DESERTS AND DESERT FLORA OF THE WEST 

 In origin and development it is wholly distinct from 

 the north temperate and boreal floras that are com- 

 mon to Europe, Asia and North America. It be- 

 longs to another floral realm. 



SAGE-BRUSH PLAINS OF THE GREAT BASIN. The 

 principal physical features of the Great Basin region 

 are the beds of ancient lakes and the surviving 

 Great Salt Lake, which are bordered by short isolated 

 mountain ranges. Many of these mountains rise to 

 an altitude of 10,000 feet, and are covered with 

 coniferous forests, while at the top they support 

 typical arctic-alpine plants. These ranges present 

 interesting problems of distribution. Biologically 

 each range is an island of boreal life, completely 

 shut off from the main northern body and that of 

 the other ranges by the intervening desiccated 

 plains. 



The ancient lake beds, or sinks, are "smooth 

 hard plains composed of bluish clay incrusted in 

 wavy lines with white saline incrustations," great 

 barren stretches with scarcely a plant as far as the 

 eye can see. The plants that do endure are such as 

 the salt grass, Distichlis spicata, and the two cheno- 

 podaceous plants, Allenrolfia (Spirostachys) occi- 

 dentalis and Salicornia herbacea. 



At higher elevations on the drainage slopes, 

 where excessive saline accumulations have been 

 prevented, the predominating plants are compo- 

 sitaceous shrubs or half-shrubs, of which the com- 

 mon sage-brush, Artemisia tridentala, is by far the 

 most abundant. This silvery gray shruo, easily 

 identified by its pungent sagey odor and small 

 wedge-shaped leaves, three-toothed at the apex, 

 spreads over the plateaus of the Great Basin like 

 an enormous sheet. Chrysothamnus is also common. 

 This is a peculiar west American genus of tufted 

 half-shrubs, with sparse foliage of small narrow 

 leaves and rayless heads of yellow flowers. 



GRAND CANON OF THE COLORADO. The Grand 

 Canon of the Colorado River lies in the arid plateau 

 region of northern Arizona. This magnificent gorge, 

 a mile in depth and over 200 miles in length, is 

 one of the sublime wonders of the world. Hori- 

 zontal beds of solid rock are cut to a depth of 5000 

 to 6000 feet, exposing a splendid series of lower 

 and upper Carboniferous marine deposits. At the 

 bottom of the gorge are 800 feet of crystalline rock, 

 an Archaean mountain range that began to sink 

 slowly in early Carboniferous time. Upon these 

 ancient granites rest the horizontal beds of sedi- 

 mentary rocks; first about 800 feet of quartzite, 

 followed by 500 feet of greenish sandstone. Rest- 



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