(NewsNation) — As millions of people head to the U.S. national parks this summer, many may be unaware of the mysterious cases of people who’ve vanished within the parks.

The National Parks Service has faithfully kept records of visitors who disappear, often without a trace. NewsNation looked into the mysterious disappearances of those who simply set out to bask in the beauty of our nation.

Whether it’s the waterfalls of Yosemite, the meteor showers over Bryce Canyon, or the slot canyons of Zion, more than 400 million Americans and foreign tourists enjoy the beauty of the national parks each year.

Unfortunately, some never make it home.

“NPS investigators are continually working to find people who, who do get lost or have gone missing national parks,” said Cynthia Hernandez, with the National Park Service.

The National Parks Service keeps a list of the missing. Many people are eventually found or, sadly, turn out to be suicides.

But some visitors, like 24 of those on the Parks Services’ cold case list, are simply missing.

“The risks are everywhere, it’s just not national parks. It’s just when people go missing at a national park, it makes headline news,” said survival expert Jason Marsteiner.

Marsteiner said lightning, snow storms, and rising flood waters make situational awareness paramount.

“The first mistake is failure to plan. That means telling somebody where you’re going, what you’re doing, and exactly your itinerary, I guess,” Marsteiner said.

Most of those who have gone missing in national parks are solo hikers, like Charles Lyon, whose car was found on the Grand Canyon’s south rim in June 2021. Or James Pruitt, 70, who set out in Rocky Mountain National Park as a snowstorm moved in, for what was supposed to be a day trip.

“A lot of people go on day hikes, they may never have spent a night outside,” said survival expert Jessie Krebs.

Krebs knows a thing or two about staying safe in extreme conditions. A former Air Force Survival, Evasion, Resistance and Escape specialist, she survived 46 days alone on the hit TV show “Survivor.”

Krebs doesn’t discourage solo hiking, but she does suggest taking certain precautions, like letting people know where you’re going before you leave.

“Tell at least two people before you head out there and, if you can, take a picture of the map and write down the map where you’re planning on going and where you’re gonna be staying each night,” Krebs said. “Take a picture of all the gear you’re taking, including what signaling devices you’re taking.”

Some of the cases tracked by the National Parks Service go back decades and include those with plenty of outdoor experience. One ranger on the list of the missing has been gone for more than four decades. Another case involves a woman who vanished in 1976. Then there’s Dennis Lloyd Martin, who was last seen in a national park in 1969.

They are all missing despite the best efforts of trained professionals trying to locate them.

“National Parks responders, officers and special agents are highly trained, experienced, and the most proficient subject matter experts to conduct the search and rescue operations,” Hernandez said.

While the national parks offer great beauty to behold, lovers of the great outdoors want people to keep safe while exploring nature.

“A rainstorm doesn’t care what we look like, doesn’t care whether or not we’re wearing makeup doesn’t care or what gender we are or what color skin is, or any of that doesn’t matter a bit, it’s just going to do what a rainstorm does. And there’s something very freeing about that,” Krebs said.

The National Parks Service website has downloadable maps, road closure info and guides on how to safely view wildlife. Those visiting the parks should also check in with a ranger station before exploring, to get the latest updates on road or trail closures and safety conditions.

GPS does not always work in National Parks, especially those that are more remote, and don’t always reflect current road conditions so paper maps are essential.

Our survival experts say a $4 safety whistle is a must. Hikers should also pack extra food and water and carry extra layers of clothing in case they are unexpectedly stranded or weather conditions change suddenly.