This one can be found at ground level.

This one can also be solved at ground level.

It can be found right after a subtle transition in the terrain.

A transition where your footsteps no longer sound so crunchy.

The transition is marked by a small cluster of rocks.

You should be at the ground-level entrance to the treehouse area.

Look to the left.

From the obelisk, head down to the ground-level entrance into the treehouse area.  Immediately after crossing the small cluster of rocks, look to your left.  You will see the puzzle as a shadow on the face of a large rock.

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