Hi, I forwarded the question on the Headwaters of the Juniata email to my brother.  He wrote his dissertation for his doctorate on that section of Pennsylvania.  Here is the reply he sent to me: "I have read this letter; in fact, I cite it briefly in an article I wrote in 1998. As far as I can ascertain, this letter was written near Holiday's Fort, which is, of course, today's Hollidaysburg. The exact location cannot be determined from the letter or anything else. The headwaters refer to the Frankstown Branch of the Juniata and the likelihood is that it was written to the east (or, less likely the south) of the fort rather than to the west or north. It was nor written at the Fort itself. So that is what I know--in TOTAL--trust me; this is a very obscure and irrecoverable part of Valley history." Happy Hunting! Bonnie