Yosemite National Park
Evolution of Yosemite Valley
500—200 million years ago
The Sierra Nevada region was once submerged beneath a sea. Sediments slowly accumulated on the ocean floor, growing thousands of feet thick and compressing the layers into sedimentary rock.
200—80 million years ago
A slab of the Earth's crust, called a plate, began to slide under the North American continent in a process called subduction. Deep within the earth, tremendous heat and pressure caused the downgoing plate to melt into magma. The magma rose toward the surface, where some of it erupted to form a mountain chain of volcanoes. Much of the magma cooled underground to become granite.
60 to 10 million years ago
After subduction ceased, prolonged erosion stripped away the overlying volcanic rocks and exposed the granite. The land destined to become Yosemite National Park was made up of low mountains with shallow river-cut canyons. Hardwood forest flourished.
10 million years ago
Over the next 5 million years, the Sierra Nevada, California's "backbone," rose. The Sierran block uplifted, tilting westward, increasing the Merced River began to carve a narrow canyon. Redwood forests flourished.
3 million years ago
The Merced River carved its canyon deeper, while its tributaries cut the land more slowly. Forests began to thin as the Ice Age approached.
1—2 million years ago
A series of large glaciers flowed from the crest of the mountain range into the river canyons. Glaciers repeatedly filled the "V"-shaped Yosemite Valley, widening, deepening and carving it into a "U" shape, forming hanging valleys from which waterfalls now cascade.
15,000 years ago
Temperatures warmed and the last glacier retreated from Yosemite Valley. Its terminal moraine (rock debris) dammed the Valley 14,000 to 15,000 years ago, creating a shallow lake. Sediment eventually filled the lake, which became the flat valley floor we see today.
Today
The same process of sedimentation continues at Mirror Lake, which is even smaller today than in this photo. Soon, sediment will completely fill in the lake, creating a meadow. Water and gravity continue to shape Yosemite's landscape. Events like the Middle Brother rockfall of 1987 and the flood of January 1997, were the most dramatic in the recorded history of the park. Be aware that rocks can fall at any time.
Yosemite In Depth
News from the Parks
Tauck Hosts its 10,000th Guest-Volunteer in Yellowstone National Park
September 4, 2008 - 4:32pm
Tauck World Discovery celebrated a unique milestone recently when it hosted the 10,000th participant in its award-winning guest-volunteer program in Yellowstone National Park. The 10,000th volunteer was in one of three Tauck tour groups working in the Park over the weekend of July 19 - 20. The volunteers each donated a portion of their vacation time with Tauck, an escorted tour operator, to work on preservation and beautification projects in Yellowstone National Park.
September 4, 2008 - 4:32pm
Tauck World Discovery celebrated a unique milestone recently when it hosted the 10,000th participant in its award-winning guest-volunteer program in Yellowstone National Park. The 10,000th volunteer was in one of three Tauck tour groups working in the Park over the weekend of July 19 - 20. The volunteers each donated a portion of their vacation time with Tauck, an escorted tour operator, to work on preservation and beautification projects in Yellowstone National Park.
Dupuyer Elementary School Offering Students Unique Learning Experiences
September 4, 2008 - 4:24pm
Dupuyer students started class Wednesday, Aug. 27, and though their numbers are way down from last year, teacher Lydia Mild has some special educational treats for her five students. To kick off the year, the Dupuyer students are doing a comparison unit between Yellowstone National Park and Glacier National Park. According to Mild, the unit will cover migratory trails, native tribes and many other aspects of the parks.
September 4, 2008 - 4:24pm
Dupuyer students started class Wednesday, Aug. 27, and though their numbers are way down from last year, teacher Lydia Mild has some special educational treats for her five students. To kick off the year, the Dupuyer students are doing a comparison unit between Yellowstone National Park and Glacier National Park. According to Mild, the unit will cover migratory trails, native tribes and many other aspects of the parks.
Boston Trustees Discuss Township Issues
September 4, 2008 - 3:52pm
Boston Township Trustee Gerald Ritch told board members at the Aug. 27 meeting that it appeared unlikely the township could obtain state Issue I grant money to repair or replace failed septic systems of some township businesses. Ritch said a Summit County official told him Coventry Township was able to obtain money in a similar situation, but septic systems are not considered infrastructure, making it unlikely township businesses would qualify.
September 4, 2008 - 3:52pm
Boston Township Trustee Gerald Ritch told board members at the Aug. 27 meeting that it appeared unlikely the township could obtain state Issue I grant money to repair or replace failed septic systems of some township businesses. Ritch said a Summit County official told him Coventry Township was able to obtain money in a similar situation, but septic systems are not considered infrastructure, making it unlikely township businesses would qualify.
Foreign Tourists Visit Park
September 4, 2008 - 3:44pm
Joy Mehrten's Kaweah Marina had a great spring, hosting droves of European tourists who stopped at the lake on their way to Sequoia National Park. As the weather warmed, Mehrten said, foreign visitation cooled. But business stayed strong.
September 4, 2008 - 3:44pm
Joy Mehrten's Kaweah Marina had a great spring, hosting droves of European tourists who stopped at the lake on their way to Sequoia National Park. As the weather warmed, Mehrten said, foreign visitation cooled. But business stayed strong.
September Featured Species: Zebra Mussels
September 4, 2008 - 11:39am
Mussels are a key part of our aquatic ecosystems. They’re filter feeders, meaning they filter the water as they eat the debris that floats in it. They also serve as a food source for birds, fish, small animals and even humans. Usually there’s not much more to say about these mollusks, but one particular species, the Zebra Mussel, has made a journey that highlights not only its hardiness, but also the vulnerable balance of native ecosystems. Zebra mussels are small, freshwater mollusk species named for the stripes that commonly line the outside of their shells. Their sizes and shapes range can vary – oblong to almost circular, measuring anywhere from the size of a fingernail to two inches long – so it can be tricky to identify at first. The species is native to the lakes of Southern Russia but has been introduced, and has since caused quite a stir, in North America, the British Isles, Spain and Sweden. In these places the species has overgrown, and while it filters the water and provides food for bottom feeders in waterways, it’s more of an unchecked pest than anything. Zebra mussels are prolific. An adult female can produce between 30,000 and a million eggs in a year, which are fertilized during spring spawning sessions. What’s more, there are too few predators to keep the species in check. Having so many mussels around may not seem like a big problem on its face, but it has proven to be quite costly not only to the other members of its ‘host’ ecosystem but to humans as well. Many native lakes in North American have seen their native mussel populations drop due to the invasion of the zebra. It tends to latch onto the hardest substrates in the watery environment. In silty sands, these objects are the native mussels themselves, which are then often killed by the attachment of the zebra. The US coastguard estimates the cost of economic losses and control measures around the zebra to be worth about 5 billion dollars each year! These are hearty creatures that can survive out of water for several days or weeks if the temperature and humidity allow for it. Since 1988 they’ve have reproduced and weathered their way to richly populate all of the great lakes and begin a sprawl into the major rivers in the US. Scientists predict that the zebra mussel will continue to spread its population range by riding along the bottoms of small vessels and tourist ships. Zebra mussels can disrupt the food chain in freshwater ecosystems, ruin facilities like docks and rams, clog pipelines and engines and litter beaches with their smelly shells. But you can help to stop this trend of their growth in the US. Before launching your boat, you can check it thoroughly. Remove all mud, plant and animal debris from the boat, trailer and other equipment to enter the water. When you’re out of the water, drain the boat, motor and live well so that it can dry out – the boat needs to be completely dry for at least five days before entering another body of water. Doing your part will help protect freshwater ecosystems around the US and in our national parks, as well as reduce the dollars spent to reduce the damage caused by this prolific species.
September 4, 2008 - 11:39am
Mussels are a key part of our aquatic ecosystems. They’re filter feeders, meaning they filter the water as they eat the debris that floats in it. They also serve as a food source for birds, fish, small animals and even humans. Usually there’s not much more to say about these mollusks, but one particular species, the Zebra Mussel, has made a journey that highlights not only its hardiness, but also the vulnerable balance of native ecosystems. Zebra mussels are small, freshwater mollusk species named for the stripes that commonly line the outside of their shells. Their sizes and shapes range can vary – oblong to almost circular, measuring anywhere from the size of a fingernail to two inches long – so it can be tricky to identify at first. The species is native to the lakes of Southern Russia but has been introduced, and has since caused quite a stir, in North America, the British Isles, Spain and Sweden. In these places the species has overgrown, and while it filters the water and provides food for bottom feeders in waterways, it’s more of an unchecked pest than anything. Zebra mussels are prolific. An adult female can produce between 30,000 and a million eggs in a year, which are fertilized during spring spawning sessions. What’s more, there are too few predators to keep the species in check. Having so many mussels around may not seem like a big problem on its face, but it has proven to be quite costly not only to the other members of its ‘host’ ecosystem but to humans as well. Many native lakes in North American have seen their native mussel populations drop due to the invasion of the zebra. It tends to latch onto the hardest substrates in the watery environment. In silty sands, these objects are the native mussels themselves, which are then often killed by the attachment of the zebra. The US coastguard estimates the cost of economic losses and control measures around the zebra to be worth about 5 billion dollars each year! These are hearty creatures that can survive out of water for several days or weeks if the temperature and humidity allow for it. Since 1988 they’ve have reproduced and weathered their way to richly populate all of the great lakes and begin a sprawl into the major rivers in the US. Scientists predict that the zebra mussel will continue to spread its population range by riding along the bottoms of small vessels and tourist ships. Zebra mussels can disrupt the food chain in freshwater ecosystems, ruin facilities like docks and rams, clog pipelines and engines and litter beaches with their smelly shells. But you can help to stop this trend of their growth in the US. Before launching your boat, you can check it thoroughly. Remove all mud, plant and animal debris from the boat, trailer and other equipment to enter the water. When you’re out of the water, drain the boat, motor and live well so that it can dry out – the boat needs to be completely dry for at least five days before entering another body of water. Doing your part will help protect freshwater ecosystems around the US and in our national parks, as well as reduce the dollars spent to reduce the damage caused by this prolific species.
