It's a large boulder (the size of a small boulder) about 4ft wide, never seen more than waist height, a little closer to one of the "walls" of the quarry.

I'll have to find an episode with it. It's mostly visible after season 1 and before season 8 or 9. Idk what happened to uncover/bury/move it, but it does move like twice during the show, even though I'm positive it's an actual rock and not a prop.

I want to say the first time I noticed it was during the episodes where they're trying to rescue Bra'tac and Ry'ac from the mine? After tretonin was developed. (Ry'ac says "it is hard to ration that which you do not have" when Bra'tac pretends to be taking his tretonin)

When I see it again, I will definitely post to Chevron 7.