russell.] HYDROGRAPHY. 25 
ARTESIAN BASINS. 
The study of the geological structure — that is, the positions the 
stratified rocks occupy — together with the information furnished by 
springs and drilled wells, has shown that there are four basins in 
southwestern Idaho and southeastern Oregon which may be expected 
to yield flowing water when wells are put down. In two of the basins 
referred to drilled wells have already proved the presence of subsur- 
face water under sufficient pressure to cause it to rise to the surface 
and overflow when the drill holes are properly cased. The four basins 
referred to have been described in the Preliminary Report on Artesian 
Conditions already mentioned, and are indicated approximately on 
the map forming PI. I. They have been named the Lewis, Otis, 
Harney, and Whitehorse artesian basins. Their combined areas below 
the artesian head in each instance is estimated at approximately 2,000 
square miles. While it is not to be assumed that all of this area can 
be irrigated *Dy means of artesian wells, the conditions are such as to 
warrant the careful testing of each basin and a judicious development 
of its water supply. 
The Lewis artesian basin, situated along Snake River, between 
Glenns Ferry and Weiser, and including Bruneau and Little valleys 
and the lower portion of Boise Valley, has an area below the known 
artesian head of not less than 1,000 square miles. Wells have been 
put down in it at several localities, as in Brnneau Valley, Little Val- 
ley, and near G-uffey, Central, and Enterprise, in Idaho, and at Onta- 
rio, in Oregon. These wells are from 200 to somewhat more than 1 ,000 
feet deep, and with one exception — near Central — are all successful so 
far as demonstrating the presence of artesian conditions is concerned, 
and in the majority of instances furnish a strong surface flow of 
water. The water in all cases in which temperature measurements 
have been made is warm and in general ranges from 60° to 100° F. The 
exceptional well at Vale, which is strictly speaking a developed hot 
spring, has a temperature of 1984-° F. The artesian wells near Central 
and Enterprise exhibit an increase in their temperature gradients — 
that is, the rate of increase in temperature with depth — as the large 
hot spring at Enterprise is approached. This and other similar 
although less definite instances indicate that the Lewis artesian basin 
is supplied in part at least by water rising through fissures from a 
considerable depth. 
The greater number of borings that have been put down in the 
Lewis artesian basin were drilled with the hope of obtaining petroleum. 
In this respect they were failures, although they attained a more desir- 
able result in demonstrating the existence of artesian water. The 
reasons for the failure to discover petroleum and the conditions which 
lead to the accumulation of that substance will be discussed later. 
The Otis artesian basin, in the region drained by Otis Creek, about 
6 miles northeast of Drewsey, Oreg... has not been tested with the 
drill, and will merit the name here given it only after such demon- 
