16 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



in aspect. The soils are varied and have even more influence than 

 differences of altitude in determining the vegetation, but through the 

 entire area only 16 species of perennials are abundant. These are low 

 in stature and usually widely spaced or else occurring in clumps. The 

 perennials are chiefly semishrubs — much branched, with soft wood, 

 indeterminate growth, and evergreen leaves — whereas true shrubs 

 with winter-deciduous or drought-deciduous leaves are few. Cacti 

 are represented by a few low-growing species, and the yuccas by two 

 acaulescent species. In many respects there is a sharp contrast 

 between the deserts of the southwestern and northeastern corners of 

 the State (pi. 4). 



The southern edge of the Great Basin Microphyll Desert, from Wide 

 Ruin to the mouth of the Little Colorado, has a very poor plant cover. 

 In the areas of the Painted Desert the topography is in an early stage 

 of active erosion, and the poverty of the vegetation makes visible the 

 brilliant display of color in the various layers of old lacustrine deposits 

 that have been exposed. Where erosion is less active Atriplex con- 

 jertijolia, A. canescens, and Sporobolus wrightii are the only common 

 plants. 



North and east of the broad valley of the Little Colorado River, 

 the Great Basin Microphyll Desert is a network occupying the inter- 

 vals between the lightly forested sandstone or limestone mesas. The 

 soils in this network are prevailingly sandy, sometimes with a level 

 stabilized surface or quite as often with a poorly stabilized one in 

 which the large plants occupy small hummocks, separated by bare 

 spaces in which the wind is constantly moving the sand. There are 

 no active dune areas involving large masses of sand. Below 6,000 

 feet the stabilized surfaces are occupied by scattered colonies of 

 Bouteloua gracilis and Hilaria jamesii, and by Ephedra viridis,E. cutleri, 

 Atriplex confertifolia, Chrysothamnus nauseosus, Yucca angustissima, 

 Opuntia hystricina, and Lycium pallidum.. The principal hummock- 

 forming plants on sandy bajadas and plains are Ephedra viridis and E. 

 cutleri, which in some localities form 90 percent of the perennial vege- 

 tation over many square miles (pi. 5). 



On very loose sand are found Ephedra viridis, E. cutleri, E. torreyana, 

 Chrysothamnus nauseosus, Poliomintha incana, Parry ella filifolia, 

 Yucca angustissima, and Oryzopsis hymenoides. After copious spring 

 rains many annuals and small herbaceous perennials appear on the 

 sandy areas, including species of Oenothera, Cryptantha, Euphorbia, 

 Stephanomeria, Abronia, Lygodesmia, Allium, Astragalus, Calochortus, 

 and Festuca. 



Above 6,000 feet the plains and bajadas on which soil has accumu- 

 lated are occupied by pure stands of Artemisia tridentata, varying in 

 height with the depth of the soil and the supply of moisture. Few 

 perennials are associated with the Artemisia, save occasional plants of 

 Yucca baccata and small root perennials. 



Where rocks other than sandstone have given rise to the soil the 

 bajadas are smooth, with gravelly surface, and are dominated by 

 nearly pure stands of Coleogyne ramosissima. North of Tuba and 

 Tyende (Kayenta), and along the Chinle Wash, there are innumerable 

 areas of bare rock, varying in size from a few square yards to many 

 acres, and devoid of plants. In favorable spots there are crevice 

 plants, notably Aplopappus spp., Eriogonum aureum, Fraxinus ano- 

 mala, Amelanchier utahensis, and small trees of Juniperus utahensis 



