572 ADAPTATION OF THE COUNTRY 
dulation, and for long distances requiring but slight excava- 
tions and embankments. The mountains may be passed through 
open defiles of easy ascent and descent. When the Gila is reach- 
ed, either the bottom or the table land may be followed ; though 
the latter will doubtless have the preference, as it presents a per- 
fectly hard and level surface. Ina few instances, ranges of moun- 
tains approach the bottom-land of the Gila. Openings may 
doubtless be found through these, or they may be passed by 
cutting away near the river. 
The Colorado River presents no difficulties for bridging. 
At Fort Yuma, where the Gila joins it, it is about six hun- 
dred feet wide, but above and below the junction, it expands 
toeight hundred and twelve hundred feet. In dry seasons — 
there is between four and five feet of water at, Fort Yuma. 
After this river is passed, we reach the great California 
Desert, about one hundred miles across, which increases in 
width towards the north. This desert is destitute of wood, 
water, and grass ; it presents a hard level surface with slight 
undulations, and seems almost graded by nature for a railway. 
After leaving the bottom or valley.of the Colorado, and before 
the table-land or desert is reached, there is a belt of moving 
sand. Its southern extremity is now about twelve miles below 
Fort Yuma, where I passed it with my parties without cross- 
ing it. Its breadth is about four, and its entire length, less 
than twenty miles. This is the only belt of moving sand that 
I know or within the district referred to, west of the Rio Grande. 
On passing this desert, we reach the Sierra Nevada, where 
a pass must be sought, and for this purpose engineers are now 
in the field. To reach San Diego, it will be necessary to tun- 
nel the coast range of mountains ; and it is probable that either 
a tunnel or an inclined plain with stationary engines will be 
indispensable to cross the Sierra Nevada, in order to strike the 
valleys leading to San Francisco. 
On the broad desert last mentioned, we found water in its 
very centre in two places by digging. ‘Sluices or basins are 
aa 
