From the campground head south up Avintaquin canyon. About 6 miles up the road will be gated. And that point will be the put-in. Actually, I'd park a little ways before the gate. Above there is the Indian Reservation, and if you park near their gate, they might think that you are trying to hike up into their land or something. I wouldn't want to see anyone have a confrontation with a sheriff, or a double barreled shotgun.