6 
MUSEUM BULLETIN NO. 11. 
Each of these is separated by a narrow valley which opens 
into the Rocky Mountain trench to the north, so that that de- 
pression bounds each of the three mountain areas in turn at their 
northern ends. The more or less continuous systems forming this 
eastern belt are prolonged southward across the United States 
border, where they are succeeded by ranges of less regularity and 
persistence to the southeast and end abruptly to the southwest 
in the great Columbia lava plateau. 
The western part of the Cordillera consists of the Coast 
range, a persistent system extending from near the International 
Boundary to Alaska. A subordinate group, the mountains of 
Vancouver island and the Queen Charlotte islands, lies to the 
west of it. Its southern end is separated by the canyon of Fraser 
river from the Hozameen and Skagit ranges of the Cascade 
system. 
Between the mountains of the eastern belt and the Coast 
range lies a tract with less rugged relief, known as the Interior 
plateaus. At the United States boundary on the 69th parallel 
the width of the Cordillera, exclusive of the mountains on Van- 
couver island, is about 400 miles. The eastern belt is over 
200 miles wide, the Coast range and Interior plateaus about 
100 miles each. Farther to the north the Cordillera narrows 
somewhat. 
THE INTERIOR PLATEAUS. 
GENERAL FEATURES. 
The region of Interior plateaus is about 500 miles long by 
100 wide and trends northwest from the International Boundary 
to about the 56th parallel (Figure I). It consists essentially of 
areas of rolling upland separated from each other by deep valley 
trenches. Unlike other units of the Cordillera its boundaries 
are not always well defined, and in places the uplands seem to 
rise to meet the mountains. 1 To the west of it lie the Cascade 
1,4 The geology and ore deposits of the Hedley mining district, British 
Columbia," by Chas. Camsell. Geol. Surv., Canada, Memoir No. 2, p. 30; 
see also p. 9. 
