ROLLING HILLS ESTATES, Calif. — A landslide is destroying a cluster of hilltop homes in a gated Southern California community and poses a threat to others. Here are some things to know:

What happened

Los Angeles County firefighters responding to a report in the city of Rolling Hills Estates on Saturday discovered cracks in buildings and on the ground. Twelve homes on Peartree Lane were red-tagged as unsafe and residents had just 20 minutes to get out.

Ten of the homes began sliding down into a canyon. Walls and decks ripped apart. Neat tile roofs shattered as they pancaked into a jumble. Although two of the red-tagged homes had not slid down as of Tuesday, county Fire Chief Anthony C. Marrone said they did move.

An additional 16 homes were being monitored but residents were allowed to stay.

How long will the lanslide continue?

Los Angeles County Supervisor Janice Hahn, who represents the area, told reporters this week that it’s only a matter of time until the homes on the Palos Verdes Peninsula fall to the bottom of the canyon.

Authorities can only wait.

“We don’t know how long that’s going to take,” said Marrone. “We don’t know how long that these homes are going to continue to move, but at this time it’s just a holding pattern that we’re in, waiting to see what the final determination is going to be.”

What happened to the residents?

Sixteen residents were displaced. The Red Cross offered hotel vouchers, but they stayed with friends and relatives in the area, according to Mayor Britt Huff.

What caused the landslide?

The cause is not known, but an obvious potential suspect is the exceptionally heavy rain that fell on California this past winter. Water percolating down through soil is known to be able to activate a slide months after the last rainfall.