PRELIMINARY SURVEY—MISSION VALLEY. 
17 
however, it should he stated, presented many serious obstacles to a comprehensive examination 
of the district. It is possible that several of the numerous passages that extend their ramifica- 
cations through these mountains may afford a practicable way for a road ; but if so, they were 
unwittingly neglected or passed by as impracticable. It is often the case that narrow canons 
lead up from between the foot-hills of this range, and finally open out into broad ravines which 
penetrate the mountains to a considerable distance. 
The valley of the San Diego river was next examined, which, though more than forty miles 
in length, had scarcely been explored by white men beyond the Cajon Rancho, eighteen or 
twenty miles from its mouth. A rapid reconnoissance of this route showed that if its grades 
were not impracticable, it would fulfil all the necessary conditions of a favorable location for the 
road. Its source being in the vicinity of the valley of Santa Isabel, which connects with 
Warner’s Pass, the best known passage for travel over which the present wagon road to Fort 
Yuma passes, and its connection with that valley by means of a tributary gorge or ravine being 
ascertained, it only remained to show whether the elevation at the summit of Santa Isabel could 
be overcome by any grade within the limits of practicability. 
An inspection of the San Luis Rey route exhibited at once its inferiority to that of San Diego 
river, and until a careful survey of the latter should prove that the expectations formed of it 
were unfounded, it was not deemed advisable to undertake an elaborate survey of any of those 
further north. 
Accordingly the requisite measures were taken to organize and equip a surveying party to 
measure and level accurately the proposed line, and examine incidentally its immediate vicinity, 
so that a change in its location might be effected without the necessity of a re-survey. 
PRELIMINARY SURVEY OF THE LINE. 
Although the survey of the interior, or mountain division of the line, was accomplished first 
in point of time, the results in this report will be given commencing at the initial point of the 
line, on San Diego bay, and reference will be made thereto in the accompanying tables of grade 
and distance. 
MISSION YALLEY. 
From the shore of the bay to the point where the line enters the Cajon gap, the route passes 
first over the marshy and sandy plain, dividing it from the plateau upon which the town of San 
Diego is built, and then follows, by a nearly straight line, the sandy bed of the river, through 
the Mission valley to the ££ Mission ” of San Diego, (a military post, garrisoned by a detachment 
of the third artillery.) The line repeatedly intersects the sinuosities of that stream in its passage, 
but this circumstance will not compel the construction of a single foot of bridging, as an 
embankment of from three to four feet in height, well guarded with gravel and firm earth, will 
suffice to retain the waters of the river during the wet season upon either side of it. The valley 
is from half a mile to a mile in width, destitute of trees, and of loose sandy soil, covered with 
a thick growth of bushes. The side hills are composed of clay and gravel, about one hundred 
feet in height, sloping uniformly from the table land above. From the bay to the Mission the 
distance is a little over seven miles, the difference of level between the two points 64.46 feet, and 
the average grade 9.14 feet per mile. From the Mission the line deflects with the course of the 
river to the left, and a good location may be had on either side of the valley to the point of 
3 W 
