182 SNAKE RIVER PLAINS OF IDAHO. [bull. 199. 
emerge onto the border of the Snake River Plains. In order to form 
" artesian wedges" of sufficient size to be of value as a source of water 
supply, the alluvial deposits need to be of considerable extent and 
thickness and to occur at the mouths of valleys down which there is a 
considerable flow of water. These conditions are best fulfilled, so far 
as I have been able to learn, where the valleys of the "Lost River 
country" open out on the Snake River Plains. In the lower portions 
of the valleys through which Big Lost River and the similar streams 
as far to the northeastward as Beaver Creek emerge onto the plains, 
the conditions are such as to warrant the drilling of wells to a depth 
of at least 500 feet in the hope of obtaining flowing water. 
In the valleys just referred to there are deep accumulations of allu- 
vium and fine examples of alluvial fans. At the mouth of each lateral 
gorge along the sides of these valleys there are local alluvial fans, which 
unite with a similar deposit in the main valley. The bottoms of the 
valleys of Big Lost and Little Lost rivers, Birch Creek, etc., are 
occupied by immense compound alluvial fans which extend far out 
onto the Snake River lava and there expand widely. Similar alluvial 
deposits were no doubt formed during the intervals between the erup- 
tions that spread out the Snake River lava, and such deposits beneath 
the surface lava sheets and interbedded with the subsurface sheets 
are in a position to become water charged. For these reasons it seems 
worth while to search for water under pressure on the border of the 
Snake River plains, adjacent to or in front of the entrances of the 
lateral valleys referred to. One such attempt has already been made 
at Reno, as has been stated, and water under pressure was discovered, 
which did not rise to the surface. This test, however, was imperfect, 
as the drill hole was not properly cased, and, although counted a failure, 
is really encouraging. It is not to be expected that water will rise 
through a hole 200 feet or more deep drilled in the Snake River lava, 
unless it is properh 7 cased, for the reason that the lava is largely 
cellular, broken by joints, etc., and would allow water to escape 
laterally. 
Another similar locality, but less favorable than those just referred 
to, where the conditions hold out some hope that flowing water may be 
obtained, is at Mountain Home. At that place there is a broad 
alluvial fan laid down by Canyon and Rattlesnake creeks, which may 
contain an alternation of pervious and impervious beds. The condi-' 
tions are not especially favorable for charging the pervious beds if 
such are present, with water, but the urgency for a water supply at 
Mountain Home is such that tests of the artesian conditions beneath 
and in the vicinity of the town should be undertaken. I venture to 
recommend that a row of borings be made at intervals of 1,000 feet 
along an east-and-west line passing through the northern portion of 
Mountain Home. Each of these borings should be continued until 
