BRITISH COLUMBIA DEPARTMENT OF MINES Hon. W.J. ASSELSTINE, Minister JOHN F. WALKER, Deputy Minister
BULLETIN No. 12
Reconnaissance
IN THE AREA OF Turnagain and Upper Kechika Rivers Northern British Columbia
by M. S. HEDLEY and STUART S. HOLLAND
1941
VICTORIA. B.C.: Photwffset by CHARLES F. BANFISLD,Printer to the King's Moat Excellent Majesty. 1941. ..J ILLUSTRATION>
Page
Keymap showing position of r'egion in northernBritish in Columbia 3
Plate I* h Looking south along Rocky Mountain Trench fromPassSifton near 4
B Lookingnorth-westward along Rocky MountainTrench from near Sifton Pass 4
Plate11* A Lookingsouth-eastward up Kechika River from Valemonk Mountain -. 9
B Lookingnorthward across the Trench from Valem ont Mountain Valemont ._ 9
Plate III* A Looking north across the Trench towards GatagaMountain ...... 10
Lookingnorth-east across the Trench near TerminusMountain ...... 10
Plate IV View lookingnorth-eastward across the continuation of the Rocky Mountains13
KechikaRiver, looking towards Terminus Mountain 1 13
Plate V Lookingtowards granite ranges at head of Dall Lake 14
TurnagainRiver valley, looking north .- 14
Plate VI Lookingsouth-eastward along the through-valleytowardsDall Lake 17
Lookingsouth-east across the head of M osquito Creek valley Creek Mosquito 17
Plate VI1 Lookingsouth-westward up the valley of theupper Turnagain from the head of M osquito Creek 18 Creek Mosquito
* The photographs on PlatesI, I1 and I11 arereproduced throughthe courtesy of the Department of Lands.
(ii) Page
Plate VI1 B Lookingnorth-eastward down the valley of theupper Turnagain from 'Kheaton Creek ...... 18
Geological map of the Turnagain and upper Kechika Rivers ._.....I._....I._...... In 'pocket RECONNAISSANCE
IN THE AREA OF
TURNAGAIN AND UPPER KECHIKA RIVERS
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1. Kechikaand Turnagain Rivers drain an extensive region of the northern Cassiar and Rocky Mounta,ins in northern British Columbia.
2. The RockyMountain Trench* separates the Rocky Mountains on theeast fromthe Cassiar Mountains on thewest. The high,deeply incised Rocky Mountains of thesouth dwindle in elevation to low wooded ridges and lose their identity north ofTerminus Mountain. The Cassiar Mountainsare more irregular and much higherthan the Rockies and ex- tend north'nrardbeyond the limits of the region.
3. The termination of the northern Rocky Mountains was not caused by greater erosion in that section but by lackof Tertiary elevation.
4. The highcentral granite range of theCassiar Mountains hasbeen sculptured by intensealpine glaciation, whem- as the Rocky Mountainshave been only slightly affecte,i. The Cassiar Niountains show theeffects of alpine glacii3- tion with cirque basins formed. and some valleys'modified. However, thedistribution of erraticsindicates an east- ward movement of continental ice from the Cassiar Moun- tains across the Trench and over the Rocky Mountains.
S. The drainagepattern in part is normal,and partly ex- hibits a trellis pattern reflecting bed-rockstructura:!. control. Over much of theregion the drainage system hasresulted from stream piracy on a majorscale.
6. A highflanking rock bench on the upper Kechika is the result of pre-glacial stream rejuvenation.
7. The Rocky Mountains are composed of longranges made U;I of a great variety of tightly folded sedimentary rocks.
8. The centralcore of theCassiar Mountains is a granitic batholith 20 to 30 mileswide and mapped for a length of 100 miles. The flankingmountains are composed largely of sedimentaryrocks and a minoramount of volcanics.For
* Rereafter the Trench refers to the Rocky MountainTrench.
(iv) 20 miles north of Sifton Pass the Trench is underlain by Upper Cretaceous or earlyTertiary conglomerate, north of which the Trench is floored with glacial drift and allu- vium. South of Dall Lake theCassiar batholith is flanked by schists acdgneisses formed b.~the action of numerous pegmatites,elsewhere there is little or no contactmeta- morphism.
9. All thesoft argillaceous rocks are highly cleaved, and contorted by drag-folding.
10. The Trench is a boundary across which it hasbeen impossible to make lithologic correlation between the two different mountainsystems. The Rocky Mountain structurecomprises regular,steeply-dipping, tightly compressed folds.Folding inthe Cassiar Mountains is more irregulsr,the structural trend is different from the Rocky Mountains,and the folds are interrupted by cross-warpsand are complicated by drag- folding,thrusting and some overturning to theeast. The core of the system is theCassiar batholith, some 20 to 30 miles wide.
11. Placer-golddeposits have been worked on "neatonand 'Walker Creeks. The countryhas not been thoroughly pros- pectedbut exploration on othercreeks should begoverned by the knowledge already gained.
12. h fewlode-deposits are known butnone has undergone any development. A sectionnear Dall Lake radialto a bulge in the eastern contact of the batholith is consideredthe mostfavourable lode prospecting area. IMTRODUCTION
The upper Kechikaand TurnagainRivers together draitn a region greater than 6,000 squaremiles in extent in northern British Columbia (seekey map). They unite,as the Kechika, to form a majortributary of theLiard River. Kechika River heads atSifton Pass, latitude 58 degreesnorth, and flows north-westward in the Rocky MountainTrench along the flank of the northernmost Rocky Mountains.Turnagain River heads on the west flank of theCassiar Mountains and cuts across them. in a general north-easterly direction to join the Kechika at Chee House, an abandoned tradingpost, about 70 miles from LiardKiver and 60 miles due south of the Yukon boundary.
During1939 topographic mapping of the Trench by the Department of Lands was completedfrom Finlay Forks to S3.fton Pass, and in addition triangulation was al.mostcompleted from Sifton Pass to Lower Post on Liard River, a few milessouth, of the Yukon boundary. This work was continued, at a reduced rate, in 1940; the Trench was mapped as far north-west a8 Gatagaand Terminus Mountains. Triangulation was completed to the Yukon boundaryand extended up Turnagain River to within 25 miles of an existing network to the east of DeaseLake.
The authors travelled with the two surveyparties from Prince George, using their base camps as headquarters from which fly trips were made during the greater part of the season. hi. S. Hedley so travelledwith the topographic party underthe direction of ?I. C. Stewart, as far as the mouth of GatagaRiver. In September he and his assistant weretra.ns- ported up Frog River by boat to the first main fork andfrom there they proceeded on foot by way of Jackstone Creek an.d Dall River to the upper TurnagainRiver. S. S. Holland started with the triangulation party under the direction of H. Pattinson, comnenced work at the mouth of GatagaRiver, and progressed down river to Chee House and thenwestward by way of the MosquitoCreek trail to 'Nheaton Creek. The authorsre- turned to the coast byway ofDease Lake and TelegraphCreek.
Topography of a' strip 10 miles wide, centering on Kechika River, was obtainedfrom vertioal aerial photographs taken duringthe season. These, together with horizontal photo.- graphs of the strip between SiftonPass and Gataga Mountain, werefurnished through the courtesy of the Department of Lands and greatly facilitated work both in the field and in theoffice. Topography lateralto the photographed strip was sketched in the field and controlled by the triangulation network. fill topography on TurnagainRiver was mapped in this
-1- fashion. Elevations of most peaks other than those occupied by triangulation stations have been calculatedby photo- topographic methods. N. C. Stewart was consistently helpful during the course of the office work. The topography at the head of the Turnagain is compi1,ed from: (1) Map 381-A of the Department of Xine's and Resources, Ottawa: (2) a sketch map published in 1933 by Mandy*; (3) a map published in Bulletin No. 2, 1940 of the Department of Mines, British Columbia.
The writers wish to express theirthanks to Messrs. Stewart and Pattinsonfor assistance in the field, especially the former,who altered his plans in the latter part of the season to make the overland trip more feasible.S. D. Town- send and R.G. McEachern gave admirable assistance throughout the season.
Acoess and Means of Travel
The region isso large that only the established routes into it may be mentioned, particularly as littleor nothing is known of other possible routes. That followedon the journey in 1940, is from PrinceGeorge. Regular travel is over the waterways from Summit Lake,32 miles northof Prince George via Crooked, Pack, Parsnip and Finlay Rivers to Ware. The distance to Ware, the Hudson's Bay Companyon postFinlay River, is 350 miles and the trip can be made by carry-boats ing a pay load of 2 1/2 tons. The only hazardous seotion on the Pinlay is Geserters Canyon; it cannot be navigatedin high water and is halfa milelong. From Ware a pack-trail follows the Fox River44 miles northward to Sifton Pass.Fox River is navigable with difficulty; for a distance of 23 miles in a straight line, from abovea short portage close to the mouth.
The,other principal route is from Telegraph Creek, the head of navigation on Stikine Rivar and served regularly by river-boat during the ope'n months from about15 Mayto October 15. A branch'road leads from Telegraph Creek to Dease Lake, a distance of 72,miles. From there a'pack-trail ar.d winter road extends eastward to'heaton (Boulder) Creek,a distance of 45 miles.
A fair pack-horse trail extends throughout the region, following the east sideof the Trenchfrom Ware on Finlay River to the river-crossing at Chee House, thence to Lower Post on Liard Biver. Another trail, in parts not very well located or cut out, extends from the mouth of Turnagain
* Ann. Rept., Min. of Mines, Brit. Col.,1933 pt. A.
-2- Key Map of northern British Columbia showing region outlined byheavy broken lines.
.. .
.... Plate I
A. Lookingsouth across the Rocky MountainTrench towards the Cassiar Mountains. SiftonPass is in themiddle distance and Fox Lake lies to the left. Note thebench flanking the heads of Kechika and Fox Rivers. A faultscarp lies along the base of the mountains in the left distance.
B. Lookingnorth-west from near Driftpile Creek. Note the area of benchland between the Trenchand the through- wlleythat continues in mid-distance. Valemont Mountain is near the right margin. Riverup Sand and Mosquito Creeks to theupper Turnagain and connectswith the trail to DeaseLake. A branch of this trail leadsfrom Deadwood Lake to L4cDame on the Dease River. fin- otherpack-horse trail leads east from the Kechika valley at the mouth of theTurnagain towards Fort Nelson. There are no otherrecognized pack-horse trails and few foot-trails other than those used by Indiansand by trappers during the winter months ..
There are fragmentary trails on the Turnagain River, Indiar. trails that lead from Deadwood Lake to Dall Lake,and a reportedtrail from Dall Lake to JackstoneCreek. Horses lightly loaded with narrowpacks could be takenover most of thesetrails, but only after some clearing. The majorvalley- bottomsand thebottoms of through-valleysafford reasona.bly good going and sufficientfeed, but oanyon sections shou1.d be avoided.Travel in the Rocky Mountainssouth of Terminus: Mountain is difficult owing to the fact that the tributary valleys flow in canyonsadjacent to theTrench.
In 1934, E. C. N. Lamarque, who was scouting a route for the Bedaux expedition, travelled with an Indian andt.hree horsesfrom Sifton Pass to DeaseLake. His routeextended up Ludwig Creek to a through-valley abreast of the third lake on that stream, thence across upper Rainbow River to Frog River, upJaokstone Creak to the edgeof the granite and thence westerly to the head of Flat Creek on theupper Turnagain. Horseswere also taken by Lamarque south-eastwardfrom Ludnrig Creek to Fox Pass by following valleys roughly parallel to Fox River.In 1939 healso blazed a trail from Chee House southward on the west side of the Kechika valley.
Horsescannot be obtainedin the district. Thoseused by the survey parties during 1939 and 1940 were driven over- land from FortSt. James. Horses may be obtainedat Tele- graphCreek and drivento the upper Turnagain, a distance of about 120 miles.
The KechikaRiver is navigable by boats of the type built at Summit Lake and in use onthe Parsnip and Finlay Rivers. Two suchboats 36 feetlong, built from whipsawnlumber at the mouth of Driftpile Creek-in 1940,and equipped with 16-horse- power motors,were in use duringthe 1940 season.Navigation is difficult even at highwater above Big Creek, and is impos- sible above DriftpileCreek. The crookedchannels and numer- ous drift-piles on theKechika make boatingdifficult, but not toohazardous for skilled men.The lowerriver, in the general neighbourhood of ScoopLake, is easilynavigable.
GatagaRiver was ascended 15 miles without diffioultiy in 1940. It is reliablyreported that the canyon 8 milesfarther upstream is passable and that a boat can be taken through it and a number of milesbeyond. Frog River was ascendedeasily on September 1st as far as the main fork and with difficulty 3 miles farther up JackstoneCreek, which is smaller than. the main stream. No boat was taken up theTurnagain and the river was not followed throughout on foot so the question of its navigability is not known. Judgingfrom the amount of water,the observed sections of theriver and thegrade, it seems possible that boats could be taken as far up as the mouth of Cassiar River at favourable stages of water.
The largerlakes make good landing for airplanes,notably Deadwood, Dall, Scoop,and DenetiahLakes. An airplanehas landed on the lake east of theupper Frog River, and landings couldbe made on Spinel Lake, the lake north of DavieCreek, the lakes on Ludwig Creek, and those at the head of Moodie Creek. Deadwood, Dalland ScoopLakes are,hvvever, the only oneswhere low clouds would not make flyingdangerous: and the other mountain lakes should be approachedonly when vis- ibility is good.
Stretches of thelower Kechika River might serve as landings, and there is onewide, straight stretch a mile or twobelow Gataga fork, but driftwood makes landinghazardous whenever theriver is high.
Freight can be shippedfrom Summit Lake to Ware for 8150 a ton. From Wrangell,Alaska, freight can be landed at DeaseLake for $120 a ton andfrom Dease Lake to WheatonCreek can be flownin for $100 a ton. Food and generalsupplies may beobtained at Prince George,Tare, Telegraph Creek, Dease Lakeand Lower Post.
Historical Notes
Fur traders were the earliest explorers of the region. In 1834 J. McLeod of the Hudson's BayCompany ascendedthe Liard from old Fort Halkett, travelled up the DeaseRiver to DeaseLake and crossed over to the head of the Stikine.
In 1824Samuel Black of the Hudson's BayCompany explored theheadwaters of theFinlay. He records in his diary when he passed the mouth of what is now known as Fox River that it heads at a pass two daystravel northward, whence a riverflows northwardinto the Liard. Thispass was subsequently named Sifton Pass by Inspector Moodie of the RoyalNorth-west Mounted Police.Nothing howeverwas known ofthe Kechika and Turnagain Rivers until many years later.
-6- Placer-gold was discovered onDease Lake in 1873and in the ensuing few years the many miners and prospectors in the countryspread far afield. Placer was foundon Walker Creek in 1,877 and by 1886 severalparties of prospectors hadgone into both the Turnagain andKechika basins.
A trading post was operated by Sylvester at Chee House in 1887, as wellas a "Lower Post"on the Liard, but .it i.s not knownwhen these wereestablished: Supplies for Chee House werepacked in with horses fromMcDqe, then know as Sylvester's Upper Post.
For many years there is no record of anybut random trappers and prospectorshaving visited the region. In 1.924 after a discovery of gold on GoldpanCreek, prospecting e.gain reachedthe headwaters of theTurnagain and in 1932 claims werestaked on %heaton(Boulder) and the nearby Bullion, Hall andFaulkner (Palmer) Creeks. Since then there has been some placer-miningactivity, including a drag-l.ineoperation on 'Wheaton Creek started in 1938.
In 1898 Inspector J. D. Moodie of the RoyalNorth-west Mounted Police passed through the Kechika valley on a trip from Edmonton to the Yukon: His route was by way of Fox Riverand SiftonPass, thence down theKechika. He crossedthe Turn- again near the mouth of Sand Greek, travelled along the existing trail to Deadwood Lake and from there to McDame. His report is the first authoritative description of the region.
No geological work was done in the region prior to 1940, withthe exception .>f theTurnagain River headwaters. .In 1887 G. M. Dawson went down Dease Riverand ascended the Liard and FrancesRivers en route to the Yukon, and in the same year R. G. McConnell descended the Liardto the Mackenzie. Geology of DeaseLake was studied in 1925 by Kerr and Johnston and from the head of the Turnagain to McDame in 1935by Hanson and McNaughton. Mandy reported on theplacer creeks at the hoad of theTurnagain in.1933. Holland studied the placer-deposits andbed-rock geology at andnear Wheaton Creek in 1939.
-7- Bibliographx
G. M. Dawson: Geol. Surv., Canada, Ann. Rept.,vol. I11 pt. 1, 1889.
R. G. McConnell:Geol. Surv., Canada, Ann. Rept.vol. IV, 1890. Geol.Surv., Canada, Ann. Rept., vol. VII, pt. C, 1897.
W. A. Johnston:Geol. Surv., Canada, Sum. Rept.,1925, pt. A P. A. Kerr:Geol. Surv., Canada, Sum. Rept.,1925, pt. A
V. Dolmage: Geol.Surv., Canada, Sum. Rept., 1927, pt. A
G. Hansonand
D. A. McNaughton: Men. 194, Bureau of EconomicGeology, 1936.
J. T. Mandy: Ann. Rept., B. C. Dept. of Mines, 1933,pt. A.
J. D. Mood.ie: Sessional Papers No. 15, vol. XXXIII, No. 12, 1899,Ottawa.
S. S. Holland: Bull. No. 2, B. C. Dept. of Mines,1940.
-8- Plate 11.
A. Looking south-eastwardup Keohika River from Valemont Monntain. Mount New incentre distance. Note the bench developed in the bottomof the Trench.
B. Looking northward across the Trench from Valemont Moun- tain. Note the canyonat the mouth of Forsberg Creek. Gataga River valley is seen beyond ridge in distance, Brownie and Gataga Mountains in left distance. Plate 111.
A. Lookingnorth across theTrench towards Gataga Mountain from a point near the mouth of FrogRiver. Nata the boldfront of the Rocky Mountains at this point.
B. Lookingnorth-east across the Trenchfrom a pointwest of TerminusMountain. The valley at thispoint is wider,the mountains much lower,and the front more subdued than in the above picture taken some 20 miles to the south. PHYSICALFEATURES
The region takes in part of the country between latitudes 58 and 59 degreesnorth and longitudes 126 and 129 degreeswest. It includes some westernranges of the Rocky Mountainsand ex- tendsalmost completely across the Cassiar Mountains. Between these two mountainsystems is the Rocky MountainTrench (see Plates I and 11). From SiftonPass at latitude 58 degrees norththe Kechika River flows north-westward in the Rocky Moun- tain Trenchbeyond the mouth of theTurnagain River. The Fox Riverflows south-eastward in the Trench from the same Pass which is one of the major divides in this remarkablylong, straight valley that flanks the western front of the Rock,y li4ountains and oontinues beyond thenorthern extremity of those mountains.In the region, the Trench is a dividingline, physiographically and geologically,between the Rocky Mou:n- tains to the east and theCassiar Mountains to the west.
The region is mountainousand for the most partdeeply incised. All major summits areF,500 feet or more in eleva- tion and a few in the granite ranges in the western part (exceed 8,000 feet, From SiftonPass, elevation 3,273 feet,the Ke- ohikadrops to an elevation of about 1,900 feet at the month of TurnagainRiver, a distance of 100 miles. The Fox River drops800 feet in 44 miles to join Finlay River at '#are. TurnagainRiver, at an elevation of 3,450 feet at the western margin of the region, drops 1,550 feet in a distance of 105 milesto its mouth.
The Rooky Mountains consist of parallel structural rj.dges that wedge out at anacute-angle against the Trench. The general summit level is inexcess of 6;OOO feetin elevation, andreaches a maximum in BrownieMountain, elevation 7,595 feet. The mountainsare deeply inoised, particularly in the sectionabreast of SiftonPass. Driftpile Creek entersthe Trenchthrough an impassable gorge and most of the smaller streams are boundedby precipitous walls that rise to the very summits. The rangejust east of GatagaRiver is ex- tremelyrugged and 5 miles east of the river roundedridges attainelevations of about 7,000 feet. This hi.gh western range of the Rocky Mountainsends at TerminusMountain (see Plate 111) and theinner ranges, which for some miles to the south-easthave become progressivelylower and more subdued inoutline, dwindle to thenorth-west into timber-covered hills andlow ridgesseparated by wide, swampy valleys(see Plate IV A).
TerminusMountain marks the north-westerrmost extremity of the Rocky Mountains,beyond which the summit levelde-
- 11 - creases to between 3,500 and 4,000 feet at a point east of Chee €louse. In thissection the valieys flare widely and theirtimbered slopes extend to comparatively lowsummits. Exceptwhere the major oreeks flow through canyons as they enterthe Trench, the valley bottoms are wide and often swampy.
The,CassiarMountains are structurally less uniform, and aresubdivided by broad-bottomed,deep valleys, some of which arethrough-valleys. They arehigher than the Rocky Mountains and lessregular; a number of peaks inthe eastern ranges are 7,000 feet in. elevation or more,and the peaks in the granite. rangesare about.1,OOO.fegt higher. The highest peak inthe district, at the head of Ludwig Creek, is 8,900 feet in eleva- tion, and SharkTooth Mountain, south of theTurnagain is 8,765 feet. The unbroken frontalong Fox Rivergives way at Sifton Pass .toan irregular bench-like area (see Plate I B) widening to 5 miles at lowerRainbow River,north-westward of which rises a prominentlimestone range. Another bench-like area about 4 mileswide lies to the east of Mount Xinstonand out of it a range rises to 5,600 feet, extendsnorth-westward beyondTurn- again River, and presents. a straight unbroken front on the Ke- chikaside. . BeyondMount Winston,however, the eastern ranges are less ruggedand their summits decrease to about 5,000 feet north of theTurnagain. In thatsection there are many long ridges parallel to the structural trend of theunderlying formations.
The CassiarMountains culminate in thegranite ranges,. west of which they are less ruggedand less deeply incised. In the section of theupper Turnagain River, although the general level is high(King Mountain .7,914 feetj there are large,poorly incised masses andlong upland slopes. There is a marked contrast on'the Turnagain between the wide, flar- ing valley with its interlocking spurs west of ThreeForks Creek (seePlate VII) and the deep,almost gorge-like valley east of the Cassiar River.
There are many small glaciers in the granite mountains. They appear to.be stagnant and not actively eroding their beds,because streams heading in that section are nearly all clear. The amount of icediminishes to the north-west and is verysmall near the Turnagain valley; one small patch of ice on King Mountain and anather south of the head of Mosquito Creek are the only glaciers, andnone are reported to the north-west, as far as Dease River.
There are no glaciers in the Rocky Mountainswithin theregion. The nearest is a largeice-field on Lloyd GeorgeMountain at the head of Gataga River.
- 12 - Plate IV.
A. View lookingnorth-eastward across theContinuation of the Roc@ Mountains from a point 15 milesnorth-west of TerminusMountain.
8. Kechika Rivk'r,; lookingsouth-eastward towards TerminusMountain. A. Looking west towards the granite ranges at thehead of Dall Lake.
B. Turnagain River valley, looking north. Dall River enters short of the low hill on the right. Glaciershave been.at one time more widespread,and the effects typical of ice erosion are seen over a larger area than thatin which existingglaciers occur. Cirque basins, ha.nging valleys,truncated spurs, gravel-filled valley-sections a.lter- natingwith canyons, pot-hole lakes, and morainalpiles are seen.from Fox Riverand the flanking range south-west.of Sif- tonPass, through the upper waters of Rainbow andFrog Rivers tothe mountains west of DallRiver (see Plate V A) and the upperbasin of MosquitoCreek (see Plate B). East of this general line there is little evidence of ice erosion and only a fewsmall cirques are seen, notably on theeast side of Mount Winstonand along the east side of the same range to the north-west. This seems to mark theformer maximum extent of intensealpine glaciation. In the Rocky Kountains a few small cirques point to former alpine glaciers on the;east side of GatagaMountain and otherhigh mountains nearby, but none of thevalleys appear to have been modified by glacial erosion.
Accumulations of glacial drift are widespread but are prominentonly in a few places, notably in the Fox River val- ley and in the angle betweenKechika and Gataga Rivers. The lowerKechika valley is filled with drift but most of this hasbeen stream-sorted, so that hummocky terrain andpot-holes &re localonly. Elsewhere the mantle of drift is thin and dis- continuous. Moraines', inthe form of irregularbottom-filling, high-levelsemi-benches and plasters on the hillsides, and lateral ridges along the walls are seen locally in the lower valleys of Frog andGataga Rivers, as well asin the Turnagain Rivervalley. Turnagain valley, aboveKutcho Creek is deeply filled with drift in which thereare many pot-holes.Glacial erratics are widespread and granitic boulders are seen not only in the front ranges of the Cassiar Mountains but in the Rocky Mountains as well; some are as far east as Rabbit River.
The drainage forms a trellis work patternbordering the Trench.This is mostpronounced inthe Rocky Mountainsbut is obviousalso in the Cassiar Mountains as far west as Dall River.North of TerminusMountain inthe more or lessuni- form slate belt it is lessobvious, whereas west of the granite,in the section of theupper Turnagain River, the drainagedoes not present a uniformpattern. Kechika and Fox iiiversfollow straight courses along the Trench, but TurnagainRiver valley cuts through the mountains in a number of prominentbends. The valleys of lowerFrog and Gataga Riversas well as that of Moodie Creek are straight.
The Rocky MountainTrench is 4 to 9 mileswide along FinlayRiver south-east of theregion. It is constricted along the Fox and.upper Kechika Rivers to a width of 1 l/k to 2 1/2 miles and widens to about 4 miles at GatagaRiver.
- 15 -
. North-west of TerminusMountain it widensagain, rather abruptly, to betiveen 6 and 7 miles.In the section at Chee House the north-easternmargin is indistinct and farther to the north- west it is more so.
All tributaries of the KechikaRiver, with the exception of the three large rivers, enter the valleythrough canyons (seePlate I1 B). The canyons are mostpronounced inthe upperKechika section, being cut through a generalbench-level, but in the lower river the tributaries also flow in canyons at themargins of the Trench.
BetweenPox Lake andKechika canyon theTrench is incised to a depth of about 400 feet across about one half its width.. This incision,with its flankingrock and gravelbenches, is one of the most distinctive features of the region (see Plate 11). The bench-level is developedalmost exclusively on the eastern side of the Kechikaand is notseen north of the canyon. It is a rockbench almost completely covered with stream- depositedgravels that have filled all irregularities in the former rocksurface. Locally the gravelsare semi-cemented so thaterosion produces bold cut-banks and, 8s at the mouth of Driftpile Creek, striking hoodoos. The bench-levelslopes slightly towards the valley andhas the same longitudinal grade as thepresent stream.
FrogRiver enters the Trench at grade as a meandering streamin a deep, straightgorge. Gataga River has a short canyon-section 23 miles from the mouth,but enters at grade through a wide, straightvalley. Turnagain River, from abreast of the head of MosquitoCreek to its mouth,flows in a deep,narrow valley that in places might be classed as a gorge. Two canyon-sections on theTurnagain, one just abovethe mouthof Kutcho Creek and one just abovethe mouth of CassiarRiver, together lower the river about 500 feet.
The streamsgenerally throughout the Cassiar Mountains are characterized by abruptchanges in grade andby hanging relationships of some members. These effectsare not all the product of glaciation, as will be shown in the next chapter.
There areseveral remarkable through-valleys. One in the Rocky Mountainsobserved to be at least 40 miles in length, is crossed by Driftpile andBig Creeks and contains streams that flow fromlow divides northerly and southerly to join thelarger crosscutting streams or simply tobreak through theranges to join Eechika andGataga Rivers. The most re- markablethrough-valley west of theTrench starts as a bench at Sifton Pass and. extendspast Dall Lake, across Turnagain Biver to Deadwood Lake. Thisvalley is cut into and across Plate VI.
A. Lookingsouth-eastward along the through-valleytowards Dall Lake fromapoint near the divide betweer the south fork of MosquitoCreek andtheTurnagain.' Turnagain Riverflows Prom rightto left and comes through the mountain front in the middle distance.
B. Lookingsouth-east across thevalley of MosquitoCreek at thedivide near its head. The high mountain on the left is 7,600 feetelevation. Note thecirques on theeastern sideofthe peaks, The rook in the middleground is granite. Plate VI1
A. Looking south-westwardup the valley of theupper Turn- again River fromthe head of MosquitoCreek. Note .. the'interlocking spurs in the widely-flaring valley. King Mountain is on the sky- line to the left of centre.
B. . Lqokingnorth-eastward down-the valley of theupper , Turnagainfrom Wheaton Crgek. Kutoho Creek comes in from the.right in the middle distance and t6e- Turnagain swings sharply to the left behindthe:high mountain on the sky- line. The mountainson the sky- line to the right are granite. by thepresent drainage, but the former,broadly-flaring out- line is still to beseen, incised to depths ranging from 100 feet by minorstreams to 1,000 feet or more by majorstreams (seePlate VI A). Other,less continuous through-valleys farther to the west extend from Finlay River headwaters into thegranite ranges.
The country is for the most part heavI.1~wooded, the kind and density of growth varying with soil and amount of precipi- tation.Spruce growseverywhere except on thelarger gravel flats; pine is abundmt on gravel flats ofthe lower Kechika andpoplar is foundeverywhere at elevations below4,000 feet. Birch grows sparsely in the lower Kechikaand Turnagain val- leys and in the valley of MosquitoCreek. ' A fewtamarack trees wereseen at ScoopLake. Willow and alder grow on thesl.opes to timberline and scrub.birch is found at and neartimberline throughoutthe region. Timberline is between 5,000 and 5,200 feet, and is somewhat lower inthe north-westernmost part; of theregion.
Yearlyprecipitation varies with the locality, but with theexception perhaps of thegranite ranges, is nowhere par- ticularly heavy.There is a marked decreasein precipitation north of SiftonPass, both in rain and snowfall. The snowfall at Sifton Pass is. saidto average between 3 and 5 feet on the ground and to lessen towards Gataga fork,north of which the averagefall is less than 1 foot, and the ground is apt to be bare of snow duringmost of thewinter months. By mid-July there is still suffioient snow to hamper field work at higher elevationsabout Sifton Pass, but farther north there is snow only on the highest summitsby that date.
On thelowest slopes of the Rocky Mountainsnorth of Kechika canyon and on some flats north of Terminus Mountain there is semi-drybelt vegetation such as open patches of grassland,groves of aspen, and a considerablemount of thymeand juniper. In thislatter seotion 30 head of horses werewintered in 1939-40 without hay. Similar conditions exist in lowerDall and lower Turnagain River valleys.
;Tintersare reported to be cold, but the sumers are -warm. In 1940, at low tomoderate elevations, there were no frosts in July andAugust and the lowerKechika valley was said to be completelybare in April. The summers, how- ever,are not altogether pleasant, and inJuly, 1940,there wereonly 4 warm, sunnydays. Local showers fallalmost daily and anobserver on a high summit sees constantly moving clouds andnumerous rainstormsin every direction. 'Wind blows almostinoessantly on the summits and can be piercinglycold even in mid-summer. The wind is notsteady anddoes not always
- 19 - blow in the same dir,ection as inthe valleys. It is likely thatthese crosswinds cause the constantly changing cloud patterns and thelocal rainstorms.
Game is sufficientlyabundant to supply the needs of anytravellers. Moose are found in all sectionsbut are not numerous,and appear to havebeen greatly hunted in recent years.Caribou are scarce in the summers butare reported to winter in large numberson RabbitRiver and to migrate to andfrom the summer feeding grounds on the west flanks of theCassiar Mountains. Deer are.occasionallyseen and bear are fairly numerous.
Sheep and goat are found in the Rocky Mountainsbetween Driftpile Creekand Terminus Mountain. Inthe Cassiar Pdcun- tains they are foundfrom Valernont Bcuntain north-west and weston the eastern side of thegranite. One band of 70 sheep was seennear Gataga Mountain.
- 20 - PHYSIOGRAPHY
Thereare many physiographicfeatures of importance and interest, the full explanation of which wouldbe anextremely valuable addition to the formativeprocesses of a large sec- tion of northern British Columbia.This reconnaissance ntakes it possible to mention only the more general features and to outline 2ossible explanations.
Rocky Mountains
Thereremains some doubt as to the aotual limit of the northern Rocky Mountain structure,but there is no doubtthat theranges become lower in elevation and eventually lose their idectity(see Plates I11 and IV A). The presentwriters did not examine the country beyond Chee House, but on days of good visibility it was possible to see many miles north and east. From long rangeobservation, from elevations determined by the triangulation survey, and from the old reports, the following seems to sum up existing knowledge.
The eastern front of theCassiar Mountains continues far tothe north-west, although perhaps with a generallowering in elevation. The front is continuouswest of Lo-wer Tost, through the lower great bend in the DeaseRiver and is, accord- ing to Dawson*, about 25 milesfrom the mouth of FrancesRiver. The Rocky Mountainshowever, do not persist as the series of bold,high ran.;es characteristic of thecountry near the upper Kechikaand Gataga Rivers.
The westernranges of the Rocky Mountains become progres- sivelylower north of TerminusMountain, and losetopographic identity somewhere south of the Liard. NcConnell noted i.n his reconnaissance of the Liard that the onlyrange of the Ro'zky Mountains that reaches the Liard was at VentsRiver, and that thishigh limestone range dwindles rapidly as it approachus the river from thesouth-east andalmost disappears topo- graphically withiwa fewmiles north-west of theriver. !!he country south of Liard River from the mouth of Vents River to TerminusMountain, east of the front of theCassiar Rangea, and north of theLiard for some miles in this Same section, is a region of rounded timberedhills and low, undulatingpltiteau with no prominent or distinguishable mountains. The structure of the Rocky Mountains is probablycontin- uous and the same rocksextend to and past Liard River, but
* Geol.Surv., Canada, Ann. Report,Vol. I11 Pt. 1, 1889.
- 21 - through a low, plateau-likeregion averaging 300 to 500 feet above theriver. Some hills may riseabout 500 feethigher or to maximum elevations of about 3,500 feet.
The country north of the.Liard in this section is not explored, but two mountainranges are known on the lower PrancesRiver, the Simpson Range on the west and theTses-i-uh Range on theeast, which are on the line of continuation of thewestern ranges of the Rocky Mountains. The westernflanks and roots of thesemountains are buried beneath rocks which wereassigned by Dawson to the Tertiary, and whichoocupy a basin of unknown extent. Dips are as steep as 20 degrees on Frances and LiardRivers and deformation has apparentlybeen much lessthan in the Sifton formation. Whether or notthese rocksare the same ageas the Sifton formation is unknown, but therehas certainly been far lessdeformation in the north- westernbasin. The rocks of the Simpsonand Tses-i-uh Moun- tains are schist andlimestone, rocks originally not dissimi- lar to types found in the Rocky Mountains,but a great deal more altered. The nextrange to the east, the Logan Range, has a core of granite which extends at least as far southward as theupper canyon on the Prances River.
Thesemountains are from 60 to 100 miles north-west of the last, high western ranges of the Rocky Mountainsand might possibly be considered the continuation of them,beyond a major downwarp in the structure, were it not for their greater deformation. The generalnorth-westerly trend of.these moun- tains is alone no proof of topographiccorrelation, because all structures in this part of British Columbiaand the Yukon haveapproximately the same trend.
it seems conclusive that the Rocky Mountains die out on the south side of the iiard, with the exoeption of a range of limestone at the mouth of VentsRiver. Terminus Mountain, thelast high mountain bordering the Trench, i.s composed of a thicklimestone member that is truncated by theTrench. Other,intermediate limestone members crossthe Liard without rising above the low, plateau-likesurface.
The inference,which seems inescapable, is thatthe north- western, Yukon mountainsare part of anolder system, and that the Tertiary uplift, to whichthe Rocky Mountainsystem owes its being,dies out on thesouth side of LiardRiver. The Liard, whichmust be an antecedent stream, flows locally in , canyons a fewhundred feetdeep. This figure is anindication of the amount of uplj.ft, an insignificant amountcompared to theuplift of the Rocky Mountains in seneral.There is no comparisonbetween this small incision in a plateau-like re- gion and the gorge of theantecedent Peace River through which the latter stream crosses the Rocky Mountains.
- 22 - Cassiar Mountains
The Cassiar Nountainscontinue many miles to the north- westand south-east of theregion. The backbone is underlain by graniticrooks and is about 1,000 feethigher in elevation than its flanking ranges and the western ranges of the Rocky Mountains.North-west of Mount Winston theeasternmost range of the Cassiar Mountains is somewhat lowerand lessrugged thanthose elsewhere in the region. But this may bedue to the softer character of theunderlying rocks, rather than to a wastage of the mountains; certainly the resistant quartzite of the mount Ninstonrange forms a series of prominentpeaks higherthan almost any others in thefront ranges. Great.er irregularity in structure and greaterdifferences in rock: compositionaccount for the fact that the Cassiar Mountains are not made up of ranges as uniform or'parallel as those that characterizethe Rocky Mountains. The high,rugged front range flanking Fox River is composed of highly metamorphosed rocks, a fact thatexplains the physical character of this rangeas well as the fact that it is situated on animportant divide.
Little is known of the actual limits of this mountain system. The north-eastern flank is apparently continuous and the south-western margin passes intohigh plateaucountry abovewhich riseisolated flat-topped masses. To thesouth theCassiar Mountains merge into what are sometimes referred to as theStikine Mountains, of uncertainextent and orie.nta- tion.Although within the region there is a centrallylocated batholith that forms a backbone,elsewhere the batholith is not apparently central.
The drainagepattern is ingeneral haphazard, in marked contrast with the drainage of the Rocky Mountains. The head- waters of .major rivers interlock and the Turnagain andDease Rivers cut completely across the highest ranges.
Very little is actually known of the history of the northern Rocky Mountains or of the Cassiar Mountains,but it seems clear fromobserved features that the history of the latter system is more complexand that mountainbuildi.ng was initiated at an earlier date.
Rocky Mountain Trench
The Rocky MountainTrench is a long, Straight trough (seePlates I and 11). It hasgenerally been considered to extend the Full length of the Province and for some distance into Montana.Throughout its known length it is a flat- bottomed valley with steep,straight sides, and is occupied
- 23 - by rivers of majorimportance. Recent work by Lay* shows that the Trenchdoes not persist as a continuousvalley, but that in the region of the McGregor River and theheadwaters of ParsnipRiver, there is no throughtrough. Here there is a change in trend of the Rocky Mountains,and each member of theTrench, projected, passes through low-ground in which no majorstream channel ever existed. If the Trenchbe considered as a structural feature quite apart from the fact that now, and for a longperiod of time, it hasbeen a locus for major drainage,then there is no proof that the basic structure is notcontinuous, whatever that basic structure may be.
Theories as to the origin of the Trenchhave been sum- marized by Evans in the Brisco-Dogtooth area in the southern Rocky Mountains**. No singletheory is adequate toexplain more than a small section and the present writers havebeen unable to find any contributingevidence in the northern sec- tion,but it seems certainthat there has been faulting along the line of theTrench, regardless of the effect of the Rocky Mountain uplift or the possible localization marginal to an oldland mass; the nature of the faulting is unknown.
Recentlycompleted topographic mapping (1939 and 1940) shows theTrench from Finlay Forks to Chee House, a distance of 260 miles,to be as straight as any feature of that length canpossibly be. The straightness and uniformity .is suchas to indicate that the drainage has been initiated along a zone of structural weaknessaccompanied by faulting. The walls have undoubtedlybeen affected by faulting in comparatively recent (pre-glacial)times but the only positive evidence of faulting known to the writers is a scarp some 100 feet in height, on the west side of upper Fox River (see Plate I A); this has little significance other than-to prove the fact of lateral movement supposedlyTertiary inage. Other evidence of move- ment is in thefact that the Sifton conglomerate, of Upper Cretaceous or 3oceneage, that was laid down only in the Trench,has at a later date been much deformed,folded and drag-folded.,while at presumably the same timethe bordering olderrocks have been sheared and deformed. There is, moreover, slight local evidence of a faulted relationship between the con- glomerate and the older rocks on the eastern margin.
The Trenchhas commonly beenconsidered as a marginal feature of the Roc& Mountains,i.e., as connectedgenetically withtheir formation. Certainly the Rocky Mountains are con-
* Bull. No. 11, B. C. Dept.of Mines, 1941.
** Geol.Surv., Canada, Sum. Rept. 1932, pt.. AI1
- 24 - tinuous,while other mountain structures such as the Selkirk andColumbia Mountains are truncated at an acuteangle by theTrenoh. The Rocky Mountains form, in many sections and particularly in the northernsection, the smoother and more uniform wall of the' Trench.
If the Trench is closely bound in origin with the Rocky Mountainsthen it should die out and disappear, if not at the exact termination of thosemountains then within a short distanceto the north-west. It is not known that it does terminateand the matter should be left in doubt, beoause there is some indicationthat the Trench continues. In the section atand immediately north of Chee House, theeastern wall of theTrench cannot be located with certainty against the low hills representing the almost completely wasted.Rocky Mountains. Still farthernorth, there is no recordedevidence of a depression,but in the low landbordering the Liard River there is notsufficient relief to produce one, and there is no evidencethat the Kechika or anyother large stream flowed alongthis section. The underlyingstructure, however, cwld continue without being detected.except by considerable de- tailedstudy. The easternfront of the Cassiar Mountains is continuousand passes west of the uppermostLiard River, a distance of at least 150 milesnorth-west of the end of the Rocky Mountains,and thestraightness of thefront sugges-ts some structurallyoontrolling feature, probably the Trench. The fact that the southeasterly-flowing upper Liard paral'lels themountain front, strengthens this view.
Drhinage
Drainage within the Rocky Mountains is by stream deeply incised in a trellis work pattern such as would be produced by long continued erosion of an elevated mass. The valleys show no modifioation by glacial erosion and the only abnor- mality is theincision of thestreams in their lowermost 5:ec- tions adjacent to the Trench.
Ijrainage in the remainder of the region contains many abnormalitiesin the form of rejuvenation,stream-piracy and interruptions.Furthermore, a remnant of a drainageentirely superseded by thepresent stream pattern is indicated.There is, withoutdoubt, a long and complicatedstream history.
A through-valleyextending from Sifton Pass, across Dall and Turnagain Rivers to Deadwood Lake has already been men- tioned. Only fragments of thisvalley remain,as it hasbeen deeplycut into and across by existingdrainage, but it un- doubtedlyrepresents a former major stream valley,apparently drainingnorthward and several hundreds of feet above present
- 25 - crosscuttingdrainage. Other through-valleys exist which suggest,but do notprove the existence of anancient drainage different from that of thepresent day.
Streampiracy, by headward erosion,has modified or re- versedthe flow of a number of streams. In some casesthis can be proved,but in others it mustbe inferred. A clear example is given by the Pox River,
Fox Riverhas captured the uppermost Kechika River from the region of Fox Lake to Sifton Pass, a distance of 10 miles. The evidencefor this is thatthe benches flanking Sifton Pass extendsouth-eastward to abreast of Fox Lakeand tributaries whichswing corthward across the bench at its innermargin swingsouthward close to Fox River. The capturetook place in pre-glacial time because the upper Pox River has not been incisedsince the recession of theice, but flows sluggishly throughaccumulations of drift. It is obviousthat a stagnant lobe of iceoccupied Fox Rivervalley belowFox Lake, as evi- denced by the depth and irregularity of the drift, but no glacial damming produced either the highbenches or the one- timenorthward flow of thetributaries. On thecontrary, the benchesare continuous with the Kechika benches (see Plate I) and thenorthward-flowing stream sections, although short, are incised in rock in such mannerand toodeeply to be the result of glacial or post-glacialerosion.
The through-valley is incised bymany of the streams flowingalong its course, some of whichare actively eroding headwards,and the valley itself is almostobliterated at a number of points by transversestreams. The most likelyex- planation of the latter fact is that the ancient stream was sapped by piratestreams from theupper Kechika, notably Rainbowand Frog Rivers and Denetiah Creek. The relation of the valleys of Dall andTurnagain Rivers is perhaps more complex,but piracy even by such streams is by no means im- possible. Moodie Creek, a strongtributary of theKechika, heads in lakes at a levelcomparable to that of thethrough- valley, and thestream flowing westward from this low pass is insignificant.Again, there is littleto prevent Deadwood Lake (elevation 2,925 feetj from eventuallybeing captured by a tributary of the mainMosquito Creek which, 6 miles dis- tant, is 375 feet lowerthan the lake.
Piracy onsuch a scale is notfrequently encountered butthere is evidencein these latitudes of otherpiracies of equalsignificance, as in thecase of DeaseLake valley which was formerly tributary to the Stikine and now drains northward.Johnston* even goes so far asto suggest pirscy * Geol. Surv., Canada, Summ. Rept.1925, pt. A p. 45.
- 26 - by an ancestral Dease River that virtually cut its way through theCassiar Mountains by headward erosion. There is also some evidencethat the Eagle River headwaters flowed into the Stik- ine.
There is some indication but noproof that part of the. upperTurnagain River was tributary to the Stikine and heis sincebeen captured with a consequentreversal of flow to the north-east. If such is thecase then the Turnagain River is not an antecedent stream but the headwaters on the western flank now drain through the mountains in a valley produced by a stream workingheadward from nearCassiar River.
The great bendsof the middle and lower Turnagain form an abnormal pattern. The pattern of theCassiar and DallRivers, with the connecting stretch of theTurnagain and the course of the combined water to Chee House is normal, as judged by the drainagepattern of the region as a whole,whereas the Turnagain flowssouth-eastward for some miles,then drops about 300 feet through a canyon to meet theCassiar River and swings almost through a rightangle. Another canyon-sectionimmediately aboveKutcho Creek drops theTurnagain at least 200 feet from a higher,widely-flaring valley.
Combine these abnormalities and suggestions of piracy in theTurnagain valiey, and thehistory is obviously complex, but j.t must also be taken into account that in the upper val- ley,tributaries such as Nheaton Creek allenter the Turnagain valley over falls or throughcanyons and it is evidentthtit therehas been a considerablemount of pre-glacialrejuvena- tion of themaster stream. The matter of rejuvenationof this section has been fully dealt with by Holland" , who estimates the indicated total amount of incision to be about 500 feet. On Wheaton Creek long continuederosion in the early Tertiary produced a mature topography in which the tributary streams enteredthe master river at grade. In the late Tertiary the TurnagainRiver was rejuvenated andbegan downcutting. Tk.is in turn initiated downcutting on iTheatonCreek, three stages of which are apparent and are represented by rock bench-levels alongthe creek. All are below thehighest rock bench which represents the bottom of the Tertiary valley prior to reju- venation. The rate of downcutting on theTurnagain was greater than on Wheaton and the other tributaries, conse- quently there is a hanging relationship betweenthem and the main.river, shown by the tributary streams entering the main valleythrough canyons and over falls or steepcascades. Subsequentglaciation has not greatly obscured this relation- ship and the pre-glacial dating of therejuvenation is sig-
* Bull. Xo. 2, B. C. Dept. of Nines,1940.
- 27 - nificantbecause it supports an.explanation greatly different from the alternative of over-deepening by glacial gouging in the bottom of the main valley.
The upperKechika, from Sifton Pass to the canyon, is flanked by rock and gravelbenches at a remarkablyuniform height of almost 400 feet above the present stream (see Plate 11). Althoughlower bench-levels occur, the upper level, developed chiefly on the north-eastern side and only locally on thesouth-western, is a continuous and veryprominent feature. The bench is almostentirely gravel-covered but it is underlain by rockwhich is seen, in a few frontal cut- banksand in tributary canyons, to extend to the top of the gravel. A veryfew rock “islands” which project above the gravelare no higherthan 30 feet above it. In short,the highestpoints of theirregular (eroded) rock bench almost exactlycoincide with the blanketing gravel terrace. This compositebench, sloping gradually upward towardsthe’ flanking , mountains,has the same down-streamgrade as the present river. It is half a mile or more inwidth and occupiesabout one-half of the former bottom of the Trench.
Thisbench is left as the result of .a pre-glacial ‘reju- venation or over-deepening of theKechika valley. The surface of therock bench is irregular, pointing to the fact that it was erodedprior to being covered by gravels.
The entrenched valley was blocked below Paddy.Creek, particularly by moraines transverse to the Trench and which are as much as 1 1/2 milesin length. Boulder-clay is seen blockingthe old channel at the upper end of the present can- yon. The damming was approximately at the same level as the ancientvalley-bottom, and behindthe dam theentrenched val- ley filled rapidly with gravels brought in by the tributary streams. The riverhas subsequently cut through the moraine andbed-rock in a canyon somewhat east of theformer channel, and has scouredthe upper valley of gravelsto its present outline.This scouring of gravels is notcomplete, and the bench front shows rockonly locally. The tributaries.in large part appear at this time to have re-cut their incised coursesin the bench, but locally the streams erodingthrough the gravel veneer have cut new canyons in rock and gravels.
It is significant that the downcutting of the tributaries did not keep pace with the rejuvenation of the trunk stream, butthe tributaries entered it pre-glacially,as at the present time,through canyons or evenover falls. In otherwords, the hanging relation of the tributaries was brought about by reju- venationand not by glacial erosion of the trunk valley.
- 28 - The entrenchment of the upper river must have been. brought about by a rejuvenation of theentire river system, and thereshould be evidence of the same or a similar bench- level. flanking the lower.Kechika and in -the valleys of Frog andGataga Rivers. There is. no suchevidence, and it must beassumed either.that rejuvenation deepened these three valleys. equally across theirentire widthsor that such E, benchhas been subsequently destroyed. It is believedthat glacial erosion did not remove the bench (if it ever existed) in lowerKechika or Gataga valleys.
The historyof upper Kechika drainage is complex and. dates backover a longperiod of time. This applies also. to theupper Turnagain, but it is impossibleto correlate the two directly.Although the canyon-sections on Liard River' proveentrenchment of that river and point to rejuvenation of the entire major river system,other influencing factors may easily haveplayed a part. It is notpossible to explain the causes of the many obviousinstances of- pre-glacialchanges in level 'or the changes in position and direction of flow of the major drain- agesystem, and particularly, to determine the time of the:ir inception, but a suggestion of. possibleprocesses may be of valueto future workers; Firstthe indicated age of the drainage is great enough to havebeen influenced by changes in elevation of the Rocky Mounta'ins in Tertiary time. ' Dovm- cutting of the Liar'dRiver across a moderate uplift has resultedin a rejuvenation that is bound to have affected the entire system.Other factors arepossible faulting .' along the line of the Trench and possible uplifts in the Cassiar Mountains,with or without tilting. Piracy of StikineRiver headwaters might be related to the great Tertiary modification of that drainage whiah undoubtedly resulted from the outpourlng of tremendous quantities 0.f lavas in the region of the GrandCanyon.
Whatever the causes havebeen;the present drainage system in the Cassiar Mounb'inshas undergone many changes in Tertiarytime. Discrepancies in elevation of about 500 feet between the master and tributary streams in the vicinity of Weaton Creek alone point to the necessity for attaching majorsignificance to stream history; the solution of the problemsinvolves not only local causes but factors which may haveaffected the region as a whole.Glacial and post,- glacial activity have, in many instances, made the solution far from easy.
- 29 - Glaciation
Two types of glaciation must berecognized: alpine glaciation by cirqueglaciers and numerous valley glaciers that extend from the summits for varying distances down the valleys and continental or ice-cap glaciation by an ice-sheet that covered all or nearly all the surface of the region.
The erosiveeffect of theformer is to sculpture the higherslopes and summits and to modifythe valleys to a U-form. The effect of thelatter is lessobvious and con- sists of rounding and smoothingkhemediumand higher slopes and also, in some cases,involves modification of the form of themaster valleys. Both typesdeposit drift andmoraines. It is believed that continental glaciation may partly obscure evidenceof.earlier alpine sculpture, and that later alpine glaciation will destroy or complicatethe evidence of contin- ental glaciation.
In the region there is much evidence of alpine glaciation in sculpture anddeposition, chiefly in the Cassiar Mountains (seePlates V A and VI B). Depositionalevidence of,contin- ental glaciation consists. chiefly in the wide distribution of erratics and in accumulations of drift in the lowerKechika andGataga valleys; erosional effects of the ice-cap are not so obvious,and in fact the presence of theice-cap is only proved by its depositional effects.
Glacialerosion is notconfined to the higher mountains thatat present support small glaciers,but extends eastward to Fox Riverand to the high-level through-valley. East of this general line there is little evidence of glaciation in theCassiar Mountainsand even less in the Rocky Mountains. Zxcept for the modification of the valleys of FrogRiver and Denetiah andMoodie Creeks, glacial erosion formed a few cirques on the eastern side of Mount Winstonand other mem- bers of the same range;east of theTrench erosion produced only a few small cirques on the east side of Gatagaand other high mountains.
Alpke glaciation was initiated.in the high granite rangesand spreadeastward with the formation of valley- glaciers that occupied all the easterly-flowing streams such as Ludwig and JackstoneCreeks, Rainbow Riverand others. These valley-glaciers reached the through-valley and spread andcoalesced, but did not, generally, modify the valley outline. Sone of thisice escaped by way of DallRiver valley, and also,transversely, over the bench between Sif- tonPass and Rainbow River and through the valleys of Frog River,Deaetjah and Moodie Creeks. The flowingice lost
- 30 - erosive power in the Trenchand its effect was mainlydeposi- tional.Lateral moraines in lowerFrog River valley and trans- versemoraines in the Trench south-easterly from its mouth, prove that an easterly-flowing ice tongue did, at least reach theTrench at this point. An icetongue also travelled d.own TurnsgainRiver and presumably reached the. Trench.
Continental glaciation is believed to have been universal inthe region. The generalice movement was eastward,as proved by the distribution of granite erratics as far as Rabbit River, 40 miles or more from the batholith; serpentine erratics alsotravelled eastward. It is not known inwhichdirection the ice moved on the western flank of theCassiar Mountains, al- thoughHanson and NcNaughton foundevidence for a southerly direction.
The part of the ice-cap that flowed eastward from the high granite ranges overrode the region andmust have filled the Trenchand other valleys that were transverse to the direction of flow. At thistime or stage of glaciation erosional effects were slightand the principal remaining evidence is depositional,although there musthave been llu-ge quantities of drift broughtinto the Trenoh also by the trans- verse valley-glaciers.
The surprising or anomalous feature is thelack of erosion or modification of form of easterly-trending valleys in the Rocky Mountainsand or" similar smaller valleys on the Cassiar Mountain front.Although the rocks are so soft artd wellcleaved for the most part that normalerosion would soon obliteratesmall cirques, yet the evidence is so slight that it seems obvious that onlylocal and small glaciers existed on the eastern sides of the highest sumits.
- 31 - GENERAL GEOLOGY
The bed-rock formations consistof great thicknesses of sedimentary rocks anda very small amountof volcanics in- truded by a granitic batholith of majorsize. Besides the mapped volcanic members, thin bandsof green schist and slate were observed at scattered localities but not suffi- ciently widespread to be mentioned separately elsewhere. The general formational strike is north-westerly. The field work having been distinctlya reconnaissance, the rockfor- mations have been divided into large lithological units. Only a few,poorly preserved fossilswere found,so the age of the rocks is largelyunknown, and lithological correlation across the Trench is impossible.
The Cassiar batholith has already been named. The Sif- ton formation isa new name proposedfor the conglomerate that occupies the bottomof the Trench south-eastward from Mount New, and that has been shown by Dolmagebe contin- to uous far beyond the region, at least 95 miles south-eastof Sifton Pass. Other members or lithological divisions are treated, not in order of age, which unknown,is but from west to east. Because of the lack of correlation across the Trench, the rocksof the Cassiar andof the Rocky Mountains are treated separately.
Cassiar Mountains
Member 1
This member consists ofwhite, flesh pink and grey rhyolite flom, and rhyolitic tuffs and breccias. The dominant rock appears to abe flesh-coloured, highly- quartzose breccia, whose constituent feldspars are kaolinized but whose quartzis clear and glassy. The rocks outcropin an elongated area about8 miles long and1 l/Z miles wide on the south forkof Mosquito Creek near the divide between it and Turnagain River.
This member appears to occupy parta trough of in the older Member 7 and though someof the volcanics dip west- ward their general structure is unknown. The general appear- ance and similarity to Tertiary volcanics elsewhere in the Province suggest that these rocks may be Tertiary in age.
Member 2
This member consists entirelyof serpentine. On a weathered surface the rock may be greenish-grey, bright-green,
- 32 - greenish-blackor reddish-brown. In placesthe serpentine is intenselysheared, elsewhere it is massiveand considerablo variationsare exhibited from placeto place.
The serpentineoutcrops in a beltranging between 3 and 8 mileswide and extendingsouth-eastward from Falls Creek near the headof the Turnagain across Wheaton Creek to the head of PerryCreek. This belt may extendfarther.to the south-east,but its extent in that direction is not known. However, it doescontinue some 30miles to the north-west as shown on Map 381-A of the Departmentof Mines and Resources, Ottawa.
Serpentineoutcrops in one otherarea about a mile wide on the north side of TurnagainRiver about midway between Kutchoand Hard Creeks.
The serpentineevidently has resulted from theserpen- tinization of.peridotite which is intrusiveinto the older Dease series.
Member 3 - Dease Series
The sedimentaryrocks that lie betweenthe western con- tact of the Cassiar batholith and the 129th meridian evidently belong to the Dease series as mapped byBanson and McNaugbton* west of thatmeridian. The series is predominantlysedimen- tarythough it includes at least onevolcanic member. It com- prises black slate with a moderatelywell developed cleavage, black slaty argillite, thin bedsof fine,grey sandstone and massivebeds of light-grey limestone 5 to 200 feet in thick- ness.
The volcanic member is 3,000 to 5,000 feet wide and is made up of green andesitic flows and some associated frag- mentalrocks.
The rocks occupy a broad belt bordering the Cassiar batholith on the .western side.Close to the batholith, and formed as a result of it, is a narrowbelt of mica schist and quartz-micaschist. These rocks are the metamorphic equivalent of argillaceousrocks which away from the batholith are little changed except for the development of slatycleavage.
The series as a whole strikesnorth-westerly and in lssge partdips to the north-east. However, insufficientknowledge. prohibits outlining the major structure of the.series where it is exposedon the upperTurnagain.
*Idem. 194,Bureau of Sconomic Geology, Ottawa, 1936.
- 33 - NO further data can be addedregarding the age of the series which was indica'ted by Hansonand McNaughton as in- cluding much of the Palaeozoic from the Silurian to the Permainand possibly even the Triassic.
Member 4
This member consistschiefly of fine-grained massive granular greenstone and andesitic flows associated with a' subordinate amount of fine-grained,thinly-bedded green tuff and brown andblack slate and argillite. The rocksoutcrop in a belt 4 to 5 mileswide flanking the Cassiar batholith on its easternside near the head ofMosquito Creek. Although theandesite is intruded by thebatholith it shows little or no alteration other than a slight increase in granularity near thecontact.
The extent of this.volcanic member to the south-east is not definitely known except that it doesnot cross the Turn- againRiver as a continuousbelt, but apparently ends some 5 or 6 miles south of MosquitoCreek. Neither is its north- westerly continuation known with certainty, yet about.15 miles in that direction Hansonand McNaughton have mapped comparable volcanic rocks flanking the Cassiar batholith on its north- easternside. In spite of thefact that the rocks are not definitely known to becontinuous, the close similarity of rocktypes and general relationship to the batholith strongly suggest that Member 4 be correlated with the McLeod series of the Eagle-McDa-e sheet.These rocks therefore are probably younger than the adjacent Member 7.
Member 5
This member consists chiefly of quartz-micaschist, alsomica-schist, quartzite, and bands of limestone. It occu- pies a broad belt bordering the batholith and hasnot been recognized north of Dall River.
The coarseness of the schists and the degr.eeof meta- morphism are greater in the southern part, in the drainage of Ludwig Creekand Rainbow River. The mica is platy and garnetsare abundant in some bands;locally the coarser quartzites are arkosic and the size of the feldspar grains suggestsgrowth and recrystallization. Local bands are gneisses. Between Jackstone Creekand upper DallRiver the metamorphism is less intense, there are no garnets and themica is finer: even at the granite contact there are no coarse, gneissic phases except within -a few feet of the actual contact. In thesouthern section the schist is folded,where- as in the northern section the schistosity is regionalacross a folded series.
- 34 - Limestone members up to 200 feet in widthoccur in both northernand southern sections, also bands of impure calcar- eousrocks. These are the only horizons capable of correla- tion:but insufficient work was done todetermine the structure.
On Plat Top Mountainand in the basin of lower Ludwig Creek dips are for the most part low,and the structure is oneof broad, considerably warped and otherwise irregular flexures,Farther west dips are steep, and there is con- siderable minor contortionas well as major folding. Nor-th of Jackstone Creek dips are moderate on the average but there is some steep drag-folding.
Member 6
Thesephyllites, schists and argillites, with minorbeds oflimestone form a narrow band that wedgesout at Ludwig Creekand widens on lower Rainbow River. Thesame rocksare found. on upper Dall River .where either the 'member is much wider or thereare changes in lithology of borderingunit:: of Members 5 and 7.
They arehighly fissile, soft rocks, considerably crum- pled for the most part, and it is evidentthat deformation. hasbeen localized in these.incompetent rocks. The thin- bedded argillaceoussediments are converted to phyllites and glistening sericite schists laced with thin bandsof lime- stone; on Dall Riverthey are principally argillites. The struoture is highly complex in detail, and themajor struc- ture is not known.
Member 7
In this.member limestone is predominant. Large bluffs and entire mountains are composed of this rock, and interbands ofslates, phyllites and argillitesare subordinate both in amountand intopographic expression. The limestone is white to greyish and weathersto a light shade ofbuff or dirty white. The argi.llaoeousrocks are thin-bedded and the lime- stone,although locally thin-bedded.and slaty, is in general thick-bedded and massive.
Themember is narrowon the south and widens at the ter- mination of theSifton conglomerate until, abreast of Valemont Mountain, it makes up theentire mountainrange. It Grosses the Frog River and continues diagonally across the Dall River valley as a series of prominentlimestone ridges, the western- most ofwhich &re trunoated by thegranite. In thesouthernmost section the member is tightly folded but on both sides of Frog Riverthe average attitude is nearly flat, with abruptwarps and local majordrag-folds.
- 35 - Member 6
The divisionbetween this and Member 7 is notsharply marked. It is more a line on thewestern side of whichthe rocksare dominantly limestone and on the eastern side argil- laceous and quartzitic,with a minor amount oflimestone. The member is h-eterogeneousand changes inlithology along the strike.
The lowerflank of ValemontMountain and the lowerparts of Froggiver and of DenetiahCreek, are underlain by phyllites, argillites andimpure gri.tty and calcareoussediments, for the most part thin-bedded.Three large bands of limestoneare in-. eluded, oneof which forms a conspicuouswall several miles in lengthnorth of the mouth of FrogRiver. Prominent bands of quartzite on the western margin are seen north of Valemont Mountain. A bandof heavy-bedded quartzite,several hundred feet thick, passes through Mount Winstonand forms the backbone of a range with several summits well in excess of 7,000 feet elevation.
Changes in lithology along the strike affect the limestone and quartzite that would otherwiseserve as markers throughout thenorthern part of the region. The massivelimestone band at the mouth of FrogRiver plays out into thin-bedded, impure limestonenorth-west ofDenetiah Creek, and the quartzite of Mount Winston,strong and prominent enough to form a high range of mountains,loses its identity somewhere southof Turnagain River.
The structure is verypuzzling. There has undoubtedly been some overturning along either warpedaxes or along axes at anangle to the genecal formational trend. In addition, the softer andthinner-bedded rocks are much contorted. As a re- sultthe structure, andeven thesimplest outline of it, is obscure.
Member 9
This member consistspredominantly of calcareousrocks, largelythick, grey limestone, thinly-bedded limestone and calcareousslate, calcareous argillite and a minoramount of blackslate and thin sandy beds. In contrast to the other members this one,with the exception of some limestonebeds, weathersto a fawn orpale buff colour. Much ofthe buff- weatheringcalcareous rock is believedto be dolomitic. The member underlies a width of but 3 miles on the low ridge to the north of Mount Winston,whereas farther to the north- west on thenorth side of TurnagainRiver it extendsacross a width of about 15 miles.Across that width individual for-
,- 36 - mations.arerepeated many times yet the detail structure .is notknown.. The more massive units dip at low ansles,whereas thethinly-bedded rocks are strongly contorted in minor d:?ag- folds.
Fossils were collectedfrom two localities, 1 and 2 miles south-.eastof the two lakes at the head of thesouth-west fork of SandCreek. These were reported on by W. A. Bell,Chief, PaleontologicalSeotion, Minesand Geology Branch, Ottawa::
"Lot A: Diphyphyllumsp. Chonophyllum centre very fragmentary Syringopora sp. Brvozoa" - at least two soecies Atrypareticularis \Linn) very small specimens Orthis sp. " Gypidula 2 sp.
"This is probably a Silurianhorizon. The fossilsare so silicifiedthat structure is lost. Gypidula is perhaps more common in the Devonian,but several species occur in the ,Silurian. The Orthis is a Siluriantype. "Lot- B: Zaphrentis 2 sp. Favositessp. Halysites or' gracilis Whiteaves cf Protarea sp. cfColumnaria alveolata Goldr'uss or Favosites sp. H poorpreservation of structure in one spotsugKests the former.
"One of theZaphrentis axd the general association of these species suggest an Upper Ordovicianhorizon of Richmond age. "
Othersimilar fragmentary fossils were seen north-west of Sand Creekand also near the main fork of Mosquito Cree:k.
Rocky Mountains Member- 10 Volcanicrocks are exceedingly rare in the Rocky Mountains, yet this member comprisesmassive, fine-grained, green volcanic flows,cleaved, fine-grained, thin-bedded green tuffs, sheared and altered coarse volcanic breccias and a veryminor amount of thinly-beddedargillaceous tuffs. Near the peakof Gataga Mountainthe rocks are cut bynarrow, red. jasperoid veinlets,
- 37 - andal'ong the front of the mountain near their contact with theadjacent sediments the volcanics are intensely sheared and altered to talc and rusty-weatheringcarbonate. Elsewhere, however, theflows aremore or less massiveand retain their amygdaloidaland porphyritic texture.
This member outcrops in a lensabout 8 mileslong and 2 mileswide mainly on the front of GatagaMountain, and appears to be an infoldinto Member 14. Althoughthe rocks are similar to Member 4, no correlation of the two is possible. '
Member 11
This is a slaty,calcareous memberof considerableapparent thickness flanking the Trench on the east andextending as far northas Kechikadanyon. The rocksare light to medium greyin colourand are characterized by beinghighly cleavable. They aredominantly argillaceous and calcareouspaper-thin slates, poorgrades of phyllites, and slatylimestones. Massive bands of limestoneare minor in amount.' The readycleavability re- sults in ravelling of outcrops and the production of great quantities of talus and of a thin cover of cleavage fragments.
The average dip of these rocks is north-eastward at moder- ateto steep angles, but there is much minor contortion. The thin-beddedrocks are'folded and crumpled, across.which a super- posed cleavagegives, in many cases, a high.degree of fissility. Therehas been more than one period of deformation,the effects of which are mostmarked closest to the Trenchbut extend at least as far eastwardas the summits of the first range. The seconddeformation has refolded the rocks, a refolding accom- plishedthrough the cleavability; there is notmerely a simple folding of the cleavage planes but a contortion and locally a mashing of the whole rock mass.
Member 12
This member is characteristically gritty, and is rkde up of siltstones,sandstones and lesslimestone and shale. 'It forms a reddish-weatheringrange, of which Mount Mew is the mostprominent summit.
The gritty or silty rocks are rather incoherentand pro- duce much fine,reddish talus. Two varieties of quartzite occuras locally prominent bands; one is fully recrystallized, vitreous white quartzite of a highdegree of purity, and the other,for some reason is a poorly cemented rock made up al- most entirely of fine, well-rounded andpitted sand grains. Intermediatetypes and some argillaceoussiates are also present.There are some limestonebands, but few calcareous slates.
- 38 - This member appears to be synclinal and the of peaks the range are aligned along the axisof the syncline. Complete confirmative evidence was not obtained, as there is consider- able local contortion, butthe dips of Members 11 acd 13 are towards this member and are seemingly continuous beneath Lt.
Member 13
This member is very similar to, if not identicalwith Member 11. If Member 12 is the bottom of a major syncline, then the two are identical.
The only difference between Members11 and 13 is that; there are less phyllites and highly-fissile, papery slates:in the latter. There is also more flaggy, caloareous slate and slaty limestone in the eastern partof Member 13, but the .oen- tral part is dominantly argillaceous slate. The absenceof true phyllites may bedue to the lesser amountof deformat.ion eastward or away from the Trench; certainly there is mash- less ing and foldingof~the cleavage than in therocks of Member 11 that border the Trench.
The dips are,in general, steep towards the west, but with local contortion and some drag-folding.
Member 14
This member is composed dominantlyof limestone in thick bands between which are bandsof argillite, phyllite and quartzite. The average dip is steepto the south-west.
The limestone formsa high, castellated range that is orossed by Gataga River and endsin Terminus Mountain, where the last of the limestone is truncated by the Trench. This range containsthe highest peaks in this general sectionof the Rocky Mountains. The baldness of the range, and the factthat frontal slopes are all limestone (manyof them dip slopes) gives the impression that the member is nearly all limestone, but actually the amount is only about one half,
The limestone isfor the most part light greyor white, and is heavy-bedded, buton Brownie Mountain there is some associated quartzite in thin bands and the limestone itself contains quar.tz grains; this rock weathersa buff to CO~OUY. Bands of limestone and bandsof argillaceous rocks, each several hundred feet thick in most cases, .alternate through- out the member. The argillaceous rocks are locally,or in some bands, altered to glistening phyllites; such bands uncler- lie depressions and lateral valleys between the ridgesof heavy-bedded limestone.
- 39 - Member 14 is truncated by theTrench, and it is in this section that the regular relation between the line of the Trenchand that of the RockyMountain structure is best'seen. Ridge after ridge reaches the river at andbelow theGataga River mouthand disappears,and with the last one,through TerminusMountain, theboldness and height of the Rocky Mountainsdisappear.
Member 15
This member is of broadextent and underlies the whole of the explored part of the region north of TerminusEiountain and east of the Trench. The lowness of thissection might be ex- plained by the softness of the rocks if it werenot for the fact that east andsouth-east of BrownieMountain the same rocksunderlie high rounded ranges that attain elevations of 7,000 feet.
Themember is composed of grey,black al;d chocolate- coloured slates and argillites, with minoramounts of lime- stoneand quartzite. The structure has notbeen worked out. One prominentlimestone band near the western margin forms a canyon on the GatagaRiver and extends north-westward from thatpoint as a high,serrate ridge. This member apparently doesnot persist, as it is notrecognized farther to the north- west,though another limestone bed was observedsouth-east of the mouth of the Turnagain River.
CassiarBatholith
This is a batholith of greatlength, known to be 150 mileslong and, if it extendsfrom Teslin Lake to the Omineca, 400 miles. The width,including pendant areas, is 20 to 25 miles in the Eagle-XcDame sheet to the north-west, and as much as 30 miles borderingthe upper Turnagain. The batho- lith was notcrossed south of theTurnagain, and onlythe easterncontact has been mapped. From theheadwaters of the FrogRiver to those of Ludwig Creek the contact is mapped onlyapproximately, and was not actually reached in 1940; its position on the accompanying map is believed to beaccu- rate within a mile or two.
The rook is all quartz-bearing and light in colour, with a small amount ofdark-coloured minerals, chiefly biotite. The dominanttype is granite,but there is alsogranodiorite and some quartz-diorite.Perhaps the commonest rock type is a pinkgranite or porphyriticgranite, of rathercoarse grain which, when prominentlyporphyritic, contains orthoclase phenocrystsup to 2 inchesin length. Another type, probably a borderphase, is a medium tofine-grained grey, speckled
-. 40 - mica-granite. A thirdtype, one occurringin the southern part, is a grey to whiteporphyry, quartz-bearing and with little or no pinkorthoclase.
In the section of theupper Turnagain the contact is irregular, andfrom a width of 30 miles on the north side of theTurnagain River the outcrop of thebatholith narrows to 15 miles between thesoutheasterly-flowing stretch of theriver and KutchoCreek. The easterscontact at the head of MosquitoCreek appears to dip at a low angle to the east. A roof pendantseveral square miles in extent was observed between the head of MosquitoCreek and the mouth of Three ForksCreek and at least oneother was seenseveral miles to the north-west.
Nothing is known of the actual contact in the southern section nor of the western contact other than that it swings eastwardbetween HardCreek and the mouth of KutchoCreek.
One outlying body is south of Ludwig Creek.about 9 miles east of the batholith and 6 mileswest of theTrench. Severalother outlying bodies of diorite and quartz-diorite outcropnear the head of Wheaton Creek,and Mandy* observed two granitic bodies'east of the mouth of Ferry Creek. Dyke offshootsfrom the batholith are rare. A great variety of dykerock, probably directly or indirectly related.to the batholith, is found as float in many streams;these include all sorts or porphyries;mostly fine-grained, andfrom light todark in colour. A dyke of dioriteoccurs onlower Rain- bow Rivernear the Trench, and a similar dyke 'is on the mountainnorth-west of the lowerbend in Denetiah Creek. Andesiteporphyry dykes are seen east of .the batholith and. south of the two lakes at the head of Sand Creek;, small mica lamprophyredykes occur near the isolated body south of Ludwig Creek.
Pegmatitesare abundant in the southernmost part'of the regionbut are rare or lackingin the northern part. A few pegmatiticphases of the granite occw in the Turnagain section, and the same is notedin the Eagle-McDame map-area. but there is no abundance of pegmatitedykes in the surround- ingrocks. In the mountainsabreast of SiftonPass and inthe basin oflower Ludwig Creek there is an abundance of pegmatites and smallbodies of stronglypegmatitic.granite. A fewpeg- matites also were seen in the mountains west of the north- westerly-flowingstretch of Rainbow River. It is a signifi- cant fact that the schists of Member 1 arecoarser and more fissile(locally garnetiferous and felspathic) in thissouthern
* Ann. Rept. Min. of Mines B. C. 1933 pt. A, p. 65.
- 41 - section where pegmatites are abundant than in the northern section where pegmatites are virtually absent.
Sifton Formation
This is named the Sifton formation because it is seen to advantage for 10 or 15 miles north and south of Sifton Pass. It occurs within the Trench and locallyto elevations of about 5,000 feet, or 2,000 feet above the valley floor.
The formation is composed almost entirelyof conglomerate, with local, minor beds of sandstone and shale. The conglom- erate is strongly cemented and ais hard,resistant rock, but on weathering tends to break downso as to free the constituent pebbles. The sands and shales, locally strongly carbonaceous, are for the most part weakly coherent.
The pebbles of the conglomerate are well rounded inand rare instances are as largeas an orange. The common size range is between thatof 'a hazel nut andan egg. The matrix is finely conglomeratic or sandy. Constituent materials are all sedimentary, among which limestone is always present and predominates locally; in someof the exposures, the proportion of limestone is 8 to 1 and the matrix is calcareous. Other pebbles are shales, sandstones, argillites, quartzites and cherts; some black chert pebbles, commonly rather small, are everywhere present. .No igneous pebbles arefound,and none of schists or rocks metamorphosed beyond the grade of phyllite.
Plant remai.ns are numerous in the sandy beds but are fragmentary and 'poorlypreserved. One collection of fossils was submitted toW. h. Bell at Ottawawho states: "There are only several .fragmentsof dicotyledonous leaves present, and none is sufficiently complete for identification. The best is seeminglya Vibur- num, not surely referableto any described species. There is a single small, poorly preserved fragment of a fern, again not certainly identifiable although comparable to Asplenium? coloradense Knowltonor to Asplenium? magnum Knowlton. The bulk of the collec- of tion consists twiEs- of a Secuoia, ~ urobablv belong-I ing to the same species as one recorded by Hollick from the 'Upper Cretaceous Chignik formationof Alaska '...... But I do not consider that an age determina- tion can be safely made on a suchslender basis and the best that may be statedis 'Upper Cretaceous?' 1. Paleocene or Eoceae Age ais possibility."
- 42 - Coal seams occurbut none were seen. One, west of the Kechikaabove Rainbow River, is said to be severalfeet wide. Inother seam in the lowercanyon on Driftpile Cree$ is covered at highwater, but a sampleand description wereobtained by G. Emerson of thetopographic party in September. This s$am is 3 feetwide at water's edge, strikes north 70 degreeseast and dips 75 degreesnorthward; the coal is poorly c0heren.tand has a strongodour. An analysis showed moisture, 3.3 percent: volatilecombustible matter, 24.5 per cent; fixed carbon, 57.3 percent; ash, 14.9 per cent; B. T. U.'s 11,857.This, and othercoal found on the river bars near Rainbow River is lignitic and burns with difficulty.
The formationhas been strongly deformed. The basin hasbeen compressed laterally, with the production of steep dips,irregular folding and some drag-foldsand shearing. The beds are clearly unconformable with the underlying rocks and there is evidence of faulting on severalobserved contacts on theeastern margin. 370 idea of thethickness was obtaineci.
Glacial Drift and Alluvium
The bottom of theTrench, from near the mouth of Frog, Rivernorth-west, is mapped as glacial drift and alluvium although a fewminor rock points are seen on the river's edge.This serves to show theapproximate margins of the Trenchbottom. Elsewhere, as inthe upper Keohika, thedrift and alluvium are too narrow to bemacped separately.
The drift consists of morainal deposits only in the angle of Gataga fork, andelsewhere comprises stratified and semi- stratifiedgravels and a minor amount of boulder-clay.Pot- holesand similar irregularsurface features occur locally, and it is believed that much of the valley-fill has been worked overand atleast partly modified by streamaction. The allu- vium consists of gravelbars and of gravel and silt banks amongstand adjoining the braided channels.
- 43 - STRUCTURAL GEOLOGY-
The following discussion deals with broad generalities in such a manner that the analysis may be of service to futurefield workers. The solution of majorproblems of cor- relation,particularly concerning the age and physical rela- ti0nshi.pbetween the rocks on eitherside of the Trench, is dependenton age determinations, and fossils were found only in the Sifton formation and in Member 9.
The region is profoundlyfolded, and there is a differ- ence incharacter of folding in the two mountainsystems. The Trench constitutes aboundary line across which lithological correlationhas proved impossible, and thereason for this fact, together with that of the origin of theTrench, is a problem of first importance.There is at present no solution of this problem,which must wait at least until the stratig- raphy of the region is well understood.
The sedimentary rocks of the RockyMountains are all steeply dipping and the folding is rather tightly compressed. The structural trend is approximately north 40 degrees west andmeets the line of the Trench at an angle of 10 degrees. This trend, and theimplied structure, is so uniform that the lines of exposure of prominent members suchas 14 and 12 are almostperfectly straight. Cross-flexures are small and in- significant. The onlyapparent major fold is thesyncline involving Member 12, which:resumably makes Edembers 11 and 13 equivalents. However, it is believedthat this syncline is really only a large drag-fold, .and not a principal axis. The failure of the limestone of Member 14 to appear on the edge of the Trench at the southern end of theregion or even far down Fox River,and suggestions of overturningbetween Gatagaand Terminus Mountains, strongly indicate that the structure is one of narrowlycompressed drag-folding on a majorscale, in spite of the fact that no suchstructures were actually seen or workedout.
Minor contortions and drag-folds are numerous in the softerrocks, even if strongerbands are continuous and straight for greatdistances. As a matter of factlarge areas of 'slates and phyllites are complexlyfolded within a singlegeneral horizon. Cleavage is presentin all but the more massivelimestones and quartzites and is developed to a highdegree of perfection in most of the softer rocks. This is regionalflow cleavage, parallel to the axial planes of the folds and parallel to the beds or nearly so through- out much of theclosely folded formations, but superposed acrosscontorted areas without regard to bedding. This suggestsdeep and close folding.
- 44 - There is evidenceof more than oneperiod of deformation in the folded cleavage and local mashingfound close to the Kechikaand along the margin of theTrench.
Folding in the Cassiar Mountains is not ,nearly so uniform. There is a generalstructural trend of.about north 50 to 55 degreeswest but individual folds tire far from regular..Anti- clinesand sypclines, at one localityseemingly continuous and of majorimportance, are at other localities interrupted by cross-flexures,lose their identity, or are so complicate(2 by drag-foldingand thrusting that they pass into other structures.
All therocks except the massive limestones and most quartzitespossess secondary flow cleavage which is developed to a high degree of perfection in the thin-bedded argillaceous rooks. It is developedregionally but, due to the complexity of thefolding is noteverywhere parallel to the axial planes of the folds..
Drag-foldsare seen on scales measurable in a few feet to 1,000 feet,with some overturning,that represent overthrusting from the west. Even larger-scaleoverturning is indicated and this seems to be the reason why it was impossibleto determine thesuccession or to'explain the general structure in any reasonablecompleteness.
The schists of Member 4 areopenly and irregularly folded in the south about Flat Top Mountain and almostas openly foldednorth of JackstoneCreek, but large drag-folding seri- ouslycomplicates the outlines of thesefolds. The schistosity is foldedin the southern locality. Member 6, composed or" in- competent rocks, is so deformed that the structure is not readilyunderstandable. Member 7 is ofwide distribution but is not believed to be very thick, possibly 3,000 feet; com- pressed into a repetition of folds abreast of the Sifton con- glomerate,the structure appears to open out to the north-.west and theaverage or regionalattitude is almost flat. This is bestseen in the mountains cut through bylower Frog River, where theflatly-warped beds .are caught up into local asym- metrical folds, some of which are the expression of thrusting fromthe west, but others are simply irregular contortions of no apparentmeaning.
The generallyincompetent rocks of Member 8 are,partitcu- larlyin the southern section, strongly contorted and the structure is notsimple. The weaker argillaceousto cal.car- eousbands are minutely rumpledand drag-folded between the stronger,competent bands. The .prominentlimestone rib at the mouth of Frog River and the southernmost end of the quartzite member dip steeply westward, but the dip of the
- 45 - same quartzite on Mount Winston is 40 degrees eastward into an apparentsyncline ofwhich the eastern limb is in the eastern- mostrange about Moodie Creek. The onlyexplanation for such anomalous dips and the failure of the quartzite to be repeated is.thatthe structure is overturnedand plunging. This explana- tion puts Member 8 below Member 7 andsupposedly the equivalent of Members 5 and 6 which lithologically, is not so. Changes in lithology over a distance of severalmiles mi&t account for thedifference, and certainly both the limestone and quartzite bandstend to play out along the strike to the north-west.
The rocks of Member 9 dip,in general, to the west, with strongminor contortions. There is probably a considerable amount of repetition in this member.
There is much definite evidence in the Cassiar Mountains of overturningin the complex structure. The overturning is in mostcases no more than a fewdegrees from the vertical, as seen indrag-folds, large and small, produced by lateralcompression or overthrusting from the west.
Inthe Rocky Mountainsoverturning is deduced.Although no structureswere worked out,there is evidence of tight foldingin sections of regional parallel dips. Therewould thenappear to be, of necessity, overturning to the east in Member 14 which is supposedlybeneath Members 11, 12. and 13. The non-appearance of this limestone on the wall of the.Trench south of the region further points to some asymmetricalmajor structure.Nevertheless it cannotbe said that there is, from thecited overturning, regional evidence of overthrustingfrom the west.
No evidenceof faulting was seenalthough the scale of the work was such that only major offsets wouldbe noticed. However,.major faultingcould occur parallel or nearly so to the regional structural trends and its presencemight be hard to detect without a better knowledge of the stratigraphy. It is atleast suppositional that the Trench is a line of structural weaknessand.involves faulting or combined folding and faulting, originally of greatage and probably repeated. It is possible that lateral or sympatheticfaulting took place parallel to the Trenchas slicing of the structures at oblique angles.
A feature of majorimportance is thevarying degree of metamorphism in Member 5. As stated,these schists in the southern part ofthe region are considerably coarser than in thenorthern part of theirextent. Mica platesare larger, locally the size of a thumb-nail;garnet is prominentlyde- veloped and therock locally is a gneiss.In the northern
- 46 - section the mica is in smallplates and schistosity,amounting commonly to no more than an advancedstage of slaty cleavage, is developedregionally across the bedding;: garnet is notseen in handspecimens.
This differencein degree of metamorphism is directly related to the.presence ofpegmatites inthe southern section andprobably tothe mapped graniticstock. About 15 mile;S south of the region, in Fox Pass,the metamorphism is more intense and therocks are intruded by many dykesand small irregular bodies of granite.In this section the sediments havebeen convertedto felspathic and garnetiferousgneisses and are? strongly contorted. Few pegmatiteswere seen in the small. area examined,but there is much fine-grained faintly pinkish granite, in very irregular bands andmasses. measuring from a few inchesto tens of feetin width. The granitecrosscut:s and alsofollows the Foliation of therocks .and has produced in some placesan intrusion breccia.
Althoughthe main batholith is about 20 mileswest of the Trench in the section between Ludwig Creek apd Fox Pass theeffects of intrusion are obvious in the production of gneisses and schists and inthe irregular introduction of granite andpegmatice dykes and masses. No sucheffects are seen Planking the batholith from Jackstone .Greek to McDame.
In short, the effects of intrusionspread about 20 miles east of the main batholithic contact, or ratherthe projec.tion of it inthe south andhave little noticeable effect in the north,where even contact metamorphism is closelyconfined,. The minor intrusives have a counterpart far to the south in the many pegmatites of the Butler Raqe west of Finlay River+.
Little is known of the structure of the Trench in the portion examined exceptthat it is an old one. The presence within it andnot elsewhere of the Sifton formation of Upper Cretaceous or Eocene ageproves this. The Trenchprobably follows a line of structural weaknessalong which faulting hasoccurred. There is a suggestion,not proved, that some faulting occurred at comparatively recent'date along a scarp several milesin length on the western flank abreast and north of Fox Lake (see Plate I A). This is at least100 feet in height and is seen to be continuous, if onlyfragmentarily preserved. It is believedto be a fault scarp of pre-glacial ageand to be related to the laststructural adjustment of theTrench.
* Geo. Surv., Canada, Sum.Rept. 1927, pt. A, p. 28.
- 47 - ECONOMIC GEOLOGY
Placer-gold deposits havebeen worked on 'Tiheaton and WalkerCreeks but therehas been no continuous production from any othercreeks in the region, A few lodedeposits are known butthey havenot been developed. Discussion will therefore be restricted to generalities, with brief men- tion of a few known mineral deposits.
PlacerDeposits
The deposits on andnear Wheaton Creekhave previously beendescribed in detail*. In 1940 thedrag-line operation continued on the Peacock lease and a small gasolineshovel was operated down-stream on theElvira and R.yan leases. Some prospectors were active in the general locality and work con- tinues to bedone on Faulkner(Palmer) Creek though as yet no pay-gravelhas been found.
WalkerCreek, discovered in the spring of 1877, has not receivedany attention for many years. kt that time it was stated: **
"The prospectobtained has been a very fair one: Foran aggregate of 48 days' work some 60 ounces Of golddust were taken out: realizing from $18 to, $21 a day tothe hand. The gold is fine,of a granulatedappearance, and heavy.quality--the largest piece obtained weighing not more than fiftycents. Mr. Walker and partyfound that thecreek prospected for about 2 1/2 milesabout the same as the ground they hadworked. The creek is about 6 miles long and the average width is 200 feet,depth to bed-rook (slate) 7 to 12 feet, no benches, with sloping banks. "
However, thenext year, 1878, the Gold Commissioner re- portedthat "the hopes entertained last year with'regard to thediscovery by Mr. Walker of a new creek,have, unfortunately not been realized," in' spite of the fact that $35,000*** worth of gold was recovered. Gold worth$24,000 was recovered in ,1879 after whichdate the production declined sharply, and in 1882one white man and six Chinese recovered only $2200. In the last recordedyear, 1887, 5 Chinese still continued work thoughthey recovered only $1000. Sincethat time the creek
* Bull. No. 2, B. C. Dept. of Nines,1940. ** Ann. Rept.,Minister of Mines, British Columbia,1877 e** Wa'lker Creekgold was valued at $19 anounce.
- 48 - appears to havereoeived little or no attention.
Tiecreek, which is between 5 and 6 mileslong, flows in a south-westerlydirection into the south end of Deadwood Lake For about 2 miles up from its mouth the creek flows onabout a 2 percent. grade and appears to be almost,completely worked over.There are many rock-piles,old sluice-boxes, whipsawn lumberand theremains of 15log cabins. For a milefarther up-streamthe creek-bottom has not been.worked so extensively, butthere are signs of its havingbeen prospected by shaf.ts to bed-rock. In thatstretch the grade steepens to about 5 percent. and the bottomnarrows to'about 100 feet in a more canyon-likevalley; there are more largeboulders and it ap- pears that the pay-streak did not justify working.
In the autumn of 1940three prospectors were encountered on thetrail, who intendedto do some work on thecreek. It seems likely however, that the lower stretchhas been thoroughly worked outand possibly only a fewsmall unworked patches of deeperground could be salvaged. At theold price WalkerCreek goldsold for $19 anounce, so at the present rate wagesmight be made on theupper stretch; however that possibility remains to be 'proved.
'@alkerCreek heads in a belt of greyslate containing many quartzstringers and veins. The slatebelt which is about half a milewide~extends south-eastward and crosses by the secondlake at the head of Sand Creek. If theplacer-gold. werederived from the quartz veins then other creeks which. cross the slate belt might warrant prospecting for placer.
Accounts in the Annual Reports of the Minister of W',mes for 1E86, 1887, 1894and 1906, indicate that in thoseyears parties of prospectors had been on the Xechika and upper TurnagainRivers. At thattime fine gold was found at low wateron bars on the Kechikaand men working with rockers on variousbars, took out good pay for shorttimes. Re- cently, two men are reportedto have recovered 10 ounces of fine gold from a bar on the Kechikabelow the mouth of Frog River.
It is not known howmuch 'of the remainder of the region hasbeen prospected, and although it is probablethat pros- pectorshave been on many of the creeks in the Cassiar MOUII- tains, it is safe to saythat the search has probably not been thorough.
It is not likely that placer-gold will everbe found in quantityin the Rocky Mountains. The sedimentaryrocks do not appear to be mineralized and the effects of igneousintrus5.on
- 49 - are confined to the western side of the Trench.
Stream flowing east of the batholith in theGassiar Mountainstraverse rocks that contain evidence of mineraliz- ation. The westernpart of thissection has been heavily glaciatedand some streamshave cut.rapidly in gorges, others head in highglacial basins and fall in cascades to the larger valleybottoms; trunk streams flow rapidly in canyons, or sluggishlyover deep valley-fills of glacialmaterial. Some creeks,particularly in the eastern part of the same section, have not been modified by glacial action and a few may repre- sentthe continuous, prolonged erosion which seems necessary to produceplacer concentrations.
The factors that have produced and permitted the reten- tion of placer-goldconcentrations have elsewhere been enumer- atedin the case of ',&eaton Creek(see page 27). To summarize, Wheaton Creek crosses a belt of slate containing numerous quartzveins. The goldreleased by erosion of thequartz veins,during the early Tertiary, was concentrated in placer depositsin the stream bed of the ancient valley. In the late Tertiary,but pre-glacially, 'Wheaton Creekwas rejuvenated and the stream incised a canyon that extended for 4 miles above its mouth; the originally concentrated placer-gold was at this timereconcentrated in favourablestretches in the canyon. During the Pleistocene the valley was occupied by ice and was to a small extenteroded and modified by it, yetthe position of theplacer-gold in the bottom of the canyon saved it from beingdispersed by ice movement. Any gold Which may havebeen left on higher exposed rockbenches was swept away. The post- glacial 'Nheaton Creek hasre-incised its course in thelate Tertiary canyonand has eroded much of the glacial fill so that-the present depth to bed-rock in most places is not greater than 30 feet.
The same conditionsand sequence of events, or approxi- mately the same, may obtain in other parts of the region, inasmuch as it hasbeen shown thatglaciation has been wide- spreadand that regional rejuvenation or incision of stream valleystook place pre-glacially. Consequently; further placerprospecting in areas of favourablerocks should be undertakenwith a full appreciation of the stream history and in the light of what is known definitely.
Lode Deposits
Knowledge of early lode discoveries is scantybut in past years interest was naturally, and for good reasons, centered on placer.Yet in 1898, Inspector Moodie states "at thelake (Deadwood Lake) I found Mr. Walker (possibly
- 50 - the discoverer ofWalker .Creek)and a companion, prospecting for the C.C. R. Company (the Cassiar CentralRailway Company). They havefound some .good prospects of bothgold and coppf?r in quartz. "
Furthermore,in the Annual Report,Minister of Nines,. Brit.ish Columbia,,1906, it is recordedthat a party'ofprospectors set out from McDame and travelled about 80 milessouth-eastward into the Turnagainsection. Some claimswere staked and recorded and it is statedthat the quartz assayed well in gold, si!.ver and copser ,but nothing further is known.
k copperdeposit is reported to havebeen staked years ago'on thelower Gataga River, and in 1940 a copperdiscovery was made and staked in HiddenValley Creek, tributary to Turn- againRiver bet3veen Mosquito andSand Creeks., Neither of these deposits was seen,but a verbal description of thediscovery on HiddenValley Creek was obtained.
No mineraldeposit was seen in the Rocky Mountains,and little evidence of quartzveining. Copper is reportedto occur east of the Finlay River, far to the south of the region, but in general these mountains have not proved to be well mineral- ized.Throughout the Rocky Mountains there is fairly wide- spread and prominentveining by calcite, for the most part insmall and discontinuousstringers, and a few of theseveins contain a minoramount of quartzthat is notmineralized. A few quartzveins were seen east ofGataga River in the lower 15miles, and a few east of GatagaMountain, but no mineral was seenin them. A search was made inthis section for the reported copper deposit but without success.
In mny parts of the Cassiar Mountainsquartz veins were sees, almost exclusivelyin the non-calcareous rocks. Pdost veinscontain ankerite, or rusty-weatheringcarbonate.
Glassywhite quartz veins are numerous in the coarse- grained schist about Ludwig Creek.Irregular veins contain- ingpyrite occur in the crumpledrocks of Member 5 onRainbow River.Float containing pyrite and a little chalcopyrite 'was seen near the mouth of Rainbow River, and in parts of the front rangeto Frog River, and onesmall vein containing chalcopyrite was seen on the mountain north-west of Paddy Creek.Quartz veining containing pyrite, chalcopyrite and galena was found 7 milessouth-west of the mouth ofDenetiah Creek.Quartz veins were seen south-east of the lakes at the head of SandCreek and also copper float below the mouth ofthat creek on the Turnagain. Some quartzfloat was seen north-west of JackstoneCreek.
- 51 - On the eastern shore of Dall Lake a small bluff at water's edge is composed'ofintensely silicified limestone andcontains manysma.11 stringers of chalcopyrite.
The discovery on HiddenValley Creek is reported to con- sist of chalcopyrite mineralization across widths as great as 40 feet, and traceablefor 2000 feet. The gangue appearsto consist of ankerite and quartz, and a little galena occurs locally. No furtherdata are available.
It should be noted that the batholithic contact makes a sharp bend abreast of Dell Lake. The countryadjacent to or radial to this bendshould make good prospectingground for some miles,particularly as there is in it a considerable di- versity of rock types and structures.
- 52 -