Landslide in San Dimas will keep freeway transition roads closed for at least a week

A hillside near the heavily traveled 10 and 57 freeways in San Dimas collapsed during rush hour Thursday morning, sending tons of dirt and boulders tumbling onto traffic lanes and shutting down two transition roads.

The transition roads will probably remain closed for at least a week while work crews clean up debris, repair the road and shore up the hillside.

There were no reports of injury, but the landslide reduced traffic to a bumper-to-bumper crawl for commuters traveling west on the 10 Freeway and north on the 57, according to the California Highway Patrol.

Highway workers used metal beams to probe the fallen earth to make sure nothing had been buried. CHP officers said it was unlikely that a car had been buried but that they would not know until the debris was removed.

Caltrans workers spent the day trying to stabilize the hillside, which they reported was still moving at midafternoon, spokeswoman Judy Gush said. Crews cannot access the area until it is stable, she said.

The affected transition roads were from the westbound 10 and the northbound 71 to the northbound 57.

Boulders began sliding down the hundred-foot hillside about 8:38 a.m. in a gradual collapse that lasted about 10 minutes, according to CHP reports. The debris eventually covered several lanes, and a light pole was knocked down by a mass of earth, CHP officials said.

CHP Officer Francisco Villalobos suggested commuters avoid the area for the immediate future or take alternative routes. Westbound commuters can take the 15 north to the 210, or the 60 to the northbound 605 to the 210. Commuters can still access the eastbound 10.

Investigators have not determined a cause for the slide, but Jonathan Nourse, a geology professor at Cal Poly Pomona, speculated it was caused by the recent rains that pounded Southern California. Landslides frequently occur weeks or even months after rainfall, he said.

my-thuan.tran@latimes.com