62 GEOLOGICAL SURVEY OF THE TERRITORIES. 



with thick grass far up on the sides, and even on the ridges between the 

 streams, so that as a grazing region it must be excellent. At a period 

 not far distant, this i^ortion of Colorado must be settled to some extent 

 by a pastoral people. 



We find, therefore, that from this crest or divide two great plateaus 

 descend in opposite directions, forming, in the aggregate, a huge anti- 

 clinal, cut deeply by the numerous streams that rise on the div^ide. This 

 inclination, on the one side to the south or south west, and on the other to the 

 north or northwest, is interrupted here and there by dikes of more mod- 

 ern origin probably than the granite nucleus of the crest. Sometimes 

 these dikes disturb the sedimentary beds, reversing their dip or produc- 

 ing great faults, and again they penetrate some fissures without chang- 

 ing their position. In the red sandstones that wall in the valley of the 

 little branch just east of Teocalli Creek is a very interesting dike of the 

 gray igneous granite, with a strike about northeast and southwest. It 

 passes across a little fork just at its junction with the main branch, and is 

 most distinctly seen at the summit of the wall on the west side. The ig- 

 neous m after seems to have flowed up through the fissure without disturb- 

 ing the contiguous strataof Triassi c sandstone, which are nearly horizon- 

 tal, and therefore there could not have been a great display of force. It is 

 probable that the origin of this dike is synchronous with the main 

 nucleus, for the materials are apparently the same. As the little mount- 

 ain-stream flows across the dike its greater hardness has formed a beau- 

 tiful cascade. We might dwell long on the great varieties of beautiful 

 forms which the crystal mountain-water assumes as it flows down the 

 rugged gorges. A dike about 50 feet wide passing across the channel, 

 the greater local hardness of the sedimentary rocks, or a reverse uplift, 

 will produce cascades of remarkable beauty. 



Mr. Jackson, the photographer of the survey, has preserved a number 

 of scenes from this region, and in each one of these almost numberless 

 gorges that extend from the mountain-crest far down to the Green and 

 Colorado Eivers, two hundred miles or more, there could be found 

 many of these charming water-falls. Scenes of great beauty meet the 

 eye at every step, and yet the area is so large that we must have left 

 unseen by any member of the party views of even greater beauty and 

 value. It is probable, however, that our determinations of the geologi- 

 cal structure of the country passed over are substantially correct. 



A great portion of the surface is covered with a thick forest of pines. 

 In the autumn the fires not unfrequently sweep through these forests, 

 destroying their vitality, and soon the winds prostrate them in every 

 direction, forming a net-work over which it seems almost impossible for 

 our animals to pass. These difficulties are met with in the mountainous 

 portions of the West ; and in Montana, 1871 and 1872, our work was 

 very much impeded, and in many cases arrested, by the intricate masses 

 of fallen timber. The Elk Mountains are not more difficult of explora- 

 tion on that account than the Sawatch range. In our description of the 

 Mountain of the Holy Cross we shall allude to this fallen timber again. 

 It is difficult for any one not familiar with this country to comprehend 

 how important an element of hinderance this is in making a detailed 

 exploration of the country. Yery frequently we are obliged to cut our 

 path through the logs for great distances, making only a few miles a day. 



At the head of Teocalli Creek is a high mountain-peak which we 

 named Whiterock, from the fact that a seam of white or light gray 

 igneous rock, 60 feet wide, passes through the middle of the summit 

 vertically. The material is quite soft, disintegrating into moderately 

 coarse sand. The rocks composing the mountain are quite varied in 



