1906] SHANTZ—VEGETATION OF THE MESA 39 
gracillima, Bouteloua hirsuta, Artemisia frigida, Gutierrezia Sar- 
othrae, Boebera papposa, Oreocarya thyrsiflora, Chrysopsis villosa, 
Schedonnardus paniculatus, Petalostemon oligophyllus, P. purpureus, 
Psoralea tenuiflora, Theles perma gracile, Gaura coccinea, Euphorbia 
gly ptosperma, Atheropogon curtipendulus, Sideranthus spinulosus, 
Lacinaria punctata, Eriogonum Jamesii, E. effusum, Asclepias 
pumila, Helianthus pumilus, Sitanion elymoides, Artemisia gnaph- 
alodes, Castilleia integra, Erigonum alatum, Pentstemon unilateralis, 
‘Stipa Vaseyi, and Euphorbia stictos pora. 
Besides the typical formation, the north Mesa is occupied by 
the Bouteloua hirsuta consocies. In this consocies the following 
8roups occur: the Chrysopsis villosa society occupying rather lim- 
ited areas, low crests, and south slopes; and the following com- 
munities: Sideranthus spinulosus, Artemisia gnaphalodes, Andro- 
pogon furcatus, and A. scoparius. 
The crests are the most xerophytic and are occupied by the Boute- 
loua hirsuta consocies. This may alternate,. however, with the 
B. oligostachya consocies. Occurring within the former consocies 
are often found the Gutierrezia Sarothae, Chrysopsis villosa, and the 
Aristida longiseta societies, as well as the following communities: 
Silanion elymoides, Muhlenbergia gracilis, Artemisia gnaphalodes, 
Andropogon Scoparius, and Tetraneuris glabriuscula. The following 
Plants are also abundant on these crests: Oreocarya thyrsiflora, 
Chenopodium leptophyllum, Stipa comata, and S. neo-mexicana. 
The hillsides and ‘slopes have usually about the same vegetation 
as the Mesa top, but the crest forms may be more abundant. 
Passing to the lowlands, the Bouteloua oligostachya consocies 
is found alternating with the Muhlenbergia gracillima consocies 
and also the Andropogon occidentale consocies. The chief societies 
of the Bouteloua oligostachya consocies are the Gutierrezia Sarothrae 
and Artemisia jrigida societies. In the Muhlenbergia consocies 
are found the Bouteloua prostrata and Atriplex argentea communities. 
Marked alternations sometimes occur between secondary species. 
Petalostemon oligophyllus occurs on south and east slopes, and P : 
burpureus on north and west slopes, where the water content 1s 
from 1-2 per cent. higher; Muhlenbergia gracile, Koeleria cristata, 
and Poitentilla pennsylvanica are usually found on north slopes; 
