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
There is a small parking lot close by and a viewing platform
built next to the road out to glacier point. There are no services
here.
Across the valley from this viewing platform are Nevada Fall,
Diamond Cascade, and Vernal Fall. These three sharp descents in the
valley form the Giant’s Staircase. However they are only part
of a series of glacial steps that start at the base of Mount Lyell
and extend 21 miles to Yosemite Valley. In that distance there is a
7,600 foot elevation drop. This geomorphological feature resulted
in the glacial erosion of sparsely fractured granite.
The Sierra Nevada Mountains are composed of the more than 100
individual plutons that are collectively called the Sierra
Batholith. The batholith solidified deep underground
between the Late Jurassic to Early Cretaceous (between 184 to 132
million years ago). As the rock above the pluton was eroded and the
Sierra Nevada were uplifted, the pressure containing the pluton
decreased. This allowed the pluton to expand. To accommodate that
expansion, large cracks formed throughout the cooled granite. These
cracks are called joints and are areas of weakness in the
granite.
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. Before
glaciation, the valley had an initial slope as shown by the dotted
line (AA) in the figure below (USGS). As the glacier flowed over
the joints in the granite, those areas were eroded at a faster rate
than the areas with fewer joints .
(Matthes 1930)
The coordinates provide a good view of three of the steps that
were created by the Merced River. The upper (Nevada Falls) and the
lower (Vernal Falls) steps are the easiest to see. Diamond Cascade
is in between and doesn’t create well defined step probably
because the joints are not limited to a small area and the erosion
was distributed over a wider area.
Above Vernal Falls is Little Yosemite Valley. The granite along
that valley is unjointed and thus creates a long step. The upper
steps (out of view) are much less defined than the three in front
of you.
Logging questions:
- The text "GC2M286 A View of the Giant's Staircase" on the first
line
- The number of people in your group.
- What effect has continued water flow had upon the edges of the
glacial steps?
- Based on the observation above, was the Merced Glacier or River
more effective at eroding the granite? .
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.