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Geology of the Vedder Mountain Silver Lake area 1956

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GEOLOGY OF TIE TEDDER MOUWTAIH - SILVER LAKE AREA by DOUGLAS NEIL HILLKOUSE B.A., University of British Columbia, 1955 A T I K I S SWMCTTTED I I PARTIAL FULFILMENT OF THE -R1QU111MEITS FOR THE BICR1I OF ' HISTER OF SCIENCE in the Department of GfOLOCY Me accept this thesis as conforming to th© required standard TBE-OTIVEBSITY OF BRITISH COLOMBIA September 1956 ' ABSTRACT Th® major rock units within th© area investigated are* the P@riala» Chilliwack Group, the Upper Lower Jurassic - lower Middle Jurassic Cultus Formation, and the Upper Jurassic Lower Cretaceous Vodder Mountain Sediments. The Chilliwack rocks examined consist of four limestone units, a thick volcanic sequence, a conglomerate and a r g i l l i t e s . Th© Cultus rocks consist of a r g i l l i t e , shale, graywaeke and c l a s t i c limeston®, Th© Vedder Mountain Sediments are gray- wackes, a r g i l l i t e s and conglomerates. A tabular body of igneous rock and a schistose eherty rock are included i n th® sequence. The regional str i k e i s to the north-east. Most of th© rocks i n the ar@a ar© strongly fractured. The Cultus Formation Is folded into a series of overturned Isoclinal folds with a x i a l planes s t r i k i n g north east and dipping south east. Th© strongly folded Chilliwack rocks are thrust over the Cultus rocks from the south and south east. The r e l a t i o n - ship of the Tedder Mountain sediments to the other major rock units is unknown. ACKHOWtEDGMEaHTS The writer is grateful for the financial assistance received through grants from t h a B.C.. Academy of Science and the Geological Survey of Canada. He expresses his sincere gratitude to D r . H.C. Gunning and D r . V.J. Okulitch who negotiated these grants. f h e writer a l s o w i s h e s t o express h i s thanks to Dr. V.J. Okulitch and Mr. V.P..Banner for the advice, assistance and encouragement which they gave the writer while he was d o i n g this work. Thanks are also due John Rlls who accompanied the writer on several traverses on Black Mountain, to Dr. J.D. Armstrong, of the Geological Survey of Canada, who suggested the problem and offered many helpful suggestions, and to Mr. J.A. Donnan, who made the thin sections for the writer. TIB LI OF COST.ESTS Pa^f Introduction . . . . . . . . . 1 •Location . . . . . . . . . . . . . . . . . . . . . 1 JkCC'SSS . • • • • • . . . . . . • . . . » » • • • . 1 Topography, Vegetation and Drainage . . . . . . . 2 C13jaat© « , . » . * • • . . . » « « . . « * • » . 3 Previous Work 3 Present Investigation . . . . . . . . . . . . . . 5 Scopa . . . . . . . . . a . . . . . . . . . . !? Methods . . . . . . . . . . . . 6 Descriptive Geology . . . . . . . . . . . . . . . . . 7 Begioaal Setting . . 7 Rock Units , , . 8 Chilliwack Group . . . . . . . . . . . . 8 Distribution . . . . . . . . . . . . . . . . . 8 Lithology « • . . . . . . . . . . • . . . . • 8 Age of the Chilllvack Group . . . . . . . . . . . 19 Cult us Formation « . 24 Distribution . . . . . . . . . . . . . . . . . 24 Lithology . . . . . . . . . . . . . . . . . . 24 Age of the Coitus Formation . . . . . . . . . 32 Vodder Mountain Sadiments . . . . . 33 Distribution . . . . . . . . . . . . 33 Lithology 34- Relationshlps Within the Vadder Mountain Sediments . . . . . . . . . . . . . . . . . 37 Age of the Tedder Mountain Sediments . . . . . 38 Structures * . » • . « * . . * . . « * . * » » » . . 40 Chilliwack Group . . . . . . . . . . 40 Cultus Formation . 40 Tedder Mountain Sediments 41 Regional Structure 42 Geological History of the Area * , « « * • * . . . . . 43 / Plat* . F_M® I. Cultus A r g i l l l t e s exposed i n Blue Canyon . . • 45 I I . Contortion of Cultus A r g i l l l t e s . . . . . 46 I I I . C h i l l i v a c k Conglomerate . . . . 47 If, Crinoidal times ton© oa Llhumitson Lake T r a i l . . 48 ?, Northwestern face of Church Mountain . . . 49 VI. Slope above Lihumitson Lake Cabin . . . . 50 VII. Thin section of Cultus Graywacke showing graded bedding . . . . . . . . 51 VIII. Thin section of Cultus Graywacke showing orientation of elongat® grains 52 IX. Thin section of Imput® Cultus c l a s t i c limestone . . . . . . . . . . . . . . 52 Map of Vadder Mountain - S i l v e r Lake Area - i n pocket I INTRODUCTION Location Tb© area mapped Is situated i n southwestern B r i t i s h Columbia along the Canadian - United States Boundary approximately seventy miles east of th® c i t y of Vancouver. It extends eastward from the summit of the Vedder Mountain to the western slope of Church Mountain and southward from the Chilliwack River to the International Boundary and a few hundreds yards beyond. The approximate geographic limits ar© meridians 121® 52* and 122° O f west longitude and par a l l e l s 49° 00* and 49® 05' north la t i t u d e . Access Cultus Lake, which i s central to the major part of th® area i s easily reached from the Trans Canada Highway by paved road. A gravel road on the east side of Cultus Lake continues south through Columbia Valley to the boundary. Much of Vedder Mountain, parts of International Ridge, and the lower portion of Lihuaitson Creek ean be reached by logging roads, several of which are accessible to automobile. Church ^fountain and the Lihumitson Lake Area are reached by a good t r a i l . The area of the headwaters of Lihumitson Creek and Isar Mountain is devoid of roads or t r a i l s . The area on th© American side is reached by the Mount Baker - S i l v e r Lake road. 2 Topography, Vegetation and Drainage Vedder Mountain i s a long, north-easterly trending ridge, tapering i n width from about three miles near the northern end to one and one half miles at the boundary. Its maximum elevation i s 3060 feet. The topography i s characterized by rounded rocky hammocks but bluffs and c l i f f s are common. The mountain has been almost entirely logged and i s now covered c h i e f l y by second growth timber and under- brush with large areas of burn, windfall, and logging slash, Th© valley between Vedder Mountain and International Ridge i s occupied by Cultus Lake i n the north-east, at an elevation of 48 feet, and by Columbia Valley to the south- west, at an average elevation of approximately 800 feet. Columbia Valley is underlain by g l a c i a l t i l l which has been cut into three terraces by stream erosion. International Ridge, with a maximum elevation of 4858 feet on Mount Amadls, is a long, steep-sided, north- easterly trending ridge with five minor peaks. Its broader and higher southern extension across the boundary forms Black Mountain. This ridge has not been so extensively logged as Vedder and is largely covered by v i r g i n and old second growth timber with very dense underbrush. Its major streams, Watt, Frost and Blue Creeks, a l l with deep canyons, flow i n a westerly to north-westerly direction, draining into Cultus Lake. 3 Th® area between International Ridge and Church Mountain appears to have once been a plateau which has been dissected into i t s present rough topography by the down- cutting of Lihumitson Creek and i t s tributaries* The drainage pattern forms a rough triangle with the north- easterly trending International Ridge and north-westerly trending Church Mountain ridge as i t s sides and i s a r Mountain as i t s base* A 4500 foot unnamed ridge juts into the centre of the triangle froa the south between th© two main branches ©f the creek. These/ ridges are very steep and are often covered by deadfall and very dense underbrush. Travel i s extremely d i f f i c u l t . Climate 1© meteorologic stations are situated i n th© area, therefore no figures are available. However, the climate is d e f i n i t e l y within the marine west coast regime. The precipitation, above 60 inches per year, is largely oro- graphic i n o r i g i n . In winter, more than twenty feet of snow aeeas&ui&tes above the 4500 foot elevation, making f i e l d work at these altitudes impractical u n t i l l a t e July. Previous Work H. Bauerman, of the Geological Survey of Canada, who traversed froa the Gulf Islands to the Rocky Mountains i n 1859-40, produced the e a r l i e s t geologic report concerning this area. Ie draws no d i s t i n c t i o n between what are now called the Cultus Formation and th® Chilliwack Group, assigning both to the Palaeozoic. He makes no attempt to solve the structure, other than on a very broad scale. The most comprehensive report to date concerning the area was produced by R.A. Daly, who traversed from th© Rocky Mountains to the P a c i f i c along the 49th p a r a l l e l during 1901*1906. He named the Cultus Formation, which he called T r l a s s i c , and the Chilliwack Group, which he assigned to the Carboniferous. He included the sediments of Tedder Mountain i n the Lower Carboniferous. Daly*s explanation of the structure of the area includes placing great normal faults at the eastern and western contacts of the Cultus with the Chilliwack, with a south-dipping thrust fault as the southern contact. He warns that his interpretation is very speculative. C H , Crickmay published a report on th® Northern Cascades i n 1930* i n which he states, without c i t i n g supporting evidence, that the Tedder Mountain sediments are Tr i a s s i c . He also concludes that the Cultus Formation con- s i s t s of schuppen of Carboniferous and Lower Cretaceous rocks.. He regards this structure as being part of a great thrust fault which continues north through Harrison Lake and forms the western boundary of the Chilliwack Group, Th© latest published report referring to the area accompanies the Hope sheet of the Geological Survey of Canada with notes by C.E. Cairnes (1942). This report includes the Vedder Mountain sediments in the Chilliwack Group. It places the Cultus i n the Upper Tr i a s s l e and accepts with reservations Crickmay*s interpretation of the structure. It shows the eastern contact of the Cultus Formation with the Chilliwack Group exactly as does Daly's map, but shows a north-westerly s t r i k i n g contact between Chilliwack rocks and the south-west corner of the Cultus outcrop. Present Investigation Scope ' The purpose of this investigation was to map the area geologically, attempting to establish the stratigraphic position of, and to solve the structural relationships between and within, the various rock units. Because of the large area covered, the short f i e l d season, the rough typography and dense forest cover, the information obtained is quite general i n nature. The f i e l d season was shorter than o r i g i n a l l y anticipated owing to the abnormally high precipitation i n June. The writer had other duties to f u l - f i l l during most of the other months. This work, therefore, must be regarded as a reconnaissance to be used as an aid to future, more detailed studies i n the area. Among the more sp e c i f i c problems are to establish? the position and nature of the Cultus - Chilliwack contact; the stratigraphic position of, and structure within the Cultus Formation! the s t r a t i - graphic position of the various units within the Chilliwack Group; the nature o f the Vadder (fountain sediments, their structure and stratigraphic position. Methods Outcrop locations were plotted on topographic maps of a scale of 1: 5 0 , 0 0 0 , or on a e r i a l r>hotographs. Both were obtained from the B r i t i s h Columbia Department of Lands and Forests. Descriptions and attitudes of the outcrops were recorded and hand specimens collected for later stud" with the petrographic microscope. Creek beds and logging road cuts were paid particular attention but many cross-country traverses were made. 7 DPCRIPTITE GEOLOGY Regional Setting The area mapped i s within the western f o o t h i l l s ©f th© Cascade Mountains, These mountains were formed during the Cascadian Revolution, which is thought to have originated i n Miocene time and persisted u n t i l Pleistocene, The regional trend of the rocks within the area is north-east with a south-east dip. The regional attitude over almost a l l of the rest of south-western B r i t i s h Columbia i s , s t r i k e north-west, dip north-east. The rocks mapped eons1st of Upper Palaeozoic c l a s t i c sediments, limestones and volcanics, and Mesozoic sediments. A l l rocks i n the area have been strongly con- torted. Just north of the area mapped, Tertiary rocks overlie the Mesozoic rocks with s l i g h t unconformity. Rocks of th® Jurasside Coast Rang® granitic province outcrop to the north-west, across the Fraser River. The g l a c i a l - f l u v i a t i l e p l a i n of the Fraser River Lowland l i e s to the west, beyond Somas Mountain. Cretaceous and Paleocene rocks around the borders of th© p l a i n are r e l a t i v e l y un- disturbed. 8 R O C K mm Chilliwack Group Distribution The type area of this Group was established by Daly along the Chilliwack River from approximately the confluence of Centre Creek to the confluence of S3 esse Creek, Its l i m i t s of outcrop have not been established, Cairnes shows Chilliwack rocks, south of the Fraser River, extending from the v i c i n i t y of Lihuaitson Creek to the summits of Sless© and Cheam Mountains, as well as i n the v i c i n i t y of Cheara View. He also includes the Vedder Mountain sediments In the Chilliwack Group, a decision which available evidence seems to invalidate, as w i l l be discussed l a t e r , Misch (1955) has mapped Chilliwack rocks south of the International Boundary as extending from the v i c i n i t y of the headwaters of Lihumitson and Tarailie Creeks to the North Pork of the Mood- sack River, The writer has examined these rocks on the north and south sides of Chilliwack River, on Church Mountain, the headwaters of Lihumitson Creek, and on Isar, Black and Bed Mountains. Chilliwack rocks have also been mapped extensively by the Geological Survey of Canada i n the area between Harrison Lake and the Fraser River. 9 Idthology Daly constructed a tentative section of the Chilliwack Group (P.514) with base and top concealed, i n which he included quartzitic sandstone, a r g i l l i t e , several limestones, andesitic flows, t u f f s , and agglomerates, shales, " g r i t s " , and conglomerate, locks of this group which the writer has examined include; a dolomitlc limestone, a thick andesitic volcanic sequence, a crinoldal limestone, a thick boulder conglomerate and graywacke, a fusullnid-bearlng dark limestone, reef limestone, a r g i l l i t e s , conglomerate, and chert. Bauerman estimated th© thickness of the section exposed along the Chilliwack River to be 24 ,000 feet, le, however, neglected to take the complex structure into con- sideration. Daly calculated a thickness of 6,780+ feet (page 514) i n constructing his stratigraphic column for the group. The writer w i l l not attempt to attach definite thickness to the formations within the group since nowhere were sections well enough exposed to permit accurate measurement. The complex and imperfectly understood structure of the area adds to the d i f f i c u l t y . For similar reasons, stratigraphic relationships within th© group as reported In this paper must be regarded as tentative, pending further investigation. Only rock units of the western portion of the Chilliwack Group are discussed here. 10 Dolomitic Limestone The apparent st r a t i g r a p h i c a l l y lowest unit of the Chilliwack Croup to he examined by the writer, crops out on Frost Creek, about 200 yards south of the International Boundary and on the adjacent slope of Isar Mountain, It con- s i s t s of: l i g h t grey, buff weathering, sandy textured dolomite; massive, medium grey, breceiated dolomite; and black medium to f i n e l y c r y s t a l l i n e limestone, fhe limestone contains what appear to be poorly preserved fusalinlds. The unit may correlate with the limestone i n Daly's section II ( P . 512) which crops out 1200 yards southwest of saonaient 45. This tentative correlation i s based only on apparent s t r a t i - graphic position since both d i r e c t l y underlie the thick volcanic unit* Daly collected f o s s i l s (Ho, 1500) from section I I , which were Identified by Dr. G.H.Girty as? B a i i i M a a ®£mm*M Shumard Itebonora sp. Produetus (?) sp. Isar Mountain Volcanic Sequences The writer traversed over Isar Mountain froa Lihualtsoa Creek to Frost Creek almost along the International Boundary, froa Lihumitson Creek, at an elevation of approximately 3000 feet to about th© same elevation oa the western slope, only voleanics and associated intrusives were seen. The one exception was on© small outcrop of limestone 11 on the western slope at approximately the 3800 foot elevation. The volcanic rocks apparently consist entirely of dark green, usually porphyritic andesites with phenocrysts of plagioclase and hornblende. These rocks are somewhat altered but are s t i l l easily i d e n t i f i a b l e . Volcanic breccias of th© same material are common. The apparently interbedded limestone i s black, f i n e l y c r y s t a l l i n e and massive. It i s possible that this limestone indicates an Infold of older or younger material. A thick-bedded white chert, about 10 feet thick, with clear quarts fragments and stringers crops out i n Lihumitson Creek, at the eastern l i m i t of the volcanic outcrop. Cairnes (1942) includes some rhyolite In his description of th© Chilliwack Volcanic Member, of which the Isar Mountain volcanics are probably a part. The most acidic rocks encountered by the writer were f a i r l y fresh, ©qui- granular, medium grained rocks of granodioritie or quartz- d i o r i t i e composition, which the writer interpreted as being of intrusive o r i g i n . Medium grained, equigranular diorites within the sequence are also regarded as being of probable intrusive o r i g i n . The intrusions seem to be in the form of s i l l s or dykes. Daly's estimate of 2000+ feet as the thickness of this sequence seems to be of the right order of magnitude. Because of th® massive nature of the rocks, the abundance of jointing, and the dense cover, no definite attitudes could be read, but the rocks appear to dip gently In a south- easterly direction. Abundant slickensldlng indicates that movement has occurred along many of the fractures. Volcanic rocks of quite similar appearance crop out on Black Mountain and on the north side of the Chilliwack River opposite Tamilie Creek. The correlation of these rocks with the Isar Mountain volcanlcs can not be made at the present time because ' of the lack of s u f f i c i e n t evidence.. Crinoidal Limestone Limestones containing abundant crinoidal debris are exposed on Red Mountain, Black Mountain and on the slope above Lihumitson Creek southwest of Church Mountain. If these various occurrences belong to the same rock unit, this unit appears to be stratigraphically higher than the Isar Mountain volcanlcs. They do not crop out i n the v i c i n i t y of the volcanlcs. However the outcrops on Black and Church Mountains appear to be quite conformable with the overlying boulder conglomerate and fus u l i n i d limestone which are ex- posed near the volcanlcs and appear to overlie them. The crinoidal limestones are dark to light grey, often with a brownish t i n t . Dae to the abundance of white c a l c i t e veinlets they frequently look white. They are medium cr y s t a l l i n e and generally massive but ar© occasionally medium 13 bedded. The massive limestones weather grey while the bedded limestones usually weather a buff colour. Approximately 150 yards below the Lihumitson Lake t r a i l on the western slope of the 5659 foot peak, limestone of the above description forms a 75 foot c l i f f . The central f i f t e e n feet of this otherwise massive, grey weathering lime- stone is medium bedded and weathers buff. Other than crinoid debris, th® only f o s s i l s observed here were hryzoan fragments. The general attitude of the beds i s somewhat obscured by jointing and folding, but th® strik e , i n places appears to be s l i g h t l y west of north. The dips are low both to the east and the west. A similar limestone crops out on th© northwest spur of Hack Mountain. It exhibits the same massive structure, although three bedded layers are exposed. The strike i s north east, the dip south east. The limestone crops out, over a small area of Karst topography and as an adjacent, almost v e r t i c a l c l i f f . The t o t a l thickness exposed i s of the order of 200 feet. Fossils collected include crinoid stems, cup corals, brachiopods and bryozoa. The limestone is overlain by a boulder conglomerate with apparent conformity. Underlying rocks were covered by snow at the time of the writer's v i s i t to this l o c a l i t y . Red Mountain was not geologically mapped by the writer but three limestone occurrences situated on It were v i s i t e d . The limestone exposed i n the most northerly quarry on the east side of the mountain i s medium grey to brownish grey, buff weathering, coarsely c r y s t a l l i n e , entirely massive and very strongly jointed. White secondary ealeite has c r y s t a l l i z e d along the joint planes, giving much of the rock a very coarsely c r y s t a l l i n e and mottled appearance. Crinoid stems were the only f o s s i l s found here. The quarries of the Olympic Cement Co. on ths west side of led Mountain/ contain the same general type of lime- stone with both massive and medium-bedded members, The limestone in the upper quarry contains a layer of greenish- gray shale interbedded with a chert pebble conglomerate of the order of 40 or 50 feet i n thickness. The t o t a l exposure her® exceeds 250 feet i n thickness. The limestones are under- l a i n by thin to medium bedded black a r g i l l i t e s and shales with some interbedded black limestone. Fossils collected from these limestones include braehiopods, bryozoa, crinoid stems a n d possible cup corals. Boulder Conglomerate! A very coarse conglomerate composed p r i n c i p a l l y of volcanic boulders d i r e c t l y overlies the erinoidal lime- stone on Black Mountain with apparent conformity. It also overlies the erinoidal limestone on the tlhumitson Lake t r a i l but a covered interval of about 100 yards separates the two outcrops. The conglomerate i s exposed also near the bottom of the ridge between the forks of the east branch of Lihumitson Creek. Th© boulders are well rounded and up to More than a foot i n diameter. They are composed of andesite porphyries, green aphanitic volcanlcs, chert, and some limestone. The conglomerate i s interbedded with a fine-grained, greenish gray, medium bedded feldapathic graywacke. On the lihumitson lake t r a i l this unit i s exposed through a stratigraphic thickness of at least 600 feet. The top was not seen. It strikes 1 35° I and dips 30° 8.E. Conglomerate i s exposed for several hundred yards below the t r a i l between the limestone and the Cultus a r g i l l i t e s . It crops out about 100 yards north along tha strike of th© limestona and for an unknown distance below. Fusullnid Limestones A dark gray to black, f i n e l y c r y s t a l l i n e , thin to medium bedded limestone containing fusulinids Is exposed on both sides of the ridge east of Isar Mountain. On the east side, about 400 yards north of the boundary i t i s exposed i n Lihumitson Creek at an elevation of approximately 2?00 feet, On the west side of the ridge i t i s exposed about 50 yards south of the boundary at an elevation of approximately 3800 feet. It cannot be stated absolutely that these are the same beds, since the fusulinids have not been s p e c i f i c a l l y identified 9 but they do possess the same type of bedding, texture and colour. On th© ridge only a r g i l l i t e s and shales, strongly resembling Cultus rocks, are found areally between the two limestones. On the western side a large a r g i l l i t e c l i f f crops out about 50 yards north of the limestone and topographically above i t . limestone crops out above th© coarse conglomerate on Black Mountain, The writer has not v i s i t e d this occurrence but ¥.!. Banner (personal communication) reports that i t contains abundant fusulinids. The writer has examined hand specimens from this l o c a l i t y . Should these various exposures of fusullnid-bearlng limestone prove to be from the same horizon, It Is believed that this i s the str&tigraphically highest rock unit of the Chilliwack Group, examined by the writer, to be exposed i n apparent contact with Cultus Rocks. Boaks Creek Limestones Another limestone, resembling none of those d i s - cussed above, outcrops approximately l*jr miles south of the crinoidal limestone on the east side of Red Mountain. This limestone is dense to f i n e l y c r y s t a l l i n e , dark grey, with f o s t i l l f e r o u s beds containing thaanopora-like f o s s i l s which have not been d e f i n i t e l y i d e n t i f i e d . A few rare cup corals were also found. The beds st r i k e north-easterly and dip 20® to 30° south-east. No other rocks crop out i n the immediate v i c i n i t y . The stratigraphic position of this limestone cannot be determined, at the present time although i t i s prob- ably a unit of the Chilliwack Group, higher than any of those discussed previously. A tentative general columnar section of th® rock units of the Chilliwack Group so far discussed i s shown i n Table I. TABUS' I Top ' unknown Doaks Creek Limestone 100* t Covered interval unknown thickness Fusulinid limestone 200* - 400* t Boulder Conglomerate 600' £ Crinoidal limestone 200» + Interv a l unknown Tsar Mountain Volcanics 2000* t Dolomitic limestone thickness unknown Bottom unknown Other Rocks of the Chilliwack Group: Rocks of the Chilliwack Group, including a r g i l l i t e s , "cherty conglomerate", graywackes and green volcanics were examined on the north side of the Chilliwack River approx- imately opposite the confluence of Tamilie Creek, The a r g i l l i t e s are thin to medium bedded, black to dark brownish gray* highly siliceous. Th© "cherty conglomerate" consists of chert pebbles or nodules In an argillaceous matrix. It is about 2 feet thick and exhibits no bedding. The gray- waeke is dark green and massive. It contains angular quartz fragments, rock particles, and & small amount of plagioclase and Chlorite in a dense matrix. Tha volcanlcs, further to the east, were not closely examined. They are dark green and massive. A l l these roeks are strongly folded and fractured. The general attitude at the western end of the outcrop is strike east-west, dip north. Towards the east the attitude changes to strike north-east, dip south-east. At th© confluence of Slesse Creek, a large outcrop of steeply dipping, dense, dark gray limestone with beds and nodules of black chert was found... These rocks were not examined thoroughly enough to permit the determination of their stratlgraphic position. On the south side of th© westerly trending ridge south of Llhuiaitson Lake, a medium grained, gray, hornblende diorite is exposed In a long, 60 foot c l i f f , at an elevation of approximately 4800 feet. Ro other rocks ar© exposed in the iwmedlat® vi c i n i t y , this intrusive-looking rock probably forms a s i l l within the Chilliwack Group. Float of the same type of rock abounds on th© lower slopes of the next ridge to the south. Indicating that th© s i l l extends in that direction. Age of the Rocks of the Chilliwack Group: Daly made large collections of f o s s i l s from the Chilliwack limestones, but his l o c a l i t i e s are to th© east and south-east of the area investigated by the writer. His l o c a l i t y No. 1512, tton top of the ridge 1500 yards southwest of Monument 48° contains an assemblage of f o s s i l s which does not resemble any of those collected i n the limestones v i s i t e d by th© writer. Th© f o s s i l s were determined by Dr. G.H. Girty and Dr. E.g. Bassler ast Plant' fragments Cllsiophyllum sp. Crlnoidal fragments Fenestella sp. Rhombopora sp, £Z£tMi£txa sp, Productus sealretlculatus Martin Productus a f f . .lakovlevi Tschern S p l r i f e r a f f . earneratus Morton Reticularia lineata Martin (?) S p l r l f e r i n a a f f . campestris White Martlnia (?) sp. gte&Mrft, c?) sp, Terebratulold (?) Hyalina a f f , M. squamosa Sowerby Pleurophorus (?) sp. Orthoeeras (?) sp. 20 A similar assemblage was collected by Daly 1200 yards west of the summit of Church Mountain on top of the ridge, which would place i t above the boulder conglomerate. This assemblage could be a fauna! facies of one of the previously described limestones. The most similar fauna is that of the c r i n o i d a l limestone on Black Mountain. The most similar apparent stratigraphic position is occupied by the Fusulinid limestone on Black Mountain. It could not, however, be correlated with the fusu l i n i d limestone on the strength of apparent stratigraphic position alone, owing to the high probability of faulting i n this area. The north-west face of Church Mountain, as seen from the ridge to the west, shows extremely complicated structure involving faults and overturned folds. It i s therefore impossible, without further examin- ation, to say which, i f any, of th© limestones v i s i t e d by the writer correlates with this outcrop. "On the same ridge as 1512, 1000 yards farther north**, Daly collected Itonsdaieia sp. Campophyllum sp, Crinoidal fragments This assemblage resembles much ©ore closely that of the c r i n o i d a l limestone previously discussed. 21 Dr. Girty writes in his summary, "... The most natural geologic section with which to compare these fauna i s that of northern C a l i f o r n i a . ... There is nothing among your c o l l e c t - ions which suggest the Baird or McCloud. The most strongly characterized of your faunas (lots 1512, 1514 and 1500), however have much that is similar to the Nosoni. At present I am disposed to correlate the two horizons." Th© C a l i f o r n i a sequence was then regarded as being of Carboniferous age. It i s now included i n the Permian, the McCloud correlating with the Wolfcamplan and leonardian, th® Kosoni with the Guadalupian. The faunas of this area show di s t i n c t a s i a t i c a f f i n i t i e s . Several of the f o s s i l s collected by W,R.Banner and the writer have never been described from l o r t h American l o c a l i t i e s , according to Miss Helen Dunean of the United States Geological Survey. For this reason, f o s s i l i d e n t i f i - cations and age determinations are very d i f f i c u l t . Black Mountain Crinoldal Limestone: Miss Helen Dunean writes concerning f o s s i l s collected on Black Mountain by W.R.Dannerf ..The most conspicuous specimen exposed on the surface is a fragment of Iranpphyllum a f f . I spongifolium Smith. This i s the f i r s t time I have seen this genus i n an American c o l l e c t i o n . The genus was o r i g i n a l l y described from the "perao- Carboniferous M of Persia. ... Iranophyllua apparently has a considerable rang© in th© Permian, so i t is not possible to say whether the occurrence i n Washington indicates Wolfcamp ag® or some later stage* ... Two of the specimens are an undetermined species of Lophyophyliidlum, and the others are tentatively 22 Identified as Can-uthersella sp. ... Th© type I am c a l l i n g Carruthersella ? has a carcinophyllid a x i a l column and a Lonsdaleoid dissepiaentarium. Several other names - Klonophyllum .... have been proposed for corals with about the same characters; and some authors have referred similar forms to Lophophylloides and Lophophyllum. This group of corals i s p r a c t i c a l l y unknown in North America. Described species occur i n the Lower Carboniferous of England and Asia and in the Middle and Upper Carboniferous of Russia, China, and the Carnlc Alps, Some of the foreign Upper Carboniferous occurrences are probably temporal equivalents of Worth American early Permian (Wolfearap). The writer collected very large, poorly preserved braehiopods from the same outcrop. They strongly resemble Olgantoproductus, which i s generally considered to be of Mlssissippian age i n Forth America. However, since these l i v e d i n seas connected to Asia and not connected to other Horth American seas, i t is highly possible that they could have persisted to the Permian, Several smaller, poorly preserved braehiopods and some corals were also collected at this l o c a l i t y but have not yet been i d e n t i f i e d . Fusulinid Limestone: Miss Helen Duncan writes concerning bryozoans collected from the fusulinid limestone by W.R.Banners ... I can recognize the following genera: Penestella, 2 or more speeies; Poiypora sp.; and Bhomboporejla sp, ... The species represented in your sample ar® non- descript small-meshed forms that occur throughout the Sarboniferous and Permian, 23 Of tho fusullnids, Dr. ,7,1; .Skinner of tho Humble O i l and Refining Company writes to w.R.Darmer There appears to be at least two species of Scterax©|l||a and two of Pseud© One of the l a t t e r is very similar to P. occidental!® from the lower McCloud. I should feel'little''"* hesitation i n correlating this bed with some part of the Coyote Butte of Oregon and the McCloud of C a l i f o r n i a . " Doafcs Creek Limestones This limestone i s highly f o s s i l i f e r o u s but none of the f o s s i l s have been p o s i t i v e l y identified yet. The internal structure of the peculiar Thamnopora-like f o s s i l i s unlike that of a coral. Miss Duncan has suggested that i t say be a T r i a s s i c stromatoporoid. A cup coral was also examined but i s as yet unidentified. I t is most probable that these forms are A s i a t i c . Froa the foregoing i t i s seen that the age of a l l of the limestones of the Chilliwack Group cannot be d e f i n i t e l y established at present. It seems most probable that a l l th® limestones discussed are of Permian Age. The lower three limestones are probably of Wolfeampian Age. However, i t i s possible that the age range may be from Mississlppian to T r i a s s i c . Fossils which have been collected but not yet id e n t i f i e d may help to solve the problem, although they represent a fauna almost unknown i n North America. 24 Cultus Formation Distribution Daly (1912), named the Cultus Formation, which he called T r l a s s i c . fhe type section is described as being on •'Cultus Ridge", which is now called International Ridge. Rocks of th© Cultus Formation crop out from the eastern side of Cultus Lake and Columbia Valley to the ridge east of Lihmaitson Creek. The southern l i m i t of out- crop l i e s very close to the International Boundary. The northern extent i s not d e f i n i t e l y known. It i s shown by Cairnes (1942) as being i n contact wit the Aluvia l plain of the Fraser River. The writer, however, mapped only to the northern end of Cultus Lake. An outcrop of Cultus rocks north of th© Chilliwack River, on th® Ryder Lake Road, reported to be f o s s i l l f e r o u s , was also v i s i t e d . ffo Cultus rocks have been described north of the Fraser River. They appear to be confined s t r i c t l y to the area outlined above. Lithology The Cultus Formation i s composed dominantly of dark gray to black, madia* bedded a r g l l l i t e s interbedded with dark gray to black shales, siltstones, fine to medium grained graywackes of various colours, volcanic breccias, probable t u f f s , c l a s t i c limestones, shaly limestones and chert. Besides the lack of f o s s i l s , the major d i f f i c u l t y encountered i n working i n the Cultus Formation is the lack of marker beds, the various sections resemble each other very closely i n gross features. Minor variations observed In a p a r t i c u l a r section which might have helped In correlation were seldom observed elsewhere. A r g i l l i t e s The major part of the Cultus Formation consists of thin to thick, regularly bedded, dark grey to black, brown weathering rocks, which i n th© f i e l d are termed a r g i l l i t e s . It i s apparent from examinations of thin sections, that a l l of tho rocks with this appearance ar© not true a r g i l l i t e s , that i s , they are not a l l simply indurated rocks of argillaceous composition. Complete gradations occur froa. true a r g i l l i t e s to graywackes* Th© majority of the rocks are s l l t y a r g i l l i t e s or argillaceous s i l t s t o n e s . When studied i n thin section, they are seen to contain a dens© matrix, which generally looks blue under crossed nicols and brown i n plane polarized l i g h t . Small, very angular quartz and chert fragments, very small, angular plagioclase fragments, occasional fragments of aphanitic volcanic rocks, and usually a very sra&ll amount of ealeite are also present* As the proportion of sand-sized particles increases, the rock grades toward a graywacke. Clean, smooth surfaces, at right angles to the. bedding t often exhibit fine colour banding from dark gray to li g h t gray and brown. These bands are 1/16" to 1/2" wide. They are apparently due to s l i g h t textural variations. The bands are usually strongly contorted, quite obviously owing to soft sediment deformation, since the bedding planes are r e l a t i v e l y smooth. Th© beds are commonly 2" to 3 " thick, but range up to several feet In thickness. They occasionally appear to be thin bedded due to very strong shearing which has broken the rock into thin slabs. South-east of the confluence of Lihuiaitson Creek, an outcrop appears to be thin bedded and dipping to the south. Close examination reveals that the rocks are actually thick bedded and dip south-east. A multitude of south dipping shear planes almost completely mask the bedding. The a r g l l l i t e s are usually s i l i c i f i e d i n various degrees. Some are so highly s i l i c i f i e d that they resemble chert i n hardness and breaking properties. Thin shaly layers, from 1/4" to l t t i n thickness, often are interbedded with the a r g l l l i t e s . These are Inter- preted as being chiefly a result of slippage along the bedding planes, rather than original sedimentary features, since they are very common i n highly contorted areas, but ar® rarely seen In r e l a t i v e l y undisturbed outcrops. Further- more, they are of a crumbly rather than a f i s s i l e nature. Separate descriptions, regarding the a r g i l l i t e s , of the numerous l o c a l i t i e s examined by the writer w i l l not be included since there is so l i t t l e variation between outcrops. Thicknesses of sections are generally Impossible to measure, owing to the strong contortion of the beds. Graywaeke: The graywackes of the Cultus Formation were f i r s t described In the f i e l d by the writer as t u f f s , since they present a very similar appearance i n hand specimens* Opon examination of thin sections, however, i t is seen that they are composed c h i e f l y of elongate, angular shale or argilllt© fragments, ranging i n length up to 1/2", volcanic rock fragments, quartz and plagioclase fragments, and c a l c i t e , set i n a dense matrix. Several small, white discs with hollow centres were observed, but their origin is unknown, The elongate fragments are oriented in the plane of the bedding* Th© beds range i n thickness from 1" to 7 feet. The thinner beds exhibit very well defined graded bedding, the medium grained graywackes grading upward Into a r g i l l l t e . The graywackes are interbedded with a r g l l l i t e . The graywackes occur i n various colours; bluish gray, l i g h t greenish gray, brown, and dark gray. It is believed, however, that this variation i n colour i s often due to leaching, which appears to have affected these rocks to a depth of several inches. One specimen is dark gray i n the centre, grading outward through l i g h t greenish gray to brown, !•§>»* from the central Material. The dark rock i s very calcareous. The rest of th® material Is non-calcareous. Leaching ©f the ealeite and subsequent s l i g h t alteration of th© remaining e l a s t i c material has apparently produced the colour variations. / A similar explanation may account for the appear- ance of a fine grained, dark brown, laminated, extremely porous, 18** thick bed which crops out on the road east of Cultus Lake at the south end of th© camp ground. This extremely soft rock contains volcanic rock fragments and highly altered, unidentifiable material. The porosity exceeds 5Q$* It i s probable that th© present.pore space was once f i l l e d with c l a s t i c c a l c l t e . Many of the graywackes ar® highly s i l i c i f i e d . It i s believed that the s l l i c i f l e a t i o a followed the d e c a l c i f i - cation, since l i t t l e ealeite i s present in the siliceous rocks. This theory amy account for the r e l a t i v e l y fresh appearance of some of the hard blue, green, and brown graywackes. I f samples could b© obtained several feet under surface exposures, they would probably be of similar colour. Graywackes occur throughout the Cultus Formation, therefor® separate l o c a l i t i e s are not discussed. They are next i n abundance to a r g i l l i t e , forming approximately \ % to 2 0 % by volume, of the rocks of this Formation, Calcareous Beds: Calcareous bads occur as c l a s t i c limestones and calcareous shales or shaly limestones. C l a s t i c limestones ar© exposed i n the lower canyons of Watt, Frost, and Blue Creeks. In outcrop, they closely resemble the graywackes In appearance. They occur i n beds 2" to 6" thick, which are generally banded or laminated. They are dark bluish gray on a fresh surface and weather to l i g h t bluish gray, or brownish gray. Upon examination of thin sections, i t is seen that the rock i s composed of 75% to 90$ c a l c i t e , with very angular fragments of quartz, plagioclase, and rock fragments. Some of the c a l c i t e i s In the form of semi-rounded, sand-sized rock p a r t i c l e s , consisting of small crystals of c a l c i t e . Much of the c a l c i t e appears to have been dissolved and re- deposited, however masking somewhat the original c l a s t i c texture since i t Is finer grained than the crystals i n the rock fragments. Th® rock fragments, which are chiefly elongat angular a r g i l l i t e fragments, are oriented i n the plane of the bedding and concentrated in thin bands. This produces the apparent lamination. The writer believes that detailed ©.jcaalna-tlon would reveal that a l l gradations exist between graywacke, calcareous graywacke and c l a s t i c limestone. Th© calcareous shales or shaly limestones crop out 500 yards south-west of Watt Creek at an elevation of 1800 feet. They ar© dark brown to black, soft and f i s s i l e . They are exposed through an apparent stratigraphic thickness of 60 feet and ar© overlain by medium-bedded, non-ealcareous • a r g i l l i t e s . Boulders of l i g h t yellowish brown travertine, up to 6 feet i n diameter are found i n Watt Creek from the Canyon to the mouth. Th© writer was unable to reach th® source of the travertin©. An outcrop above the second waterfall, which has been staked for i t s lime content by a prospector, proved upon examination to be a r g i l l i t e with a thin, white, calcareous coating. Shales Shales of this Formation are brownish-black to black and very rarely f i s s i l e . They appear to grade into a r g i l l i t e s and ar© probably a finer grained phase of the same material. There are vary few true shales i n the sequence. Immediately above the f i s h hatchery on th© east side of Cultus Lake, a hard, b r i t t l e , 1/8" to 1/2" bedded "shale* crops out. On© hundred yards north, on© of the rare occurrences of f i s s i l e shale i s exposed through an apparent stratigraphic thickness of 50 feet. 31 Cherts Very l i t t l e true chert i s found in this sequence, hut cherty rocks, formed by th© s i l i c i f i c a t i o n of a r g i l l i t e and graywacke are common, A few beds of true chert were found on th© east side of Cultus Lake, These were very li g h t gray to black, i n beds from 1** to 2B In thickness. They appear to have been formed by the replacement of other rocks by s i l i c a . Volcanic Breccias Only two occurrences of volcanic breccia war© found, one on top of th© ridge west of Frost Creek Canyon, th® other In Blue Creek Canyon, above the f i r s t waterfall* It occurs i n both l o c a l i t i e s i n a 2 foot thick bed. In hand specimen, i t i s mottled green and of medium to coarse pyroelastie texture. In thin section i t i s seen to contain c h i e f l y aphanitic and porphyritic volcanic rock fragments, with soma a r g i l l i t e and graywacke fragments and a small amount of quartz and secondary c a l c i t e . The presence ©f volcanic breccia adds some support to the writer's b e l i e f that many of the graywackes in this sequence wer® once tuffaceous, but that the tuffaceous nature has been subsequently destroyed by induration. Impure Cherts A very dense.massive siliceous rock, which i s usually li g h t green but grades to dark green and gray, crops out at 32 the bottom of the two small h i l l s on the east side of Columbia Talley between Blue Creek and the boundary. This type of rock also forms the nearly v e r t i c a l c l i f f immediately t© the south east of the small h i l l s . Bocks of this type underlie th© a r g i l l i t e s with apparent conformity. They are seen i n thin section to be of extremely dense texture, dark under crossed nicols and brown i n plane polarized l i g h t , with small scattered grains o f quartz and rock fragments. Quartz vainletr. form a mosaic pattern throughout the chert. Age of the Cultus Formation Daly (1912) found distorted ammonites "about 500 yards south of the Boundary and 900 yards west-south-west of Monument 47." Dr. T.W.Stanton of Washington identified these f o s s i l s as Arnlotites vancouverensls Whiteaves? Daly concludes that, " l i t t l e doubt need be entertained as to the T r i a s s i c age of the Cultus beds." Dr. Hans Frebold of the Geological Survey o f Canada has since re-identified these f o s s i l s , placing them i n the Lower Jurassic (personal communication with Dr. Jack Armstrong o f the G.S.C.},. Dr. Frebold writes to Dr. Armstrong, concerning f o s s i l s found by Dr. Armstrong in the Cultus rocks exposed on the Ryder Lake Road. 33 "Ammonites, probably Harpoceratids. Th® poor state of preservation does not permit any de- ta i l e d determination. Age: Probably Toarclan (upper part of Lower Jurassic) or Lower Bajocian (lower part of Middle Jurassic)" A few more ammonites have reportedly been found i n the Cultus Formation, but the writer was unable to find any. The Lower or Middle Jurassic age of the Cultus Formation appears to be quite well established. It is possible, however, that this very thick formation may represent a considerable range i n time. Vedder Mountain Sediments The nam® 'Vedder Mountain Sediments* is used by the writer to designate the sedimentary rocks which comprise approximately the eastern half of Vedder Mountain* Distribution The V%dder Mountain sediments crop out on Vedder Mountain froa about 500 yards west cf the summit, where they are i n apparent fault contact with a metaaorphic series called (Daly 1912) The Vedder Greenstone, to the western edge of Columbia Valley and Cultus Lake. They extend froa 1/2 mile »©rth of the lake southwestward to about 2 miles south of the boundary. Thes® rocks may correlate l i t h o l o g i c a l l y with 34 part of th® Nooksack Group of northwestern Washington (Dr. J.E. Armstrong, personal communication). Lithology Rocks comprising the Vedder Mountain Sediments includes a conglomerate, graywackes of various colours, a r g i l l i t e , schistose argillaceous chert, and altered rocks of igneous o r i g i n . The regional s t r i k e i s north-east, the dip almost v e r t i c a l . Conglomerate: A strongly cemented conglomerate, with components ranging from pebble to cobbla s i z e , crops oat along the western shore of Cultus Lake, at an elevation of 48 feet, from the south end of the lake, northward for a distance of s l i g h t l y over 1-1/2 miles. It extends westward up the steep slop® of Tedder Mountain to an elevation of approximately 2000 feet. Th® conglomerate contains cobbles and pebbles of granitic rocks, volcanic rocks and chert, which range up to 4* i n diameter. It i s intembedded with, and has a matrix of medium grained, dark greenish gray graywacke. The con- glomerate i s massive, but, judging from the interbedded gray- wacke, the regional strike i s north-east and the dip is almost v e r t i c a l . The cobble conglomerate grades into a pebble con- glomerate of the same composition along strike toward the north-east corner of the outcrop. Graywacke: Massive graywacke crops out over a major part of Vedder Mountain. It i s , however, noticeably scarce i n the area between the north end of the lake and a point 2000 yards southwest. In this area, up to an elevation of 2500 feet, only three small outcrops of graywacke were seen, fhey are laterbedded with a r g i l l i t e . fo the south-west and west of th© conglomerate outcrop, graywacke is the dominant rock type. On top of the ridge, graywacke i s interbedded with a r g i l l i t e . Along the International Boundary from Monument 41 to 100 yards west of Monument 42, only graywacke Is exposed. Th® graywacke is doainantly dark green In colour and very closely resembles greenstone. It also occurs In brownish gray and blue-gray colours. It i s fine to medium grained, containing rock fragments and quartz. Small angular shale fragments are noticeably common i n the rock. A r g i l l i t e : Very strongly contorted a r g l l l l t e s crop out extensively from north of the conglomerate outcrop to the north end of Cultus lake. They are Interbedded with the graywacke on top of tha ridge. Along the International Boundary, they are exposed from the base of the mountain to 100 yards west of Monument 42. The a r g i l l i t e i s dark gray to blaek, dense, and 36 quite b r i t t l e . I t i s so highly sheared throughout that the nature of th® original bedding is usually impossible to determine. The shearing has broken the rock into thin, elongate splinters and slabs. However, a few beds were observed to possess fine banding similar to that of the Cultus a r g i l l i t e s . Argillaceous Chert: From the north end of Cultus Lake, to a point 2000 yards south-west, and from the shore to an elevation approx- imately 100 feet above, a rock consisting of chert nodules in an argillaceous matrix is exposed, The nodules occur in layers separated by argillaceous or phyllitic material. They ar® light gray to white, ellipsoidal, about 2" long by 1" thick, and strongly fractured. The matrix is bluish black, often with a high lustre, and forms only thin layers around th© chert nodules. The planes that ar® now visible are probably not original bedding planes. They would b® more aptly called schistosity planes. Their general attitude i s , strike 1 65° E t dip S.E. 7 5 ° . These rocks are strongly folded and faulted. Relatively undisturbed, evenly bedded a r g i l l i t e crops out topographically above them 1700 yards southwest of the north end of the lake. One 2 foot thick bed of dark gray banded chert crops out on the lake shore about 1500 yards southwest of the north end of the lake. It strikes east-west and dips 43° south. I t is underlain by schistose argillaceous chert. 37 Altered Igneous Rocks A highly altered rock of Igneous origin forms a 20 to 40 foot c l i f f cropping out along the eastern edge of the top of the ridge on Vedder Mountain. In hand specimen this rock i s medium grained and black with brown and white spots. It Is seen i n thin section to contain astphibole, zoislte and a l i t t l e highly altered plagioclase. The amphibole appears li g h t green i n plane polarised l i g h t and appears to be secondary after some ori g i n a l mafic mineral. The z o i s i t e Is secondary. The outcrop is massif® and very strongly fractured. The rock seems to be interbedded with the-graywacke and a r g i l l i t e . Relationships Within th© Vedder Mountain Sediments Because of the massive nature of most of the rocks, the high degree of folding and faul t i n g , and the dense vegetation, the relationships between the various lith-ologic units of the Vedder Mountain Sediments are extremely d i f f i c u l t to solve. The sediments are d i v i s i b l e into the following HthologlQ units s (a) fhe schistose argillaceous chert. (b) The predominantly argillaceous sediments character- i s t i c of the north-eastern part of the mountain. (c) The predominantly graywacke section, characteristic of the south-eastern part of the mountain. (d) Tho internodd®a a r g i l l i t e s and graywackes, characteristic of tha top of the mountain. (e) Ths Interbeddod conglomerate and graywacke, found i n the lower, central part of th® mountain. Since the few dips that ar® obtainable, ar© almost v e r t i c a l , i t is impossible to say, without further evidence, what end of the outcrop i s the top. It i s not known whether th© l a t e r a l change froa north to south, apparently along s t r i k e , from predominantly a r g i l l i t e to congloaorat© to graywacke, is due to structure or to facies changes. It i s conceivable that conglomerate and graywaek® were deposited i n a channel cut i n older gray* wackes and a r g i l l i t e s . Age of the Vedder Mountain Sediments Ho f o s s i l s have baen found in the Tedder Mountain Sediments. Daly (1912) Included these sediments i n the lower part of the Chilliwack Croup, which he called Carboniferous. Crickmay (1930) 'assigned tha rocks to the Triassic S l o l l l c u a Series,, Misch and Armstrong (personal corcnmnication) believ that these rocks aay correlate l i t h o l o g i c a l l y with a similar 39 appearing part of the Upper Jurassic-Lower Cretaceous ? Ifooksack Group of north-western Washington. The abundance of granitic-textured pebbles and cobbles in the conglomerate, presents strong evidence that this unit is no older than Upper Jurassic, since granitic rocks were not common in any potential source area until after th© intrusion of the Coast Bang® Batholith supposed to have occurred during Upper Jurassic time. 40 STRUCTURES The regional strike over the entire area mapped is to the north-east. Chilliwack Group The regional dip of the Chilliwack rocks is to the south-east. The internal structure of this group i s not known, but folds overturned toward the north-west are exposed along the Chilliwack River, west of Slesse Creek, and on Church Mountain. The limestone units examined by the writer show evidence of gentle folding. A l l units examined ar© strongly fractured, with evidence of movement along many of the fractures. Cultus Formation Within the Cultus Formation, the regional dip is 30° - 60° to the south-east. Only a few, lo c a l occurranees of north west dips were observed. The dominant structures within this formation are overturned, i s o c l i n a l folds, whose axi a l planes have a similar attitude to the regional trend. These folds are not apparent except in sections cutting across the s t r i k e . They are very well exposed In a l l of the canyons of the creeks draining west from International Ridge. Th® a x i a l region of only one synelln© was seen, while the a x i a l regions of at least ten anticlines were found. Th© a n t i c l i n e s are exposed, approximately at r i g h t angles to t h e i r a x i a l planes, over a l e n g t h o f 20 to 60 feet and a width of 10 to 50 f e e t . In F r o s t Creek Canyon, three such f o l d s were seen to l i e one d i r e c t l y above another. I t i s p o s s i b l e t h a t low angle t h r u s t i n g accompanied t h i s type o f f o l d i n g , but only two w e l l d e f i n e d , low angle f a u l t traces were seen, and both were exposed over a le n g t h o f only 100 f e e t or l e s s . F a u l t s o f small displacement ar© common throughout most of t h i s Formation, but they cannot be traced along s t r i k e because of th© dense v e g e t a t i o n . They occur i n / an innumerable v a r i e t y of a t t i t u d e s . Small 'faults are con- centrated i n s e c t i o n s which appear to be crumpled, that i s , the rocks are inv o l v e d i n many s m a l l f o l d s , o f only a few- f e e t 'in width. These f o l d s have been o f f s e t i n many d i r e c t - ions' by small f a u l t s . Vedder Mountain Sediments The r e g i o n a l dip of the Vedder Mountain sediments i s almost v e r t i c a l and v a r i e s from south-east to north west. The i n t e r n a l s t r u c t u r e s o f these rocks are not understood. k c o n s i d e r a b l e mount of f a u l t i n g has occurred as evidenced by the abundant s l l e k e n s l d i n g throughout many o f the rocks, e s p e c i a l l y the igneous rock and the a r g i l l l t e s . The only well defined s t r u c t u r e i n v o l v i n g these roeks, that was observed by the w r i t e r , i s an overturned a n t i c l i n e , 42 which crops oat 1-1/2 miles south-west of the south end of th® lake a t th© bottom of Tedder Mountain. The outcrop i s 200 feet long by 40 feet high and consists of the a n t i c l i n e , whose a x i a l plan® s t r i k e s north 55° west and dips north. Th® axis of the f o l d plunges to the north west. Regional S t r u c t u r e The rocks ©f the C h i l l i w a c k Group have apparently be@n thrust f a u l t e d over rocks of the Cultus Formation, From the nature of th® contact, i t seems most probable that two high angle thrusts are i n v o l v e d , one dipping to the south- east and one to the south. The south-easterly dipping f a u l t would crop out on the -ridge west of Church Mountain, Th© southerly dipping f a u l t would crop out on Isar Mountain, Just north o f , and quite p a r a l l e l to the I n t e r n a t i o n a l Boundary. I t i s possible that only one south easterly dipping f a u l t , t h r u s t i n g s t r o n g l y folded C h i l l i w a c k rocks over the Cultus i s i n v o l v e d . The s t r u c t u r a l r e l a t i o n s h i p of the Tedder Mountain Sediments to th© other rock units i s unknown. GEOLOGICAL HISTORY OF THE AREA 43 This area has been highly unstable, at least since early Permian time until late Hesozolc time as evidenced by the geologic record contained in the roeks exposed. The alternation of limestones with conglomerates and volcanlcs in the Chilliwack Group indicates strong tectonic activity at the time of deposition of these rocks. The graywackes, argillltes and elastic limestones of the Cultus Formation indicate conditions ©f rapid depos- ition during early Jurassic time. The occurrence of these rocks through a great thickness without any noticeable change in lithology, indicates that a nearby, high-standing source area was constantly rising to compensate for the rapid erosion. Similar, but more active conditions during late Jurassic-early-Cretaceous time are indicated by the nature of the Vedder Mountain Sediments. All of the rocks exposed In the area were, there- fore, deposited in a very active geosyncline. The major deformation of th© region occurred after Paleocene tiro. f t Bauerman, H., Calrnas, C.E. Crickmay, C M . Daly, R.A., Frebold, H», Misch, Peter, BIBLIOGRAPHY 1 $ $ 4 , Report of Progress, Geological Survey of Canada f o r 1 & 0 2 - 3 - 4 , Part B. 1942, Hope Yale and Sew Westminster D i s t r i c t s B r i t i s h Columbia Geological Survey of Canada 1930, The Structural Connection Between The Coast Range of B r i t i s h Columbia and the Cascade Range of Washington, Geol. l a g . Fo, 67 1912, Worth American C o r d i l l e r a F o r t y - n i n t h P a r a l l e l , Memoir I o . 3 8 , G.S.C. 1953, C o r r e l a t i o n of The Ju r a s s i c Formations of Canada, Geol. Soc. of Am. Bull. Vol. 6 4 , ff 1229-1246, 1955, Geological Sketch l a p of Wooksack l o r t h Fork Region, llhateoffi County, Washington, Unpublished Map. 1952, Geology of The Northern Cascades of Washington, The Mountaineer, Vol. XLV, I o . 1 3 , P. 4-22. Banded, medium bedded Cultus A r g i l l i t s s . View looking S.E, up Blue Creek Canyon, 46 Highly contorted, thin bedded a r g i l l i t e s , exposed in road cut 1 mile east of Llhumitson Greek. General strike north east. Plate I I I . ChilliwackjCqnglojgerate Outcrop exposed on Lihumitson Lake t r a i l . Thickness expos ad i s about 25 f e e t . ¥%kTM tTf.» C r i n o i d a l Liis-estoa@ on Liha.mit5on Lake ,_Tra.ll Massive upper part of Crinoidal l imestone . The c l i f f shown here i s approximately 2C feet h i g h . 4r; PLATE ¥. Horthyest.ern__face _of ̂, C h u r c h M o u n t a i n Church Mountain as seen from south slope of f i r s t peak on Lihumltson Lake T r a i l . Slope above LIhtcoltsoQ Lake Cabin A large limestone outcrop is v i s i b l e i n tha b a c k g r o u n d .  j2 i Plate VIII. Thin Jjegti.gn.__gf._S,El|ag^yg£Hggfeg. showing orientation, of elongate grains P l a t e IX. Thin s e c t i o n of^impure Cultus c l a s t i c limestone. Scale l''=l/a mile GEOLOGY by ETEIL HlLtHOUSE Torograp&y 9at» Top©. 9B!/9» 926/1» and U.S.C.S# Van Stendt Qasdrangl© C o n s i d e r a t e and grayfeacka L_J Schistose Arglllsefeous chart E l Oraya-acka and argillit® EI) Igneous v&dder ffount&in Upper Jurassic » T-over Crctacocas? ? no Argilllts tdasstoo* Volesj&I© Breeeia Cttlttts formation [ZD Da *• Ooaks Cre®k F« «- Fusulinid Cr «- Cytnoidal Dl - Dolositic Conglomerate Volcanlcs Mori t a Chilliwack Croup Permian Gh &SS«BNK$ Fault SeMatosity Assu&sd Contact Contact Fault Overturned fold 54   ft


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