As America's first national park and one of its most important biosphere reserves, Yellowstone holds a unique place in our national consciousness — more than four million people visit the park each year. However, with its rich history, there are likely many facts you've probably never heard of, even if you consider yourself a park aficionado. Here are 10 fascinating Yellowstone National Park facts that will take your knowledge of America's favorite national park to the next level.

There's Another Grand Canyon at Yellowstone

Waterfall from above surrounded by pine trees in Yellowstone National Park
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When most people think of the Grand Canyon, they think of Arizona. But, what about the Grand Canyon of the Yellowstone River? This 20-mile long canyon is said to be an important example of river-type erosion, with a depth of more than 1,000 feet. On the ridge of the canyon lies Artist Point, which offers one of the most beautiful views in the park. From this spot on the trail, you can see a majestic, 300-foot waterfall flowing into the canyon. If you look down, you'll see steep canyon walls in gorgeous hues of pink, orange, yellow, and red.

Half of the World's Geysers Are in the Park

Colorful geyser with people walking on bridge behind in Yellowstone National Park
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Yellowstone is home to a whopping 10,000-plus hydrothermal features, including 500 geysers — which scientists estimate is about half of the world's geysers. The most famous is Old Faithful, which erupts around 17 times a day. Other breathtaking features, like the Beehive Geyser and Grotto Geyser, are somewhat less popular but still provide a thrilling show of geothermal action. So, if you're worried about Old Faithful being too crowded at peak times of the year, don't worry — you still have hundreds of other geysers to see.

Norris Geyser Is Poisonous to Bison

Landscape of Norris Geyser Basin in Yellowstone National Park
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In the Norris Geyser Basin, chemical releases from eruptions are strong enough to kill huge mammals. In 2004, park rangers found five dead bison right after the eruption of Norris, and chemical analysis revealed that it was high levels of carbon dioxide and hydrogen sulfide that did them in. While incidents like this seem scary, don't let that stop you from visiting. Although the park's active geothermal sites produce gases such as carbon dioxide and hydrogen sulfide, few are located in enclosed, low-lying areas. So, the probability of a fatal exposure is unlikely.

Yellowstone County Has Its Own Judicial System

Meadow with stream and trees, mountains in the background in Yellowstone National Park
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For 30 years, the United States Army kept order at Yellowstone. Until 1916, soldiers patrolled the park to protect the wildlife from unscrupulous poachers. The park spans three states — Montana, Idaho, and Wyoming — all of which have differing laws pertaining to wildlife and preservation. To fix this decades-old issue of disputes in different parts of the park, Yellowstone officially created the Yellowstone County judicial system in 2006. That means if you break the law while you're visiting the park, you'll be put in the official Yellowstone jail. And, your mugshot may just be the only souvenir you get to take home.

The Park Is One of Only UNESCO World Heritage Sites in the U.S.

Incredible landscape with hundreds of bison crossing the Lamar river in the Lamar Valley in Yellowstone National Park
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Around the world, 878 extraordinary locations have been designated as United Nations Education, Science, and Cultural Organization (UNESCO) World Heritage Sites. The United States only has 20 sites across the entire country, and Yellowstone is one of the most important.

UNESCO's website provides a list of reasons for Yellowstone's coveted honor, including its distinctive manifestation of geothermal forces and vast number of rare species. These ecological features are why Yellowstone stands alongside culturally significant sites like the Great Barrier Reef and Machu Picchu.

Yellowstone Is Actually a Giant Supervolcano

Mammoth hot springs in Yellowstone National Park
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Hot spots and geysers represent just a fraction of the action beneath the surface at Yellowstone. The whole park is actually a supervolcano, although it's not supposed to erupt anytime soon. But, how do we know this? Despite the warnings, Yellowstone is quite safe: Its supervolcano is made up of two magma chambers. The first chamber contains no more than 15% molten. Meanwhile, the second chamber contains only two percent molten. According to Forbes, it's practically impossible for a supervolcano to erupt unless its magma chambers contain at least 50% molten. So, rest easy — and don't forget to enjoy the view.

The Bears Aren't as Dangerous as You Think

Black bear with cubs playing in the forest in Yellowstone National Park
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In the entire history of Yellowstone, only eight people have ever been killed by bears in the park. To put this in perspective, that means only one in 2.7 million visitors will have a fatal bear encounter. Getting injured by a bear is a bit more common, but still happens only about every 20 years. The National Park Service cautions people to look out for falling trees instead, which kill the same number of people (but gets a lot less media attention).

Hundreds of Unique Flowers Thrive in Yellowstone

Lupine flowers at Yellowstone National Park
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An estimated 1,350 different types of flowering plants grow wild at Yellowstone, the vast majority native to the region. One remarkable plant that calls the park home is Yellowstone sand verbena, a flower which normally thrives in warm environments but has managed to grow at a 7,700 foot altitude inside the park. Another unique floral trademark of Yellowstone is Ross's Bentgrass, which grows exclusively in hot, vapor-heavy environments. This plant is a common sight at the park but rare everywhere else in the world.

Bison in Yellowstone Are the Oldest in America

A herd of bison at Yellowstone National Park
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While many other grassland areas have been over-hunted and bison have been driven to extinction, Yellowstone's herd has remained intact. According to the History Channel, Yellowstone's bison population is the only herd that has existed since prehistoric times in the United States. In the 19th century, the herd was hunted down to its last 23 members by avid fur traders exploring the Wild West. Today, however, the park is home to 5,500 bison, making it the biggest bison population in the country.