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120 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
gradient. The hills on both sides of this valley are largely bare of vege- 
tation, so that the outcropping strata of red or brown sandstone give a 
characteristic hue to the landscape, which can be seen at great distances. 
Pl. XIV is a view of the northern side of this Lenado Valley in the 
sandstone district. It is taken from the top of the hill on the south side of 
the valley, at a point about 1,500 feet above the creek, and looks across 
the valley and up one of the side gulches. On the left of this side gulch 
are the perfectly bare outcrops of westerly dipping strata of Maroon sand- 
stone. This type of valley continues until the stream emerges from the 
red sandstones into the comparatively flat and much softer Cretaceous rocks. 
Where the stream flows through these, as it does for several miles above its 
junction with Roaring Fork, the rocks have been worn down to nearly the 
level of the stream bed itself, so that there is no very deep valley. 
FAULTS. 
Silver fault—The contact. between the Weber shales and the Leadville 
dolomite is, throughout the whole of the area shown on this map, appar- 
ently a true fault contact, for it is characterized by a brecciated zone and 
by evidences of slipping in the formation of polished and striated surfaces 
and in little slip faults parallel to the maia contact. These features are, of 
course, best exposed in underground workings, and are especially well 
shown in the Clark tunnel and in the Bimetallic tunnel. As far as the 
evidence on this map alone goes, the fault seems to be strictly parallel to 
the bedding. In all places the formation lying above the fault is the 
Weber, and that below is Leadville dolomite. There is not found in this 
area, so far as observed, any of the blue foraminiferal limestone which lies 
above the dolomite at the top of the Leadville formation on Aspen 
Mountain and in Tourtelotte Park. 
There may be made three suppositions to account for its absence: 
(1) That the blue limestone referred to was a local deposit, which was not 
formed at all in this region; (2) that the limestone was deposited over this 
area originally as over the area farther south, but that during the erosion 
interval between the Leadville and the Weber formations the blue limestone, 
and probably a part of the underlying dolomite, were worn away, so that 
the Weber shales were deposited directly upon the dolomite; (3) that both 
the dolomite and the blue limestone existed in this district up to the time 
