I've just been exploring instead of doing Chapter 4 (so I won't have a Skell for a while). I was hoping to get all of the FrontierNav locations (in Primordia at least) but it appears that the center one is on top of that outcropping. I believe I have made it to the Fifth? Terrace (might just be the third, it was definitely two above the area with the large turkey like indigens.) But I did not see a way up further that I could reach. Is it possible to actually get all the way up just on foot or is a Skell required and that Nav spot has to wait?
A map would also be nice if it is.