134 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
movement. At the extreme northeastern corner of the district there is an 
area which is also faulted, and between this and the northern part of the 
Hunter Park area the strike of the beds becomes more nearly north, devi- 
ating considerably from the normal trend across Hunter Park. This 
change in strike indicates an uplifting of the strata shown in Section G, 
Atlas sheet VIL This uplifting is accompanied by faulting, and as ore has 
also been found in this district, it may be that the disturbance was similar 
to that of the Tourtelotte Park uplift. In the undisturbed region between 
these two uplifts the rocks, so far as yet known, are practically barren of 
mineral values. 
The uplift of Tourtelotte Park and Aspen Mountain is one of the most 
interesting structural features in the district. By comparing the amount of 
uplift, as seen in the longitudinal section, with the corresponding difference 
in throw of the Castle Creek fault at various points, it is seen that all the 
uplifting has taken place subsequent to the formation of the fault, and that 
the beds on the east have moved upward along it. The uplifted region 
stopped short at the fault, the beds on the west side having had no corre- 
sponding movement. On the west side the beds have a uniform northerly 
pitch, which reveals successively lower strata toward the south. South of 
the northern limit of the fault, as shown on the map, the formations occur 
in normal succession, from the Laramie, through the Montana, Colorado, 
and Dakota of the Cretaceous, the Gunnison formation of the Jurassic, the 
Triassic, the Maroon and Weber formations, and even the intercalated sheet 
of porphyry, which is found in the lower part of the latter; this porphyry 
outcrops in the extreme southern part of this district, as the Laramie does 
in the extreme northern part. 
The beds east of the fault, however, have no uniform pitch, but show dif- 
ferences at different points, forming a strong contrast with the uniformity of 
the beds on the west. From the northern part of the district to Red Butte 
there is a gentle northerly pitch, which is somewhat less than that to the 
west of the fault at this place, so that the amount of displacement increases 
northward from Red Butte. South of Red Butte there is a sudden steepen- 
ing of the pitch on the east side. Near the pomt where the beds begin to 
pitch most steeply there comes in a series of faults which, like the increase 
in pitch, operate to upthrust the beds on this side of the fault. Thus West 
Aspen Mountain is simply an isolated block which has been uplifted above 
the surrounding strata between certain of these faults. 
