How many times have you wondered about Lake County’s fascinating geology? With the spate of highway improvement projects going on it has been interesting to note the variety of rocks unearthed throughout the county. For example, the Lake 29 Expressway project has revealed gleaming tracts of black obsidian among other geologic wonders. This igneous rock formed due to the volcanic nature of the region. Our Mount Konocti is only one of many volcanic features in our surroundings. Along with a volcano, we have hot springs at The Geysers Geothermal Field in the Mayacamas Mountains which are bordered by the Collayomi and Mercuryville Faults. Geologists tell us that beneath the surface lies a magma body. We live within an active volcanic field known as the Clear Lake Volcanics, which includes not only The Geysers and Cobb Mountain but extends down into Lake Berryessa.
The formation of Lake County’s obsidian gave the Indigenous people here material for innumerable tools and trade items. Anthropologists called the villages which once lined lakes, streams, and valleys here for thousands of years in what is now Lake County ‘city states’. Then, the Pomo, Wappo, Miwok, Yuki, and Patwin peoples thrived here. Famed anthropologist A. L. Kroeber described this area as one of the most diverse cultural areas in all of the United States, until most were decimated by missionaries, settlers and disease. Then, each village contained a dance house, sweat house and various huts in which to live. Each person in the village had an occupation, be it hunter, fisherman, basket weaver or tool-maker. The tool-maker’s job, that of chipping arrowheads, scrapers, fishing hooks and other tools was vital. Since the volcanic glass within the surroundings of Mount Konocti was abundant and sharp, this was the rock of choice. Along with obsidian from Mount Konocti, other igneous obsidian such as that from nearby Borax Lake was utilized for tools as well. In fact, so valued was the obsidian found here, that archaeological excavations throughout our state have found that it was a valuable trading commodity up and down what is now California. Native American trade routes have been studied in-depth, and it has been determined that Lake County obsidian tools and obsidian cores, the unfinished pieces of obsidian, have been located north and south of here, as well as in the eastern Sierra Nevada and far west, to the coastal regions. Archaeologists are able to learn a great deal from a tiny obsidian flake, through a process known as obsidian hydration and X-ray fluorescence spectrometry. Their studies of the rock’s hydration bands can reveal both the age and type of obsidian, along with its source. In this special region, the Clear Lake Volcanics, an unusual, translucent, gray-black to gray colored glass was prized. Jasper and chert rock was also valued as a tool-making material.
The volcanic rock known as obsidian is created in nature due to the nearly crystal-free magma which has made its way to Earth’s surface and solidifies. Obsidian is not considered a true mineral, but is sometimes called a mineraloid due to its formation as glass and not crystalline. Obsidian in many forms can be found around the world where specific kinds of volcanic eruptions have occurred, such as those in Australia, Canada, Italy, Argentina and more. Usually, black to gray in color, as previously mentioned, sometimes obsidian is found in red to red-brown colors.
Most obsidian quarries were easily accessible to the various groups of Indigenous people, however, there were times when obtaining the glass was denied, as in cases of thievery, but that was rare.
You’ll find more information on Native American tools by visiting one of our local museums, such as Ely Stage Stop in Kelseyville, Gibson Museum in Middletown, Lakeport Historic Courthouse Museum, and Lower Lake’s Historic Schoolhouse Museum, or visit archaeologist, Dr. John Parker’s interesting website.