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 tliis nar- 

 row passageway the rixev 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 vip 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 originalh^ 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 sit© 



