568 ADAPTATION OF THE. COUNTRY 
the north and at the south. Coming from the north, they 
present but few openings until they reach the parallel of about 
32° 40’, where they suddenly fall off eight miles south of Fort 
Webster and disappear entirely. At Fort Webster,* between 
the Gila and the Rio Grande, these mountains attain a height 
of more than eight thousand feet above the level of the sea.7 
They rise in peaks, separated by narrow and intricate valleys, 
and maintain this character until they terminate on the pla- 
teau, as stated. This plateau extends southwardly through 
the greater portion of Mexico. 
In about the latitude of 31° 15’ north, the great Cordillera 
range again begins to appear on the western border of the 
table-land, and is as it were the concentration of many lesser 
ridges into one vast chain, elevated, compact, and impassable, 
extending through the entire length of New Mexico to the 
Cordillera of the Andes in South America. The wagon road 
of Colonel Cooke, followed by the Commission, crosses a spur 
of the Sierra Madre here. A second pass, for mules only, 
exists a short distance further south, connecting Correlitos 
with Babispe ; after which there is no passage through, nor can 
these mountains be crossed again with mules for several hun- 
dred miles, 
The river Gila, from its source to a point about fifty miles 
below where the San Pedro enters, is closely hemmed in by 
lofty and impassable mountains. After this they appear only 
at intervals, and not in continuous chains. The rest of the 
valley of the Gila is quite open to its junction with the Colo- 
rado. The mountains in a few instances reach the banks of the 
* Fort Webster was established at the Copper Mines, or Santa Rita det 
Cobre, after they were abandoned by the Boundary Commission in October, 1851. 
+ Mr. Henry C. Force, the indefatigable officer in charge of the meteorologi- 
eal department attached to the astronomical party of Lieutenant Whipple, as- 
cended to the highest summit of the Bufa del Cobre, near our encampment, 
with a barometer, and ascertained its height to be seven thousand nine hun- 
dred and ninety seven feet above the level of the sea, and one thousand eight 
hundred and one feet above the valley where we were encamped. 
