14 
ADAPTATION OF COUNTRY TO THE CONSTRUCTION OF A RAILROAD. 
tracted valley than below, the number of lateral ravines and streams are greater, requiring a 
greater amount of masonry and earth work. The graduation, however, will be compara¬ 
tively easy, for the cuts and fills will nearly balance each other, and a large majority of 
the lateral ravines will require hut small culverts or percolating drains, and many of them 
none at all. There will he five first class bridges required across the San Lorenzo, the Salinas, 
the San Antonio, the Nacimiento, and Pasa Robles creek. The materials for the construction 
of the piers and abutments of these bridges are at hand at the respective places, though not of 
a first rate character. Several smaller works of this character will also he necessary at several 
points throughout the division. The line pursuing, for the most part, the windings of the valley, 
is throughout a curved line ; hut it is believed, from careful observation, and measurement where 
practicable, that no curve of less than 4° will he required ; nor, indeed, throughout the entire 
distance, from San Jose to Los Angeles, will a radius of less than 1,000 feet be necessary. 
The length of this division is ’71.50 miles. 
Maximum grade required, 70 feet per mile. 
Probable cost of graduation and superstructure, $3,575,000. 
Cost per mile, $50,000. 
Fifth Division. — From Santa Margarita valley to the mouth of Arroyo Grande. —This division 
comprises, perhaps, the most difficult and costly portion of the route, from the boldness of the 
work required to overcome its difficulties ; it contains the celebrated San Luis Pass through the 
(Coast Range) Santa Lucia mountains, and is the only passable point of these mountains between 
the Bay of Monterey and its southeastern extremity. The wagon road occupies this pass.* The 
height of the summit is 1,556.5 feet above the level of the sea. The height of Santa Margarita 
valley is 978 feet, and the San Louis plain about an average height of 300 feet. The point 
of tunnelling is two hundred feet helow the summit, and at the foot of the cuesta or sharp divide 
which lies between the disjointed mountains. To reach this point the line is projected on the slopes 
of the hills on the west of Santa Margarita, and ascends with an uniform grade of eighty feet per 
mile. This ascent will not he attended with any excessive cost of graduation, the side slopes of 
the mountain being remarkably tenable, there being no gorges to fill, or wide valleys to span, and 
presenting favorable cross sections for side cutting and embankments. The tunnel, three- 
fourths of a mile in length, is through serpentine and sandstone rock, and can be advantageously 
worked from both sides. In the construction of a road through this pass, should this tunnel he 
considered too formidable a work, there is no obstacle to passing this mountain, without cutting, 
by a system of heavy grades, similar to those which have been worked so successfully for several 
years across the Blue Ridge at Rockfish Gap, where the traffic and travel of a great part of the 
valley of Virginia has been carried over this mountain, over a grade of 275 feet per mile. To 
accomplish the passage of the San Luis summit, there will he required a much less rate of 
gradient, probably not over 200 feet per mile. On the west side of the cuesta the San Luis 
creek heads, and descends rapidly to the plain through a wide valley, flanked on either side by 
rib-like spurs from the mountain, which have a slope of about 30°, the alternating ravines 
being, except in one instance, shallow; four and one-half miles below there is a lateral ravine, 
heading with a stream which flows through the plain to theocean, called Corral de Piedras creek, in 
a summit 1,191 feet above tide, and in the prolongation of the valley from the cuesta. A glance 
* A line of levels was run through this pass from Santa Margarita valley to the mouth of Arroyo Grande, but upon plotting 
them they were found to have irreconcilable errors in them ; and as it would have involved a great loss of time to run a second 
series to check these errors, it was not deemed advisable to do so. A longer series of barometric observations than we were able 
to take, in connexion with these levels, would have been necessary to institute comparisons between these several modes of 
determining elevations. 
