4 BULLETIN 1388, U. S. DEPARTMENT OF AGRICULTURE 
SOIL AND TOPOGRAPHY 
The soil, generally speaking, is a silt loam with deep subsoil, espe- 
cially on the bench lands. The lower lands close to the rivers are 
to a large extent composed of gravelly subsoil covered by sandy 
soil ranging from a few inches to a few feet deep. Alkali spots, in 
a few of the lower areas, have given more or less trouble, but this is 
being partly overcome by drainage, a better understanding of the 
management of alkali lands, and a better knowledge of the appli- 
cation of water. The topography of most of the irritable land varies 
from almost level to gently rolling (fig. 2). The elevation of these 
Fig. 2.— The more rolling irrigated land's that permit good air drainage are devoted largely to 
fruit; the lower and more level lands are used largely for field crops and pasture 
lands ranges from about 400 feet at the lower end of the valley to 
about 1,200 feet in the upper end, near Yakima. 
CLIMATE AND IRRIGATION SEASON 
High temperatures are usual throughout the summer, especially 
during July and August (Table 1); but owing to the dryness of the 
atmosphere, the heat is seldom oppressive and the nights, even in 
midsummer, are agreeably cool. On account of the mild winters — 
the temperature seldom goes below zero — farm operations are usually 
interrupted only for a few weeks. The precipitation, which comes 
mostly during the nonirrigating season, averages considerably less 
than 10 inches, ranging from 6 inches at Kennewick to 11 at 
Ellensburg. 
The growing season ranges from five months in the upper valley 
to seven months in the lower valley. The irrigation season on the 
Sunnyside division is from April 1 to October 31, or 214 days. 
