Grass Valley was named for its spring-fed meadows, but its history springs from deep below the soil. An immeasurable wealth of gold lay in ancient river courses, embedded in quartz, or scattered capriciously in surface gravel. Vibrantly entrepreneurial since its inception, Grass Valley echoed with the roar of stamp mills crushing gold-bearing quartz 24 hours a day, every day, for decades. Its mines produced $350 million, and millions more are thought...