You've just revved your sled to the top of the ridge, all white with heavy snow. On this new snowmobile you rode out further than ever before, and higher up steep terrain that you could never run up before. Now you idle atop a world of white and take in the view.

You've just revved your sled to the top of the ridge, all white with heavy snow. On this new snowmobile you rode out further than ever before, and higher up steep terrain that you could never run up before. Now you idle atop a world of white and take in the view.

The first thing you see is a crack in the snow near your knee. It opens up, and you feel the ground disappearing beneath you. The last thing you see is the terrain around you breaking into chunks that fall with you and on you. Snow and ice rake your body against rocks and strain you through a thin stand of trees.

Everything stops. You are buried in a avalanche.

"You can't move, not even a finger. You can't dig yourself out," avalanche specialist Nick Meyers told his audience Saturday morning during an avalanche awareness course in Mount Shasta. "You can't breathe. It's like you have a plastic bag over your face. You can pass out quickly. You can die quickly."

In a situation like this, Meyers said you would have about 15 minutes for someone to dig you out alive.

About 30 people attended Saturday's free presentation in the Mount Shasta Avalanche Center conference room, across the street from the US Forest Service ranger station on Alma St. Meyers said it was the first time they've tailored the course for snowmobilers.

The message, repeated often during the hour and a half class, stressed the possible dangers for those who shred carelessly in avalanche terrain – and how to avoid getting caught in a snow slide.

After the indoor session, participants rode up Mt. Shasta's snowy slopes to the Old Ski Bowl for instruction on companion rescue techniques.

"Ninety percent of avalanches are triggered by someone in your group," Meyers said in the conference room. He outlined factors that contribute to the likelihood of avalanche.

Recognizing the conditions

Terrain is the major contributor to avalanche conditions. Meyers warned to pay particular attention to slope angles between 30 and 45 degrees. "Thirty-eight is the magic number," he said, referring to the angle for snow to most likely break away and fall hard.

He also cautioned snowmobilers against relying on others' tracks to determine a slope's safety. "A lot of tracks looks good to go," he said. "But avalanche can still happen."

He advised audience members to consider the consequences of taking a given hill. He said to look at the rocks and trees, which can anchor snow, stabilizing an area, or present danger if located downslope in a fall zone.

He cited weather as another key factor. "Watch for wind loading," he said, pointing to a slide showing the leeward roof of a cabin piled high with snow. "Especially if the wind is building up depths of snow faster than it's falling."

He said rapid rises in temperature can create surface instability quickly. "Same with rain," he added.

"You take all these things into account," he said, conceding there is no quick way to learn all the contributing factors for an avalanche. "The rule of thumb is there is no rule of thumb."

He said the main purpose of the course is to raise awareness of conditions.

Meyers said 34 outdoor enthusiasts died in avalanches in the United States during the 2011-12 winter season. "Attitude is the gatekeeper of perceptions," he said. "You want to go out there and do what you want to do. You ignore the signs. You get into trouble."

All those killed were males, ages 13 to 64.

"So you go out there aware. Look around you," he concluded.

Companion rescue training

Up in the Old Ski Bowl, Allison Murphy of Redding knelt and scanned the snow closely with her transceiver. Standing over her with a snow probe, Jeremy Pike of Redding watched to see if she could locate the practice beacon buried beneath them.

The beeps made by her transceiver increased in frequency. "I've got 0.2 meters," said Murphy. Pike stepped in and slipped the probe into the snow. He said he hit something hard.

Meyers said they set up that spot with a strike plate to show a false find while probing for an avalanche victim. "It's hard to tell if its a stump or an ice layer," he said. He pointed to an area bordered by tape. "We buried a backpack there, so they can feel the difference."

Pike said Mt. Shasta is "home territory" for his and Murphy's snowmobiling. He appreciated Saturday's instruction because, "It helps you realize that an area we're in has the potential for danger."

Scott Irvine of Dunsmuir said, "We've had the gear, but we've never really put it to use." He said he tested his transceiver one time in his six years of snowmobiling. "I'm getting better," he said of his rescue skills. He said it's better he learn now. "In crunch time, it would be nerve-wracking."

Irisa Lingemann of Weaverville said she also appreciated the awareness brought by the training. "It's not something you normally think about when you go out," she said.

The Mount Shasta Avalanche Center, which organized the day's instruction, hosts an online advisory, which rates current avalanche danger in the Mt. Shasta, Mt. Eddy, and Castle Lake regions as "low." Visitors can find it and more information on avalanche safety at www.shastaavalanche.org.