16 
MUSEUM BULLETIN NO. 11. 
DESCRIPTION OF THE' BEAVERDELL MAP-AREA. 
Summary. 
That part of the Interior plateaus included within the 
Beaverdell map-area consists of a rolling upland with a relative 
relief of 2,000 feet. It is drained for the greater part by the 
West Fork river whose bottom lies from 1,000 to 1,500 feet below 
the surface of the upland, increasing the total relief to about 
3,250 feet. The West Fork flows southerly and joins the main 
Kettle river which is roughly parallel to it, and 12 miles east, 
about 16 miles south of the area. The Kettle flows south along 
the eastern foot of the Midway mountains near the International 
Boundary where it turns east and finally enters the Columbia 
south of the Ross! and mountains. In its north-south course the 
deep valley of the Kettle forms the eastern border of the Interior 
plateaus which wedge out a few miles south of the International 
Boundary. The Beaverdell map-area, therefore, whose eastern 
boundary is nearly on the edge of the trench of the Kettle, lies 
in the southeastern comer of the Interior plateaus. 
The rolling surface of the high country is diversified by 
buttes and mesas of Miocene lavas, often surrounded by high cliffs 
which lend a rugged element to the scenery. It consists of 
broad ridge areas trending north to northeast, each of which is 
a composite of a number of small, parallel ridges. These major 
ridges slope gently down to more or less steep bounding valleys. 
Their crest lines are sometimes nearly flat for several miles, but 
often pitch strongly toward some valley, or from some lava- 
covered butte (Plate III). The average elevation of individual 
flat topped ridges ranges from about 4,000 feet near the deep 
West Fork valley to 4,700 feet in most of the country east of it, 
and over 5,700 feet near the large volcano-covered area of Nipple 
mountain. Nipple mountain, the highest point on the map, is 
5,758 feet high. Nipple mesa, north of it, and Red mountain, 
3§ miles to the southwest, both outside the quadrangle, are 
at about the same elevation. Goat peak, a volcanic plug on 
Wallace mountain, is 5,675 feet high, while lava mesas to the 
northeast of it are over 5,500 feet. 
