54 - NEW TRACKS IN NORTH AMERICA. 
‘the middle, and the Sierra de la Santa Catarina the outer 
most westerly. Between these ranges are two troughs: 
eastern trough is called the Valley of the Aravaypa, north of 
Railroad Pass ; south of that pass it goes by name of Sulphur 
Spring Valley. The western trough consists of the long 
narrow valley of the Rio San Pedro. Both these troug 
were explored, and as no practicable pass could be fom 
through the first of these ranges but Railroad Pass, and as tl : 
one was unusually good in every respect, this entrance at 
the first trough was made use of by both parties. From this 
point the parties again separated, the one under Mr. Eicholt 
to follow down the first trough, through the stupendous 
gorge, the Aravaypa Cafion—a narrow passage cut by nature 
through the middle range—into the San Pedro valley # 
Camp Grant, a point sixteen miles from the junction of that al 
river with the Rio Gila; the second party, under ‘Mr. Runk 
to deflect southward fiom Railroad Pass, to cut through 
middle range (Sierra Calitro) by Nugent’s Pass, and to follo : 
down the San Pedro valley to the same point—Camp Gran 
—where the Arayaypa and Rio San Pedro unite. 
One may naturally ask, How does the Rio Gila, in its cou 
from east to west, make its way through the cordille 
This river strikes the mountains almost at right angles, 
passes through them in a succession of cafions, three 
number, Varying, as far as has yet been ascertained, 
twelve to twenty-five miles each in length. 
At Camp Grant we are still in one of the troughs (the t 
Pedro valley) between the mountains ; one range more § 
bars the way, and there are three routes by which it is poss 
to escape. The first and most northerly is by following ’ 
Rio San Pedro down to the Rio Gila, and then passing we 
ward along the latter stream through its last cafion, twe 
