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That means recreational skiers assume certain risks, such as potential collisions with rocks or trees and changing snow conditions.

McDevitt and other attorneys in California, Colorado and Utah who handle civil cases resulting from skiing accidents said they had not previously heard of a fatal avalanche during a guided trip that sparked a criminal investigation.

But is drawing a closer look likely because of its scale and the decision to proceed despite forecasts indicating potential avalanches, McDevitt said. The slide was , when 11 climbers were killed on Mount Rainier in Washington state.

Utah ski injury attorney Rob Miner points out that the waivers signed by backcountry tour clients don’t absolve the guide companies of responsibility if they don’t follow appropriate safety protocols or fail to fully inform their clients of the risks they face.

“They’re guides. It is presumed they will not guide you into an experience that may kill you, or that creates an unreasonable risk of death,� Miner said.

The large avalanche hit the group as they skied out of the remote Sierra Nevada wilderness on Tuesday. The victims included three of the four guides from Blackbird Mountain Guides leading the trip. Six people survived.

Pivotal moments for investigators may include the guides’ choice to embark on the three-day backcountry trip with 11 clients at a time of , followed by the decision to ski out Tuesday after avalanche conditions had worsened because of a severe storm.

The Nevada County Sheriff’s Office declined to share more information when it announced the investigation Friday. A state agency that regulates workplace safety also said it opened an investigation into the tragedy.

The guides' decisions — and how they were communicated with their clients — also could shape the outcome of any lawsuits filed over the deaths, attorneys said. It's not yet known what access the guides had to the latest weather reports when the group started to ski out.

“There’s a lot of speculation,� said attorney Ravn Whitington, who specializes in ski injury and wrongful death cases in Truckee, California, near where the avalanche happened. “What investigators know at Nevada County Search and Rescue, the Nevada County Sheriff’s Office and the Nevada County District Attorney’s Office are just not known to the public.�

Blackbird Mountain Guides said in a statement that the four guides were certified in backcountry skiing and were avalanche education instructors. The company said its guides stay in touch with senior employees at Blackbird's base during trips to go over conditions and potential routes.

“There is still a lot that we’re learning about what happened. It’s too soon to draw conclusions, but investigations are underway,� the company said.

The 15 skiers began their trip Sunday, just as were intensifying. By early Tuesday, officials cautioned that avalanches were expected. Safety experts say it is not uncommon for backcountry skiers to go out when there is an avalanche watch or even a more serious avalanche warning.

The families of the six Blackbird clients who were killed said that the trip was well organized in advance and the victims were equipped with avalanche safety equipment. “They were trained and prepared for backcountry travel and trusted their professional guides on this trip,� the families said in a Thursday statement.