DESERT REGIONS OF NORTH AMERICA. IQ" 
alluvial slopes, which at the northern end of the Sierritas extend for 7 or 
8 miles from the more abrupt rocky slopes (plate 7). 
TORRES. 
The plain in which lies the railroad station Torres has an elevation of 
about 800 feet above the sea. Its most characteristic vegetation is a 
growth of small leguminous trees, notably palo fierro (Olneya tesota) and 
palo verde (Parkinsonia), two species of Cereus of large dimensions (C. 
thurbert and C. schotti1) (plate 8), and two cylindrical-stemmed species 
of Opuntia. The palo fierro, meaning iron-wood, produces a very hard 
wood, which, with the lighter but still hard mesquite (Prosopis) and the 
zygophyllaceous guaiacan, or lignum-vitz (Guaiacum coultert), consti- 
tutes the greater part of the fuel used on the railroad locomotives. Palo 
fierro is considered by the railroad officials a better fuel, by about 25 per 
cent, than mesquite, and guaiacan about 10 per cent better than palo 
fierro (plate 9). A metric cord (that is, a pile 3 meters long by 1 meter 
high and 0.75 meter in length of stick) of mixed palo fierro and guaiacan 
was considered by an engineer of experience as the equivalent, for fuel, of 
a tonand a halfof the ordinary soft coal available in the Southwest. The 
palo verde, of which the region contains two species and perhaps more, is 
an especiallyabundanttree. Itisin useeverywhere for household fuel, and 
one of the species (Parkinsonia microphylla) is commonly employed as 
green forage for horses in winter, the branches being cut and thrown into 
the corrals, where the horses eat the twigs to the diameter of nearly half 
an inch. It is probable that at this season the twigs contain a large 
amount of stored food. Cereus schottiit, as well as another smaller species 
of the same genus, is known as sina. Cereus thurberi is called pitahaya. 
One of the common species of Opuntia, probably O. thurbert, known as 
siviri, forms a small tree 8 to 15 feet high, with cylindrical joints about 
half an inchin diameter. It possesses a sour fruit which during the 
season of drought is an important source of refreshment to wild animals 
and even to man. The other common cylindrical-stemmed Opuntia, 
called cholla, has joints several times thicker and grows only 2 or 3 
feet high, but forms large patches which are a conspicuous feature of 
the vegetation. Other woody plants showing adaptations to desert con- 
ditions are sangre de drago (Jatropha), a shrub with whip-like, at this 
season wholly leafless, brown stems, from which the Papago Indians make 
some of their baskets; vinorama, a tree acacia (A. farnesiana) with yellow 
scented flowers; papachi, a small rubiaceous tree (Kandia thurbert) with 
fruit resembling in appearance a small green orange; bebelama, an un- 
identified tree with a trunk sometimes 18 inches in diameter, its wood so 
hard and tough that it is commonly used for wagon fellies; and desota, 
or tree mimosa, with pink flowers which have the delicious odor of the 
black locust flower (Robinia pseudacacia). This desert produces also 
