First, let me say you have a wonderful site. I've been to many of the same places you've visited.
I've been recording rock art sites in Georgia for many years, including giving presentations at the Archaeological Society of America, the Southeastern Archaeological Society, the Society for Georgia Archaeology, the Greater Atlanta Archaeological Society, and numerous historical societies. I now have over 300 petroglyph, pictograph, and stone pile sites recorded.
I knew John Sissell (retired in 2005) who was the park ranger at Kennesaw Mountain for 12 years. He showed me numerous sites around the area that he believed are prehistoric. The site you show with the soapstone bowl stem and the cupule was on our list, but we never quite made it there. I would really appreciate letting me know where that site is located. Of course, I can also help you with any sites you are looking for. I have a map I can send you of North Georgia, with site info you might find interesting.
Thanks so much for your time.