PRE-LACUSTRINE RELIEF OF BONNEVILLE REGION 361 



features connected with other large waterless trihiitaries of the Grand 

 Canj^on region. 



The ]\Iiiddy-Virgen Canyon conld only liave been excavated hy a stream 

 at least as large as tlie Snake River of Idaho or the Green River before 

 it unites with the Grand River. It seems impossible for such a diminu- 

 tive waterway as that now flowing in the canyon to have accomplished 

 such an amazing amount of work. 



TYPICAL TIIROUGH-FLOWIXG STREAM OF DESERT 



If before the lake period the long Bonneville Valley was occupied by a 

 river the waters of which flowed through to the sea, there is added to this 

 small and special group of streamways another example. tStarting as a 

 considerable stream fully as large as the present Green River is in the 

 IJintas, ]3robably it received along its course little or no augmentation to 

 its waters and entered the Colorado River through a long, deep canyon. 

 Doubtless, also, it was larger when it entered the Bonneville Valley than 

 when it left it. In all respects it was a typical through-flowing stream of 

 the desert, heading extralimitally and taking no part in the relief devel- 

 opment of the country through which it passed. Although smaller than 

 any of them, it was a fit companion of the Rio Colorado, the Rio Grande, 

 tlie Rio Pecos, and the Nile River. 



This old Virgen River stands for a distinct stage in the natural course 

 of elimination of all waterways through gradually increasing aridity. 

 Had it been somewhat larger it could have readily overcome the orogenic 

 harrier which began to arise across its path, and had its extralimital 

 headwaters not been diverted it would have remained today a typical 

 large desert stream flowing through to the ocean. Had it failed to sur- 

 mount its growing southern Ijarrier and had its lieadwaters not been cut 

 off, Lake Bonneville in its fullest development woidd doul)tless have per- 

 sisted to tlie present time instead of only its shallow last remmint that 

 we call Great Salt Lake; hut iiiuisual viscissitudes defeated all its efforts 

 to remain a through-liowing river. Depedali/ation, ('()r])oral inllation. 

 and decapitation are unusual misfortunes for rivers to undergo. Tliey 

 fall to the lot of very few streams. Possibly the old Virgen River is the 

 sole representative of its kind, 



IIFA'RM'V OF SXAKF UIVER. CUANNRL 



The most striking feature connected witli Snake Ri\er is the general 

 absence throughout its course in southern Idaho of any marked valley. 

 It flows over the la\'a plains in a cbannel that is often without appre- 

 ciable banks. WbeucNcr it has beiimi to corrade a notic(nd)le trenc-h the 



