Dumped on the trail tends to rule out that the owner is on a side-trip unless they are somewhere out of sight fertilizing the flowers.

Blowing a whistle and waiting awhile to see if the owner turns up would be the first step.

If no one shows up then it gets tougher. If I were on my way IN on my own trip I might just leave it alone and go on. If I were on my way out after my trip then there is the question of whether I could even carry the darn thing to take it to authorities.

If there were an attractive nuisance such as a falls nearby it might be worthwhile to go there and look for the owner.