 Tunnels were then dug in all directions to reach the richest veins of pay dirt.In the most complex placer mining, groups of prospectors would divert the water from an entire river into a sluice alongside the river, and then dig for gold in the newly exposed river bottom.Modern estimates by the U.S. Geological Survey are that some 12 million ounces (370 t) of gold were removed in the first five years of the Gold Rush (worth over US$16 billion at December 2010 prices).