TOURTELOTTE PARK SPECIAL MAP. 101 
that the movement along these faults was not accomplished suddenly, but 
has been a gradual process extending over long periods. The evidence is 
conclusive that this has been the case with many, if not all, of the faults 
of the Aspen district, and that many of them are even now in process of 
formation. It is, however, also evident that the maximum amount of 
movement in some was accomplished at a different time from that in 
others, and the difference in time of this maximum movement in two 
systems is taken as their relative age. So, while in the Justice system 
the movement has occurred mostly since the maximum development of 
the West Aspen system, yet there is no conclusive evidence of great 
movement in very recent times. In some of the faults of the Butte 
system, on the other hand, nearly all of the dislocation has been brought 
about in very recent times, and there is good evidence to show that in 
some cases these faults have developed entirely since the Glacial period. 
The whole of the Aspen district, so far as examined, shows many proofs of 
extensive glacial erosion, in the accumulation of morainal drift, the trans- 
portation of bowlders, and the carving of the bed rock into rounded, 
fluted, or drumlinoid forms. This glaciation occurred in such relatively 
recent times that the forms resulting from it are still comparatively 
unaltered by subaerial erosion. It is this fact which indicates the recent 
age of the faults. 
Perhaps the best example of these post-Glacial faults is the Butte 
fault, the chief one of the east-west system. On going south on the west 
side of the Tourtelotte Park basin, alone the divide between the basin and 
the gulches on the west side of the hill, one passes from Weber shales 
across the Sarah Jane fault to blue limestone, which outcrops on a flat- 
topped hill. Proceeding along this flat-topped hill, one comes suddenly to 
an abrupt escarpment or cliff, which is in large part nearly vertical, and 
has a total height of about 400 feet. This striking topographical form has 
received the name of Castle Butte. 
Pl. V is from a photograph of this cliff, taken from a point across 
Queens Gulch, at a distance of about a mile, and shows well the bold, 
abrupt break, and the castellated structure produced by erosion. In detail 
the butte presents several distinct variations. At the bottom there exists, 
where not obscured by talus, a strikingly peculiar cliff, probably 150 feet 
in height, which, in the plate, is shown just to the left of the highest point 
