The “Bridger Map” is the obvious source of the Yellowstone data found on the fifth De Smet map, embracing the western United States, which is more carefully drawn than the others. This large untitled map, with a bold floral border, is dated 1851, and contains the following fading inscription within curved palm fronds: “respectfully presented to Col. David D. [?] Mitchell [by] P. J. De Smet, Soc. Jes.” As to the circumstances under which this map was drawn, De Smet explains as follows in a letter dated July 1, 1857, to officials of the Department of the Interior: When I was at the council ground in 1851, on the Platte River, at the mouth of the Horse creek, I was requested by Colonel Mitchell [superintendent of Indian Affairs at St. Louis] to make a map of the whole Indian country, relating particularly to the Upper Missouri, the waters of the upper Platte, east of the Rocky mountains and of the headwaters of the Columbia and its tributaries west of these mountains. In compliance with this request I drew up the map from scraps then in my possession. The map, so prepared, was seemingly approved and made use of by the gentlemen assembled in council, and subsequently sent on to Washington together with the treaty then made with the Indians. In my humble opinion, therefore, it can be of very little service for your purposes, in which accuracy of instrumental measurements and observation seems to be absolutely necessary.... The final gesture of modesty may explain why this revealing map, prepared and made available to the government twenty years before the first official Park exploration got under way, was duly glanced at by the department authorities and then tucked away, a needle in the haystack of official files, in Washington, D. C., where it still reposes. It contains all the features of the “Bridger Map,” but with refinements. Here is a “Great Volcanic Region [?] now in a state of eruption,” drained by “Fire Hole Riv.” The lake now appear as “Yellowstone or Sublette’s Lake,” still oddly sausage-shaped. There is a “Little Falls” at the head of the canyon but the more impressive Lower Falls are unexplainably omitted. To the southwest, in the position of present Shoshone Lake, is “De Smet Lake.” To the east at the forks of “Stinking Fr.” appears the “Sulphur Springs or Colter’s Hell Volcano” which, due to the unavailability of this map, has led so many historians astray. This map, with its manuscript forebears, ranks with the Ferris journal and map and the Potts letter as one of the principal historical documents pertaining to early Yellowstone. [Illustration: Trappers in Pierre’s Hole, west of “Les Trois Tetons”]