You might think you know America's national parks – from wild, hot-spring-filled Yellowstone to the sprawling red rocks of the Grand Canyon – but each one hides some surprising secrets. Here, we've rounded up some of the most fascinating facts about America's beloved national park sites, covering weird and wonderful wildlife and record-breaking wonders.

Click through this gallery to uncover surprising details about America's national parks...

All the trees in the aptly named 'Giant Forest' in California's Sequoia National Park thrust a long way skyward – but General Sherman is the largest of them all. It soars to 275 feet (84m) and its base has a 36-foot (11m) diameter, making it the biggest tree by volume in the world. Take to the Main Trail to see the giant sequoia in all its green glory.

The glaciers in Alaska's spectacular Glacier Bay National Park and Preserve are mesmerising – but did you know they have some tiny inhabitants? Minuscule ice worms (related to the common earthworm) live in the ice, feeding on snow algae and thriving at freezing temperatures. Various myths about the hardy species exist, including that they give the formations their blue hue (this sadly isn’t true). They’re also found in the glaciers of the Pacific Northwest and Canada's British Columbia.

Yellowstone, which covers parts of Wyoming, Montana and Idaho, has many treasures. It’s a land of steaming geysers, sizzling mud pots and colourful hot springs, and it’s also thought to have America’s oldest free-roaming bison herd. According to the National Park Service, this world of natural wonders is the only place in the USA where bison have existed since prehistoric times. The herd is the largest found on public land in America too.

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From bison and bears to the elusive grey wolf, Yellowstone is well known for its epic wildlife. But did you know that wolves were only reintroduced to the park in the last 30 years? The fascinating creatures were hunted to near-extinction in the US during the 20th century, with habitat loss also contributing to their decline. They were finally reintroduced to the park through the 1990s, and today are closely monitored. It’s thought that more than 120 wolves currently live in the park, split between 10 packs.

OK, so the waterfall isn’t actually made of fire – but when conditions are just right it looks as though Horsetail Fall has been set ablaze. The spectacle at California's Yosemite National Park occurs when the cascade is backlit by a fiery sunset – a phenomenon that typically occurs in the second half of February. Still, if you miss the show, the plunging waterfall, which pours over the east edge of El Capitan, is a beautiful sight at any time of year.

The hoodoos at Utah’s Bryce Canyon are a spectacular sight, not least because of the sheer volume of them. The national park is thought to hold the largest concentration of these otherworldly rock formations on the planet, and they appear in shades of flaxen, sunset orange and pink. They were created in a process that began some 50 million years ago, involving the deposition of rocks, an uplifting of the land and long periods of erosion.

This one might not come as too much of a surprise. Sweltering Death Valley, which seeps over the California-Nevada border, is a swathe of desert tipped as the hottest place on the planet. On 10 July 1913, at Furnace Creek, the world’s highest air temperature was recorded: 57°C (134°F). Despite this, hardy species, including the desert tortoise and roadrunners, survive in these harsh conditions.

One of the country’s most underrated national parks, Colorado’s Black Canyon of the Gunnison is made up of crags and gorges formed over many millions of years. It’s a paradise for hikers, but its depths are often plunged into darkness. It’s said that the very deepest parts of the canyon are so low that they receive just 33 minutes of sunlight per day at certain times of the year.

The chambers and intricate stalactites and stalagmites of Kentucky's Mammoth Cave are mighty impressive and, what’s more, it’s dubbed the longest cave system in the world. It wriggles out for a whopping 420 miles (676km) – a new record-breaking total that was reached after an additional eight miles (13km) were mapped in autumn 2021. You can take ranger-led tours of the cave and hear about the fascinating rock formations and their history. Evening explorations by lantern light are extra special.

The Smokies conjure images of rippling, forested peaks and iconic American wildlife like elk, deer and black bear – but you might not know that this beautiful park is also known as the 'salamander capital of the world'. About 30 species and five families of this amphibian thrive in the park, including the hard-to-miss red salamander – look out for them wriggling across forest floors or frolicking in creeks and streams.

The rippling sand mountains of Colorado’s Great Sand Dunes National Park are impressive enough, but even more so when you consider that they can hold a tune. The phenomenon of 'singing dunes' is caused when an avalanche occurs, typically during a storm. The avalanche causes bold vibrations and an intense humming sound that ripples across the stirring sandscape.

When you gaze up at the Big Apple’s soaring skyline, it’s hard to imagine that the cityscape could fit beneath a lake in the state of Oregon (in height, at least). The intense sapphire-blue Crater Lake is the deepest in the United States, plunging to 1,943 feet (592m). That means the neck-craning One World Trade Center – the tallest building in the country – would sit comfortably beneath the surface, rising as it does to 1,776 feet (541m).

Indiana Dunes might not be the first place you think of when it comes to wildlife, but it’s actually one of the most biodiverse places in the country. The park unfolds along the banks of Lake Michigan, and is filled with giant dunes, wetlands and woodlands – and, surprisingly, more plant and animal species than the state of Hawaii. Some 46 species of mammal and more than 350 species of bird live here, and it’s even known as the 'birthplace of ecology', due to several important studies conducted in the area.

This New Mexico national park looks like something from another planet with its endless ripples of glistening gypsum sand. The resident wildlife stands out against the stark white backdrop, with species including desert turtles, snakes and lizards. But perhaps its most fascinating animal is the African oryx. These striking horned creatures were introduced from Africa's Kalahari Desert into White Sands between 1969 and 1977 by the New Mexico Department of Game and Fish to increase the opportunities for big game hunting. Hunting is now prohibited, and thousands of the non-native animals exist in the park.

Another spectacular New Mexico landscape, Carlsbad Caverns National Park is made up of a labyrinth of 119 caves, plus canyons and stark desert scrub. And, best of all, you can enjoy a subterranean lunch. Sitting 750 feet (229m) underground, there’s a simple lunchroom that dates back to 1928, predating the formation of the park by two years. It's pictured here in a retro postcard. 

Take a look at the world's most beautiful caves and caverns

There’s a whole underwater world protected at Florida’s Biscayne National Park. The preserve is filled with colourful coral reefs, scattered islands and open waters, and it’s one of the most spectacular diving sites in the US. It’s estimated that over 40 wrecks languish beneath the water, of which six are mapped on the Maritime Heritage Trail. Sites range from forgotten lighthouses to an iron-hulled steamer.

Channel Islands National Park, a string of five Pacific islands off the coast of California, is best known for its wildlife, from frolicking dolphins to migrating grey whales. But there’s also a fascinating history to be discovered. A tiny part of a human femur was discovered on Santa Rosa Island (pictured) in 1959 and, upon analysis, scientists concluded that the person in question would have lived some 13,000 years ago. That would make the remains the earliest ever dated in North America. Today, the specimen is known as the Arlington Springs Man.

Alaska’s wildlife is pretty epic and residents of Denali National Park and Preserve include grizzly and black bears, wolves and moose. However, some of the park's smaller species are pretty fascinating too. Denali’s wood frogs are especially interesting since they freeze themselves almost solid during the winter. About 60% of their bodies turn to ice, their hearts pause and their blood stops flowing. When spring has finally sprung, their little bodies thaw and they move on.

Epic sunrises from the top of Haleakalā – a dormant shield volcano also known as the 'House of the Sun' – are the highlight of this national park, yet it’s also home to some incredible wildlife. Sadly, though, a high concentration of the plants and animals that exist here are endangered. More than 100 endangered species live in the park, including 81 flowering plants and two mammals. Among them is the Hawaiian monk seal, of which it’s estimated there are about 1,600 left in Hawaii. The nēnē, or Hawaiian goose (the state bird, pictured) has happily moved from being endangered to threatened in recent years.

The brooding mangrove swamps of Florida’s Everglades National Park attract around a million people each year, and visitors are enthralled by the critters that live here. There’s abundant birdlife, plus frogs, snakes and cute West Indian manatees, but most fascinating of all are the American crocodiles and alligators. South Florida, which includes the Everglades National Park, is the only place on the planet where crocodiles and alligators coexist. Want to tell the difference? Crocodiles (pictured) have fairly pointed snouts, while alligators’ are more soft and rounded.

Prickly cacti are almost synonymous with America’s Southwest, and Arizona’s Saguaro National Park has some of the most impressive anywhere in the world. Some 25 species of cacti live here, with the most striking being the giant saguaro cactus. These magnificent plants only grow in the Sonoran Desert, and they’ve been known to reach heights of 78 feet (24m). More commonly, they stand around 40 feet (12m).

The enormous Big Bend National Park in western Texas provides plenty of fodder for palaeontology buffs. In fact, its fossils tell tales of the land from as far back as 130 million years ago. The crowning jewel of the park’s fossil finds is the skeleton of an enormous pterosaur (a kind of ancient flying reptile). The quetzalcoatlus, as it is known, has a giant wingspan of 36 feet (11m), and is the largest flying creature scientists have ever discovered.

The Golden State is blessed with a wide roster of national parks, so it’s unsurprising that some fly under the radar. Among the less touristed spots is Pinnacles National Park, which is as intriguing as it is beautiful. The striking landscape was formed by ancient volcanic activity and, remarkably, activity along the San Andreas Fault has since caused the rock formations to shift some 195 miles (314km) south of their original location. They're still moving today – at a rate of about 0.59 inches (1.5cm) per year.

It's no secret that Arizona's Grand Canyon is enormous – but some comparisons are still bound to leave you in awe. With an area of 1,904 square miles (4,931sqkm), the spellbinding, rocky landscape is larger than the entire state of Rhode Island (the smallest state in the US). It plunges down for about a mile (1.6km) too.

Washington’s Mount Rainier is one of the most popular parks in America’s west, but scientists are concerned for its future. The United States Geological Survey tips the formation as “potentially the most dangerous volcano in the Cascade Range”. That’s because its large concentration of glaciers would cause severe mudflows if melted by volcanic activity, plus earthquakes are a regular occurrence in the region. Its enormous size – it’s a whopping 14,410 feet (4,392m) – is a factor too.

In most national parks, wildlife is skittish, preferring to move about at dusk or dawn when the sites are typically at their quietest. That's not the case for some bold inhabitants of Montana's Glacier National Park. The resident mountain goats here prefer to spend time near park visitors – apparently because the presence of humans lessens the risk from predators. The natural salt from human urine (left behind by off-the-beaten-track hikers) attracts them too. Nice.

Another of the country's underrated national parks, Nevada's Great Basin has some spectacularly strange trees. The ancient great basin bristlecone pines here are among the oldest trees on the planet, seeing out thousands upon thousands of years. They look old too, with their gnarled, twisting trunks, jagged branches and knobbly roots. The park has the remains of the so-called Prometheus tree, estimated to be between 4,700 and 5,000 years old. Its stump is all that remains.

Utah's Zion is best known for the views you get from the soaring Angels Landing rock formation and the narrow passageways at its foot – but the park also rivals Arches National Park for majestic arched formations. Kolob Arch is one of the largest free-standing structures of its kind on the planet – it spans an impressive 287 feet (87m).

A national park might be the last place you'd expect to see an airport – but you'll find just that at Wyoming's Grand Teton. The Jackson Hole Airport is the only commercial airport that's situated within a national park proper. It dates right back to the 1930s and today airlines including Delta and United operate here.

Katmai National Park and Preserve is wonderfully remote, set out in the far southwestern reaches of Alaska. And, as you'd expect, it has some wild and wonderful inhabitants. The park is home to mammals including the elusive grey wolf, humpback whales and, best of all, brown bears – some 2,200 of them in fact. According to the NPS, the Alaska Peninsula has more of these formidable furry creatures than it does human inhabitants.

Alaska does nature on a scale not seen in the rest of the US. Wrangell-St Elias National Park is America's largest national park, and however big you think it is – it's bigger. Covering a vast chunk of the state's southeast, along the Canada border, the park and preserve eat up 13.2 million acres of land – larger than the entire states of Vermont, New Hampshire and Rhode Island. To put it another way, that's bigger than Yellowstone, Yosemite and the entire country of Switzerland combined.

Now discover stunning images of the world's incredible canyons