290 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
thence declines gradually .southward, through New Mexico, and enters 
the Republic of Mexico with an elevation of about 4,000 feet. 
In Southern Wyoming we meet first the Laramie Range, which rises 
to an elevation of about 9,000 feet above the sea. At its eastern base, 
and far up its slopes, the fine grass of the plains extends, growing more 
luxuriant with the altitude. On the summit of the mountains is a strag- 
gling growth of timber, nowhere heavy. The western slope is but a 
repetition of the eastern. 
At the western base we enter the plains of Laramie. These; lie be- 
tween the Medicine How ;m<l Laramie Ranges, are limited on the north 
by the latter of these ranges, where it sweeps around to the west, and 
on the south they extend up into the angle of the junction of the Medi- 
cine Bow and Laramie Ranges. The surface of these plains, like that 
of the (Ireat Plains, is chiefly rolling, entirely bare of timber, and cov- 
ered mainly with bunch-grass. Here sage becomes rather more abun- 
dant than on the east side of the mountains, but is by no means the chief 
product. 
Passing the Medicine Bow Range, we find the country, as far west as 
the valley of the North Platte, to resemble in most respects that of the 
Laramie Plains, being open and grassy. 
West of the North Platte comes a broad plateau, separating the 
drainage of the Platte from that of the Colorado. This broad, ill-de- 
lined divide extends from the South Pass southeastward to tlie north end 
of the Park Range. It has an uneven, rolling surface, containing many 
sinks, in which disappear the waters gathered over large areas. 
This region, from the railroad northward to the base of the Sweetwater 
Mountains, and from the North Platte to the Green River Basin, is 
almost a desert. It has a heavy, cold, alkaline, clay soil, which produces 
only a sparse growth of greasewood and stunted sage. It is not a region 
in which the locusts are likely to breed or frequent, neither is it to be 
burned over easily. 
South of the railroad, these plateaus extend up to the base of the Park 
Range. As they recede from the railroad southerly, they rise to greater 
elevations and become correspondingly more inviting. The soil becomes 
more gravelly, greasewood disappears, while a luxuriant growth of sage 
and bunch-grass takes its place. Should it become necessary, these 
plateaus can be burned over at no great expense. This improvement 
in the vegetation seems to commence with Bridger's Pass and extends 
southward to the north end of the Park Range, and along its western 
flank far into Colorado. The western limit of these more fertile plateaus 
it is not easy to point out, as they grade insensibly into a more desert 
region, as the elevation decreases. 
The valley of the Sweetwater River is everywhere well grassed, with 
but little sage brush. It is mainly bench land, with a gravelly soil, and 
is free from timber. The river bottom has an average width of about 
half a mile. 
