YOSEMITE The Evolution of the Valley

Heather McNennyGeology 103, LTCC

Mark LawlorJune 20, 2013

“It is by far the grandest of all the special temples of Nature I was ever

permitted to enter.” —John Muir

OVERVIEWYosemite has captured the eyes of photographers and travelers since it's increased accessibility by the Yosemite Valley Railroad in 1907.

The scenery of the glaciated landscape marked the necessity of preservation as a national park.

Through this presentation, the evolution of such dramatic polished granite landscape will be discussed.

THE BEGINNING

The origins of the Sierra Nevada began with rock

forming on the sea floor of the western part of North

America. This rock was lifted above sea level and formed into a mountain

range, surrounded by volcanoes. The core of the Sierra Nevada was formed by the granite caused by

molten rock from the volcanoes.

After erosion of sedimentary and volcanic rock over the granite took

place , green scenery covered the land. Streams,

valleys, and hills were prevalent .

The Merced River flowed through the forests and

hills.

50 Million Years Ago

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10 Million Years Ago

Uplifting and westward tilting causing the Merced

River to flow faster and stronger, cutting into the

valley.

During this time, there was an abundance of conifers, beginning the dominance of the Sequoia tree. The

climate was drier, and cool.

3 Million Years Ago

The climate was getting cooler due to the

approaching Ice Age. This affected the forests,

causing them to die off.

There was continual uplift in the land, causing the Merced to cut into it's valley by 3,000 feet.

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Glacier Activity

Glacial events occurred, filling the valley with ice

and snow completely.

Most of the peaks seen today were completely engulfed, though Half

Dome still towered at 900 feet.

The valley was shaped into a "U" form by the

glaciation.

Cascades were formed above the valley caused by the tributaries formed by the run off of the Merced

River.1 Million to 250,000 years ago

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The Yosemite Glacier an event that occurred during the Tioga Glaciation. This ice sheet had little impact

to erosion on the valley because it was very small, and lacked the powerful erosion it needed to cut

into the valley.

30,000 Years Ago

10,000 Years Ago

The last glacier melted, creating Lake Yosemite. This was something that

occurred after each freeze/thaw episode.

Eventually the lake filled with silt, creating the valley floor. What is left behind is now called "Mirror Lake." It

is filled by snowmelt in a similar process.

Mirror Lake

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Yosemite's Waterfalls

Though glaciers are not responsible for the creation

of the waterfalls, they carved the land that they

fall over. Snowmelt determines the force and longevity of the falls each

year.

Yosemite Falls is 2425 feet high, making it the

tallest waterfall in North America. It dries up by the

end of summer.

Ribbon Falls- Typically the first fall to dry up towards

summer

All of Yosemite's streams and waterways end up in

the Tuolumne and Merced Rivers. The Tuolumne feeds Lake Eleanor and the Hetch Hetchy Resevoir, which are

water sources for California. All of the famed waterfalls of Yosemite end

up in the Merced at the valley floor.

National Park Service

TYPES OF ROCK IN YOSEMITE

Plutonic Igneous Rock- GraniteGranodioriteTonaliteQuartz monzoniteQuartz monzodioriteQuartz dioriteDiorite Gabbro

Plutonic rocks formed during Cretaceous Period

Formed by continual intrusions of magma

beneath the Earths surface into older rocks.

El Capitan-Consists of El Cap Granite

National Park Service

Volcanic Igneous Rock

-Basalt Flows-Latite Tuff

-Latite Lava Flows

Though unable to locate any for photos, there are some small amounts of volcanic igneous rock in

Yosemite Valley. The photo to the right is an example of volcanic igneous rock.

Metamorphic Rock can also be found around Yosemite. Caused by two northwest

treding belts of metamorphic rock, on each side of the batholith before it's exposure, and creation.

Cathedral Peak Granodiorite-Photo Credit:

National Park ServicePhoto Credit: Mike Dunn

Dunn, Mike. 2006 Yellowstone Ecology Institute Highlights. National Park Service

References

Yosemite National Park CA. National Park Service. Web. June 15,2013.Yosemite. Yosemite Online.<yosemtie.ca.us> Web. June 15, 2013.Yosemite National Park. National Geographic. Seventh Edition, 2012. Web. June15, 2013.Evolution of Yosemite Valley. OhRanger.Com. Web. June15,2013.*Visited Yosemite for 3 days and took most information from Rangers, as well as information boards on hikes and points of interests. All photos taken by myself unless otherwise credited appropriately

"North America Wall"- El Capitan