152 The American Geologist. March, 1903. 
the deposit at the mouth of the gulch must have been a cloud- 
burst. 
Even at the present time, this particular mountain has a 
peculiar power to produce excessive precipitation. In August, 
1 90 1, there was a small cloud-burst on the western side of the 
peak, draining into Big Bend creek, which stream rose to a 
hight of ten or twelve feet, although its ordinary winter max- 
imum is only two or three feet. All the tangle of the fallen 
trees in the bottom of the gulch was swept out and boulders 
three feet in diameter were easily moved. 
The formation of the alluvial fan at the mouth of Crosby 
gulch rearranged the drainage. Crosby creek excavated a new 
canon into very resistant hornblende schist. This is from 
50 to 150 feet deep and very narrow. The river was lifted 
over 200 feet above its previous bed and forced to flow against 
the southern side of the valley. Then it cut a new cafion from 
200 to 300 feet deep, encountering bed-rock and trenching 
into it from 50 to 100 feet. 
For over one mile above Cooper's mine, the river flows in 
a narrow cafion. The precipitous rock wall on the south side 
terminates on a line about even with Cooper's flume on the 
north side of the valley, and above this line there is a gentler 
slope. Remnants of the old river deposit corresponding to the 
gravel in Cooper's mine are buried under the gentle slope and 
it is evident that the river has been displaced here also. In 
fact, a series of rather suddenly formed alluvial fans can be 
traced along the valley for several miles up the river and they 
have displaced the stream repeatedly. Each temporarily ob- 
structed the valley and ponded the water behind the barrier. 
In these ponds the river deposited fine gravel without the 
coarse boulders of the older and the present bed. 
Above the gorge the valley enlarges to a basin over a mile 
in length and several hundred 3'ards in width. Some obstruc- 
tion caused the accumulation in the bottom of the basin of 
several hundred feet in thickness of horizontally stratified 
fine gravel, alternating with layers of clayey silt of reddish 
color. The silt layers have some distinguishing character- 
istics. Silt layers of identical character occur in Cooper's mine 
in the lower part of the local alluvium, not very far above the 
old river channel. Thev seem to have been due to a condition 
