——————— EDO 
EXPLANATION OF MAP.—PROFILE. 15 
tinuous travelling reached the river-bottom at noon. After halting a couple of hours, we moved 
on to our camp at the post; distance thirty-five miles. - ` 
The map has been constructed simply from bearings taken by a prismatie compass, and 
distances along the route measured by a viameter. Before entering upon the field of the survey, 
my chronometer most unfortunately met with an accident, rendering it unserviceable. For the 
latitude and longitude of the point of departure on the Gila, of Tuczon, and of the point of 
striking the Rio Grande, I am indebted to Major W. H. Emory, topographical engineers, in 
charge of Mexican boundary survey. 
The red full line is the line of survey over which the wagons passed. The red dotted is the 
line of survey made by returning from camp on Rio Bravo, having a small party with pack- 
mules. The full blue line indicates where, and how, obstacles encountered upon the full red 
may be avoided, as shown in the profile and notes; and although it does not indicate a line 
actually passed over and surveyed, it nevertheless is located from observations made while on 
the field. The blue dotted is suggestive, and indicates where still further improvements may 
probably be made, depending upon other explorations and detailed surveys. By referring to 
the map it will be seen that the dry bed of stream passing Tuczon has, after leaving the point 
of the hill at camp No. 12, station 2, a slope and direction towards the northwest, which, 
according to information obtained at Tuczon, it retains until reaching the Rio Gila, opening 
out into its bottom at a point about twenty-five miles below camp No. 10. In that case a saving 
of distance will be had, and a continuous grade obtained from the Gila to Tuczon. 
In the Puerto del Dado it may be found practicable and advantageous, after a minute survey, 
to pursue the blue dotted line, crossing the ridge of a low spar, and thus obtain a less curved 
trace; and in case the cutting and embankments upon either of the lines in the Puerto require 
too much work, the whole ridge may be turned on the north, the maximum elevation to be over- 
come being not more than 4,862 feet, the approximate altitude of camp Castro, in the foot-hills 
of Mount Graham, furnished me by Major W. H. Emory, topographical engineers; but this 
detour will be made greatly at the expense of distances. From the plain of the Playa de los 
Pimas a gap was seen extending towards the mouth of the San Pedro, apparently a continuation 
of the plain. 
- Should a practicable descent be found in this direction to the San Pedro, and thence to the 
Rio Gila, this route will possess decided advantages when taking into consideration the questions 
of water and distance. 
After turning the Chiricahui mountains, à more direct route eastward may be had, depend- 
ing upon the practicability of the gaps in the ridge to the east of the Valle de Sauz. 
From camp No. 24, station 4, an open plain extends in the direction of blue dotted line, pre- 
senting, as far as could be observed, no other obstacle than the lack of water, to the running of 
an almost direct route tangent to the northern end of Sierra de Florida. 
When reaching the Rio Bravo I found that to pursue the survey through northern Texas, as 
was suggested in my instructions, would involve the necessity of incurring a debt equal to the 
amount of appropriation allowed me; and as Captain Pope, of topographical engineers, had 
started about one month previous on this line, I deemed it advisable to close my work, discharge 
such of my party as could be dispensed with, and start to this city by the most direct and ex- 
peditious route via San Antonio and Indianola, Texas. 
PROFILE, 
No. 1, the lower, is the profile of line passed over by the wagons during the survey, indi- 
: cated upon the map by a full red line, and is constructed from altitudes measured by Green's 
cistern barometer 387 and 392, and distances measured by a viameter attached to a wheel of the 
instrument wagon, by assuming the altitude of the starting point on the Rio Gila as zero, and 
referring the altitudes of the several points along thelinetoit. It therefore gives approximately 
