The “route,” as traced on the map, starts from a point on Pryor’s Fork, the first considerable tributary of the Yellowstone above the mouth of the Bighorn. Colter’s intention seems to have been to skirt the eastern base of the Absaroka Range until he should reach an accessible pass across the mountains of which the Indians had probably told him; then to cross over to the headwaters of Pacific or gulf-flowing streams; and then to return by way of the Upper Yellowstone.
Opp. page 22.
Colter's Route in 1807.
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Accordingly, after he had passed through Pryor’s Gap, he took a south-westerly direction as far as Clark’s Fork, which stream he ascended for some distance, and then crossed over to the Stinkingwater. Here he discovered a large boiling spring, strongly impregnated with tar and sulphur, the odor of which, perceptible for a great distance around, has given the stream its “unhappy name.”
From this point Colter continued along the eastern flank of the Absaroka Range, fording the several tributaries of the Bighorn River which flow down from that range, and finally came to the upper course of the main stream now known as Wind River. He ascended this stream to its source, crossing the divide in the vicinity of Lincoln or Union Pass, and found himself upon the Pacific slope. The map clearly shows that at this point he had reached what the Indians called the “summit of the world” near by the sources of all great streams of the west. That he discovered one of the easy passes between Wind River and the Pacific slope, is evident from the reference in the Missouri Gazette already alluded to and here reproduced for the first time. It is from the pen of a Mr. H. M. Brackenridge, a contemporary writer of note on topics of western adventure. It reads:
"At the head of the Gallatin Fork, and of the Grosse Corne of the Yellowstone [the Bighorn River], from discoveries since the voyage of Lewis and Clark, it is found less difficult to cross than the Allegheny Mountains. Coulter, a celebrated hunter and woodsman, informed me that a loaded wagon would find no obstruction in passing."
The “discoveries” are of course those of Colter, for no other white man at this time had been in those parts.