ASPEN, Colo. -- Snowplow crews clearing the highway over Independence Pass between Aspen and Leadville say the snow is the deepest they've seen it in 25 years.

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They've encountered drifts at least 7 feet deep so far and expect to plow through 20 foot-deep snow by the time they reach the summit, nearly 12,100 feet above sea level.

One crew is working from the west and another from the east. They began work a week ago and expect to have the entire route open by Memorial Day.

They get help from helicopter crews that watch for potential avalanches and drop explosives to trigger slides before the heavy equipment operators get into danger areas.