DENVER & RIO GRANDE WESTERN ROUTE. 



161 



through ridges and spurs of gravel and boulders which constitute a 

 part of the high terrace already mentioned. Near milepost 222 it 

 enters the canyon which Poncha Creek has cut in the hard rocks that 

 compose the mountains. 



A quarter of a mile above milepost 223 the railroad swings to the 

 left in a broad curve around a mass of loose material which has been 

 swept doAvn from a small gulch on the right, and almost immediately 

 after swinging back into its normal position it has to make another 

 curve in order to pass a 

 second mass of similar 

 loose material. Such 

 masses, if fairly flat, are 

 known as alluvial fans, 

 but if steep they are 

 called alluvial cones. 

 The fans in Poncha 

 Canyon are shown in 

 the accompanying dia- 

 gram (fig. 42). On the 

 first fan the radial lines 



occupied by the streams figure 42.— Alluvial fans in Poncha Canyon. The ma- 



4- A'iV 4- 1-' terial that has been swept out of two ravines in the 



at Qllierent times can mountains is spread out in semicircular fans, which 



easilv be seen from the ^'^^ railroad is obliged to pass around in two sharp 



train, as they are marked 



hj straight depressions and by ridges of boulders and angular pieces 



of broken rock which have been swept down b}' the stream. 



The canyon is narrow and V-shaped as far as Mears Junction, 



where it abruptly changes to a rather broad valley with a flat, 

 swampy bottom, which bears all the marks of hav- 

 ing been occupied by moving ice — that is, by a 



DenTe*r226'mUes!^*' gl^cier.^^ At Mears Junction a branch railroad 

 turns to the right and after circling about over the 



main line turns back on the left and climbs the mountain slope to 



Mears Junction. 



"A glacier that occupies a ratlier 

 broad, flat-bottomed valley almost in- 

 variably builds a ridge at its lower 

 end, composed of fragments of rock 

 mixed with clay that it ground away 

 from the rocks over which it passed. 

 All this material is carried on or in 

 the moving mass of ice and is laid 

 down at its extremity in a ridge that 

 is known as a terminal moraine. 



If Poncha Valley had once been occu- 

 pied by ice it should contain some 

 trace of a terminal moraine, although 



a moraine in a narrow valley may be 

 more or less washed away by the 

 stream after the ice has disappeared. 

 A close examination o^ the side of 

 the valley below Mears Junction shows 

 such an accumulation, though it may 

 not be noticed from the moving train. 

 It consists of a distinct ridge of loose 

 material which projects from the east 

 (left) wall of the valley and causes 

 the stream and the railroad to curve 

 to the right in order to pass it. At 

 the point where the railroad rounds 



