248 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
several of these there are small ponds of standing water, which are being 
rapidly converted by encroaching vegetation into swamps. Throughout 
this soft lake sediment the river has carved very beautiful meanders, as 
may be seen in the accompanying plate (Pl. XXXVI). These meanders 
have met and cut off repeatedly, some of the cut-offs being complex, 
double, or triple, and in the plain on the opposite side from that where the 
river now is can be seen the scars of old meanders, showing that the 
stream has swung across the whole valley and worked over the sediments 
pretty thoroughly since the Glacial era. 
Below the terminal moraine which is found just above Aspen the valley 
widens out into a broad, level plain, through which the streams of Roaring 
Fork, Castle, and Maroon creeks have cut post-Glacial gorges. The glacial 
material in the bottom of this valley is probably in places several hundred 
feet thick, and is composed of coarse morainal material, which has been 
worked over by water action so as to possess a rude stratification. In some 
localities there is also a deposit of fier, sandy material, more perfectly — 
stratified. On the sides of this valley, as is best seen on Red Mountain, 
are broad terraces carved in the bed rock, but sometimes strewn with glacial 
material. On Red Mountain these terraces are chiefly two in number, and 
on the upper one some agriculture has been carried on. Here the terraces 
are carved in the red Maroon sandstones, but farther down the valley, on 
the west side of Castle Creek fault, they are well marked in the soft Cre- 
taceous rocks. These terraces must have formed since the disappearance 
of the main ice sheet, for if they had existed previously they would have 
been scored away by the glacier. The highest and most strongly marked 
terrace on Red Mountain is 400 or 500 feet above the present valley, and 
so can not be accounted for by ordinary stream action. ‘The terraces, there- 
fore, probably indicate the shores of a long, narrow lake, which filled up the 
Aspen Valley near the close of the Glacial period. The same broad valley 
is continuous for several miles downstream below Woody Station. Near 
this point a prominent hill, capped with basalt, juts out into the valley, so 
as to reduce it to comparatively narrow dimensions. This hill must have 
constituted a continual barrier to glaciers, and here toward the close of the 
Glacial period there may have accumulated a wall of ice or a moraine 
which backed up water so as to form alake. The terraces on Red Mountain 
are shown in Pl. XX XVII. 
