The triangular rock leaning up against the boulder generally means the boulder is part of a triangle, but not always. The split tree may be a gunsite that shows a line thru the bigger triangle or even the topline of the triangular rock, or shows where another corner is, or is being used like a goal post with the adjacent tree.. They liked putting trees or certain bushes that stick out by the boulder markers so they could locate them and to verify them or the alignments near them. Also vice versa, Sometimes the boulders will be placed by the trees as well to verify them as markers. Alot of times the trees will be blazed in some way. It's meant to look fairly natural as well. Also if the two trees line up like a goal post with a post centered between the uprights behind it, then that is a line to follow out.