I thought the control description symbol was boulder cluster but Glen reminded me it was boulder field, which on the map uses the sharply angled triangles. Maybe too many triangles to map them as individual boulders (or stone pillars, which they are)?
Ah, the stone pillar symbol I remember doesn't exist in ISOM2017
I didn't have any trouble finding it for the GO control; but, when I was kinda disoriented on my way to my #14, I was VERY confused for a few moments (since I was looking for black X, like all the other sculptures...). :-P