We didn't get out of the car at Dooneen as it was pissing down and all we could see from the road was dunes and not cliffs. I understand the dunes are high enough to qualify as cliffs by the river. It's worth remembering that sand dunes have a tendency to be eroded far faster than chalk or granite and the cliffs may have had a better view across the Sahnnon when the song was written. And no, it doesn't seem to have been written by an aviator as we speculated.