Yosemite National Park

Yosemite National Park

Preserve Yosemite

In Yosemite, the natural forces at work such as rockfall, fire and flood are respected. This is a place where wildness prevails. The National Park Service recognizes the importance of Yosemite's natural processes and is mission-bound to protect them for the benefit and enjoyment of future generations.

Seasonal Flooding

In Yosemite, the natural forces at work—such as rockfall, fire and flood—are respected. This is a place where wildness prevails. The National Park Service recognizes the importance of Yosemite's natural processes and is mission-bound to protect them for the benefit and enjoyment of future generations.

Seasonal Flooding

Each spring, the run-off from snowmelt causes flooding. The water level gradually increases, eventually spilling over the riverbanks and into meadows. These floods sustain meadows and other wetland areas that support a rich diversity of plants and animals. In January 1997, a dramatic flood occurred in Yosemite when a warm rain fell on an already deep snowpack in the high country. This resulted in one of the largest floods in Yosemite's recorded history. Damage to human-made structures was extensive, but it underscored the need to remove facilities from the floodplain. A number of restoration projects have been initiated and are still in progress today. Signs posted around Yosemite Valley indicate the water level during this flood's peak.


As long as Yosemite's walls stand, its rocks will continue to fall. Outward pressure from deep within the granite causes rock to peel away at the surface in a process known as exfoliation. Water pressure within cracks or joints, and the freezing and thawing of this water, act like prybars, loosening the rock enough to where a rockfall will occur. Winter and spring are the most active periods for rockfall activity in the park, but large rockfalls have occurred during the summer and fall as well. These events are dynamic—and dramatic—natural processes. It is impossible for the park to monitor every potential rockfall. In Yosemite, and in any natural area, it is up to visitors and employees to be aware of their surroundings.

Rockfalls are dangerous and can cause injury or death. Use caution when entering any area where rockfall activity may occur, such as Valley walls, climbing areas or talus slopes. To learn more about rockfalls and geology in Yosemite National Park, stop by any park visitor center.

Fire at Work

As a natural result of California's climate, Yosemite plant and animal species have adapted to, and in some cases, depend upon fire for survival. Years of fire exclusion, however, has caused dangerous accumulation of material throughout Sierra Nevada forests.

Since 1968, the National Park Service has recognized the essential role fire plays as a natural process in ecosystems and has put management practices into place in an attempt to restore fire to its necessary role.

Fire managers in Yosemite use wildland fire and prescribed fire to restore the benefits of this natural process. Wildland fires caused by lightning may be allowed to burn under strictly monitored conditions. Prescribed fires are ignited under approved conditions by qualified park fire staff to protect developed areas and other areas with unnaturally high amounts of woody debris.

If you notice smoky skies during a summer or fall visit, it may be a lightning fire that is being allowed to burn or it may be fire intentionally ignited by fire crews to eliminate the buildup of forest debris. In any case, know that this is a vital natural process at work restoring the health of Yosemite's forests. (Those with respiratory conditions should use caution when exerting themselves in smoky areas.)

Haze, Air Quality, and Your Health

Even without active fire in Yosemite, there is sometimes a noticeable haze, often caused by urban and agricultural pollutants or large wildfires elsewhere in the region. This haze is not usually unhealthy, and trends show that regulatory efforts to reduce that haze are working.

During the hot, stagnant conditions that can create unhealthy air, Yosemite air quality is nearly always better than the lower elevations to the west. Current air quality and webcam available at http://www2.nature.nps.gov/air/ webcams/parks/yosecam/yosecam.cfm.

Black Oak Woodland Restoration

Years of trampling have compacted soils in sensitive California black oak woodlands within the Valley. As a result, seedlings are unable to take root. Black oaks provide important habitat for bear, deer, squirrels, birds, and other animals, and acorns are a traditional food of the native people.

Around Yosemite Valley, you may see plastic tubes standing within roped-off areas. The tubes protect black oak seedlings. This particular project is restoring black oak woodland that was heavily trampled by people and overrun with conifers, which compete with the oaks for space and sunlight. You can help this effort by staying on designated trails wherever black oak woodland restoration is underway.

The Merced River

Years ago, settlers and park managers placed boulders and barriers in the Merced River, restricting the river and changing its flow. Also, years of trampling destroyed plants and accelerated erosion along the river's banks. Lack of vegetation deprives aquatic life of shelter, food and nutrients. The National Park Service has begun a restoration program to return the Merced River and its ecosystem to a more natural condition. Unnatural barriers have been removed and fallen trees along river banks are left alone. You can help minimize damage to riverbanks by accessing the river at sandbars.

Meadow Restoration

Meadows act like an enormous, wet sponge. When people walk into meadows, soils are compacted, plants are damaged and nests and small creatures can be crushed. Several of Yosemite's meadows have received intensive care in recent years. Restoration projects funded by The Yosemite Fund and the National Park Foundation have been carried out by numerous volunteer groups.

Drainage ditches and old roadbeds have been removed and boardwalks have been installed to protect meadows from trampling. Teams of volunteers, organized through the NPS volunteer office, have planted native vegetation, placed protective fencing around sensitive meadow areas and removed nonnative plants. You can help these meadow restoration efforts—and the meadow's complex networks of life—by staying on maintained trails and boardwalks.

Wildlife Studies

Yosemite is home to over 300 species of wildlife. The National Park Service and teams of scientists are studying mountain lions, goshawks, great gray owls, black bears, bats and amphibians in order to learn more about the animals and help ensure their survival. To learn more, visit online at www.nps.gov/yose/naturescience.

Over 150 years ago, hundreds of Sierra Nevada bighorn sheep once roamed the Yosemite region. After sheepherders and other settlers arrived, the bighorns were eradicated from the park by hunting, disease and competition for food. If you are lucky, you might see a ram in spring or winter on the Highway 120 corridor outside the park. The annual census of Sierra Nevada bighorn sheep counted 35—40 in the Lee Vining/ Bloody Canyon area, with a total of about 300 for the entire Sierra Nevada region.

Mountain yellow-legged frogs were once the most abundant aquatic vertebrate in the Sierra Nevada. They now teeter on the brink of extinction, with 95% of their populations gone. Park and other biologists are actively studying this decline and reintroducing frogs into available habitat. The known causes for this population crash include predation by non-native fish, disease, and possibly pesticides drifting up from the Central Valley. Climate change could also be playing a role.

Trail Maintenance

When a hiking trail fills with water, hikers tend to step to the side, out of the mud, and thus create a new trail. In some meadows, four or more trails may be cut, side by side. The National Park Service, with the support of the California Conservation Corps, The Yosemite Fund, and park volunteer groups, has been filling and replanting these ruts. They also have been constructing raised causeways to keep hikers from creating new trails and protecting the natural integrity of the meadows. You can help by staying on established trails and not cutting corners on switchbacks.

Yosemite Recycling

Yosemite has the most comprehensive recycling program in the national park system. Yosemite's primary concessioner began recycling in 1975 and has since won several national and state awards for its program. Delaware North Companies, the current concessioner, has been recognized for having one of the highest solid-waste diversion rates of any business in California. DNC Parks and Resorts at Yosemite recycles 33 different materials and diverts another 13 from our landfills. Over 40% of Yosemite's waste is being diverted from landfills.

Glass, aluminum, paper, cardboard and plastics #1—#7 are accepted at the DNC recycling centers at the Village Store (year-round), and seasonally at Curry Village Recreation Center. Refunds are given for beverage containers at the centers, park gas stations and park stores where such drinks are sold.

Recycling has been made convenient with green recycling receptacles in campgrounds, in picnic, and residential areas, and at many roadside turnouts.

Commitment to the environment is strong in Yosemite National Park. Hotel restroom paper towels, tissues and most printed materials are made from recycled paper. Park offices separate white paper, computer paper and scrap paper. Freon used in refrigeration systems is recycled, as are alkaline and rechargeable batteries, along with cell phones.

You Can Help, Too

Find out more about the park's ongoing preservation efforts by participating in a park naturalist program or sightseeing tour. The National Park Service conducts regular public open houses in Yosemite Valley where you can learn about the latest park improvement efforts.