The California Division of Occupational Safety and Health (Cal-OSHA) has cited Mammoth Mountain Ski Area in connection with the deaths of three ski patrol members in April 2006.

The victims fell into a volcanic gas vent and were overcome by carbon dioxide. A fourth person who tried to rescue them survived. The three patrollers had been trying to uncover a snow-buried fence, which surrounded the vent. At one point, a snow bridge over the vent collapsed, resulting in the workers plunging 20 feet (six meters) into the hole.

Cal-OSHA said the victims lacked both the training and the equipment needed for the task they were performing. They also were unaware of the atmospheric hazard that existed. The citations carry proposed fines of about $50,000.

One of the patrollers fell face down and was immediately immobilized. A second patroller started yelling for help before being overcome by the gas, while a third entered the hole with an oxygen bottle and was overcome.