8 BULLETIN 675, U. S. DEPARTMENT OE AGRICULTURE. 
the drainage of water from these high basins that, in rushing through 
to the steep canyons, relatively little of the rain is absorbed by the 
soil ; most of it plunges into the valleys below. Obviously, therefore, 
if the run-off from such areas is to be properly controlled, steps must 
be taken to maintain the soil cover. Unfortunately, it is these very 
basins that have been damaged most from overgrazing, consequently 
the soil and the ground cover are in the worse condition. Originally 
they supported a superb lot of feed especially sui'ted to sheep, and 
being less broken in topography, less, brushy, and more easily acces- 
sible than other parts of the range, generally they were the areas most 
sought for. 
As is shown by the accompanying topographic and type map of 
the selected areas, A and B (fig. 1), seven rather distinct plant 
associations occur, viz: Yarrow-needlegrass-cinquef oil ; yarrow- 
Douglas knotweed; adder's tongue-larkspur-sweet sage; currant- 
gooseberry-yarrow ; bluegrass- wheatgrass-needlegrass ( semi-scab- 
land) ; giant larkspur-blue foxglove-Douglas knotweed; and yellow 
bush-sweet sage-peavine. The density of each of these associations is 
shown on the map. Most of the species are valuable as forage and as 
soil binders. 
The soil is of limestone and sandstone origin, though chiefly the 
former, and varies in depth from a few inches to several feet. While 
there is some outcrop on both areas, the soil for the most part is 
fairly well decomposed. The principal drainage channels vary from 
2 to 9 feet deep. In many places wherever a vegetative cover is 
lacking rills occur, though most of these are less than a foot in depth. 
Although the two areas, as stated, are as nearly comparable as 
could be selected locally, yet several dissimilarities as to soil, slope, 
drainage, and vegetative cover occur, which occasion a much greater 
run-off from area A than from area B, other factors being equal. 
First, as shown in figure 1, area B has a vegetative cover exceeding 
that on area A by a density of 20 per cent. Accordingly, the soil on 
area B is bound together much more firmly by the plant roots than 
that on area A; the erosion is in a less advanced stage; and the 
greater amount of organic matter makes possible a greater absorption 
and retention of the rainfall. Area A, on the other hand, with its 
steeper slope lacks vegetation most where the greatest slope occurs 
and this tends greatly to increase run-off. Finally, area A has a 
different t}^pe of drainage system from area B. In cross section area 
A is broadly V-shaped and the main drainage is confined to one large 
channel running lengthwise through the area. Area B, on the other 
hand, is relatively flat in cross section and the drainage is divided 
among three principal channels. Naturally, there is more resistance 
to run-off which is distributed over the drainage than to run-off 
