142 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
of the valley, where Castle Creek runs into Roaring Fork, is the point of 
West Aspen Mountain. The rocks on this mountaim which are shown in 
the picture are Archean, Silurian, and Cambrian, and the Castle Creek fault 
runs along the base of the mountain, parallel to and just east of Castle 
Creek. The whole of the left-hand side of the valley is of bright-red 
Triassic sandstone, which has a dip of 50 degrees or so toward the east, 
forming part of the overturned fold which lies against the fault. From this 
point the fault pursues a comparatively straight course, crossing the Roaring 
Fork Valley and running across the southeastern end of-Red Butte. 
Pl. XVIII is a view taken from near Red Butte on the northeast side 
of Roaring Fork. The river and the butte occupythe foreground. In the 
center of the picture is the flat Roaring Fork Vale. y, with Aspen at the left 
side. The even terrace which the river has carved in post-Glacial time is 
very well seen. In the background is Aspen Mountain, the projecting 
ridge of West Aspen Mountain just left of “he center. The woody gulch 
on the right side of Aspen Mountain is Keno Gulch, across which, as 
described, the Castle Creek fault runs. In this picture the Castle Creek 
fault runs from Roaring Fork, across the southern point of Red Butte, 
south-southeast for 14 miles, and just to the right of the smokestack on the 
lixiviating works, then swings to the south and crosses Keno Gulch, and so 
on out of the area represented on the plate. 
From Red Butte the fault continues northward over the gently sloping 
western side of Red Mountain to Woody Creek. Pl. XIX shows this part 
of Red Mountain. The view is taken from the west bank of Maroon 
Creek at Red Butte. The sharp ridge in the foreground is the north- 
western extension of the butte, and along this ridge the outcropping beds 
of the Triassic, Gunnison, and Lower Cretaceous formations dip steeply to 
the east and are overturned, as shown in Section C. The ridge separates 
Maroon Creek from the Roaring Fork, and the two streams unite just to 
the left of the pictured area. The fault runs diagonally across the pictured 
area from behind the ridge of Red Butte at the right to near the western 
edge of the horizon, which it crosses at about the point where the short, 
level outline changes to a slope. Along this mountain side the fault is 
often obscured by the heavy covering of glacial drift, but its course is 
made sufficiently clear by occasional outcrops, which show that it separates 
the Triassic sandstones on the east from the Montana shales on the west. 
