154 
VOLCANIC ROCKS OF THE DISTURBED DISTRICT. 
without dislocating the strata so much as to tilt them up sharply. They have been dislocated 
very much in places, hut the result has apparently been to produce faults, as if the whole strata 
had been elevated, and afterward, settling down unequally, produced the fissures or faults. It 
is worthy of remark that each valley, from the Santa Catarina range, with one exception, is at 
a higher level the more east it lies, thus: 
Elevation of the San Pedro at Tres Alamos___ 3,413 feet. 
Elevation of Valle de 1 os Pimas...-. 4,127 “ 
Elevation of Valle del Sauz.... 3,815 “ 
Elevation of Valle de los Playos, west side..______ 4,269 “ 
Elevation of Valle do los Playos, east side .......... 4, 330 “ 
Thus, the effect of the Peloncillo range is to elevate the valley east of it over 450 feet, and 
the smaller range of the Pyramids appears lo lift its valley 60 feet above its neighbor. 
The trachyte and basalt country here blend together, forming a very elevated rugged land of 
hill and small valley, with rough canons ; it abounds in small wells and springs, which are found 
in the canons, from four to six miles apart, the water being clear and wholesome. 
BURRO MOUNTAINS, PENASQUITAS. 
Leaving this valley of the Playas to the east, the foot hills of the Burro mountains are entered. 
These, in constitution, resemble the Peloncillo and the Pyramid hills, and differ from Chiricahui 
in this regard, that they have not a central igneous nucleus around which the strata are inclined, 
hut are rather a series of waves, upraising great breadths of land, with bluffs generally to the 
east, and sloping more gradually westward ; and though these hills individually attain no great 
elevation, the whole country appears to have been lifted up considerably. These porphyritic 
chains appears to have a pretty uniform direction N. 60° W., which is a much greater inclina¬ 
tion than either Chiricahui on one side, or the Organ mountains, on the Bio Bravo, on the other. 
By this trend of the hill ranges open low canons running east and west traverse them every¬ 
where, and passes from one valley to another are easily found. The yellow sandstone is in 
some places hardened like enamel; in others, converted into agatized layers. The Burro hills, 
whose southern extension is crossed at Penasquitas, and forms the rolling country at Ojo de la 
Inez and Ojo de la Vacca, lie more to the north, where they are gathered round the hanks of 
the Gila, through which the river canons. They are there lofty rugged masses of sandstone, 
broken through by trachyte and porphyries, narrowing the bed of the river, and diverting it 
northerly from its previous southern course. As the chain passes south, it drops down at the 
point where the trail crosses. None of the hills exceed YOO or 800 feet in height. 
Exposures of rock in the canon leading to the Ojo de la Inez showed the same succession of 
trachyte and porphyry rocks as on the Peloncillo ridge. The valley of the canon ran up north¬ 
west, and was about 250 yards wide near the spring or water-pool. On each side the hills rose 
from 250 to 300 feet, capped at the summit by trachyte, covering up yellow sandstones and 
conglomerates. Thus, one hill, on the south side of the valley, viewed from above, downwards, 
afforded the following structure : 
The estimation in feet is approximate. 
Trachyte porphyry_ 30 feet. 
Metamorphic sandstone___ 25 “ 
Blue silicious and chalcedonic rock... 20 “ 
Talcose and trachyte layer__ 2 “ 
Yellow sandstone shale, dip 12° N. 20° W._____ 45 “ 
Conglomerate of agatized pebbles...... 50 “ 
172 “ 
