Feb. 16,1914 
Indicator Significance of Vegetation 
38i 
wilting coefficient in much the greater part of the area occupied by this 
association. That this is the case is strongly indicated by the fact that 
most samples of soil collected during the month of June, 1912, showed 
very little or no moisture above the wilting coefficient to a depth of 4 
feet (Table IV). 
In places where the conditions for the reception of water and removal 
of alkali salts are more than usually favorable—e. g., along drainage 
channels, in depressions, and in places where the soil has been loosened 
by burrowing animals—there is probably available moisture within reach 
of the roots during a longer period. Artemisia tridentata was not seen 
growing under natural conditions where the water table is near the sur¬ 
face of the soil. 
Fig.4.— Artemisia tridentata (sagebrush): A, Detail showing the wedge-shaped, 3-toothed leaves by 
which this plant is easily recognized; B, a small plant growing where hard pan occurred, showing the 
deflection of the taproot from a vertical to a horizontal direction after reaching a depth of 5 inches. 
Optimum soil-moisture conditions for the growth of Artemisia triden¬ 
tata are rarely realized in Tooele Valley. This is shown by the much 
larger size and more vigorous appearance of the plants which grow on 
sand hills and along irrigating ditches. In many places the maximum 
depth reached by the roots is only from 18 to 30 inches and is marked by 
the presence of a hardpan consisting of coarse gravel cemented by cal¬ 
careous material. The depth at which this hardpan is formed probably 
represents the limit of penetration of the rain water, and consequently 
most of the roots of the sagebrush do not penetrate farther. The shal¬ 
lowness of the moisture-holding layer of the soil greatly reduces the 
absolute quantity of moisture available for growth. The effect is shown 
in the thin stand and in the small size and sickly appearance of the 
plants (fig. 4). The eastern part of the valley, where most of the dry- 
