TOPOGRAPHIC FEATURES 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 hke 
_the Sand Springs salt deposit described on page 16. The divides between these 
1U.S. Geol. Sur., Monog. I (1891). 
