170 SNAKE RIVER PLAINS OF IDAHO. [bull. 199. 
nated on faults, which incline downward to the .south at a high angle 
in reference to a horizontal plane. The depth to which it would be 
justifiable to continue drilling in the case of the Mountain Home hot 
springs, as indicated by their temperature, is about 5,000 feet. This 
is on the assumption that the temperature gradient in the Snake River 
lava is one degree for each 45 feet, as indicated by the wells along the 
Oregon Short Line Railroad. This assumed gradient will no doubt 
be found incorrect when more observations are available, but it prob- 
ably indicates the minimum depth to which drilling would have to be 
carried to reach the stratum from which the water rises in the spring 
referred to. There is, however, a chance that an open fissure that 
will yield an abundant supply of water will be struck at less depth. 
The drill hole put down for the purpose of developing these and other 
similar springs should be at least G inches in diameter, and thoroughly 
cased, to prevent all possibility of an escape of water on the outside 
of the casing. In seeking to develop springs in this manner when 
water, even in small amounts, of the same temperature as that rising 
in the spring is encountered, it will probably be desirable to explode a 
charge of dynamite in the hole with the hope of so shattering the rock 
that a free communication with the cracks through which the spring 
water rises may be obtained. 
It is scarcely necessary for me to urge that efforts should be made 
to develop the Mountain Home hot springs, since there is abundant 
land near them which could be irrigated. It may be found, however, 
that they are of more value for bathing purposes, or even for furnish- 
ing warm water in Mountain Home, than for irrigation; but even if 
these demands are not assured, there is sufficient justification for their 
development for irrigation purposes. The conditions at Mud Springs 
are less favorable than at the Mountain Home hot springs, but are 
sufficiently promising to warrant a trial. 
In brief, I may state that wherever warm or hot springs rise on the 
Snake River Plains an attempt should be made to enlarge them and 
to prevent their waters from escaping by percolation. By this 1 
mean that an open pipe should be provided in which the water may 
rise, in place of the fracture provided by nature, and that the space 
between the outside of the pipe and the inner surface of the bore hole 
at the bottom of the pipe should be packed so as to prevent leakage. 
This suggestion is made with the understanding that the pipe has been 
put in place after all necessary tests have been made for the purpose 
of discovering precisely where the water enters the bore hole. The 
lower end of the pipe should be just above that locality. 
A spring developed in the way suggested, when a surface flow of 
water is obtained, becomes an artesian well. Probably in most cases 
of this nature, however, the water does not come from a well-defined 
artesian basin or artesian slope, bub from irregular and what may be 
