REPORT AND ESTIMATE. 337 
at an elevation of four thousand three hundred and forty feet. There is a high ridge five and 
six-tenths miles beyond the crossing of Crown Butte creek, and twenty miles from Sun river, 
where a tunnel will be required a half mile in length. This ridge has an elevation of four 
thousand two hundred and thirty-five feet above the sea, and the summit level of the tunnel 
. will be four thousand and seventy-two feet. The grade, on the supposition that it will be 
uniform from Sun river to the tunnel, will be forty-four feet per mile, but the work will be 
difficult, and it will not probably be found practicable to dispense with less than sixty feet 
grades. 
From this tunnel to the Dearborn there will be a rise in the whole distance of two hundred 
and sixty-eight feet, giving grades, on the supposition that they are uniform, of sixteen and a 
half feet to the mile. From the crossing of the Dearborn to the entrance to the tunnel is a 
distance of ten miles, requiring grades of sixty feet to the mile. "This work will be very costly 
and heavy, and require very careful side-hill location. Besides heavy excavations and embank- 
ments, there will be a great number of small bridges and culverts. The eastern debouche of 
the tunnel will be in the debouche of a ravine, described by me in the narrative of 1855, which 
gives a much better approach than the usually travelled trail. The tunnel will be 4.19 miles 
in length, when there will be'a cut commencing fifty feet deep and coming out into the valley 
of the Blackfoot five hundred and fifty-eight thousandths of a mile west of the tunnel. The cut 
and the tunnel have a grade of sixty feet to the mile. The highest point of the road, therefore, 
will be at the entrance to the cut, at an elevation of five thousand one hundred and ninety-five 
feet above the sea, and eight hundred and forty-nine below the mountain summit. The entrance 
of the cut will be two and nine hundred and forty-eight thousandths miles west of the western 
base of the mountain, which is five hundred and sixty-seven feet higher than the eastern. This 
section, from Fort Benton to the entrance to the tunnel, is in the near vicinity of materials for 
construction; there is good building stone near the crossing of the Sun and Dearborn rivers and 
near the Crown Butte creek. The Teton, Sun, and Dearborn furnish sand and gravel as well 
as good cotton-wood. The Missouri and the mountains in the vicinity of the pass will furnish 
the yellow and pitch pine. Cadotte’s pass can be reached more readily on this route than hy 
going high up Sun river, crossing over to the Dearborn, and over the broken country lying 
between the Dearborn and the entrance to the pass. wr 
The route by the Missouri to the crossing of Sun river will be easier in its grades than that 
over the plateau, but it will be heavier work of excavation and embankment. There are many 
sharp points running down to the Missouri which must be dealt with in the same manner as the 
similar places which occur below Fort Benton. The distance will be sixty-three miles, or 
seven and a half miles further than the route over the plateau. There will be advantages, 
however, on the line of the Missouri in the unfailing supply of pure water, and its greater 
accessibility to all the materials of construction. à; 
To reach Lewis and Clark’s Pass, either of these routes may be taken to Sun river, when we 
continue up Sun river and its Elk or south tributary, a distance of forty-eight miles, or ten 
miles above the forks. The valley of the Sun river and that portion of the Elk Fork » very 
easy for railroad construction, and the Brides will vary from 43.5 feet to 5.03 tart per nei 
Starting from Fort Benton we make a rise in eleven and a half, twenty-five, sixteen, nie y 
two, fifteen, ten and a half miles, respectively, eighty-three, one hundred and sixteen, four 
one hundred and eighteen, one hundred and ninety-seven, three 
inety-five ў 
hundred and ninety-five, respective gradients of seven and 
hundred and twenty-five and one-tenth feet, giving the 
43 5 
