ASPEN DISTRICT MAP. 141 
down into the formations, so that there is found on its lower side the 
Silurian dolomite, with the Cambrian quartzite not far below. The Weber 
formation, however, is still on the upper side. This cutting down of the 
fault is only local, for farther southwest it cuts up across the Parting 
Quartzite into the Leadville dolomite. The line of this fault throughout 
the Hunter Park region, as compared with the line of the formation 
beneath, is suggestive of unconformity, and, as has been stated, there was 
actually some unconformity at this period. It is certain, however, that 
this plane is representative of a true fault, and that the fault is a heavy 
one, for it is marked by great brecciation. It may be that some uncon- 
formity existed previous to the faulting, and that the disturbance simply 
caused the Weber sediments to slide over the beds which lay beneath, or 
it may be that the disparity in the beds was not always so strongly marked 
as now, but was brought about by the removal of some formations through 
the faulting. The only positive facts are that there was a heavy fault 
along this plane, and that along this fault certain formations have locally 
been removed. 
In the southwestern part of the section is a heavy porphyry sheet, 
which lies very close to the Silver fault, being separated from it only by a 
thin and variable sheet of broken shale. Only the main faults are shown 
in this section, such as the two chief faults at Lenado, the Della fault on 
Smuggler Mountain, and the principal faults of Aspen Mountain. These 
are, however, such as bring out the actual structure best. 
By putting all the cross sections together the general structure of the 
beds on the west side of the Castle Creek fault is seen to be about that of a 
permanent synclinal fold. In Section F, in the southern part of the district, 
the fold is deep, broad, and open. ‘Toward the north it becomes somewhat 
shallower, but also more closely compressed, and is overturned throughout 
the central part of the area, while in the northern part it again becomes 
open, and is here still shallower. 
The fault itself is continuously traceable throughout the whole district. 
In the extreme southern part, in Section F, its throw is only 2,600 feet, 
while in Section E it has increased to about 6,300 feet, and in Section D to 
9,000 feet. This last point, which is opposite Aspen Mountain, is the point 
of maximum throw. Pl. XVII gives a view looking down Castle Creek 
across the Roaring Fork Valley to Red Mountain. On the right-hand side 
