An apparently dramatic expansion of the Rolling Hills Flying Triangle landslide into a rugged Rancho Palos Verdes canyon has prompted the two cities to join forces to determine the nature of the slide and how to stop further land movement.
"This is a problem that doesn't respect municipal boundaries," said Rolling Hills Mayor Godfrey Pernell after formation last week of a joint slide task force headed by him and Rancho Palos Verdes Mayor Douglas Hinchliffe. Geological experts retained by both cities will work with the group, which also includes Rancho Palos Verdes Councilman Mel Hughes and Tom Heinsheimer, a Rolling Hills councilman.
The move came on the heels of new geological information from Perry Ehlig, Rancho Palos Verdes' city geologist, who said the Flying Triangle slide--previously believed to cover 60 acres in Rolling Hills--actually is 88 acres and has crossed to the eastern side of Klondike Canyon.
He said it is likely that this southward movement of the Flying Triangle slide is the cause of a small local landslide first detected last year on the eastern side of the canyon. It is unrelated to the larger Klondike Canyon slide farther south.
The geologist, in two reports to the city, said the most significant thing about the new discovery is that it is in a location not previously recognized as a slide area and that, in crossing Klondike, it has cut across an area previously believed to be solid bedrock. He said the slick underground slide plane lies beneath the solid bedrock, adding that this deep movement is evidenced by the fact that the slide is not thrusting out of the canyon bottom but is causing it to heave and crack.
Ehlig said in an interview that he does not know if the slide will move farther south. However, he said, continued pressure could cause it to break through. He said this is one of the questions the cities must answer.
He said he is especially concerned that further southward movement could cross part of the property where 47 homes are planned, and that it eventually could affect Seaview, a developed portion of Rancho Palos Verdes east of Klondike Canyon.
"It's hard to imagine its going into Seaview, but the problem is I don't know how big it can get to be," Ehlig said.
Palos Verdes Properties, which is planning to build the 47 homes at an abandoned quarry site at the end of Forrestal Drive, has postponed the development and has started its own geologic investigations as a result of Ehlig's report, according to Rancho Palos Verdes city planner Steve Rubin. "There is concern and the developer (wants to) determine what the situation is,"' Rubin said.
Ehlig and Rancho Palos Verdes officials said the expansion of the Flying Triangle slide does not now endanger any homes other than the six already in trouble in Rolling Hills. The slide, which began in 1980, already has destroyed five homes.
The officials also said the slide will not hamper a three-year, $2-million effort Rancho Palos Verdes plans to start this summer to stabilize the Portuguese Bend landslide. Ehlig said that the two slides, while close together, "are unrelated, no matter how much people attempt to relate them." Ehlig was referring to opinions by some geologists who have studied the slides that they are in some way connected.
Task Force Studies
Work by the two-city task force will include deep borings to analyze the geological structure beneath the slide. They also will determine if the Flying Triangle is, as believed, affecting the localized eastern Klondike slide, and if ground water is contributing to the instability. A new topographical map of the area is being made. Formation of public assessment districts to finance slide work also may be considered.
Ehlig said the cities also should consider wells to remove ground water, a canyon drainage system and installation of an above-ground sewage system in the slide area, which now has cesspools that are believed to contribute to the ground-water problems.
Rolling Hills has shelved a proposal by a resident that Klondike Canyon be filled to buttress and stop the Flying Triangle slide. Officials said that since the slide apparently has moved beneath the canyon, filling it would have no effect.
Change in Attitude
The cooperation between Rolling Hills and Rancho Palos Verdes contrasts with an exchange of letters and words last fall. Rancho Palos Verdes, concerned about the effect of Flying Triangle debris and water runoff on efforts to tame the Portuguese Bend slide, sent letters to Rolling Hills officials and Flying Triangle residents warning of possible legal liability if they did not act to stop the slide. Some in Rolling Hills termed the letters threatening.
Hinchliffe said the extension of the slide into Rancho Palos Verdes has made it a mutual problem that both cities should try to solve together. "It doesn't solve the problem for us to say this is the Flying Triangle slide problem in Rolling Hills and you ought to do something about it," he said.