Cedar Resources Site
History
Cedar Resources is a small, gold and silver mine located in Platoro, Colorado. Mining and milling operations took place at Mammoth Revenue, also known as Cedar Resources, throughout the 1960s.
In 1979, the mill was sold, dismantled and removed. Later that year, Union Gold, Inc, a subsidiary of Umicore, acquired the Mammoth Revenue property. In 1991 the mine was allowed to flood after operations ceased. In 1992, the site contained mine portal facilities, a small mill, mine dumps, a warehouse, a tailings dump, a maintenance shop, and a water treatment facility. Site reclamation began during the 1993 construction season.
EPA conducted a preliminary assessment and site inspection in 1994 and 1995. At that time, the site did not move forward because the mine was actively conducting reclamation activities under the authority of the Colorado Division of Reclamation, Mining and Safety. Those activities were completed in 2016.
In March of 2026, EPA received a citizen petition requesting additional evaluation of groundwater in the area.
Current Activities
EPA is planning to conduct a Site Reassessment to evaluate the site for metals. EPA's main sampling event is currently planned for September 1 - 4, 2026. EPA is contacting property owners in the area to request consent for access to sample properties. EPA will not sample on a property without a consent for access form. EPA will schedule sampling in advance with interested residents.
EPA plans to sample:
- Soil
- Surface water/Sediment
- Groundwater (from pre-established wells)
If you are interested in sampling, you can sign the consent for access form (pdf). You can return the form via email to EPA’s Madison Semach at (semach.madison@epa.gov) or mail it to:
Maidson Semach, EPA SEM-EMB-ARS
1595 Wynkoop St, Denver, CO 80202
Site Documents & Maps
View all publicly available documents online:
- Sampling Consent For Access Form 2026 (pdf) (818 KB)
- Site Inspection Report 1996 (pdf) (3 MB)
- Preliminary Assessment 1994 (pdf) (1 MB)
What Are the Risks at the Site?
EPA is investigating whether metals concentrations at the site pose an unacceptable risk to humans or wildlife. Prior sampling at the Platoro area showed elevated levels of metals compared to background. These metals included: manganese, cadmium, arsenic, lead, zinc, and iron.