The company as now organized, in addition to the scientific gentlemen already named, included Dougherty and four other men to serve as interpreters, baggage handlers, and the like, and a detachment of seven soldiers from the troops at Camp Missouri--a total of twenty. Leaving the Missouri on June 6, the expedition visited the Pawnee villages on Loup River, where two Frenchmen were engaged as guides and interpreters. An effort was made to introduce the process of vaccination among the Pawnee, who, in common with other tribes, had suffered heavily from the ravages of smallpox; but the vaccine having been thoroughly drenched by the wreck of one of the keel-boats of the Yellowstone expedition, the attempt was unsuccessful. After two days at the villages, progress was resumed on the thirteenth, and from this time until the mountains were reached, little was encountered to excite interest, save herds of buffalo and the mirage. From near Grand Island the company followed the north bank of the Platte, until they reached the forks, where they crossed to the south bank of the South Fork.
On the thirtieth the Rockies were first sighted--their route along the Platte having borne directly towards the mountain which has since received Long's name, and which was, at first, mistaken for Pike's Peak. The fourth of July, which they had hoped to celebrate in the mountains, found them still at some distance from them; on the fifth they encamped upon the site of the present city of Denver, and the following day directly in front of the chasm through which issues the South Platte. Here two days were passed while James and Peale, with two companions, sought to cross the first range and gain the valley of the Platte beyond; but after surmounting several ridges, each of which appeared to be the summit, only to find higher land beyond, the undertaking was abandoned. They did reach, however, an elevated point from which they could distinguish the two forks of the South Platte.
A few days later, members of the expedition performed a more memorable exploit. On the twelfth of July, the camp then being a few miles south of the site of Colorado Springs, James set out with two men, and two days later succeeded in reaching the summit of Pike's Peak, being, so far as history records, the first to accomplish this feat. In honor of the achievement, Major Long christened the mountain James's Peak; but by force of local usage, the present name supplanted this appropriate designation. Lieutenant Swift had meanwhile quite accurately calculated the height of the peak above the basal plains, although an erroneous estimate of the elevation of the latter produced an error of nearly three thousand feet in the determination for the elevation of the summit above sea level. Here, as elsewhere, the observations for longitude and latitude involved a considerable error.