As a kid, Dry Creek Valley native Paul LeBrett would collect distinctive, olive-sized, pitted gray rocks, not knowing what they were, except they were the perfect size for his slingshot.
"They were just weird rocks," said LeBrett, 58, a Healdsburg resident. LeBrett would look for arrowheads when the ground in his grandfather's vineyards was stirred up, "and these just stood out like sore thumbs."
It turns out those rocks are tektites, part meteor and part earth, and are designated Healdsburgites after where they were first found, said Rolfe Erickson, a Sonoma State University geology professor emeritus who has been studying them for 20 years.
Tektites Found In Healdsburg
Tektites are the result of strikes by meteors that would have been almost a mile across and hit with enough force to melt the Earth's crust, Erickson said.
The strikes created craters that would be miles wide and "strewn fields" that could cover a thousand square miles with tektites, Erickson said.
The strewn field that was discovered in Healdsburg's Dry Creek Valley is one of only five known to exist in the world, and the result of a meteor that struck 2.8 million years ago, Erickson said.
"The asteroid would have been traveling faster than a rifle bullet and generated tremendous kinetic energy," Erickson said.
At impact, billions of the molten droplets, part Earth crust and part meteor, were slung into space, where they froze and then rained back down to Earth. As they fell, the friction from the atmosphere would char their surface, leaving pits and striations.
"You would have a layer of these objects, tektites . . . for a thousand miles," Erickson said.
The identification of the rocks in Dry Creek Valley and documentation of the strewn field has been the work of Erickson and the late Steven Norwick, also an SSU geology professor, for 20 years.