It started with a petrified tree, half-buried in the mud of the Mokelumne River watershed in the Sierra Nevada foothills. The site intrigued Greg Francek, a ranger for East Bay Municipal Utility District, as he was walking the valley last summer. He inspected further, and what he recently discovered led to one of the most significant fossil discoveries in California history. Advertisement "I looked around the area further and I found a second tree," Francek said in an EBMUD statement released this week, documenting the discovery. "And then a third and so on. After finding dozens of trees I realized...