176 ALASKAN MINERAL RESOURCES IN 1906. 
stream placers — (1) those of the smaller gulches and creeks and (2 
those of the main river. The gulch and creek placers are usually ( 
small extent, but are so situated that many of them have been profii 
ably mined by pick and shovel. On the other hand, many of th 
placers of the main river are of considerable extent and are difficult t j 
exploit except with equipment that permits the handling of a lar| 
amount of material and provides for both high-water and low-wat( 
conditions. 
Bench gravels have been reported at various localities, but those c| 
proved economic importance are confined to the main Kougarok. 
River and some of its larger tributaries. These are chiefly within 25 
feet of the present water level, but some higher benches are reported 
to be auriferous. 
KOUGAROK RIVER. 
The Kougarok is a swiftly flowing stream carrying at its mouth i 
10,000 to 15,000 inches of water and having an average gradient off 
about 20 feet per mil* 1 . Most of the material transported is coarse, 
varying from fine gravel to coarse cobblestone. 
Undoubtedly the most extensive deposit of auriferous alluvium yew 
found in the district is that of the main Kougarok, occurring both in 
the present stream bed and on the benches. For at least 40 miles of 
its course the gravels of this stream have been found to be auriferous, 
though it is impossible to state at present what part of these carry > 
commercial values. The valley of the Kougarok has a meandering 
course and varies greatly in its cross section. In some places it is 
steep walled, narrow, and without benches; in others it opens out 
into a broader basin, with gentle slopes or bounded by well-marked 
rock benches. A striking feature of its topography consists of thd< 
various levels of erosion, which are marked by benches both along: 
the main river and along many of its tributaries. These clearly indi- 
cate a succession of uplifts that have brought about the incision of 
former valley floors, remnants of which are preserved as benches. 
Evidences were observed of at least three of these uplifts, of which 
naturally the last is best preserved, and consists of a rock bench 
covered by gravels standing 15 to 25 feet above the present water 
level. Where the Kougarok enters the Kuzitrin lowland both valley 
walls show well-marked benches. Two levels are here marked — one al 
50 feet and one at 25 feet. These are traceable for about a mile anc 
a half above Windy Creek; then the walls become steeper, and as far 
as Left Fork the river occupies a canyon-like valley. From this point 
to Washington Creek, 20 miles above, some evidence of benching caij 
be observed at most places, though it is not intended to imply that 
the benches are continuous. The individual benches have not been 
traced, but in that part of the valley which lies below Taylor Creel| 
there are at least two levels and possibly three. 
