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Carbon dioxide at Mammoth Mountain

High concentrations of carbon dioxide (CO2) gas in soil are killing trees on the flanks of Mammoth Mountain. First noted in 1990, the areas of tree kill total about 170 acres in six general areas, including the most visually impressive tree-kill area adjacent to Horseshoe Lake on the south side of Mammoth Mountain. The soil gas in the tree-kill areas is composed of 20 to 90 percent CO2; there is less than 1 percent CO2 in soils outside the tree-kill areas.

As snow levels accumulate in the winter, toxic levels of CO2 can develop in tree wells, around buildings, and immediately below the snow surface in areas of high CO2 emissions. Pay serious attention to signs warning of CO2 hazards.