Landforms of British Columbia 1976 - Department of Geography

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The Purcell Mountains (see Plate XXXIA) include some extremely high and
rugged mountainous country, and the highest peak, Mount Farnham (11,342 feet),
is only slightly inferior in height to Mount Sir Sanford ( 11,590 feet), which is the
highest in the Selkirk Mountains. The ranges at the north end of the Purcell Mountains
gradually increase in summit level south from Beavermouth, reaching their
maximum heights in the area between the heads of Bugaboo and Findlay Creeks in
Mount Farnham (11,342 feet), Jumbo Mountain (11,217 feet), Hamill Peak
( 10,640 feet), and Mount Findlay ( 10,780 feet). The northern ranges are inferior
in height to the ranges in the Selkirk Mountains due west in Glacier Park, whereas
due west of the highest Purcell Mountains lie the somewhat lower Slocan Ranges of
the Selkirks. South of Mount Findlay, summit heights diminish gadually, Mount
Loki (9,090 feet), northeast of Riondel, and Mount Evans (8,949 feet), southwest
of St. Mary Lake, being the highest. At the International Boundary the summit
heights arc in the vicinity of 7,000 feet and the topography is comparatively subdued.
The axis of the mountains lies closer to their western margin than to their
eastern. Westward drainage is by short steep streams, whereas eastward drainage
is on gentler gradients by longer tributaries. Along the east side of Kootenay Lake
the tributary creeks flowing in narrow deep valleys have carved out a series of narrow
ridges running east and west, ranging in elevation from 7,000 feet on the ends
overlooking the lake to 8,000 feet and higher on the eastern ends.
The mountains are drained by tributaries of the head of the Columbia River
and by the Kootenay River and its tributaries. Kootenay Lake at 1,755 feet elevation
and Columbia Lake at 2,852 feet elevation are significant heights in the drainage
systems, above which the mountains rise to a maximum regional relief of about
8,000 feet.
The Purcell Mountains are underlain by sedimentary and metamorphic rocks,
largely of Proterozoic age but extending upward into the Lower Palazozoic, which
are intruded by batholiths of granitic rocks. The sedimentary and metamorphic
rocks comprise thick quart&e, argillaceous quart&e, argillite, and limestone members;
the lithology is far more uniform in the Purcell Mountains than in the Selkirks.
The rocks are involved in overturned and frequently complex folds about axes which
regionally have an arcuate plan, being northeasterly in the south, northerly in the
central ranges, and northwesterly in the north. The trends of individual ranges are
controlled by this fundamental bedrock structure.
The northern ranges contain rugged high peaks which are massive and bold
when composed of quartzite or granite, and sharp and pinnacled when composed of
slates. The highest peaks projected above the Pleistocene ice-sheet, whose level lay
at 8,000 feet in the north and at about 7,000 feet in the south. The peaks were
shaped by intense cirque glaciation, and active cirqw glaciers are still present on
some of the highest peaks. The summits are separated by deep, steep-sided glaciated
valleys, and interconnecting ridges are few and mostly serrate. In the southern Purcell
Mountains south of Mount Findlay and Skookumchuck Creek “ the mountains
up to 7,000 feet are rounded and well wood& to the summit, higher ones are commoody
extremely rugged, and those carved out of gmnite or massive quart&es are
climbed only with extreme difficulty. Near the International Boundary few peaks
rise above 7,000 feet and the topography is comparatively subdued. To the north,
where the elevation of.the higher peaks is 8,000 or 9,000 feet, the terrain is extremely
rugged. A feature that causes the abrupt relief and consequent steepness of the
mountains is the deeply incised valleys that reach far back into the heart of the
range.“*
” Glacial striae, erratics, and glacial debris occur at all elevations,up to 8,000
feet.
* Rice, H, M. A, f&o,. sm., Cm7d.T. blem. 2% ,94,, p, *
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