4 BULLETIN 30, U. S. DEPARTMENT OF AGRICULTURE. 
face ; and (5) temperature, especially the frequency of killing frosts 
which limit the growing period. These factors will be discussed as 
they have been recorded! at the Nephi substation. Figure 2 shows 
the apparatus used in recording these data. 
Fic. 3.—View of one wallofa deep gully or small canyon near the Nephi substation, showing stratified 
soil formation to a depth of 20 feet. The light-colored stratum is the blue clay mentioned in the 
text. 
SOIL. 
The soil of the Nephi substation is reasonably typical of a large 
proportion of the soils of the Great Basin, which are mostly alluvial. 
1 With the exception of the rain gauge, the physical apparatus in use at the substation was installed by 
the Biophysical Laboratory of the Bureau of Plant Industry, which is cooperating in the work. The 
apparatus includes an evaporation tank, an anemometer, an air thermograph, thermometers, psychrom- 
eters, and a complete outfit for making soil-moisture determinations. 
