Originally Posted by
JimR
"Jun Shou Honzam/Honyama" (Pure and True Source Mountain) is kind of a generic term applied to natural stones that come from Atagoyama in the Shoubudani/Narutaki area of Kyoto. Nakayama, Narutaki Mukaeda, Oozuku, Ookudo, and many more are all labeled with that.
Since they're all from the same mountain, and they come from the same strata of rock (the Honguchi Naori) they are all from "the true source."
If it's from Imanishi, and he said it was Nakayama, it is...he's no fly-by-night.