Case Histories

During the fall of 1993, the Colorado Geological Survey (CGS) inventoried mines in the Cinnamon Gulch area of the Dillon Ranger District, White River National Forest, near the town of Montezuma. This project was part of an eight-year, Statewide inventory of abandoned mines on USFS-administered lands in Colorado. In September 2000, the Forest Service requested a watershed characterization study for Cinnamon Gulch, and more detailed studies on five mines in the area.

Field work for this study included a visit to each site to see if major changes had occurred since the inventory work in 1993. Although water samples were collected at some of the sites in 1993, additional samples and water tests were collected in 2001. In-stream samples were collected from some of the receiving streams in efforts to bracket selected mines or groups of mines and better quantify impacts to the watersheds. In addition, waste-rock piles on some of the mines were sampled on a grid pattern to assess their potential environmental effects. Waste-rock samples were analyzed for gold, silver, mercury, paste pH, acid neutralization potential, and potential acidity. Samples are also analyzed using X-Ray fluorescence to determine a suite of major, minor, and trace elements. A total of 39 water samples were collected from the Cinnamon Gulch watershed over two sampling events in 2001. During the high-flow sampling event in July, 19 water samples were collected, and during the low-flow event in October, 20 water samples were collected.