Fatalities secondary to inhalation of volcanic gases in the United States have rarely been reported. We report the deaths of 3 ski patrol members at a popular California ski resort. After a snowstorm, ski patrol members were fencing off a well-known volcanic fumarole when the snow around the vent collapsed. Two members slid into the deep hole and rapidly lost consciousness. A third member carrying oxygen descended into the hole and also lost consciousness. A fourth member affixed an oxygen mask, but still lost consciousness upon descent. The 3 initial victims expired at the scene, while the fourth victim survived. Autopsy results for all 3 were consistent with a suffocation/asphyxiation death. In the case described, the involved fumarole is a well-known source of toxic gases. Atmospheric sampling data dating back decades demonstrate that carbon dioxide levels typically range from 97% to 99%, nitrogen gas from 1% to 3%, and hydrogen sulfide from .004% to .07%. Other gases in smaller concentrations include oxygen, hydrogen, and carbon monoxide. Given the rapidity with which our victims lost consciousness and the historical data available on the Mammoth Mountain Fumarole (MMF), it is plausible that our patients suffered from acute asphyxiation, although the contribution of the directly toxic effects of the gases involved cannot be ruled out. During winter months, snow can build up and disguise volcanic vents and potentially trap toxic fumes to form dangerous, gas-filled pits. Recognition of such potential hazards is essential when working in or venturing into volcanically active areas during the winter.