Legacy Mining in the Yuba River Watershed

The Gold Rush in California changed the landscape in California. Miners and settlers displaced native people and denigrated their communities and practices, resulting in clearcutting and the washing away of hillsides by hydraulic mining.

What is Hydraulic Mining?

Historic photograph of hydraulic mining operations

Hydraulic mining redirects and pressurizes surface water through water cannons to break down placer ores and wash away gravel deposits. Once washed off the hillsides, mud slurries abundant with placer gold from weathered gold-quartz veins were directed through sluice boxes to locate gold. To extract the gold from the sluices, liquid elemental mercury was used to make a gold-mercury amalgam. This amalgam was recovered and then heated in order to volatilize the mercury leaving the gold behind. This process released mercury vapor into the air and liquid elemental mercury was lost into the surrounding environment. Loss of mercury during the Gold Rush was estimated to be 10 to 30 percent per season,[1] totaling about 10,000,000 pounds across California.[2]

Why are we worried about Mercury?

For a long time, the mercury found at hydraulic mine sites was ignored, in part because mercury found in soil remained at very low levels. However, new research on the transport of mercury from mine sites into streams and rivers has created a serious public health concern about mercury once they reach aquatic environments. Low levels of mercury can bioaccumulate and biomagnify to dangerously high levels in top predatory fish.[3]

The mercury lost to the environment during the hydraulic mining era still persists in the Sierra Nevada.[4] Today, hundreds of abandoned hydraulic mine sites remain, leaving thousands of acres of largely barren soil contaminated with mercury and exposed during large storms. The South Yuba River is 303(d) listed for mercury contamination. During rain events, these areas are highly susceptible to surface erosion, creating highly turbid run-off that contributes elevated levels of metals and sediments to our headwater tributary streams.

What is SYRCL doing about this?

Setting up ISCO autosampler

To understand the impact of abandoned mines on water quality and the local community in the Yuba, SYRCL conducted outreach with landowners and stakeholders, partnered with The Sierra Fund and The San Juan Ridge Taxpayers Association, identified potential sources of contamination in the watershed, and conducted extensive water quality monitoring to better understand how these mines were contributing to turbidity and mercury contamination.

We identified three watersheds that potentially contained high levels of mercury and sediment loss including Spring Creek, Shady Creek, and the Scotchman Creek watersheds and have spent the last several years (between 2014 and 2017) collecting data to better understand how much mercury and sediment were still moving out of these hydraulic mine sites and into the Yuba River watershed.

SYRCL recently completed two reports as part of work that was funded by the Cosumnes American Bear Yuba (CABY) Integrated Regional Water Management Group in partnership with The Sierra Fund and funded by California Department of Water Resources and The Rose Foundation for Communities and the Environment.

Spring and Shady Creeks: Mercury and Suspended Sediment

The Spring and Shady tributaries of the South Yuba River contain dozens of historic mine locations, the largest of which is the San Juan Ridge Mine. To understand the present-day impacts to Spring and Shady creeks from legacy mining and to look at how increased water flow across a mine site may lead to decreased water quality downstream, SYRCL worked with the San Juan Ridge Taxpayers Association and The Sierra Fund to develop a sampling plan aimed at quantifying the annual sediment and mercury loads (or total annual amounts of mercury) in the system. Read the Full Report  Background information on San Juan Ridge Mine

Scotchman Creek Watershed Assessment: A Focus on Abandoned Mine Impacts

The objective of the Scotchman Creek Watershed Assessment was to understand the potential sources of contamination from past mining activities in the Scotchman Creek watershed through stakeholder outreach and the identification and quantification of mercury and turbidity within the watershed. Read the Full Report


[1] Bowie, A.J. 1905. A practical treatise on hydraulic mining in California: New York, Van Nostrand, 313 p.

[2] Churchhill, R.K.. 2000. Contributions of mercury to California’s environment from mercury and gold mining activities; Insights from the historical record, in Extended abstracts for the U.S. EPA sponsored meeting, Assessing and Managing Mercury from Historic and Current Mining Activities, November 28-30, 2000, San Francisco, Calif., p. 33-36 and S35-S48.

[3] Fleck JA, Alpers CN, Marvin-DiPasquale M, Hothem RL, Wright SA, Ellett K, Beaulieu E, Agee JL, Kakouros E, Kieu LH, Eberl DD, Blum AE, May JT. 2011. The Effects of Sediment and Mercury Mobilization in the South Yuba River and Humbug Creek Confluence Area, Nevada County, California: Concentrations, Speciation, and Environmental Fate—Part 1: Field Characterization: U.S. Geological Survey Open-File Report 2010-1325A, 104 p. https://pubs.usgs.gov/of/2010/1325A/

[4] James, Allan L. 2005. Sediment from Hydraulic Mining Detained by Englebright and Small Dams in the Yuba Basin. Geomorphology 17(1-2):202-226.