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A8 Saturday, January 10, 2015 Imperial Valley Press QUESTIONS? Contact Local Content Editor Richard Montenegro Brown at [email protected] or 760-337-3453. Land of Extremes I n 1858, Dr. William Blake recoded the shoreline of an ancient lake in the Imperial Valley while completing a rail- road 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 written by Pat Laflin, Con- gress authorized a series of surveys in 1843 to discover a practical railroad route to the Pacific. A topographic engineer, named Lt. K.S. Williamson, led the southern expedition, and Professor William R. Blake of New York served as geologist. Professor Blake was the first to explain the origin of the Salton Sink. As the survey party moved from the San Gorgonio Pass to the Coachella Valley, Blake noticed the mark of the an- cient sea along the base of the Santa Rosa Mountains. The ancient waterline mark, measured at 42 feet above sea level, is visible at many places. He traced the ancient history of the fresh- water lake and gave it its name. The deposits are still visible today as you drive up High- way 86 at the north end of the Salton Sea. They look like a line of discolor- ation along the rocks, and are some- times compared to a bathtub ring. Up close the discoloration looks a little like coral or some kind of marine growth. In actuality, the deposits are tufa-solids, a form of lime- stone left behind on the rocks after the water in the lake evaporated. The science of tufa Tufa is formed by the pre- cipita- tion of calcium carbon- ate in ambient tem- perature water bodies. Calcium car- bonate is a common chemical compound found in rocks all over the world. It is also the main component of sea shells, snails, pearls and egg- shells. Calcium carbonate is difficult to dissolve in water. In warm water, it reacts with the environment becoming increasingly insoluble until it precipitates out of the solu- tion. Under different tempera- ture conditions, it naturally takes the crystalline form of calcite or aragonite. Basically, tiny solid parti- cles fall out of the water solu- tion and collect on rocks. Aragonite is precipitated when temperatures are hot, and calcite precipitates when temperatures are cooler. Scientists are studying the impact of small micro bac- teria, like algae, that may activate the precipitation process. This would explain why tufa deposits are found along the shallow edges of Lake Ca- huilla where there is plenty of access to sunlight. The idea of “precipita- tion” seems simple to a chemist, one even told me a joke: “if you are not part of the solution, then you are part of the pre- cipitate.” But it was difficult for a historian to grasp ... when I think of precipitation, I think of rain. The Oxford definition of precipitation is “to cause (a substance) to be deposited in solid form from a solution.” Rain is the atmo- spheric water vapor that falls under gravity: it precipitates — it falls out of the solution. So in the case of tufa, the cal- cium carbonate is like a rock “raining” out of the water. All of this to say, the lines on the rocks that you see along Highway 86 are limestone deposits created by the lake. The most notable de- posit line is at a place called Travertine Point. What is travertine Geothermally heated hot- springs sometimes produce calcium carbonate deposits known as travertine. This is a sedimentary lime- stone 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 sta- lagmites. 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 Col- osseum in Rome to the lobby walls of the Sears Tower in Chicago, travertine has been a sought after decorative limestone, often confused with marble. The main source of travertine has been Tivoli, Italy, where the stone gets its name. Here, the deposits are hun- dreds of feet deep. The stone is lighter than granite or marble and is easy to quarry. Travertine Point Native Americans migrat- ed seasonally between the mountains and the lake. Campsites and villages were located along the shore. Peo- ple caught fish and turtles and hunted birds. When the lake started to dry the people followed the receding shore- line. Archaeological sites have been found between 40 feet above sea level and 203 feet below sea level. As the lake receded it also left its mark in the tufa clearly seen on the western side of Imperial County. This marker is both geolog- ical and cultural. It should remind us that at one time Imperial County looked very different and that the lake provided a resource to ear- ly peoples for thousands of years. But it should also remind us that it is not that differ- ent. The Salton Sea can be seen as a remnant of the an- cient lake. Driving along Highway 86 offers a view of both, the high water-line formed a thou- sand years ago and the cur- rent lake formed 100 years ago. All a part of a geological process that we see every day. Neal V. Hitch is director of the Imperial Valley Desert Museum in Ocotillo. DEPOSITS ARE STILL VISIBLE TODAY Blake’s Sea or Lake Cahuilla? BY NEAL V. HITCH | Special to this Newspaper/Imperial Valley MAP: Map of Ancient Lake Cahuilla. ABOVE and LEFT: Archaeological exca- vations at Travertine Point in 1958. IMPERIAL VALLEY DESERT MUSEUM COL- LECTIONS FAR LEFT: Tufa on a rock from Travertine Point. IMPERIAL VALLEY DES- ERT MUSEUM PHOTO BOTTOM: Tufa line that can be seen from High- way 86 at the north end of the Salton Sea. PHOTO COURTESY OF MICHAEL FIELD People caught fish and turtles and hunted birds. When the lake started to dry the people followed the receding shoreline.
