130 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
in faults is well shown in the case of the neighboring Della fault, which 
has a different slipping plane, but a similar direction of movement. 
Age of Alta fautt—In the mines there are some ore shoots which apparently 
have formed along fractures belonging to the Alta fault system, but these 
are on the outskirts of the chief displacement and have only a slight 
movement. Along the main fault there does not appear to be any 
mineralization, but there are, instead, fissures and open watercourses. It 
may be judged from this that the fault movement probably began immedi- 
ately before the mineral deposition, but was mostly developed at a later 
period. These conclusions in regard to age are almost surely true in the 
case of the neighboring Della fault. 
Della faut—The Della fault was not actually located in this district, but 
was extended across the map on account of calculations based on data 
obtained in mine workings on Smuggler Mountain. Its location, therefore, 
is not of necessity exactly correct. It is represented on the map as having” 
a throw similar to that which it possesses in Smuggler Mountain, but with 
the amount of this throw diminished; and it is represented as dying out 
in the granite. These are, however, assumptions. This fault will be 
described in detail in considering the geology of Smuggler Mountain; but 
it may be stated that its apparent displacement is to the east on the south 
side; that its trend is east and west, and its dip about 30 degrees to the 
south, and that the striz along this plane show that the movement has 
been to the southeast on the south side of the fault, at an angle of about 
45 degrees to the horizontal. 
RESUME OF THE STRUCTURE OF HUNTER PARK. 
First. The first deformation of the original strata was a heavy folding. 
This resulted in a general steeply dipping monocline, which in the eastern 
part of the district, near the contact with the granite, shows a flattening of 
the dip and an approach of the strata to the horizontal. But the beds thus 
dipping are often removed by erosion. 
Second. Almost contemporaneous with the folding was the develop- 
ment of the Silver fault, which runs very nearly parallel to the bedding, 
but often cuts across it at a slight angle so as to remove whole formations. 
Along the southern end of this fault many ore deposits exist; its age, 
therefore, is premineral. 
