Ca AGE aes 2 ial: 
GENERAL DESCRIPTIVE GEOLOGY. 
ASPEN SPECIAL MAP. 
This map incloses an area which has been the most productive of the 
whole district. For this reason it- has been made the subject of more 
detailed investigation than the other areas, and two special maps have been 
constructed on the 300-foot scale—one of Aspen Mountain and one of 
Smuggler Mountain (Sheets XXV and XXVII of the accompanying atlas). 
These detailed maps embrace the most complicated parts of the district, 
and it is in describing them that most of the strneture will be brought out. 
Through the whole central part of the area, ranning from southeast to 
northwest, lies the broad, drift-filled valley of the Roaring Fork. This 
offers a barrier to close investigation, since the valley drift is so thick that 
the underlying bed rock is nowhere shown. Judging from the attitude 
and position of the strata on the north and south sides of the valley, how- 
ever, there is no great complication beneath the valley itself, and the 
actual structure may be inferred with comparative accuracy. It is prob- 
able that the drift is not of exceedingly great depth, and that the actual 
bed-rock valley bottom is a shallow, basin-shaped depression, having a 
broad, curved surface, resulting from glacial erosion. This opinion is based 
on an examination of mine workings which run underneath the valley. 
Parts of these workings have traversed nearly the whole of the distance 
between Smuggler and Aspen mountains, and the comparatively slight 
depth at which they lie shows that there can not be any canyon-shaped 
indentation in the bed rock. The present outline of the valley, therefore, 
has been determined by glacial erosion. 
The whole northern part of the area mapped is made up of red 
Maroon sandstones, which have a uniform westerly dip, forming a simple 
monocline, and which therefore offer no structural difficulties to the investi- 
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