358 C. R. KEYES OROGRAPHIC ORIGIN OF LAKE BONNEVILLE 



PpvE-lacustkine Belief op Bonneville Kegion 

 early quaternary drainage 



111 Lis iiirluctive picture of the geograiiliic cycle developing imcler con- 

 ditions of arid climate, Prof. W. M. Davis depicts the withering away of 

 the old pre\ailiiig lines of drainage and the conversion of all stream val- 

 leys into ^\ate^k'ss desert })hiins. In the main this trans rormation is 

 regarded as taking ])lacc so early in the cycle that only iiiider rare cif- 

 (aimstances would any ^estiges of the ancient stream features he pre- 

 served. If ever trace Avere left ot'^this early stage, it appears that in the 

 long Great Salt Lake basin there might be one. 



The broader features of tlie pre-arid drainage of the region lying be- 

 tween the central chain of the Eockies and the Sierra Nevada are not so 

 very difficult to fancy. A few of the larger watercourses having extra- 

 limital heads survive all the viscissitudes of climate and diastrophism. 

 In the cases of others all vestiges ha^'c long since disappeared. There are 

 some of whicli shadowy traces might still persist. 



Between the Eocky Momitains and the Wasatch Eange the master- 

 streams doubtless occupied much the same positions that the large 

 tlirough-flowing rivers do now. The Grand and the Green rivers were 

 the main streams which, uniting to form the Colorado Eiver, ran throngh 

 to the sea. Under originally moister climatic conditions it would be ex- 

 pected that the Colorado Eiver would receive at least one otlier large 

 tributary — one from the west side of the Wasatch Eidge. Possibly still 

 another large watercourse also helped to drain the extreme western parts 

 of the Great basin. 



ANCIENT YIRGEN MASTER-STREAM 



The possibility of a large river having once occupied tlie succession of* 

 valleys on the west side of the Wasatch Eange seems never before to have 

 been carefully considered. The inducti\e reasoning conducted by Pro- 

 fessor Davis in support of the idea of streams formerly traversing many 

 of tlie long liolsons of the arid regions is yet so new that its necessary 

 consequences Ivan a not yet been Avidely tested in the field. 



In most deserts the especial forces of aridity La^■e acted so long and so 

 vigorously that all traces of any former stream systems, if they ever ex- 

 isted there, have long since disappeared. In the instance of a possible 

 master-stream on the west side of the Wasatch IMountains the conditions 

 are peculiarly favorable to the detection of some direct testimony bearing 

 on its former presence. Moreover, there is the Green-Colorado Eiver to 

 aid in determining what features to expect. The latter stream is remark- 



