 It is estimated that by the mid-1880s, 11 million ounces (340 t) of gold (worth approximately US$15 billion at December 2010 prices) had been recovered by "hydraulicking".A byproduct of these extraction methods was that large amounts of gravel, silt, heavy metals, and other pollutants went into streams and rivers., many areas still bear the scars of hydraulic mining, since the resulting exposed earth and downstream gravel deposits do not support plant life.