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?

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]

Historic photograph of hydraulic mining operations
Setting up ISCO autosampler

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?

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.

This article includes a summary of two reports that SYRCL completed 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.


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. Mining operations in the area began in 1850 and have been more or less driven by the price of gold since that time. [5] In 1995, the San Juan Ridge Mine Corporation stopped gold mining operations following the breach of an underground aquifer that caused flooding and the overflow of containment ponds. [6] This breach released millions of gallons of mine waste into Spring and Shady creeks, drained and contaminated 12 local wells through the oxidation of naturally occurring heavy metals- including a well that supplied drinking water to a local K-8 school. [7] The mining company proposed to re-open their mine for gold extraction in 2012, which would require pumping up to 3.5 million gallons of groundwater to operate each day. [8] Pumping groundwater at this scale would likely deplete the underground aquifer that provides water to hundreds of community members. This could potentially cause serious impacts to surface water quality in Spring and Shady creeks due to increased surface flows from mining practices. 

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. 

Figure 1: Mercury and TSS loads for the 2014, 2015, and 2016 water years

The mercury and total suspended solids (TSS) loads calculated for both Spring and Shady creeks demonstrate that there is a continued water quality impact from past mining activities. These results highlight the importance of remediating abandoned mine sites like the San Juan Ridge Mine. This study also provides us with data to support the concept that mines located on smaller tributaries have a cumulative impact on the watershed and places the water quality, habitat quality, and the health of the watershed at risk.

Contamination at this scale is compounded in the downstream direction, resulting in contaminated fish stocks, which impact public health and fisheries; and water quality impacts that reduce reservoir storage capacity and habitat health for aquatic organisms.

To read the whole report, click here.


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.

The Scotchman Creek watershed is a tributary to the South Yuba River. Ongoing erosion and sedimentation throughout the sub-watershed creates turbid surface water that carries particulate-bound mercury. The watershed contains two major hydraulic mine sites, Alpha Diggins and Omega Diggins, in addition to the Scotchman Debris Dam and many smaller mine sites and gravel deposits. The Omega Diggins hydraulic mine site is not remediated and privately owned while the Alpha Diggins hydraulic mine site is in the process of being remediated and is owned by the Tahoe National Forest. In addition to quantifying mercury and sediment levels across the watershed, we compared the contribution of mercury and total suspended solids during storm events directly downstream from Alpha and Omega Diggins, at an upstream control point, and the mouth of the watershed to understand whether mine remediation actions were effective at reducing contaminant sources.

Figure 2: Log transformation between total suspended sediment and particulate-bound mercury

Results indicate that particulate-bound mercury is the primary form of mercury moving through these watersheds. Controlling mercury at its source, before it methylates and incorporates into the food web is a key element to protecting the health of an entire watershed. Mercury bound to clay particles can be managed on site by decreasing erosion potential within the abandoned mine. Settling ponds, check dams, and hotspot removal are current techniques of slowing down runoff, allowing toxic sediments to filter out, or removing material. Revegetation techniques could also aid in the long-term remediation of hydraulic mines and should be considered. From a management perspective, stopping the particulate-bound mercury at the source, rather than letting it move downstream into environments where it can be methylated and become bioavailable is key.

To read the whole report, click here.

Scotchman Falls during a storm event
A day after a storm event

[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. http://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.

[5] Meals, Hank. 2012. History of Mining on Spring Creek and Shady Creek. http://www.sjrtaxpayers.org/wp-content/uploads/2012/09/HistoryOfMiningHankMeals.pdf

[6] Associated Press. 1997. Gold mine taints school’s water. The Register Guard 29 December 1997: 3A. https://news.google.com/newspapers?nid=1310&dat=19971229&id=T01WAAAAIBAJ&sjid=7-sDAAAAIBAJ&pg=6858,7618085&hl=en

[7] Pogash, Carol. “Efforts to Revive Rich California Mine Hit Strong Resistance.” The New York Times, The New York Times, 22 Aug. 2014, www.nytimes.com/2014/08/23/business/energy-environment/a-clash-of-gold-and-water-in-the-california-pines.html

[8] Brenner, Keri. 2014 Locals Rally against Reopening the San Juan Ridge Mine. The Union, 26 Feb. 2014, www.theunion.com/news/local-news/locals-rally-against-reopening-the-san-juan-ridge-mine/