At the time, I had searched the Jefferson papers at the Library of Congress and turned up nothing. Since then, I’ve also reviewed the archives of the Monticello Museum and the New York Historical Society, and I have read all of the existing correspondence to and from Meriwether Lewis about his expedition. After reviewing this material, I have a tentative reconstruction of what actually happened.
Rhys (who also spelled his name Rhees or Rees), in turn was very interested in the work of John Evans, a Welshman who got a commission from the Spanish government to search the Louisiana territory for, among other things, Welsh Indians. Yes, this is how much of a threat to sovereignty this story really was: the enemy government was happy to find out about them, too. Rhys wrote about this in 1795 (in excerpt):
You have heard I expect before this time that John Evans is at length gone up the Missouri. I was the beginning of last May within about 300 miles of him … He has obtained from the Commandant passports in Spanish french & English to go on his journey… and whether he meets with the Welsh Madogians or not - he will receive on his return 2 or 3000 dollars from the Spanish government - I have heard many additional tales concerning what they call the Welsh Indians but as yet I have my doubts about them. I have conversed with the acting partner in the Missouri Co. He has been among more Indians than any other white man on this continent. He knows nothing of the Welsh language but by my conversing in Welsh - he could not recognize the words nor the idiom altogether among the Indians North of the Missouri - he thinks the Padoucas are out of the question. however I deliver'd him a Welsh Vocabulary & begg'd of him to give all the assistance he could to John Evans should he meet him. This man is to remain on the Missouri for 3 or 4 years to trade with the Indians. He has promised to write to me from time to time, and I do assure you it afforded me much pleasure to meet with a man of his disposition & information engaged in the Indian trade.
It is a confirmed fact that there are white Indians on the Missouri and in many places far west of the Mississippi. I have seen deer and buffaloe skins with various other articles dressed by them in a most capital manner. A frenchman has lately been up the Missouri for fifteen hundred miles and by what he could judge of the stream & country, that river must be about 2,400 miles in length. I have seen a map likewise of the Mississipi by actual survey to its source. It is no more like the present Mississipi on paper, than a cow is to a snake. It forms an elbow and runs westward long before it meets the line appointed for the limits of the United States. Every part of this continent affords sufficient proofs of a more civilised people having existed here than the present Indians …
Now, as Jefferson and Lewis planned the expedition to explore Louisiana, neither made any mention of Welsh Indians. In fact, it is not until 1804, when the expedition was underway, that any mention of Welsh Indians occurs. And it does so because of Rhys.
Jefferson wrote to Lewis on January 22, 1804 his only mention of Welsh Indians:
In that of the 13th inst. I inclosed you the map of a Mr. Evans, a Welshman, employed by the Spanish government for that purpose, but whose original object I believe had been to go in search of the Welsh Indians, said to be up the Missouri. On this subject a Mr. Rees of the same nation, established in the Western parts of Pennsylvania, will write to you.
Sadly, Rhys’s letter does not exist, or else was never sent. He died suddenly in December of 1804. The subject, though, appears to have captured the fancy of Lewis and Clark. Here’s exactly how much of a state secret they considered it. The expedition wrote about finding Welsh Indians in their journals, in the entries below, but these were not written by Lewis. Both entries are by Joseph Whitehouse, who intended to publish the journal for a profit upon his return from the expedition (some secret!), but gave up on the idea after putting together a final draft and preface in 1806. These journals were not published until 1904.
Thursday 5th Sept. 1805.
a clear cold morning, the Standing water froze a little last night. we hoisted our large flag this morning. Several men went out a hunting, about 10 oClock our officers held a Council with the flat head nation and told them nearly the Same as they told other nations, only told them that we wanted a flew horses from them, and we would give them Some marchandize in return. Gave 4 of their principal men meddles made them chiefs gave each of them a Shirt and a nomber of other articles also 2 flags &c. then told them that we could not Stop long with them and that we were ready to purchase their horses, and that we could not talk with them as much as we wish, for all that we Say has to go through 6 languages before it gits to them and it is hard to make them understand all what we Say. these Savages has the Strangest language of any we have ever Seen, they appear to us to have an Empeddiment in their Speech or a brogue or bur on their tongue but they are the likelyest and honestst Savages we have ever yet Seen, our officers lay out Some marchandize in different piles to trade with the natives for horses, our officers bought twelve horses and gave a Small quantity of marchandize for each horse, we swapped 7 horses which were lame &c. Gave Some Small articles to boot. we bought 10 or a Dozen pack Saddles from the natives, our hunters all came to Camp towards evening, one of them had killed 2 young Deer and one brarow. (source)
Friday 6th Sept. 1805.
a clear cold morning, we began to pack up our baggage and look up our horses &c. bought a nomber of lash chords and other Small articles from the natives at 10 oClock A. M. the natives all got up their horses and Struck their lodges in order to move over on the head of the Missourie after the buffalow. they make a large Show as they are numerous and have abundance of horses, we take these Savages to be the Welch Indians if their be any Such from the Language. So Capt. Lewis took down the names of everry thing in their Language, in order that it may be found out whether they are or whether they Sprang or origenated first from the welch or not. about noon we got ready to Set out. we have now 40 good pack horses, and three Colts, we loaded the horses Several men had to take 2 horses &c. 4 hunters were furnished horses without loads to hunt constant. about 1 oClock P. M. we Set out. the natives Set out at the Same time to go over on the Missourie. we proceeded on our journey, crossed a large creek went over a mountain about 7 miles came down on the Same creek and Camped nothing to eat but a little pearched corn. on[e] hunter Stayed out all night. light Sprinklings of rain through the course of the day. (source)