Soils of the - Agriculture and Agri-Food Canada

Subalpine Section of the Subalpine Forest Region (Rowe) . Here mountain hemlock, Pacific silver fir and yello w
cedar are the dominant trees . This zone grades into the Alpine Zone at elevations above 1500 to 1800 m .
Exposed bedrock dominates parts of the upper Mountain Hemlock Zone and much of the Alpine Zone .
BEDROC K
Exposed bedrock is uncommon south of the Fraser River except on Sumas, Vedder and Chilliwac k
mountains . The rock is usually buried by 150 m or more of unconsolidated deposits (Armstrong, 1957) in most o f
the valley. Sumas Mountain consists mainly of granitic and volcanic bedrock, mostly andesite, quartz diorite
and granodiorite although in the Kilgard area some sedimentary rocks also occur . Chilliwack Mountain i s
composed dominantly of volcanic rock while Mount Vedder is green graywacke, conglomerate, shale an d
arkose with a strip of variable, highly metamorphosed rock along the northwest slope .
The extreme southeast corner of the map area intrudes into the Cascade Mountains which here are mainl y
argillite and shale .
The Coast Mountains occupy the northern part of the map area and are composed dominantly of Coasta l
Plutonic rocks including granite, granodiorite and quartz diorite (Roddick, 1965) . In a few, isolated areas, suc h
as on Blue Mountain, conglomerate and sandstone also occur. Grant Hill and an area near Silverdale are
basaltic while Nicomen Mountain and the area south and west of Chehalis Lake is mainly andesite and dacit e
porphyry. Remnants of the Tertiary erosion surface also cap scattered areas elsewhere including Seymour an d
Hollyburn mountains . Central and eastern Gambier Island and the lower slopes along the east side of How e
Sound consist of a variety of volcanic and metamorphic rock while most of Bowen Island and the Mt .
Elphinstone area is greenstone, chert and graywacke. Apart from Mt . Elphinstone and South Thormanby Islan d
which are mostly volcanic rock, the Sunshine Coast (in the map area) is mainly Coastal Plutonic rock similar to
that east of Howe Sound (Roddick and Wordsworth, 1979) .
PHYSIOGRAPHY AND DRAINAG E
The Langley-Vancouver map area contains parts of three physiographic subdivisions (Holland, 1976) . Th e
mountainous areas are mainly part of the Pacific Ranges of the Coast Mountains, although a small part of the
Skagit Range of the Cascade Mountains intrudes into the extreme southeast corner of the map area . The Lowe r
Fraser Valley falls in the Fraser Lowland subdivision which, together with the lower elevations along the
Sunshine Coast, are part of the Georgia Lowland .
The Georgia Lowland essentially follows the contact between the granitic rocks of the Coast Intrusions an d
older rocks of the Vancouver Group and others that lie to the west . It is typically a dissected, late Tertiary erosio n
surface which is warped and rises gradually east and northward until it is sufficiently high in the Coas t
Mountains to be completely dissected and destroyed. In the map area it consists mostly of gently slopin g
upland surfaces .
The Fraser Lowland is part of the Georgia Lowland from which it differs in being of depositional rather tha n
erosional origin . It extends in a triangular shape from Georgia Strait eastward to Laidlaw (about 110 km), thence
southeast to the coast at Bellingham, Washington and includes the delta of the Fraser River . It is bounded on th e
north by the Pacific Ranges of the Coast Mountains and on the southeast by the Skagit Range of the Cascad e
Mountains, all of which rise abruptly from the plain .
The Fraser Lowland consists of extensive low hills (in this report called uplands) ranging in elevation fro m
about 15 to 300 m separated by wide, flat-bottomed valleys (Armstrong, 1956, 1957, 1960) . The uplands, a s
described by Armstrong, are of four main types :
(1) A core of glacial till and glaciomarine deposits with rolling, hummocky surfaces ;
(2) a core of unconsolidated deposits with commonly flat, terraced surfaces of glacial outwash ;
(3) a bedrock core overlain by a thin mantle of glacial till and glaciomarine deposits ; and
(4) raised marine deltas with a possible core of bedrock .
The uplands are separated by flat-bottomed valleys up to 5 km wide and ranging in elevation to about 25 m .
The main valleys are the present valley of the Fraser River ; the valley occupied by the Pitt River from Pitt Lake t o
the Fraser River; the Alouette River valley from north of Haney to the Pitt River valley ; the upper Nicomekl-Salmo n
River valley ; the lower Nicomekl-Serpentine River valley and the lower part of Campbell Creek valley. All thes e
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