The calcite terraces at Mammoth Hot Springs. These springs flourished with water until the late 1970s, but are currently dry.
Yellowstone is the first and oldest national park in the world and covers 3,472 square miles (8,987 km²), mostly in the northwest corner of Wyoming. The park is famous for its various geysers, hot springs, and other geothermal features and is home to grizzly bears, wolves, and free-ranging herds of bison and elk.
Long before any recorded human history in Yellowstone, a massive volcanic eruption spewed an immense volume of ash that covered all of the western U.S., much of the Midwest, northern Mexico and some areas of the eastern Pacific Coast. The eruption dwarfed that of Mt. St. Helens in 1980 and left a huge caldera. Yellowstone typically erupts every 600,000 to 900,000 years with the last event occurring 640,000 years ago. Its eruptions are among the largest known to have ever occurred on Earth, producing drastic climate change in the aftermath. Although it is commonly assumed that the park was named for the yellow rocks seen in the Grand Canyon of the Yellowstone, the park's name comes from the Yellowstone River that flows through it, which is in turn named after sandstone bluffs found farther down its course in eastern Montana.
On March 1,1872, Yellowstone became the first National Park reserve declared anywhere in the world, by President Ulysses S. Grant. In 1978 it was designated a World Heritage Site by UNESCO .
Geological characteristics form the foundation of an ecosystem. In Yellowstone, the interplay between volcanic, hydrothermal, and glacial processes and the distribution of flora and fauna are intricate and unique. The topography of the land from southern Idaho northeast to Yellowstone results from millions of years of hotspot influence. Some scientists believe the Yellowstone Plateau itself is a result of uplift due to hotspot volcanism.
Flora and fauna
The park is the core of the Greater Yellowstone Ecosystem, one of the largest intact temperate zone ecosystems remaining on the planet. Black bears, grizzly bears, deer, elk, bison, bighorn sheep and wolves can all be found within the park borders.
Raptors such as Bald Eagles (pictured above), Golden Eagles, and Falcons are commonly seen throughout the park. This Bald Eagle was photographed while hunting for prey near Mammoth Hot Springs, in the northern portion of the park.
It is not at all unusual to see many types of bears, like this black bear, near the roadways or up on the ridges of Yellowstone in the summertime, usually foraging for food.
Primary geothermal features include geysers, mud pots, hot springs and fumaroles, which exist because of the active volcano that Yellowstone sits on top of. Geothermal features are formed by superheated water heated by the volcano. The pressure is so intense that it gets released into the air as hundreds of gallons of steaming water, or, when the pressure is not as intense, hot springs or mud pots are formed. Various colors of the pool are due to different types of bacteria growing in different temperatures. A good way to learn about the geothermal features is through the Young Scientist Program. Please check with a Ranger at the Old Faithful Visitor Center.
The weather in Yellowstone National Park can change very rapidly from sunny and warm to cold and rainy, so it's important to bring along extra layers of clothing which can be used as needed.
Summer: Daytime temperatures are often in the 70s (25°C) and occasionally in the 80s (30°C) in lower elevations. Nights are usually cool and temperatures may drop below freezing at higher elevations. Thunderstorms are common in the afternoons.
Winter: Temperatures often range from zero to 20°F(-20°C to -5°C) throughout the day. Sub-zero temperatures over-night are common. The record low temperature is -66F (-54°C). Snowfall is highly variable. While the average is 150 inches per year, it is not uncommon for higher elevations to get twice that amount.
Spring & Fall: Daytime temperatures range from the 30s to the 60s (0 to 20°C) with overnight lows in the teens to single digits (-5 to -20°C). Snow is common in the Spring and Fall with regular accumulations of 12" in a 24 hour period. At any time of year, be prepared for sudden changes. Unpredictability, more than anything else, characterizes Yellowstone’s weather. Always be equipped with a wide range of clothing options. Be sure to bring a warm jacket and rain gear even in the summer.
Official map from the National Park Service; in the public domain and not protected by copyright.
The principal airport serving Yellowstone is the Jackson Hole Airport (IATA: JAC)  located within Grand Teton National Park. United and Delta serve Jackson Hole year-round, from Denver and Salt Lake City respectively. American and Frontier provide service on a seasonal basis.
Alternative airports with limited/seasonal commercial service can be found in:
Alternative airports may have less airline service than Jackson Hole.
The park has 5 entrances. The nearest cities to each entrance are given.
North - Accessed from Gardiner (Montana) via US Route 89 (56 mi, 90 km from Livingston). This entrance is open all year and leads to the park headquarters at Mammoth Hot Springs, 5 miles (8 km) inside the park boundary. The iconic Roosevelt Arch is located at this entrance.
Northeast - Accessed from Silver Gate and Cooke City via US Route 212 (Beartooth Highway). The entrance and road to Cooke City are open all year, but Route 212 past Cooke City is closed in winter (mid-October to late May).
East - Accessed from Cody (53 mi, 85 km) via US Route 14/16/20. This entrance is closed in winter (early November to early May).
South - Accessed from Grand Teton National Park via US Route 89/191/287. This entrance is closed in winter (early November to mid-May).
West - Accessed from West Yellowstone via US Route 20/191/287 (60 mi, 97 km from Ashton (Idaho). This entrance is closed in winter (early November to late April).
All vehicles and individuals entering the park must pay an entrance fee that is valid for seven days. The entrance fee provides entry to both Grand Teton and Yellowstone National Parks. Fees are $25 for non-commercial vehicles, $12 for hikers and cyclists, and $20 for motorcycles and snowmobiles.
One year passes are available as an alternative to the seven day fee. The Park Annual Pass is $50 and provides entrance to Yellowstone and Grand Teton National Parks. The Interagency Annual Pass is $80 and provides entrance to most federal recreation sites across the country including Yellowstone and Grand Teton National Parks.
Most visitors use private vehicles to get around inside Yellowstone National Park. There is no public transportation available within the park. Roads can become very crowded whenever people stop to view wildlife; use pullouts, and be respectful of other motorists to help avoid bear-jams.
For a fee, classic buses will lead passengers on a guided tour of the Grand Loop Road
Xanterra Resorts  provides bus tours within the park during the summer season. The Lower Loop Tour departs from locations in the southern part of the Park only. The Upper Loop Tour departs from Lake Hotel, Fishing Bridge RV Park, and Canyon Lodge to tour the northern section of the park only. The Grand Loop Tour departs from Gardiner and Mammoth Hot Springs Hotel to tour the entire park in one day. During the winter season snowcoach tours are provided from various locations. Call (307) 344-7311 for information or reservations.
In addition, during the summer season, commercial businesses offer tours originating from many area towns and cities. During the winter season, some businesses provide snowcoach tours for most park roads or bus transportation on the Mammoth Hot Springs to Cooke City road.
Cycling in the park can be a very rewarding experience, but due to the great distances in the park some additional planning is necessary to ensure that lodging is available each night. The park reserves a number of campsites for cyclists, but during the busy summer season it is probably best to reserve sites in advance wherever possible.
Clepsydra geyser at play, Lower Geyser basin.
Yellowstone is world-famous for its natural heritage and beauty - and for the fact that it holds half the world's geothermal features, with more than 10,000 examples. Travelers to Yellowstone can view more than 300 geysers (such as "Old Faithful"), pools of boiling mud, and an amazing assemblage of wildlife, such as grizzly bears, wolves, bison and elk, all while standing on the surface of the Earth's largest known "super-volcano".
Mammoth Hot Springs. Mineral-laden hot water flows from springs, depositing calcite and other substances in its wake. Over time, these deposits form large terraces and other shapes. Some of the terraces grow several inches per day.
Fort Yellowstone. The historic center of activity during the United States Army's tenure of the park.
Bunsen Peak. The hike to the top of this 8,564 foot peak takes approximately three hours round trip. The peak overlooks the old Ft. Yellowstone area and it is only a gradual climb. Bring water and snacks (and bear bells if you think they'll work).
Boiling River. This small swimming hole is one of very few spots in the park where visitors can soak in naturally-heated water. It tends to be very crowded, so try to visit very early in the morning during peak season.
Looking like an image from space, mattes of cyanobacteria thrive in the scalding waters of Biscuit Basin.
Norris Geyser Basin. One of the parks many spectacular thermal areas, and home to Steamboat Geyser, the world's largest geyser, which can throw water more than 300 feet into the air when it erupts. The Norris area is the hottest, most acidic, and most changeable in the park.
Roaring Mountain. A collection of steam vents and hot springs which make noises ranging from a nearly inaudible whisper to a roar that can be heard miles away. This thermal feature is right beside the park highway.
Artist Paint Pots. A half-mile hike takes you past many colorful hot springs, steam vents and bubbling mud pots.
Monument Geyser Basin. Although largely extinct, Monument Geyser Basin contains several intriguing travertine structures and some great views on its mile-long access trail.
Gibbon Falls. These 84-foot falls tumble down a staircase-like rock -- easy to see from a pullover area on the park highway.
Madison River. The river creates a canyon with steep, tree-covered rock walls on each side.
Firehole Canyon Drive and Firehole Falls.
National Park Mountain. The mountain where the Madison and Firehole rivers meet. As legend has it, this is where the idea came about to preserve Yellowstone as a National Park.
Geyser basins, including Old Faithful
Upper Geyser Basin. The most popular visitor area in the park, the Upper Geyser Basin is home to the largest number of geysers in the park, with over 100 located within a one square mile area. Boardwalks allow access to the most interesting areas. Do not leave the trails; the surface here is thin and unstable and has a real chance of depositing you in a boiling pool of water if you walk where you're not supposed to.
Old Faithful The world's most famous geyser, with large eruptions occurring an average of about once every hour and a half. Despite its reputation for having eruptions you can set a watch to, the timing between each eruption has actually been increasing over the past several decades. Rangers are able to predict the geyser's eruptions to within about 10 minutes, provided the duration of the previous eruption is known.
Other geysers in Upper Geyser Basin that are well enough understood to be predictable (sort of!) are Grand Geyser (probably the finest predictable geyser in the park), Castle Geyser, Daisy Geyser, and Riverside Geyser. Check at the Old Faithful visitor center for predictions, which will have uncertainties of an hour or so associated with them, sometimes more.
Lower Geyser Basin. Unlike Upper Basin, most active areas here are accessible by car. Great Fountain Geyser is the largest geyser in this group, is easily reached by car, and is well enough understood to be predicted, after a fashion; check at the Old Faithful visitor center, and when you get to the geyser, check the bulletin board again, as its behavior allows periodic updating of the predictions.
The Grand Prismatic Spring, viewed from above. There is a trail that goes around the back of the spring which has a small turn-off that lets intrepid climbers rise about 400 feet above the spring, and capture the entire basin in one view. For a closer view, there are raised boardwalks around the spring and nearby pools (viewable in the detail of the picture)
Midway Geyser Basin. This geyser basin is on a hill overlooking the Firehole River. The runoff from its thermal features flows into the river, leaving steaming, colorful trails in its wake. Absolutely spectacular!
Grand Prismatic Spring. Perhaps this geyser basin's most famous feature, this is a mass of sapphire blue hot water with bands of yellow and orange around its edges. This spring is more than 300 feet across.
Excelsior Geyser once had such violent eruptions that it seems to have blown itself up. This geyser hasn't erupted in years, but it still discharges over 4000 gallons of water per minute into the nearby Firehole River.
Lone Star geyser erupting, Check at Old Faithful Visitor Center for times
Lone Star Geyser Basin. This and the following are more "Do" than "See," as they require some hiking to reach them. The route takes off from the loop road south of Upper Geyser Basin and follows an old, now-closed road for a total of about 3 miles (5 km). Bicycles can make it most of the way to Lone Star. Nice hike for families.
Shoshone Geyser Basin. Serious hiking is required to reach this remote basin, which is beyond Lone Star and a good 7 miles (12 km) one way from the trailhead.
West Thumb Geyser Basin. With a little imagination, Yellowstone Lake looks like a left hand reaching southward. This thermal area is along the western thumblike section of the lake. Several geysers and hot springs (even a couple that are just a few inches across!) are in this area, including the following two sights:
Abyss Pool. There is an optical illusion with this brilliant blue hot spring that makes it look bottomless.
Fishing Cone. In the past, people used to catch fish in Yellowstone Lake and then cook the fish by dipping them into this partially submerged hot spring. This stunt is no longer allowed.
Yellowstone Lake. This is the largest freshwater lake at an elevation over 8,000 feet in the country. It spreads 20 miles east to west and 30 miles north to south. The Yellowstone River empties out into the lake.
Mud Volcano/Sulphur Cauldron. This area of the park has pools of mud that are constantly seething and boiling.
Mud Volcano This was once a hilltop thermal feature that would hurl mud into the nearby trees during eruptions. One particularly large eruption blew apart the Mud Volcano, leaving a hot, bubbling mud pool at the base of the hill.
Dragon's Mouth Spring Steam and hot water surge forth from within an underground cavern, creating waves in the surface mud pool. These surges of water and steam reverberate inside the cavern and make loud thumping or roaring sounds.
Sulphur Cauldron This vast hot spring is strongly acidic thanks to the action of microorganisms.
Dead trees near the summit of Mt. Washburn. These trees are the victims of a massive forest fire in 1987 that burned through over 30% of the forest running through the park. In a controversial decision, it went unchecked by the National Park Service, but has allowed for new growth to sprout in large parts of the park.
The Grand Canyon of the Yellowstone. Chemical processes over time have left stripes and patches of different colors in the rock of this canyon. Depths of the canyon reach 800-1200 feet. Trails lead along the north and south rims of the canyon, but while traveling the entire trail in one day is possible, it makes for a long and tiring day. Best to make it two shorter (~3 hour) day hikes. If you're a photo buff, plan your walks so the sun illuminates the opposite side for great pictures.
Artist point - great spot to view the canyon and the lower falls.
The Upper and Lower Falls of the Yellowstone. These are the two largest waterfalls in the park. The Upper Falls is 109 feet tall and creates a small canyon. The large Lower Falls is about 309 feet tall, and creates the Grand Canyon of the Yellowstone.
Hayden Valley. Some people say it's the best place to watch bison in Yellowstone. Hayden Valley is home to a large number of animals, and includes the infamous Mud Volcano.
Mt. Washburn. One of the best places in the park for spotting bighorn sheep, a trail leads up the mountain to a lookout tower near the 10,243 foot summit. The altitude may affect some hikers, so it is best to be acclimatized to the higher elevation before attempting this hike. In addition, bring extra layers, even in the summer, since the top can be windy and cold.
Petrified Forest. This is home to a large petrified forest. It is accessible along the highway.
Tower Fall. The 100-foot tall waterfall plunges down a rock, creates a thin canyon, and a rapid creek.
Car Free Week. Yellowstone opens its roads to bicyclists and hikers one week before car traffic resumes each spring (usually in April). This week is a rare opportunity to see Yellowtone's sights and wildlife without the crowds and traffic. Several West Yellowstone businesses rent bikes.
Young Scientist, . Students ages 5 and up can learn about Yellowstone's geothermal features. Students are given scientist toolkit, including an infrared thermometer, stop watch, magnifying glass and other gear. Once you've finished it, you have a choice of a patch or key chain.
Jr Ranger Program, . Jr Ranger Program provides an opportunity for children 5 - 12 to earn a Jr Ranger patch. Ages 5-7 can earn the wolf patch and Ages 8-12 can earn the Bear patch. In order to get a patch, a 12 page activity booklet needs to be answered correctly and checked by a ranger. An activity booklet costs $3.
Many visitors believe they can visit all 2.2 million acres of Yellowstone in 1-2 days - all the while staying within sight of their car or tour bus. To truly appreciate this vast park, get off the park roads and paved tourist paths.
A bison ambles along Norris to Canyon Road. Despite their docile appearance, bison are temperamental and can move extremely fast.They should be viewed from a safe distance through binoculars or telephoto lenses.
Hiking -- Walking as little as 100 feet away from the camera gangs will give you more of an appreciation for the park. Taking a few 3-4 hour day hikes on established hiking trails is even better, yet will still allow you the luxury of a hot shower in the morning and prepared dinner in the evening.
Wildlife Viewing -- There is a lot of wildlife to view within the park limits. Birds (osprey, bald eagles, and many, many other species,) bison, big cats, deer, wolves, fox, bears, big-horn sheep, elk, and other animals can all be seen within the park over a short period of time. The more time that you spend in the park, the more wildlife that you will see. Some animals, such as the wolves, bears, and the big-horn sheep are generally not viewable from the park roads. The spaces within the park are grand, so make sure to bring binoculars and/or a spotting scope to best view animals safely.
Horseback Riding -- There are many opporunities to enjoy YNP and the scenery there. Endulge in horse riding opportunities in YNP and a famous battlefield.
Photography -- Yellowstone holds unprecedented photo opportunities with natural environments, beautiful hydrothermal features and animals to be found throughout the park. The colors of the hot springs range from bland white (for the very, very hot) to yellows and blues, greens and oranges. Some of the features are very large, and the challenge can be finding a way to get them in the frame. Be creative! There have been a lot of pictures taken in Yellowstone, and there are a lot more still waiting to be taken.
Swimming -- Swimming is allowed (but not encouraged) at the Firehole Cascades swimming area, a section of the Firehole River that is warmed by hot springs. This area, accessible via the Firehole Canyon Drive, has a toilet but no lifeguard and not much parking.
Every major village within the park offers food, camping supplies, and souvenirs for sale, although these stores all close during the winter months.
Gasoline and automotive services are available in the following locations:
Canyon (late April to early November). Gasoline, diesel and auto repair.
Fishing Bridge (mid May to late September). Gasoline, diesel, propane and auto repair.
Grant Village (mid April to mid October). Gasoline, diesel, propane, and auto repair.
Mammoth (early May to mid October). Gasoline and diesel.
Old Faithful (Lower) (mid April to early November). Gasoline and diesel.
Old Faithful (Upper) (late May to late September). Gasoline and auto repair.
Tower Junction (early June to early September). Gasoline.
Vintage sign at Mammoth Hot Springs: There are a variety of restaurant venues scattered throughout the park.
Most of the villages sell food supplies and may offer snack bars. The following restaurants and cafeterias are also available:
Old Faithful Inn Dining Room.
Old Faithful Snow Lodge Restaurant.
Old Faithful Lodge Cafeteria.
Lake Yellowstone Hotel Dining Room.
Lake Lodge Cafeteria.
Grant Village Restaurant.
Grant Village Lakehouse Restaurant.
Canyon Lodge Cafeteria. Great breakfast with omelet of the day ($4.2), links ($1.05 for two), bacon ($1.05 for two), hot oatmeal and a few other choices.
Canyon Lodge Dining Room.
Mammoth Hot Springs Hotel Dining Room.
Roosevelt Lodge Dining Room.
Cocktails can be purchased in the lodge restaurants, and lighter beverages can be obtained at the snack bars.
A small cauldron bubbles in the Upper Geyser Basin across from Old Faithful Inn.
Lodging in the park fills quickly and should be booked in advance. Cancellations are common, so if a particular lodging option is unavailable it is a good idea to re-check frequently to see if it becomes available. Reservations for all lodges and cabins in the park can be made through Xanterra Parks & Resorts  or by calling (307) 344-7311. All park accommodations are non-smoking and, reflecting the natural surroundings of Yellowstone, televisions, radios, air conditioning, and Internet hook-ups are not available.
Canyon Lodge and Cabins, . In the Canyon area the lodge options include the Canyon Lodge, Cascade Lodge, and Dunraven Lodge. Cascade Lodge and Dunrave Lodge offer hotel-style rooms, while the Canyon Lodge is actually a group of cabins. All lodging has a private bath.
Grant Village, . Offering an array of hotel-like rooms and cabins for families, this hotel complex provides the basic amenities without some of the flair of the Old Faithful Inn but at prices that are a bit lower, and Grant Village may have greater availability due to the number of rooms available there. There is a post office nearby, as well as a cafeteria, a soda-jerk diner, and a sandwich shop in the complex, as well as a reservations-only restaurant serving local fare. Even if you decide not to eat at the restaurant, do go in to check out the large array of beautiful photographs taken by one of the long-time Yellowstone Maintenance heads, who is also one of the park photographers.
Lake Yellowstone Hotel & Cabins, . Located right on Lake Yellowstone (there's a boat pier and a restaurant right on the edge of the lake), the Lake Yellowstone Hotel and Cabins provide a rustic experience that probably won't excite a luxury traveler, but the staff provides the basics - decent rooms, reasonably good food, and breathtaking views of the lake and its surroundings. Watch out for mosquitos especially as you walk near the lake in mornings and afternoons in the summer, they come out in swarms, but DEET or similar mosquito repellant will keep them away.
Mammoth Hot Springs Hotel & Cabins, . Open year-round. The hotel offers rooms both with a private bath or with a shared bath. Another option is to stay in the many cabins located next to the hotel, also with private or shared bath. For hikers just looking to clean up, showers are available for $3.25 (inquire and pay fee in advance at front desk).
Old Faithful Inn, . A national historic site, this rustic hotel was originally constructed entirely of logs before two wings were added in the early 20th century. The vast lobby incorporates large tree trunks as pillars and a stone fireplace. Range of accommodations from rooms with shared bathrooms and showers nearby, to suites with private bathrooms and refrigerators. Located near Old Faithful Geyser. Open from May through October.
Old Faithful Lodge Cabins, . Large windows in the lobby face Old Faithful Geyser. Gift shop, restaurants, bakery. Open from May-Oct.
Old Faithful Snow Lodge, . Open December through March.
A trick of refraction, blue steam rises off the waters of Grand Prismatic Spring
Xanterra Parks & Resorts  operates campgrounds at Bridge Bay, Canyon, Fishing Bridge, Grant Village, and Madison. Same-day reservations can be made by calling: 307-344-7901. Future reservations can be made by calling: 307-344-7311 or by writing: Yellowstone National Park Lodges, PO Box 165, Yellowstone National Park, WY 82190.
Reservations should be made well in advance and/or campsites should be secured as early in the day as possible. Campgrounds may fill by early morning, especially during peak season (early July - late August). Recreational vehicles over 30 ft should make reservations since there is a limited number of RV sites available in Yellowstone. Large RV sites are located at Flag Ranch, Fishing Bridge RV Park and West Yellowstone.
Indian Creek, Lewis Lake, Mammoth, Norris, Pebble Creek, Slough Creek, and Tower Fall are operated by the National Park Service and do not accept reservations; all sites are first-come, first-served.
Bridge Bay. (27-May to 18-Sep). 432 sites, flush toilets, RV dump station.$17 per site.
Canyon. (06-Jun to 11-Sep). 272 sites, showers, flush toilets.$20.15 per site.
Fishing Bridge RV. (20-May to 02-Oct). 344 sites, showers, flush toilets, RV sewer station. This is the only campground offering water, sewer, and electrical hookups, and it is for hard-sided vehicles only (no tents or tent-trailers are allowed).$31 per site.
Grant. (21-Jun to 02-Oct). 425 sites, showers, flush toilets, RV dump station.$19 per site.
Indian Creek. (10-Jun to 19-Sep). 75 sites, pit toilets.$12 per site.
Lewis Lake. (17-Jun to 06-Nov). 85 sites, pit toilets.$12 per site.
Madison. (06-May to 30-Oct). 277 sites, flush toilets, RV dump station.$20.35 per site.
Norris. (20-May to 26-Sep). 116 sites, flush toilets.$14 per site.
Pebble Creek. (03-Jun to 26-Sep). 32 sites, pit toilets.$12 per site.
Slough Creek. (27-May to 31-Oct). 29 sites, pit toilets.$12 per site.
Tower Fall. (20-May to 26-Sep). 32 sites, pit toilets.$12 per site.
Artist's Point -- the classic, iconic overlook of Lower Yellowstone Falls.
Permits are required for all backcountry camping, and quotas are placed on the number of people that may use an area at a given time. The maximum stay per backcountry campsite varies from 1 to 3 nights per trip. Campfires are permitted only in established fire pits, and wood fires are not allowed in some backcountry campsites. A food storage pole is provided at most designated campsites so that food and attractants may be secured from bears. Neither hunting nor firearms are allowed in Yellowstone's backcountry.
Permits may be obtained only in person and no more than 48 hours in advance of your trip, although backcountry sites may be reserved through the mail well in advance for a non-refundable $20 reservation fee. To reserve a site, download the reservation form from the Backcountry Trip Planner , call (307) 344-2160, or by writing: Backcountry Office, PO Box 168, Yellowstone National Park, WY 82190.
During the summer season (Jun-Aug), permits are available 7 days a week between 8AM and 4:30PM at the following locations:
Bechler Ranger Station
Canyon Ranger Station/Visitor Center
Grant Village Visitor Center
Lake Ranger Station
Mammoth Ranger Station/Visitor Center
Old Faithful Ranger Station
South Entrance Ranger Station
Tower Ranger Station
West Entrance Ranger Station
In addition, permits may sometimes be obtained from rangers on duty at the East Entrance and Bridge Bay Ranger Station. However, these rangers have other duties and may not be available to provide assistance at all times.
During the spring, fall, and winter seasons, ranger stations and visitor centers do not have set hours. To obtain a Backcountry Use Permit during these seasons, check the office hours posted at the nearest ranger station or visitor center.
Fragile sinter crusts and ledges can give way, plunging a careless tourist into the boiling waters below
Though many of the animals in the park are used to seeing humans, the wildlife is nonetheless wild and should not be fed or disturbed. Stay at least 100 m away from bears and 25 m from all other wild animals! Bison, elk, moose, bears, and nearly all large animals can attack! For any doubters, the National Park Service has put a series of animal attack videos  online -- these animals are large, wild, and potentially dangerous, so give them their space.
In addition, be aware that odors attract bears and other wildlife, so avoid carrying or cooking odorous foods and keep a clean camp; do not cook or store food in your tent. All food, garbage, or other odorous items used for preparing or cooking food must be secured from bears. Treat all odorous products such as soap, deodorant, or other toiletries in the same manner as food. Do not leave packs containing food unattended, even for a few minutes. Animals which obtain human food often become aggressive and dependent on human foods, and many can suffer ill health or death from eating a non-native diet.
When camping, either filter, boil, or otherwise purify drinking water. Waters may be polluted by animal and/or human wastes, and intestinal infections from drinking untreated water are increasingly common.
Always stay on boardwalks in thermal areas. Scalding water lies under thin, breakable crusts; pools are near or above boiling temperatures. Every year visitors traveling off trail are seriously burned, and people have died from the scalding water. No swimming or bathing is allowed in thermal pools.
The weather can change rapidly and with little warning. A sunny, warm day can quickly become a cold, rainy or even snowy experience. Hypothermia can be a concern. Be prepared for a variety of weather conditions by bringing along appropriate clothing. Lightning can and does injure and kill people in the park, so watch the sky and take shelter in a building if you hear thunder.
Grand Teton National Park. Yellowstone's southern neighbor is famous for its dramatic mountain vistas and its alpine lakes. Admission to Grand Teton is included in the Yellowstone price. Note, however, that the road connecting the two parks is closed during winter (early November to mid-May).
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