The area of the park was astride a passive continental margin during the Precambrian and early Paleozoic. Sediment was derived from continental sources and was deposited in shallow water. These rocks have since been deformed and metamorphosed.
Heat generated from the Farallon Plate subducting below the North American Plate led to the creation of an island arc of volcanoes on the west coast of proto-North America between the late Devonian and Permian periods. Later volcanism in the Jurassic intruded and covered these rocks in what may have been magmatic activity associated with the early stages of the creation of the Sierra Nevada Batholith. 95% of these rocks were eventually removed by uplifted-accelerated erosion.
The first phase of regional plutonism started 210 million years ago in the late Triassic and continued throughout the Jurassic to about 150 million years before present (BP). Around the same time, the Nevadan orogeny built the Nevadan mountain range (also called the Ancestral Sierra Nevada) to a height of 15,000 feet (4,600 m). This was directly part of the creation of the Sierra Nevada Batholith, and the resulting rocks were mostly granitic in composition and emplaced about 6 miles (9.7 km) below the surface. The second major pluton emplacement phase lasted from about 120 million to 80 million years ago during the Cretaceous. This was part of the Sevier orogeny.
Starting 20 million years ago (in the Cenozoic) and lasting until 5 million years ago, a now-extinct extension of Cascade Range volcanoes erupted, bringing large amounts of igneous material in the area. These igneous deposits blanketed the region north of the Yosemite region. Volcanic activity persisted past 5 million years BP east of the current park borders in the Mono Lake and Long Valley areas.
Starting 10 million years ago, vertical movement along the Sierra fault started to uplift the Sierra Nevada. Subsequent tilting of the Sierra block and the resulting accelerated uplift of the Sierra Nevada increased the gradient of western-flowing streams. The streams consequently ran faster and thus cut their valleys more quickly. Additional uplift occurred when major faults developed to the east, especially the creation of Owens Valley from Basin and Range-associated extensional forces. Uplift of the Sierra accelerated again about two million years ago during the Pleistocene.[citation needed]
The uplifting and increased erosion exposed granitic rocks in the area to surface pressures, resulting in exfoliation (responsible for the rounded shape of the many domes in the park) and mass wasting following the numerous fracture joint planes (cracks; especially vertical ones) in the now solidified plutons. Pleistocene glaciers further accelerated this process and the larger ones transported the resulting talus and till from valley floors.[citation needed]
Numerous vertical joint planes controlled where and how fast erosion took place. Most of these long, linear and very deep cracks trend northeast or northwest and form parallel, often regularly spaced sets. They were created by uplift-associated pressure release and by the unloading of overlying rock via erosion.
A series of glaciations further modified the region starting about 2 to 3 million years ago and ending sometime around 10,000 BP. At least four major glaciations have occurred in the Sierra Nevada, locally called the Sherwin (also called the pre-Tahoe), Tahoe, Tenaya, and Tioga. The Sherwin glaciers were the largest, filling Yosemite and other valleys, while later stages produced much smaller glaciers. A Sherwin-age glacier was almost surely responsible for the major excavation and shaping of Yosemite Valley and other canyons in the area.
Glacial systems reached depths of up to 4,000 feet (1,200 m) and left their marks in the Yosemite area. The longest glacier in the Yosemite area ran down the Grand Canyon of the Tuolumne River for 60 miles (97 km), passing well beyond Hetch Hetchy Valley. Merced Glacier flowed out of Yosemite Valley and into the Merced River Gorge. Lee Vining Glacier carved Lee Vining Canyon and emptied into Lake Russel (the much-enlarged ice age version of Mono Lake). Only the highest peaks, such as Mount Dana and Mount Conness, were not covered by glaciers. Retreating glaciers often left recessional moraines that impounded lakes such as the 5.5 miles (9 km) long Lake Yosemite (a shallow lake that periodically covered much of the floor of Yosemite Valley).
With its scrubby sun-baked chaparral, stately groves of pine, fir, and sequoia, and expanses of alpine woodlands and meadows, Yosemite National Park preserves a Sierra Nevada landscape as it prevailed before Euro-American settlement. In contrast to surrounding lands, which have been significantly altered by logging, the park still contains some 225,510 acres (91,260 ha) of old-growth forest. Taken together, the park's varied habitats support over 250 species of vertebrates, which include fish, amphibians, reptiles, birds, and mammals.
Much of Yosemite's western boundary has habitats dominated by mixed coniferous forests of ponderosa pine, sugar pine, incense cedar, white fir, Douglas fir, and a few stands of giant sequoia, interspersed by areas of black oak and canyon live oak. A relatively high diversity of wildlife species is supported by these habitats, because of relatively mild, lower-elevation climate and the mixture of habitat types and plant species. Wildlife species typically found in these habitats include black bear, coyote, raccoon, mountain kingsnake, Gilbert's skink, white-headed woodpecker, bobcat, river otter, gray fox, red fox, brown creeper, two species of skunk, cougar, spotted owl, and a wide variety of bat species.
Going higher in elevation, the coniferous forests become purer stands of red fir, western white pine, Jeffrey pine, lodgepole pine, and the occasional foxtail pine. Fewer wildlife species tend to be found in these habitats, because of their higher elevation and lower complexity. Species likely to be found include golden-mantled ground squirrel, chickaree, fisher, Steller's jay, hermit thrush, and northern goshawk. Reptiles are not common, but include rubber boa, western fence lizard, and northern alligator lizard.
As the landscape rises, trees become smaller and more sparse, with stands broken by areas of exposed granite. These include lodgepole pine, whitebark pine, and mountain hemlock that, at highest elevations, give way to vast expanses of granite as treeline is reached. The climate in these habitats is harsh and the growing season is short, but species such as pika, yellow-bellied marmot, white-tailed jackrabbit, Clark's nutcracker, and black rosy finch are adapted to these conditions. Also, the treeless alpine habitats are the areas favored by Sierra Nevada bighorn sheep. This species, however, is now found in the Yosemite area only around Tioga Pass, where a small, reintroduced population exists.
At a variety of elevations, meadows provide important, productive habitat for wildlife. Animals come to feed on the green grasses and use the flowing and standing water found in many meadows. Predators, in turn, are attracted to these areas. The interface between meadow and forest is also favored by many animal species because of the proximity of open areas for foraging and cover for protection. Species that are highly dependent upon meadow habitat include great grey owl, willow flycatcher, Yosemite toad, and mountain beaver.
The black bears of Yosemite were once famous for breaking into parked cars to steal food. They were also an encouraged tourist sight for many years at the park's garbage dumps, where bears congregated to eat park visitors' garbage and tourists gathered to photograph the bears. Increasing encounters between bears and humans and increasing damage to property led to an aggressive campaign to discourage bears from relying on human food or interacting with people and their property. The open-air dumps were closed; all trash receptacles were replaced with bear-proof receptacles; all campgrounds were equipped with bear-proof food lockers so that people would not leave food in their vehicles, which were easy targets for the powerful and resourceful bears. Because bears who show aggression towards people usually are eventually destroyed, park personnel have continued to come up with innovative ways to have bears associate humans and their property with unpleasant experiences, such as being hit with rubber bullets. Today, about 30 bears a year are captured and ear-tagged and their DNA is sampled so that, when bear damage occurs, rangers can ascertain which bear is causing the problem.
Despite the richness of high-quality habitats in Yosemite, the brown bear, California condor, and least Bell's vireo have become extinct in the park within historical time, and another 37 species currently have special status under either California or federal endangered species legislation. The most serious current threats to Yosemite's wildlife and the ecosystems they occupy include loss of a natural fire regime, exotic species, air pollution, habitat fragmentation, and climate change. On a more local basis, factors such as road kills and the availability of human food have affected some wildlife species.
Yosemite National Park has documented more than 130 non-native plant species within park boundaries. These non-native plants were introduced into Yosemite following the migration of early Euro-American settlers in the late 1850s. Natural and human-caused disturbances, such as wildland fires and construction activities, have contributed to a rapid increase in the spread of non-native plants. A number of these species aggressively invade and displace the native plant communities, resulting in impacts on the park's resources. Non-native plants can bring about significant changes in park ecosystems by altering the native plant communities and the processes that support them. Some non-native species may cause an increase in the fire frequency of an area or increase the available nitrogen in the soil that may allow more non-native plants to become established. Many non-native species, such as yellow star thistle (Centaurea solstitialis), are able to produce a long tap root that allows them to out-compete the native plants for available water.
Bull thistle (Cirsium vulgare), common mullein (Verbascum thapsus), and Klamath weed (Hypericum perforatum) have been identified as noxious pests in Yosemite since the 1940s. Additional species that have been recognized more recently as aggressive and requiring control are yellow star thistle (Centaurea solstitialis), sweet clover (Melilot spp.), Himalayan blackberry (Rubus armeniacus), cut-leaved blackberry (Rubus laciniatus) and large periwinkle (Vinca major).
Increasing ozone pollution is causing tissue damage to the massive giant sequoia trees in the park, making them more vulnerable to insect infestation and disease. Since the cones of these trees require fire-touched soil to germinate, historic fire suppression has reduced these trees' ability to reproduce. The current policy of setting prescribed fires is expected to help the germination issue.
Forest fires seasonally clear the park of dead vegetation, making way for new growth. These fires damage the income generated by tourism. The Rim Fire in 2013 destroyed nearly $2 billion in assets and revenue, though natural woodland assets are renewable, and closed off much of the park to tourists. This fire was the third largest on record, and burned nearly 500 acres of wild habitat.
During late July and early August, 2018, sections of the park, including the Valley, were temporarily closed due to the Ferguson Fire at its western boundary. The closing was the largest in almost thirty years at the park.
Yosemite Valley is open year-round and numerous activities are available through the National Park Service, Yosemite Conservancy, and Aramark at Yosemite, including nature walks, photography and art classes, stargazing programs, tours, bike rentals, rafting, mule and horseback rides, and rock climbing classes. Many people enjoy short walks and longer hikes to waterfalls in Yosemite Valley, or walks among giant sequoias in the Mariposa, Tuolumne, or Merced Groves. Others like to drive or take a tour bus to Glacier Point (summer–fall) to see views of Yosemite Valley and the high country, or drive along the scenic Tioga Road to Tuolumne Meadows (May–October) and go for a walk or hike.
Most park visitors stay just for the day, and visit only those locations within Yosemite Valley that are easily accessible by automobile. There is a US$25–30 per automobile user fee to enter the park, depending on the season. Traffic congestion in the valley is a serious problem during peak season, in summer. A free shuttle bus system operates year-round in the valley, and park rangers encourage people to use this system since parking within the valley during the summer is often nearly impossible to find. Transit options are available from Fresno and Merced.
In addition to exploring the natural features of the park, visitors can also learn about the natural and cultural history of Yosemite Valley at a number of facilities in the valley: the Yosemite Valley Visitor Center, the adjoining Yosemite Museum, and the Nature Center at Happy Isles. There are also two National Historic Landmarks: the Sierra Club's LeConte Memorial Lodge (Yosemite's first public visitor center), and the Ahwahnee Hotel. Camp 4 was added to the National Register of Historic Places in 2003.
In the winter, it is snowed in, but the area of Tuolumne Meadows has a great deal of hiking, rock climbing, and mountain climbing; see also the highest mountains of Yosemite National Park.
Over 800 miles (1,300 km) of trails are available to hikers—everything from an easy stroll to a challenging mountain hike, or an overnight backpack trip. One of the most popular trails leads to the summit of Half Dome and requires an advance permit from Memorial Day weekend in late May, to Columbus Day in early October. A maximum of 300 hikers, selected by lottery, are permitted to advance beyond the base of the subdome each day, including 225 day hikers and 75 backpackers.
The park can be divided into five sections for the day-user—Yosemite Valley, Wawona/Mariposa Grove/Glacier Point, Tuolumne Meadows, Hetch Hetchy, and Crane Flat/White Wolf. Numerous books describe park trails, and free information is available from the National Park Service in Yosemite. Park rangers encourage visitors to experience portions of the park in addition to Yosemite Valley.
Between late spring and early fall, much of the park can be accessed for multiple-day backpacking trips. All overnight trips into the back country require a wilderness permit and most require approved bear-resistant food storage.
While some locations in Yosemite require hiking, other locations can be reached via automobile transportation. Driving locations also allow guests to observe the night sky in locations other than their campsite or lodge. All of the roads in Yosemite are scenic, but the most famous is the Tioga Road, typically open from late May or early June through November.
As an alternative to driving, bicycles are allowed on the roads. However, bicycles are allowed off-road on only 12 miles (19 km) of paved trails in Yosemite Valley itself; mountain biking is not allowed.
Rock climbing is an important part of Yosemite. In particular Yosemite Valley, which is surrounded by famous summits like Half Dome and El Capitan. Camp 4, a walk-in campground in the Valley, was instrumental in the development of rock climbing as a sport, and is listed on the National Register of Historic Places. Climbers can generally be spotted in the snow-free months on anything from ten-foot-high (3 m) boulders to the 3,300-foot (1.0 km) face of El Capitan. Classes on rock climbing are offered by numerous groups.
Yosemite Valley is open all year, although some roads within the park close in winter. Downhill skiing is available at the Badger Pass Ski Area—the oldest downhill skiing area in California, offering downhill skiing from mid-December through early April. Much of the park is open to cross-country skiing and snowshoeing, with several backcountry ski huts open for use. Wilderness permits are required for backcountry overnight ski trips.
The Bracebridge dinner is an annual holiday event, held since 1927 at the Ahwahnee Hotel, inspired by Washington Irving's descriptions of Squire Bracebridge and English Christmas traditions of the 18th century in his Sketch Book. Between 1929 and 1973, the show was organized by Ansel Adams.
Bicycle rentals are available in Yosemite Valley spring through fall. Over 12 miles (19 km) of paved bike paths are available in Yosemite Valley. In addition, bicyclists can ride on regular roads. Helmets are required by law for children under 18 years of age. Off-trail riding and mountain biking are not permitted in Yosemite National Park.
Water activities are plentiful during warmer months. Rafting can be done through the Yosemite Valley on the Merced River. There are also swimming pools available at Yosemite Lodge and Curry Village.
In 2010, Yosemite National Park was honored with its own quarter under the America the Beautiful Quarters program.
Horsetail Fall flows over the eastern edge of El Capitan in Yosemite Valley. This small waterfall usually flows only during winter and is easy to miss. On rare occasions during mid- to late February, it can glow orange when it's backlit by sunset. This unique lighting effect happens only on evenings with a clear sky when the waterfall is flowing. Even some haze or minor cloudiness can greatly diminish or eliminate the effect. Although entirely natural, the phenomenon is reminiscent of the human-caused Firefall that historically occurred from Glacier Point.
The opening scenes of Star Trek V: The Final Frontier (1989) were filmed in Yosemite National Park. Films such as The Last of the Mohicans (1920) and Maverick (1994) have also been shot here. The 2014 documentary Valley Uprising is centered around Yosemite Valley and its history. The Academy Award-winning 2018 documentary Free Solo was filmed in Yosemite.The Dawn Wall, a 2017 documentary, was also filmed in Yosemite.
