90 ANNALS NEW YORK ACADEMY OF SCIENCEtS 



The migration of the divide from the crest line toward the eastern 

 margin of the block is most pronounced in the central part of the range. 

 Big and Little Cottonwood canyons are good examples of long and deep 

 valleys pushed back from the western face of the range well toward its 

 eastern margin. The streams which have cut them have a more direct 

 course to the base level of the region than those on the opposite side of 

 the divide. This advantage has enabled them to send the divide east of 

 the center line, where it should be expected to come to rest if the stream 

 grades were equal in both directions (see Fig. 1). 



At present, the Salt Lake Basin is the base level for the drainage of 

 the east slopes as well as the west. The two through going streams, the 

 Provo and Weber Eivers, bring the eastern drainage by long round-about 

 courses back into the Bonneville Basin. No special field work has been 

 done by the writer to determine the conditions which have established 

 these streams in their present courses, but the thought suggests itself very 

 strongly that they began as Big and Little Cottonwood creeks did to cut 

 headward, and being more successful penetrated far enough to capture all 

 of the eastern drainage of the central Wasatch and much of the western 

 Uintas and the plateau region to the north and south of the Uintas. 

 Their headwaters approach each other very closely at the western end of 

 the Uinta uplift and are here separated by a low divide near the southern 

 limit of the Kamas prairie. This divide becomes more pronounced as we 

 follow it westward, rising as a high ridge between Parley's Park and 

 Provo, or Heber Valley, and eventually culminating in Clayton Peak on 

 the Wasatch divide, at the head of Big Cottonwood Canyon. The eastern 

 slope of the Wasatch in this neighborhood is thus drained by two river 

 systems which lead off in opposite directions, at length turning westward 

 and cutting across the Wasatch to the Bonneville Basin. The small con- 

 sequent streams which lead north-east and south-east from the Wasatch 

 divide on opposite sides of Clayton Peak have the disadvantage of a long 

 detour to the base level and have therefore been unable to cope with the 

 streams west of the divide which have a much shorter and more direct 

 course to the same base. 



Structure and hardness of the rocks seem to have exercised only a 

 minor amount of control in the determination of the position of the 

 stream channels west of the divide. In Big Cottonwood Canyon, where 

 the hardest rocks of the region are exposed, the stream seems to have cut 

 indifferently across the beds in a peculiar diagonal fashion in the lower 

 half of its course. In the upper half, it has much less fall and follows 

 the strike of the beds more closely. The rocks here are limestones, shales 



