Landforms of British Columbia 1976 - Department of Geography

Although they have been dissected by late Tertiary stream erosion and subsequently
glaciated, their original shape has been largely preserved.
Flat-lying or very gently dipping olivine basalt flows underlie great expanses
of the Nechako and Fraser Plateaus. The plateau surface in many instances coin-
cides with an original flow surface, and the minor relief is due mostly to erosion
within the veneer of glacial drift. Dissection by streams has produced canyons
and step-like slopes which are controlled by vertical jointing within the horizontal
flows.
Rising 2,000 and 4,000 feet respectively above the general level of the Stikine
Plateau are the two shield volcanoes of Meszah Peak (7,010 feet) (see Plate XVIIB)
and Mount Edziza (9,145 feet) (see Plate XLVIIA). They are dominantly pre-
Pleistocene in age and have been partly dissected and glaciated, yet they retain
much of their original shape, only slightly modified by later processes. At Mount
Ed&a, however, volcanic activity has continued into Recent time-a number
of small, perfectly formed, breached volcanic cones lie between elevations of 4,500
and 7,000 feet on the slopes leading up to the peak, and distinct lava flows extend
northward and eastward down the mountain slopes toward Buckley and Nutdude
Lakes.
Prominent features of the Kawdy Plateau between Meszah Peak and the At&la
Range are isolated flat-topped conical mountains called “ tuyas ” (see Plate XVIB
and pp. 51-52). These are volcanoes which melted their way up throueh the Pleis-
tocene ice-sheet and which, because of the peculiarity of their origin, differ in form
and constitution from normal volcanic cones. * There are in addition a considerable
number of small yet easily discernible cinder cones on the Kawdy and Tanzilla
Plateaus and on the western margin of the Cassiar Mountains.
Extending in a line northward from Mount Garibaldi to the head of the Bridge
River are numerous centres of Pleistocene and Recent volcanic activity (see Fig. 1).
The main centres of volcanic accumulation are represented by conspicuous tnoun-
tains as well as by lava fields and other volcanic features. Mounts Cayley, Meagher,
and others, in large part, are piles of volcanic materials which have been modified
by erosion. Recent explosions (probably less than 6,700 years ago) at centres
at the head of the Bridge and Lillooet Rivers cast a great volume of coarse white
pumice over an extensive area of the Bridge, Yalakom, and upper Lillooet Rivers.
The summit of Mount Takomkane (east of Williams Lake) is a cinder cone
300 feet high of olivine basalt lying on a glaciated granitic surface. in the area
south of Clearwater Lake a number of interesting volcanic landforms include Pyra-
mid Mountain (3,590 feet), which is a perfect small cinder cone, a small breached
cinder cone blocking the east end of Kostal Lake, and several explosion pits nearby.
Lava from a conical vent on the southwest side of Ray Mountain flowed down Falls
Creek for 6 or more miles almost to the outlet of Clearwater Lake, and lava from
three cones in the valley of Spanish Creek flowed 6 to 8 miles down Spanish Creek,
where, in addition, there is an explosion caldera. Thus in a comparatively small
area south of Clearwater Lake, volcanic activity in Pleistocene and Recent time has
produced features of importance and of considerable geologic and scenic interest.
Two volcanic centres have recently been mappedt on the eastern edge of the
Fraser Plateau. One, 3 miles east of Mount Brew, is a nearly perfect volcanic cone
that could be post-Pleistocene. The other, south of Keno Lake, is a cone that is
much modified by glacial erosion and is Interglacial or pre-Pleistocene in age.