This location is adjacent to the unpaved
road. While easy for all vehicles in dry weather, wet weather
may make the road impassable. No off road vehicle travel is
allowed to reach the site. Collection of plants, rocks, or any
artifacts is prohibited. If turning around, stay within the
road bed and do not go into the field. Practice
Leave No
Trace principles.
The Carrizo Plain is the only closed watershead in the southern
California coastal mountain ranges. (See Soda Lake for how the area
became a closed watershead) All the rain that falls on the plain
ends up in Soda Lake. The high temperatures and low rainfall during
the summer quickly evaporates the water. This means that salts
dissolved from the surrounding hills get transported and
concentrated in the two parts of Soda Lake creating a hypersaline
landscape.
Clay dune formation requires the specific set of environmental
conditions found in this hypersaline environment. The salinity of
the soil inhibits plant growth preventing roots from stabilizing
the soils. Salt crystals promote the formation of pellets (more on
that later). The seasonal flooding concentrates the salts and clay
grains into the temporary lake. Summer heat and lack of rainfall
quickly dries out the lake exposing the clay, keeps the water table
low and facilitates efflorescence (the loss of water from a
hydrated salt to the atmosphere on exposure to air see
wikipedia).
Strong dry season winds are needed to transport the pellets. All of
these characteristics are found at the Soda Lake of the Carrizo
Plain.
The formation of the clay dune begins in the wet season when the
clay particles and salts are transported to Soda Lake. As the lake
dries the dissolved salts crystallize (precipitate) incorporating
the clay particles into their crystals forming pellets. Spring and
summer heat further dries the crystals (efflorescence) making them
lighter. Then strong summer winds transport the pellets downwind to
accumulate on the windward (stoss) side of the dune. (This is
opposite of where sand accumulates on a sand dune). Then the winter
rains dissolve the salt out of the pellet and transport it back
down to the basin leaving the clay on the dune. The clay particles
become compacted by the water and effectively become stable.
A variety of plants have established themselves on the sides of
the dune to the south of the coordinates indicating that dune
formation is not occurring on in those areas and likely hasn’t been
occurring for a few thousand years. Those areas appear to be
adjacent to areas of Soda Lake with a thick salt crust which likely
prevents the summer winds from transporting any particles. However
at the coordinates clay dune formation can continues.
Logging requirements:
Send me a note with :
- The text "GC1VKBD Clay Dunes of the Carrizo Plain " on the
first line
- The number of people in your group.
- An explanation of why this area still has sediment to be
transported by the wind.
- In relation to the coordinates, where is the clay accumulating,
does it continue all the way up the side of the slope to the
south?
- At the coordinates describe the material you are standing on
and relate that to the clay dune formation process.
The following sources were used to generate this
cache:
- David K. Lynch 2006, field guide to the San
Andreas Fault, Thule Scientific, Topanga, CA
- RHODES, Dallas, et.al. (1998?)CLAY DUNES AT
SODA LAKE, CARRIZO PLAIN, CALIFORNIA on the web at
http://personal.georgiasouthern.edu/~drhodes/gsa98/GSA98paper.html
-
http://www.physicalgeography.net/physgeoglos/s.html
Placement approved by the Carrizo Plains National Monument