Yellowstone National Park is a national park in the United States located in the northwest corner of Wyoming, with small parts extending into Montana and Idaho. It was created by the 42nd U.S. Congress through the Yellowstone National Park Protection Act and signed into law by President Ulysses S. Grant on March 1, 1872. Yellowstone was the first national park in the United States and is also widely believed to be the first national park in the world. The park is known for its wildlife and geothermal features, including Old Faithful, one of its most famous geysers. While it includes many types of ecosystems, subalpine forest is the most common type. It is part of the South Central Rockies forests ecoregion.
Native Americans have lived in the Yellowstone region for at least 11,000 years. Before the late 1860s, organized exploration of the area was limited to visits by mountain men during the early-to-mid-19th century. Initially, the U.S. Department of the Interior managed the park, with Columbus Delano as the first secretary of the interior to oversee it. Later, the U.S. Army was assigned to manage Yellowstone for 30 years, from 1886 to 1916. In 1917, the National Park Service, which had been established the year before, took over management of the park. Hundreds of buildings in the park are protected for their historical and architectural value, and researchers have studied more than 1,000 indigenous archaeological sites.
Yellowstone National Park covers an area of 3,468.4 sq mi (8,983 km²), including lakes, canyons, rivers, and mountain ranges. Yellowstone Lake is one of the largest high-elevation lakes in North America and is part of the Yellowstone Caldera, the largest super volcano on the continent. The caldera is a dormant volcano that has erupted twice in the last two million years. More than half of the world’s geysers and hydrothermal features are in Yellowstone, powered by the area’s volcanic activity. Lava flows and rocks from past eruptions cover most of the park’s land. Yellowstone is the central part of the Greater Yellowstone Ecosystem, the largest nearly intact ecosystem in Earth’s northern temperate zone. In 1978, Yellowstone was named a UNESCO World Heritage Site.
Hundreds of species of mammals, birds, fish, reptiles, and amphibians live in the park, including several that are endangered or threatened. The forests and grasslands also support unique plant species. Yellowstone is the largest and most famous location in the contiguous United States for megafauna, which are large animals. The park is home to grizzly bears, cougars, wolves, and free-ranging herds of bison and elk. The Yellowstone bison herd is the oldest and largest public bison herd in the United States. Forest fires occur in the park each year, and in the large fires of 1988, more than one-third of the park burned. Yellowstone offers many recreational activities, such as hiking, camping, boating, fishing, and sightseeing. Paved roads provide easy access to major geothermal areas, lakes, and waterfalls. During winter, visitors often enter the park through guided tours using snow coaches or snowmobiles.
History
The park is divided by the Yellowstone River, which gives the park its name. In the late 1700s, French trappers called the river "Roche Jaune," which may have been a translation of the Hidatsa name "Mi tsi a-da-zi," meaning "Yellow Stone River." Later, American trappers changed the French name to "Yellow Stone." Many people think the river was named for the yellow rocks in the Grand Canyon of the Yellowstone, but the exact reason for the Native American name is not clear.
People have lived in the park area for at least 11,000 years. Native Americans hunted and fished there. In the 1950s, when workers built a post office in Gardiner, Montana, they found a tool made of obsidian (a type of black volcanic glass) that was about 11,000 years old. These early people, called Paleo-Indians of the Clovis culture, used obsidian to make tools and weapons. Arrowheads made from obsidian found in the Obsidian Cliffs have been discovered as far away as the Mississippi Valley and Ohio, showing that tribes traded obsidian over long distances. Later, Native American tribes like the Bannock, Shoshone, Nez Perce, Blackfeet, Crow, Salish, and Kootenai visited Yellowstone until the 1870s. Some lived there, and a few were hunting there as late as 1889 under treaty rights.
In 1805, when the Lewis and Clark Expedition reached present-day Montana, they met the Nez Perce, Crow, and Shoshone tribes. These tribes told them about the Yellowstone region to the south, but the explorers did not go there. In 1806, John Colter, a member of the expedition, left to join trappers. After separating from them in 1807, Colter traveled through what is now Yellowstone during the winter of 1807–1808. He saw a geothermal area near Tower Fall. After surviving injuries from a battle with the Crow and Blackfoot tribes in 1809, Colter described a place he called "fire and brimstone," which others thought was delirium. This place became known as "Colter's Hell." For the next 40 years, many reports from trappers described boiling mud, steaming rivers, and petrified trees, but most people believed these stories were myths.
In 1856, Jim Bridger, a mountain man, said he saw boiling springs, spouting water, and a mountain of glass and yellow rock. People did not believe him because they thought he made up stories. In 1859, Captain William F. Raynolds led a survey of the southern central Rockies. His team included geologist Ferdinand V. Hayden and guide Jim Bridger. They tried to cross the Continental Divide but were stopped by heavy snow. If they had succeeded, they would have been the first organized group to explore Yellowstone. The American Civil War delayed further exploration until the late 1860s.
The first detailed trip to Yellowstone was the Cook–Folsom–Peterson Expedition of 1869. The Folsom group followed the Yellowstone River to Yellowstone Lake and kept a journal. Based on their report, Montana residents organized the Washburn–Langford–Doane Expedition in 1870. Led by Henry Washburn, the surveyor-general of Montana, and including Nathaniel P. Langford and U.S. Army officer Lt. Gustavus Doane, the expedition explored the area for about a month, collected samples, and named sites of interest.
Cornelius Hedges, a Montana writer and lawyer who joined the Washburn expedition, suggested the region should be protected as a national park. He wrote about his observations in the Helena Herald newspaper between 1870 and 1871. Hedges repeated a comment made in 1865 by Thomas Francis Meagher, the acting governor of Montana, who had also suggested protecting the area. Others, like businessman Jay Cooke, encouraged Ferdinand V. Hayden to include Yellowstone in his official report. Cooke said his friend, Congressman William D. Kelley, had proposed a bill to protect the Great Geyser Basin as a public park forever.
In 1871, Ferdinand V. Hayden finally explored Yellowstone with government support. His expedition, the Hayden Geological Survey of 1871, included photographs by William Henry Jackson and paintings by Thomas Moran. His report helped convince Congress to stop selling land in the area. On March 1, 1872, President Ulysses S. Grant signed the Act of Dedication, creating Yellowstone National Park.
Hayden was the first and most active supporter of protecting Yellowstone. He believed the area should be a place for people to enjoy and warned that others might exploit it. He feared Yellowstone could suffer the same damage as Niagara Falls and said the area should be "as free as the air or water." In his report to Congress, he warned that without protection, the park’s natural wonders could be destroyed by people who wanted to take resources.
Hayden and his team saw Yellowstone as a special place worth studying and preserving. In 1873, Congress funded a survey to find a wagon route to the park, completed by the Jones Expedition. The park was not created only for nature but also to create scenic areas like those in Europe.
Some people opposed the park in its early years, fearing it would hurt the local economy. Others wanted the park’s size reduced so mining, hunting, and logging could happen. Many bills were introduced to Congress by Montana representatives to remove federal restrictions on land use.
Nathaniel Langford became Yellowstone’s first superintendent in 1872, appointed by the Secretary of the Interior, Columbus Delano. Langford worked without a salary, funding, or staff and had few ways to protect the park from poachers or vandals. He wrote about the challenges in the 1872 Report to the Secretary of the Interior and predicted Yellowstone would become a major attraction needing government care.
Research and recognition
Yellowstone National Park has a long and rich history, which has been recorded through the discovery of 1,000 archaeological sites. The park includes 1,106 historic structures and features, and two of these, Obsidian Cliff and five buildings, are recognized as National Historic Landmarks. Yellowstone became an International Biosphere Reserve on October 26, 1976, and a UN World Heritage Site on September 8, 1978. From 1995 to 2003, Yellowstone was listed on the World Heritage in Danger because of problems like too many visitors, sick animals, and invasive plants. In 2010, Yellowstone National Park was featured on a special coin as part of the America the Beautiful Quarters Program.
Justin Farrell studied three different ideas that influenced people who worked to protect Yellowstone. The first idea was using natural resources as much as possible, which was common among developers in the late 1800s. The second idea was seeing nature as something special, inspired by Romanticism and the transcendentalists in the mid-1800s. In the 1900s, a new idea called the biocentric moral vision focused on keeping ecosystems healthy, as explained by Aldo Leopold. This idea helped increase the size of federally protected areas and their surrounding ecosystems.
The Heritage and Research Center is located in Gardiner, Montana, near the park’s northern entrance. The center holds Yellowstone National Park’s museum collection, archives, research library, historian, archaeology lab, and herbarium. The Yellowstone National Park Archives keep historical records about Yellowstone and the National Park Service. These records include administrative files, resource management documents, records from major projects, and donated manuscripts and personal papers. The archives are connected to the National Archives and Records Administration.
Geography
Yellowstone National Park is located in a square-shaped volcanic area that extends slightly beyond the northwestern corner of Wyoming. About 96% of the park is in Wyoming, 3% is in Montana, and 1% is in Idaho. Montana’s part of the park includes trails, facilities, and swimming areas, while Idaho’s part has no developed areas. The park’s eastern edge follows the highest point of the Absaroka Range.
The park is 63 miles (101 km) from north to south and 54 miles (87 km) from west to east. It covers 2,219,789 acres (8,983 km²; 3,468 sq mi), which is larger than the states of Rhode Island and Delaware. Rivers and lakes cover 5% of the land, with Yellowstone Lake being the largest water body. Yellowstone Lake covers 87,040 acres (352 km²; 136 sq mi), is up to 400 feet (120 m) deep, and has 110 miles (180 km) of shoreline. It is the largest high-elevation lake in North America and sits at 7,733 feet (2,357 m) above sea level. Forests cover 80% of the park, and the rest is mostly grassland.
The Continental Divide runs diagonally through the park’s southwestern area. This landform separates water that flows to the Pacific Ocean from water that flows to the Atlantic Ocean. One-third of the park is on the west side of the divide. The Yellowstone and Snake Rivers begin near each other but on opposite sides of the divide. The Snake River flows to the Pacific Ocean, while the Yellowstone River flows to the Gulf of Mexico.
Yellowstone sits on the Yellowstone Plateau, which averages 8,000 feet (2,400 m) above sea level. The plateau is surrounded by mountain ranges in the Middle Rocky Mountains, which range from 9,000 to 11,000 feet (2,700 to 3,400 m) in height. The highest point in the park is Eagle Peak at 11,358 feet (3,462 m), and the lowest is Reese Creek at 5,282 feet (1,610 m). Nearby mountains include the Gallatin Range to the northwest, the Beartooth Mountains to the north, the Absaroka Range to the east, the Teton Range to the south, and the Madison Range to the west. Mount Washburn, at 10,243 feet (3,122 m), is the most prominent peak on the plateau.
Yellowstone has one of the world’s largest petrified forests. These trees were once buried by ash and soil and later replaced by minerals. The ash and volcanic material likely came from the park itself, as the central area of Yellowstone is a massive caldera formed by a supervolcano. The park has 290 waterfalls, with the tallest being the Lower Falls of the Yellowstone River at 308 feet (94 m).
Three deep canyons are found in the park, carved by rivers through volcanic rock over the past 640,000 years. The Lewis River flows through Lewis Canyon in the south, and the Yellowstone River has created two colorful canyons: the Grand Canyon of the Yellowstone and the Black Canyon of the Yellowstone.
Geology
Yellowstone is located at the northeastern end of the Snake River Plain, a large, bow-shaped area that stretches about 400 miles (640 km) from the park to the Idaho-Oregon border.
The volcanic activity in Yellowstone is connected to older volcanic activity in the Snake River Plain. Yellowstone is the active part of a hotspot that the North American Plate has moved over in a southwest direction over time. Scientists disagree about the origin of this hotspot. One idea suggests that a hot plume of material from deep inside Earth caused the hotspot to move. Another idea says the movement of the hotspot is linked to changes in a plate that sank deep into Earth long ago, called the Farallon Plate.
The Yellowstone Caldera is the largest volcanic system in North America. It is only matched in size by the Lake Toba Caldera in Sumatra. It is called a supervolcano because it was formed by extremely large eruptions. Under Yellowstone, there is a large magma chamber estimated to be about 37 miles (60 km) long, 18 miles (29 km) wide, and 3 to 7 miles (4.8 to 11.3 km) deep. The most recent major eruption happened 640,000 years ago and released more than 240 square miles (1,000 square km) of ash, rock, and volcanic materials. This eruption was over 1,000 times larger than the 1980 eruption of Mount St. Helens. It created a caldera nearly 5/8 mile (1 km) deep and 45 by 28 miles (72 by 45 km) in size. This eruption also formed the Lava Creek Tuff, a type of rock. A much older eruption, 2.1 million years ago, released 588 square miles (2,450 square km) of volcanic material and created the Huckleberry Ridge Tuff and the Island Park Caldera. A smaller eruption 1.3 million years ago formed the Henry’s Fork Caldera and the Mesa Falls Tuff.
Each of these major eruptions sent large amounts of ash across much of central North America, sometimes hundreds of miles away. Scientists believe the ash and gases released into the atmosphere may have changed weather patterns worldwide and caused some species to become extinct, especially in North America.
A smaller caldera-forming eruption happened about 160,000 years ago, creating the West Thumb of Yellowstone Lake. Since the last supereruption, many smaller eruptions between 640,000 and 70,000 years ago have filled the Yellowstone Caldera with lava. These eruptions included rhyolitic lava, like the rocks at Obsidian Cliffs, and basaltic lava, like those at Sheepeater Cliff. The layers of lava are best seen in the Grand Canyon of the Yellowstone, where the Yellowstone River has carved a V-shaped valley, a sign of river erosion rather than glacier erosion.
Each eruption is part of a cycle that ends with the collapse of the volcano’s magma chamber, forming a caldera and releasing volcanic material through cracks around it. The time between the last three major eruptions in Yellowstone has ranged from 600,000 to 800,000 years. However, scientists cannot use this pattern to predict future eruptions accurately.
Old Faithful is the most famous geyser in Yellowstone and possibly the world. It is located in the Upper Geyser Basin, along with other geysers like Castle Geyser, Lion Geyser, Beehive Geyser, Grand Geyser (the tallest predictable geyser), Giant Geyser (the most powerful geyser), Riverside Geyser, and many others. The park also has the tallest active geyser, Steamboat Geyser, in the Norris Geyser Basin. A 2011 study found that at least 1,283 geysers have erupted in Yellowstone, with about 465 active each year. The park has at least 10,000 geothermal features, including geysers, hot springs, mudpots, and fumaroles. More than half of the world’s geysers and hydrothermal features are found in Yellowstone.
In 2001, the U.S. Geological Survey, Yellowstone National Park, and the University of Utah created the Yellowstone Volcano Observatory (YVO) to monitor geological activity in the area and share information about potential hazards.
In 2003, changes in the Norris Geyser Basin caused some trails to close temporarily. New fumaroles appeared, and some geysers became hotter, changing their activity. Some geysers turned into steaming features because their water became superheated. This happened around the same time as a study that mapped the bottom of Yellowstone Lake and found a structural dome that had risen in the past. Scientists said these changes did not indicate an immediate risk of volcanic activity. In July 2024, a hydrothermal explosion occurred in Biscuit Basin.
Yellowstone experiences thousands of small earthquakes each year, most of which are too small for people to feel. About two-thirds of these earthquakes happen in an area between Hegben Lake and the Yellowstone Caldera, along a buried fracture zone from a 2.1-million-year-old eruption.
Six earthquakes with a magnitude of 6 or higher have been recorded in Yellowstone’s history. The largest was the 7.2-magnitude Hebgen Lake earthquake in 1959, which caused a landslide, a dam collapse, and the formation of Earthquake Lake. Twenty-eight people died, and property damage was widespread. The earthquake also caused some geysers to erupt, cracks to form, and hot springs to turn muddy. Scientists believe the stress from this earthquake may still affect earthquake activity in the park’s northwest area. A 6.1-magnitude earthquake occurred inside the park in 1975, but it caused little damage.
On average, Yellowstone has 1,000 to 3,000 small earthquakes each year. On March 30, 2014, a magnitude 4.8 earthquake struck near the Norris Basin, but no damage was reported. This was the largest earthquake in the park since 1980.
Biology and ecology
Yellowstone National Park is the center of the 20 million acres (80,940 km²; 31,250 mi²) Greater Yellowstone Ecosystem, which includes Grand Teton National Park, nearby National Forests, and large wilderness areas within those forests. This ecosystem is the largest continuous area of mostly undeveloped land in the contiguous United States and is considered the world's largest intact ecosystem in the northern temperate zone. The reintroduction of wolves, which began in the 1990s, has helped restore many of the original animal and plant species that lived in the area when early explorers arrived. The park is also a key observation site for the National Ecological Observatory Network.
Over 69,000 species of trees and other vascular plants are native to the park. Another 170 species are non-native. Of the eight conifer tree species found in the park, lodgepole pine forests cover 80% of the total forested areas. Other conifers, such as subalpine fir, Engelmann spruce, Rocky Mountain Douglas-fir, and whitebark pine, grow in scattered groves throughout the park. The whitebark pine is threatened by a fungus called white pine blister rust and was listed as a threatened species in 2023. Quaking aspen and willows are the most common deciduous trees. Aspen forests declined significantly in the early 20th century, but scientists believe the recent recovery of aspen is due to the reintroduction of wolves, which changed the grazing habits of elk.
Dozens of flowering plant species have been identified in the park, most of which bloom between May and September. The Yellowstone sand verbena is a rare flowering plant found only in Yellowstone. It is closely related to plants usually found in warmer climates, making it a mystery. About 8,000 of these plants live in the sandy soils along the shores of Yellowstone Lake, above the waterline.
In Yellowstone's hot waters, bacteria form unusual mats made up of trillions of organisms. These bacteria are among the oldest life forms on Earth. Flies and other arthropods live on the mats, even during cold winters. Scientists once believed these microbes relied only on sulfur for energy.
Thermus aquaticus is a bacterium found in Yellowstone's hot springs that produces an enzyme (Taq polymerase) useful in DNA replication through the polymerase chain reaction (PCR) process. These bacteria can be collected without harming the ecosystem. Research on thermophiles in Yellowstone has helped develop virus tests and new types of biodegradable plastic. In 2016, scientists discovered a group of thermophiles called Hadesarchaea in Yellowstone's Culex Basin. These organisms can convert carbon monoxide and water into carbon dioxide and hydrogen.
Non-native plants sometimes harm native species by taking nutrients. Though exotic species are often found near roads and tourist areas, they have also spread into remote parts of the park. Most exotic species are removed by hand or with sprays, which are time-consuming and costly.
Yellowstone is considered the best large animal habitat in the lower 48 states. The park is home to nearly 60 mammal species, including Rocky Mountain wolves, coyotes, Canadian lynx, cougars, black bears, and grizzly bears. Other large mammals include bison (often called buffalo), elk, moose, mule deer, white-tailed deer, mountain goats, pronghorn, and bighorn sheep.
The Yellowstone bison herd is the largest public herd of American bison in the United States. Bison once numbered between 30 and 60 million in North America, and Yellowstone remains one of their last strongholds. Their population increased from fewer than 50 in 1902 to 6,000 in 2023, leading to a cull of 1,150 bison.
Large bison populations concern ranchers, who worry that bison may spread diseases to their cattle. About half of Yellowstone's bison have been exposed to brucellosis, a disease that came to North America with European cattle and can cause miscarriages in livestock. The disease rarely affects bison, and no cases of transmission from bison to cattle have been reported. Elk also carry the disease and may spread it to horses and cattle.
To reduce the risk of disease transmission, park workers often move bison back into the park when they leave. In 1996–1997, 1,079 bison that left the park were either killed or sent to slaughter. Animal rights groups argue this is cruel and that the risk of disease is not as high as some ranchers claim. Ecologists note that bison are simply moving to seasonal grazing areas within the Greater Yellowstone Ecosystem, which now include land used for cattle grazing. Scientists say brucellosis could be eliminated through vaccination and other methods.
In 1914, Congress funded efforts to kill wolves, prairie dogs, and other animals considered harmful to agriculture. Park Service hunters killed 136 wolves by 1926, nearly eliminating them from Yellowstone. Extermination continued until the practice ended in 1935. The Endangered Species Act of 1973 listed the wolf as one of the first protected mammals. Without wolves, coyotes became the top predator in the park, but they could not control large animals, leading to more sick or injured large animals.
By the 1990s, the government changed its stance on wolves. In a controversial decision, wolves from Canada were reintroduced to Yellowstone. The program has been successful, with stable populations. A 2024 survey found 9 wolf packs totaling 108 individuals. The recovery of wolves in Wyoming, Montana, and Idaho was so successful that the Northern Rocky Mountain wolf population was removed from the endangered species list in 2008. Wolves in Yellowstone are part of a larger population across the Greater Yellowstone Ecosystem.
Black bears are common in the park and were once a symbol because of interactions with visitors starting in 1910. Feeding bears has been banned since the 1960s to prevent them from seeking human food. Yellowstone is one of the few places in the U.S. where black bears and grizzly bears coexist. Black bears are often seen in the park's northern ranges and in the Bechler area in the southwest.
As of 2017, an estimated 700 grizzly bears lived in the park.
Forest fires
Wildfire is a natural part of many ecosystems, and plants native to Yellowstone have developed ways to survive and thrive in fire-prone areas. Douglas-fir trees have thick bark that helps protect the inside of the tree from fire damage. Lodgepole pines, the most common tree in the park, have cones that only open when exposed to fire heat. Their seeds are held in place by a strong resin, and fire melts this resin, allowing the seeds to spread. Fire also clears away dead and fallen wood, making it easier for lodgepole pines to grow. Other tree species, like subalpine fir, Engelmann spruce, and whitebark pine, grow in colder, wetter areas where fires are less common. Aspen trees grow new shoots from their roots, and even if a fire destroys the above-ground parts of the tree, the roots often survive because they are protected by soil. In natural conditions, grasslands in Yellowstone burn on average every 20 to 25 years, while forests in the park experience fire about every 300 years.
About 35 natural forest fires each year are caused by lightning, and 6 to 10 are started by people, usually by accident. Yellowstone has three fire lookout towers, each staffed by trained firefighters. The easiest to reach is on Mount Washburn, which has exhibits and an observation deck for visitors. The park also uses air monitoring and reports from visitors to track fires. Fire towers are staffed nearly all the time from late June to mid-September, the main fire season. Fires burn most intensely in the late afternoon and evening. Most fires burn less than 100 acres (40 hectares), and the majority burn only a little over 1 acre (0.5 hectares) before going out. Fire management focuses on monitoring dead wood, soil, tree moisture, and weather to identify areas at risk of fire. Current policy is to stop all human-caused fires and assess natural fires to determine if they help or harm the ecosystem. If a fire threatens people or structures, or if it becomes uncontrollable, firefighters will suppress it.
To reduce risks of uncontrolled fires and protect people and property, park employees monitor fire potential. Controlled burns are fires started intentionally to remove dead wood under safe conditions, allowing firefighters to manage how much wood is burned. Natural fires are sometimes treated as controlled burns if they are allowed to burn naturally. In Yellowstone, few fires have been started intentionally by employees as controlled burns, but over 300 natural fires have been allowed to burn over the last 30 years. Firefighters also remove dead wood and other hazards to reduce fire risks. Fire monitors educate the public and may temporarily ban campfires during high fire danger. In early U.S. land management policies, all forest fires were considered harmful, and efforts focused on suppressing all fires. This led to more dead trees and forests, which later fueled larger, harder-to-control fires. The latest Fire Management Plan (2014) allows natural fires to burn if they do not immediately threaten lives or property.
In 1988, the spring was wet, but by summer, drought spread across the northern Rockies, making it the driest year recorded at that time. Grasses and plants that grew during the wet spring turned into dry fuel. The National Park Service began firefighting efforts, but the extreme drought made suppression difficult. Between July 15 and 21, 1988, fires spread from 8,500 acres (3,400 hectares) across Yellowstone and surrounding areas to 99,000 acres (40,000 hectares) within the park alone. By the end of July, fires were out of control. On August 20, 1988, the worst day of the fires, more than 150,000 acres (61,000 hectares) were burned. Seven large fires burned 95% of the 793,000 acres (321,000 hectares) affected over several months. The cost of fighting the fires, involving 25,000 firefighters and U.S. military forces, was $120 million. By winter, snow helped put out the last fires, but 67 structures were destroyed, and damage totaled several million dollars. No civilians died, but two firefighters were killed.
Surveys showed that few animals were killed in the fires, with only about 345 elk (of an estimated 40,000–50,000), 36 deer, 12 moose, 6 black bears, and 9 bison lost. Changes in fire management policies were made nationwide after the 1988 fires, based on scientific evaluations. By 1992, Yellowstone adopted a new fire management plan with stricter guidelines for managing natural fires.
Climate and weather
Yellowstone's climate is affected by its elevation, with lower areas usually being warmer throughout the year. The highest temperature ever recorded was 99 °F (37 °C) in 2002, and the lowest was −66 °F (−54 °C) in 1933. During summer months from June to early September, daytime temperatures typically range between 70 to 80 °F (21 to 27 °C), while nighttime temperatures can drop below freezing (0 °C), especially at higher elevations. Thunderstorms often occur during summer afternoons. In spring and fall, temperatures range from 30 to 60 °F (−1 to 16 °C), with nighttime temperatures often between −5 to −20 °C (−18 to −29 °C). Winter temperatures are usually between 0 and 20 °F (−18 to −7 °C), with nighttime temperatures often below 0 °F (−18 °C).
Precipitation in Yellowstone varies greatly, with areas near Mammoth Hot Springs receiving about 15 inches (380 mm) of rain each year, while parts of the southwestern region receive up to 80 inches (2,000 mm). The amount of precipitation is influenced by a moisture channel created by the Snake River Plain to the west. Snow can fall any month of the year but is most common between November and April. Annual snowfall averages about 150 inches (3,800 mm) near Yellowstone Lake, with higher elevations receiving twice that amount.
The climate at Yellowstone Lake is classified as subarctic (Dfc), while the climate at the park headquarters is classified as humid continental (Dfb) according to the Köppen-Geiger system.
Tornadoes in Yellowstone are rare. However, on July 21, 1987, the strongest tornado ever recorded in Wyoming touched down in the Teton Wilderness of Bridger-Teton National Forest and entered Yellowstone National Park. Known as the Teton–Yellowstone tornado, it was classified as an F4, with wind speeds estimated between 207 and 260 miles per hour (333 and 418 km/h). The tornado caused damage over a path 1 to 2 miles (1.6 to 3.2 km) wide and 24 miles (39 km) long, destroying 15,000 acres (6,100 ha; 23 sq mi) of mature pine forest.
In June 2022, the park closed entrances and evacuated visitors due to record rainfall and flooding. Heavy rain and rapid snowmelt caused the Yellowstone River to reach a new record height of 13.88 feet (4.23 m), surpassing a previous record from 1918. Flooding on the Lamar River reached 16.7 feet (5.1 m), breaking a 1996 record. Flooding damaged roads, bridges, and infrastructure such as electricity and water systems. Initially, it was expected that the north entrance near Gardiner, MT, and the northeast entrance near Cooke City, MT, would not reopen during the 2022 season. The park partially reopened on June 22 after a 9-day closure. The north entrance opened on October 30, two days earlier than planned, and the northeast entrance opened on October 15. To manage visitor numbers, the park temporarily limited vehicle entry based on license plate information.
Recreation
Yellowstone is one of the most popular national parks in the United States. Since the mid-1960s, at least 2 million visitors have come to the park each year. From 2007 to 2016, the average number of visitors increased to 3.5 million yearly, with a record of 4,257,177 visitors in 2016. This record was broken in 2023, when 4.5 million people visited the park. July is the busiest month of the year. During peak summer, 3,700 employees work for companies that manage services in the park. These companies operate nine hotels and lodges with 2,238 rooms and cabins. They also manage gas stations, stores, and most of the campgrounds. Another 800 employees work for the National Park Service either all year or during the season.
Roads managed by the National Park Service lead to major attractions. However, road repairs sometimes cause temporary closures. Yellowstone is working on long-term road improvements, but progress is slow because repairs can only happen during a short season. In winter, only one road from Gardiner, Montana, to Cooke City, Montana, is open to vehicles. Most roads are closed to vehicles from early November to mid-April, and some remain closed until mid-May. The park has 310 miles of paved roads accessible from five entrances. There is no public transportation inside the park, but tour companies offer guided or self-guided motorized tours. In winter, companies provide snowmobile and snow coach tours, but the number of vehicles and access is limited by rules set by the National Park Service. Areas near Old Faithful, the Canyon, and Mammoth Hot Springs are very busy in summer. Traffic jams from road construction or people watching wildlife can cause long delays.
Yellowstone offers many recreational activities, but these activities also carry risks. Between 2007 and 2023, 74 deaths were recorded in the park. Driving is the leading cause of death, responsible for more than 45%, often on roads that cross difficult terrain. Water-related activities, such as fishing, swimming, and boating on Yellowstone Lake and rivers, account for 16% of deaths. Hiking, climbing, and walking make up 38% of deaths, often on trails or near geothermal areas.
The National Park Service manages nine visitor centers and museums and maintains 2,000 buildings, including historic landmarks like the Old Faithful Inn (built from 1903 to 1904) and the Fort Yellowstone–Mammoth Hot Springs Historic District. Camping is available at 12 campgrounds with over 2,000 campsites. Backcountry campsites require a permit and can only be reached by foot or horseback. There are 1,100 miles of hiking trails. Wooden and paved trails near thermal features help keep visitors safe and are accessible for people with disabilities. A clinic at Mammoth Hot Springs provides medical care year-round, and emergency services are available throughout the year.
Hunting is not allowed in the park, though it is permitted in nearby national forests during hunting seasons. Fishing is popular, and a Yellowstone Park fishing license is required. Many waters allow only fly fishing, and all native fish must be released after being caught. Boating is not allowed on most rivers and creeks, except for a 5-mile stretch of the Lewis River between Lewis and Shoshone lakes, where only non-motorized boats are allowed. Yellowstone Lake has a marina at Bridge Bay and a boat ramp at the Lewis Lake campground.
Other protected areas near Yellowstone include Caribou-Targhee, Gallatin, Custer, Shoshone, and Bridger-Teton National Forests. The John D. Rockefeller, Jr. Memorial Parkway is to the south and connects to Grand Teton National Park. The Beartooth Highway provides access from the northeast and offers views of high-altitude landscapes. Nearby towns include West Yellowstone, Montana; Cody, Wyoming; Red Lodge, Montana; Ashton, Idaho; and Gardiner, Montana. The closest airports are in Bozeman, Montana; Billings, Montana; Jackson, Wyoming; Cody, Wyoming; and Idaho Falls, Idaho. Salt Lake City, 320 miles to the south, is the nearest large city.