Landforms of British Columbia 1976 - Department of Geography

dissected upland surface of the plateau and its continuation across the highland to
the mountains.
A large part of the plateau is underlain by flat or gently dipping late Miocene
or Pliocene olivine basalt flows. The fiows have steep escarpments along rivers and
creeks and almost horizontal upper surfaces. Flat plateau areas separated by near-
vertical cliffs are characteristic of lava regions. The existing lava is largely between
elevations of 3,000 and 4,500 feet and represents remnants of a large lava plain
from which tongues extended outward along major valleys and depressions.
Much of the plateau is covered with glacial drift, and possibly less than 5 per
cent of bedrock is exposed. The glacial drift has been modelled into drumlin-like
forms by the movement of ice across it. These and the eskers provide much of the
low relief on the plateau surface. The ice moved across the Fraser Plateau eastward
and northeastward from the vicinity of Anahim Lake, and northeastward to north-
ward from the area between Chilco Lake and the mouth of the Chilcotin River (see
Fig, 10). Striations on Mount Alex Graham (5,455 feet), 35 miles west of Wil-
liams Lake, trend north 25 degrees east, and farther east at The Dome (4,517 feet)
trend north 10 degrees east.
A remarkable belt 5 miles wide containing many icemargina1 m&water
channels trends northwestward from Clinton for 15 miles. It is visible on aerial
photograph R.C.A.F. Al3320:118.
A number of ranges worth special mention lie within the confines of the Fraser
Plateau and project above the general plateau level. In the vicinity of Anahim Lake
three shield volcanoes of late Miocene age form the Rainbow Range, Ilgachuz
Range, and Itcha Range. These volcanoes have built up dome-like piles of lava
and fragmental rocks to a height of 8,130 feet at Tsitsutl Peak in the Rainbow
Range, 7,87,3 feet at Far Mountain in the Jlgachuz Range, and 7,760 feet at Mount
Downton in the Itcha Range. The Rainbow Range is a low dome-like cone about
20 n&s in diameter, with Anahim Peak (6,160 feet) an obsidian plug on its north-
east flank. The Ilgachuz Range is 15 miles or more in diameter, and the Itcha
Range (see Plate XXVI.&) is 10 miles wide and about 40 miles long. All have been
dissected by late Tertiary, pre-Pleistocene stream erosion.
Three ranges on the southwestern side of the Fraser Plateau lie between it and
the border of the Coast Mountains along the Yalakom and Fraser Rivers. These
are the Cam&foot Range between the Yalakom and Fraser Rivers, the Marble
Range east of the Fraser River and north of the Marble Canyon, and the Clear
Range east of the Fraser River and south of the Marble Canyon.
The Cam&foot Range and the Clear Range are separated from the Coast
Mountains by the structural line of the Fraser River fault, which in this section is
a graben. The Camelsfoot Range (see Plate XXVIB) reaches summits in excess of
7,500 feet at Yalakom and Red Mountains and at Nine Mile Ridge, presents a steep
front along the Yalakom River, and slopes more gently eastward to the Fraser. The
Marble Range east of the Fraser River is characterized by bold castellated peaks
and ridges of pale grey Upper Permian Iimestone. This limestone, the upper
member of the Cache Creek Group, extends northward from the Cornwall Hills on
Upper Hat Creek to Big Bar Creek and beyond. The Clear Range extends south-
ward from Pavilion Lake to Lytton. From its axis, with high points of 7,640 feet
at Blustry Mountain and 7,650 feet at Cairn Peak, it has a steep front along the
Fraser River to the west and a somewhat more gentle slope down into the Hat
Creek valley on the east where transition to the plateau is gradual.
[References: Campbell, R. B., “ Quesnel Lake (West Half),” Geol. Surv.,
Canada, Map 59-1959; Tipper, H. W., “Quesnel,” Geol. Swv., Can&r, Map
12-1959; Tipper, H, W., “Anahim Lake,” Gwl. Swv., Camda, Map 10-1957;
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