URCONSOLIDATED DEPOSITS AI?D GLACIAL OEOLOOY

COLUMBIA RTVPR! RFVELSTOKE TO GOI,:DEB, BO C, By H, Nasnith November, 1958

IRTRODUCTIO H

The following report on B survey of unconarall- dated materials along the Coluenbla R1ve:r from Revelstoke to Golden eonslsts of annototed maps, photographa, and a brief rsuPtrnary of the Pleistocene and mmnt history of the area as far as could be Interpreted from the obsema- tlons which were made.

A total of 24 days VQ# spat :ln the cecomia- same of unconrolidated deposits. Elewn days ware spent during the latter part of June 1958 and the remainder during September of the %me year. The work Wa8 under- taken to supplesent other geologlcral ~orkdone a8 part of the investigation of damr9iter. Examlnotlon and Interpretation vas mde of most of the readily aCC.8- sible road cuts and river bank expoarures of m6mnsolidatcrrd materials,

The di0CU8S$On la divided Into three metions dealing with the following areas, Revelretoke to Bigmouth Creek (Mags U,S, 24 to 291, Mica Creek (lamite to Bwh -2-

River (Maps KS. 31 to 351, and Blackwater-.._l__l___--- Cre.&-gg.Qolaan-- (Maps H.S. 38 to 41). The discussion ia speculative and many of the Interpretations arb based on limited evidence, The opinions expressed in the discussion should be used as guides for future work and not as ultimctte conclusions wir;tti, which may be reached by further studies,, The notes,on the maps are intended to be factual but It :is necessary to Interpret many exposures in order to describe tbm and this fact should be kept in mind in reading the notes.

IOTES ON COLUMBIA RIVER WSH.S. 24. TO 29 REVELSTOKE TO BIOMOUTE CWXK A sequence of late glacial and postglacial events can be postulated to account for the distribution and character of the unconsolidated deposit:I which are exposed along the valley of the Columbia River between Revelstoke and the mouth of the Goldstream River. llfhis sequence of events is speculative and In many Instances based on frag- mentary evidence. Nevertheless It should be useful ab a guide to planning, BRb as an aid in inturpreting the results of subsurface invsstigstlona of' unconsol.idated deposits along this section of the river. In summary the sequence of evcstnts appears to be: 1, Deglaciatlon, with the deposition of sorted and unsorted .

-3- glacial debris. 2. Trenching of earlier deposits to a level a%or below the present river level, Revelstoke Canyon might hatre been cut at this time. 3. Blocking of the Columbia River somewhere south of Revelstoke to form a lake. 4. Rapid rise of lake level to an elevation greater than 1,800 feet. This may be associated with a late re- advance of glaciers, 5. Lowering of lake level to about 1,flOO feet and stability

of the lake at this level for 8 tinte. 6. Development of alluvial fans and tdus deposits graded to the 1,800-fo0t lake level. 7. Rapid lowering of lake level and establishment of present drainage system. 8. Erosion of earlier deposits, landsliding, slopewash, formation of talus cones and alluvlal fens. mese factors are still modifying the diatributlon of uncon- solidated deposits in the valley, A d$8CuSSi~mof some of the deposita and features associated with these events will show some of the evidence on which this sequence is postulated. It will also inblcate that additional evidence from drilling or other exploration -4- may modify this sequcsnce of events. 1. The chief unsorted deposit of deglaaiation is till, an unsorted mixture of rock fragments, gravel, sand, silt, and clay. It Is generally dense and oonipaot but my ctontain lenses of sorted rock fragments. Although often impervlour it say oontain extremetly pervious soma. Till and various morainal materials were deposited with alsost no aorting direotly from tha glacial Ice. Where th.ey oan be positively identified they show the proximity of glacial Ice at the time of Usposltion~ Xn many cases till an8 morainal deporits may be confused with unsorted talu, and laad81ide deposlts, especially where only lilrrited exposurss em be seen. Where the deposits have a topographic ~xpresrlon this Is usucrlly 8uff'icient to dlstingulsh them, bat the distinction Is not so readily made from drilling resulta.

The distinction as Q rule Is inaportant~ different Inferences will be drawn from the presence of till and moraine deposits than fmm landslide and talus deposits, Meltwater flowing from the decrlinhg glaclarr washed, sorted, and deposited rook d.brir, whicrh had b6n initially trsutsported by the glaalers. These sortsd deposita 1ald dovn by running water some distanae in front of the glaoiers are known collectively a8 outwash sands and gf.av818. -5- Outwash gravels along this section of the Columbia River are generally well-rounded sand and gravel nrixtures containing some cobbles. The size distribution varies con- siderably, but the deposits are generally well washed and lacking In silt. They have no characteristic topographic form, probebly because of subsequent erosion, but are dis- tinguished from sands and gravels deposited from tributary streams by being generally more rounded and better vashed and by the fact that the distribution of the outwash deposits bears no close PelatIonsNp to present-day creeks. In addition to the gravels, there are a few arxposrpMss and some drilling records which show considerable thiCkne8888 of washed coarse sand, Some of these at least are believed to be part of the outwash sequence rather than later laoustring deposits.

These outwaah deposits probab3:y filled the valley of the Columbia River to elevations greater than 1,800 feet, In places they may have buried stagnant :ice, but within tho narrow valley no extensive areas of ketthd outwash are found. 2. The period of dovn-cutting by ‘the Columblol River through the outwash deposits has left only a few scattered rramnants of river gravels, These are we:Ll-warshed andl rouadsd

4 -6- gravels which locally appear to rest on outwash close to present river level, In many places these river gravels have been reworked during the present river cycle and form gravel beaches along the s?~ore. The main deposits of thla event are no doubt located beneath the broad river valler south of Revelstoke, In spite of limited evldenoe It Is thought that thls period of down-cutting took place before the depoaition of lacustrine silts and clays. It was perhaps during this period that Revelstoke Canyon was first cut. As the Columbia River cut down through e the outwash deposits, it was not everywhere superirnposd exactly on the earlier channel, At Revelstoke Canyon the present channel Is cut through bedrock to the east of the interglacial or preglaclal channel. ff sands and gravels in the old channal whloh drilling records show resting on soft lacustrine clayey silt are correlated with outwash deposits then cutting of Revelstoke Canyon dates from this period of down-cutting and the preceding events of deglaciation included extensive lscruatrlne depo8itlOn, If however the mnds and gravel8 are thick alluvial depolrlta the underlylzlg clayey sllts are depoarlts of the last lake to occupy the Columbia valley and eattimg of Revelstoke CPLngton followed th43 draining of this -7- lake. The drilling did not outline the entire section of the channel or show the character of the deepest deposits of the old ahamel, 3. After the period of down-cutting through the outwash deposits, the Columbia RiveF appears to hava been bloake8 somewhere south of Revelstoke to form a lake. Steeply dipping faresat beds of medim angular gravel am exposed in sections on La Forme Creek, Carnes Creek, $xLB Mars Creek. These gravels are believed to be remnants of deltas built into an early stage of the lake by these ureeks, ;Io0 doubt most other creeks built slallar deltas. The lowest lacustrine splndy silts and clayey silts would correlate with these deltaic deposits. 4, After the lake wars fomd there appears to have been a period during vhlch the lake level ro8e rapidly to some elevation well above 1,800 feet. The lake flooded the gravel deltas which ware beirsg halt by the varlaus creeks, an8 lacustrlns sandy gilts were depositad on top of deltaic gravels, This relationship Is shorn in exposures at Hars Creek, Carnes Creek, and Xa Forme Creek, but lacuastrlne deposits probably overlls deltaic gravef.8 near %he mouths of moat creeks. 5. After the lake level reachad 3.ts maxioaupa elevation, -8- it appears to have fallen to about 1,800 Feet and remained at about that level for some time. Sandy silts and clayey silts were deposited in the lake, and tributary streams built deltas. The level of the lake at about 1,800 feet may have been controlled by a spillway through Eagle Pass into the Shuswap Lakes . 6. In myplaces extensive fans and talus cones developed, which are) graded approx1matel.y to the 1,800-foot level. This period of lacustrine and al.luvla1 deposition is marked In places along the river valley by a discontinuous and Irregular terrace. Because the earlier outwash deposltfon was graded to a somewhat similar base level, the terraas, where It exists, may have a compound orl.igln. 7. The lake at about 1,800 feet appears to have been drained In a relatively short the, and the Columbia River cut down to its present level without forming extensive or well- defined terraces between present river 1cave1 and the 1,800- foot terrace. As noted on page 6 Revelstoke Canyon may have been cut during this period. If this wme the case, the lacustrine sediments In the old channel irest of Revelstoke Canyon are deposits of the latest lake. 8. During the time since the Columbia River reached Its present grade, the earlier unconsolidated deposits have -9- bsen considerably modified. Much of the lacustrine silts and clays have been disturbed by landsliding which @8rrIed them into the river to be washed way. Tributary creeks have cut down through glacial a& postglacial deposit8 and redeposited them in the form of alluvial fans. The Columbia River has reworked the dep081tS through whioh it cat, and the shorelines reflect the character of those deposits, Some taluaa deposits have been built, although less talus appears to have been deposited than during the construction of the 1,800-faot tsrraoe. NOTES OR COI.tMBIA RIVER MAPS M.8, 31 TO 35 MICA CREEX DAMSIITE TO BUSH LAKZS Between Mica Creek deunsite and Burh Lakes there Is a complex distribution of unconsolidated deposits. Only in a few inatanctss is it posslble to rdoognise over any sizable isire& deposits referable to EL particular event

01" source. This is due in part to the @roeionand burial of many of the deposits by the aechanlsnis of normal atrosion within a narrow valley. In part, however, it is thought that mng of the unconsolidated taaterPlals are dlscontinuous as the result; of the particrulaz type OF glaciation vhiceh produczced and deposited the=. 0 0 - 10 - It is thought that glacial ice moved Into the Columbia valley in this area from many tributary valleys and spread out in the form of piedmont glaciers which gradually coalesced and filled the valltry before iue flowed along the valley, These glacierkr would be some- what similar to the Bear River glacier north of Stewart, , as It exists today, The tributary glaciers coming In from one aide of the valley @ad then the other would block the valley, and between the ice lobes a complex mixture of ice-cantact end lacustrim depolaits would form, Terminal moraines of these lobe8 0 would be very suaceptlble to destruction by an Ice advance or by subsequent river erosion. The fluctuating ice levels would prevent the development of high-level drainage patterns sufficiently stable and well defined to be recognizable today, '0 As a result of this complexity It is not possible to suggest any general sequence of events for this ssatlon of river and only afew of the unconarolldoted dsposlts warrant discussion except as examples of the various pro- cesses involved. Glacial lake silts and silty c:Lays were noted in the widening of the Columbia Vi3lley at the head of the 0 - 11 - Big Bead where Wood River and River join tho Columbia, The thlckest exposed section is in a slltle whiclh has taken out part of the road about 2 miles west of Boat Encampment 4 (w M.S. 31, photo IBo, 5). Other shallow exposures were seen along the highway toward Boat Encarq3ment and on the trail to the Wood River Burn, Clay subsoils are reported from along the west bank of the Columbia toward Yellow Creek and from just north of the outlet of . An extensive glacial lake must have filltsd the Columbia River valley In the vicinity of Boat Encampment and may have extended up the Columbia River to or beyond Kinbasket Lake. This lake was a fairly lata feature of the Pleisto- cene sequence of events, but the maximum lake level and the control on the outlet of the lake are no& known. The relationship between the lacustrine deporits and a group of sand and gravel deposits ctxpoaed In road cuts between the gravel pit (H.S. 31, photo 80. 4.1 just west of the lanaslide on the highway and Mica Creek 8uBf't;e Is uncertain. It is thought that they 81'8 sand# and gravels deposited subsequent to the draining of the lake, and, izT this is the case, they should In some places rest on the lacustrine clay, Possibly an ice daa existed in the vicinity of' Mica Creek damsite and extended upstratam past Potlatch I 'i

- 12 - Creek. If this is the case the clays am not seen under the gravels because the clays were not deposited. It seems reasonably clear that the lacustrine clays are not deposited on top of these gravels. The gravels in the pit referred to above show some features which suggest ice contact depo- sition. It may be important to resolve the uncertainty e regarding the relationship between these clay and gravel deposits but more detailed work, includlmg; test drilling and test pits, would probably be needed. On the east bank of the Columbia River near Boat Encampment an area known as the "Wood River Burn" has been 0 investigated by Federal Government Surve;ys as a possible

IIOUTCB of impervious fI11. Glaolaltill mantled by coarse bouldery moraine including some large er:ratic boulders is exposed in shallow road cuts throughout this area. A test hole is reported to have been drilled 80 feet to test the character of the till. This till is a glacial deporit laid down prior to the formation of the lake into which the silts and clays were deposited, A similar lake aay have preceded the advance of ice, as silty sands containing thin layers of organic material are exposed along the highway beneath glacial till (M.S. 32, photo Bo. 2). A $pollen analyslrr, and radiocarbon dating of these organic layers would be extremely e - 13 - interesting. In other places along the highway exposures of coarse bouldery material were seen which. could be inter- preted as remnants of terminal noraines. The following are a few of the localities: M.S. 33, photo 1; Mas. 35, photo 1; and 14,s. 35, photo 3. There are exposures of laeustrine silty clays south of Carib00 Creek (N.6. 35, photo 2 and photo 3). The distribution of all these deposits seems to fit a pattern whieh could be interpreted as indictating that, following an earlier period of river erosion by the Columbia River, tributary glaciers advanced down some of the major tributary valleys and blocked the Columbia River. Bouldery moraines were built at th. termini of these glacier8 and the old river channel filled with silts that were deposited in lakes between the glaeieru. When the glaciers retreated river erosion largely removed the evidence of this event and only a few scattered remnants of moraines and lacustrine silts are to be seen at present. The absence of shoreline featurea and clearly remgnieable spillways makes it difficult to relate them silts to my partiaular lake and to dlrrtinguish them from the deposits of the more extensive lakes which occupied the valley at various times. - 16 - Between the outlet of FJnbasket Lake and a few miles south of Boat Encampment the Columbia River i3 flanked by poorly defined terraces up to an elevation of about 2,500

, feet. The terraces are not readily outlined either on the map or in the field an8 there are almost no exposures to show the character and Internal structure of the unoonsoll- dated deposits in which these terraces are cut. The stability of the bank8 from landsliding and lack of river bank erosion along the Columbia River 2s a striking feature of the section of river between Kinbasket Lake and Boat Encampment. Some

data is available from drilling done on EL sits 9,000 feet below the outlet sf Kinbasket Lake. On the basis of llnited observations the following origin is suggested for the terraced deporsit of unconsoli- dated material between Kinbasket Lake am9 Boat Enaampment. At one or mope tlmes during the glacial :perlot5 an ice 1oM occupied approximately the present basin of Kinbasket Lake. The ice lobe vas fed by tributary glaciers from valleys such as Khbasket River, Sullivan River, Windy Creek, and others. From the terminus of the ice near the present outlet of Kinbasket Lake, meltwater !‘loved northward and built 8 gravel outwaah train up to an elevation of perhaps 2,500 feet. This process may have been repeattad more than onoe, - 15 - and successive outwash trains separated by layers of lacustrine sediments or of glacial till may have been deposited. During one or more periods of river erosion, this outwash train was trenched and terraced. During periods of deep down-cutting, circulating groundwater may have dissolved some of the limestone sands and redeposited the lime to cement firmly some gravel strata. The deposit is not entirely late glacial, and deto1l.s by which its history could be interpreted have been obsoured by erosion and deposition. The dominantly granular texture of the deposit combined with a fairly extensive cementing by llm acc\?unts for the lack of exposures produced by land- sliding and river bank erosion. A layer of recent volcanic as]?.was observed In various places between Boat Encampment end Golden. It occurs in the topsoil just beneath the tree roots in many places and probably could be recognized in peat bogs and other recent deposits. Its origin and date are not known for certain but it might prove a useful marker horizon in studying recent sedimentation, as for example, in Kinbasket Lake. It probably fell during postglacial time from 4,000 to 8,000 years ago, and the area of postglacial volcanic activity in the vicinity of Clearyater on the Aorth Thompson - 16 ” River seems to be the most likely source. !W!PCS ON CULWXA RIVFR PU?S #,S,, 38 TO 41 BLACKWATER CREEK TO GOLDEN Unconsolidated deposits and geomorphic features along the Columbia River valley From nem Blackwater Creek to Golden provide evidence of a pariod of glaciation when the Columbia River valley was fillrid with a southward flowing ice tongue followed by a complex: sequence of lacustrine deposition and river erosion, A well-developed drrxl31lin pattern can be seen In airphotos of the bench which flanks the Columbia River on the west at elevation of 3,OOO to 3,SQO feet between Golden and Donald, Where it was examined west of Donald this bench Is a b&rock topographic feature thinly mantled by a sandy-clay tlll, Since the drmmliuoid ridges lie parallel to rock ridges which reflect bedrock structure, it may be that the drumlin texture intensified the evidence of bedrock structure). Nevertheless these drumlins are believed to mark the movement of A powerful valley glaeier discharging southward along the , On map M.S, 39 a mile or so south and east of Redgrave there is an area of meltwater channels and glacial 1 0 0

outwaah. Along the C,P.R, tracks near Redgrave coarse bouldery gravels are exposed which are believed to be glacial outwash and which indicate the character of material which may be anticipated In unconsolidated fill along this section of the Columbler River. None of these features however give mueh Information regarding the melting of the last glacier to occupy th.e Columbia River valley between Donald and Golden, Following the last retreat of the glaciers from the valley between Donald and Golden, the valley was filled by an extensive glacial lake, The maxirriua level of the lake appears to have been about 3,000 feet above sea level, This level is marked by conspicuous raised deltas near the mouth of Bbuewatsr and Blackwater Creeks; and by the, raised delta of the Kicking Horse River near Gcblden, Above an elevation of about 3,000 feet on the bench on the east side of the Coltmbia River between Golden and. Donald lacustrine silts and silty clays are absent and the depth of ve&thering and development of soils appears to be auch greater than below this elevation. This factor Is not easy to evaluate and could probably justify nore field arld laboratory studies, but it seems to indicate that above 3,OCO feet where the evidence Is not obscured by eroslon or l.andsliding, the ground .. 18 - has been subjected to weathering processies for a much longer time than elsewhere in this part of the Rocky Mountain trench , A complex sequence of 1-acustrine deposition and river erosion is indicated by exposures of the raised delta at the mouth of the Kicking Horse River and by exposures in road cuts along the Trans Highway from Golden to Donald, At least three events of lacustrine deposition are indicated, During intervening periods when the lake was drained lacustrine arediments were eroded and redeposited partly by landsllding, At least one of the interlake periods was rliarked by extensive deposition of washed river gravels. Drilling for bridge foundations near Donald seems to show

8 river channel eroded at least 200 feet below prs8ent river level and subsequently filled with vePy soft uncompacted lacustrine silts. The moat likely explanation tor the succession of lakes separated by periods of erosion is that downstream from Donald and Columbia River vas blocked at various times by glaciers from tributary valleys. During one mah event at least, glacial meltwater flowed through the valley of Succour Creek and Blackwater Creek from glacial ice in the valley of the Buerh River, This me1twatc:r stream built an - 19 - extensive gravel delta into the lake att an elevation of about 3,000 feet. At the highest level the control on the lake was probably through some spillway to the south of Golden, At lower lake levels the water may have drained through various spillways around the ice to the north. Differential varplng of the land as it was loaded and unloaded by glacial ice could also account for various lake levels, though the present study did not reveal any ooncluriive evidence of this process.

British Columbia Department of !dines, Vlotoria, E. C.