Las Vegas, Nevada, US - The summer travel season is nearly here which means millions of people will be heading for national parks and national forests. As it turns out, a few of them won't be coming back.

Each year, hundreds of people are reported missing in national parks and forests. Most are eventually found, but there's a smaller category of cases that are never solved, including a few close to home.

It is not a revelation to report that people get lost in wilderness areas or forests. The I-Team is investigating a different kind of mystery that involves disappearances which are not caused by predator attacks, criminals, or bad luck.

A former cop has put together hundreds of case files regarding clusters of missing persons in national parks where the circumstances are strange.

"I was staying in a hotel off park service land and there was a knock at the door," said David Paulides.

The person who came to confide in law enforcement veteran Dave Paulides was a government employee who told one heck of a story about people who vanish in national parks, places like Yosemite, but also national forests, including the Toiyabe west of Las Vegas.

In the years since the knock at the door, Paulides has scoured small town newspaper archives and pestered federal agencies for records. He found so many cases of missing people that one planned book became two, filled with more than 400 cases of people who went into national parks but never came out.

CANAM Missing Project

"People disappear in the wilderness all the time. We're talking about something different. These are unusual things that don't make sense, that happen to cluster together in three to four, sometimes as many as 20 to 30 people missing at one location," Paulides said.

The individual cases are strange enough, Paulides says, but stranger still were the reactions of federal agencies when he asked for public records. Since even small police departments keep lists of missing persons from their jurisdictions, he figured a large federal law enforcement agency like the National Park Service would do the same.

"When we FOIA'd (Freedom of Information Act) them, we got a response back that we don't keep any lists of missing people," he said.

The response was not only no, but hell no, he says. So Paulides began putting his own lists together and discovered what appears to be nearly 30 clusters of disappearances in national parks or forests; cases which meet a narrow set of odd characteristics.

See the map of missing person clusters

The people who vanish often do so under the noses of other people. In the many cases of kids, they disappeared while with the parents.

"Being parents, being responsible people, we understand there is no way my son or daughter wouldn't know their way back from just being down the road getting a ball. But it happens all the time."

The missing defies logic. They hike uphill, for instance, often steep climbs. Children as young as 2 or 3 years old are found a day or two later, many miles away and over mountain ranges.

"Some kids are found phenomenal distances away that would make no logical sense to any parent," Paulides said.

Weird things happen to their clothing. The missing often shed their clothes right away, even in bad weather. Clothes are found, but not the people.

"The ranger described to me if you were standing straight up and you just had your pants on and you melted directly into your pants. That's what it looked like to him. The pants were lying on the ground in a very neat pile."

The missing defy normal search and rescue practices. Bodies are found in places that are all but inaccessible, or they are found in the open, in areas that were repeatedly searched earlier. Bloodhounds or other tracker dogs are often befuddled.

"If a dog can't find a scent, that's a red flag. If a dog, a trained dog K-9, is put on the scent at the site and it lays down and it doesn't want to track anymore, red flag. That happens more than you think."

Nevada doesn't have a major cluster, but it has plenty of cases including children who vanished around Lake Tahoe, in the center of the state near Tonopah, and at Mt. Charleston.

In 1966, 6-year-old Larry Jeffrey of Henderson disappeared while playing with his two brothers, setting off a massive 16-day search by as many as 1,000 men. Former Sheriff Ralph Lamb remembers it clearly.

"We walked shoulder to shoulder but couldn't find him," Lamb said.

"There are no large predators per se, so we can't worry about mammals taking them. He was in a fairly remote area where there is no vehicular access; so there is no car abduction. The boy just walked into oblivion.

Other aspects of this mystery are even more bizarre, though difficult to explain in just a few minutes. For example, many of the vanished who are found alive are kids too young to speak or kids who can't communicate because of disabilities. Some who are found alive say they can't remember what happened to them.

In his books, David Paulides reports on why some obvious explanations simply don't apply here but he stops short of giving his own theory. Paulides says he doesn't want to scare people away from visiting parks but thinks people need to be made aware. A month ago, the I-Team asked the park service and forest service for their lists of local missing person's cases. The I-Team has not received that list.