PHYSIOGRAPHY OF THE BEAVERDELL MAP-AREA. 
17 
Many local irregularities in slope occur within the uplands; 
small parallel steep sided ridges are common within areas under- 
lain by plutonic batholiths; contrasts of flat hilltops and sheer 
cliffs are often seen within the lava areas, some of the cliffs, as 
in the Goat Peak region, reach a height of several hundred feet. 
The soil covering is irregular in thickness and everywhere char- 
acterized by the presence of rounded pebbles foreign to the rock 
formation below. These erratics are found upon the highest 
points within the quadrangle. The upland surface cuts across 
contact surfaces between the formations older than the Tertiary 
lavas at all angles. Tertiary lavas, however, generally occupy 
higher ground than the adjacent older rock formations; very 
often the contact is at the base of a lava cliff, such cliffs being 
the rule rather than the exception. To the west the upland 
surface appears to rise gradually to the watershed between the 
Okanagan and Kettle rivers; on the east of the quadrangle it 
ends at the canyon of the Kettle river ; northward it appears to 
become less rugged ; but about 20 miles north of the quadrangle 
the flat surface is interrupted by a high ridge coming from the 
northeast, known as the Black ridge, with Ptarmigan mountain 
apparently near its southwest end; to the southwest the upland 
is rugged and apparently much broken by canyons; to the 
southeast the plateau surface ends or merges into the Midway 
mountains. 
The West Fork river occupies a steep sided, flat bottomed 
valley which crosses the western half of the quadrangle in a 
north-south direction. It falls from an elevation of over 3,000 
feet on the northern to about 2,500 feet at the southern end of 
the quadrangle. Its tributary, Beaver creek, drains a large part 
of the quadrangle to the east and occupies the same type of 
valley in the lower 5 miles of its course. Numerous streams 
coming from the broad troughs on the upland surface flow 
through V-shaped canyons into the larger valley bottoms of the 
West Fork and the Beaver. The upland draws resemble a 
flattened V, in cross section, and are a part of the upland surface. 
The change from valley side to upland slope is abrupt and forms 
a distinct knee, convex upward, in profile (Plate IV and Figure 
