A sliding hillside prompted Caltrans today to reduce Highway 101 to one lane in each direction about five miles north of the Sonoma County line in Mendocino County, just north of an area known as Squaw Rock.

The speed limit for the stretch through the slide zone was cut to 25 mph. The lower speed and lane closures are expected to last into summer. Caltrans spokesman Phil Frisbie Jr. said the hillside by then should be dried out and crews can grind down and repave the highway.

He said the slide is a regular headache for Caltrans and typically causes problems that can be fixed with minor roadwork once or twice a week in winter. But this winter, he said, the slide is pushing under the road and lifting up parts of the pavement, creating cracks and bulges. The right lanes in both directions are particularly affected, he said, so traffic is being narrowed to just the north and southbound left lanes.

“We’ve reduced (the highway) down for the safety of the public,” Frisbie said.