160 SNAKE RIVER PLAINS OF IDAHO. [bull. 199. 
portion of its course referred to, a minimum of over 5,000 cubic 
feet per second continues on below Montgomery Falls. From Ameri- 
can Falls westward to the Idaho-Oregon boundary Snake River is in a 
canyon, and practically no use is made of its waters for irrigation. 
On Boise River, from the point where it emerges from the canyon por- 
tion of its course, just above Boise, to its mouth, many canals have been 
constructed for the diversion of its water, and 61,000 acres of land are 
irrigated, but much good land remains for which there is at present no 
water available. This is the largest i ract of land under irrigation in 
Idaho. Payette River is utilized in a similar way and made to water 
28,000 acres of land. 
The utilization of the easily available water supply of the surface 
streams has thus far been made principally by individuals and small 
companies. The development of this branch of the water resources 
in a more comprehensive and economical way, based on a thorough 
understanding of the conditions, has recently attracted attention, but 
is not yet fully initiated. This broader view of the problem has been 
grasped by the State engineer, and comprehensive plans for its elabora- 
tion have been outlined. The larger tract of laud, which, so far as engi- 
neering questions are concerned, can be watered by diverting Snake, 
Boise, and Payette rivers, as shown on the maps accompanying the 
report of the State engineer just referred to, is about 1,800,000 acres. 
Such measurements of these rivers as arc available, however, indicate 
that not over half of this area, or, in round numbers, 1,000,000 acres, 
can be supplied with the requisite amount of watc during years of 
average precipitation. Great fluctuations in the amount of water flow- 
ing through the river channels during the growing season, however, 
occur from year to year, and the amount of land that can be continu- 
ously cultivated without loss during years of minimum precipitation is 
probably much less than the area just stated. Including also the 
smaller streams, an estimate shows that when all available water in 
surface streams is economically used about one-twelfth, or, we will 
assume, 8 per cent of Snake River Plains can be cultivated. It must 
be remembered that this is a rough estimate, based on insufficient data, 
but I believe it is too liberal. A safer estimate, considering all the 
difficulties and uncertainties attending large irrigation schemes, is prob- 
ably that one-twentieth, or 5 per cent of the portion of the Snake 
River Plains where favorable soil conditions occur, may ultimately be 
irrigated from surface streams. 
The lessons of public interest which the study of the surface streams 
clearly indicates may be briefly stated as follows: 
First. Water being highly valuable and an inheritance of the peo- 
ple in common, the strictest economy in its use should be obligatory. 
No more water should be used than is essential to proper cultivation; 
but in this connection a natural adjustment will no doubt in part be 
