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:
- Please keep trash with you at all times, do not leave it behind
in these pristine places.
- 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.
- Keep food and all scented items on your person at all
times.
- Support wildlife by allowing them to find their own food, do
not feed them.
- 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:
- The text "GC2M28R Merced River Talus Slope" on the first
line
- The number of people in your group.
- Looking up the slope, has the all of the wall of the valley
eroded down into the talus slope?
- 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.
http://www.nps.gov/history/history/online_books/geology/publications/pp/160/index.htm
Last Updated: 28-Nov-2006
- Kiver, Eugene and David Harris. 1999. Geology
of U.S. Parklands Fifth Edition, John Wiley & Sons,
Inc.