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YOSEMITE VALLEY

YOSEMITE VALLEY. GENERAL CHARACTERISTICS. Yosemite means ‘grizzly bear’ 7 miles in length 1-2 miles in width Elevation almost exactly 4,000’. Merced river meanders along. 50-10 million yrs ago - a broad valley. Valley Stage: 50-10 My.

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YOSEMITE VALLEY

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  1. YOSEMITE VALLEY

  2. GENERAL CHARACTERISTICS • Yosemite means ‘grizzly bear’ • 7 miles in length • 1-2 miles in width • Elevation almost exactly 4,000’

  3. Merced river meanders along 50-10 million yrs ago - a broad valley

  4. Valley Stage: 50-10 My • The land destined to become Yosemite National Park was made up of gentle, rolling hills and streams. • The Merced River was a slow-moving, sluggish stream. • Hardwood forests flourish

  5. The land rises- the valley becomes a canyon 10-3 million years ago, tilting of Sierras

  6. 10-3 Ma Canyon Stage • 10-3 million years ago, the Sierra Nevada, California's "backbone", rose. • The Sierran block uplifted, tilting westward, increasing the Merced Rivers flow so it carved the valley into a canyon. • Redwood forests flourished. • 3 Ma ago the Merced River is a steep, V-shaped, riverine canyon.

  7. 40-60 miles in length The Ice Age begins, glaciers carve the valley El Portal/Sherwin glacial stage: 1 My

  8. Major Glaciation • Probably lasted about 300,000 years • Glaciers filled the V-shaped Yosemite Valley, widening, deepening and carving it into a "U" shape, forming hanging valleys from which waterfalls now cascade. • Gouged out basin that lies more than 1,000’ below present valley floor • Half dome a nunatak

  9. The last glacier surge- 30,000 yrs ago

  10. Tioga Glacial Stage • Yosemite Glacier entered the valley but did little to alter the landscape. Older glaciers had already excavated 2,000 feet into the bedrock. • Only advanced as far as Bridalveil Falls. • At this location the forward movement of the glacier was balanced by the melting of ice at its front, producing a large terminal moraine.

  11. The ice age ends: Lake Yosemite

  12. 14,000-10,000 years ago • Temperatures warmed and the last valley glacier melted. Its terminal moraine (rock debris) dammed the valley 14,000 to 15,000 years ago, creating Lake Yosemite. Sediment eventually filled the lake, which became the flat valley floor we see today.

  13. Following pictures from the USGS site at: http://geology.wr.usgs.gov/docs/usgsnps/yos/topobk.html

  14. El Capitan on left

  15. Cathedral Spires

  16. Bridal Veil Falls, Leaning Tower

  17. Sentinel Rock

  18. Yosemite Falls

  19. Royal Arches, Washington’s column

  20. Half Dome

  21. Hetch Hetchy Canyon, next to Yosemite Valley Now Hetch Hetchy Reservoir, San Fran water supply

  22. SUMMARY • Broad-valley stage (50-10 My) • Canyon stage (10-3 My) • Pleistocene glaciation begins (2 My) • Last glacial stage 30,000 years ago (Wisconsin/Tioga) • Lake Yosemite formed by recessional moraine about 10,00 years ago • El Capitan and Half Dome nunataks

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