1877.] Vegetation in Nevada and Arizona. 337 
disappearing before sunset. The rain seldom reaches the base, 
as the parched sandy soil absorbs it before it descends half-way 
down to the foot-hills, except in case of cloud-bursts when the 
water tears up a new channel and rushes out over the desert 
to sink at once in the soil. These storms do not affect the at- 
mosphere of the plains perceptibly. Differences of wet and dry 
bulb readings show variations ranging from 5° to 45° F. 
The flora of that portion of Arizona under consideration may 
likewise be classed under the same divisions, excepting that the 
fourth class gradually diminishes, giving place to that of the dry 
sandy deserts — which we will include with the third class — of 
the plains in Nevada. 
The following table is arranged according to the latitudes, 
commencing at the northernmost point (Bull Run Mountain) 
and running south : — 
Name, above Sea Level.| ‘Timber Line. | Latitudo. | Wearest Plains, 
Bull Run Mountain....... 8,450 8,300 41° 40/ 5,800 
Prospect Hill... ... trees Pas 9,650 9,400 39° 30 6,000 
Belmont pies 12,000 9,700 38° 407 ` ,000 
Mt. Nagle i 11,000 11,000 1 37° 46/ 200 
Mt. Macgruder........... 11,500 11,150 37° 40/ ,200 
San Francisco Mountain.. 13,500 { 12,500 35° 19/ i 6,500 
4 13 2 6,800 
Bill Williams Mountain. .. 10,030 3 35° 13/ 6,500 
Mr. J. M. Coulter,‘ in his report upon the flora of Colorado, 
ete., says “ that there is a very regular increase in the elevation 
of the timber-line as the latitude decreases, subject, of course, to 
variations when in the neighborhood of high table-lands or seas.” 
This not only holds true in that region between the Rocky 
Mountains and the Sierra Nevadas, but, in taking a view of the 
section from Bull Run to Mt. Macgruder in Nevada, and as 
far as Bill Williams Mountain in Arizona, we have a barometric 
profile upon which not only the timber-line follows that law, but 
likewise different genera of plants and trees. The level of the 
prairie at Bull Run is 5800 feet above the sea, while at Mt. 
Macgruder — the southernmost point of observation in Nevada 
—it has risen to 7200 feet. At Bull Run the timber-line, at an : 
altitude of 8300 feet, terminates with the upper line of the belt 
1 The altitude of Mt. Nagle does not reach that of the timber-line. 
* The timber-line on this mountain is irregular, approaching to within one thou- 
Sand feet on the eastern side and five hundred feet on the western. 
. Williams Mountain does not reach the elevation of the timber-line. 
r F. V. Hayden’s Report, 1872, page 751. 
VOL. XI. — No. 6. 22 
