The footpath that connects Bernardholt to the causeway is the one that crosses the Rillwater. I don't remember any reference to the causeway crossing the Rillwater. Basically, I think the pine barrens, Bernardholt, the forest near Bernardholt, and the Princeps Memorium, and the X marks for Amara and second herdbane should be farther east relative to Garados. Also, the causeway leads to Garrison.