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    DR H E ARMSTRONGedited by Chad Roots and Chris Staargaard

    Vancouver 199

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    Geological Association of '- ' ''uca, CordilleranBox 398, Station AVancouver, B.C. 2N2Satellite of southwestern British Columbia copyrightAdvanced Satellite Productions Richmond, B.C.Production: Terri WershlerDesign: iona MacGregorTypesetting: The Vancouver Desktop Publishing Centre Ltd.Printing: Imprimerie Gagne Ltee.

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    Geological Association o CanadaVancouver GeologyDr John E Armstrongp. 23 line 3 for Coast Range read Coast Mountainsp. 30 line 16 for Bowen Island Formation read Bowen Island Groupp. 47 photo caption substitute Glaciomarine stony mud (top left) overlies till consisting

    of rounded stones in a darker mixture of sand and siltp.47 diagram for glaciomarine till read glaciomarine stony mudp. 51 photo caption for Glaciomarine mud read Glaciolacustrine mudp. 61 photo caption for Agassiz , 1928 read Mission , 1948p. 69 photo caption for Eocene read upper cretaceousp. 74 upper photo caption for glaciomarine read glaciofluvialp. 83 paragraph 5 line 4, for 150m for 250mp. 85 in photo caption add last sentence, The bouldery till layer immediately above thesand bags is now thought to have been deposited during the SemiahmooGlaciation.P. 85 paragraph 3, line 1 for green banded glaciomarine read green bandedglaciolacustrineMap legend add Quadra sand, minor silt, Coquitlam till to be included under

    Vashon drift heading and glaciation terminated about 10,000 years beforepresent time

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    Fraser RiverCascade MountainsVancouver Island and Olympic Peninsula




    PLATE TECTONICS 2BEDROCK 27Older Volcanic Sedimentary RocksIntrusive Rocks the Coast Plutonic Complex 31Sedimentary Rocks the Georgia BasinCascade Volcanic Rocks 38GLACIAL AND RIVER SEDIMENTSGlaciersFraser Delta 53FORCES AT WORK 58Ongoing Geological Evolution 58Geological Hazards 6Human 6FIELD TRIPS 63Stanley Park 63Kitsilano Point Grey Beaches 72Renfrew Park 76Burnaby Mountain 77C oquitlam Valley 79Caulfeild Cove and Lighthouse Park 8CapUano and Lynn Canyons 83Hiking in the North Shore Mountains 89Mount Seymour 9Lynn Headwaters and Grouse Mountain 92Mount Strachan and Hollyburn 95Mount Brunswick and Howe Sound Crest Trail 99Howe Sound 1 2SOURCES OF GEOLOGICAL INFORMATION 117GLOSSARY 12INDEX 128

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    EBorn in Cloverdale in the heart of the Fraser Jack loved theoutdoors and collected agates in his He entered theprogram at thehis doctorate from the University of Toronto. In the summer of 1934 heassisted in the geology of the central Yukon. the staff ofthe Geological Survey of Canada in 1937, Jack s entire career wasdevoted to understanding the rocks and sediments of western Canada.From 1940 to 1949 he supervised the systematic geologic mapping ofnorth-central British ColumbilL Jack s and insistence uponhigher education encouraged a remarkable number of his summer assis-tants to pursue in their own careers.

    In 1949 Jack was transferred to the Vancouver office of the GeologicalSurvey. After several years of geologic mapping in the mountains north ofthe city, he entrusted the work on granitic rocks to his senior assistant, JimRoddick, and concentrated on the Pleistocene mostly glacial) sedimentsof the Fraser Lowland. The complex distribution and interleaving ofdeposits were elucidated here on a scale matched in few other parts of theworld. He recognized that during the Ice Age an arm of the sea extendedas far east as Chilliwack, and glaciers surged out of the mountains at leastthree times. Jack headed the Vancouver office from 1955 to 1968, afterwhich he was seconded to Ottawa to organize the 24th InternationalGeological Congress. With Bill Mathews, a close friend and professor atthe University of British Columbia, he organized section meetings inVancouver for the Geological Society of America in 1960 and 1985.

    Jack s enthusiasm for geology extended beyond office hours and hefounded the Vancouver Geological Discussion Club. This club eventuallybecame the Cordilleran Section of the Geological Association of Canada,and Jack served many years s the secretary-treasurer and continues ashonorary councillor. He has also been president of the Vancouver NaturalHistory Society, and is an honorary life member. With more than fortyyears of local geological experience, Jack has greater familiarity with therocks and sediments of the Vancouve r area than any other individual. TheCordilleran Section salutes his scientific career and acknowledges hisefforts in helping us all to better appreciate our geological environment.

    Jack Armstrong s original manuscript of Vancouver Geology moretechnical than this book, is available from: The Geological Association ofCanada, The Cordilleran Section, P.O. Box 398, Station A, Vancouver,B.C. V6C 2N2.

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    l cc G E

    was written. 1972 byG.H. the GeologicalSurvey of Canada as as former professors at UniversityBritish and Simon Fraser This and ex-been produced by the Cordilleran of theGeological of Canada between andMost of the information was supplied J.E. Armstrongportions of the text have been addressed by these members: GCarlson M Hitzman M. Keep C Roots C. Staargaard and S. Taite.Field trips near sea level were described by J R Armstrong and themountain hikes by C Roots. Reviews by C. Kissinger J Ricker andA Tempelman-Kluit have also guided our efforts. Significant improvements in the manuscript were suggested by our independenteditors B Scrivener and N Thompson. Ultimate responsibility forthe final draft however rests with us.Technical aspects of production have been expedited by manyvolunteers. Early drafts were transcribed by E. Woolvertonsecretary for the Cordilleran Section with additional typing by J.Getsinger and B. Vanlier. Diagrams were drafted by M Keep C.Roots C. Staargaard and A Stanta. Donations of time money andeffort were instrumental and many of these were procured by VSterenberg President of the Cordilleran. Section. Contributions included computer plotting by R.W.R. Mineral Graphics and PlacerDome Inc. as well as drafting by the Geological Survey of Canada.A digitized base map was supplied by the B.C. Forest Service whereK Lee P. Pitzakis and D Herchmer were most helpful. GulfInternational Minerals Ltd. supported some of the plotting with agenerous grant. Variom; photographs were contributed by GaryWesa and Jack Armstrong and the Vancouver Public Library isthanked for their cooperation. The concept and much of the cost ofthe cover were respectively supported by MacDonald Dettwiler andAdvanced Satellite Productions Inc.

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    Annual Meeting inguidebookRootsC Staargaard

    Conversion scales:Distance

    0 50 5 1

    Elevation0 5 1 150 2 4

    1 metres= 328 feet1 f ee t 3 5 metres

    1 15 milesi 2 2 s kilometres

    2 25 3 metres6 8 o o o feet

    Mile= 1 6 Kilometres5 k i l o m t r s ~ 3 miles


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    T 10

    mosttutheir home on the basisthough, to wondersplendid combination

    surroundings appear permanent in comparison with Man s con-tinuous effort to excavate, and But processes such asthe uplift of mountains, the subsidence of plains, and the advanceand retreat of glaciers have had a much more profound impact on thefinal architecture of our land.The study of the Earth and natural forces acting on the land iscalled geology. Geologists are still a way from understandingthe ultimate causes of processes shaping the planet but by carefulwork in the field and laboratory, they have pieced together anintriguing history of the Earth. For geologists, periods millions ofyears long are distinct and comprehensible geological time intervalsduring which the Earth has changed its face many times. Some of thechanges are slow, as in the uplift of mountains and the movement ofcontinents, but others are rapid, such as floods and volcanic erup-tions. It is by understanding these natural processes we canminimize the adverse impacts of our own activities.This book offers some glimpses into Vancouver s past and thegeological framework that uniquely determined the distributionof water land here. It has two parts. The first describes localgeography, the structure of the Earth s crust below us, the rocksvisible at the surface and the loose sand and gravel deposits overly-ing them. The second part includes field trips to show some of theaccessible geological features in the Vancouver area.

    e hope this book encourages you to learn and experience moreof our natural surroundings. t will help you to see how thelandscape has changed, and is changing, through time.


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    area is composed of two distinct geographicalareas: Mountains along the North Shore the raserLowland encompassing of city and extending south to theCanada USA These are flanked on the and east thelympic and Cascade Mountains and to the west by the

    Georgia and the Insular on Vancouver Island.


    The Fraser Lowland is a triangular plain not a true valley that resulted fromerosion by rivers. t is a depression between the Coast Plutonic Complex Van-couver Island and the Cascade Mountains that has been filled with sedimentsduring the last 70 million years.

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    The southern peaks o the Coast Mountains are a lofty backdrop t the city oVancouver, seen here Queen Elizabeth Park. The Lions are on the left,Crown Mountain on the right, and the Capitano River valley, Vancouver s watersupply, between them. (GW)

    Coast MountainsThe most striking geologic feature in the Vancouver area is thebackdrop of rugged mountains rising up from the North Shore.These mountains form the southern end of the Coast Mountainswhich extend 1700 km north from Vancouver to the Yukon. Unlikethe Rocky Mountains along the British Columbia-Alberta border,which are made of sedimentary rock, the Coast Mountains arecomposed primarily of granite and other igneous rocks. These arethe frozen remnants of subterranean magma chambers whichformerly lay beneath and supplied magma molten rock) to ancientvolcanoes on the Earth s surface above. What we see as mountainstoday are actually the roots of volcanoes similar to the Cascadevolcanoes stretching from Mt. Lassen in Northern California to Mt.Baker just south of British Columbia in Washington State.As the Coast Mountains began to be uplifted, they were subjectedto erosion by streams and rivers but maintained their existence sincethe rate of uplift was greater than that of the erosion. However, thestreams and rivers cut deep, narrow canyons and valleys in themountains, many of which are still visible today. Later, between


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    wasice ages.due to high snow faclimate t during the summerwere slowly formed. Atperiods of glaciation are recognized in the Vancouver area.from the Coast and Cascade Mountains formed large

    ' ' ' ' ' r ~ the Fraser Lowland and extended outthe Strait of Georgia.Because sea level was during each ice advanceglaciers were able to cut below present day sea level in the

    coastal many valleys. As sea level rose during last10 000 years these valleys were partially submerged resultingthe creation of fiords. The fiords in the Vancouver area such asIndian Arm and Howe Sound are among the most southerly ones in

    BRIH DESCRIPTION OF VARIOUS ClASSES O f ROCKSIgneous rocks are those formed bycooling of molten rock. f the cooling takes place beneath the Earth ssurface the rock is called plutonic.These rocks consist of an interlocking mass of mineral crystals. Themost common minerals are quartzwhite feldspar tan to pink potassiumfeldspar black flaky biotite micalight-coloured flaky muscovitemica and dark ferromagnesian silicate minerals such as amphibole andpyroxene. Many combinations ofthese are found.

    f the molten rock cools after ithas been erupted onto the Earth ssurface it is known as volcanic.These rocks are made up of the sameminerals as plutonic rocks exceptthat they are generally in muchsmaller crystals many or aU ofwhich may not be visible to thenaked eye. Rapid cooling doesn tallow them time to grow. Volcanicrocks may occur as lava flows or asdeposits of fragments from more explosive volcanism. Typical examples include basalt andesitedacite and rhyolite.


    Sedimentary rocks are formedfrom small grains of mineral androck eroded from pre-existing rocksand deposited by water wind or icein relatively uniform horizontallayers called strata or beds. Initiallyunconsolidated deposits of mud siltsand and gravel become hard whenthey are buried and compacted.Sedimentary rocks are composed ofmany of the same minerals as igneous rocks but also include fragments of older rocks and fossils. Themost common sedimentary rocksseen in the hills in the Fraser Lowland area are sandstone shalesiltstone and conglomerate.metamorphic rock is formedwhen changes in temperature pressure or a few other factors causechanges in a pre-existing rock.These might be changes in the typesof minerals present how theminerals are arranged or the chemistry of the rock. Metamorphic rocksgenerally form at some depth in theEarth and include schist gneissmarble and amphibolite.

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    Point Atkinson lighthouse is built upon granodiorite o the Coast Plutonic Com-plex. Lighthouse Park includes some o the best exposures granitic rock nearVancouver.

    Howe Sound which extends 32 km north from Vancouver is a fiord that wasoccupied by a glacier as recently s 12 000 years ago. Highway 99 follows theeastern shoreline passing the former mining town o Britannia on its way toSquamish and points north.4

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    riseHill, Silverdale Hill and furthereast, the rocks. These are ..freshwater sedimentary rocks that were in a depressioncaHed the Georgia Basin starting million years ago.Geologically, these are relaHvely young rocks. The Canadian Shieldcontains rocks more than 3.9 biHion years old.Although these sedimentary rocks were deposited horizontally,they have been tilted over the ages and are now slightly inclined tothe south. Along northern edge of the Fraser Lowland they formonly a thin veneer over the granitic rocks of the Coast Mountains.However, they thicken to the south and reach a maximum thicknessof 4400 metres near the Canada-USA border.The Cretaceous and sedimentary rocks are coveredby up to 300 metres of unconsolidated sediments, those which havenot yet hardened into rock. The latter include material depositedduring glaciation by both water and ice together with that deposited

    8URRARD INlETBurrard Inlet is part of the IndianArm fiord. Looking at a map of theVancouver area, it is tempting tospeculate that Burrard Inlet wasonce a branch of the Fraser River.However, there is no geologic evidence to support this and t appearsthat the present course of the FraserRiver was established after the finalretreat of the last ice sheets 11 ,000years ago. Burrard Inlet is in fact thedrowned valley of a stream which


    drained the Indian River and Seymour River valleys. The CapilanoRiver presently deposits sediment atthe Inlet s entrance and until theCapilano dam was built in the1950 s, a dredge was needed toremove this sediment so that thechannel could be kept open for shiptraffic. Without man s intervention,Burrard Inlet would soon tum intoBurrard Lake.

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    Beneath the Fraser owland are glacial and river sediments underlain y sedimentary rocks Georgia Basin.

    water between glacial events. They are best seen in the sea cliffsaround UBC Spanish Banks and Point Grey), at White Rock andalong the narrow Coquidam River valley near Port Moody.Because these sediments are unconsolidated, they are potentiallyunstable and can be easily washed away by major floods along riversand streams that cut through them. Exposed headlands composed ofD TING ROCKSOne of the ways in which geologistsare able to estimate the age of a rockis through the use of isotopic dating.There are a number of naturally occurring radioactive elements andisotopes which are widely distributed in common minerals. Overtime, they decay into other elementsor isotopes at a constant rate whichis different for each element. Bycarefully determining the relativeproportions of new and old elementsin a sample, geologists are able todetermine how long the radioactiveelement has been decaying and thusthe amount of time since that mineral, and presumably the rock, wasformed. The analysis is done in alaboratory and requires great careand patience.

    Different pairs of elements areused, depending on the time involved. Radiocarbon dating is useful


    for the last 50 000 years or so. f therock or fossil was formed beforethat, all of the measurable radioactive carbon will have changed intoordinary carbon and no ratio can becalculated. Other element pairs commonly used include:K-Ar potassium-argon1 million to 4.5 billion yearsRb-Sr rubidium-strontium10 million to 4.5 billion yearsU-Pb uranium-lead10 million to 4.5 billion yearsSm-Nd samarium-neodymiummore than 200 million years

    The choice of any of these willdepend on the quality and abundanceof radioactive minerals in the rockand the approximate age expected bythe geologist on the basis of othercriteria.

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    The organic-rich soil and river silt, as well as fl t ground and favourable climatemake the Fraser Lowland one of Canada s prime agricultural areas. As the urbanarea of Vancouver (middle distance) expands, this land is increasingly used forhousing and industrial development. (GW)this material such as in the Point Grey area are vulnerable toerosion by storm-generated waves and could quickly be eroded ifthere were a significant rise in sea level.The oldest Quaternary sediments were deposited in a shallow armof the sea which probably covered much of the present day FraserLowland. The hills of older rocks such as Burnaby Mountainformed islands similar to the Gulf Islands we know today. Duringthe major glaciations and the intervening nonglacial intervals theareas between the islands were fined by debris carved fromsurrounding mountain valleys by the ice.fraser River and DeltaThe raser River one of the largest in Canada occupies aglacial t post-glacial valley which is 5 kilometres wide and 225metres deep. The river branches into three main arms as it flowsacross triangular shaped delta which extends from NewWestminster into the Strait of Georgia a distance of nearly 30kilometres. On the coast the delta is 20 kilometres wide and coversthe area between the Oak Street Bridge and Tsawwassen. deltaalso extends at least 20 kilometres underwater into the Strait of


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    is some in thebecause of Hs rich Although the sand isfor the large buildings whenwater it is prone to liquifaction. be-comes fluid during vibration such as that occurring anearthquake and large structures built on t tend to and eventopple over.In addition to Fraser River two other flat bottomed valleyscross the Fraser The and Serpentine Riversbegin near Fort Langley flow into Boundary Bay. valley inflow is about kilometres and kilometres wide

    and is bordered low lying hills. The Sumas valley which extendsChilliwack to the Canada-USA border is about 25 kilometreslong and averages 5 kilometres in width.Cascade MountainsAlthough the Cascade Mountains do not form part of the immediateVancouver area they bound the east and southeast edge of the FraserLowland and are prominent on the Vancouver skyline

    The Cascade Mountains extend from Washington State northwardto Lytton in the Fraser Canyon. They are made of sedimentaryand volcanic rocks of Mesozoic and Paleozoic age many of whichhave been highly deformed and metamorphosed. These rocks are cutby plutonic rocks of several younger ages. Like the Coast Mountains most of these rocks did :not form in North America but areexotic fragments which formed in the Pacific Ocean and collidedwith and attached to the continent.The most obvious features of the Cascade Mountains inWashington are major volcanoes one of which Mt. Baker is visiblefrom Vancouver. Geologically speaking the Cascade volcanoes arevery young a of them are potentially active. The CascadeMountains present a picture of what the eroded top of the CoastMountains must have looked like in the geologic past.

    Vancouver Island nd the lympic PeninsulaThe other mountain ranges visible on a clear day from Vancouverare on Vancouver Island and on the Olympic Peninsula ofWashington State. The Vancouver Island ranges are composed of


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    These originallyand were pushed up onto

    W TER SUPPlY fOR VANCOUVERUmike most of the rest of the FraserLowland which depends on groundwater, the of Vancouver relieson rivers, namely, the andSeymour Rivers flowing Bur-rard Inlet and the Coquitlam Riverflowing into the Fraser River. Theirwatersheds are closed to the public.The high annual precipitation in theCoast Mountains, normally in excess of 2500 mm, ensures a goodrunoff, which is stored for use inreservoirs created by dams on allthree rivers. Several pipelines underBurrard Inlet and the Fraser Rivercarry the water to the city.

    The rivers flow in U-shaped valleys with steep slopes developed ingranitic and metamorphic rock of theCoast Plutonic Complex, which in


    most places is covered up toseveral metres of soil, glacialdeposits, and talus. This mantlemaintains about a 60-80 year oldsecond growth conifer forest. Because these rocks aren t easily dissolved or otherwise weathered, thewater is of outstanding quality, thehardness rarely exceeding 10 partsper million ppm), with total dissolved solids at 23 ppm. Chlorination is the only treatment required.On occasions, mainly during theperiod from October to April, thewater may become dirty looking as aresult of landslides, which increasethe silt content of the water in thereservoirs. However, t remains perfectly safe to drink.

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    know that the Earth is a number ofwith a central core of nickel-iron surroundedsilicate rock rich and magnesium. The crust isand outermost shell; its proportion to the remainder ofless than that of the skin of an apple to the fruit inside,crust exist, oceanic and continental, bothmantle, which is relatively cold and rigid, The crust uppermostmantle together are called the lithosphere,According to plate tectonic theory, the lithosphere is intosix major and numerous smaller plates which like rafts on apartly molten portion of the mantle and are constantly in atspeeds comparable to the growth rate of fingernails (about 5 em peryear). Much of the volcanism and earthquake activity as wen asmost of the younger and higher mountain ranges we see on the Earthtoday are concentrated at the boundaries where the plates are incontact. They are a direct result of this slow but steady motion.Three main types of plate boundaries exist:1 Divergent - Here two plates move away from each other andnew crust is formed between them. An example would be the two

    plates carrying North and South America moving away from thoseTYP S OIF RUSTThere are two types of crust makingup the tectonic plates on the Earth ssurface, Continental crust, that forming the continents, is rich in aluminum and silicon and is between 30and 80 km thick. t often consists ofa very old central portion called ashield, as much as 3.9 billion yearsold, surrounded and partly overlain


    by younger rocks.Oceanic cmst underlies most ofthe world s oceans, is rich in siliconand magnesium and ranges betweenand 10 km in thickness. Because itis continually forming at spreadingzones and being consumed in subduction zones, none of it is olderthan about 200 million years.

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    C/I.SCAD A



    The wedge at lef t shows the various parts the Earth s interior. t right is anenlarged view of the Earth s crust and surface showing the tectonic elements ofsouthwestern British Columbia. The Juan de Fuca plate under the ocean issubducted beneath continental crust and Vancouver Island.carrying Europe and Africa along a split down the middle of theAtlantic Ocean. Volcanic activity is producing new ocean crustalong this split, also known as a spreading zone or ridge.

    2 Convergent Here two plates approach one another, with onesliding beneath the other and the compression forming chains ofmountains in the upper plate. As the lower plate descends, meltingoccurs and some of the resulting magma rises through the upperplate to accumulate in large chambers. These eventually freeze inplace to form plutons. Magma also may reach the surface to formvolcanoes, which are typically found in belts parallel to the plateboundary. Earthquakes are often generated in the downgoing plate.Depending on the types of plates involved, different things canhappen. f the downgoing plate is oceanic, it may be overridden byeither an oceanic or continental plate and the process is calledsubduction. An example is the west coast of South America, underwhich the Pacific plate is being consumed. The other possibility isthat a continental plate is being overridden, in which case theprocess is called collisional. Because continental plates are lessdense than plates, they going down and these


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    Tectonic elements in southwestern British Columbia. The Georgia Basin overlaps thejunction of hree thicker crustal blocks: Wrangellia the Coast Plutonic Complex andthe Cascade Fold Belt. It has existed as a depression for about 7 million years as aresult of tectonic stresses beMeen these blocks. The accretionary prism consists offault-bounded slices of sediments eroded off Vancouver Island and pushed up alongthe leading edge of he orth American plate.

    British Columbia can be divided into five geologically distinctareas which are all products o the convergence o crustal plates.They include fragments o older continents and islands togetherwith various remnants o ocean floor. These pieces accreted ter-ranes) have been stuck against North America as the NorthAmerican plate moved westward over the Pacific Ocean floor overat least the past 150 million years. Geologists examine and interpret22

    te tonibound ries ne r

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    PL TE



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    the rocks in each area and can make good estimates o the ancientsurroundings o these fragments. Many o the older sedimentary andvolcanic rocks in central B.C. the Coast Range and VancouverIsland probably originated hundreds or thousands o kilometres tothe south and southwest as island arcs chains o volcanic islandsformed over ancient subduction zones. The various collisions andaccretions through time resulted in great pressure and thickening othe crust along the western coast o North America forming themountain ranges we see today.As little as 200 kilometres offshore from Vancouver Island newoceanic crust is being formed at Juan de Fuca spreading ridge at


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    exotic worms,the hot springsAs Pacific movesnwves southeasterly,plate at a rate of about 4.5 em per year in theZone. This zone lies between 60 150west coast Vancouver Island. The Juan de Fuca plate islast of many oceanic plates that have been subducted under NorthGeologists estimate that over 11,000 kilometres of oceaniccrust have already been consumed at this boundary.

    IEAIUHQUAKIES IN THE VANCOUVER AREAOne of the more common situations inwhich large or mega-earthquakes aregenerated is in a subduction zone. fthe contact between the plates is welllubricated and the relative motion iscontinuous, few, if any, earthquakeshappen. However, if the contact issticky, the plates will not slidesmoothly past one another and longperiods of little or no movement,when stresses are building, will be interrupted by sudden motion of severalor more metres. When this happens,large earthquakes result, reachingvalues of magnitude 8 and more on theRichter scale.British Columbia s southwest corner is the most active earthquake region in Canada. More than 200 earthqua lces are recorded each year on theFraser Lowland and Vancouver Islandand although most are too small to befelt, an earthquake capable of structural damage can be expected to occursomewhere in the region about once


    every ten years. These areearthquakes registering at least 6 onthe Richter scale. Within a radius of200 km from Vancouver, eightearthquakes measuring or more havebeen recorded in about the last 120years and four of these have been at amagnitude of 7 or slightly higher.Two occurred on Vancouver Island1918, 1946), one east of Vancouver,possibly in the Hope area 1872), andone to the south in Puget Sound1948).Contrary to a widely held misconception, the San Andreas Fault Zonedoes not lie off the Coast of BritishColumbia. Although we are also nearthe boundary between the Pacific andNorth American plates, the nature ofthis boundary differs along its length.In the B.C. area, t is a subduction zonerather than a fault. Our earthquakesare mainly related to the subductionprocess but seismic monitoring of theCascadia Subduction Zone has shown

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    thconverging motion of In addition to this piling up, at leastsome the sediment lying on the ocean floor is off by theNorth American plate attached to its leading edge in a depositan accretionary prism, Recent research has also suggested

    of from time to timestick to the in a process known asunderplating. entire package of rocks and sediments attached to

    plates is known as an accretionary complex.Joining accretionary on its eastern side, and partly

    overlying is an accreted terrane known as Wrangellia. VancouverIsland is part this terrane, which consists of volcanic rocks andrelated sediments Mesozoic age. Still further east is the CoastPlutonic Complex, a large body of granitic rocks underlying theMountains. Both are surrounded on the east and to the south

    Cascade Fold Belt, a series of very strongly deformed volcanic and sedimentary rocks underlying the Cascade and easternCoast Mountains.

    that not even very small earthquakesoccur on the interface between theJuan de Fuca and North Americanplates. All of the ones recorded hereso far have originated either in theoverriding North American plate, orin the downgoing Juan de Fuca plate.The lack of earthquake activity at theinterface between the plates is causefor concern. Are they actually stuckand is there a chance for a very largeearthquake?Studies of other seismically activeareas in the world have suggested thatearthquakes of this type take place instages. Before the earthquake, sincethe plates are not moving across eachother, the upper plate will graduallybend and shorten somewhat, withsome areas being uplifted and othersdepressed. When the plates becomeunstuck and the earthquake occurs,sudden changes in elevation (and thussea level) take place. In both cases,patterns of sedimentation will be affected and these changes preserved in

    the rock record. While not complete,studies in the southern British Columbia coastal area indicate that manysudden changes in sea level havetaken place in the past, the most recentabout 300 years ago. In addition, precise surveys carried out on VancouverIsland show that shortening and deformation is taking place in the upperplate at the rate and in the patternsexpected in a locked plate situation.As to whether a large earthquakecan be expected in Vancouver, thebest answer we have so far says thatthe geological setting is right and thatlarge earthquakes appear to havetaken place in the past. Most WestCoast seismologists believe that amega-earthquake of magnitude 8 orhigher should be expected at anytimein the next 200 years. Unfortunately,not enough information is available tomake a better guess of when t willoccur. One thing s for sure, however.It can t hurt to be prepared.


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    t ins h ve

    Vancouveron Upper Cretaceous to Upper

    rocks that were in the Georgia Basin beginning70 minion years ago. The basin was a formed overthe more crust possibly asfloor. InVancouver


    by the underplating of oceanyears or so compression between

    have caused folding in theThe shapes of many Gulf Islands reflect some

    Crustal plates move very little in a human and we aretempted to think that tectonics no longer affect this region.

    however, the West Coast an active continentalactivity is still taking place. Precise measure

    tops on Vancouver Island show the north-directed squeezing of the land and the Coast Mountains are

    rising-almost a during our lifetime. Rain andstreams wear the at a similar rate and the materialremove eventually ends up in the lowland areas modifying the

    landscape there as In some ways tectonically active regions,their steep mountains and spectacular scenery provide anagreeable environmeni: in which to live. However this area may notbe without geologic risks from earthquakes, and more remotely,from volcanic



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    edrockunconsolidated surficial u v ~ u ' ' '. .. . ... nw based on ages of bedrock in

    area. Beginning with P r e ~ u r a s s i c to Middle metamor-phosed volcanic and sedimentary succeedingdescribe Jurassic and Cretaceous igneous rocks of theCoast Plutonic Complex Cretaceous to Miocene sedimentaryrocks the Georgia Basin and finally Tertiary and Quaternaryvolcanic rocks.Before 140 million years ago volcanic islands and shallow seasgave rise t the rocks now uplifted in the Coast Mountains. Deep

    Before 140 million years ago volcanic islands and marine basins formed the rocksthat presently underlie the Vancouver area. These rocks were buried metamor-phosed and intruded y granodiorite plutons between 140 and 95 million yearsago. Later volcanic activity resulted n the andesite dykes and sills that arepresent ly exposed in the Vancouver area.


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    Mt. Garibaldi formedMt. Boker formed

    Cascade VolcanismCascade Volcanism

    oast Plutonic. ..- intruded} Gambier Group rocks

    } Harc;son L. Gcoup cocks

    } Bowen Is. Group rocks

    below these islands, large masses of magma slowly rose through thepile of volcanic and sedimentary rock that was being deposited,layer by layer, on the Earth s surface. During its slow ascent, themagma cooled, forming plutonic rocks such as granite. Parts of theolder volcanic islands and existing sedimentary rocks were incor-porated into the hot granitic magma. Later erosion exposed the


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    such hornblende and p y r o x n ~are called andesite. The darkestare dominatedhornblende and pyroxene and arecalled basalt.

    environmental conditions before the intrusive rocks formed. Fractures in

    changed into thin seams of lignite, a20 years ago and continuing to the present,large volcanoes have erupted and andesites in a long chainalong the west coast of North On Mount Baker, 100kilometres southeast of hot steam still escapes theice-filled crater. Near Mount Garibaldi, volcanic tookplace a few thousand years ago.

    STRATIGRAPHIC TERMSOne of the basic methods in geologyinvolves the organization of rocksinto units based on their character.The fundamental unit is known as aformation . This is a body of rockstrata which is distinct from adjacentstrata on the basis of one or morefeatures. t may consist


    dominantly of one rock type or combination of related types and wasdeposited or put in place underuniform conditions. Formations maybe combined into groups which intum may be combined into supergroups .

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    What were onceare now gneiss. As a result, theships between individual to ascer-tain. In of this, geologists been able to distinguish be-tween several different ages of pendant.What might be the oldest of aH the rocks are found in theIndian and Buntzen Lake, at Horseshoe Bay andCove. Rocks the on Bowen areknown as the Bowen Island Formation. They are lessmetamorphosed than those in the mentioned pendants,which may suggest that are younger in age, not having had asduring

    ++ ++ + + + + + + + ++ + + 4 + + + + +I+ + + + pluton + + + ++ + + T T + + + I++++++++++++.++++++++++++++++++++++++VVVYVVVVVVVVVVVvvvvvvvvvvvvvvvvvv + +vvvvvvvvvvvvvvvvvv/r /A + + 1vvvvvvvvvvvvvvvvv 'J/ + +volcanic rocks + + + + +vvvvvvvvvvvvvvvvv + + +v v vvv vv vv + + .vvvvvvvvvvvvvvvvv + +vvvvvvvvvvvvvvvvv 1 +vvvvvvvvvvvvvvvv + + +vvvvvvvvvvvvvvvv + + +vvvvvvvvvvvvvvvv + + +

    Present time, after erosion

    Erosionaremnantof roof


    Two possible ways in which pendants are formed and surrounded by graniticrocks. Older sedimentary rocks which form the roo above a pluton may be almostcompletely eroded. Other pendants are formed y faults along which portions othe overlying strata are dropped down into the


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    Beds o siltstone now metamorphosed belonging to the Gambier Group. Theserocks are best exposed where Highway 99 has been blasted through cliffs nearBrunswick Point on Howe Sound.much time to be metamorphosed. The only accessible outcrops ofthe Harrison Lake Formation in the Vancouver area are in a pendanton Sumas Mountain.The largest pendants of these older sedimentary and volcanicrocks belong to the Gambier Group and are found mainly on Gam-bier Island and along Howe Sound at Brunswick Point and PorteauCove. Smaller examples can also be seen in Mt. Seymour Park andin the upper reaches of Lynn Creek. They include andesitic volcanicrocks as well as banded green, brown and white sediments such assiltstone and argillite. A single fossil of Cretaceous age has beenfound these rocks, indicating that they are approximately 110million years old.Intrusive Rocks The Coast Plutonic ComplexThe Coast Plutonic Complex is a 60 to 200 kilometre wide belt ofgranitic rocks stretching from the Fraser River 1700 kilometresnorth to the Yukon border. t is one of the largest collections ofplutons in the world, the intr icate relationships between them lead-ing to the name complex . The most common rocks within it arequartz diorite or granodiorite, with roof pendants of metamorphosedsedimentary and volcanic rocks. Masses of molten granitic rock, 1km or more across, were formed deep within the crust, rose slowlyas they tended to be less dense than their surroundings, and were


    heCoas:t Plutonic Com.

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    omedants are shown here.


    ~ILOM TR S

    _100 million years ago Between 40 miHion

    the overlying rocks have been erodedto expose them

    The North Mountains are underlain by the southern end ofthe Coast Plutonic Complex. Several different ages and types ofplutonic rock are present. The oldest is hornblende diorite which

    the pinnacles Lions Crown Mountain The quartzdiorite underlies most of Grouse Mountain and Mount Seymourincludes several individual bodies places varies in composi-tion It i s the sea cliffs Lighthouse


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    The Lions, seen here from Unnecessary Mountain on the Howe Sound Crest Trail, arecomposed o vertically jointed, hornblende-rich diorite. Lower ridges are youngergranodiorite, also o he Coast Plutonic Complex.

    The Upper Levels Highway in West Vancouver was carved through granitic rockso he Coast Plutonic Complex Caulfeild interchange).

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    Granitic rocks are given names according to the proportions of quartz, v o t a ~ ~ s i t mfeldspar, and plagioclase. These three minerals are the corners of a classificationtriangle. Only the lower portion s shown here, n which diorite consists ofalmost pureplagioclase and syenite s mostly potassium feldspar. Local granitic rocks occur in thepatterned area. A quartz diorite for example, has beMeen 5 and 20 quartz, 90-100plagioclase and less than 10 potassium feldspar (in addition to biotite andhornblende which are not used to classify the rock).

    Squamish Chief is part of a granodiorite pluton near Squamish. The western cliff,rising 600 m above Highway 99, is a mecca for experienced rock climbers,although the top can be reached by a well-built trail up the valley on the right handside.


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    yearsGeorgia n

    Beginning about million years ago, the rocks ofPlutonic were eroded by streamssand mud and plant debris down into a large

    an area that is now borderedMountains. During this time, the Coast Mountains wereof low hills with a temperate , climate tocoastal region of present California. Thewhich the lake was situated is known as the Basin.

    The Georgia Basin has a complex history of uplift, rocks areoften eroded away, and subsidence, are likely to bedeposited. Three main periods when rocks were have beenidentified by plant fossils. Each of three is separatedfrom the others by an interval in which either erosion occurred orsediments were not deposited and these breaks are unconfor-mities. These occurred during the Paleocene, Lower Eocene andOligocene epochs.

    All of the rock types are similar and can often only bedistinguished from one by studying their palynology, that is,their fossil pollen content Most of as sedimentsdeposited by streams flowing south and southwest offlocal hills andmmmtains The streams deposited their load in coalescing


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    Sandstone beds exposed at low tide at the west end o Kitsilano Beach belowTrafalgar Street). They were deposited in the Georgia Basin the Eoceneepoch. Faint diagonal streaks in rh rock are cross-beds indicating deposition ycurrents from the north left to right).plains in the freshwater basin which continued to subside as moreand more sediment was laid down. Conglomerates appear to haveformed from gravels in stream channels at edges o alluvial plains.However where they are very thick as in the Burnaby Mountainarea they may represent fan deltas such as the present day mouth ot he Capilano River. the possible exception o conglomeratesall the alluvial sediments were deposited flat lying beds. Sub-sequent tectonic activity tilted them 8-12 towards the south.An idea o the amount o uplift and erosion in this area can be hadby considering the amount sedimentary rock present. AU o it isbelieved to have been deposited in shaHow fresh water yet the entireaccumulation is up to 4400 metres thick. As the basin collectedsediment it grew deeper at about the same rate sediment was fillingit up. The surrounding hills were in turn being uplifted from belowat about the same rate as erosion was wearing them down so thatthey maintained a constant height relative to the lowland. Givenenough time a very thick pile sediments can form in this manner.Among the oldest and lowest sedimentary layers is a conglomerate o Upper Cretaceous age up to 60 metres thick which restsdirectly on quartz diorite o the Coast Plutonic Complex. The conglomerate contains fragments up to 30 em across with occasional



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    is thand spores. I t isgeologis t as fossil and sporesare abundant in alluvial sedimentsand are generally recognizable afterburial and Hthifaction. Specialistsare able to determine species,geographical location, and theprevailing climate from them. ycompiling this information and correlating it with other geologicaldata, they are able to catalogue the

    various types of and sporesthat were produced at different timesln geologic history. Some sedimentary rocks may then be dated on thebasis of which are present.Study of the rocks the Vancouverarea show that the climate changedfrom tropical. to subtropical in LateCretaceous and Eocene time to awarm, temperate climate in Miocenetime.

    rounded boulders in a of mica and feldspar-rich sandstoneweathered the underlying quartz diorite. It represents thedeposit derived from erosion of the Coast Mountains and can be seennear the Upper Levels Highway bridge across the CapUano River.On top of this is a 540 metre thickness of interbedded feldsparrich sandstone, siltstone, and silty t sandy shale. The sandstonesfound between Prospect Point and Third Beach in Stanley Parkexhibit cross-bedding and cut-and-fill channels, structures createdby moving water at the time the sediments were deposited. Thesefeatures allow geologists to estimate the current direction and speedat the time the sediment was deposited.Rocks deposited during Eocene time included interbeddedfeldspar-rich sandstone, siltstone, sandy shale and conglomeratehaving a total thickness of as much as 1600 metres in some areas.The conglomerate contains stones derived from the Coast PlutonicComplex and is 150 metres thick where exposed on Burnaby Mountain. Thicknesses of up t 250 metres have been encountered elsewhere in drill holes. The sandstones often show good cross beddingand cut and fill channeling. Seams and lenses of coal are also foundinterlayered with some of the finer grained sediments, havingformed from plant debris which accumulated in bogs and swamps.Although they have a total thickness of about 1200 metres, rocksof Miocene age are buried beneath surficial deposits in the Vancouver area and cannot be seen in outcrop. Drill holes havepenetrated poorly consolidated shale, sandstone and conglomeratewith interbedded volcanic ash and coal.



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    Mount Garibaldi top) is an inactive volcano about 60 km north ofVancouver. MountBaker km south is an active volcano that last erupted in 1843.

    the west coast of North America is ofof Fire , a series of subduction-related

    edges of Pacific plate. A chain of theseCalifornia to southern British Columbia.between the two northernmost: Mount Garibaldi to

    of and Mount Baker in Washington State,about 40 km southeast Chilliwack Both volcanoes had majoreruptions Late Quaternary time and are presently dormant

    their cycle of is not yet complete. The rock types andthese particular volcanoes indicate that their erup-

    tions occur hundreds to thousands of years apart, and are usuallysmall, producing only steam and Some of the others, such asMount St. Helens Washington State, have erupted more violently.

    Mounts Garibaldi and Baker are the most recent demonstra-tions of forces in this area, Evidence of three separateperiods of volcanic activity, collectively called Cascade volcanism,can be found around and under Vancouver. Most Cascade volcanic

    in the Vancouver area are remnants of intrusive dykes andare hard resist erosion, forming cliffs or underlyingexamples an age of about 50 million years are

    not seen at the surface and were drilling beneath the city in38

    ndesite exposed belowapartments on GreatNorthern Way The cracksare called coZumiWJr

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    joints andshrinkage during coolingmagma

    the northern part of False Creek. About 18 m below sea level arethin layers of basalt within the Eocene sandstone and shale beds.They are pockmarked with holes that were gas bubbles, whichindicate that the rock formed as lava at or near the surface.The next period of Cascade volcanism took place between 3 and34 million years ago. This particular event was responsible for somewell-known landmarks in the city. Sentinel Hill in West Vancouveris a small remnant of an andesite silL Little Mountain, now QueenElizabeth Park, is also underlain by andesite, and the formerries provide a splendid backdrop to the attractive gardens. Much ofthe rock quarried from here was used as road material in the Gastown area. Another andesite outcrop, which may have been part of asill or a lava flow, occurs along Great Northern Way just west ofChina Creek Park. At these three localities, the rock is fracturedwith a polygonal pattern. These columnar joints formed byshrinkage during cooling of the magma.


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    Siwash Rock is parto a 3 million year old andesite yke that crosses the western edgeo Stanley Park

    Siwash Rock and Prospect Point, at the west end o Stanley Park,are part o a single vertical mafic dyke that intruded about 32 millionyears ago. The rock is dark grey and contains larger black augitecrystals in a matrix o microscopic feldspar and hornblende crystals.Both these landmarks are prominent because the igneous rocksresisted erosion by the waves and runoff better than the enclosingsandstone.Grant and Silverdale hills, which are two cuestas hills with onesteep and one sloping side) on the north side o the Fraser River easto Haney, are upheld by resistant basaltic layers that have beendated at 17 million years. The layers are exposed where LougheedHighway cuts through the southern edge o Grant Hill and SilverdaleHilL The basalt is dark grey and has small cavities containingminute crystals quartz, the last to form as the rock cooled.In addition to these major periods o nearby Cascade volcanism,the rock record shows evidence o volcanic activity much furtheraway. Quaternary sediments the Fraser Lowland containvolcanic ash layers, sometimes visible in road cuts as narrow whitebands in sediments that were deposited quiet water. These cover awide area and act as a time marker, allowing geologists to correlaterocks in widely scattered areas.


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    QUATERNARY S E I I ~ E N T SB S LT SiLL (17 million years old)

    ::::>:>:::: GEORG A BASiN S E H ~ E N T S

    aand one steep side where the resistant rocks are exvoseu


    mineral structure toweaken nd progressive-ly the igneousrock outward from theoriginal cracks

    The ascade volcanoesare related t s u d u e ~r on oce nic crustbene th the continent l

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    In summary rocks in the Vancouver area are the product o fourdistinct geological episodes. Before about 140 million years agoislands formed composed o volcanic flows and sediments. Thesewere intruded by numerous granitic plutons between 140 and 9miHion years ago. As the rocks were uplifted over the next 70million years they were eroded by streams and rivers. The resultingsediment was deposited in a large freshwater lake occupying theGeorgia Basin a large depression between the Coast and CascadeMountains. Finally volcanic activity at several times forced dykessills into the sedimentary rocks and constructed Mounts Bakerand Garibaldi. The relatively recent sculpturing the land byglaciers together the reduced but continuing sedimentation inthe Georgia Basin is the o the next chapter.


    RECENT VOlCANOESOur two local vokanoes, Mounts mountain, but if magma

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    Baker and Garibaldi, arein terms.are among the highestarea, volcanic rockthe uppeJIIDost 600 metres oftheir summits. Both were built on anirregular surface of older rocksbeginning about 6 minion years ago.Since that time, erosion has loweredthe surrounding hills and valleys, sothe volcanoes on their ofolder rock are even more prominent.Heavy precipitation falls on thesesummits mostly as snow, and theglaciers are grinding downthe mountains that were coneshaped originally.Mount Baker m is an an-desitic volcano that reached itspresent form over the last 400,000years, with the most recent ash eruption in 1843. A 90 m wide cratersouth of the summit has issued sulphurous gases and steam since 1975.There is no present hazard from the

    more heat to the vent in thefuture, t could melt themudflows andsurrounding valleys.Mount Garibaldi m has

    andesite flows as old as 100,000years, but most of its surface features were created by dacite lavaflows filling valleys during the lastice age, between 25,000 and 8,000years ago. The angular south peak isa remnant of the old volcanic cone,but the irregular main mass of themountain consists of block and ashrubble, and a central dacite plug oflava too viscous to flow. The mostrecent flows were extruded fromnearby satellite vents: one headingnorth to Garibaldi Lake, anothersoutheast from the Opal Cone. Theseyoungest volcanic features can bereached in a full day s hike from theBarrier and Diamond Head trailheads respectively.



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    bythe Quaternarywere

    sediments not been subjected to heat and pres-They are not yet rock but form unconsolidateddeposits sw h as seen in sand and gravel pits. Their studysurficial geology is important to civil engineers

    planners Buildings and roadways throughout theFraser Lowland are situated on Quaternary deposits as is n of themost agricultural land. Our to day lives in waysdepend upon our understanding their properties.

    The study surficial geology provides many clues to pastenvironmental fluctuations-their timing intensity andcauses. glaciers to and then retreat from

    portions of America not once but several times?term global we are now being warned about theGreenhouse Effect significance on a longer geologi-we on the threshold of a major environmental

    could have a significant effect on life as wethe Earth s Quaternary history in particular

    the future

    forces in shaping the land surface inVancouver area has been glaciation. Giant slow moving rivers ofice scoured and shaped valleys pushing enormouseroded rock their paths and in the process grinding it

    H'- Hvu back they left great sheets moundstill Large rivers of meltwater furthereven more the glaciers


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    >62 000

    1 metre rise in sea level

    Bicth of Fcoser River Delta

    r Fraser Glaciation

    Olympia Non Giacioi Interval

    Semiahmoo GlaciationHighbury Non Glacial IntervalWestlynn Glaciation

    selves by carving new channels and redistributing the glacialdeposits. The distribution o sediment types in the Vancouver arearesults from multiple glaciations and fluctuations in sea level whichleft the Fraser Lowland underwater during parts o Quaternary time.At least three and possibly many more major periods o glacia-tion took place in the northern hemisphere in the last two million


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    highest peaks rose surface.The two earliest glaciations, known as theWestlynn, occurred more sixty thousand years ago.evidence for these n o n ~ g l c i l haseither been advance. Where theyOlympiayears ago are not as widelydistributed or thick as glacial Most areas subduedtopography were probably relatively stable and did not experienceeither significant erosion or deposition. Rivers deposited layers ofclay, silt, sand and and peat formed in swamps. The climate atthat time was cool and relatively similar to that of the northernGlOBAl WARMINGIncreasing concentrations of atmospheric carbon dioxide, methane,nitrous oxide, chlorofluorocarbonsCFC), and other greenhouse gassesare changing and even destroyingthe ozone layer which protects usfrom some of the sun s rays. s aresult, the temperature of the Earthis expected to increase by severaldegrees over the next decades orcentury. This is likely to increasemelting of mountain glaciers and thecontinental ice sheets in the Arcticand Antarctica, causing the oceans

    t warm and expand. Global sealevels will undoubtedly be higher inthe next century.Uncertainty in rates of emissionof greenhouse gases, their atmospheric lifetimes, oceanic heat absorption, and many other factorsmake it difficult to predict sea levelsin the future. A current range of estimates indicates that sea level islikely to rise 3-5 em by the year2000, 10-21 em by 2025, 20-55 em


    by 2050, and 36-192 em by 2075.However, the largest destruction ofthe ozone layer is over Antarcticaand the second largest over theArctic. f these ice-sheets weredestroyed first, sea level would beincreased much more rapidly, evencatastrophically, ending up as muchas 5-7 m higher in the span of a fewyears.Areas around Vancouver thatwould suffer most from sea levelrises are the low-lying deltas andfloodplains along major rivers suchas the Fraser. The municipalities ofDelta and Richmond are only anaverage of about four metres abovepresent sea level. They are now surrounded by dykes to protect themfrom floods and high tides. As sealevel rises, the lower reaches mayflood more frequently than in thepast. The dykes will have to beupgraded at considerable expense ifthe expected sea level rises occur.

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    Animal Hfe Several setsmoth tusks were found silt in the easternraser near Vedder Crossing. Radiocarbon hasshown them to be between 24 000 and 21 000 years placing

    them at the beginning the raser Glaciation. They are currentlydisplayed in the museum at Simon Fraser University.

    Till consists of rounded stones embedded in a mixture of sand, silt and clay, ll ofwhich were dropped out ofa melting glacier as it receded. JEA)


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    Glacially polished and scratched striated) granodiorite. This outcrop is in thepullout beside Highway 99 below the Squamish Chief.


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    The large boulder is a glacial erratic left y ice receding from the Fraser Lowlandabout 12,000 years ago. Near 12th Avenue and 200th Street in South Surrey. JEA)The Fraser Glaciation which began about 25 000 years ago andlasted until about 12 000 years ago was the last major advance inthe Vancouver area. At its peak a glacier up to 1 800 metres thickflowed down what is now the Fraser Lowland at one point extending

    G LAC J L DEPOSIT SThe general term for all types ofrock material moved or deposited byglaciers or the water melting fromthem is drift. Drift can include anycombination of material ranging insize from boulders to extremely finesilt and clay. The form and composi-tion of various glacial drift depositsreflects how the sediments were car-ried and deposited by the ice andwhether they were subsequentlymodified by water.As the glacier moves the rockmaterial is carried within it mainlyconcentrated at the base. The weightand grinding action of the movingglacier not only breaks up the ma-terial being carried i t erodes andpolishes the underlying bedrock.


    Till is the name for unsorted andunlayered boulders clay sand andgravel deposited in a random fash-ion s the glacial ice simply meltsaway. Where this material accumu-lates at the end of or along the side ofan ice sheet it is called a moraine.The further action of water onthese deposits tends to separate thecoarse from the fine material. Inother words the sediments aresorted. While the coarser bouldersare moved only by the most torren-tial streams the fine d ys and siltsare carried into lakes and oceansbefore they settle out to form sedi-mentary deposits. When the glacieritself reaches the sea icebergs maycarry rocks even further out.

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    The extent o Fraser Glaciation ice at various points n time during its recessionbetween 15,000 and 11,000 years ago. Since then, the area formerly covered by ice hasbeen rising, in a process called isostatic rebound .out into the Strait of Georgia and south into Puget Sound. Otherglaciers moved down side valleys to merge with the larger ice sheetcovering the Lowland. The effect on the valleys was pronounced.Once relatively angular with V shaped cross-sections they werebroadened and rounded out into U shapes. The Capilano andSeymour Rivers and Lynn Creek all begin in these broad glacialvalleys although their lower reaches include narrow gorges andglacial drift deposits.Enormous volumes of rock were scraped from the valley floorsand sides carried with the ice and finally deposited in ridges and


    laciomarine mud ands ltthe

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    hills called moraines. Many of the glacial deposits that are moreprominent today however result from the melting of ice rather thanits direct action. When the glaciers finally retreated between 13 000and 11 000 years ago much of the rock debris in the ice dropped outas a thick layer of till blanketing many parts of the Lowland.The smaller glaciers occupying the valleys of the North Shoremountains melted and retreated before the ice covering the Lowlanddid resulting in the formation of temporary glacial lakes. At othertimes meltwater streams from these smaller glaciers formed smalldeltas called kames. Kame sediments have been exploited by manysand and gravel pit operations.Geologists have noted that typical glacial landforms like eskersand moraines were more common in the Fraser Lowland east ofAbbotsford than further west. The distribution of fossil shells indi-cates that an arm of the sea once extended across the Lowland as fareast as Abbotsford. Furthermore sedimentary structures suggestthat much of the material here was actually deposited y icebergs.


    nowJack Armstrong of theare more varied and complex inelse North America.

    , wereSurvey of._. .area than anywhere

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    There was a association between the fluctuating ice front inthe central and eastern Fraser Lowland and sediment deposition onthe sea to the west. The ice calved the sea to produceicebergs which, upon melting, dropped stones taken from the CoastMountains into the muds on the sea flooL Thick layers of sand andgravel were deposited in marine deltas kames on the landwardside of the calving ice margin. Most of the fine sediment was carriedby glacial meltwater out into sea. Later, some theseglaciomarine sediments were then redistributed as a result of underwater slides and turbidity currents.Many of the larger shells found the glaciomarine sediments arefrom species still found off the coast of North America. They livedin a shallow water environment similar to that in the Gulf of Alaskatoday. The water s salinity changed from time to time due to varyinginflows of glacial meltwater.

    Sea level fluctuated greatly during each glaciation. For example,CHANGING SEA lEVEl IN THE VANCOUVER AREAThe Vancouver area has undergonemore than one sea level change of upto 50 or 60 metres in the past 10,000to more than 100,000 years. Twomain factors have been responsiblefor this. The first is the depression ofthe Earth s surface under the weightof an ice sheet (called isostasy).The second factor is the amountof water in the ocean (called eustasy). When much of the Earth swater is frozen as ice in glaciers, asduring periods of major glaciation,sea level can be lowered 100 metresor more relative to what t is presently. On the other hand sea levelduring especially warm periods between glaciations was probablyhigher than it is now. This complexinterplay between ice and oceanwater continues. The current concerns with the greenhouse effect


    stem from the melting of glaciersthat the warming would cause. Almost all of the resulting water woulddrain into the oceans and raise sealeveLEarthquakes have also resulted inchanges of sea level. In 1960, amajor earthquake caused about 2metres of sudden subsidence alongthe coast of Chile. About 7,500years ago, sea level suddenly rose10-12 metres in the Vancouver areaand one possible explanation is thata very large earthquake dropped thelevel of the land. Many smaller andapparently sudden changes in sealevel here have also taken place, thelast about 300 years ago. In spite ofthis, the most dramatic ones in termsof size have been mainly due to isostasy or eustasy.

    sheet meltedpresent position over a rebounded to near3 000 years. The many

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    and terraces on ' ' ' ~ ' ' 'are evidence that the has risen relative to sea leveL At the samebut to a lesser degree absolute sea was becausethe water had been locked up ice worldwide was nowrefilling the oceans Many o the glacial valleys along coastsouthwestern B.C. were partially submerged during this in sealevel after the end o the Fraser Glaciation. The submerged valleysare called fiords and Howe Sound and Indian Arm are the mostsoutherly in Canada.Fraser DeltaMost o the landforms the Fraser Lowland were produced duringor since the last major glaciation. The most important agent for thedeposition and sculpturing o these sediments has been the FraserRiver which developed after ice left the Lowland some 8 000 to10 000 years ago. Currently t discharges approximately 8 milliontonnes o sand silt and mud each year mostly during May June andJuly. In order to keep the river channel open for navigation about2.4 million tonnes o sediment mostly sand has to be dredgedannually.The nearly flat delta top is nowhere more than a few metres abovehigh tide level. Between it and the open water tidal flats are sweptby currents and waves. A three metre high dyke or berm has beenconstructed around the seaward edge o the municipality o Rich-mond. The dyked area is largely underlain by fine sediments laiddown when the Fraser River overflowed its banks and when the seaflooded over the land during storms and at extremely high tides. OnLulu Island and south o the present course o the river thesesediments are overlain by peat which accumulated in large swampsand bogs. Sand underlies most o the tidal flats and mud occurs in afringe o marsh around the edge o the delta.Crossing both dyked area and tidal flats river channels floored bysand and minor gravel are the arteries o the Fraser Delta. Becausethe channels are now guided by manmade training walls most o thesediment discharged by the river is deposited underwater on thewestern foreslope o the delta. The distribution o sediment there isgoverned by patterns o currents and waves. Typically mud is


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    Tidal latl i ~ ~ ~ ~ ~ yked elio Top

    t '" Peat Bog

    The Fraser Delta built outward from New Westminster during the last 10 000years has a surface of ertile land and peat bogs that has been drained and isprotected from flooding y a dyke. The tidal flats outside the dyke are a vitalhabitat for migrating birds and other shore life.deposited north of the main distributary channel while sand isdiverted to the south.By studying the buried sediments in drill holes and usingradiocarbon dating, geologists have been able to reconstruct thedelta s evolution over time. About 10,000 years ago, the entire areaof the present Fraser Delta was n expanse of sea, and Point Robertspeninsula was n island. Sea level was lower than it is now butsediment accumulated and the delta emerged above the sea. A tenmetre rise in sea level between 7,500 and 6,000 years ago floodedthe young delta top but sediments carried by the river rapidly rebuiltthis submerged surface above water. Since sea level has not changedsignificantly for the past 5,000 years, the delta continued to grow.



  • 8/12/2019 Vancouver Geology


    repeatedly shiftednarrow bodies sand the uppersequence record long-abandoned river channels.

    Until recently several of the majorpeat bogs of the Fraser Delta contained the largest agricultural peatoperations in Canada. The ByrneRoad bog covers more than 600 hectares of which more than one halfare under cultivation. The peat hereis from less than 1 m to 5 m thick.The Lulu Island bog covers about1400 ha of which only about 100 haare under cultivation. Much of thepeat in this bog which is from 1 to 7 mthick has been badly burnt firesare common in the bogs in dry summers. The Bums Bog extends overan area in excess of 4500 hectaresthe margins of which are under cultivation. Much of this bog has alsobeen damaged by fire. The peatvaries in thickness from less than 1 mto 8 m. These bogs and others havevery acid topsoils well-suited forgrowing blueberries and cranberries.

    AU the peat produced from thesebogs is composed of sphagnummoss. The top l ayer is referred to asunhumified peat. This is dead sphagnum moss only slightly decomposed. t is fibrous elastic lightgreyish green or yellowish to lightbrown becoming somewhat darkeron drying. It has an absorptive value

    of up to 6 times its own weight ofwater and is light in weight andporous. The layer of moss of highvaries greatly in thickness;in some places it is as much as 2.15 mthick but averages nearer 1.22 m.This undecomposed peat gradesdown into and is interlayered withhumified peat. Humified peat in itsnatural state is dark brown to blackwith homogeneous composition andtexture and is somewhat elastic. Itdries into a hard solid mass that willnot float and does not absorb verywell. A piece of dried humified peatmay be under water for weekswithout taking up any water. Unhumified peat left in its natural statewill humify in the course of timeand all fibrous material eventuallydisappears.Burns Bog landfill is the maingarbage disposal site for VancouverCity. There has been a proposal forthe city to install a methane gas collection system there. Estimates arethat as much as 17 million cubicmetres would be generated annuallyover the next ten years. In the interim the gas will be flared in the sameway as at the Coquitlam landfill inorder to p revent odour.

    Stages in the growthFraser Delta sinceice receded romLowland about 10 000years ago

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    10 000 ye rsgo



    l nd re s

    ENGINEEIHNG GEOlOGY ON TH fRASER DEHAPeat foundationhighways and otherstructures including lighte r ones

    built before this preloading t e h n i ~que was developed. At the time itwas built the approach was to re

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    such as homes. Peat will hold up to6 times its own weight of water andwill sett le and in a

    way when loaded. Presently wherethe peat is less than 2 m thick it isnormally excavated. If it is morethan 2 m thick the standard procedure in recent years has been preloading. This is done by placing finnormally sand on the peat to compact i t as much as possible. Ageotechnical engineer calculates theamount of fill required and theperiod of time it should be in placeto bring about this compaction. Oncompletion of the preloading part ofthe fill is removed and the structuresand highways are built on the remainder. However Highway 99 was

    move all the peat and fill the excavation with sand. This was done sue-where 99 crossespeat bog on Lulu Island.Also during the construction ofHighway 99 a major tunnel wasconstructed under the Fraser River atDeas Island. It was constructed asprecast sealed lengths that werefloated over the tunnel line and sunkinto place in a previously preparedtrench in the sands of the FraserRiver bed. The trench was preparedby dredging. During construction

    water wells were drilled along theline of the tunnel and pumped at thehighest rate possible in order tolower the local groundwater table.



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    p to point we have looked at geology of the Vancouverarea as a historyo From the few outcrops gravel and drill coresgeologists have pieced together ancient environments in whichthe various rocks formed the forces eventually deformed themand how much later glaciers and rivers reworked them and theirerosional products. t seems long ago but the geological storydoes not end with the presento Many of the forces at work in the pastare still at work today and will be in the future. Some of them suchas the movement of crustal plates will take place despite ourpresence. Others such as the formation of deltas and the glacialcycle may be influenced for better or worse by human activity.ngoing Geological Evolution

    The most obvious of the major ongoing geological processes iscontinued sedimentation by various rivers. Most of the deltas in theFraser Lowland area have built themselves up since the end of theFraser Glaciation 10 000 to 12 000 years ago. Currently the FraserRiver discharges approximately 8 million tonnes of sand silt andmud each year mostly during May June and July. In a relativelyshort geological time span the Fraser Delta might have eventuallyformed a land bridge connecting the mainland with the Gulf Islands.The delta of the Capilano River was also formed during the past10 000 years and was almost 6 km wide before being built over. Leftto itself i t would probably have extended across First Narrows in afew thousand years turning Burrard Inlet into Burrard Lake.The normal evolution of many of these deltas has been inter-rupted however by extensive human modification of naturalsedimentation patterns. For instance the channels of the FraserRiver are now guided by manmade training walls and the river canno longer shift its course on the delta. As a result most of thesediment it carries is now deposited underwater on the westernforeslope of the delta and further out to sea. The river rarely over-flows its banks anymore to deposit mud on the delta top. In the long


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    Changes in sedimentrich fauna andThe Capilano has intervention.Until the 1930 s, the river was east of the footing for LionsGate Bridge has now been artificially channelled further west.Furthermore the obstruction Cleveland Dam and controlledwater flow have sediment transport in the lower riverthe no longer expands at its previous rate. However relativelylarge amounts of sediment are still deposited at the inlet s entranceand dredging is periodically required at the mouth of the river.On a somewhat longer time scale both volcanic activity and theglacial cycle become important geological forces. Within the lastseveral hundred thousand years numerous glacial cycles have occurred including the Fraser Semiahmoo and Westlynn. In the normal course of events it could be expected that many more willfollow. During each large ice sheets covered the area of the FraserLowland and extended out into the Strait of Georgia. Studies haveshown that the buildup and advance of ice takes much longer than

    does melting and retreat. The pattern of future glaciations wouldlikely be similar.In terms of volcanic activity both Mounts Baker and Garibaldiwere constructed within the last 400 000 years. Hot steam stillescapes from the ice-fil led crater at Mount Baker where the lasteruption was in 1843. Volcanic eruptions were quite common nearMount Garibaldi only a few thousand years ago. Activity at bothhowever has tended to involve mainly steam and ash. Even in theevent of a larger eruption the Vancouver area would probably onlyexperience ash fall and then only if an easterly wind were blowing.Several ash layers in the Quaternary sediments indicate that this hashappened from time to time in the past and almost certainly will inthe future.More extensive periods of volcanism involving the emplacementof lava flows and dykes such as Siwash Rock in Stanley Park haveoccurred at intervals of about 7 million years in the last 50 or somillion years. It is possible that in the next few few million yearsanother such event will take place.


    In addition to the above processes, the more subtle butmovement of tectonic plates continues beneath our feet. TheFuca plate currently plunges beneath the North American plate at arate o about 4.5 em per year. This results in other stresses and

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    movements in the North American plate, some which can actuallybe observed. Precise measurements between mountain tops on Vancouver Island show the northeasterly squeezing o the landat rates o 2-4 mm per year. Coast Plutonic Complex waselevated to its present position within last 5 million years and iss U rising, up to 4 mm per year in some places.Geological HazardsSome o the longer term geological processes include events thathappen on a short enough time scale that we may directly observethem. Unfortunately, some o these are almost too quick and mayimpact adversely on our lives. Floods and landslides are relativelycommon in the Vancouver area, mainly because the climate, physical features and geology of the Fraser Lowland and adjoining mountainous areas make them inevitable under natural conditions.The Fraser River would normally overflow its banks in the springo every year i t were not for the extensive system o dykes that hasbeen built over the years. Some flooding still occurs because thedykes are in many places built on permeable sand and gravel whichlet some water through when the river level is higher than the land.During periods of particularly heavy rainfall, mainly in the autumnand winter, lower reaches o the Fraser delta may be inundated athigh tide. Mountain streams may overflow their banks during theseheavy rainstorms and cause much damage to surrounding communities.Landslides are mixtures o water and solid debris that movedownhill after slope failure. Many result from the same basic causesas floods, often grade into them and are capable o great destruction.The slides along the Squamish Highway are only the most wellknown.The most significant to us) short term geological processes are,strangely enough, related to those o the longest term. Earthquakesare a fact o life on the southwest coast o British Columbia. Theyare caused primarily by the subduction o oceanic crust under continental crust in the nearby Cascadia Subduction Zone. In the last 90years, seven earthquakes large enough to do damage have occurredhere. Recently, geoscientists have begun to understand that we are at


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    Fraser River in flood near Agassiz, t the eastern end of the Fraser Lowland, circa1928. (Vancouver Public Library Photo 44489A.)risk from another and much more serious event called a megaearthquake . Studies have suggested that no movement is takingplace along the contact o the converging plates and that sooner orlater, all o the built-up stress will be relieved in a very large anddestructive earthquake. We cannot be sure that this will not occurduring our lifetimes.

    uman InvolvementPeople have been able to intervene directly in some geologicalprocesses, mainly when they constituted a threat or formed anobstruction. We construct dykes and retaining walls t channelrivers and control floods and landslides. In other cases, there is littlethat can be done to influence the course o events. Earthquakes arephenomena that we must withstand rather than expect to control. Inaddition to our direct intervention in some parts o the geologicalprocess, however, we have had a more subtle and significant impacton others. This has largely been through the addition o ourcivilization's byproducts to the natural environment.

    The effects o pollution are wide ranging and are present at avariety o scales. In the simplest cases, pollution may involve local6

    substances. Poorlydesigned sewage uncontrolled garbage andlandfills industrial effluents and fertilizers of various typescontribute to gradual accumulation of substances toxic to life.More complex and subtler types of are beginning to be

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    recognized ones even greater potential Atmosphericcarbon dioxide and methane generated during generations ofagricultural and industrial activity have reduced and are reducingthe ability of the Earth to reflect solar energy back into space. Thiswin result in global warming affecting not only the weather patterns on which we all depend but also the glacial cycle. A rise inaverage temperature of even a few degrees would be enough to meltall of the glacial ice and raise sea level enough to flood large areasof coastal land including Fraser Delta.In the foreseeable future civilization is here to stay. Its i n t e r c ~tion with nature including geological processes is inevitable andglobal in scale. t is possible however to minimize both the extentto which our impact on nature is an adverse one and the extent towhich natural disasters affect us. We must be able to make informeddecisions in these matters and the best means of achieving this isthrough knowledge of how natural processes occur and why.As in many other sciences there is a growing concern in geologythat we should see the world in a larger context. What sorts oflong-term natural fluctuations are there and how do they comparewith the changes we incur? To what extent have we harvested theEarth s resources and what are the most responsible ways of continuing to do so both in terms of our needs and the effects of theirextraction? In which ways are the byproducts our civilizationassimilated by the Earth and how can we minimize their adverseimpacts? How may we avoid the catastrophic natural disasters thathave plagued us in the past? The answers to these questions startwith the desire to know and understand how the Earth works.



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    geologic outlined in preceding chapters is not theproduct library or research-it was worked outgeologists in the act of outside toand sediments can be a challenge body and mind, as one triesto imagine what took so ago. Although rock outcrops areuncommon in urban Vancouver, many public parks contain visiblegeological features addition to their well-known attractions.Their geology is described following field trips spirallingoutward from downtown. These areas provide nature walks lastingfrom an hour t a full In addition, a driving tour on Highwayleads along Howe Sound, where many of the landforms and rocktypes of the Coast Mountains may be seen. We hope that you ll usethese brief guides to enhance your explorations of Vancouver'sscenery.Stanley ParkAn oasis of forest and seashore only 2 km from downtown by citybus, this park can rejuvenate your spirit. It provides a place to walk,run and cycle, to observe plants and animals and to see the mountains and ocean surrounding the city. The park covers a 400 hapeninsula jutting into Burrard Inlet, and is connected to NorthVancouver by the Lions Gate Bridge. f you are on foot, you canexplore forest paths, or walk around the edge on the seawall. For aperson city-bound, Stanley Park is a haven of natural beauty, freshair and sea breezes.HistoryUntil the 1870's, the Coast Salish people under Chief Khatsahlanohad a village near present-day Prospect Point. There were (and stillare) cormorant colonies on cliffs and seals on nearby shoals, as wellas good fishing in the tidal rip off Brockton Point. When the youngshantytown spread westward from Gastow:n during the 1880's,


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    The forested peninsula of Stanley Park the downtown area and Fraser Lowlandbeyond are visible from the lookout on Cypress Parkway above West Vancouver.glaciomarine clay near Lost Lagoon for brickmaking and ligniteattracted developers. They wishfully dubbed the area Coal Harbour.Most of the large trees were removed, and the British Royal Engineers took over the land for their barracks. After lobbying by citycouncillors (some say to protect land prices in the West End ofVancouver) a city park was dedicated in 1886 and named after theGovernor-General of the time, Lord Stanley.The park s management must balance the demands of those wishing to develop public attractions and those desiring to minimizehuman disturbance in this pocket wilderness . The geography hasalready been considerably modified by human activity. In 1889, abridge was built across the inlet of Coal Harbour and was laterreplaced by a causeway, creating Lost Lagoon in 1936. Lions GateBridge and the expressway leading to it were built then, virtuallybisecting the park. At that time, few imagined that vehicle trafficusing the bridge would reach the volume it has today. Only enclavesof old-growth forest remain (north and west of the Hollow Tree ).Removal of deciduous trees and undergrowth are part of the currentmanagement plan.Parks near downtown Vancouver. The sand for the many beaches is naturallysupplied by three sources: the North Arm of the Fraser River erosion ofglaciallydeposited sand in cliffs t Point Grey and the deltas ofmountain rivers flowingfrom the north.


    vegetationwalking routes to

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    Beaverthe :routetwo to three hours. ou willof cliffs

    to1 Begin your trip at the Prospect Cafe, where can parkyour car From the you can see a splendid view

    of West Vancouver extending 380 m up the slope of HollybumMountain. The forest above that is second growth-much ofVancouver's early prosperity derived from logging of the NorthShore mountains. Far to the left along the North Shore is the winkingPoint Atkinson light. Lighthouse Park is one the best nearbyplaces to view granitic rocks of the Coast Plutonic Complex.From the lookout, a set of concrete steps leads to the top of thecliff. This platform was built for a searchlight and gun battery, partof the harbour defenses during the Second World War. We ll belooking up at the rocks of this cliff later on.Immediately behind the cafe is a secondary path (near the washrooms) that descends to the righL Follow switchbacks beneath thedeck of the Lions Gate Bridge, where the glacial clay and silt thatcover most rock in the park are visible between the bushes. Whenyou reach the seawall, tum left.

    2 Above the seawall and beneath overhanging bushes are outcrops of sandstone. Within them, dark lines slant east to west.These cross-beds indicate that the current that deposited the sandswept from the north.The south abutment for the Lions Gate Bridge is set in sandstoneand engineers are concerned about this footing. Strong tidal currentsscour the rock underwater, and the bridge is subjected to increasingly heavy use and attendant vibration. Steel pilings have been drivenat the sides of the abutment to improve its strength. From the bridge,i t is 1.5 km along seawall to Siwash Rock, and 2.3 km toFerguson Point where the geology trip ends. (There are no shortcuts



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    0 200beds

    4 6 m

    Map ofStanley Park Numbers correspond t stops described in thefiel tripup the cliffs, but from Ferguson Point you can return to ProspectPoint Cafe on paths through the forest.)

    3) Just past the whitewashed ship s beacon during heavy fog itsbooming note is heard downtown and throughout West Vancouver),is a 20m high cliff with the Prospect Point lookout on top. The cliffis igneous intrusive rock called andesite-the same as Siwash Rock.The rock is blocky and hard: it is resistant to erosion and keeps thesandstone behind it from wearing away. Was this a lava flow? Thereare two clues that it was not.Firstly, high in the cliff you can see a network of cracks that breakthe rock into columns, the ends of which are sticking out likecordwood. Called co lumnar joints, these cracks form at right anglesto the cooling surface of the magma. In this case, if the rock