ASPEN SPECIAL MAP. 59 
side of the fault. In these tunnels the fault seems to be dipping to the 
east, as well as can be judged from the limited exposures. A little distance 
westward down the gulch from the outcrop of the fault there come in the 
bright-red, more massive sandstones, which probably form the lower part 
of the Triassic beds. From this pomt northward along the west side of 
the fault the northerly pitch of the Triassic beds brings in successively 
higher and higher strata. In this way nearly the whole Triassic comes to 
the surface along the narrow strip shown on the Aspen special map, for the 
Maroon formation is found in the southwestern corner, and a short distance 
beyond the limits of the map, at Red Butte, the Gunnison formation 
comes in. 
Where the Castle Creek fault outcrops in Keno Gulch it has nearly 
its maximum displacement, which is indicated, as shown by sections of the 
Aspen district map, by an upthrow on the east side of about 9,000 feet. 
From this pot the fault is traceable northward to the northern end of 
Aspen Mountain, where it passes under the drift of the Roaring Fork 
Valley, and does not outcrop until it reaches Red Butte, on the opposite 
side of the valley. Near the northern extremity of West Aspen Mountain 
the fault is cut by a tunnel which runs from near the bed of Castle Creek 
eastward through the Triassic sandstones into black Weber shales. The 
amount of displacement indicated by the passage from the Triassic into the 
Weber is very much less than that shown by the contact of upper Maroon 
and granite in Keno Gulch, although the distance between the two points 
‘is very slight. his great diminution in throw is explained by the presence 
of a cross fault with a northeast trend, which has been discovered running 
diagonally across the northern end of West Aspen Mountain at this point. 
This fault is called the Mary B., and although short, has a heavy throw, 
bringing the lower Maroon and upper Weber formations against the 
Silurian, Cambrian, and Archean rocks, which southward from here lie on 
the east side of the Castle Creek fault. The throw of the Castle Greek 
fault, as measured at Red Butte, which is not far from the northern termi- 
nation of the fault on the Aspen special map, is only about 2,600 feet, a 
great decrease from the 9,000 feet at the southern end of the map. This 
decrease in throw is partly owing to the difference in the dip of the beds 
on the east side and on the west side of the fault; for while both have 
a northerly pitch, those on the east side are, on West Aspen Mountain, 
