As far as Grindstone Mountain. i sure would like to see the Clarksville Letter you are referring too here. I would guess it would have been two locations. The most likely to me would have been the hill that the School for the Blind is on in Muskogee which would certainly been very near to Rabbit Ford. I know from my research on other subjects that the hill was used for many years as a scouting point for outlaws (among others) and it was said you could see all the way over to Fort Gibson from it. Even today, when you get to the top you can get a pretty panoramic view of the area. The other possible location to me would be Agency Hill or what is know know as Honor Heights hill. It is farther away, but certainly is taller. The one thing here is yes, at one time their was historically a mill located upon it. I have some information indicating that it was in existence during the time of the Creek Agency before the railroad arrived and formed Muskogee. These would make the most sense to me.