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
National Parks Escape, This Time Around
January 8, 2009 - 5:17pm
Unlike the last two years, popular recreation areas in Western Washington have escaped serious damage from this week’s heavy rain. Mount Rainier National Park and Gifford Pinchot National Forest were devastated by flooding in 2007. Last year, flooding hit Olympic National Park.
January 8, 2009 - 5:17pm
Unlike the last two years, popular recreation areas in Western Washington have escaped serious damage from this week’s heavy rain. Mount Rainier National Park and Gifford Pinchot National Forest were devastated by flooding in 2007. Last year, flooding hit Olympic National Park.
Dorgan with Game and Fish
January 8, 2009 - 5:06pm
Sen. Byron Dorgan, (D-N.D.) said he agrees with the North Dakota Game and Fish Department on the elk situation at Theodore Roosevelt National Park. Since the unveiling of the National Park Service’s Draft Elk Management Plan and Environmental Impact Statement on Dec. 17, Game and Fish officials have voiced their displeasure that the document did not include their “Alternative G,” as a viable option.
January 8, 2009 - 5:06pm
Sen. Byron Dorgan, (D-N.D.) said he agrees with the North Dakota Game and Fish Department on the elk situation at Theodore Roosevelt National Park. Since the unveiling of the National Park Service’s Draft Elk Management Plan and Environmental Impact Statement on Dec. 17, Game and Fish officials have voiced their displeasure that the document did not include their “Alternative G,” as a viable option.
Coming to the Inauguration? Read This First, Then Think Again
January 8, 2009 - 5:05pm
All roads will lead to Washington on Inauguration Day, but many of them will be closed. With packed trains, buses and planes, how will as many as 2 million people who are hoping to witness history crowd into a city whose subway system usually accommodates 718,000 a day?
January 8, 2009 - 5:05pm
All roads will lead to Washington on Inauguration Day, but many of them will be closed. With packed trains, buses and planes, how will as many as 2 million people who are hoping to witness history crowd into a city whose subway system usually accommodates 718,000 a day?
Scientists Ready to Analyze Yellowstone Park Quake Data
January 8, 2009 - 5:01pm
Between Dec. 27 and Jan. 2, more than 500 small earthquakes shook Yellowstone National Park. The swarm of quakes was centered below Yellowstone Lake, beginning southeast of Stevenson Island and migrating north toward Fishing Bridge before quieting.
January 8, 2009 - 5:01pm
Between Dec. 27 and Jan. 2, more than 500 small earthquakes shook Yellowstone National Park. The swarm of quakes was centered below Yellowstone Lake, beginning southeast of Stevenson Island and migrating north toward Fishing Bridge before quieting.
Haleakala National Park Gets New Superintendent
January 8, 2009 - 5:00pm
Sarah Creachbaum, a 15-year veteran of the National Park Service, has been named superintendent of Haleakala National Park.
January 8, 2009 - 5:00pm
Sarah Creachbaum, a 15-year veteran of the National Park Service, has been named superintendent of Haleakala National Park.
