40 FAIRBANKS AND RAMPART QUADRANGLES. 
valley floor at its mouth is about 1,000 feet wide, narrowing rapidly 
upstream. The bed rock of the main creek is chiefly quartz-mica 
schist, much of it carbonaceous, but a granite mass is found to the 
south and also in the valley of Hill Creek, a small tributary. The 
alluvium, which is 50 to 60 feet deep near the mouth of Gilmore 
Creek, shoals rapidly upstream and 2 miles above is only about 10 
feet deep. Most of this is muck, which ranges from 45 feet near the 
mouth of the stream to less than 5 feet 2 miles above. The gravels 
are chiefly schist of several varieties, with considerable quartz, which 
occurs to some extent in large bowlders, and much granite. An im- 
portant commercial feature of the creek is the presence of an ill- 
defined bench on the north slope of the valley. This is in some places 
separated from the main valley floor by a rock rim with an escarp- 
ment of a few feet, but usually slopes directly to it. The bench 
gravels are auriferous and have been mined at three localities. Much 
of the material is angular and ill stratified and in many places it 
resembles a talus slope rather than a water-laid deposit. These bench 
placers are favorably located for economic mining and have yielded 
some gold but in dry times there is not sufficient water for hydrau- 
licking. The pay streak in the Gilmore Creek gravels is said to be 
30 to 40 feet wide but in places attains a width of 100 feet. On the 
hill-slope terraces it appears to embrace the entire bench, from 100 
to 300 feet wide. The placer gravel of this creek is usually found 
down to or in the bed rock. In places 3 to 4 feet of the bed rock is 
mined, with but a foot or two of the overlying gravels. The gold 
ranges from medium coarse to fine and that of the benches appears 
to be more angular than that of the creek. Nuggets up to a value of 
$20 are reported. The gold is said to assay $19.25 to the ounce. Some 
bismuth has been found with it. 
Tom Creek, a tributary to Gilmore Creek 3 miles from the mouth, 
lies in the extension of the main valley. No values have thus far 
been reported on it. Hill Creek, a southerly tributary of Gilmore 
Creek, has its source well back in a high granite dome and the bed 
rock for much of its length appears to be granite. Near its head is a 
small basin 200 or 300 yards long. Below this basin the valley floor 
falls away with steep descent for about a quarter of a mile. The bed 
rock is a coarse porphyritic biotite granite, which in the basin is 
deeply weathered and stained with iron. Here some open-cut mining 
has been done. No one was at this place when visited by the geolo- 
gists but the pay streak appears to be very narrow. The alluvium 
consists of granitic sand about 8 feet deep. This occurrence is of 
interest because it shows that the gold has been derived from the 
granite. This deposit is near the contact with the schists and indi- 
cates that the granite intrusives may bear a genetic relation to the 
occurrence of the gold in bed rock. 
