2 
MUSEUM BULLETIN NO. 11. 
southeastern corner, the Tulameen sheet at the southwestern 
edge, and Hedley about midway between the other two (see 
Figure 1). 
The Beaverdell map embraces an area of about 163 square 
miles between north latitudes 49° 25' and 49° 37-5' and west 
longitudes 118° 55' and 119° 10'. It takes in a part of the 
valley of the West Fork river and its eastern edge lies within a 
mile or two of the trough of the main Kettle river. This trough 
divides the Midway mountains of the Columbia system from the 
Interior plateaus. The southern edge of the map lies less than 
30 miles from the International Boundary between Canada and 
the United States. 
The Tulameen map covers an area about 170 square miles 
in extent, the western side of which touches the foothills of the Ho- 
zameen range on the southwest side of the Interior plateaus. 
The southern edge of the area is 31 miles north of the International 
Boundary. Thirty-two miles north of the Tulameen map-area 
is the southern boundary of the Kamloops area and directly 
east of it lies the Shuswap area. The map sheets of the two 
latter areas, which were also used in this work, together cover 
12,800 square miles, about 9,000 of which lies within the Interior 
plateaus (Figure 1). 
Methods of Study and Conclusions . 
In extending the conclusions arrived at in the Beaverdell 
district to cover a wider area, advantage was taken of the Tula- 
meen map and of the knowledge, gained in its preparation, of 
the topographical forms in that part of the Plateaus. The 
Kamloops and Shuswap maps furnished a means for studying a 
large section of the region lying farther to the north. Between 
these areas no extensive portions of the country have been 
topographically mapped ; but descriptions of the topography by 
G, M. Dawson have served to some extent to bridge the gaps. 
The Plateaus consist of an old land surface dissected by 
deep valleys. It is the apparent flatness of this old surface that 
has given rise to the name “Plateaus” and it is to the character 
of that surface that the most attention is paid in this bulletin. 
In determining the stage to which the old land surface had pro- 
