Every single year, Americans and international visitors visit national parks to partake in wholesome outdoors activities. They hike, fish, hunt, and go camping. It's fun, wholesome activity.

National parks are considered to be one of the healthiest places to go, and that's why so many families visit them every single year. But, as wholesome and safe as people assume national parks to be, there seems to be a rarely-discussed dark side to these places that most people don't seem aware of.

More specifically, it's the fact that strange disappearances in national parks seem to be way more frequent than they should be. Every year, hundreds of cases of strange disappearances happen. Only a handful are ever seen again.

Moreover, the disappearances that happen often seem totally illogical, bizarre, or unexplainable — even to those who are highly equipped to solve mysteries.

The phenomenon was first covered in Missing 411, by researcher David Paulides. Here are some of the more chilling cases that Paulides and others uncovered, all of which happened in America's national parks.

John Doe

Perhaps the most baffling of all the strange disappearances in national parks we'll discuss is the disappearance (and reappearance) of a young boy known only as John Doe. John Doe was actually mentioned on a George Knapp Coast to Coast interview.

According to the interview, three-year-old John Doe was last seen near a fly-fishing river — and then he promptly vanished for five hours. A search party found him, dazed but unharmed, in the middle of a grove of trees.

John Doe really had a strange story to tell.

When investigators asked the boy what happened while he vanished, he said that he followed a woman who looked like his grandmother to a mountain. He then found himself in a room that had a bunch of motionless robots and weapons lying all over a dusty floor.

The boy then claimed that he noticed a strange glow coming from the strange old woman's head. And then, most puzzlingly of all, she asked him to defecate on a piece of paper — and then the boy claimed she got agitated and aggressive when he refused to do so.

The woman then said that the boy was from outer space, and that he was planted in his mother's womb. She then told him to go and wait in the trees until he was found.

No one has any idea where the boy was when he disappeared.

It'd be so easy to say that the disappearance of John Doe was just a child's overactive imagination. However, there is something very bizarre about this disappearance case that gives credence to John Doe's insane story.

His grandmother, who had gone camping with him, claimed that she was dragged out of her tent late at night. She woke up to a strange pain in the base of her neck, and found two small holes near the back of her head.

So, what happened to young John Doe? While many strange disappearances in national parks can be explained by kidnappers, it seems like one of the more believable explanations here is really out of this world.

Alfred Beilhartz

In 1938, four-year-old Alfred Beilhartz was vacationing with his family in Colorado's Rocky Mountain National Park. His parents were watching him carefully as they went out for a quick hike near a river.

Then, without warning or a trace, he vanished. It is among one of the strange disappearances in national parks.

He was only feet away from his family, and then, he was gone. A 6-mile search of the area that he disappeared showed nothing, however, dogs were able to trace his scent 500 feet uphill from where he vanished.

The only problem was that there were no footprints, and no Alfred to be seen. Stranger, the dogs that traced the scent seemed to be confused by what they were smelling — and they quickly lost the scent.

Once dogs traced the scent uphill, the two pups began to cock their heads and look nervous. Eventually, both bloodhounds ended up lying down on the ground, unable to go any further on any trail.

Alarmingly, some hikers who were walking six miles away from where Alfred disappeared claimed they saw a young boy in a particularly dangerous (and difficult to reach) rock outcropping called the Devil's Nest.

The two hikers said that they had only seen the boy minutes after he allegedly disappeared. Stranger, they claimed that the boy seemed dazed and upset, but then appeared to be jerked back by an unknown force.

A four-year-old boy would not reasonably or logically be able to travel six miles and uphill over 3,000 feet on his own. Even the survival specialists who searched for him needed specialized equipment to get up there.

So, who or what grabbed little Alfred?

What happened to him?

We may never know; Alfred Beilhartz was never found. To this day, his case is one of the most unexplained and disturbingly strange disappearances in national parks to record.

Kenny Miller

Kenny Miller was 12 in 1992, but he had the mental capacity of a four-year-old. As a result, his parents knew that they had to be careful and watch over him when they went to Yosemite National Park.

His parents left him to throw pebbles at a pond while they prepared dinner, taking occasional seconds to make sure that he was still where he was supposed to be.

However, much like what happened to young Alfred, Kenny Miller ended up being one of many victims to the strange disappearances in national parks. He vanished without a trace.

A month later, a group of hikers found Kenny's body 1,500 feet above the area where he was last seen. The area where he was found was notoriously inaccessible, rocky, and filled with painful bushes.

No one knows how a boy with the mental capacity of a young child would have been able to figure out how to get there.

David Gonzalez

Nine-year-old David Gonzalez went camping with his family in San Bernardino National Forest. At one point, he asked his mother if he could go get some cookies from the family car. 40 minutes passed, and his mother realized that David never returned — and that the cookies he wanted to grab were still inside the car.

He was never found alive again. His death is viewed as one of the strange disappearances in national parks.

A week later, his badly decomposed body was found only a mile away from where he went missing. Mysteriously, this area was already combed days prior. So, this means that the boy must've been dropped there by someone or something.

An autopsy revealed no trauma and no overt injury. David Gonzalez was just dead, without any reason or clue as to why. This already is baffling, especially considering the power of forensics and the skill of investigators.

But, what makes the case of David Gonzalez so strange is not his disappearance alone; it's the way the local authorities and investigators seemed to handle the case.

To put it simply, the police and investigators were flippant about it. Any questions asked were answered with vague replies. Even when Paulides asked authorities for records about David, he was met with hostility.

The officials claimed that David was dragged off by a mountain lion, despite no injuries that would suggest that to be his fate. No one nearby heard David scream, either. Doesn't that seem a bit strange?

Authorities, in most cases involving strange disappearances, are rapt with attention and will scour every last inch of terrain to find a missing child. However, when it comes to strange disappearances in national parks, many officials seem unwilling to be fully open and honest.

David's parents have gone on record to say that they don't believe David got dragged off by a cougar. They believe he was kidnapped, and that he still may be alive somewhere and that the body wasn't his.

Some believe that authorities know more than what they're saying. At the very least, it's clear that there's a lot more mystery and danger in the woods than we're willing to admit.

Thelma Pauline Melton

Not all of the strange disappearances in national parks happen to young children. Thelma Pauline Melton, also called "Polly" by her friends, was 58 when she vanished during her camping trip with friends in the Great Smoky Mountains.

Polly was not exactly a normal candidate for a disappearing act–for a number of reasons. For one thing, she had medical problems that caused her to hike at a very slow pace. She also was a happy, well put-together person that no one believed would have any reason to want to disappear.

Simply put, it didn't seem like she would want to do something drastic. To make matters stranger, Melton had been hiking the trail that she had vanished on for over 20 years. She knew the terrain; it wasn't like she got lost.

Perhaps that's why her friends were so alarmed when she vanished while hiking with them. Just like with the other national park disappearances, one moment she was there, and the next she wasn't. She didn't make any noise, and no trace of her was ever found.

Dennis Martin

Perhaps one of the most famous strange disappearances in national parks happened in 1969, to a young boy named Dennis Martin. Six-year-old Dennis Martin was vacationing with his family in the middle of the Great Smoky Mountains, in a popular spot called Spence Field.

While his parents were talking to another adult, Dennis, his brother, and some kids decided it'd be funny to play a prank on his family. They all decided to split up, hide, and jump out to scare their parents in a harmless prank.

Three of the boys went one way, and Dennis went the other. The four kids hid, but only three jumped out. Dennis just vanished, and that was the last anyone ever saw of him.

Six miles from Spence Field, a young boy screamed—and claimed that he saw what first looked like a bear, but then looked like a large man with something strange slung over his shoulder.

A frantic search party started almost immediately, but no trace of Dennis was found. The search party lasted until night, when torrential rain washed away any scent that could potentially be used by bloodhounds to find the missing child.

Within the subsequent days, the FBI, the Green Berets, the police, and just about every other form of official aid was dispatched to find Dennis Martin, but no footprints or articles of clothing belonging to him ever showed up.

What's really bizarre about this case is the government reaction to it. The leader of the FBI group who organized the search committed suicide for unknown reasons.

Another special forces member by the name of Harold Cleveland later issued a statement in 2014, in which he says something paranormal must have been afoot.

In a statement that he sent to News of the Weird, he wrote:

"Our Special Forces are NEVER called to assist in civilian operations. That falls to the local National Guard and approved by the state governor. The fact that they were armed as well is another huge no no. During my command and every other mission I was aware of we were NOT allowed by Federal protocol to do either.

Something is very wrong with this missing kid scenario. I’ve done some research on this case both while on active duty and after my retirement. The inside facts of this case depict a frightening investigation. Bottom line is that searching started within a few minutes of the boy’s disappearance and lasted three months with every resource imaginable being deployed.

Don’t even start with “the terrain was difficult, holes and caves and cliffs and creeks, etc."

Our special troops can find almost anything, anytime and in ANY terrain. We have the highest technology available worldwide and easily the best training and real world wartime and mission specific experience that the normal civilian populace can scarcely imagine.

After studying this case, the fact that NO TRACE of the boy was ever found is mind boggling.

The Green Berets that were tasked in this search were there for a specific reason. They were armed for a specific reason. I can’t and won’t saywhy because my oath documents won’t allow it. But I will remind you of these facts. Nationwide there have only been four occasions where the special forces were brought in on a civilian missing persons case.

Two of these involved a possible armed perpetrator. The other two were this case and another similar to it about three years later and regionally nearby. This is out of thousands of missing cases since the early sixties when our special troops were born."

In other words, there's something potentially terrifying living in the national parks related to all the strange incidents. We civilians don't know what it is, but judging by the note that he wrote, we probably don't want to know what's out there.