84 FAIRBANKS AND RAMPART QUADRANGLES. 
the divide, where there arc some dikes and masses of a monzonitic 
rock. Quartz occurs generally only in small veins, and these are not 
prominent. In places there is a considerable amount of pyrite in the 
rocks in small crystals and grains, but no large masses or veins have 
been seen. 
THE CREEKS AND BENCHES. 
EUREKA CREEK. 
General description. — Eureka Creek, on which gold was first dis- 
covered in this area (in February, 1899), flows southwestward along 
the foot of the Baker-Minook divide. It runs in a straight southwest 
course for about 4^ miles, then turns and runs south 2^ miles to its 
junction with Pioneer Creek. It has a number of small tributaries 
from the northwest side, but none from the southeast. The largest 
is Boston Creek, about 2 miles long, which joins Eureka Creek at its 
bend. The other tributaries are mere rills. Eureka is a small creek 
carrying barely a sluice head of water above the mouth of Boston 
Creek during the ordinary seasons. From aneroid barometer read- 
ings the gradient of the stream is about 100 feet per mile. The valley 
slopes gently to the divide on the northwest side, but on the southeast 
side the slope is almost precipitous, rising 400 to (500 feet above the 
valley. The creek flows close to the foot of the steeper side. 
The gravels of the creek are not much worn, as is characteristic in 
weak streams, and have been left for a considerable distance, in 
places at least 500 feet, up the slope of the hill as the stream bed has 
moved to the southeast. The bench gravels, like those of the present 
stream bed, are made up entirely of the country rocks. The deposit 
varies in thickness from 5 to 18 feet, and the overlying muck varies 
from nothing to 8 feet, the distribution being rather irregular. The 
total thickness varies from 5 to 20 feet. The gravel contains a con- 
siderable amount of very sticky clay, which makes sluicing difficult. 
The clay seems to come from the decomposition of both the grit and 
the slates. 
Mining. — Only one claim above and one below the mouth of Boston 
Creek have so far been made to pay, but prospectors on the bench 
gravels about 2 miles above the mouth of Boston Creek reported that 
they had found gold in sufficient quantities to pay for ground sluicing, 
if not for drifting. On this part of the bench it is 8 feet to bed rock 
near the creek, and 450 or 500 feet back from the stream it is 20 feet. 
The elevation above the creek at this distance, as shown by the aneroid 
barometer, is 70 feet. % 
The gold is said to be in the lower 18 inches of gravel and in a foot 
of bed rock. Along the creek the bed rock is largely blocky, and in it 
gold is found to. a depth of 3 feet; but it is not found at such depths 
