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- A triples 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. 

 1 6). 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 nauxeosus in- 

 cluding the variety graveolens, C. viscidiflorws, and Tetradymia 

 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 townsendi, 

 replaces the larger Columbian squirrel, C. columbianus, so plenti- 

 ful eastward. Likewise the presence of the burrowing owl and 

 rattlesnake is characteristic. 



72 



