Colter's whereabouts during the three years following his discharge are difficult to fix upon. It may, however, be set down as certain that he and his companions ascended the Yellowstone River, not the Missouri. Captain Clark's return journey down the first-mentioned stream had made known to them that it was better beaver country than the Missouri, and Colter's subsequent wanderings clearly indicate that his base of operations was in the valley of the Yellowstone near the mouth of the Bighorn, Pryor's Fork, or other tributary stream. In the summer of 1807, he made an expedition, apparently alone, although probably in company with Indians, which has given him title to a place in the history of the Yellowstone Park, and which was destined in later years to assume an importance little enough suspected by him at the time. His route appears upon Lewis and Clark's map of 1814, and is there called "Colter's route in 1807." There is no note or explanation, and we are left to retrace, on the basis of a dotted line, a few names, and a date, one of those singular individual wanderings through the wilderness which now and then find a permanent place in history. 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. [Illustration: /* _Opp. page 22._ */ Colter's Route in 1807.] 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: