170 



GUIDEBOOK OF THE WESTERN UNITED STATES. 



As both the character of a country and its scenery depend entirely 

 upon the kind of rocks in it and upon their rehitions to one another 

 it is well, perhaps, to outline briefly the essential features of the 

 geology of this region before attempting to describe the valley of 

 the Gunnison. The most striking element of the scenery along both 

 lines of the Denver & Rio Grande Western is the very old granite 

 and gneiss that are exposed in the Royal Gorge, the Eagle River 

 canyon, and the canyon of Colorado River, on the main line, and 

 in the Black Canyon and adjacent parts of the Gunnison Valley. 

 These rocks, which are without true bedding, have been crushed 

 and folded until their structure is generally very complex. After 

 they were crumpled they were planed down by the action of the 

 weather and the streams until their upper surface was fairly even 

 and probably lay near sea level. The land sank somewhat irregu- 

 larly, and on the smooth slopes of the granite were laid down sand 



and gravel, which later 

 became sandstone and 

 conglomerate. Upon 

 these rocks other sedi- 

 ments, which became 

 shale and Ihnestone, were 

 afterward deposited. 

 Some of these rocks are 

 of Cambrian age (see 

 the table, p. ii), and 

 some are as late as Upper Cretaceous. These rocks then passed 

 through many changes caused by uplift and erosion and prob- 

 ably during several epochs were planed down by the streams 

 almost to sea level. The latest movement in the earth's crust has 

 been one of elevation, which lifted the region to its present posi- 

 tion, many thousands of feet above the sea, where the streams are 

 vigorously attacking the rocks and cutting broad valleys or deep 

 canyons, the results of their action depending on the kind of rock 

 they encounter, A stream may at first cut down through relatively 

 soft limestone and shale and may then encounter the massive granite, 

 so that the top of the canyon may be broad and have gentle slopes 

 (see fig. 45), whereas the bottom may be no wider than the stream 

 that has cut it and may have practically vertical walls. The planing 



Hard 



Figure 45. — Section showing the effect of hard and 

 soft rocks on the form of a canyon. 



this part of the basin has been baked 

 and converted to anthracite through 

 the heat generated by the great intru- 

 sions as well as by the surface flows 

 which accompanied the volcanic activi- 

 ties of the past. Both bituminous coal 



and anthracite are mined in this field 

 and find their way to market through 

 Gunnison. The coal output of Gunni- 

 son County rose steadily to a maximum 

 of 640.984 tons in 1910. The output in 

 1918 was 582,905 tons. 



