Caltrans starting Monday will restrict traffic to one lane in both directions on a stretch of Highway 101 between Ukiah and Willits because of emergency work to repair a slipout.

For now, only southbound traffic is down to one lane on the 2.1-mile stretch of 101, which is on the Willits Grade south of Ridgewood Ranch Road.

Caltrans says construction crews will dig down to stable soil and use expanded polystyrene blocks to serve as fill.

“This type of light fill has proven effective in other repairs along this section of highway where unstable Franciscan soils (bluish clay) tend to move when saturated with winter rains,” Caltrans spokesman Phil Frisbie Jr. said in a statement.

The repair work is expected to take at least six weeks, he said.