February 28, 1907 . 23 
SOILS 
The distribution of plants in the valley is greatly influenced 
by the many different kinds of soils. The foothill region on the 
west, consisting as it does largely of sagebrush, gives little op- 
portunity for the presence of any considerable quantity of humus 
in the soil. The sagebrush (Artemzsza tridentata) being more 
or less evergreen in character, loses only a few of its leaves at 
any one time. Owing to the aridity of the region, the fallen 
leaves become so dry that they are blown away in the form of 
dust. 
The soils on the hills to the north of Reno are sparsely 
clothed with vegetation and consist largely of rhyolite, which, 
when decomposed, varies in color from yellowish-white to red, 
brown, or purple. During the summer this rhyolite has a very 
fine, soft texture like fine powder, but in winter the particles 
hold together so tenaciously that in wet weather it is frequently 
very difficult to drive a two horse wagon along the road. On 
such soils the characteristic vegetation is A/riplex confertifolia; 
Cleome Hilimant, and Helianthus annuus. 
At higher elevations on the western side of the valley 
within the timbered area there is a much larger precipitation, 
and consequently a larger amount of humus produced from the 
decaying needles of the yellow pine, Douglas spruce, and the 
leaves of the mountain mahogany and other shrubs of minor im- 
portance. Where the granitic soil is plentiful it seems to offer 
an especial attraction for such plants as Pinus contorta Murray- 
ana, Arctostaphylos patula and A. Nevadensts. 
LIFE ZONES 
The distribution of the plants occurring in the region ac- 
cording to their life zones must at the present time be consid- 
ered somewhat uncertain until a more prelonged study with this 
definite object in view is undertaken. The Austral region is 
represented in this locality by the Transition and Upper Austral 
zones, and the Boreal region by the Canadian, Hudsonian, and 
Arctic-Alpine zones. 
