26 SNAKE RIVER PLAINS OF IDAHO. [bull. 199. 
bordering plains. A possible exception to this statement is furnished 
by Malade River, which would perhaps reach the Snake in summer if 
its waters were not used for irrigation. The fact that Snake River 
does not receive a perennial tributary from the north throughout the 
portion of its course just indicated is the more remarkable when it is 
remembered that this part of its basin is largely occupied by lofty 
mountains, on which the mean annual precipitation is probably greater 
than on the less extensive and lower mountains, in which the streams 
coming from the south, such as the Portneuf, Salmon, and Bruneau, 
have their sources. The principal reason for the absence of surface 
tributaries to the Snake on the north is that broad lava plains intervene 
between it and the mountains, and all of the water which flows down 
to the plains or falls on their surfaces is either evaporated or lost in 
the cellular and fissured lava. 
Some of the streams flowing southward from the mountains of cen- 
tral Idaho, as Camas Creek and Little Lost and Big Lost rivers, form 
temporary lakes on the lava plains, from which the water is removed 
by evaporation, or descends into fissures in the undertying rocks and 
joins the underflow. To a large extent, however, the disappearance 
of streams from the mountains on reaching the plains is due, as just 
suggested, to the descent of the water into fissures and cellular lava, 
or into beds of gravel and sand that underlie the lava sheets. The 
streams, to be sure, tend to fill the openings in their beds with silt, 
but the extent of the lava-covered country they have to cross in order 
to reach the master stream to which they would be expected to flow 
is so great that the task of filling the cavities in the rocks is as yet in- 
complete. The water which disappears below the surface, particularly 
on the northern border of the Snake River Plains, to a large extent 
emerges again in the canyon of Snake River as springs. 
SPRINGS, a 
One of the remarkable features of Snake River Canyon is the 
abundance of large springs which pour out from its northern wall, 
especially in the portion of its course between Shoshone Falls and 
Bliss. The aggregate volume of these springs is many thousand cubic 
feet per second. They flow steadily without observed fluctuations in 
volume throughout the year. During August and September, when 
the Snake is low, their combined volume is estimated to be equal I 
to if not greater than that of the river itself where it passes overj 
Shoshone Falls. Perhaps the finest known exhibition of cataracts 
formed by springs of large volume issuing from rocks far up the 
faces of nearly vertical precipices is furnished at what is known as 
The Thousand Springs, situated on the northern side of Snake River! 
a See also pp. 162-171. 
