Nov 1, 2005
Chuck Mueller, Staff Writer
BARSTOW - In the multicolored hills overlooking the Mojave River Valley, the excavation of stone tools and flakes reveals human activities from the distant past.
A new system of geologic dating has confirmed that an alluvial deposit bearing the stone tools and flakes at the Calico archaeological site is about 135,000 years old.
But the site could even be older.
Calico project director Fred Budinger Jr. said a soil sample, taken at a depth of 17 1/2 feet in one of three master pits at the dig near Yermo, verifies that the deposit dates to the Middle Pleistocene Epoch - the Ice Age.
"This new date confirms earlier estimates that humans were in the Manix Basin, near the base of the Calico Mountains, as early as 125,000 to 200,000 years ago," Budinger said.
The dating system, known as thermo-luminescence, reflects the amount of time that has elapsed since a layer of sediment was exposed to sunlight.
Another system, called uranium-thorium dating, pushed the age of sedimentary layers at the digging site to about 200,000 years ago.
But studies now under way with beryllium 10, an element used in dating exposed surfaces, could open the door into the more distant geological past.
"Beryllium 10 can date rock forms back almost to the formation of Earth itself,' said Budinger, senior archaeologist with Tetra Tech Inc., an environmental engineering and consulting firm with offices in San Bernardino.
Meanwhile, another system of dating known as optically stimulated luminescence also may be used to determine the age of artifact-bearing beds at the Calico site. This system is used to date sand dune layers.
Lewis Owen, a former geology professor at UC Riverside and now with the University of Cincinnati, is in charge of the new research.
"No other archaeological site has made use of these dating methods," Budinger said. "And until we get results (from Owen), expected this winter, we say the Calico site is 100,000 to 200,000 years old."
Humans who inhabited the Manix Basin chipped tools from chalcedony and chert, rocks that break like glass, to serve as scrapers, choppers, gravers, saws and digging tools. The Calico area was a workshop, and no direct evidence of man, such as bones or teeth, have been found at the site.
Manix Lake, a 91-square-mile freshwater lake extending from present-day Yermo to Afton Canyon, drained 18,000 years ago. A unique combination of environmental factors - erosion, faulting, and folding - exposed the alluvial deposits.
Excavations at the Calico Early Man site, often simply called the Calico Digs, began in November 1964.
Heading the project was
Click to learn more...
world-renowned archaeologist Louis Leakey, famed for discoveries with his wife, Mary, at the Olduvai Gorge in Tanzania over three decades.
Among their finds was Zinjanthropus, an early man dating back 1.75 million years. Louis Leakey was project director at Calico from 1965 until his death in 1972.
San Bernardino County archaeologist Ruth DeEtte Simpson, field director under Leakey, then became project director.
Calico's current site manager, retired electronics engineer Chris Christensen, served as Leakey's chauffeur and body guard.
"The archaeological world was concerned with his safety out here," Christensen recalled.
He now oversees digging operations and guides visitors to the site.
"Volunteers from as far away as Berkeley and San Diego take part in digs the first weekend of every month from October through May," he said. "Some are professional geologists and archaeologists."
Since excavations began, more than 64,000 tools, flakes and stone chips have been collected at Calico, said Johanna Lytle, president of the nonprofit Friends of Calico. Most are housed in the San Bernardino County Museum in Redlands.
Extensive improvements have been added to the site, which includes three master digging pits and 22 test pits.
"One of Louis Leakey's favorite tools was 'the Calico Cutter,' as he called it," Christensen said, displaying a replica of the artifact in the small museum on the grounds. "It shows bifacial flaking and use-wear patterns ... evidence of human activity that could not be caused by nature."
The site, two miles off Interstate 15 at Minneola Road, attracts visitors from across the nation and around the world.
Dennis and Patricia Pollet of Redondo Beach stopped by Wednesday.
"While my wife and I are very interested in ancient man, this is our first chance to see a dig of consequence," Dennis said. "People who visit Calico have a rare opportunity to see an actual excavation site."
"You can actually get the feel of an old civilization here," said Patricia. "You get a chance to touch our human past."