160 GUIDEBOOK OF THE WESTERN UNITED STATES. 
14,179 feet) on the right. The lower slopes are more or less covered 
with timber, which becomes scanty as the height increases, until 
finally even the stunted balsams disappear (see Pl. XLV, A, p. 92) 
and at the summits there is nothing but wind-swept rock. The slopes 
vary in color according to the light, at times being rich red or bright 
yellow in the strong sun- 
light and at others deep 
purple or a steely blue. 
The color of the lower 
slopes depends largely on 
the vegetation, but that of 
the upper slopes depends 
on distance and light. In 
spring and summer the 
shrubs and trees present 
many shades of green and yellow, but they are most brilliant in Sep- 
Fieurk 41,—Formation of a gravel terrace. 
tember, when the first frost touches them and tinges them with red _ 
or gold. 
The railroad follows the valley up to the village of Poncha, where 
the road to Marshall Pass turns to the south (left), but a branch 
Poncha. 
keeps straight ahead to the mining town of Mon- 
Elevation 7,480 feet, arch, 15 miles distant, where it ends. From Monarch 
Fopulstion ba the principal highway between Salida and the Gun- 
a 
ngs) 3 
Denver 220 miles, 
nison Valley is an automobile road across the range. 
The Marshall Pass line turns to the south in a 
broad curve and begins to climb the range. For half a mile it cuts 
the material would fill this pond and 
form a plain that would stretch ed 
e 
at ¢, far above bedrock. If the stream 
then succeeds in cutting through the 
dam of lava it quickly trenches the 
sand and gravel laid down in the pond, 
except the parts that lie at some dis- 
tance back from the middle of the 
channel. The result is shown by sec- 
tion B, in figure 41, in which the 
stream has cut the trench d-f-e, leav- 
ing d@ and e as terraces on the sides of 
have had such an origin, except that 
the ponding has generally been due 
not to lava flows but to the sinking 
ch 
water flowing in the stream, and al- 
though at first thought this may not 
seem to be comparable to the lava flow 
in its effects, a careful study will show 
that the carrying power of a stream 
is directly affected by its volume and 
grade, so that if its volume or its 
grade is reduced its carrying power 
will be reduced—it will not be able to 
sweep along the boulders that it had 
before handled readily. A stream thus 
reduced in volume or grade silts up its 
bed, and if later its flow or grade is in- 
creased it cuts away ‘all this material 
except the remnants that form terraces. 
