Welcome to Yellowstone, the world’s first national park; home to three-quarters of the world’s geysers, also home to the powerful grizzly bear, bison and wolf, and the one-and-only Old Faithful geyser.

The army constructed Fort Yellowstone in a traditional military style, using local materials. Thirty-five of these structures remain today including the park chapel, administrative offices, and officer’s quarters. A walking tour of the Fort Yellowstone area begins at the Albright Visitor Center. Mammoth Hot Springs continues to serve as park headquarters for the National Park Service today.

Mammoth Hot Springs is geology in hyperdrive. In some locations, active springs are building up the terraces at a rate approaching two feet per year. That means the spectacle you see today will likely be very different from the one you see on your next visit. Even the boardwalks are constantly being re-routed to avoid being swallowed up by the mountain.

Norris Geyser Basin is the oldest and hottest thermal area in all of Yellowstone. A scientific drill hole at Norris once measured 401 F (200 C) at just over 265 feet below the surface. The test well had to be abandoned, when steam pressure and temperature threatened to destroy the drilling rig. Most springs and all geysers here are hot enough to release boiling water.

The surreal-colored steam that seems to rise from Grand Prismatic’s enormous pool is an optical illusion – the reflection of brightly colored thermophiles in a cloud of moisture. Measuring approximately 370 feet in diameter and over 121 feet in depth, Grand Prismatic is the park’s largest hot spring and the third largest on Earth (two larger hot springs are found in New Zealand).

On September 7, 1988, a 200-foot wall of fire was on a collision course with the Old Faithful Inn. The intensity of the fire produced gale-force winds strong enough to snap trees in half. For the first time in its history, the Old Faithful complex was evacuated. About 200 firefighters stayed behind to try and save the historic inn and the surrounding structures. Fortunately, at around 3 pm, the winds shifted, driving the firestorm south of the complex and sparing the inn. To learn more about the fire, listen to the story "The Fires of 1988".

Old Faithful Geyser is the world’s most famous geyser and the symbol of America’s first national park. Compared to other big geysers, which can sometimes remain dormant for days or even years between eruptions, the size and consistency of Old Faithful’s eruptions have not changed dramatically during the entire recorded history of the park. To predict Old Faithful’s next eruption, rangers examine factors like the time interval between eruptions and the length and character of the last eruption. The rangers claim to be accurate (within 10 minutes) over 90% of the time. Historically, the interval has ranged between 30 minutes to two hours. If you thought Old Faithful performed every hour on the hour, you’re in for a disappointment. These days, it’s in the range of every 90 minutes. In general, the longer the eruption, the longer the interval will be. Park Rangers post the predicted eruption times for Old Faithful and several other major geysers at the visitor center.

What's the difference between a hot spring, geyser, and mud pot? Listen to the story "Geothermal Features" and find out.

The Absaroka Mountains and Yellowstone Lake form a spectacular backdrop for this small geyser basin. Despite its modest size, you can find examples of every kind of thermal feature here: geysers, hot springs, mud pots and fumaroles. West Thumb has it all. Some of the features are actually submerged in the lake and are only exposed during the late summer, when lake levels are low. All together, the basin dumps an average of 3,100 gallons of hot water into the lake every day.

Yellowstone Lake is the largest high-altitude lake in North America. Sitting at 7,733 feet above sea level, the lake collects the frigid snow melt of over a hundred mountain streams. Consequently, the average summer water temperature is about 45°F (7°C). Swimming in the lake is dangerous. Survival time is estimated to be only 20 to 30 minutes. During the winter, ice as thick as two feet covers most of the lake. In some locations, like West Thumb Geyser Basin, thermal waters create holes in the ice, where otters can often be seen fishing.

Hayden Valley was once covered with an icecap 3,500 feet thick. Later, it was covered with water, forming a section of a larger Yellowstone Lake. The glacial till and lake sediments that were left behind helped create the marshy, treeless terrain you see today. The valley’s abundant grasses make it one of the best places in the park to see large herds of bison, especially in August when they congregate in this valley for their mating season. Don’t be surprised if you get caught in one of the infamous “bison jams.” Spring is also a great time to see grizzly bears feeding on carrion and preying on elk calves. It is important to always remember that Yellowstone is a wilderness. If you're not convinced, listen to the story "A dangerous landscape". Note: The story contains depictions of events in Yellowstone that may not be suitable for young children.

The spectacular array of colors you see in the canyon are the result of hydrothermal alterations to the rhyolite rocks that make up the canyon walls. Geologists believe an ancient geyser basin cooked the rhyolite, causing chemical changes in its iron components. Combine the chemical alterations with the rusting caused by exposure to rain and oxygen and you get a kaleidoscope of reds, pinks, oranges and yellows.

Referred to as the American Serengeti, Lamar Valley is home to a large variety of the park’s charismatic “mega fauna” – grizzly bears, wolves, bison and elk. The valley’s large open meadows, framed by low hills, treelines and high mountains, provide a range of habitat that supports a large variety of animals. Wide open vistas offer plenty of opportunities to viewing them safely. In the spring, grizzly bears emerge from their winter dens to feed on carrion and elk calves. Wolves prey on the elk and an occasional bison. Scavengers eat what is left behind. Look for circling ravens indicating a wolf kill may be within your view.

Constructed of local columnar basalt rock, like that found in Sheepeater and Overhanging cliffs, Roosevelt Arch stands at the northern entrance to the park. The 50-foot high archway was dedicated by President Theodore Roosevelt in 1903, becoming Yellowstone’s first of five entrances. The arch was designed by renowned architect Robert Reamer, best known for designing the Old Faithful Inn. Engraved above the archway are the words “For the benefit and enjoyment of the people,” a phrase taken from the legislation that created Yellowstone.