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GUIDEBOOK OF THE WESTERN UNITED STATES. 



Poncha Pass, which stands at an altitude of 9,059 feet, and then 

 descends into San Luis Park. Curiously enough, this branch line, 

 in the heart of the Colorado mountains, has one of the longest 

 stretches of straight track in this country — 52 miles without a curve. 

 Poncha Pass is much lower than Marshall Pass, and the traveler may 

 look down into it when he is part way up the mountain. 



Above Mears Junction the character of the A^alley is different in 

 different parts, making the answer to the question whether it was 

 occupied by ice somewhat doubtful.^° 



About 2 miles above Mears Junction the valley is again wide and 

 flat-bottomed and has all the features generally attributed to occupa- 

 tion by ice. In this wide part of the valley the railroad crosses to 

 the east side, where it runs for nearly a mile, and then swings across 

 the creek and returns on the opposite slope. As the road curves 

 across the creek the traveler may see by looking upstream that this 

 branch of the valley is not broad or U-shaped and was therefore 

 probably never occupied by ice. As the train climbs the west wall 

 of the valley many interesting view^s of the features described above 

 come into sight. It turns in around the head of every ravine and then 

 out around every projecting point, as shown in Plate LXIX, 5, until 

 finalh' it comes to the top of the hills that face the valle}'. On one 



the outermost point of the moraine 

 there is a sign marked " Yard limit." 

 Here, then, is a fragment of a terminal 

 moraine, which indicates that the 

 valley above has been broadened and 

 its walls steepened since it was carved 

 by running water, so we must conclude 

 that a great glacier long ago gathered 

 on some of the high peaks that border 

 the headwaters of Poncha Creek and 

 flowed down to this point. 



"" About a mile above Mears Junction 

 the valley changes from a broad, flat- 

 bottomed swale to a narrow rocky 

 ravine down which a glacier could 

 probably not have moved without 

 scouring it and changing its form. 

 Where, then, did the glacier come from 

 that scoured the valley at Mears Junc- 

 tion and built the terminal moraine a 

 short distance below? It is not appar- 

 ent from the train where this body of 

 ice could have originated, but if the 

 traveler could climb some of the low 

 hills on the right he would find that 

 they are composed of gravel and sand, 

 and that instead of being the foothills 

 of the mountain they are only low hills 



that separate Poncha Creek from the 

 wider valley of a tributary on the 

 west, which drains the valley between 

 Ouray and Chipeta peaks and joins 

 Poncha Creek through a narrow gap 

 in the hills just above Mears Junction. 

 It thus seems that the glacier came 

 down this broad valley before the hills 

 on the west side of Poncha Creek were 

 built and that it extended down the 

 main valley to the terminal moraine 

 already described and then retreated. 

 After a long interval it readvanced, 

 though not so far as formerly, and 

 built on the west side of Poncha Creek 

 a terminal moraine which now could 

 be easily mistaken for the normal walls 

 of the valley. Another glacier must 

 have come down Poncha Creek, for the 

 valley broadens a short distance far- 

 ther up and has all the appearance of 

 having been occupied by ice. This 

 glacier came down the valley of the 

 east fork, which has been scoured out 

 until its cross section is a symmetrical 

 U. This glacier originated near Pon- 

 cha Pass and extended only a few hun- 

 dred feet into the main valley. 



