IRRIGABLE LANDS OF THE VALLEY OF THE SEVIER. 131 
colors of these rocks give a somber aspect to the scenery, and the gloomy 
fronts of the towering precipices are rendered peculiarly grand and 
imposing. 
The prevailing winds of this region are from the west, northwest, and 
southwest, and are a portion of the more general movement of the atmos- 
pherie ocean which moves bodily from the Pacific to the heart of the 
continent. In crossing the Sierra Nevada a large portion of its moisture is 
wrung from the air, which blows hot and arid across the Great Basin. 
Notwithstanding the aridity of the basin area, the air gains about as much 
moisture as it loses in crossing it, until it strikes the great barriers on the 
east side of the basin—the Wasatch and the chain of high plateaus which 
are mapped as its southerly continuation. Here the winds are projected by 
the bold fronts several thousands of feet upward. The consequent cooling 
and rarefaction condense from them an amount of moisture which, relatively 
to that arid country, may be called large, though far less than that of more 
favored regions. In the valleys the rainfall is exceedingly small ; almost 
the whole of the precipitation is in the high altitudes. It is no uncommon 
thing to see the heavy masses of the cumulus clouds enveloping the summits 
of all the plateaus while the valleys lie under a sky but little obscured. 
The plateaus, then, are the reservoirs where the waters accumulate, and 
from which they descend in many rivulets and rills, while around their 
bases are copious springs fed by the waters which fall above. The rainfall 
in the valleys is very small, as compared with that upon the plateaus, and 
it is also highly variable. No record has been kept of the precipitation 
within the drainage system of the Sevier, and the nearest point where such 
a record has been kept is at Fort Cameron, near Beaver, at the western 
base of the Tushar Mountains These observations cover but a_ brief 
period, and no doubt represent a much larger precipitation than that 
which occurs in the valleys and plains generally, because the situation of 
the point of observation is just at the base of the loftiest range in southern 
Utah, where the air currents from the west first strike it. Moreover, these 
observations are not yet published, and are not at present available. In 
the narrow valleys between closely approximated and lofty mountain walls, 
like the valley of the Sevier at Marys vale, the rainfall is greater than where 
