1877. ] Vegetation in Nevada and Arizona. 339 
tata and Algarobia glandulosa in excess. The plains and salt 
marshes in this vicinity are at an elevation of 7200 feet above 
the sea, and gradually slope towards the Colorado River, until 
we reach the deserts just north of that valley, where the average 
elevation is 1400 feet. This descent is so rapid, comparatively, 
that as we proceed southward, zones or belts of vegetation are 
passed through — underlying that upon the salt deserts at Mac- 
gruder— not encountered heretofore, and which partake of a 
sub-tropical nature in predominating species, that is, Cactacea, 
such as Hehinocactus, Mamillaria, Agava, and Larrea Mexicana. 
Southward and eastward of the Colorado River, in following 
this elevated portion of the country, we encounter the Colorado 
Plateau, having an elevation of from 6000 to 6700 feet. Upon 
this we have San Francisco Mountain and Mt. Bill Williams. 
Upon the former, the timber-line rises to within one thousand 
feet of the summit upon the eastern side (12,500 feet) and to 
within five hundred on the western (13,000 feet). 
The belt of Conifere extends down to the base of this mount- 
ain as well as on Mt. Bill Williams,! and is subdivided into two 
divisions, the upper being composed chiefly of Pinus brachyptera 
and P. edulis Engelm., and the lower of Abies Douglasii and 
Juniperus occidentalis. Throughout the ravines and moist de- 
pressions we now find Frazinus velutinus common, and searcely 
any Populus monilifera. Around the base of both mountains 
we find Quercus Gambelii extending up the eastern slopes but 
not upon the western. 
: After leaving the plateau, going southward, and again descend- 
ing to an elevation of 3500 feet, we meet the belts of sub-tropical 
Species which occur above the plateau (in Southern Nevada) at 
a corresponding place, allowing the increase of elevation which it 
gains in this distance proportionately. 
As we descend toward the valley of the Rio Gila, Cactaceæ 
predominate, nine species having been identified, not embracing 
varieties which are undoubtedly present and which could have 
been detected upon closer examination. Farther west, including 
the Mojave Desert, and northward as far as Vegas Valley, we 
find this thorny vegetation to a great extent ; and in various de- 
pressions and ravines occur Eriodiction, Algarobia, and Prosopis. 
There is a gradual elevation, as we proceed southward, of all 
these zones or belts of vegetation, which may at times consist 
1 For information regarding San Francisco Mountain I am indebted to Mr. G. E. 
Gilbert (Geologist Geolog. and Geograph. Exp. for Explor. Nevada and Arizona, 
1871-2, Lt. G. M. Wheeler, Corps of Engineers, commanding). 
