161 
The San Pedro River was the Rio Nexpa of the era when De Niza 
and Coronado made their expedition from Mexico to the Indian 
pueblo of Zufii in quest of the somewhat legendary ‘Seven Cities of 
Cibola.” It seems probable that their route led from Mexico down 
the San Pedro Valley as far as the site of Benson, thence eastward 
over Dragoon Pass and Railroad Pass to the San Simon Valley, which 
it followed northward to its junction with the Gila River. A hun 
dred and fifty years later Padre Kino made an exploration wih 
Lieutenant Mange and Captain Bernal along the San Pedro from 
Quibure northward along the base of the Rincon Mountains to its 
junction with the Gila and thence to Casa Grande and beyond. The 
valley was fertile and irrigated, and the Indians were industrious, 
raising maize, frijoles, calabashes, and cotton. There were 14 villages 
and 2,000 Indians, all very friendly to the friar. This line of travel 
from Benson north was followed by the road from El Paso to Yuma 
for which Congress appropriated $200,000 in 1857; Bancroft gives it 
as the route of the Butterfield stages, but Hafen includes Tucson in 
their itinerary. The road previously opened by Colonel Cooke and 
the Mormon Battalion left the San Pedro Valley at Benson, turning 
west to Tucson, the course now followed by the railroad. It leads 
through the broad divide between the Whetstone ® and Rincon 
Mountains at Mescal. On this rather steep climb there are many 
cuts through the valley fill and extensive badland slopes, and as the 
top of the grade is approached there are excellent views of the Rincon 
Mountains to the north and the Whetstone Mountains to the south- 
west. The Rincon Mountains consist of pre-Cambrian schist with 
SOUTHERN PACIFIC LINES 
19 The Whetstone Mountains consist 
3 wa cgansic block of pre-Cambrian 
y Paleozoic limestones 
ibid Cretaceous ee but as in most 
mountains of this character rising out 
of alluvial valleys, the structural rela- 
tions at the sides and ends are no 
et 
Granite constitutes the foot- 
hills and peaks on northeast end of 
the range except a irting 
ski 
ridge of Lower Cretaceous (Comanche) 
sandstone and shale lying about 5 miles 
south of the railroad. A small area of 
Pinal schist appears on the east slope, 
faulted against Carboniferous lime- 
stone, and a thick mass of Cretaceous 
strata constitutes the southern third of 
the range, sa is not visible from the 
railroad. e 39 shows the prin- 
cipal tana § in me northwestern part 
of the range. The succession, which is 
typical for southern Arizona, has basal 
quartzite (Bolsa) of Upper Cambrian 
age, overlain by Abrigo slabby lime- 
stone (Cambrian) which closely re- 
sembles the El Paso and Longfellow 
limestones. The Abrigo weathers to a 
light gray-blue color with brown retic- 
so 
layers of sandstone and sandy shale. 
The Martin limestone, next above, 
contains numerous fossils of Devonian 
age, some of them finely preserved, and 
the overlying limestones, which are 
1,000 feet or more thick in the center 
of the mountain, include representa- 
tives of the E. 
The high southern summit, known as 
Granite Peak, appears to be a mass of 
| intrusive porphyry cutting Cretaceous 
strata. 
