Stone basins may be Miwok salt ‘factory’
by David Perlman, SF Chronicle, December 30, 2009 [here]
Somewhere in the Sierra Nevada, a granite terrace the size of a football field holds hundreds of mysterious stone basins representing what geologists believe is one of the earliest known “factories” created and used by ancient Miwok Indians to make tons of salt to trade with tribes up and down California.
James G. Moore, a geologist with the U.S. Geological Survey in Menlo Park, learned of the strangely pitted terrace from detailed maps made more than a century ago and hiked the region in May to study what he determined were clearly hand-hewn objects.
He examined 369 of the circular artifacts only a few yards from two streams of saltwater fed by a nearby spring and a lake that was equally salty. …
The basins average more than a yard in diameter and are more than 2 feet deep.
To create them, Moor and Diggles said, Miwok tribe members built fires on the granite surface that heated the stone until it fractured. They then crumbled and pounded the fractures with stone tools and removed the debris, inch by inch, until the basins were formed.
Salt springs are extremely rare in the Sierra Nevada, but Moore said the salt in the nearby streams probably comes from a layer of ancient marine sediment formed many millions of years ago when the area was covered by an ocean.
He said he believes the Miwok people carried water from the streams in watertight woven baskets, poured it into the basins and let it evaporate in the summer heat until the dry salt could be scooped out. The salt content of the water and the rate of water flow indicate that the two streams probably yielded about 3 tons of salt each year, Moore said.
The people of the area, he said, “had a large and valuable surplus to trade with other tribes - an early example of commerce by hunter-gatherer people.” … [more]