River Valleys. Lakes in valley west of Lake Penticton fell to Lake Shuswap, Mabel Lake at 1220 and 1170 O'Keefe Stage at 1160 Tappan and Blind feet continuous with lakes f e e t . Bay S tages a t in Okanagan and Eagle River 1220 and 1170 V a lle y s . f e e t . p rio r to Drainage assumed present Lake Okanagan at pre­ Shuswap Lake at 6600 yrs. B.P. configuration; ice retreated sent level after present level; north of area. loss of Shuswap basin basin drainage drainage to Thompson captured by R iver. Thompson-Fraser system .

* Information from Fulton (in press). 124

occur in shallow depressions on the flat uplands, notably over the

Okanagan Highland at the southern margin of the area. Other large bodies of bog sediment occupy depressions in ice-contact deposits, as in the Trinity Valley, Augerlng of the bog deposits indicates that the sediments are generally thin on the uplands, ranging from

1 to 3 feet in thickness. Thicker accumulations, ranging from

5 to 20 feet, were measured in bogs developed on ice-contact d e p o sits.

Historical Significance of Eagle Valley Sediments

The fluvial and lacustrine deposits of the Eagle Valley

Sediments provide a sedimentary record of the present stand of local baselevel within the Btudy area. Volcanic ash occurs at several localities throughout the area within modem alluvial fans, talus, and in bog deposits on river floodplalns. The ash haB been identified as the Mazama ash which records an event that occurred

6600 years ago. At one locality in the Eagle River Valley, one mile east of Yard Creek, a thin layer of volcanic ash was sampled from a depth of 13 inches below the surface of the floodplain within a thick accumulation of peat and silt. This ash is petro- graphically distinctive in that it contains cummingtonite and hornblende, and no pyroxene. It has been assigned on the basis of its petrography to the St. Helens "Y" ash, which has been radio­ carbon dated at about 3000 years B.P. (Mulllneaux, D.R., 1964). 125

Within this area, drainage was s till influenced by the presence of ice 7640 years ago (p. 107), hence establishment of present local baselevel took place less than 7600 years ago, at

least in the northern valleys of the area. Although the data is

incomplete, information presently available from radiocarbon dates

and the occurrence of volcanic ash indicates that present condi­

tions of fluvial and lacustrine deposition were initiated between

7640 years ago and 6600 years ago. OUTLINE OF DEGLACIATION AND DRAINAGE CHANGES

Introduction

Deglaclatlon in areas of moderate and high relief, such as that presently under consideration, is controlled as much or more by the nature and orientation of topographic elements as it is by the regional regimen of the Ice sheet. During deglaciation, the ice sheet that covered the study area separated into a series of disconnected valley tongues, each tongue behaving as an individual unit and wasting in response to conditions exerted by the local topography.

Perhaps the single unifying aspect of deglaciation in an area of moderate relief is the changing pattern of drainage asso­ ciated with the melting ice. Thus in the present area of study, although it is not possible in all cases to trace the glacial deposits from one valley to the next, it is generally possible to correlate the development of lakeB and streams in these valleys.

The purpose of this chapter is to consider the changing conditions of ice regimen and the successive positions of the ice margin during deglaciation. Table 5 outlines the major events in the d e g la c ia tio n of the Shuswap drainage system and adjacent areas.

126 127

Ice Regimen

During deglaclatlon, regional flow of Ice in areas of moder­ ate relief depends largely upon the relationship between ice thick­ ness and relief (Davis and Matthews, 1944). As long as the Ice thickness is much greater than relief, the ice sheet maintains active flow, although the effect of topography on the direction of ice flow may be pronounced even when the ice is thick. The trends of glacial lineatlons (Plate II) suggest that the direction of movement of bottom (valley) ice diverged from that of the main body of the ice sheet when it was thick enough to still cover the northern highlands. As the surface of the ice sheet is lowered by down-melting, however, the effect of topography on the regional ice flow becomes increasingly more pronounced. First, mountains become nunataks. Then, the uplands gradually become ice-free, and the glacial ice is confined to the valleys. At this stage the

Ice begins to be separated from the regional ice source and is greatly reduced in surface area.

Slowly the ice becomes stagnant. This process of gradual stagnation has been described by Taylor (1962) for Bimllar topo­ graphic conditions in southeastern Alaska during the last century.

Ice movement in a regional sense ceases when the ice becomes stag­ nant, although the valley tongues are generally thick enough to retain a surface gradient, and thus to maintain some local flow.

In modern cases (Taylor, 1962) it has been shown that this flow may locally reverse or cross the previous trend of ice movement. The stagnant Ice maintains a convex cross-profile and an appre­ ciable down-valley slope, so that meltwater drains along the ice margins. Locally, ice-marginal drainage channels may slope in a direction opposite to the regional slope of the ice surface during this stage of ice wastage (Mannerfelt, 1949; Goldthwait, in press). The distribution of lateral drainage channels in the v a lle y s of the Eagle R iver and the Shuswap River w est of Mabel

Lake indicates that such reversals of ice-marginal drainage did occur during deglaciation of this area.

When the surface of the ice lowers to a point where the ice tongues become thin masses and lose their surface gradients, the ice ceases to move at all. The ice at this stage is dead, and meltwater from the ice flows across the surface of the ice or beneath the ice rather than along the valley aides.

The changing conditions of ice regimen during deglaciation of the area have been inferred from the character, distribution, and presumed genesis of glacial features and deposits. Thus, deposits of Lumby T ill, and particularly drumlinoid till, are indicative of active ice. Lateral channels, kame terraces, and channel deposits of the Monashee Sediments were formed during progressive stages of ice stagnation. Normal stream and delta

terraces formed during final stages of deglaciation when ice had

disappeared from much of the area but s till impounded drainage in the northern valleys . 129

Deglaciation and Drainage Development

In order to expedite the discussion of deglaciation and drainage development, the area of study has been subdivided into three separate map areas. Map-area 1 comprises the southern one- third of the study area and includes the Monashee Pass-Cherryville area, C reighton V a lley , and the Shuswap R iver V alley from Sugar

Lake to Shuswap F a lls . Map-area 2 in clu d es the Mabel Lake V a lley , the Lumby-Beseette Creek low land, and the Shuswap River V alley from Dolly Varden Beach to Enderby (see Plate II). Map-area 3 consists of the Eagle River Valley between Sicamous and Revelatoke.

Map-Area 1

The earliest features that can be related to ice retreat in this area are several ice-marginal channels between elevations of 4400 feet and 5200 feet immediately south of Monashee Pass.

These channels slope southward and record a stage of deglaciation when meltwater drainage was southward into the Kettle River

V a lle y . S im ilar channels a t the heads of Yeoward and Heckman

Creeks were formed contemporaneously. A direct overflow channel leading from the divide between Yeoward Creek and the Kettle

River indicates that ice filled this valley and forced meltwater

to overflow the divide at an elevation of 4800 feet. Another overflow channel at the head of the valley of Heckman Creek records

the overflow of meltwater across the divide into Coalgoat Creek 130

at an elevation of 4500 feet.

Figure 32 Illustrates the probable position of the ice front when the divide between Monashee Pass Creek and McIntyre Creek was free of ice, and water ponded in the upper part of the valley of

Monashee Pass Creek flowed southward through the direct overflow channel of Monashee Pass into the Kettle River drainage at an elevation of 3900 feet. Monashee Pass was the last of the low cols along the southern drainage divide to carry meltwater drainage into the Kettle River syBtem. Subsequently, meltwater drainage was confined within the present Shuswap River system.

When the ice front had retreated to the position shown In

Figure 33, the valley of Monashee Pass Creek was free of stagnant ice, though small blocks of dead ice remained along the valley

floor. The Monashee Creek Valley was also ice-free, and the valleys of creeks draining the southern highlands were occupied by small ice-daramed lakes. The Hilton-Cherryville lowland was still covered by stagnant ice. Meltwater drained westward along the Ice margin,

cutting a series of lateral channels on the hills lopes south of

H ilto n .

Ice melting westward in the Creighton Valley (Echo Lake

Valley) left in its wake masses of dead ice in positions now occu­ pied by Echo Lake and the broad bench at the east end of the valley.

Meltwater streams flowing along the southern margin of the ice and

streams draining the adjacent ice-free uplands eventually issued

into the eastern end of the Creighton Valley and around the margins Figure 32. Deglaciation of Map-Area 1. Explanation in text. North toward top of man.

Potifian of Direction of Direction of ice margin ice-marginal englacial drainage drainage pf

V.

Figure 33. Deglaciation of Map-Area 1. Explanation in text. North toward top of map.

C L >1000 ft. Petition of Direction of Direction of 0 ml 1*1 ice margin ice-marginal englocial drainage drainage d 133

of the dead Ice masses, forming the thick accumulations of ice- contact deposits that fill the valley.

Withdrawal of the ic e to the p o sitio n shown in Figure 34 uncovered much of the lowland south of Cherryville. Meltwater was ponded behind the retreating ice front forming a lake (Lake

Cherryville) that overflowed through a narrow channel on the upland west of Ferry Creek at an elevation of approximately 2700 feet.

The highest deltas (2690 feet) in the valleys of Monashee and

Cherry Creeks began to form at this time. Further withdrawal of the ice opened the lowland east of Cherryville, and the lake ex­ panded to its maximum extent (Lake Cherryville - Hilton Stage).

The outlet at 2700 feet was maintained during this lake stage, and meltwater flowed westward along the ice margin into the valley of

Blue Springs Creek. Drainage into the Blue Springs Valley was blocked i n i t i a l l y by ic e at the mouth of the v a lle y . Further melting of the ice opened the mouth of the valley and permitted drainage westward along the ice margin into the lowland south of

Lumby. Radiocarbon dating of bog-bottom material from the Blue

Springs V alley in d ic a te s that ic e had withdrawn from the mouth of the valley at least 10,200 years ago.

Continued retreat of the ice opened lower ice marginal channels in the Shuswap Valley west of Cherryville, drawing the level of Lake Cherryville down first to 2580 feet (Cherry Creek

Stage), and later to 2500 feet (Currie Creek Stage). Lower lake levels at 2300 feet and 2050 feet are poorly documented, but Figure 34. Deglaciation of Map-Area 1. Explanation in text. North toward top of map.

C L -1000 ft. Position of Direction of Direction of milos teo margin k*-marginal ongloclol Lake droinoflo 135

probably did exist and drained through outlets first In the vicinity of Relswlg and eventually through the valley of Bessette Creek.

The d istr ib u tio n of la t e r a l drainage channels In the Shuswap

River Valley between Cherryville and Shuswap Palls Indicates that the Ice confined to the valley bottom separated into two tongues west of Ferry Creek. One tongue withdrew westward and northward

Into the Mabel Lake Valley, the other melted northward toward

Sugar Lake. Figure 35 Illustrates the probable configuration of

the Ice front shortly after the Mabel Lake and Sugar Lake tongues had sep arated .

Map-Area 2

Lumby-Besaette Creek Lowland

When the Mabel Lake and Sugar Lake ice tongues had receded

into their respective valleys and ice withdrew Into the Coldstream

Valley west of Lumby (see Plate II), a lake was formed in the

Lumby-Bessette Creek lowland (Figure 36). A dead Ice mass occupied

the Shuswap V alley e a st of Shuswap F a lls and prevented the expan­

sion of the lake Into this valley. Kame terraces and kame fans

and patchy accumulations of lacustrine silt accumulated against

the Ice margin during this stage of deglaciatlon.

The highest deltas In the Lumby-Bessette Creek lowland

record the existence of a lake level at approximately 1800 feet Figure 35. Deglaciation of Map-Area 1. Explanation in text. North toward top of map.

C.L*1O0O«t. Flotiliafl of (Nrvction of DlrocHon of 0 ico morgin *c«-marginal onglociol drataogo draiaoga ICE

ICE fo

Figure 36. Deglaciation of Map-Area 1. Explanation in text. North toward top of map.

C l.*1000 ft. Position of Direction of Direction of ice margin ice-marginal engiacial lake drainage drainage 138

(Lake Lumby). Kame deltas above this elevation show no accordance

of elevations from valley to valley, and probably accumulated in

small disconnected ice-marginal lakes. Lake Lumby extended into

the Coldstream Valley (Figure 37) and drained through a prominent

ice marginal channel at the west end of the valley (Fulton, in

press). Continued withdrawal of the ice from the west end of the

Coldstream Valley opened lower outletB along the ice margin at

the mouth of the valley (Fulton, in press). The level of Lake

Lumby dropped first to 1690 feet and then to 1650 feet.

When the level of Lake Lumby dropped below 1690 feet, the

lake was no longer continuous with lakes in the west end of the

Coldstream Valley. It was probably at this time that the alluvial

fan constructed by Coldstream Creek (see p. 31) enlarged to block

the valley weBt of Lumby. Drainage from the Lumby-Bessette Creek

lowland continued westward for some time after the lakes separated,

and the level of lakes in the Lumby area were controlled by lake

levels in the west end of the Coldstream Valley. Eventually,

however, the outlet at Dolly Varden Beach was opened and drainage was Bhifted to the new outlet.

Subsequent sta g es of d e g la c ia tio n in the Shuswap River

drainage relate to progressive stagnation of ice in the Mabel

Lake V alley and continued r ecessio n of ic e in the Okanagan

V a lley . c.i. -looort.

O j n l l i t

Position of ic* Lako Lako outlot margin > (1*00 ft.)

Figure 37. Deglaciation of Map-Area 1. Extension of Lake Lumby into Coldstream Valley at 1800-foot level.

w VO 140

Mabel Lake V alley

The ic e su rface In the Mabel Lake b asin downwasted to an elevation of about 1780 feet before major lakes formed. Widely scattered delta terraces between the highest well-defined lake level and the lowest occurrences of ice-contact deposits were constructed into ice-marginal lakes which drained along the edge of the ice and in to the Coldstream V a lley.

The highest well-defined lake level in the Mabel Lake Valley occurs at an elevation of 1650 feet (Mabel Lake - Ireland Creek

Stage). Ice remained in much of the Mabel Lake basin at this time (Figure 38). Mabel Lake at this stage extended southward into the Lumby-Bessette Creek lowland and northward as far as

Tsuius Creek; the lake drained southward through the Coldstream

Valley. Ice blocked the valley east of Dolly Varden Beach and probably occupied much of the Wap Creek Valley. Shore features of the Ireland Creek Stage vary in altitude from about 1650 feet in the southern part of the valley to 1750 feet in the vicinity of

Tsuius Narrows. The water plane has been tilted southward on a gradient of between five and six feet per mile (Figure 25).

Withdrawal of the ic e from the Shuswap V alley west of D olly

Varden Beach opened a channel between Mabel Lake and the Okanagan

Valley (Figure 39), and lowered the lake level approximately 80 feet (Mabel Lake - Dolly Varden Stage). Bog-bottom material from a small bog north of Dolly Varden Beach has been radiocarbon dated at 9280 years B.P. (see p. 103), indicating that ice had withdrawn 141

Figure 38. Deglaciation of Map-Area 2. Explanation in text. Legend same as Figs. 32 through 36,

C.I. • 2 0 0 0 fool

0 mtUi S

R • Rovolttok*

TV - 3 Volloy $ - Slcomow* E • Endorby DV - Dolly V ordtn Booth a Lumby

c 142

Figure 39. Deglaciation of Map-Area 2. Explanation in text. Legend same as Figs. 32 through 36. — I C.l. • 2 0 0 0 foot

O mil** 1

R - Rovolstoko

TV - 3 VolUy 5 - Sieamou* E - Endtrby DV - Dolly VarcUn Boach Lumby

c from the Shuswap Valley here at least that long ago.

Delta terraces recording the Dolly Varden Stage were con­ structed at the mouths of most creeks entering Mabel Lake, and shorelines were locally developed. A large delta terrace at the southern end of the Wap Creek Valley (Figure 27) was constructed into this lake, indicating that the Wap Creek Valley was largely free of ice at this time, The present elevation of delta terraces in the vicinity of Dolly Varden Beach is 1570 feet, and the water plane of this lake stage slopes southward at approximately A.5 feet per mile (Figure 25).

Evidence for the Dolly Varden Stage in the Shuswap Valley west of Dolly Varden Beach is poor, and it is possible that stag­ nant ice still occupied the western part of this valley, preventing the development of deltas and shorelines of the Dolly Varden Stage.

Fulton (in press) records a temporary stand of Lake Penticton

(Grandview Flats Stage) in the North Okanagan Valley at about 1600 feet, and indicates that in the initial phases of this lake stage, ice occupied the Okanagan Valley north and east of Enderby (see

Plate I I ).

Withdrawal of the ice from the Shuswap Valley west of Mabel

Lake opened temporary ou tlets along the ice margin at the mouth of the v a lley . Lake le v els in the Mabel Lake basin and in the Shuswap

Valley west of Mabel Lake have been recorded at elevations of 1520 fe e t, 1490 fe et, and 1430 fe e t, and relate to the progressive down- melting of ice in the v ic in ity of Enderby. 144

When«ice in the Okanagan Valley had melted north of Enderby,

Lake Penticton was continuous with lakes in the Mabel Lake basin

(Figure 40)• Prominent deltas at elevations of about 1390 feet

(Mabel Lake - Cooke Creek Stage) occur throughout the Mabel Lake

Valley and in the Shuswap Valley west of Dolly Varden Beach. This stage of Mabel Lake extended southward to the town of Mabel Lake and northward for a distance of about three miles into the Wap

Creek Valley. T iltin g of the Cooke Creek Stage shoreline in the

Mabel Lake basin is about 3,5 feet per mile toward the south

(Figure 25).

After Mabel Lake had become continuous with lakes in the

Okanagan Valley, the water level in the Mabel Lake Valley fell steadily in response to falling lake levels in the Okanagan

Valley. Poorly-defined delta terraces at elevations of about

1330 feet record the last stage in which Mabel Lake was continuous with lakes in the Okanagan Valley. When lake level fell below

1330 fe e t, Mabel Lake had assumed much i t s present configuration and had established the outlet at Dolly Varden Beach. Downcutting of the outlet has lowered the level of Mabel Lake approximately

40 feet and has superimposed the outlet channel on bedrock at

Skookumchuck Rapids.

Final stages of lake development in the valley east of Mabel

Lake were controlled by the disappearance of ice and the continued development of lakes in the Okanagan Valley and the Shuswap Lake basin. These final lake stages are discussed in connection with 145

7 ^777*

Figure 40. Deglaciation of Map-Area 2. Explanation in text. Legend same as Figs. 32 through 36.

C.l. • 2 0 0 0 feel

O m llti 5

I R - Revelitoke

TV - 9 Valley 9 - licemout E ■ Endirby DV • Dally Varden d Beach Lumpy c 146

lake stages recorded in the Eagle River Valley.

Map-Area 3

Glacial retreat in the Eagle River Valley left a record of stagnation, except in the vicinity of the Perry River. Once ice had melted below the northern uplands it was effectively cut off from the regional source, and stagnation resulted in the downwast- age of ice in place. Ice in the Perry River Valley was not cut

off from the regional source and probably continued to be fed by

ice in the mountains north of the study area.

Withdrawal of the ice from the uplands appears to have been

from west to east in the western part of the Eagle River Valley

(see p. 106). When ice in the vicinity of Cambie had melted below

an elevation of approximately 2500 feet, it separated into two

ice tongues, One tongue withdrew eastward into the Perry River

Valley, the other melted westward into the Shuswap Lake basin

(Figure 41).

Ice-marginal channels in the vicinity of Endiver (Figure 41)

indicate that ice in the central part of the Eagle River Valley

separated into two masses. One ice mass melted westward into the

Perry River Valley, the other melted eastward toward Three Valley

Lake. Gradients of kame terraces and lateral drainage channels

likewise record the separation of ice into two masses in the

vicinity of Clanwilliam (Figure 41). East of Clanwilliam, the ice 5 -SICAMOUS Cd - CAMBIE M -MALAKWA Cr -CtAlOILLACHIE E -ENDIVES TV- THBEE VALLEY Cl ~ CLANWILLIAM

Figure 41. Successive positions of ice margin during deglaciation of Kap-Area 3. 148

withdrew into the Columbia River Valley; west of Clanwilliam* the ice melted back toward Three Valley.

During early stages of ice retreat from the Eagle River

Valley, meltwater from ice in the eastern part of the valley drained southward into the Wap Creek Valley. In the western part of the valley, meltwater drained along the ice margin into the Okanagan

Valley.

When ice east of Eagle Pass had withdrawn into the Columbia

River Valley, ice between Three Valley and Clanwilliam discharged meltwater eastward into the Columbia River Valley, as well as southward into the valley of Wap Creek. The large kettled delta east of Eagle Pass (see p . 109) w s b constructed into an ice-marginal lake which formed between the two ice masses at the east end of the valley. Stream terraces which slope eastward from the vicinity of

Eagle Pass indicate that this eastward drainage was maintained after the temporary lake drained and ice had melted from this section of the valley.

Remnants of kame terraces west of Eagle Pass slope toward the west, indicating that as ice melted west from the vicinity of

Eagle Pass, meltwater drained westward along the ice margin and southward into the Wap Creek Valley. This drainage into the Wap

Creek Valley may have been joined by eastward drainage from the retreating Perry River Ice tongue. Evidence for eastward drainage from the Perry River has been obscured by subsequent stream erosion and alluvial fan deposition. Yet the large volume of 149

gravel and sand which occurs as terraces within the Wap Creek Valley would seem to require a greater source of sediment than could be

expected from the stagnant ice masses in the west end of the valley

alone. Drainage from the Eagle River Valley into the Wap Creek

Valley ceased when ice melted from the vicinity of Three Valley,

approximately 7600 years ago (see p. 107).

Although drainage from the Perry River ice tongue may have

been eastward into the Wap Creek Valley, kame terraces and lateral

drainage channels west of the Perry River Indicate that meltwater

drained westward into the Shuswap Lake baBin. Retreat of ice into

the Shuswap Lake basin took place contemporaneously with ice

retreat into the Perry River Valley. Continued withdrawal of these

two ice masses opened the west end of the Eagle River Valley to

several lakes which were continuous with lakes in the Shuswap Lake

basin and the Okanagan Valley.

The development of major lakes in the Eagle River Valley

did not take place until relatively late in the deglaciation of the

valley. Kame deltas and accumulations of kettled lacustrine silt

are found at elevations between 2700 feet and 1600 feet (see p. 106),

indicating that numerous isolated ice-marginal lakes were formed

throughout the valley during stagnation of the ice.

The highest clearly-defined lake level in the Eagle River

Valley occurs at an elevation of approximately 1570 feet. The

existence of this lake level is recorded by the presence of

lacustrine silts in the vicinity of Solsqua and Malakwa and by 150 delta terraces at the mouths of creeks throughout the west end of the valley. The lake In which these features accumulated extended as far east in the valley as Taft. A lower lake level, at an elevation of approximately 1520 feet, likewise occupied the west end of the Eagle River Valley as far east as Taft. Ice still occupied the Shuswap Lake basin at the time that these two lakes existed (Fulton, in press), so that the lake levels were controlled by outlets along the ice margin.

A lake level at 1380 feet is recorded by delta terraces in the Eagle River Valley as far east as Craigellachle. This lake level may correspond with the B.X. Stage of Lake Penticton in the Okanagan

Valley, which Fulton (in press) suggests might have extended into the Eagle River Valley. However, the 1400-foot elevation cited by Fulton for the B.X. Stage shoreline in the vicinity of Vernon

(see Plate II) is high for the 1380-foot level in the Eagle River

Valley, particularly in light of subsequent isostatic tilting of the B.X. shoreline. More probably, the 1380-foot lake level in the Eagle River Valley represents a temporary h alt in the fa llin g level of the Okanagan Valley lakes following the B.X. Stage of Lake

Penticton.

Evidence for the existence of lakes at levels of 1290 feet,

1220 fe e t, and 1170 feet is well-documented by delta terraces in the west end of the Eagle River Valley. These lakes correspond, respectively, to the Magna Bay Stage, the Tappen Stage, and the

Blind Bay Stage of Lake Shuswap (Fulton, in press). Delta 151

terraces corresponding to these three levels are found at similar elevations in the Shuswap Valley east of Enderby, and Indicate that

Shuswap Lake during these stages was continuous between the two valleys. During the two higher stages (1290 feet, 1220 feet)

Lake Shuswap extended to Craigellachle in the Eagle River Valley and to a point about four miles east of Trinity Creek In the Shuswap

River Valley. When the level of Lake Shuswap fell to 1170 feet, the lake withdrew to Cambie in the Eagle River Valley and to the mouth of Trinity Creek in the Shuswap River Valley. The controls for these lake levels and the establishment of present drainage in the Okanagan Valley and the Shuswap Lake basin have been discussed in detail by Fulton (in press), and w ill not be repeated here. HISTORICAL SUMMARY

The major physiographic features of the Shuswap River-

Mabel Lake area are genetically related to bedrock structure and preglacial stream erosion. Major streams have developed coinci­ dent with major north-south fault and Joint systems, while tributary streams and drainage normal to the grain of the topo­ graphy have developed parallel to eaBt-west fold axes.

Prior to mid-Pliocene uplift, the land surface of the

Shuswap and Okanagan Highlands was one of low r e lie f that trans­ ected a wide variety and age of rocks. This upland surface is here named the Shuswap Erosion Surface. Differential uplift in mid-

Pliocene time raised the Monashee Mountains higher than the uplands of the adjacent Okanagan and Shuswap Highlands. Streams, rejuvenated by the uplift, began to dissect the Shuswap Erosion

Surface and cut rapidly and deeply in the mountain valleys.

At the end of the Tertiary, with the advent of glaciation,

the land stood comparatively high, and the pattern of major valleys was eBBentlally as it is today. Drainage within these valleys, however, was altered from a well-integrated parallel- dendritic system draining southwestward into the Okanagan Valley

to an irregular, almost rectangular, system draining northwestward

into Shuswap Lake.

152 153

The oldest surflcial deposits that have been recognized in the area are the Bessette Sediments, These deposits are river floodplain and lacustrine sediments; colluvial material consti­ tutes a subordinate element of the exposed deposits. The Bessette

Sediments record a major non-glacial interval within the area, and apparently throughout much of the eastern Interior Plateau. On the basis of radiocarbon dates it appears that the non-glacial

Interval represented by the Bessette Sediments began more than

43,800 years ago and extended here to 19,100 years ago. This event correlates with the Olympia Interglacial interval in south­ western British Columbia and northwestern Washington.

Deposits of Lumby Till appear to relate to a single stage of glaciation in the study area. Onset of glaciation began after 19,100 years B.P. and deglaciation was in progress by 15,000 years B.P.

This glacial episode correlates with the Fraser Glaciation in south­ western B ritish Columbia and northwestern Washington. During the climax of glaciation, an ice sheet covered the entire area below an elevation of 8000 feet and flowed south and southeast across the area from an ice divide in the Interior Plateau near the 52nd par­ a lle l. Only the sharp alpine peaks of the Gold Range stood above

the ice, and mountain glaciers from cirques on these peaks probably

fed into the continental Ice sheet.

Accumulation of the MonaBhee Sediments occurred after glacial ice had begun a general retreat. This phase of the last glaciation was a time-transgresBive event, beginning first on the southern up­

lands and on high nunataks, and ending when the last stagnant ice 154 had disappeared from'the Eagle River and Perry River Valleys. Radio­ carbon dates provide the following information regarding the deglacia­ tion of the area: (1) uplands in the central portion of the area were free of ice at lea st 15,000 years ago; (2) ice had withdrawn into the valleys south of Lumby prior to 10,200 years ago; (3) ice had melted from the vicinity of Kingfisher Creek, west of Mabel Lake,

9280 years ago; and (4) stagnant ice had disappeared from the v icin ity of Three Valley approximately 7600 years ago.

As the ice downwasted in the valleys a complicated series of drainage changes occurred and temporary lakes developed. The terraced stream and delta deposits of the Monashee Sediments record a succession of lake levels first in the vicinity of Cherry- v i l l e , then in the Lumby-Bessette Creek lowland and the Mabel Lake

Valley, and finally in the Eagle River Valley. These lake levels were initially controlled by the presence of ice within the valleys. With the disappearance of ice, final major changes of lake lev els were produced in response to iso s ta tic adjustment.

The fluvial and deltaic deposits of the Eagle Valley Sedi­ ments provide a sedimentary record of present drainage conditions within the area, Initiation of these conditions postdates 7600 years ago since ice still influenced drainage in the northern part of the area as late as 7640 years ago. Volcanic ash, dated at 6600 yearB

B.P. occurs near the upper part of a llu v ia l fans and bog sediments

throughout the area, and indicates that present conditions of fluvial and lacustrine deposition were in effect by that time. REFERENCES

American Society for Testing Materials, 1958, Grain-size analysis of soils, D422-54T: jLn Procedures for testing soils, pp. 83-94.

Armstrong, J. E., D. R. Crandell, D. J. Easterbrook, and J. B. Noble, 1965, Late Pleistocene stratigraphy and chron­ ology in southwestern British Columbia and northwestern Washington: Geol. Soc. Amer. B u ll., v. 76, pp. 321-330.

Bull, W. B., 1964, Alluvial fans and near-surface subsidence in western Fresno County, California: U.S. Geol. Survey Prof. Paper 437-A, 71 pp.

______, 1968, Alluvian fans: Jour. Geol. Education, v. 16, pp. 101-106.

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Dawson, A. B., and C. C. Kelley, 1964, Soil Survey of the Eagle River Valley, B ritish Columbia: Interim Rept., B ritish Columbia Dept. Agriculture, 71 pp.

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155 156

Dawson, G. M., 1890, On the later physiographical geology of the Rocky Mountain region In Canada, with special reference to changes in elevation and to the history of the Glacial Period: Roy. Soc, Canada Proc. and Trans., v. 8, pp. 3-74.

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______, J. G. Fyles, and W. Blake, Jr., 1965, Geological Survey of Canada radiocarbon dates IV: Geol. Surv. Canada Paper 65-4, pp. 9-14.

______, J. A. Lowdon, J. G. Fyles, and W. Blake, Jr., 1966, Geological Survey of Canada radiocarbon dates V: Geol. Surv. Canada Paper 66-48, pp. 14-18.

Flint, R. F., 1957, Glacial and Pleistocene Geology: John Wiley and Sons, In c ., New York, 553 pp.

Fulton, R. J,, 1963, Deglaciation of the Kamloops region, B ritish Columbia: Ph.D. d issertation , Northwestern Univer­ s ity , 125 pp.

______, 1967, Deglaciation studies in Kamloops region, an area of moderate r e lie f , B ritish Columbia: Geol. Surv. Canada Bull. 154, 36 pp,

______, 1968, Olympia Interglaciation, Purcell Trench, B ritish Columbia: Geol. Soc. Amer. B u ll., v. 79, pp. 1075-1080.

______, in press, Surficial geology of the Merritt and Okanagan map-sheets, B ritish Columbia: Geol. Surv, Canada Memoir.

Fyles, J. G., 1963, Surficial geology of the Horne Lake and Parksville map-areas, Vancouver Island, British Columbia: Geol. Surv. Canada Mem, 318, 142 pp. George, W. 0., 1924, The relation of the physical properties of natural glasses to their chemical composition: Jour. Geology, v. 32, pp. 353-372.

Glen, J. W., J. J. Donner, and R. G. West, 1957, On the mechanism by which stones in till become oriented: Amer. Jour. Sci., v. 255, pp. 194-205.

Goldthwait, R. P., in press, Surficial geology of the Wolfeboro- Winnipesaukee area, New Hampshire: State of New Hampshire.

Hansen, H. P., 1955, Postglacial forests in south-central and central British Columbia: Amer. Jour. Sci., v. 253, p. 640.

Holland, S. S., 1964, Landforms of British Columbia, a physio­ graphic outline: B ritish Columbia Dept. Mines and Petrol. Res. Bull. 48, 138 pp.

Inman, D. L ., 1952, Measures for describing the siz e distribution of sediments: Jour. Sed. Petrology, v. 22, pp. 125-145.

Jenness, S. E., 1967, Report of Activities, part A: May to October, 1966: Geol. Surv. Canada Paper 67-1, pp. 58-60.

Jones, A. G., 1959, Vernon map-area, British Columbia: Geol. Surv. Canada Mem. 296, 186 pp.

Kujansuu, R ., 1967, On the deglaciation of western Finnish Lapland Bull. Comm. Geol. Finlande, no. 232, 98 pp.

Lowdon, J. A., and W. Blake, Jr., 1968, Geological Survey of Canada radiocarbon dates VII: Geol. Surv. Canada Paper 68-2, pp. 18-19.

______, J. G. Fyles, and W. Blake, Jr., 1967, Geological Survey of Canada radiocarbon dates VI: Geol. Surv. Canada Paper 67-2, pt. B, pp. 16-19.

Mannerfelt, C. M., 1945, Nagra Glacialmorfologiska formelement: Geogr. Annaler, v. 27, pp. 1-239 (English summary pp. 222-228)

______, 1949, Marginal drainage channels as indicators of the gradients of Quaternary ice caps: Geogr. Annaler, v, 31, pp. 194-199.

Matthews, W. H., 1944, Glacial lakes and ice retreat in south- central B ritish Columbia: Trans. Roy. Soc. Canada, v. 38, pp. 39-57. 158

McKenzie, G. D., 1968, G lacial history of Adams Inlet;, southeastern Alaska: Ph.D. d isserta tio n , The Ohio State U niversity, 200 pp.

Mullineaux, D. R ., 1964, Extensive recent pumice la p llli and ash layers from Mt, St. Helens volcano, southern Washington (abst.): Geol. Soc. Amer. Spec. Paper 76, p. 285.

Nasmith, H., 1962, Late glacial history and surficial deposits of the Okanagan V alley, B ritish Columbia: B ritish Columbia Dept, Mines and Petrol. Res. Bull. 46, 46 pp.

Porter, S. C., 1966, Pleistocene geology of Anaktuvuk Pass, central Brooks Range, Alaska: Arctic Inst, of North Amer. Tech. Paper 18, 100 pp.

Price, R. J., 1964, Landforms produced by the wastage of the Casement Glacier, southeast Alaska: Ohio State Univ. Inst, of Polar Studies Report No. 9, 24 pp.

Rigg, G. B., and H. R. Gould, 1957, Age of Glacier Peak eruption and chronology of p ostglacial peat deposits in Washington and surrounding areas: Amer. Jour. S c i., v. 25'i, pp. 341-363.

Sharp, R. P ., 1951, G lacial history of Wolf Creek, St. Elias Range, Canada: Jour. G eol., v. 59, pp. 97-117.

Sharpe, C. F. S., 1938, Landslides and Related Phenomena: Columbia University Press, New York, 137 pp.

Sprout, P. N., and C. C. Kelley, 1960, Soil survey of the North Okanagan Valley: interim Rept., British Columbia Dept. Agriculture, 75 pp.

Taylor, L. D ., 1962, Ice structures, Burroughs G lacier, southeast Alaska: Ohio State Univ. Inst, of Polar Studies Report No. 3, 106 pp.

Twidale, C. R., 1956, Longitudinal profiles of some glacial overflow channels: Geogr. Jour., v. 122, pp. 88-92. I O f-n.ii-r/'v I ’ I’liir

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j ^ u V N ^ S i ^ ! v \ x SURFICIAL GEOLOGY-SHUSWAP BRITISH COLUMBIA (82L/NE). S for explanation.

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P A ft K Plate IB.

SURFICIAL GEOLOGY - SHU5WAP RIVER DRAINAGE, BRITISH COLUMBIA (82L/NE). See accompanying legend for explanation.

G.W. Smitf tf>9. N N O Z O I C LITCN AD RECENT ANDPLEISTOCENE 5 8 Wap Sediments Valiev al Vle Sediments Valley Eagle Lacustrine and glacio-lacustrine deposits; deposits; glacio-lacustrine and Lacustrine Terraced fluvial and deltaic deposits; deposits; deltaic and fluvial Terraced rvl sn silt. sand gravel, lva ad eti Deposits Deltaic and Fluvial ie ad sit clay. ilt, s sand, fine . ercd eti deposits. deposits, deltaic Terraced floodplain b. river Terraced a. . ete lcsrn deposits. lacustrine Kettled deposits. lacustrine c. veneer Thin deposits. b. lacustrine Thick a. . ercd luil a deposits. fan alluvial Terraced c. a. Alluvial fan deposits; poorly sorted sorted poorly deposits; fan Alluvial River floodplain and deltaic deposits; deposits; deltaic and floodplain River w m dpst; peat. Swamp silt. deposits; sand, gravel, peat. ilt, s sand, gravel, LEGEND Landslide and talus deposits; deposits; talus and Landslide blocky rubble, poorly sorted sorted poorly rubble, blocky rvl sn, silt. sand, gravel, C C E N O Z O I C 4 5 3 eois cluil eois gravel, deposits; colluvial till; deposits, beneath deposits Interglacial Lumbv Till este Sediments Bessette Ground moraine deposits; ti ll, local lenses lenses local ll, ti deposits; Ground moraine Lacustrine and glacio-lacustrine deposits; deposits; glacio-lacustrine and Lacustrine rvl sn, l, ess f till. of lenses deposits; ilt, s sand, glacio-deltaic gravel, and Glacio-fluvial s ilt, peat, Shown only as fractional fractional as Shown only peat, ilt, s f rvl sn, ilt. s sand, gravel, of ie fodli dpst, lacustrine deposits, floodplain river ybl eet t l n yugr deposits. younger and ll ti symbol beneath rvl sn silt, s sand gravel, ie ad sit clay. ilt, s sand, fine . rmiod rud moraine. ground Drumlinoid b. . hne deposits. Channel d. . rud oan, undifferentiated. Ground moraine, a. . ae a deposits. Kame fan c. deposits. Kame delta b. . ae erc deposits. Kame terrace a. deposits. lacustrine veneer Thin b. . ete lcsrn deposits. lacustrine Kettled c. . hc lcsrn deposits. lacustrine Thick a. deposits. fan alluvial Terraced deposits. c. deltaic Terraced b. . Hummocky moraine. ground c. . ercd ie fodli deposits. floodplain river Terraced a. 2 o itntv dit topography drift distinctive no htgah i frse upland forested in photographs showing l l i t mainly drift; glacial Undifferentiated colluvium and younger deposits. deposits. younger and colluvium with mixed generally and areas.) (Mapped mainly from aerial aerial (Mapped from mainly -LilLCLg-Ldi^XciJ- Lit-u 44 irAxj. , river floodplain deposits, lacustrine deposits, colluvial deposits; gravel, silt, peat. Shown only as fractional symbol beneath till and younger deposits.

Bedrock; includes areas of bedrock outcrop and bedrock thinnly veneered by till and younger deposits.

Geological boundary (approximate)

Glacial meltwater channel.

Abandoned lake shoreline,

Geology by G. W. Smith, 1966-1967. Base map by Surveys and Mapping Branch, 1956, 196

Scale -1:63/360

O miles 1

(To accom pany Plates IA and IB - Surficiol Geology Shuswap River Drainage, British Columbia.) 82 L 1:250,000

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Nuu-.h Mill i DIRECTION OF GLACIAL MOVEMENT jc ojb ASSOCIATED WITH THE LAST REGIONAL GLACIATION.

I D L’l. EXPLANATION »tr*°

I < SlDjlNT \ 4. ^ wl^£wit'l*ll ?' . • / • n a. Strict and graovat altedottd with tfeit-and'lii profllai and crag-and-lail t'rJ'-i?* i h farntij fe. llrlt* and groovti; d)ri(ll»n T !> ?n •f let mpvtmtnt nal knawn,

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