Yosemite National Park is a United States National Park and a UNESCO World Heritage Site located in the Sierra Nevada mountains in east-central California. Yosemite is internationally recognized for its spectacular granite cliffs, waterfalls, clear streams, giant sequoia groves, and biological diversity. The 750,000-acre, 1,200 square-mile park contains thousands of lakes and ponds, 1600 miles of streams, 800 miles of hiking trails, and 350 miles of roads.

History
Efforts to protect Yosemite Valley began as far back as June 30, 1864 when President Abraham Lincoln signed a bill granting Yosemite Valley and the Mariposa Grove of Giant Sequoias to the State of California as an inalienable public trust. This was the first time in history that a federal government had set aside scenic lands simply to protect them and to allow for their enjoyment by all people. The area became a national park on October 1, 1890 following several years of struggle by John Muir against the devastation of the sub alpine meadows surrounding Yosemite Valley. Despite its national park status, California controlled the initial grant area until 1906. Prior to ceding control, the city of San Francisco became embroiled in a bitter political struggle over the Hetch Hetchy Valley, in which the city wanted to dam the Tuolumne River as a source of drinking water and hydroelectric power. In 1913, conservationists led by John Muir lost the battle when Congress passed the Raker Act, authorizing the construction of O'Shaughnessy Dam. To this day, crusades to restore Hetch Hetchy are ongoing.

Flora and fauna
Yosemite has more than 300 species of vertebrate animals, and 85 of these are native mammals. Black bears are abundant in the park, and are often involved in conflicts with humans that result in property damage and, occasionally, injuries to humans. Visitor education and bear management efforts have reduced the bear-human incidents and property damage by 90% in the past few years. Ungulates include large numbers of mule deer. Bighorn sheep formerly populated the Sierra crest, but have been reduced to only a few remnant populations.

There are 17 species of bats, 9 of which are either Federal or California Species of Special Concern. Over 150 species of birds regularly occur in the parks. Other species that are found within the park include bobcat, gray fox, mountain beaver, great gray owls, white-headed woodpeckers, spotted owls, golden-mantled ground squirrel, martens, Steller's jays, pika, yellow-bellied marmot, and white-tailed hare. The vegetation in the park is primarily coniferous forest. Most notable among the park's trees are isolated groves of giant sequoias, the largest trees in the world, which are found in three groves in Yosemite National Park.

Climate
Weather can change rapidly during all seasons of the year, and will also vary greatly with elevation. When visiting it is wise to pack for any season with clothing that can be layered, ready to peel off or add on as conditions dictate. Always include some kind of rain gear; the park receives most of its precipitation in the months of January, February and March, but storms are common during the transitional spring and fall seasons, and spectacular thunderstorms may occur during summer. For Yosemite Valley and Wawona (subtract 10-20°F (5-10°C) for Tuolumne Meadows), average weather is as follows:

 • Summer: Typically dry, with occasional thunderstorms; temperatures from 50°F (10°C) to the low 90°F (30°C) range.
 • Fall & Spring: Highly variable, with typical high temperatures ranging from 50-80°F (10-27°C) , with lows from 30-40°F (-1 to 4°C). Rain is less likely early in fall/late in spring and rain or snow is likely late in fall/early in spring.
 • Winter: Snowy, rainy, or (sometimes) even sunny days are possible, with highs ranging from 30-60°F (-1 to 16°C) and lows in the high 20°F (-4 to 0°C) range.

Stay safe

For any emergency in Yellowstone National Park, dial 911 from any phone.

Medical
Yosemite Medical Clinic - Ahwahnee Drive in Yosemite Valley, +1 209 372-4637 Emergency care: 24 hours daily; Drop-in and urgent care: 8:00 a.m. to 7:00 p.m.; Appointments 8:00 a.m. to 5:00 p.m. Monday - Friday. Routine and emergency medical care, 24-hour paramedic/ambulance services, limited pharmacy, lab, x-ray, physical therapy, and Mountain Crisis Services for victims of domestic violence.

Wildlife
Over the years the park's bears have become accustomed to scavenging trash and food left out by humans, and will even break into cars and tents to get it. While not the larger grizzly bears that once roamed California, black bears are strong enough to tear a door off of a car with ease. Luckily they usually prefer to avoid humans, so they'll most likely do their work on vehicles left at trailheads or in parking lots. Prevention is remarkably simple: never leave food or scented items (deodorant, air fresheners) in your car or bring it into your tent. Bears have incredibly keen senses of smell and will detect anything left behind, so heed this warning. Bear-proof storage units are provided at park campgrounds and overnight parking areas: use them.

To avoid bear encounters while hiking, make noise so that the animal knows you are coming. This approach will also help to avoid encounters with mountain lions, which also inhabit the park. Other animals, such as the herds of deer which can be found in the park's meadows, can be equally dangerous; a young boy was killed by a deer in Yosemite Valley several years ago. Give all animals their space, and never feed any park wildlife.

Weather
Other natural dangers in the park come from the weather. Hypothermia can be a concern at higher elevations where temperatures can drop below freezing throughout the year. Dress in layers, and be prepared for storms and rapid changes in temperature. When storms are approaching avoid open areas such as the summits of the park's many granite domes; lightning strikes these areas regularly. If a storm does approach, get off of high, open ground. When hiking wear sturdy footwear and drink plenty of water - if you are thirsty that is an early sign of dehydration.

Waterfalls
Do not attempt to get close to the waterfalls, especially in the spring. The force of the water will easily sweep a person off their feet and over the falls. Being swept over any of Yosemite's waterfalls is invariably fatal. Several people a year are swept away and sometimes the bodies are never found.

Theft
Currently, the greatest danger in the park comes from the thousands of park visitors. Petty thieves and traffic accidents are two issues to be aware of. Follow park speed limits, lock your vehicle, and be aware of your belongings, especially in Yosemite Valley. Violent crime is extremely rare in Yosemite, although in 1999 a woman and two teenage girls were murdered in the backcountry.