TOPOGKAPHIC FEATUEES OF THE DESERT BASINS. 19 



This early lake and its history have been fully studied by Gilbert/ 

 and the reader is referred to his report for all details. From the pres- 

 ent viewpoint the most important feature of Gilbert's work is the 

 conclusion that the lake acquired and long retained an outlet into 

 Snake River and thence to the sea. During the greater part of the 

 existence and fluctuations of Lake Lahontan, Lake Bonneville was 

 an overflowing lake of normal character and was undoubtedly fresh. 

 This fact alone is sufficient to remove most of the importance of the 

 basin to the present inquiry. The salt contained in the Great 

 Salt Lake, which is the present remnant of Lake Bonneville, is simply 

 that present in the waters of the early lake at the time when 

 overflow finally ceased plus that added in the drainage since that 

 time. However large, it is probably not comparable with that which 

 accumulated in Lake Lahontan. 



The present Bonneville Basin is divided by a low and recent parting 

 into the basin of the Great Salt Lake to the north and the Sevier 

 Basin to the south. Local divides, for the most part recent as well, 

 have cut off a few small basins from the two main divisions. The 

 total drainage area of the Bonneville Basin during the Lahontan 

 period was 57,960 square miles. 



THE GREAT SALT LAKE BASIN. 



This basin is the central remnant of the original Bonneville Basin and includes the 

 valley of the Great Salt Lake and all valleys now tributary thereto. The north-south 

 trend of ranges and valleys, though here less marked, than in the Lahontan Basin, is 

 still quite distinct and the long parallel ranges form islands in the present lake or 

 divide the trough valleys which drain into it. As in the Lahontan region, des- 

 iccation and stream decay have reduced the vigor of the rivers which once occupied 

 these valleys and many local playas and marshes have been produced. The chief 

 present tributaries of the Great Salt Lake are the Bear River from the north, the 

 Weber River from the east, and the Jordan River and Utah Lake drainage from the 

 south. Having their sources in well- watered highlands, these streams have retained 

 a considerable measure of their former vigor and are, indeed, largely responsible for 

 the persistence of the Great Salt Lake itself. There was once another considerable 

 tributary entering the lake from the southwest through the Snake Valley. This has 

 entirely decayed and the Snake Valley and some of its tributaries have acquired 

 small local playas and brackish marshes of very recent origin. The obstructions to 

 drainage out of the valleys are not considerable even now, and would be overcome 

 and removed by a very moderate increase in average rainfall. 



The Great Salt Lake has a present area of about 2,200 square miles and a maximum 

 depth of approximately 50 feet, being somewhat variable in both dimensions. It 

 is extremely saline. West and southwest of the present lake is the Great Salt Lake 

 Desert, a broad playa-like flood plain but recently abandoned by the lake and cover- 

 ing an area of over 3,000 square miles. Innumerable local depressions in this plain 

 have become small and shallow areas of inclosed drainage and salt concentration and 

 have come to contain greater or lesser deposits of common salt formed essentially like 

 the Sand Springs salt deposit described on page 16. The divides between these 



1 U. S. Geol. Sur., Monog. I (1S91). 



