Great Basin Elements. 51 
Jamesia americana Torr. & Gray. 
ew Mexico, Colorado, Utah. 
Juniperus californica Carr. var. utah- 
ensis Engelm. 
Central and Southern Utah, Nevada, 
California, Arizona. 
Juniperus occidentalis Hooker var. 
monosperma Engelm. 
Southern Colorado, N. Mexico, 
Southern Arizona, S. California. 
Physocarpus Torreyi Maxim. 
Colorado to Nevada. 
Pinus Balfouriana Murray var. aristata 
ngelm. (— P. aristata Engelm.) 
Colorado, Utah, Nevada, S. E. Cali- 
fornia. 
Pinus monophylla Torr. & Fremont. 
Utah, California, Arizona. 
*Prosopis juliflora DC. 
Southern Colorado, New Mexico, 
Southern California, western Texas, 
Southern Utah, Mexico. 
*Prosopis pubescens Benth. 
New Mexico, western Texas, Ari- 
zona, California, Mexico. 
Sarcobatus vermiculatus Torr. 
Southern Wyoming, Great Basin, 
to the Upper Missouri River. 
Another group of Rocky Mountain trees and shrubs, if we admit those 
occurring in New Mexico and Arizona, are those which in all probability 
have had their origin in Mexico, or the arid region of New Mexico, 
Arizona and southern California and have either remained near their 
primitive seat, (A) or have migrated northward from this common center along 
the Rocky Mountains, (B) or through California and the Rocky Mountains 
simultaneously (C). In the Rocky Mountains these elements may be classed 
together, as the Mexican, or southwestern contingent of the flora. In all pro- 
bability, this migration took place just before the final recession of the glaciers 
from the mountains and when the great interior lakes Bonneville and Lahontan 
had shrunken extensively in size with the gradual approach of an arid climate. 
In each case, the range of the species is given in the list which follows. 
Those marked by an asterisk are known to occur in Mexico. 
A. Acacia millefolia Wats. Arizona. 
*Alnus oblongifolia Torr. Arizona, New Mexico, California. 
Canotia holacantha Torr. Arizona on dry plateaus. 
*Chilopsis saligna D. Don. Southern Arizona. 
*Cowania mexicana Don. New Mexico, Colorado, Utah, N. Mexico. 
Condalia obovata Hooker. Southern New Mexico, Arizona. 
Cupressus guadalupensis Watson. Southern New Mexico and Southern 
Arizona and southward. 
*Juniperus pachyphloea Torr. Southern Arizona, New Mexico, Texas, Mexico. 
*Morus microphylla Buckl. Mountain canyons of Southern New Mexico, 
also in western Texas and Mexico. 
Pinus chihuahuana Engelm. Southwestern New Mexico extending into 
Arizona. 
Pinus reflexa Engelm. Southwest New Mexico and southeast Arizona. 
*Platanus Wrightii Wats. Mountain canyons southwestern New Mexico, 
in southeastern Arizona and Mexico. 
