Background for Exploration
The exploring parties of 1869, 1870, and 1871, whose cumulative accomplishment was a definitive knowledge of the Yellowstone region, were a direct outgrowth of an earlier interest in the area’s wonders. Thus, it is necessary to go back a few years for the genesis of those efforts through which the true nature of “wonderland” became generally recognized.
An incidental outcome of the visit of Father Francis Xavier Kuppens to the Yellowstone region in the company of Blackfoot Indians in the spring of 1865 (see Part I) was his relation of that experience to a party of gentlemen who were stormbound for several days at the old St. Peter’s Mission near the mouth of Sun River the following October. These men, among whom were acting Territorial Governor Thomas Francis Meagher, Territorial Judges H. L. Hosmer and Lyman E. Munson, two deputy U.S. Marshals—X. Beidler and Neil Homie—and a young lawyer named Cornelius Hedges, were traveling from Helena to Fort Benton to assist in negotiating a treaty with the Piegan Indians when overwhelmed by a sudden, savage blizzard and forced to seek shelter at the mission.
Hedges says: “. . . We were received with a warm welcome and all our wants were abundantly supplied and we were in condition to appreciate our royal entertainment.”  Concerning the story-telling with which the time was passed during that stay at the mission, Father Kuppens adds: 
On that occasion I spoke to him [Meagher] about the wonders of the Yellowstone. His interest was greatly aroused by my recital and perhaps even more so, by that of a certain Mr. Viell —an old Canadian married to a Blackfoot squaw—who during a lull in the storm had come over to see the distinguished visitors. When he was questioned about the Yellowstone he described everything in a most graphic manner. None of the visitors had ever heard of the wonderful place. Gen. Meagher said if things were as described the government ought to reserve the territory for a national park. All the visitors agreed that efforts should be made to explore the region and that a report of it should be sent to the government.
As previously mentioned, the Indian unrest occasioned by the opening of the Bozeman Trail route prevented an implementation of Meagher’s suggestion during 1866, and, when conditions were at last satisfactory for an expedition into the Yellowstone region—through establishment of Fort Elizabeth Meagher and Camp Ida Thoroughman by the Montana volunteers early in 1867—the tragic death of Acting Governor Meagher cooled the enthusiasm of most of the gentlemen who had made plans to explore the headwaters of the Yellowstone River. While a party did go as far as Mammoth Hot Springs (the Curtis-Dunlevy expedition mentioned in Part I), their visit was essentially a prospecting junket.
No effort was made during 1868 to organize a general exploration of the Yellowstone region, at least so far as the public records show; but there was individual interest in such a project. Of this, Charles W. Cook says:
The first attempt made by me to make an exploration trip to the headwaters of the Yellowstone and Madison rivers was in 1868. At that time I had charge of the “Boulder Ditch Company” at Diamond City. A Mr. Clark, who as I remember, was connected with some mining operations was at Diamond City, and since there was no hotel, was staying at the “Ditch Office.” I found he had traveled extensively and had, at times contributed articles to magazines. I told him about the region at the headwaters of the Yellowstone and Madison rivers, which had not been explored, and he became very much interested. We went to Helena to see H. H. McGuire, who published a paper called the Pick and Plow at Bozeman, Montana, but who was at that time visiting Helena. Mr. McGuire advised us that since it was getting late, being then about the middle of September, it was not best to attempt the trip that year. 
The following summer, 1869, there was a renewed interest in implementing Meagher’s suggestion that the Yellowstone region should be explored. This was publicized in the Helena Herald, in an item announcing:
A letter from Fort Ellis, dated the 19th, says that an expedition is organizing, composed of soldiers and citizens, and will start for the upper waters of the Yellowstone the latter part of August, and will hunt and explore a month or so. Among the places of note which they will visit, are the Falls, Coulter’s Hell and Lake, and the Mysterious Mounds. The expedition is regarded as a very important one, and the result of their explorations will be looked forward to with unusual interest. 
That notice is undoubtedly the “rumor” which Cook notes as inducing himself and his friend, David E. Folsom, to hold themselves “in readiness to make the trip,” to which he adds:
. . . but sometime in the month of August, not having heard from the party, I made a trip to Helena to find out if anyone intended going, and was unable to find anyone who had any intention of making the trip that year. After I returned to Diamond City, David E. Folsom and William Peterson volunteered to make the trip with me. 
The manner in which that decision—certainly no trivial one—was arrived at is indicated in the reminiscences of William Peterson:
Myself and two friends—Charley Cook and D. E. Folsom who worked for the same company at Diamond that I did—after having made a trip to Helena to join the big party and finding out that they were not going to go, decided to go ourselves. It happened this way: When we got back from Helena, Cook says, “If I could get one man to go with me, I’d go anyway.” I spoke up and said, “Well, Charley, I guess I can go as far as you can,” and Folsom says, “Well, I can go as far as both of ye’s,” and the next thing it was, “Shall we go?” and then, “When shall we start?” We decided to go and started next day . . . .