SOUTHERN PACIFIC LINES 159 
grain, possibly of pre-Cambrian age, although it resembles the 
younger intrusive granite of the Dragoon Mountains. This pictur- 
esque granite area is traversed by the highway northwest of Dragoon, 
where it presents an extraordinary variety of remarkable erosion 
forms, notably rounded masses. The rock contains large crystals of 
feldspar, which weather out conspicuously, and also veins of tungsten 
ore (wolframite and scheelite), which were mined during the World 
War.” Pre-Cambrian schist is also exposed, in places overlain by 
Bolsa quartzite, Abrigo and Martin formations, and limestones of 
Carboniferous age that constitute the crest of the high ridge just west 
of the mining camp and also a ridge on the east side of the valley, 
east of Johnson. The general features in this vicinity are shown in 
Figure 38. The Abrigo limestone consists mostly of slabby beds and 
includes considerable sandy shale. At the top is a sandy member, as 
t 1 1 
J a eee 3 J 
rs 
Qkatah As h Te 1, 1 oe 33. 
FIGURE 38. through t 
in the Bisbee region. An outlier of this formation alae rg ridge 
which is skirted by the railroad 4 miles southwest of Drag 
From Dragoon west there is a steep down grade into ns dies valley 
of the San Pedro River (pay’dro). This depression is very different 
in character from the broad, high basin of Sulphur Spring Valley—a 
difference due to the presence of a vigorous stream which has cut a 
deep, wide trench into the thick body of old stream deposits that 
originally occupied the valley. The San Pedro River rises in Mexico 
and has many affluents from the Mule, Huachuca (wa-choo’ ca), 
Whetstone, and other mountains. Ordinarily its flow is not large, 
but in times of heavy rainfall there are freshets which erode the soft 
valley deposits and carry a large volume of detritus to the Gila River. 
The railroad in its descent to Benson requires many long loops to 
diminish the grade, and there are numerous deep cuts through the 
materials of the valley fill. On this grade near and beyond Ochoa 
siding there are fine views of the Rincon Mountains (rin-cone’) to the 
northwest and the Whetstone Mountains to the west. The Huachuca 
Mountains lie far to the south; to the southeast, in the Dragoon 
Mountains, the impregnable western wall of Cochise’s Stronghold can 
17 Tungsten is used mostly for the | one-seventh from the United States. 
filament in electric lights and for hard- | Tungsten ore also occurs in veins in 
ening steel, especially tool steel. A | granite on the east slope of the Whet- 
large proportion of the ore now used | stone Mountains southwest of Benson. 
comes from China and Burma and only pli 
