From the Roanoke Ridge North dreamcatcher ride south along the river to the Annesburg Crossroads. The dreamcatcher is in the very large tree with no leaves at the crossroads.
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.
View the Dreamcatchers Guide to start collecting them in the optimal route.