136 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
and a point opposite the top of Aspen Mountain, which is the point of 
ereatest disturbance in the uplifted beds lying to the east, is about 6,400 
feet, as nearly as can be estimated. The amount of uplifting as shown by 
the longitudinal section, therefore, is amply accounted for by the differen- 
tial movement which has gone on along the fault. The inference from this 
is that the main uplifting and faulting in this disturbed area has gone on 
since the formation of the Castle Creek fault. The amount of increase in 
the throw of the fault, producing its maximum displacement of 9,000 feet, 
is due mainly to the increased steepening of the dip on the north side of 
Aspen Mountain and to the associated faulting, while to the south of the 
region of greatest displacement the dip changes, so that the rocks on both 
sides of the fault tend to converge, and therefore the throw steadily 
decreases. The local and enormous increase in the amount of displace- 
ment is, therefore, to be entirely accounted for by this local uplifting on 
the east side of the fault; and there is no evidence that the beds on the 
west side have had any part in this movement. 
The summit of the dome is traversed by an intricate system of faults, 
which have their greatest development at the point of greatest uplift, but 
are conspicuous and important over the whole of the uplifted area. North 
of this area they disappear as quickly as the uplifting itself, while on the 
south they disappear somewhat more slowly, as does the upliftmg. The 
faults may be divided into two chief sets, one parallel to the axis of 
greatest disturbance and to the Castle Creek fault, and a second at right 
angles to the first. It is probable that both these originated simply as sets 
of fractures and were formed at about the same time, but the maximum 
displacement along each took place at different periods. This period must 
be worked out from every fault separately, for movement has been going 
on continuously from the formation of this uplift to the present day. As a 
general rule, those faults which were parallel with the longest axis of the 
uplifted dome, or which run in a north-south direction, had their greatest 
movement at an earlier period than the other set; and the movement along 
these has been greater than that along the others, as might be expected 
along faults developed parallel with the axis of greatest disturbance. ‘The 
east-west faults have less importance, and the amount of their throw in no 
case attains anything like the proportions which are found in several of 
the other set. 
