GEOGRAPHICAL MEMOIR. 247 
much of it is wooded. The prairies occupy but an inconsiderable portion of its valley and the 
surrounding country, yet there is no deficiency of grass, even for large trains, on this route, 
where care is taken in selecting camps. On the contrary, on this river are several very cele- 
brated wintering places for Indian horses. Horse Plains derives its name from this circumstance. 
Thompson’s prairie and the country about the Pend d'Oreille lake are other instances. Тһе 
Koutenay river enters into our territory for a short distance, preserves a general parallelism to 
Clark's Fork, and flows into the Columbia some twenty miles north of the boundary. From its 
headwaters are at least two passes over the Rocky mountains, but there has been no exploration 
of the river, and it is not probably navigable for any considerable distance. 
Having now described somewhat the rivers and the adjacent country of this mountain 
region, I will proceed to describe the passes which take you to the plains of the Missouri and 
to the plains of the Columbia. Big Hole Pass, as approached from the north, or Bitter Root 
valley, has an excellent road for fifteen miles above the forks, where it becomes somewhat 
difficult for wagons for two or three miles across the spur called Ross Hole mountain. Above 
this is another broad, open prairie called Ross's Hole. "This mountain can, however, easily be 
avoided by cutting away the trees which occupy the valley around its base. From Ross’s Hole 
Lieutenant Mullan thinks that wagons can ascend, without much difficulty, the dividing ridge 
called Big Hole mountain to the waters of Wisdom river, to which the descent is perfectly easy, 
without any obstruction. The pass called Hell-Gate, sixty-five miles further east, crossed over 
by him on December 31, 1853, in returning north from Fort Hall, was found to offer no obstacle 
whatever to wagons, the ascent and descent being both easy and gradual. It leads into the 
large and beautiful Deer Lodge prairie, on Hell-Gate river. From Wisdom river, at their passes, 
down to its junction with the Jefferson Fork, is an excellent prairie route, which i is believed, 
from Lewis and Clark's account, to extend down to the forks of the Missouri. 
The Southern Little Blackfoot was traversed by Mr. Tinkham in November, 1853, and by 
Lieutenant Mullan in March, 1854, when going from the Bitter Root valley to Fort Benton. It 
is considered by Lieutenant Mullan practicable for a wagon road, but less advantageous than 
the northern. Its elevation, as ascertained by Mr. Tinkham with the barometer, is 6,283 feet. 
The dividing ridge is but from 300 to 500 feet high, and the eastern approach is practicable for 
a railroad with a grade of 50 to 60 feet per mile, the ridge being passed with a two-mile tunnel, 
and the western descent with a grade of 30 feet. The broken character of the country between 
it and Fort Benton makes it, however, less fit for a main route than the passes further north, 
though it may be suitable for a direct route in the direction of Council Bluffs. It passes from 
Big Prickly Pear creek on the east to the south branch of the Little Blackfoot on the west. Its 
distance from the Hell-Gate Pass is about fifty miles, in a northeast direction. The Northern 
Little Blackfoot Pass, six miles to the north of this, is the one crossed by Lieutenant Mullan 
With a wagon in March, 1854. Itis described by him as perfectly easy, the descent being so 
gradual on the west side that his wagon was driven down with the mules trotting. The descent 
of the Little. ‘Blackfoot and Hell-Gate river is 221 feet per mile, and with a little cutting this 
can be made a better wagon route than any other. Cadotte’s Pass, forty miles northeast of the : 
last described, connects a tributary of Dearborn river on the east with a branch of the Big 
Blackfoot on the west. The approach from the east is up the narrow valley, bordered on each 
side by high wooded hills. The summit is a narrow, sharp ridge, about a mile and a half wide 
from base to base, and partially covered with small trees. The western base is about 500 feet 
higher than the eastern, and the descent is very rapid, favoring the construction of a tunnel. 
