russkll.] LOST RIVERS. 131 
deposited in the mouths of the tributary valleys and on the border of 
the great plain, so as to form alluvia] fans; while the finer portion is 
carried farther, and, in rase of the stronger streams, deposited prin- 
cipally over the bottoms of temporary lakes. The weaker streams, 
which disappear either by evaporation or by percolation, deposit the 
fine sand and silt the} r bring down from the mountains in a broad fringe 
about the outer margins of their low, widely expanded alluvial fans. 
In these several ways an attempt is being made, as one may say, to 
upgrade the lower portions of the stream channels, so as to enable the 
waters flowing down them to cross the plain. The principal reason 
why the streams have done this is because their water supply is insuf- 
ficient. But, if properly graded water-tight channels could be pro- 
vided there is no doubt but that the stronger streams, such as Camas 
Creek and Big Lost River, would be enabled to reach Snake River dur- 
ing the time the snow is melting on the mountains from which they 
flow and perhaps live throughout the summer. In addition to the light 
rainfall, therefore, other adverse conditions must be present. Chief 
among these is the fact that the lava covering the plain across which 
the streams naturally tend to flow is not smooth and level as it appears 
to be when seen from a distance, but rough, irregular, and undulating. 
The waters are ponded, and before they can accumulate in sufficient 
volume to overflow the obstructions and continue on their course their 
expansion to form lakes leads to an increase in evaporation, which at a 
certain stage equals the inflow. That is, the inflow is spasmodic, but 
evaporation continues so long as the lake basins contain water, although 
fluctuating with temperature, strength of the w T ind, etc., and the quan- 
tity of water delivered to the lake basins each year, or during a period 
of several years, is all evaporated or lost by percolation. Allowing 
for the conditions just mentioned, however, there is still evidence that 
the popular belief that the waters sink into the lava and that the 
streams are "lost" beneath the surface is well founded. When the 
waters of Little Lost River are expanded so as to form a lake, I have 
been informed by observant residents of the region that there is at a 
certain stage an escape through fissures. 
The surface portions of the lava sheets covering the plains are 
broken and jointed, so that water if spread over the land would imme- 
diately sink from sight. This is indicated also by the fact that few if 
any surface rills or brooks are formed on the plains during rains or 
when their covering of snow is melting, but this may be due to the 
absorbent nature of the soil. In order that streams may cross such a 
surface it is necessary that the openings in the rocks should first be 
closed. The streams are active in this direction, as is to be seen where 
they are spreading out alluvial fans and silting up lake beds, but the 
task is not far advanced. The processes now in action, given time 
enough, will lead to the upgrading of the plain so as to till the cavities 
