The
closest shuttle stop is No. 17. In the winter months, the shuttles
do not make it up that far. There is a paved road up to the start
of the lake/meadow and then becomes hard packed dirt. Vehicles with
handicapped placards can drive up the steep hill to within a few
hundred feet of the coordinates.
Mirror Lake formed after a rockfall from Washington Column (the
north side of the creek behind the restrooms) blocked the flow of
Tenaya Creek. Tree size, lichen growth, and evidence of Native
American occupation of caves that were formed in the rockfall
suggest that the evant occurred about 300 to 500 years ago.
Initially the lake extended about 1.2 miles (2 km) upstream but
from the moment the lake formed, it began filling in. Sediment that
is eroded from the fast flowing water of Tenaya creek up stream are
deposited in the lake as the flow of water slows decreasing the
capacity of the water to move large particles.
The upstream end of the lake filled was the first area to fill
in as a delta extended into the lake from where Tenaya Creek
entered Mirror Lake. This process of lake infilling is the natural
evolution of every lake, natural or man-made.
The lake would likely have already filled in if the National
Park Service had not attempted to maintain the lake. Small dams
were constructed upstream to catch the sediment before it reached
the lake. They also dredged the lake using the sand on the roads
during the winter. However, since about 1970, these practices were
abandoned allowing natural processes to begin filling the lake
again.
Now Mirror Lake forms only during high water and is mostly a
meadow at other times of the year.
On March 28, 2009 another rock fall occured on the Half Dome
side of the canyon. This rockfall is the largest event in Yosemite
National Park since the 1987 . Even larger than the rockfall near
Happy Isles. Take note of that rockfall as some of the logging
questions are about it.
Logging requirements (note that the answers to these questions
are not on a sign. They are your own observations):
Send me a note with :
- The text "GC1QN2X Mirror Lake, Mirror Meadow - Which one is
it?" on the first line
- The number of people in your group.
- What does the size of the particles that are now filling lake
bottom say about the speed of the water that deposited them?
- How does the shape of the rocks that make up the dam show that
they came from a rockfall and not a glacier?
- Since the upstream end of the lake filled in first, the trees
at that end should be older. Can you see a difference in the age of
the trees between the area near the rockfall, the most recent
rockfall and further updtream?
- Did the recent rock fall from Ahwiyah Point form another dam in
the river creating a new lake?
The above information was compiled from the
following sources:
- Wieczorek , Gerald F. 2002, Catastrophic
rockfalls and rockslides in the Sierra Nevada, USA Geological
Society of America, Reviews in Engineering Geology, Volume XV,
2002
- http://virtual.yosemite.cc.ca.us/ghayes/roadside.htm
http://www.yosemite.ca.us/faq/4.html
- http://www.nps.gov/yose/parknews/ahwiyahrockfall.htm
Trial listing approved by
Yosemite National Park