Marshall Gold Discovery Site.  James W. Marshall discovered gold in 1848 on the South Fork of the American River in the valley the Nisenan Indians knew as Cullumah (beautiful valley). This event led to the greatest mass movement of people in the Western Hemisphere and was the spark that ignited the spectacular growth of the West during the ensuing decades. The gold discovery site, located in the still visible tailrace of Sutter's sawmill in present day Coloma, California, is one of the most significant historic sites in the nation.