72 A Study of the Vegetation of. 
inches respectively, never exceeded 2.8 per cent., while that at a 
depth of 2 and 3 feet was only slightly higher. Conversely, the 
soil temperature at 3 inches ranged from 77° F. to over 112° F. 
Even at 12 inches the temperature was usually above 78° F. 
The Artemisia-Atriplex association is represented in this region 
by the Artemisia consociation. 
The Artemisia Consociation 
This consociation, dominated by Artemisia rigida, is a very 
' characteristic type of vegetation over large areas of scab-lands. 
The scab-lands, as elsewhere indicated, are areas of basalt, prob- 
ably the flood-plains of former streams, in part, thinly covered 
with soil. These extend as long tongues over the branching sys- 
tem of river tributaries between the hilly divides. While many 
of these flats in this region are dominated by communities of 
Agropyron or Poa-Polygonum, still large areas are characterized 
by the scab-land sage. This perennial, low, scrubby growth is 
well adapted to the driest situations on the thin, rocky soil (Fig. 
16). Many species typical of the above mentioned communities 
occur associated with the sage, as might be expected in this zone 
of transition. Plants characteristic of the desert scrub forma- 
tion occurring with the sage are Chrysothamnus nauseosus in- 
cluding the variety graveolens, C. viscidiflorus, and Tetradynua 
canescens. It has already been pointed out that some of these 
play an important role in the Agropyron consociation. 
In the Snake River Canyon beautiful examples of the abrupt 
transition from the sage to the Agropyron community are abun- 
dant. Rocky, exposed slopes reveal the former, while sheltered 
slopes only a few meters distant show a well developed Agro- 
pyron community. : 
In passing from the prairie into the scab-land the change in 
animal population is no less striking than that of the vegetation. 
In the drier region the Townsend squirrel, Citellus townsendt, 
replaces the larger Columbian squirrel, C. columbianus, so plenti- 
ful eastward. Likewise the presence of the burrowing owl and 
rattlesnake is characteristic. 
72 
