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
About 90 million years ago a series of granitic intrusions
created the Tuolumne Intrusive Suite. Through uplift and erosion
they become exposed at the surface. A series of glacial episodes
(including the Tahoe and Tioga glaciations) scoured the valley down
to bedrock. Following the last glacial episode, the Tuolumne River
found its path along the exposed granite. At this bridge, the
flowing water and sediment began forming two geomorphic features of
bedrock river environments, flutes and potholes.
Flutes
Flutes are wavy smooth channels ground into the bedrock by fast
flowing water. These form by the erosion of the bedrock by the
unending grinding of suspended, saltating, and rolling particles
against the bedrock. As the water flows over the same pathway
across the bedrock and forms a smooth channel. Overtime, the
surface of the bedrock becomes polished and smooth.
Potholes
Potholes form where a rock (or many rocks) is spun around in the
same spot by circular eddy of water. The constant abrasion begins
to wear away the bedrock into a hole. Once started, the feature is
self-reinforcing as the hole creates an even stronger eddy. The
rock being spun in the hole is called a grinder and as one grinder
wears away another rolls in to fill its place. In a waterfall, the
rocks at the bottom of the waterfall are swirled around by the
water coming in from above. During high flows, flood events, larger
rocks are even pushed over the edge of the waterfall to fall down
into the pothole at the bottom helping to deepen the pool at the
bottom of the falls.
Logging questions:
- The text "GC2M28Y Tuolumne River Flutes and Potholes" on the
first line.
- The number of people in your group.
- How many potholes are upstream of the bridge and how many are
below?
- What feature is under the bridge?
The above information was compiled from the
following sources:
- Jennifer Mikolajczyk , University of
Wisconsin
at Eau Claire, Interstate Park,
http://www.uwec.edu/jolhm/Interstate2006/potholes.htm
- http://libwiki.mcmaster.ca/clip/index.php/Main/FORMATION
- Thomas Juon and Dak Helentjaris, Last modified
May 17, 1999,
http://gemini.oscs.montana.edu/~geol445/hyperglac/eroproc1/
- 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.