26 
MUSEUM BULLETIN NO. 11. 
70 feet in diameter, and about 10 feet deep, in olivine basalt, 
with a rock rim 6 feet high which, except for 15 feet on the north 
side, completely surrounds it. Such a depression might be formed 
by the collapse of a gas chamber in the lava after it has partially 
cooled. The depression would have to be filled up at least 3 
feet before water could flow out of it, and it is difficult to explain 
as an erosion phenomenon. Nearby lavas in the same mass 
are amygdaloidal, and the writer believes this to have been formed 
near the surface of the original flow and to be as yet practically 
unaffected by erosion. The patch of lava at upper Collier lake 
lies in a trough between hills of older rocks. It lies higher than 
the adjacent valley floor to the west, and has a cliff 20 feet high 
facing the lake. Its flat rock surface does not appear to have 
been very much modified by water action. In the two cases 
cited the topography seems to be very largely dependent upon 
the original rock structure. 
THE VALLEYS. 
The West Fork river and its tributary, Beaver creek, drain 
all of the quadrangle except that part which flows into the Kettle 
river by way of Cedar and Canon creeks. The West Fork flows 
southerly and joins the main Kettle, which is roughly parallel 
to it here and 12 miles to the east, about 16 miles south of the 
quadrangle. The principal streams entering the West Fork are 
Curry, Beaver, China, and Trapper creeks on the east, and 
Carmi, Wilkinson, and Hall creeks on the west side. Beaver, 
Wilkinson, and Trapper are the largest of these. Beaver creek 
drains the larger part of the east and south of the area, while 
only the lower part of Trapper and Wilkinson lie within the 
map-area. Trapper creek drains an area of unknown extent 
north of the quadrangle, the Wilkinson basin lies west and 
northwest of it. As seen from Nipple or Red mountain the basin 
of Wilkinson creek appears to cover about 100 square miles. 
To the south of the quadrangle the wedge-shaped area 
between the Kettle and West Fork canyons drains into them by 
Dominion, Deep, and Cedar creeks; Cranberry creek drains the 
rather high upland directly to the southwest of the quadrangle. 
