It is a little obscure, but think about the two altars dotted about the area - one where the twigroots are, the other up on a cliff nearby - and what items they yield if you place the correct offering upon them, as described in the notes left by previous adventurers.

These two altars are in the same place. I just don't know what to put in each one.

As I said, there are two messages in the area with the turtles that tell you what you need. One mentions stealing a branch and being attacked for it, while the other mentions hunting turtles for their meat in order to dedicate such.