Part of the road was washed out and slid down the hillside after this week's heavy rain.
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Caltrans says it could be days or even weeks before the roadway is fixed.
For now the agency says people should use other ways to get around.
They urge drivers to avoid travel on mountain roads during the storm.
The agency noted that washouts on mountain roads during storms is common, saying there were similar problems on state routes 243 in Riverside County and 111 heading toward Palm Springs.
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