Crews Try to Stabilize Sliding Hill : Disasters: Workers dig large trench in effort to save homes in Rowland Heights.

In a round-the-clock effort, workers are digging a 30-foot-deep trench as a short-range solution to keep a sliding hillside from crashing into homes in the San Gabriel Valley community of Rowland Heights.

Crews, which began work Saturday, continued their efforts Monday and planned to work through the night. The trench extends for 350 feet and is 90 feet wide. Geologists say the V-shaped trench cuts into the slide area as a means of relieving its force.

Friday, families in four homes on Morning Sun Avenue voluntarily evacuated after the sliding hillside jacked up adjacent Shepherd Hills Road by 10 feet, crashed into concrete block retaining walls and buried hot tubs. The damage to Shepard Hills Road also left nine other homes reachable only by foot.

Last week, the 100-foot-high hill was sliding up to four feet a day. Monday, a spokeswoman for the Los Angeles County Department of Public Works said the pace was much slower, although she could not give an exact rate.

County officials are taking test borings before they decide on any other action to shore up the sandstone and siltstone hill, said county spokeswoman Donna Guyovich.

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During the weekend, crews used bulldozers to clear debris and remove unstable trees from the back yards of the four homes most threatened last week. The homes’ residents have not yet returned.

County Fire Department and Walnut Valley Unified School District crews also are using bulldozers to remove about 50,000 cubic yards of dirt, about a third of the landslide volume, in an effort to relieve pressure on the hill.

Homeowners blame the school district for the hill’s collapse. In November, contractors for the district began moving 1 million tons of dirt to make room for a new school on the hill. The hill has been sliding since then, the homeowners said.

District officials, citing reports by geologists they have hired, deny that the activity caused the slide.

Geologists believe that the slide is being caused by movement in shallow bedrock under the soil, which had been loosened by spring rains, Guyovich said. They are unsure what is causing the bedrock action or when it will stop moving.

“You just don’t know when it’s going to reach equilibrium,” Guyovich said.