100 GUIDEBOOK OF THE WESTERN UNITED STATES. 
The canyon which the railroad enters at’ milepost 252, although 
short, is rather picturesque and has a steep granite wall on the east 
side, against which the stream has been crowded by the glacial drift 
that was brought down Pine Creek from the west. Through this nar- 
row passageway the river boils and surges over and around the great 
boulders that obstruct its course. The glacial drift is first seen as the 
railroad bends sharply to the left, a little above milepost 252. At 
first sight it may not be apparent that this material differs from the 
gravel that composes the terraces below, but careful inspection will 
show that the boulders are all composed of fresh rock and that their 
surfaces are generally smooth and unweathered. It also shows that 
many of them are scratched, or striated, as the geologist calls it, as 
they were brought down by the glacier and held like a giant rasp 
against the rocky sides of the canyon. Such scratches are regarded as 
reliable indications that the boulders have been transported by ice. 
At milepost 254 the railroad crosses the river to the east side and 
follows the east bank for a long distance. In some places the west 
wall of this canyon is composed of granite and in others of glacial 
drift, but the traveler on the railroad train can not determine the 
reason for the presence of the drift until the train has rounded the 
broad curve above the bridge and he is able to see on the west (left) 
up the open valley of Clear Creek. As this view up the creek, 
which is well worthy of attention, can be had only while the train 
is running a quarter of a mile the traveler who wishes to see it clearly 
‘should be ready to look this way as soon as it becomes visible. By 
looking up Clear Creek he will see that the stream issues from the 
high mountains in a canyon that has a broad U-shaped cross section, 
and that outside the mountains it is walled in by parallel ridges 
of broken rock and gravel that was deposited or heaped up by the 
ice. Such ridges along the sides of a valley are called by geologists 
lateral moraines. The moraine on the north side of Clear Creek, 
at the point where the stream emerges from the mountains, is 700 
feet high, and its front, which is composed of loose material, is as 
steep as it can stand. The moraines run parallel with the creek until 
they reach the river, where they curve around and nearly meet, 
forming a loop that originally inclosed the mass of ice. The glacier 
not only reached the river, but at times pushed a little farther and 
heaped up the loose gravel on its east side. Naturally when such 
a glacier melts away the part of the valley it occupied will be left 
relatively free from boulders, and it therefore generally forms a 
swampy tract or a lake surrounded by a ridge or ridges of gravel. 
The stream quickly cuts a trench in this bounding ridge, so that the 
valley is thus drained through a narrow cleft. The users of water 
far down the Arkansas have taken advantage of this natural site 
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