HATDEN.J GEOLOGY FKOM ELK MOUNTAINS TO MIDDLE PAEK. 75 



There are great numbers of side-canons formed by tlie little streams 

 that have their origin high up in the Blue Eiver range. 



We find here two forms of river-channels or caSons; one nearly 

 parallel with the lines of fracture, monoclinal, as I have called them for 

 want of a better term, and the other at right angles to the ridges and 

 carved out of the solid mass. In the first class the drainage must have 

 commenced in a fracture, but erosion has been the main agency in the 

 formation of the caSou ; in the latter, the channel is in most instances 

 entirely due to erosion, the strata corresponding in position to a greater 

 or less extent on both sides. Between the northwest end of the Sa watch 

 range and the Blue Eiver range there is an immense mass of sedimen- 

 tary strata crushed in between the two great axes of uplift as it were, 

 forming a sort of synclinal. The beds incline witb tolerable regularity 

 from the Sa watch toward the northeast, though the dip varies from 10° 

 to 50° or 60°. Sometimes the dip, close up to the margin of the mount- 

 ain-summits, is nearly vertical, but in a few instances great masses of 

 strata seem to have been carried up on the underlying granite, produc- 

 ing extensive faults, as seen in the Park range. But the elevation of 

 the Blue Eiver range seems to have been somewhat peculiar, the force 

 having acted nearly vertically, so that on the west side of the- range the 

 sandstones jut up against the sides with but a slight dip. Following 

 up one of the branches of Eagle Eiver, which rises high up in the west 

 side of the range and carves a channel across the uplift, we find the in- 

 clination from Eagle Eiver extending eastward for about six miles, 

 where there is a sort of sag or depression and a reversed dip from the 

 Blue Eiver range. 



Erom Eagle Eiver Valley we made a side-trip to the Blue Eiver 

 range, ascending the highest peak, Mount Powell, by way of one of the 

 little streams that rise on the west side. There is no name for this little 

 stream, but it reveals in the sides of its canon a thick group of the 

 brick -red sandstones. The caiion is carved out of the solid mass, from 

 the amphitheater higb up on the west side of the range, down for sev- 

 eral miles through the sandstones at right angles to the inclination of 

 the strata. The sides of the caiion are 1,200 to 1,800 feet high on either 

 side, and rise in abrupt steps, depending upon the texture of the differ- 

 ent layers of sandstone. The valley varies from one-eighth to one- 

 fourth of a mile in width, and rising up in various places in the bottom 

 are the worn edges of tbe sandstones. At one place they appear above 

 the surface completely across the valley, showing most conclusively 

 that this gulch or caiion is entirely one of erosion. 



On the west side of the Blue Eiver range the sandstones lap on to 

 the granite nucleus, so that the usual valley of separation is wanting ; 

 or, in other words, the ridge of sandstone lies so close to the mountain- 

 side as to be continuous with it. As far as one can see from the summit 

 of Mount Powell, north and south, these sedimentary beds hug the 

 west side of the range with a very moderate dip, not usually over 10°. 

 There are numerous streams that flow from the west side of the range 

 and cut deep channels, which expand or contract, depending upon the 

 texture of the rocks through which the erosive agent has wrought its 

 way. 



Everywhere there are more or less proofs of old glacial action. The 

 moraines are common, but not on such a scale as we have already de- 

 scribed, on either side of the Sawatch range. In the amphitheaters, as 

 well as in the upper portion of the valleys where the granites are ex- 

 liosed, we find the same rounded glaciated masses which were so con- 

 spicuously shown near the Mountain of the Holy Cross. 



