rydberg: vegetative life zones of rocky mountains 493 



Pinus ediilis and Sahina monosperma, and, on the western side, 

 Sahina occidentalis also. It extends on the eastern side over the 

 Arkansas Divide to South Platte River (Lat. 39°). North of 

 that river both the piiion and the cedar are only local and soon 

 disappear altogether. On the western side it forms foothills of 

 the Rockies and a few isolated mountains, as well as low plateaus 

 apparently as far north as the Yampa River. On the western 

 slope of the Wasatch Mountains and in the mountains south 

 thereof as far east as the Henry Mountains, Pinus edulis is mixed 

 with P. monophylla, which takes its place in the isolated moun- 

 tains of the Great Basin as far north as southern Idaho. In the 

 part bordering the deserts the Piiion-Cedar Belt is often broken 

 and intermixed with patches of sage brush, Artemisia tridentata, 

 as for example, on the mesas between the Elk Mountains and 

 San Juan River in southeastern Utah. 



On the western slopes of the La Sal Mountains the Piiion-Cedar 

 Belt reaches the top of Wilson's Mesa, nearly 8,000 feet in alti- 

 tude, and is separated by a narrow belt of chaparral only a few 

 hundred feet high, from the Spruce Zone above, both the foothill 

 Pine Belt and the Montane Forest Zone being lacking. The Piiion- 

 Cedar Belt, furthermore, was there separated from the valley 

 below with the Upper Sonoran flora by a belt of low shrubs of 

 Amelanchier utahensis, Cercocarpiis, Coelogyne, Petradoria, Yucca, 

 Fendlera, Ephedra, Cowania, Fallugia, and Quercus, some of 

 which belong to the Upper Sonoran flora, and some to that of 

 the chaparrals. 



The undergrowth of the Piiion-Cedar Belt is often the same as 

 in the Transition Pine Belt, but often many southern plants are 

 added, as for instance Arctostaphylos platyphylla, Ceanothus 

 Greggii, Berberis Fremontii, etc. In southeastern Utah large 

 stretches are covered by Amelanchier utahensis and other shrubs. 

 Towards the San Juan River the mesas are sparingly covered by 

 Coelogyne, which, if I am not mistaken, associates further south 

 with Covillea, one of the characteristic plants of the Lower Sonoran 

 Zone. In southern Utah, Arizona, and New Mexico, the place 

 of the pinons and cedars is often taken by live oaks, especially 

 on the sides of caiions. In the canons, Fraxinus anomala is 

 common. In southern Arizona and New Mexico many other 

 trees and shrubs are added to the belt, but as that region belongs 



