Lithograph from a drawing by John Mix Stanley1
Isaac Stevens, in the report on his exploration of possible routes for a railroad from the Mississipi to the Pacific, wrote of the Souris, or Mouse, River:
High ridges divide the plateau bordering the stream from that extending into the prairie, with coulées intersecting it and opening into the river on the one side, gradually growing imperceptible as they make into the prairie on the other. The general course of the river, and of its principal branch, the Riviere des Lacs, is nearly parallel to that of the Missouri, for the distance we followed it, of eighty-seven and a half miles to its source,2 and separated from that river by the Plateau du Missouri, varying from thirty-five to fifty-five miles in width. Many of the coulées reach to the edge of the Missouri plateau; and in the examination for a good passage for the wagon train, secluded spots were found where beetling crag and winding stream, venerable trees and greenest sward combined in scenes of much picturesque beauty.
Its valley is from half a mile to a mile wide, about two hundred feet below the prairie level, and is well wooded with maple, oak, ash, and elm. The deep coulées run back from it for fifteen or twenty miles, and must be avoided by keeping far from the river itself. They usually contain a stream of good water, and sufficient timber on the banks for camping purposes. One of the bluffs of the cateau, twenty miles from the Mouse river, was found by Mr. Moffett to be seven hundred and two feet above its level, and a hill seven miles from camp rose to two hundred and fifty-six feet.3
The Stevens expedition, incidentally, traveled by wagon train: "Our experience thus far had shown how well adapted ox-trains were to transportation."
1. Isaac I. Stevens, Reports of Explorations and Surveys to Ascertain the Most Practicable and Economical Route for a Railroad from the Mississippi River to the Pacific Ocean (1853–55), Vol. XII, Book I, Plate 15.
2. Evidently they didn't quite reach the Souris's source. It begins a short distance west of Carnduff, Saskatchewan, about 10 miles (17 km) north of the U.S.-Canada border. The Riviere des Lacs originates 54 miles (87 km) above the border (49° North), west of Carlyle, Sasketchewan, 144 miles (232 km) from the Souris's nearest approach to the Missouri River.
3. Stevens, p. 84.