Sergeant Nathaniel Pryor had been told of his mission sometime earlier, perhaps back at Travelers' Rest. But it was on July 23, 1806, the day before Clark's contingent shoved off from their Canoe Camp on the north bank of the Yellowstone near today's Park City, Montana, that Clark handed him his written orders, along with the letter to Hugh Heney.1
The following morning, assisted by Privates George Shannon and Richard Windsor, Pryor was to take their remaining seventeen horses to the Mandan villages, where he was to see whether trader René Jusseaume could tell him Heney's whereabouts. If Heney were at one of the North West Company's outposts on the Assiniboine River, Pryor was to take twelve or fourteen horses and proceed north, leaving three to five with the Mandan chief, Black Cat, presumably for Clark to use in buying corn and beans when he got there.
Pryor was also instructed to keep a journal, including "courses, distances, water courses, Soil production, & animals to be particularly noted." Unfortunately, no such journal is known to exist today; reportedly it was lost in shipment to France for publication.
Clark's final order tells us something about how the Corps of Discovery was faring, as far as supplies were concerned, after more than two years on the trail. He wrote out a shopping list; Pryor was to pay the bill with horses.
Early on the morning of July 24 Pryor was to proceed downriver to the mouth of the Bighorn River, where Clark, with the canoes, would help him and his detail across the Yellowstone to its south bank. Clark didn't know precisely where the Bighorn was—"which we suppose to be at no geat distance," for he had only Sheheke's sketch map to work from. Actually it was almost 100 miles downstream from their Canoe Camp at present-day Park City, Montana,5 but they happened upon a good fording place at today's Billings, and seized the opportunity.
At the outset , Private George Gibson was to have been part of Pryor's detail, but he had not sufficiently recovered from his accident on July 18, and the sergeant had set out with only two helpers, Privates George Shannon and Richard Windsor. But before the end of the first day of his mission, he found that even with only seventeen horses to drive, he would need more help. Some of the animals were stronger and faster than others, and every time they came upon a herd of bison the leaders would race ahead to circle them up, as the horses' original Indian masters had trained them to do. The best solution seemed to be to send one man ahead to try to haze the big bovines out of the way, and for that Pryor needed an extra hand or two. So Clark assigned him Hugh Hall, a non-swimmer who perhaps had been nervously hoping for some excuse to get out of those tippy canoes.6
It is impossible to know which of two possible routes Pryor and his men would have followed back to the Mandan villages.7 The land route down the Yellowstone and Missouri rivers, which François Larocque followed, would have would have been nearly 550 miles long, taking them through several stretches of badlands where travel would have been slow and dangerous. (Of course, Clark couldn't have known that in advance.) The "War Path of the Big Bellies," which is shown as a direct, straight line on Clark's map of 1805, would have taken them over some low ranges of hills, such as the Little Wolf Mountains and the Pine Hills, and would have been only about 360 miles (580 km) long. So the shorter, straight-line route seems the more logical one.
Via the shorter route, had all gone well and Pryor had averaged thirty miles per day, he would have arrived at the Knife River villages by about August 6. The distance from there to Fort Assiniboine had been estimated by Clark at 150 miles, although actually it would have been a little over 200 miles, so it would have taken him another thirteen or fourteen days to make that round trip, not counting time to conduct his business with Hugh Heney. It is unlikely he could have gotten back to the Knife River before August 20, even under the most agreeable of circumstances. Clark, in his July 12 letter to Heney, had figured he would arrive there "about the beginning of September, perhaps earlyer,"8 but he actually got there on August 14, so he would have had to wait a week or more for Pryor to get back.
Drifting along with the Yellowstone's current—Pryor's party couldn't have endured the dizzying Indian mode of paddling a bull boat, "around and arround"—which Clark estimated flowed at 2.5 to 2.75 miles per hour, they spent at least twelve hours a day on the water, and caught up with the main party on August 8 approximately 70 miles below the mouth of the Yellowstone, near Tobacco Creek in North Dakota.
1. The letters are in Clark's handwriting, but the wording and spelling are clearly in Lewis's style.
2. Paint pigment was sold by the pound. The first ready-mixed paint was patented in the U.S. in 1867. The captains may have intended to paint marks on the canoes to make them easier to identify from a distance.
3. Properly capotes—long, hooded cloaks or coats—either for the captains or else for sentries during cool nights.
4. This item suggests the general condition of the men's health at this point, possibly because of the imbalances in their diet. Glauber's Salts, or Sal Glauber, is a mild laxative. Gary Lentz, "Meriwether Lewis's Medicine Chests," We Proceeded On, Vol. 26, No. 2 (May 2000), 10–17.
5. The Canoe Camp was 392 miles from the mouth of the Yellowstone by today's measurement—and this river has not changed its channel appreciably within the past 200 years. The mouth of the Bighorn was probably at about mile 296. River Mile Index of the Yellowstone River (Water Resources Division, Montana Department of Natural Resources and Conservation, 1976), 29, 41.
6. Clark, July 24, 1806.
7. Moulton's Atlas map 116, shows "Sargent Pryors route with the Horses" as a short dotted line which, as he points out, roughly parallels the route of today's Interstate 90. However, the modern superhighway turns abruptly southward some 20 miles east of where Clark's map leaves off, and heads toward Gillette, Wyoming.
8. Jackson, Letters, 1:312.