ASPEN DISTRICT MAP. 137 
The intersection of these two systems of faults has produced many 
blocks, and, in the process of uplifting, these blocks have often been moved 
one upon the other in such way as to result in a very complicated structure. 
The portion of the district which lies to the southeast of the areas of 
the detailed maps which have already been described is entirely in gran- 
ite and without important structure, so far as the present study goes, and 
so need not further be dwelt upon. It is all glaciated and in places thickly 
covered with morainal deposits. That portion which lies to the northwest 
of the special areas includes, besides the formations already described, the 
upper part of the Triassic, which consists of massive deep-red sandstones, 
the sandstones and variegated shales of the Gunnison formation, and the 
heavy sandstones or quartzite of the Dakota, which is throughout this region 
the lowest member of the Cretaceous. Above these comes the Colorado 
formation, which is capable of division into its two members, the Benton 
and the Niobrara. Above the Niobrara comes the Montana formation, con- 
sisting of a great thickness of black shales, and above this the lower part 
of the Laramie, which is the youngest pre-Glacial formation shown in the 
district. These formations are crumpled into folds, in part overthrown, in 
the immediate vicinity of the Castle Creek fault, but these die out in a sur- 
prisingly short distance westward, the beds assuming a horizontal or gently 
dipping attitude. The chief feature in the folding immediately west of the 
fault is a northerly pitching syncline. In the central part of the district 
this syncline is closely compressed and overturned, while in the northern 
and southern parts it is open. The general structure of this fold and its 
relation to the Castle Creek fault may best be seen from the study of the 
accompanying sections. 
DESCRIPTION OF SECTIONS. 
(ATLAS SHEET VII.) 
Section A——The eastern part of Section A has already been shown on a 
larger scale in a cross section through the Lenado maps, where the steeply 
dipping Cambrian and Silurian rocks are seen to lie upon the uplifted 
granite. These are cut off by the Lenado fault, which brings the Weber 
formation in outcrop against the Parting Quartzite. Westward from this 
outcrops the whole of the Maroon formation, which is overlain by the 
Triassic. The Triassic is continuous from the point of its contact with 
the Maroon to the Castle Creek fault. There is probably, as is shown by 
