180 SNAKE RIVER PLAINS OF IDAHO. [bull.199J 
;i hasty reconnaissance, are seemingly so favorable, that the people who 
are interested in the development of this region can well afford to 
continue drilling- to a depth of 1,000 or 2,00(> feet, unless water is sooner 
reached. To make a complete test, drilling should be continued until 
the Snake River lava and its associated lacustral beds are passed 
through. Beneath these formations it is probable that the drill will 
strike either granite, rhyolite like that which forms Mount Bennett and 
the Rock Creek Hills and which appears also at Shoshone Falls, or 
quartzite. When the drill reaches rock like any of them, or some 
other rock clearly distinct from the Payette formation or the Snake 
River lava, the possibilities for obtaining artesian water will have 
been exhausted. Deep drilling is also justified for the reason that 
the sheets of lava which supply the great springs in the vicinity of 
Hagerman dip gently westward, as may be seen between the mouth 
of Clover Creek and Bliss, and pass beneath the region included in 
the Lewis artesian basin. As the continuation of a lava sheet after 
it disappears from sight is uncertain, it can not be said from definite 
evidence that the open, water-charged lava sheets referred to have a 
wide extent west of where they dip beneath the level of Snake River, 
but there is a possibility that fchey extend far and are abundantly water 
charged. The manner in which the sheets of basalt in the western 
portion of the Snake River Plains vary in thickness is an important 
matter in reference to the search for artesian water, but one concern- 
ing which no predictions seem possible. This and other qualifying 
conditions can be discovered only by the use of the drill. 
SHOSHONE ARTESIAN SLOPE. 
Judging from surface elevation and the nature of the rocks exposed 
in the north wall of Snake River Canyon between Shoshone Falls and 
Bliss, the strata of lava, associated lacustral deposits, etc., beneath the 
plain to the south and southwest of Shoshone slope from the moun- 
tains toward Snake River. Coupled with this fact is the marvelous out- 
pouring of water from the north wall of Snake River Canyon between 
Shoshone Falls and Bliss. This water, although no doubt supplied 
in part by precipitation on the surface of the Snake River lava, comes 
mainly from the mountains to the north. The great springs referred 
to are fed by lost rivers and by the water which disappears by percola- 
tion on the northern border of the Snake River lava sheets. There is 
thus evidence of a strong underflow beneath the lava plain to the south 
and southwest of Shoshone. For these reasons I venture to term tin 1 
region referred to the Shoshone artesian slope, although the name 
will be justified only when the drill demonstrates that the water is 
under sufficient pressure to cause it to rise to the surface. 
The nature of an artesian slope has already been explained, and 
persons familiar with the conditions existing in the triangular area, 
