GEOLOGICAL SURVEY OF THE TERRITORIES. 147 



CHAPTEE III. 

 FROM COLORADO CITY TO SPANISH PEAKS. 



Looking toward Colorado City from tlie south, it would seem that the 

 rift, or pass in the mountains through which Fountain Creek (Fontcmie qui 

 bouillej flows, formed a line of separation between the ranges of moun- 

 tains ; that the north range died out suddenly, in its southern extension, 

 at this point. There is a plain valley of separation visible. 



A little below the city, the ridges, or "hog-backs," flex to the southwest 

 and jut up against the base of the mountains and disapjDear. These 

 mountains are of that abrupt tjjie which I have before referred to ; that 

 is, they form the west portion of an anticlinal, the east half of which is 

 not visible. These mountains I call abru]3t because the summits are 

 formed of projecting masses of rocks leaning over eastward beyond the 

 base, where this class of mountains occur. The sedimentary beds jut up 

 against the base without any special dip, or, at any rate, there is no wide 

 belt of upheaved ridges, but the most recent formations in the region 

 lap on to the base of the mountains. The immediate eastern range north 

 of Colorado City, and the one south, are, it seems to me, fine illustrations, 

 of this statement, and I am more and more convinced that it is correct. 



Passing over that jjortion of the country south of Colorado City, be- 

 tween Fountain Creek and the base of the mountains, the ux)per creta- 

 ceous beds, ivTo. 4, are quite extensive, with BacuUtes ovatus and Inoce- 

 ramus in great quantities. The cretaceous rocks are well shown, espe- 

 cially the upper portions, in the valley of Fountain Creek, from Colorado 

 City to its junction with the Arkansas Eiver. A number of species of 

 fossils, especially shells- and saurian remains, are found quite abundantly. 

 There are also scattered about, remnants of the Monument Creek group ; 

 and below Colorado City these recent tertiaries occupy considerable area, 

 and reach a good thickness. 



But the most conspicuous feature that we observe is the vast quan- 

 tity of granite boulders scattered over the surface near the base of the 

 mountains, extending at least to Fountain Creek. They diminish in size 

 as they recede from the mountains, and are not much worn. 



About ten miles below Colorado City the "hog-backs" appear again 

 faintly in the form of one or two narrow ridges. The lofty mountain, 

 rising u\) abruptly two thousand or three thousand feet above the base, 

 stops suddenly, and lower granite ridges, with their eastern sides sloping 

 and covered with grass, come in. 



About fifteen miles south of Colorado City a little wooded stream that 

 issues from the mountains seems to form the northern limit of a high 

 ridge, which at first extends from the foot of the mountains in the forni 

 of a pretty high "hog-back," but soon passes down southeast into the 

 variegated sands of the Monument Creek group. From this point to 

 within a few miles of the Arkansas, the recent tertiary beds are quite 

 prominent. The mountains seem also to be composed largely of igneous 

 rocks. 



About fifteen miles south of Colorado City the road to Canon City 

 passes among the upheaved ridges which form a very narrow belt at 

 first, but continues to increase in width until we come to the valley of 

 the Arkansas, where they spread out to a great breadth. 



At the point south of Colorado City where the upheaved ridges reap- 

 pear, the mountains begin to break up into low hills and fragmentary 

 ranges which continually run out in the plains. Indeed, the entire 

 eastern flank of the mountains, as we pass from the north southward, 



