40 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
It seems probable that before the glaciation the basin near Gillett drained north¬ 
ward into Oil Creek (see Pikes Peak folio), but that later this drainage was 
diverted southward to West Beaver Creek. 
The drainage of the volcanic area presents some interesting features. A 
fairly uniform volcanic cone will immediately develop a radial drainage system 
which is very apt to be superimposed upon the underlying rocks when these are 
reached by erosion. This kind of drainage is in fact indicated by Wilson Creek 
above Goldfield, by Arequa Gulch, and by Squaw Gulch, but to the north and east 
there is no indication of such a radial drainage. This shows, we believe, that the 
volcanic cone was not symmetrical, the southwest slope being much more prominent 
than the others, and also that the horizontal extent of the base of the volcano was 
probably confined within the limits of the special map. Had the deposits covered 
Big Bull Mountain and sloped uniformly eastward, gulches leading in that direction 
would surely have been established. The southward turn of upper Wilson Creek 
at Goldfield indicates that Big Bull Mountain existed at the close of the volcanic 
epoch and that it diverted the course of the gulch to correspond to an old pre- 
volcanic drainage channel. On the north slope toward Cameron there are no indi¬ 
cations of deep gulches in the volcanic area and it seems very unlikely that Grassy 
Creek, which in its flat course shows little evidence of the rejuvenating influence 
of the uplift, could have been established had not a slight depression existed 
between the volcanic hills and the granitic ridge west of Calf Mountain. 
