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Merced River Talus Slope

A cache by TerryDad2 Send Message to Owner Message this owner
Hidden : 01/04/2011
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Geocache Description:

Talus slopes are common throughout the Yosemite National Park. These landforms are found where ever rock falls off of a steep mountain or cliff and pile up at its base.

As you embark or continue your journey to discover and explore beautiful and historic rocks, waterfalls, peaks, creeks and other wonders, please keep in mind that these places need to remain wild and protected so that they may be enjoyed by others for generations to come. Please be diligent in respecting these sites by doing the following:

  1. Please keep trash with you at all times, do not leave it behind in these pristine places.
  2. Bury human waste 6 inches deep, make certain you are at least 50 paces away from any water source and PLEASE bring your toilet paper and sanitary items back out with you.
  3. Keep food and all scented items on your person at all times.
  4. Support wildlife by allowing them to find their own food, do not feed them.
  5. Allow plants to grow and water to stay clean by staying on trails, bike paths and roads.
Thank you, Yosemite Wilderness Management

The trail to the coordinates is paved but relatively steep at times. Cold weather will make the trail slippery. It is a popular trail, so expect company.

Talus slopes form as pieces of rock fall away from the bedrock of the cliff or hillside above. Usually the main mechanism that splits off these pieces of rock is ice or frost heaving. Water gets into small cracks and freezes, expanding and pushing the crack wider. Eventually the rock is wedged off falling down onto the pile of rocks below.

In glacially cut valleys, the sides of the valley are sometimes eroded to a very steep angle. After the glacier retreats, the valley walls are too steep to stand and begin to fall apart creating talus slopes.

These rocks pile up to a maximum angle called the angle of repose, the same term used to describe the maximum angle a sand dune will achieve. This angle is dependant upon the size of the grains. Larger more angular rocks will have a higher angle of repose than smaller grains

The term scree slopes is also used to describe these landforms, but typically scree is used for rocks that are smaller than about 1 foot.

The rocks here along the Merced River are part of the Sierra Nevada Batholith. The batholith solidified deep underground between the Late Jurassic to Early Cretaceous (between 184 to 132 million years ago). Millions of years later, during the Wisonsonian Glaciation that occurred between 70,000 and 10,000 years ago (divided into the Tahoe, Tenaya, and Tioga glaciations in the Sierra Nevada,) glaciers eroded the various features found throughout Yosemite. The Merced Glacier filled Little Yosemite Valley and flowed down into Yosemite Valley along the path of the Merced River you see below you.

With the retreat of the Merced Glacier, ice no longer holds up the sides of the valley and pieces of the granite wall began to fall off the cliffs above. Even now, the valley walls continue to break off building up larger talus slopes at the base of the valley walls (see Rock Fall EarthCache)

Logging questions:

  1. The text "GC2M28R Merced River Talus Slope" on the first line
  2. The number of people in your group.
  3. Looking up the slope, has the all of the wall of the valley eroded down into the talus slope?
  4. Is there a change in size of rocks (boulders) of the talus slope from the top to the bottom of the valley?

The following sources were used to generate this cache:

  • Matthes, Francois. 1930 USGS. Geological Survey Professional Paper 160 Geologic History of the Yosemite Valley. Last Updated: 28-Nov-2006
  • Kiver, Eugene and David Harris. 1999. Geology of U.S. Parklands Fifth Edition, John Wiley & Sons, Inc.

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Coordinates are in the WGS84 datum

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