Here is a case that has always intrigued me (but not really haunted me):
In September 1971, Thelma "Polly" Melton, 58, disappeared from The Great Smoky Mountains National Park in TN.
Polly and her husband belonged to a group of about 10 families who rented out a campsite and lived in Airstreams. "The group did not admit any newcomers into their campground unless all the families voted unanimously to admit them. Most of them were retired, came in April or May, and stayed until October or November."
Polly had been camping there for almost 20 years. On the day she went missing she took a walk with two long-time friends, Red and Trula. This was a regular activity. The trail is four miles, round trip, allows vehicles and is considered an easy trail.
On the return trip, "without explanation, Polly began to walk very fast, as if she intended to leave them behind."
"Just as Polly was going out of earshot, Red called out, I wouldnt want to be in a foot race with you, Polly. Polly looked back, grinned impishly and chuckled as though satisfied with the situation. She picked up her pace and kept going."
Polly was not back at camp when her friends returned. They began an immediate search which involved many other campers. Within three hours the Park Rangers were involved and launched a wide-scale search.
Many hours and resources were put into locating Polly. Most of the Rangers knew her. There were no signs anyone had left the trail. There was no area between her location and the campsite where she could have fallen down an embankment, or other similar fate. Bear & other wild animal attacks were ruled out.
Polly has never been located.
The quotes are from the book,
Unsolved Disappearances in the Great Smoky Mountains by Juanitta Baldwin and Ester Grubb.
Here is the Charley Project link
http://www.charleyproject.org/cases/m/melton_thelma.html