48 GEOLOGICAL SURVEY OF THE TERRITORIES. 



Park. On tlie west side of the Sawatch range we have the valley of 

 the Gunnison, and west of that the sedimentary rocks incline to the 

 westward, unless disturbed by some center force, for the Elk Mountains. 



On either side of the valley small streams iiow into the main channel 

 of the Arkansas from the source to Carton City. These streams usually 

 have their origin at the very crest or water-divide of the two ranges, 

 and in most instances have cut their way through the solid mass to the 

 main river. Many of these streams have numerous side-branches which 

 have also carved out wonderful gorges near the crest of the mountains, 

 giving to these mountain ranges a ruggedness that is almost inconceiv- 

 able to one who has not actually explored them. It is in the study of 

 these gorges that the geologist learns to appreciate the immense results 

 of erosion in giving form to the rocky range of the West. Even yet the 

 power of this force has not been adequately understood, but the wider 

 our range of observation, the greater is our conception of its power. 

 We may safely assert that at some period comparatively modern, 

 10,000 or 15,000 feet of sedimentary beds extended uninterruptedly 

 from the South Park across the intervftl now occupied by the Sawatch 

 range, all of which, but insignificant remnants, have been swept away, 

 while a mass of the granite nucleus, of inconceivable dimensions, has 

 also been removed. The general elevation of the Sawatch range for 

 60 to 80 miles is 13,000 to 14,000 feet above the sea at this time, and it 

 is highly probable that hundreds and perhaps thousands of feet have 

 been removed from the summit. I find it difficult to estimate the 

 extent of the erosion in this region, and can only speak of it in general 

 terms as almost inconceivable to a finite mind. 



From the nature of the interval or valley, the greater number of 

 streams How into the Arkansas from the main Sawatch range. They 

 are quite numerous from the Tennessee Pass to CaQon City; a few come 

 in from the east side, but the drainage tends toward the east or south- 

 east, so that the streams that rise in the Park range and flow into the 

 Arkansas are comparatively few and of little importance. The charac- 

 ter of this drainage is well shown on the map accompanying this report. 



In the last annual report I dwelt with considerable detail on the elfects 

 of glacial action in this valley, and, in this report, I can only describe 

 them in general terms, hoping that the beautiful maps and illustrated 

 sketches by Mr. Holmes will render the story plain to the reader. As 

 an illustration of the effects of glacial action in this valley. Lake Creek 

 might be taken as an example. This stream rises in several branches at 

 the very crest of the divide, forming vast amphitheaters. The signs of 

 past glacial action are not very evident about the sources of their side- 

 branches, and they do not reach higher than 12,000 or 12,500 feet. The 

 summits of the high mountains are often covered with debris of broken 

 rocks, apparently not m uch worn. In some places the tops of the m oun tains, 

 like Mount Lincoln for example, are, with the exception of the extreme 

 summit, covered with a thick covering of earth, filled with rocks more 

 or less worn. The most conspicuous signs of glacial action are seen 

 along the sides of the gorges lower down the streams. In the valley of 

 Lake Creek, the sides of the gorge are worn smoothly for an elevation 

 of at least 12,000 feet or above timber-line, and from 1,000 to 1,500 feet 

 above the bed of the creek. In many places the sides of the gorge or 

 canon are worn so smooth that the surface has the appearance of 

 enamel, and a thin crust usually peels off, which I have hitherto denom- 

 inated a " glacial crust." About four miles above the Upper Twin Lake 

 on the north side of the canon there is a round mass of granite 

 projecting from the side 300 feet or more, and 1,000 feet high, with 



