176 GUIDEBOOK or THE WESTERN UNITED STATES. 



this climb the traveler will notice that the hard rocks through which 



the Gunnison has cut its canyon form a large, high mesa on the 



north (right), considerably higher than the summit over which the 



railroad passes. The shale was once probably at least as hrgh as 



the granite, but it is so much softer that it has been worn away 



until it now lies distinctly below the hard rocks. It would thus seem 



that Gunnison River has gone out of its way to cut its canyon 



through the highest land and the hardest rocks in the region. This 



statement, however, represents merely the conditions as they appear 



to-day, but when Gunnison River first assumed this course it must 



have been flowing on the lowest land or it could not have remained 



there. At that time all this country probably stood at a much lower 



level and was nearly a plain, the hard rocks having been worn down 



as low as the soft rocks. Under such conditions the river found it 



as easy to flow over the granite as over the shale, and so its course 



was not iji any sense abnormal. 



In making the climb to Cerro Summit the traveler will see on the 



south (left) the great mass of Tongue Mesa, which owes its preser- 



A^ation to a protecting cap of hard rock that was originally lava 



which came down from some of the numerous volcanoes in the San 



Juan Mountains, to the south, which are visible from the open 



valley near Montrose. The traveler is now ap- 



Cerro Summit. preaching one of the most arid parts of Colorado, 



Elevation 7,968 feet. ^hcre Water is the most valuable natural re- 

 Denver 335 miles. 



source. In order to irrigate a part of the great 



Uncompahgre Valley, which lies ahead, a long ditch has been dug 



to take water from far up on Cimarron Creek, carry it across Cerro 



Summit at a higher point than the railroad, and distribute it on 



the slopes to the west. Where this ditch crosses the summit it forks, 



and the right-hand branch, known as the Montrose and Cimarron 



ditch, passes under the railroad at the summit and is carried a long 



distance to the northwest to irrigate the broad terrace which the 



traveler will see later. 



From Cerro Summit and the slopes beyond an extended view to 

 the west may be obtained across the broad Uncompahgre Valley to 

 the great Uncorapahgre Plateau beyond. The ride down the slope 

 is not particularly interesting, except as the traveler unfamiliar with 

 the semiarid regions may see what it means to get water onto the 

 land. The effect of irrigation is well illustrated by the verdant ter- 

 race which the traveler may see on the right at an altitude of at least 

 1,000 feet above the middle of the valley at Montrose. Where water 

 is not available the surface is a desert, but where the land is supplied 

 with all the water it needs, it will support a luxuriant vegetation. 



For a long time private enterprise was engaged in irrigating small 

 parts of the Uncompahgre Valley from such streams as Cimarron 



