This is the entrance to the US Gypsum Mine. This mine is
one of the major producers of gypsum in the US. Gypsum is used
a wide variety of building products, including dry wall,
toothpaste, molds (used to make many plates and silverware and
bathroom fixtures), and Portland cement.
The mine extracts gypsum from a geologic unit called the Fish
Creek Gypsum. This unit formed about the time the North American
plate moved over the East Pacific Ridge causing the opening of the
Gulf of California (see Salton Geothermal and Lake Cahuma
Earthcaches). The Imperial Valley fell below sea level and the
area, all the way north to about Palm Springs, was covered in a
shallow sea. It was in this shallow sea that the gypsum was formed
about 6.5 to 6.0 million years ago. (However this age is not
exactly agreed upon, but it’s in the ballpark)
The exact way the Fish Creek Gypsum formed is not completely
agreed upon by geologists, but all of the theories do involve some
form of marine environment described above. There are three main
theories about its formation, a marginal-marine evaporite setting,
a restricted shallow-marine basin, and a marine basin with a
hydrothermal vent. In a marginal-marine evaporite setting, the
gypsum crystallizes along the edges of a shallow sea as the
seawater evaporated. Similarly, in a restricted shallow-marine
basin, gypsum would crystallize from evaporating seawater in an
area where there was little exchange of water with the ocean. In
the theory with the hydrothermal vent, heated water saturated with
the chemicals that form gypsum were vented into the cooler ocean.
The as the saturated hydrothermal water cooled, it could not hold
as much of the chemicals, so they crystallized into gypsum and fell
to the ocean floor.
The Colorado River then filled in the middle of the ancient Gulf
of California and much of the Imperial Valley burying the Fish
Creek Gypsum and returning the area to a non-marine setting.
As you travel through Spilt Mountain (located to the west,
earthcache), part of the Fish Creek Gypsum
is exposed high on the eastern walls of the gorge. You may need
to go through the gorge and then look back. It is the white to
light gray layer. You can also find pieces of gypsum in the mud
hills near Elephant Knees (see Elephant Knees Earthcache)
Logging requirements:
Send me a note with :
- The text "GCZ5X5 Fish Creek Gypsum - US Gypsum Mine" on the
first line
- The number of people in your group.
- The pieces of rock by the road have some discarded gypsum. Find
it and compare what you find to the sheet rock that you find at the
hardware store.
The following sources were used to generate this
cache:
- Paul Remeika and Lowell Linsay, Geology of
Anza-Borrego: Edge of Creation, Kendall/Hunt Publishing Company,
Dubuque, Iowa, 1992
- Rebecca Dorsey, 2005, A Summary of Late
Cenozoic Stratigraphy, Tectonics, and Basin Evolution in the
Anza-Borrego Desert Region, Ver. 14 July 2005
- Rebecca J. Dorsey, undated, Stratigraphy,
Tectonics, and Basin Evolution in the Anza-Borrego Desert State
Park Region, University of Oregon, Eugene, Oregon.
- National Gypsum Company 2006, The Rock That
Nobody Knows,
http://www.nationalgypsum.com/about/therock.html