DEVIATIONS FROM THE LINE OF SURVEY. 
61 
the dotted line upon the map. Should it be desirable to terminate the road at San Diego or 
Los Angeles, it might be found preferable even to descend the Rio Verde and the Salinas to Rio 
Gila, and there unite with the southern route. Such a connexion would join, bv a cultivable 
valley, the most favorable parts of the two routes ; and present a line bordered with arable soil 
adapted for settlement throughout a great portion of the distance between the Mississippi and 
the Pacific. 
Other lines, dotted upon the map, are respectfully recommended for examination. One is 
from Rio Gallinas, via Ojo de Vernal, to liio Pecos at San Miguel; and thence across the mesa 
to a branch of Rio Galisteo, which leads to Rio del Norte, at San Felipe. Crossing the river 
at that point, the line keeps a south-southwesterly course, to ascend the bluffs which bound it, 
then enters the valley of Rio Puerco, and joins the line of survey in the valley of Rio San Jose. 
Another route is indicated from the Val de China, through a break in the Aztec range near 
Sierra Prieta, and thence down Rio Santa Maria and Williams’ river to the Colorado. From 
the latter point a practicable route is believed to lead in nearly a direct course to Soda lake. 
By some of the methods suggested, it is believed that the greater part of the steep grades 
shown upon the profile, and given in the table, may be avoided. The length of the line might 
thereby be somewhat increased, but the expense of construction would probably be diminished. 
By a reference to the general maps it will be perceived that, in two instances, the trace for the 
profile departs widely from the positon of the wagon and reconnoitring trails. The first is 
from Big Sandy creek to the Colorado ; the second, from the Sacramento Springs to Soda lake. 
The country, however, in those regions is so open, that the several parts of it were plainly visible 
from various points upon our trail ; and the plotting of the triangulation notes, connected by 
the topographical sketches, left no doubt upon our minds that its character is such as is repre¬ 
sented. By the former, the great bend of Williams’ river is avoided, making the distance to the 
Mojave village considerably less, and producing also a saving in expense for rock-cutting and 
bridging. The grades, on the other hand, are greatly increased. The latter deflection effects 
a saving both in distance and in grade. Upon both, tanks would probably be required at some 
of the necessary watering stations. 
With reference to the elevation of the interior portion of the continent, as determined by 
comparative barometric measurements, it has already been stated that, from the non-application 
of a correction believed to be due to the diminution of the force of vapor in that region, the 
altitudes upon the central part of our line are probably several hundred feet too great. In the 
consideration of this subject, another idea has been suggested, viz : that a column of air upon 
the seacoast, the weight of which is taken as the standard of comparison, may contain, not only 
a large amount of vapor of water, but salts and other impurities in suspension, such as the air 
of the interior of the continent would be free from. In consequence of such unequal conditions 
of the air, differences of altitude would be too great, when deduced from the measured weights 
of the atmospheric columns. The amount of error due to this cause is probably small, yet it 
seems to be a subject worthy of investigation. However we may regret to throw doubt upon 
the final accuracy of the profile, it is gratifying to believe that the errors it contains have con¬ 
stantly the effect of exaggerating the difficulties to be overcome, and that future examinations 
will lead to more favorable results. 
In the table of grades, which has been carefully deduced from the field-notes of the survey, 
the maximum inclination is believed to have been noted upon every portion of the line, except 
from the point of leaving the Mojave river to Tah-ee-chay-pah Pass. There, but few points are 
given in altitude, and, between them, mean inclinations are represented. The intermediate ele¬ 
vations and depressions would increase the grades; but, from the general appearance of the 
country, I should have estimated the amount somewhat less than Lieutenant Williamson has 
stated in his report. In order to exhibit the proposed termination of this line upon the Pacific, 
by the consent of the department, the profile of Lieutenant Williamson is adopted from Tah- 
ee-chay-pah Pass to San Francisco. 
