russell.] RAILROADS AND HIGHWAYS. 33 
The total population of Idaho in 1900 was 161,772, or 1.9 to the 
square mile. In the region embraced in the Snake River Plains the 
people are, to a great extent, segregated in communities where water 
can be had for irrigation, leaving vast tracts entirely uninhabited. 
The counties which include portions of the plains within their border, 
however, contain more than half of the population of the State and 
represent about one-half its area. The leading topographic feature of 
southern Idaho is the great plains, and of its central and northern 
parts, rugged mountains. The influence on the density of population 
of barren, uninhabitable plains, encroached upon by agriculture and 
stock growing, and of mountains where mining industries have been 
established, is thus seen to be about the same. 
RAILROADS. 
As is indicated on the map forming PI. I, the Snake River Plains 
are traversed throughout their entire length by the Oregon Short Line 
Railroad. One division of this road, starting from Pocatello, leads 
westward, and traverses the plains all the way to the Idaho-Oregon 
boundary, with one branch leading northward to the mining regions 
about Hailey and another terminating at Boise. A branch about 50 
miles long leads southward, crossing Snake River to Murphy. Another 
division of the road, starting also from Pocatello, leads northward and 
traverses the northeastern border of the plains to the Idaho-Montana 
boundary. An important branch of this northern division, built in 
1901, begins at Blackfoot and crosses the widest part of the plains, 
passing between Big and Middle buttes and reaching the region drained 
by Big Lost River. The aggregate length of the railroads now in 
operation across the Snake River Plains is about 500 miles. Travelers 
over these two divisions and various branches of the wi O. S. L.," as it 
is familiarly termed, will be enabled to see nearly all the variations that 
the plains present and to obtain an idea of their vast extent. To 
travelers who make such a journey, the most pronounced need of the 
country — namely, water — will become painfully apparent. 
HIGHWAYS. 
Owing to the flatness of the Snake River Plains and the fact that the 
lava rocks when present are generally covered with at least a few feet 
of fine soil, traveling is easy in all directions, except where canyons 
break the surface. Roads lead across the plains in various directions, 
and all parts of them can be reached by wagons. The exceptions in 
this connection are the fresh lava flows, sometimes hundreds of square 
miles in area, and the portions of the canyons bounded by precipitous 
walls. In several instances, however, good roads, or " grades," as they 
ire termed, have been constructed which lead into the canyons where 
Bull. 199—02 3 
