18 
POOLE’S SURVEY FROM SAN DIEGO TO FORT YUMA. 
entrance at Cajon gap. By the left bank the distance is 2.65 miles, the rise 36.53 feet, giving 
a grade of 13.7 feet per mile. The ground is precisely similar in character to that below. 
CAJON GAP. 
At this point the nature of the ground changes, and the line is carried through a canon, of 
which the sides are composed of fragmentary masses of rock, the mountains rising on either side 
to a considerable height. The width of the pass varies from sixty to two hundred feet, and its 
course is somewhat tortuous and irregular, though its general direction is straight. Throughout 
its whole extent, on the right hank of the river bed, is an ancient canal or aqueduct leading 
from the valley above to the gardens of the Mission below. The water way of this structure is 
lined with brick, and is raised several feet above the hank by a substructure of durable rock 
masonry, averaging five or six feet in breadth. From the fact that this extensive work was 
built by Indian artificers, under the direction of the superintending priests of the Mission, and 
that it is now nearly half the width required for a railroad track, it appears evident that no 
great difficulty would be experienced in constructing a road bed for a railway upon nearly the 
same line and with the same material. 
The stream at the upper end of the gap is crossed by a solid dam of masonry laid in mortar, 
and is now in an excellent state of preservation. This dam formed a reservoir for the system of 
irrigation that was pursued in the entire Mission valley below. With trifling expense it could 
now be made available as a water-station for railway purposes. The distance to this point is 
2.76 miles, and the difference of level 181.78 feet, giving a grade of 65.8 feet per mile. 
CAJON VALLEY. 
On leaving the G-ap, the line passes into a long valley, bounded on each side by gently 
sloping hills, and filled in the middle with a wide belt of trees along the bed of the stream. 
These gradually inclined side hills offer an unsurpassed location for a road-bed, enabling the 
engineer to adopt any grade that circumstances may require, without a sacrifice of economy. 
The components of the soil are sand and a coarse gravel with pebbles, and at one or two points 
rock in a disintegrated form appears on the surface. It is also possible that hard red clay may 
be found in some of the excavations, as it frequently appears in the more elevated portions of 
the hills. The timber in the river “bottom” is chiefly willow and cotton-wood with occasion¬ 
ally some sycamore, which may be used economically for ties throughout all this portion of the 
work, renewable by a more durable material after the lapse of a few years. No bridges and 
but' few culverts will be required for this section, which extends to .the rancho of Cajon or 
“Santa Monica,” a distance of 7.3 miles. The elevation for this distance is 129.67 feet, and 
the natural grade of the surface 17.75 feet per mile. 
VALLEY OF CAPITAN GRANDE. 
Beyond the rancho of Cajon the valley becomes more narrow, is bounded by loftier hills, 
and covered with a denser growth of trees and foliage, among which are found large specimens 
of the sycamore and many oaks. The sandy bed of the stream is, in some places, obstructed 
by having heavy rocks that have been loosened from the hill sides by rains and fallen into the 
channel. The hill slopes are, in general, well adapted to the proposed construction, being 
gravelly and not difficult of excavation. There are some obstacles, in the form of rocky spurs, 
