164 
GEOLOGICAL STRUCTURE OF THE PINALENO GROUP. 
south of the Gila, commencing in longitude 112° west and extending to 110°, and running 
obliquely north and south from latitude 31° 40' to 33° 40' N. 
The Salinas river skirts around the northern border. The Gila river canons across the whole 
series of ranges, on parallel 33°, and the San Pedro runs between the two western ranges from 
south to north. The three ranges ruu parallel during their entire course, preserving a pretty 
uniform direction of N. 45° W. and S. 45° E. The granitic axis lies to the west, constituting 
the Santa Catarina mountains. Basalt outpourings are on its eastern and western flanks, and 
on the eastern slopes are immense overflows of trachyte and porphyry, which have not only 
perforated and intermingled with the granite rock, hut by forming rents and fissures and 
injecting fluid mineral into the sandstone rock has metamorphosed it completely. An analysis 
of the trachyte of this range is given in the chapter on chemical analysis. The rock was reddish 
felspathic rock, with crystals of quartz disseminated throughout. 
The same trachyte is found extensively in the Sierra Calitro, hut the great mass of this latter 
range consists of the secondary rock upheaved; Devonian sandstones and conglomerates, 
resembling in lithological character the Caatskill sandstones, with metamorphic quartz, consti¬ 
tute the lower portions of the mountain, which has a thick stratum of limestone capping the 
Devonian rock. Trachyte and amygdaloid rock are injected in some places, and forms capping 
and intruded beds in others. 
The general dip of the strata of these hills is to the east, or rather east 12° south ; but they 
are broken, and dip variously in places. The sandstones are very thick, and are in contact 
with primary rock, either granitic, lamellar, feldspar, or trachyte. 
The Pinaleno range (properly called) forms the third and the most easterly of the system. 
This range is the loftiest and the most important of the three ; in it lie Mounts Turnbull and 
Graham, Chiricahui mountains, and the Guadalupe range; the two latter are locally uncon¬ 
nected with the northern range, but they lie in the same trend, and have the same structure, 
and are, therefore, geologically one. The whole range has a central granitic axis of great 
breadth, (ten to twelve miles,) upon which lie conformably the Devonian and lower car¬ 
boniferous rocks. The same sandstones and limestones which were seen on Calitro are here, 
the sandstones less displayed, the limestones more perfectly. Of the age of this last rock there 
could be no doubt, from the productus and encrinal stems so extensively distributed ; it is very 
argillaceous in composition and highly metamorphic, passing into a fine saccharine marble in 
places. Trappean and serpentine rocks are found in this range, the latter being auriferous. 
As the cretaceous strata of the San Pedro valley lie unconformably between two ranges of this 
system, it appears that the whole was elevated anterior to the cretaceous period. There are no 
rocks of the later carboniferous period found, nor do the sandstones of the Permian epoch, which 
are found east, appear in this range. Such may exist on the lower slopes of Chiricahui, hidden, 
perhaps, by the clays and gravel, in which case their elevation would not date further back than 
the Jurassic period. Since their elevation and the deposition of the unconformable cretaceous 
beds the whole western portion of the system was subjected to the action of a heavy current, de¬ 
positing the conglomerates, which are found in the south of the San Pedro valley, from 80 to 
130 feet thick, a deposit which is not found further east, but to the west may be traced to the 
very slopes of the Cordilleras, and occupying the sides of every hill of any elevation in the 
intervening space. 
Limestone, serpentine, and porphyries are the chief rocks of the eastern range, and granite 
and sandstones of the west. The minerals are few—marble in Chiricahui, and gold in the ser- 
