To get here from the Caliban's Seat dreamcatcher head northeast on the trail towards Valentine. Take a right at the first fork. Take a left at the second fork going up the hill. Head east until you see a rocky wall. Go left around the rock wall to get to the top of it. The dreamcatcher in a tree right next to the largest tree in the area.
Finding all 20 dreamcatchers will reveal the location of the Ancient Arrowhead treasure; A unique item that makes Arthur's stamina last twice as long when using the bow.