This is an interesting picture I took of a beaver scent mound:
Scent Mounds (or Castor piles): How a beaver marks territory. The piles are started by placing mud and leaves in a clump in a prominent area near the pond, and then a yellowish substance is deposited on the top if it. This substance is called castoreum and is secreted from a scent gland near the tail. If you find a scent mound, smell it. This is a sure sign that there are beavers in the area.