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 Columbia River 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.