Landforms of British Columbia 1976 - Department of Geography

sloping areas of upland remain undissected. The boundary of the plateau on the
north is the Stikine River, which for 50 miles upstream from Telegraph Creek
(2500 feet) flows in a steep-walled canyon many hundreds of feet deep. The
canyon was eroded by the river probably after it was diverted from its old channel
by Pleistocene and Recent lava flows originating at Mount Edziza.
Glacial ice, which once covered the plateau, now remains as a capping of Edziza
Peak in the Tahltan Highland to the west, but its erosional and depositional effects
are visible over the entire plateau surface. Cirques are cut into northern and
eastern peaks and ridges, and upland surfaces have been subdued by erosion and
the deposition of drift. Modification of drainage has resulted from the ice occu-
pation, and numerous lakes occupy basins created in drift-blocked valleys. Drumlin-
like forms in the upper Iskut River valley (see Plate XVB), from Mowdade and
Kinaskan Lakes southward, indicate that ice poured southward from the Klastline
Plateau down the Iskut River valley from an ice divide that existed somewhat
north of Nuttlude Lake (see Fig. 10).
[Reference: “ Stikine River Area,” Geol. Surv., Canada, Map g-1957.1
[Photographs: B.C. 537:64, 85, 108; B.C. 538:13,45, 87; B.C. 695:89.1
Spatsizi Plateau
The Spatsizi Plateau (see Plate &Xc) is an area of wide, drift-filled valleys
and open, gently rolling upland surfaces extending from Mount Brock on the western
end in a curve to Thutade Lake on the southeast. The plateau is drained by the
Stikine and Finlay Rivers and is enclosed by mountains. On the southwest the
plateau is flanked by the Skeena Mountains, on the east by the Omineca Mountains,
and on the northeast and north by the Cassiar Mountains.
The plateau is almost entirely underlain by sandstone, shale, conglomerate,
and minor coal of Upper Cretaceous and Paleocene age. The rocks are mainly gently
warped to flat lying, but along their southwestern border they have been folded across
widths of a mile or more into overturned and recumbent structures which are probably
related to movement along a thrust fault along their contact with older rocks.
The gently sloping upland surfaces of the plateau represent remnants of the late
Tertiary erosion surface. Its slopes have been at least partly controlled by the gently
dipping beds, and its surface was differentially uplifted and raised to a maximum of
7,000 feet on Skady Mountain and others. Characteristic features of the plateau are
the wide drift-filled valleys that are only sparsely timbered, the Stikine River flowing
at or just below 3,500 feet elevation, and the Finlay River below 4,000 feet, with
gentle slopes leading up to unwooded upland areas.
The pre-Pleistocene topography was only slightly modified during and since the
Pleistocene. The region was covered by ice to a height of about 7,000 feet, some of
which moved out from the plateau in a northerly and northeasterly direction up
Tucho River.
[Reference: “ Stikine River Area,” Geol. Surv., Canuda, Map g-1957.1
[Photograph: B.C. 538:31.]
PHYSIOGRAPHIC HISTORY OF THE STIKINE PLATEAU
The Tertiary was a time of widespread attack by subaerial erosion. Through-
out British Columbia during that time the land was being reduced in elevation by the
erosion of the various river systems of the country. By late Tertiary the land surface
had been reduced to one of variable but generally low to moderate relief.
This old land surface, which is an erosion surface rather than one built up
through deposition of sedimentary or volcanic materials, is represented in the Stikine
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