ROLLING HILLS ESTATES, Calif.—The cause of a landslide responsible for the destruction of several homes in Rolling Hills Estates remained a mystery on July 11, as the city council declared a local emergency due to the devastating slide.

Nearly a dozen upscale homes in the Palos Verdes Peninsula community along Peartree Lane have been crumbling as a result of the massive landslide that began on July 8 and forced the evacuation of the structures.

By July 10 a total of 12 homes had been red-tagged—meaning they cannot be occupied—although only 10 of them appeared to be actually moving.

County fire officials were closely monitoring 16 other homes in the area to ensure they were not shifting. County Fire Department Chief Anthony Marrone said officials were watching two homes in particular—one at the top of the street and the other at the bottom—and were in close contact with those homeowners, who have not been told to evacuate.

The shifting land also caused a sewer line to break, forcing an additional five houses to be evacuated Tuesday, the Southern California News Group reported, citing Assistant City Manager Alexa Davis.

The Rolling Hills Estates City Council unanimously passed a resolution declaring a local emergency in response to the slide on Tuesday night.

“The estimated costs in responding to the Peartree Lane Land Movement Incident are unknown at this time due to the evolving nature of the situation,” according to a staff report prepared for the council.

“Adoption of this resolution will facilitate the ability for the City to request resources including financial support and reimbursement from the State Office of Emergency Services and Federal Emergency Management Agency for costs incurred for the response of this emergency,” the staff report said.

A house in Rolling Hills Estates is severely damaged after a landslide on the Palos Verdes Peninsula in Los Angeles County, Calif., on July 9, 2023. (Michael Hixon/The Orange County Register via AP)

On Monday evening, Los Angeles County Supervisor Janice Hahn and Rolling Hills Estates Mayor Britt Huff held a meeting with affected residents.

Among the other officials attending was county Assessor Jeff Prang, who said earlier his office would work with residents to ensure they would not be forced to pay hefty property tax bills for homes and properties that have been largely destroyed.

Mr. Prang said his office will be expediting the process of re-assessing the affected properties to prevent any of the owners from receiving hefty tax bills for destroyed homes.

“In a tragedy like this, people have experienced all types of hardships that you don’t really think about,” Mr. Prang said. “One of them is paying taxes on houses or a piece of land that no longer exists. We just need to make sure that we do everything we can do to relieve them of any burdens, especially this financial burden, as quickly as possible.”

Mr. Prang said the county would not provide a blanket waiver of property taxes, but he said the re-assessing of the properties would result in them having either no or dramatically reduced tax bills due to the damage.

Ms. Hahn noted Monday after that the “land has moved 20 feet since I was here in Rolling Hills Estates yesterday afternoon.”

“Homes have completely fallen into the canyon now,” she wrote on her Twitter page.

Homeowners have been left to basically stand back and watch their houses collapse on themselves and sink into the turf. Ms. Hahn noted that some rooftops were now at ground level due to the continued collapse.

The homes were largely considered complete losses, Ms. Hahn said.

LA County Supervisor Janice Hahn stands with homeowners watching their houses sink from a landslide in Rolling Hills Estates in Los Angeles County, Calif., on July 9, 2023. (Courtesy of Los Angeles County Supervisor Janice Hahn)

Mr. Marrone said fire crews were basically in a holding pattern, simply waiting for the homes to stop sliding or shifting.

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

Ms. Hahn said that after the homes stop sliding, the homeowners association in the area can bring in geologists and soil experts to examine the area.

“We think after it’s all settled, a good geologist and soil expert maybe will give us a clue about how this happened and if there’s any way of preventing it from happening on some other hillside,” Ms. Hahn said.

Electricity in the area was turned off Saturday and utility crews made sure no gas or power lines were disrupted, authorities said.

The American Red Cross was helping to find shelter for the evacuated families. Ms. Huff said the Red Cross offered hotel vouchers to displaced residents, but most had already made other arrangements.

There have been no reports of any injuries.

Ms. Hahn said she reached out to Gov. Gavin Newsom Monday but had not yet spoken to him about the situation. She said she would like to invite him to tour the neighborhood.