108 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
DESCRIPTION OF SECTIONS. 
On account of the extremely complicated structure in the Tourtelotte 
Park area, it was necessary to construct many sections in order that the 
geology might be made reasonably clear. (See Atlas Sheets XIII, XIV, 
XV.) Inasmuch as the axis of the main fold runs parallel to the main 
ridge in Tourtelotte Park, cross sections were constructed at right angles 
to this ridge, and six east-west sections were finally selected for publica- 
tion. Another series of sections was constructed at right angles to the 
others. Thus the two sets form a sort of rectangular grating, as shown 
on the map (Atlas Sheet XII), and by taking the east-west sections 
together with the north-south ones a comparatively clear idea of the 
structure of the district may be obtained. All the east-west sections look 
toward the north, and all the north-south sections toward the east, a 
system which has been adopted throughout this report. 
Section a—At the western end of the section the Maroon beds are over- 
turned at the surface, while with depth the return of the strata to their 
normal succession is seen. The overthrown fold rests against the Castle 
Creek fault, and the curved form of this fault, which has been inferred 
from its change of dip toward the south, is shown in the section. On the 
east side of the fault is the Archean granite, showing how great the throw 
has been at this point. Toward the east granite outcrops in the section 
continuously nearly to the Saddle Rock fault. Just west of this fault, how- 
ever, there comes in, probably in its normal succession above the granite, 
the Cambrian quartzite, which contains in its lower part a thin sheet of 
diorite. These beds dip to the east, forming a part of the west limb of the 
Aspen Mountain syneline, and they are successively downfaulted to the east 
by the Saddle Rock and the Sarah Jane faults. These two faults are shown 
in the section as cut and displaced by a lower fault. This belongs to the 
east-west system, but on account of its dip cuts the plane of the section in 
somewhat the manner represented.’ This east-west fault has a slight down- 
throw to the south, and is called the Dixon fault, from its being best shown 
in the mine of that name. Last of the Dixon fault is shown a very shallow 
syneline, the axis of which lies nearly under the ridge of the hill. This 
1Tn studying the sections care should be taken to remember that the angle of the faults as 
plotted is not always the actual dip, for the angle represented is that which the fault plane makes 
with the plane of the section. Thus a fault which has a dip of 70 or 80 degrees may appear as a 
horizontal line in a section parallel to its trend. 
