PHYSIOGRAPHY OF THE BEAVERDELL MAP-AREA. 
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about 6 square miles. It contains a number of lakes and swamps, 
including Joan and Lassie lakes. South of Joan lake the end 
of St. John ridge slopes into it at the rate of 600 feet to the mile. 
On both sides of Lassie lake olivine basalt rises from the basin 
surface forming cliffs 40 feet high in places, from one of which 
one may look far over the plateau area to the north. 
Ridge tops are often quite flat and smooth. These are 
from a few hundred to over 1,000 feet across, with gentle slopes 
in the direction of the ridge. They are as well developed upon 
a low ridge like the part of King Solomon mountain overlooking 
Beaver creek, as upon St. John ridge which lies in the centre of 
a large upland area and is about 900 feet higher. The tops of 
hills within the Tertiary lava areas are often comparatively 
flat. Such is often the case in areas partly or wholly surrounded 
by cliff faces such as the mesas northwest of Goat peak and the 
larger mesa north of Nipple mountain, which lies just outside 
the quadrangle. 
Drainage Upon the Upland. 
What has been said about the parallelism of the hills upon 
the upland and their slopes, applies also to the valleys between 
them, since valley bottom and hill top are roughly parallel and 
the hillsides are the valley walls. Cross valley profiles are in 
general much gentler than those of the main trenches into which 
these upland valleys drain. Stream bed profiles steepen very 
abruptly at the head of the canyons by which the upland valley 
is connected with the main valleys, forming a break in profile 
corresponding to that between upland surface and valley wall. 
The upland drainage will be treated in more detail in discussing 
the valleys. 
Soil Covering . 
The amount of bare rock varies from place to place upon 
the upland. Rock outcrops seem to be more abundant upon the 
ridge tops than in the troughs which separate them. The tops 
of ridges within Tertiary volcanics are especially bare of soil. 
Parts of the tops of Cranberry and other rather flat topped 
