92 



GUIDEBOOK OF THE WESTERN UNITED STATES. 



The boulders are distributed in a fan-shaped, delta-like area, show- 

 ing that on emerging from the canyon the current that transported 

 them swung first to one side and then to the other 

 Brown Canyon. ^^ ^j^-g ^^.^^^ ^^j^^ ^^^ ^^d, naturally, as it reached 

 Elevation 7,324 feet, ^j^g open countrv, lost its transporting power and 



Denver 222 miles. , ^,. , ",^1 ,.• p-o"' r^ 



dropped its load. Ihe station ot rsrown Canyon 

 is at the point where the stream emerges from the canyon which it has 

 cut in the hard granite. (See fig. 20.) 



SAWATCH RANGE S *■ 







S§ 



'}:^^m: 



FiGUHE 20. — Ideal section from Sawatch Range to Brown Canyon, showing the deep 

 gravel filling in the old channel of the Arkansas. 



The canyon is not straight but, as shown in figure 20, winds about 

 in the hard rock, and at one place, half a mile beyond milepost 223, 

 it touches the very edge of the granite mass, so that the recent cutting 

 of the stream has exposed the gravel filling on 

 the west (left; see fig. 21), showing conclusively 

 that when the river established its present course 

 it was flowing on gravel of fairly uniform com- 

 position and that the slope of its bed was so 

 slight that it meandered over a broad, flat- 

 bottomed valley in great well-rounded curves. 

 When the uplift came that gave it power to 

 trench its valley, the stream cut directly down- 

 ward in its established course, and although in 

 some places its couree was on granite and in 

 other places on gravel, the river persisted in 

 following that course even to the present day. 



The point of hard rock which the traveler may 

 see on the left before he reaches the rift in the 

 canyon wall is a large dike, which was once 

 molten rock that was forced up from below 

 through some great fissure in the crust of the 

 earth. It is now solidified into a mass more 



resistant than the surrounding granite, so that it stands up as a nearly 



vertical wall. 



At some places in this canyon there are great granite boulders, 



around which the water surges furiously when the river is above the 





M-WM 



mm 



FiGCEE 21. — Sketch 

 map of Brown Can- 

 yon, showing its rela- 

 tion to the granite 

 and the gravel. 



