ROUTE NEAR THE THIRTY-FIFTH PARALLEL. 75 
from Fort Smith 1,182 miles, and from the crossing of the Rio Grande 328 miles. Here it 
ascends to the dividing ridge between the waters of the Gila on the south, and of the Colorado 
of the West on the north, and continues (or nearly so) upon it for about 200 miles, to the Aztec 
Pass, (elevation 6,281 feet ;) distance from Fort Smith 1,350 miles. The highest point reached 
upon this undulating ridge is 7,472 feet at Leroux’s spring, at the foot of the San Francisco 
mountain. From the Aztec Pass the descent to the Colorado of the West is made by a circuitous 
route northward along valleys of its tributaries, the largest and last being Bill Williams 
fork, the mouth of which, on the Colorado, is 1,522 miles from Fort Smith, and at an elevation 
above the sea of about 208 feet. 
The Colorado is now ascended thirty-four miles, the route leaving it at the Needles. The 
supposed mouth of the Mojave river was examined: by the valley of this stream it was 
expected to ascend to the Cajon Pass in the Sierra Nevada. This proved, however, to be the 
valley of a stream, dry at the time, whose source was in an elevated ridge which, probably, 
divides the Great Basin from the waters of the Colorado. It is not yet ascertained that the 
valley of the Mohave river is continuous to the Colorado, though Lieutenant Whipple is san- 
guine that it will be found to be so. From the summit, 5,262 feet (cut thirty feet) above 
the sea, the descent is made to Soda lake, the recipient, at some seasons, of the waters of 
the Mohave river, 1,117 feet above the sea, at an average grade of 100 feet to the mile for 
forty-one miles, the steepest grade yet required on this route. The ascent to the summit of 
the tunnel, elevation 4,179 feet, in the Cajon Pass in the Sierra Nevada, is made by following 
the valley of the Mojave river. The summit of this pass, by the line of location, is 1,798 
miles from Fort Smith, and 242 from the point of crossing the Colorado. Here, according to 
Lieutenant Whipple, a tunnel of 24 miles, through white conglomerated sandstone, is required. 
But, according to Lieutenant Williamson, who spent more time upon it, it would be 3, 
miles. The tunnel descends to the west with an inclination of 100 feet per mile, which grade 
will be the average for twenty-two miles, into the valley of Los Angeles, by side location, 
and thence to the port of San Pedro, 1,892 miles distant from Fort Smith. 
Lieutenant Williamson reports upon the Cajon Pass, that, in his opinion, the natural 
grades, varying between 90 and 171 feet per mile, cannot be much reduced by side-location, 
on account of the broken character of the hills. 
Should it be desired to reach San Francisco by the Tulares and San Joaquin valleys, the 
route should leave the Mojave valley some thirty miles before reaching the entrance to the 
Cajon Pass, 1,768 miles from Fort Smith, elevation about 2,555 feet, and proceed across the 
southwest corner of the Great Basin, towards the Tah-ee-chay-pah Pass, reaching its entrance 
at an elevation of 3,300 feet, in a distance of about eighty miles, and without crossing ridges 
that would increase the ascents more than 500 feet beyond the difference of elevation of the two 
points. The route is then coincident with that described for the 32d parallel. 
The general features of the country indicated lines for examination at more than one point, 
which will, probably, greatly improve the route by reducing the ascents and shortening dis- 
tances. The party was, however, unable to examine them. 
An examination of the profile of this route shows that, in respect to grade, it is not only 
practicable, but that the heaviest grades that will probably be required do not equal those in 
use on the Baltimore and Ohio railroad. ; 
SOIL. 
Grama grass being found on the north bank of the Canadian, in longitude 96°, and extend- 
ing westward in greater or less abundance to the Sierra Nevada, indicates that the change 
from fertility to barrenness begins in that longitude, at least north of the Canadian. Cac- 
taceew also make their appearance with grama grass. South of it, however, the geological 
formation is that of a good soil to about longitude 984. At this point the change to uncul- 
