70 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
east across the Castle Creek fault, black Weber shales are found on the 
east side of the fault. It seems very probable that in this case the shales 
lie on the northwest side of the Mary B. fault, as represented on the map, 
and that the contact of basal Maroon limestone and of Weber rocks lies 
between the two tunnels mentioned. The displacement of the fault is 
indicated by the change from the base of the Maroon to the Silurian, which 
shows a downthrow on the northwest side of about 2,000 feet. The fault 
probably splits off from the Castle Creek fault near the northern end of 
West Aspen Mountain, and, assuming a northeasterly trend, and thus 
diverging from the Castle Creek fault, which has a northwesterly trend, 
it soon runs into the Pride fault. 
At the extreme northern point of West Aspen Mountain the throw 
of the Pride fault is almost identical in direction and amount with that of 
the Mary B. fault, so that the contact of Maroon and Weber is seen on 
the opposite sides of the mountain, separated only by the wedge-shaped 
upthrust block of Silurian, Cambrian, and Archean. Where these two faults 
come together, therefore, as they evidently do at the very end of the 
mountain, the effect must be to neutralize each other, so that while the 
Pride fault may be continuous farther northwest into the Castle Creek fault, 
its throw has become very slight. Along the Mary B. fault there has been 
discovered in the Mary B. tunnel a body of ore, in part at least high grade, 
which has evidently been formed in place; therefore this fault is, so far as 
can be ascertained, identical in age with the faults already described, bemg 
antecedent to the ore deposition. 
Cross faults —Qn the map near the northern end of West Aspen Mountain 
are shown three parallel east-west faults, which have a northerly dip some- 
what steeper than the slope of the mountain. (See Section B, Aspen special 
map; Atlas Sheet X.) These faults divide the point of the ridge into par- 
allel slices, which have moved one upon the other. The general movement 
appears to be a downthrow to the south, and since the faults have a northerly 
dip, they come under the head of reversed faults. This movement is indi- 
cated by the outcropping blocks of quartzite on the west side of the moun- 
tain. In one of the blocks, however, there outcrops, as shown on the map, 
a narrow belt of Parting Quartzite. The rocks in this block seem to differ 
from those in the adjoining blocks, in that there has been a change in the 
position of the beds, giving a more easterly dip. In this way the Parting 
