172 SNAKE RIVER PLAINS OF IDAHO. [bull. 11 
SURFACE WELLS. 
On the Snake River Plains ordinary surface wells, such as are coin 
mon in humid regions, are seldom possible. Where streams cominc 
from the mountains have spread oat Hood plains or alluvial fans sur 
face wells, however, are sometimes successful, the water supply being J 
furnished 03^ the outward percolation from the streams themselves anc| 
not by direct precipitation on the adjacent surface. Such wells arc 
situated, for the most part, in canyons and stream-cut valleys. Theiij 
depth is regulated by the height of the surface at the locality choser 
above the bed of an adjacent stream. 
A modification of the process just referred to is to be seen wherei 
water is spread over the land for purposes of irrigation. In suet 
instances a part of the irrigation water sinks below the surface and 
may saturate the subsoil. When the soil and subsoil are porous a 
large amount of subsurface water is stored more or less permanently 
in this manner, and furnishes a supply for surface wells. On isolated) 
ranches wells fed by surface water from irrigation are not, perhaps,: 
objectionable, but when towns arc supplied in this manner a serious 
disarrangement of sanitary conditions results. One instance of a 
town which depends on shallow surface wells for water for household 
uses, and where the adjacent gardens and fields are irrigated, is fur- 
nished by Mountain Home. This town has a population numbering 
about 550; many of the houses are surrounded by gardens and orchards: 
the subsoil is gravel; there is no sewerage system; shallow cesspools 
are numerous and mostly in an insanitary condition; numerous stable! 
and poultry yards are present, and the surface is flooded from time tor 
time for purposes of irrigation. The water, after standing on the 
surface, in part percolates downward into the gravelly subsoil, which 
is underlain by an impervious stratum, and which is penetrated by 
wells ranging in depth, usually, from L5 to 20 feet. A more insani- 
tary arrangement could scarcely be devised, yet Mountain Home is a 
typical example of many communities in the arid region. Strange ag 
it may seem, practically no attempt is made in the majority of these 
towns to insure sanitary conditions. 
As previous^ pointed out, ordinary surface wells are analogous to 
hillside springs. As the subsoil in arid regions is not saturated by 
direct precipitation, hillside springs are absent, and surface wells are 
not as a rule practicable. 
ROCK WELLS. 
The conditions which favor the occurrence of canyon springs also 
insure the success of deep wells which reach a water-bearing stratum. 
In the Snake River Plains, where deep borings have been made, water 
has generally been obtained. It is usually under pressure, so that it 
