BOTANY. il 
trom the true O. arborescens, we called Cacto-dendron, finds its western limits near the termi- 
nation of this region. We also find here a mamillaria, very common, and the only one we 
saw between this point and the Rio Grande. 
At the southern base of Bill Williams’ mountain we found an Opuntia never before seen on 
our route, and from its peculiar appearance, it will doubtless prove to be a new species. It is 
an upright flat-jointed species, thickly beset with yellow spines, of a much lighter green color 
than most other species, or, indeed, any other that I have seen. Lieutenant Tidball, of our 
escort, kindly sketched it for me, and provisionally named it after him, to distinguish from 
other allied species. Opuntia fragilis, and Cer. Fendleri,.also occur here. There is an Opuntia 
in this region, very near, if not identical with the one on the Rio Grande, with long brown 
spines. It is published in Plantae Fendleriane, by Dr. Engelmann, as Op. pheacantha. As 
we proceed westward into the neighborhood of Picacho and Val de China, the 0. Tidballit 
becomes much more frequent, and we observed that it was never found on the northern and 
western exposures of the hills and rocky arroyos, but mostly on the southern, (as where we first 
found it,) and more seldom on the eastern exposures. In Cafion creek, the head-waters of Bill 
Williams’ fork near the western extremity of this region, it grows seven or eight feet high, 
spreading so as to form an immense head, with upwards of one hundred joints, all branching 
from a single stalk. At Aztec Pass an Opuntia was found, which in the size of the joints, and 
appearance of the spines, was very similar to Opuntia Engelmanni, but, unlike this well known 
species, it is spreading and prostrate. Unfortunately, we could obtain no fruit of it. 
Section VIII. Santa Maria Vailey.—The space embraced within this section lies between 
Cactus Pass and the Colorado Grande, following the course of Bill Williams’ fork, from near 
its sources, to the great river of the west. Cactus Pass is the last of the highlands that we 
cross before reaching the Rio Colorado. The distance from this point, in a direct line, to the 
Colorado, is only about sixty miles; but by the road we travelled, through the valley of Bill 
Williams’ fork, it is about one hundred and thirty miles. 
The timber of this valley is composed almost exclusively of cotton-wood, or alamo, mezquite, 
‘¢ green-barked acacia,’’ of Major Emory’s report, curly mezquite, (Strombocarpa pubescens,) 
two other leguminous trees, and some willows. One of the leguminous trees is the Olneya 
Tesota of Dr. Gray, in Plant. Nov. Thurberianae, pages 313 and 328.—1854. It was collected 
by Mr. Thurber on the Gila. It has very much the habit ofa Robinia. The foliage of the tree 
is very dense and heavy, and although dark green, the leaves were sometimes crisped as though 
they had been bitten by frost ; yet there were no evidences of frost on other tender vegetables 
in its vicinity. Our Mexicans were not acquainted with it, nor with the name Zesota. The 
alamos grow to a good large size, and are quite abundant. The two mezquites are rather 
small in this valley, seldom attaining more than fifteen or twenty feet in height. The Tesota, 
“‘ green-barked acacia,’ and the other leguminous tree, grow fully as large as the mezquites, 
and in an economical respect, it is presumed, will prove equally useful for domestic purposes. 
Although willows in many places grow quite large and abundantly, yet, for anything but 
browsing animals in times of great scarcity of grass, and for fire-wood, they appear to be nearly 
useless. 
Grass in the upper portions of this valley is quite good, and sufficient to support consider- 
able numbers of mules and stock in passing through. But in the lower portions, as we approaeh 
the Rio Colorado, grass of all kinds becomes quite scarce ; mules then resort to the twigs of the 
willow, and the twigs and bark of the alamo, upon which they have been known to subsist the 
whole winter. 
The water of Bill Williams’ fork, in many places, flows ina bold current; but, like the 
Mimbres, and other streams in this country, it sinks again in the sand, sometimes within a 
very short distance of its head. It rises and sinks this way, alternately. until it reaches the 
Rio Colorado. This valley, which is generally narrow, cannot be worth much for agricultural 
purposes ; yet there are several places where it widens, so as to form very pretty sites for settle- 
