138 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
observation farther north, a slight syneline in the red beds against the fault 
at this point. On the west side of the fault there outcrops the top of the 
Montana formation, and a short distance farther west comes the contact of 
Montana with Laramie. The throw of the fault at this point is estimated 
at about 5,500 feet. The beds to the west form a comparatively shallow 
syncline, which, so far as is known, is not at all overturned. The Laramie 
sandstones which outcrop along this section show that this fold is really in 
the nature of a synclinal basin, for the dip is toward the center on all sides. 
Section B.—In this section the Lenado fault is shown with a lessened 
throw. This location of this fault was not actually made in the field, but 
by extension from its known outcrop. In these uniform red beds there is 
no possibility of determining accurately any extensive fault. As in Section 
A, the steeply dipping monocline which lies to the west of the granite core 
of the Sawatch changes into a gentle syncline at the Castle Creek fault. 
On the west side of the fault the shales of the Montana outcrop, while 
a very short distance below the Niobrara, Benton, and underlying forma- 
tions are represented as running into the fault. This representatio1 is 
based upon the actual outcrop of these beds a little farther south, where 
the general northerly pitch of the fold brings them to the surface. 
Section c-—This section illustrates the nature of the Castle Creek fault 
and the folding in the beds on both sides of it. Nearly all its features are 
based on reliable data. The slight synclinal fold in the red beds east of 
the fault is shown by outcrops on the flanks of Red Mountain. The 
prominent hill to the west of the fault is Red Butte, and on the steep side 
of this hill the different formations as represented, namely, the top of the 
Triassic, the Jurassic, the Dakota, the Benton, Niobrara, and the Montana, 
are actually found in outerop, lying in the reverse of their usual order 
and dipping to the east. The representation of the rocks west of Red 
Butte is based upon an almost continuous section along the river bank 
and railroad cut. The fold, as shown by these exposures, becomes very 
gentle a short distance west of the fault, so that the beds have only a 
slight easterly dip. A short distance west of this section the dip gradually 
changes so as to form a slight anticline, the western limb of which has a 
gentle westerly dip. 
Pl. XVI is a view taken looking west from near Red Butte. In the 
center of the foreground is the valley of the Roaring Fork, while the ridge 
