100 
ROCKY MOUNTAIN PASSES. 
wagons. A wagon can now, it is reported by Lieut. Mullan, be taken through the Hell Gate 
and the southern Little Blackfoot passes. 
The two passes of the Big Blackfoot trail are both practicable and have good approaches. The 
divide of this pass is a narrow and sharp ridge, at whose opposite bases, 2J miles apart, head small 
tributaries of Beaver creek in the east, and Blackfoot river in the west. 
Lewis and Clark’s Pass connects the headwaters of Dearborn and Blackfoot rivers, and but 
a few miles north of Cadotte’s Pass at the sources of other branches of the same two rivers. 
The summit ridge has here an elevation of 6,323 feet, in a narrow and sharp ridge, at whose 
opposite bases, 2J miles apart, head small tributaries of Beaver creek in the east, and Blackfoot 
river in the west. 
The pass involves a tunnel of two and a half miles, grades of approach of forty feet to the 
mile, and grades descending into the valley of not exceeding fifty feet. Cadotte’s Pass requires 
a tunnel of four and a quarter miles at an elevation of about 5,000 feet above the sea. The grades 
approaching it from the east will be sixty feet, and those from the west forty feet. 
This pass connects a tributary of Dearborn river in the east, with a tributary of the Blackfoot 
river in the west. From the foot of the divide in the east a small tributary falls off with a rapid 
descent of over one hundred feet to the mile. On either side of the brook are high wooded hills 
making up into the mass of wooded mountains. The approach to the pass is on the side-hills 
to the north of the brook. Between the pass and the plains are the tributaries of Beaver creek, 
rapid mountain streams flowing in deep ravines. The summit is a narrow sharp ridge, about 
one and a half mile between its opposite bases, and is only partially covered with a small-size 
growth of trees. The western base is some five hundred feet higher than its opposite, and the 
least descent, like that of the east, is for a short distance very rapid, favoring the use of a tunnel. 
Both passes will, on the map, be represented as practicable, but that of Lewis and Clark’s will 
be adopted in the railroad estimate. For full details in relation to these entrances I will refer 
you to the report of Lieut. Donelson and the sub-reports of Messrs. Lander and Tinkham. 
It is proper here to observe that the railroad line was not carried down the entire distance 
from Lewis and Clark’s Pass to its connexion with the line from the pass in the Blackfoot trail by 
Mr. Lander; a link of about four and a half miles is wanting. As regards the former, it is estab¬ 
lished that it can be approached by a grade of forty feet, that the mountain can be pierced by a 
tunnel 2.59 miles in length, and that for seven and a half miles the general inclination of the 
valley is forty to fifty feet per mile. The connexion has not been made, though believed to be 
practicable at a grade not exceeding fifty feet per mile. Should this be established by subse¬ 
quent examinations, it will prove the preferable route. I have shown on the sketch a comparison 
of the two routes, in which I indicate the portion not examined on the route pursued by Mr. 
Lander. 
In the Blackfoot trail the grades will vary from thirty-five to forty-five feet per mile. There is 
a somewhat narrow gorge, ending in Hell Gate, extending some twenty miles, of which the work 
will be expensive, but the grades will be light, and no sharp curvature. 
From Hell Gate the road can run in the valley of the Bitter Root river to Clark’s fork, or, 
by crossing a divide, Clark’s fork can be reached by the valley of the Jocko river. The 
valley of the Bitter Root will involve several heavy bridge crossings, some sharp curvatures, 
but no grade exceeding fifty feet, and few approaching forty. 
Barometrical observations w r ere not made by Mr. Lander in going down the Bitter Root val¬ 
ley, but it is believed no difficulty will exist as to grades. The fall of the river from Lieut. 
Donelson’s camp, on the Bitter Root, of October 5th and 6th, to Plorse Plain, is eight hundred 
feet, and the distance seventy-two miles, and gives, on the supposition of a uniform grade, llyg 
feet to the mile. By reference to Dr. Suckley’s report it will be seen that he made the whole 
distance with boats, meeting no rapids that interfered with the navigation of the river, and his 
observations in reference to its practicability for a railroad confirm the opinion of Mr. Lander, 
