The science of tufa What is travertine Travertine Point

A8  Saturday, January 10, 2015  Imperial Valley Press
Land of Extremes
QUESTIONS? Contact Local Content Editor Richard Montenegro Brown at [email protected] or 760-337-3453.
DEPOSITS ARE STILL VISIBLE TODAY
Blake’s Sea or
Lake Cahuilla?
BY NEAL V. HITCH | Special to this Newspaper/Imperial Valley
I
n 1858, Dr. William Blake recoded the shoreline of an ancient lake in the Imperial Valley while completing a railroad survey. He noted a discoloration of the rock along the western shore at around 40 feet above sea level. He
named it Lake Cahuilla, though early writers also called it Blake’s Sea.
According to a 1995 article shells. Calcium carbonate is
written by Pat Laflin, Condifficult to dissolve in water.
gress authorized a series of
In warm water, it reacts with
surveys in 1843 to discover a the environment becoming
practical railroad route to the increasingly insoluble until it
Pacific.
precipitates out of the soluA topographic engineer,
tion.
named Lt. K.S. Williamson,
Under different temperaled the southern expedition, ture conditions, it naturally
and Professor William R.
takes the crystalline form of
Blake of New York served as calcite or aragonite.
geologist.
Basically, tiny solid partiProfessor Blake was the
cles fall out of the water solufirst to explain the origin of
tion and collect on rocks.
the Salton Sink.
Aragonite is precipitated
As the survey party moved when temperatures are hot,
from the San Gorgonio Pass
and calcite precipitates when
to the Coachella Valley, Blake temperatures are cooler.
noticed the mark of the anScientists are studying the
cient sea along the base of
impact of small micro bacthe Santa Rosa Mountains.
teria, like algae, that may
The ancient waterline
activate the precipitation
mark, measured at 42 feet
process.
above sea level, is visible at
This would explain why
many places. He traced the
tufa deposits are found along
ancient history of the freshthe shallow edges of Lake Cawater lake and gave it its
huilla where there is plenty
name.
of access to sunlight.
The deposits are still
The idea of “precipitavisible today as you
tion” seems simple to
drive up Higha chemist, one even
People
way 86 at the
told me a joke: “if
caught fish
north end of
you are not part
and turtles and
the Salton
of the solution,
Sea.
then you are
hunted birds.
They look
part of the preWhen the lake
like a line
cipitate.”
started to dry the
of discolorBut it was
people followed
ation along
difficult
for a
the receding
the rocks,
historian to grasp
shoreline.
and are some... when I think
times compared
of precipitation, I
to a bathtub ring.
think of rain. The Oxford
Up close the discoloration
definition of precipitation is
looks a little like coral or
“to cause (a substance) to be
some kind of marine growth. deposited in solid form from
In actuality, the deposits are a solution.” Rain is the atmotufa-solids, a form of limespheric water vapor that falls
stone left behind on the rocks under gravity: it precipitates
after the water in the lake
— it falls out of the solution.
evaporated.
So in the case of tufa, the calcium carbonate is like a rock
“raining” out of the
water.
All of this
to say, the
Tufa is
lines on
formed by
the rocks
the prethat you
cipitasee along
tion of
Highway
calcium
86 are
carbonlimestone
ate in
deposits
ambient
created
temby the lake.
perature
The most notable dewater bodies. Calcium carposit line is at a place called
bonate is a common chemical Travertine Point.
compound found in rocks
all over the world. It is also
the main component of sea
shells, snails, pearls and eggGeothermally heated hot-
The science
of tufa
calcium carbonate deposits
known as travertine.
This is a sedimentary limestone rock. Travertine exists
in white, tan, cream-colored,
and even rusty varieties.
It is often formed at the
mouth of a hot spring or in
a limestone cave. In caves, it
can form stalactites and stalagmites.
The most well-known
travertine formation in the
United States is Mammoth
Hot Springs in Yellowstone
National Park. For centuries
travertine has been used as a
building material.
From the arches of the Colosseum in Rome to the lobby
walls of the Sears Tower in
Chicago, travertine has been
a sought after decorative
limestone, often confused
springs sometimes produce with marble.
The main source of
travertine has
been Tivoli,
What is travertine
MAP: Map of Ancient
Lake Cahuilla.
ABOVE and LEFT:
Archaeological excavations at Travertine
Point in 1958. IMPERIAL
VALLEY DESERT MUSEUM COLLECTIONS
FAR LEFT: Tufa on a
rock from Travertine
Point. IMPERIAL VALLEY DESERT MUSEUM PHOTO
BOTTOM: Tufa line that
can be seen from Highway 86 at the north end
of the Salton Sea. PHOTO
COURTESY OF MICHAEL FIELD
Italy, where the stone gets its
name.
Here, the deposits are hundreds of feet deep. The stone
is lighter than granite or
marble and is easy to quarry.
County.
This marker is both geological and cultural. It should
remind us that at one time
Imperial County looked very
different and that the lake
provided a resource to early peoples for thousands of
years.
But it should also remind
Native Americans migratus that it is not that differed seasonally between the
ent. The Salton Sea can be
mountains and the lake.
seen as a remnant of the anCampsites and villages were
located along the shore. Peo- cient lake.
Driving along Highway 86
ple caught fish and turtles
and hunted birds. When the offers a view of both, the high
lake started to dry the people water-line formed a thoufollowed the receding shore- sand years ago and the current lake formed 100 years
line.
ago. All a part of a geological
Archaeological sites have
process that we see every day.
been found between 40 feet
Neal V. Hitch is director of
above sea level and 203 feet
the Imperial Valley Desert
below sea level. As the lake
Museum in Ocotillo.
receded it also left its mark
in the tufa clearly seen on
the western side of
Imperial
Travertine Point