SAN DIEGO - Residents of million-dollar homes in a hilltop La Jolla neighborhood scrambled to rescue pets and secure belongings Wednesday after a landslide cut a 50-yard-long chasm in a four-lane street, destroying one home and damaging eight others. View A Slide Show

"The street was sinking before our eyes," said Holli Weld, who was walking one of her sons to preschool when the ground moved.

No injuries were reported but by late afternoon the evacuation had expanded to 111 homes on three streets.

The neighborhood is in an area that has a history of landslides dating to the 1960s.

The earth moved at 9 a.m. the day after city officials warned residents of four homes not to sleep in them because the land might give way. It wasn't clear whether those residents heeded the warnings.

The landslide left a 15-foot-deep ravine overlooking Interstate 5 hundreds of feet below.

Orange traffic cones and sections of big concrete pipes sat in the fissure across the crumpled residential street, which serves as a busy shortcut between the surf neighborhood of Pacific Beach to the south and the tony enclave of restaurants and shops in downtown La Jolla, a major tourist draw.

Authorities said most residents had gone to work and only seven people were inside homes near the collapse when it occurred.

Many homes that weren't in the immediate slide zone were yellow-tagged - meaning that occupants could come and go, but not stay overnight.

Weld packed up her car and took her two children to her parents' house in Pasadena, near Los Angeles, after city officials said her family shouldn't sleep in their house on the opposite side of the street from the collapse.

Weld's husband, Bryan Smith, a researcher at UC San Diego, stayed behind to take care of their dog and cat.

Smith said many of his neighbors were affiliated with the university or retirees who had moved into their split-level homes when the area was first developed in the 1960s.

A firm hired by the city last month was in the area in the hours before the collapse installing measuring devices after a large section of slope on Mount Soledad began to slip, said Robert Hawk, a city engineering geologist. The city began noticing cracks on Soledad Mountain Road in July and water and gas main breaks in August.

Officials first became concerned about a landslide three or four weeks ago. A water line in the neighborhood was replaced with an above-ground pipeline in September to avert damage from moving earth.

After the outside firm advised that some residents should not stay overnight in their homes, the city sent letters to residents on Monday and on Tuesday sent officials to the four homes that now border the collapse, Hawk said.

The letter delivered Tuesday to homeowners stated that they should not stay overnight but said that the city was not making any recommendations about whether the homes should be occupied.

The landslide sent earth sliding into backyards of houses in the street below, Hawk said.

"It is fairly well-defined and localized," Hawk said.

Electricity was initially cut off to 2,400 customers but restored to 2,000 within two hours, according to San Diego Gas & Electric Co. Gas was cut off to about a dozen customers.

At least three significant hill slides have occurred in the area between 1961 and 1994, including a major failure in 1961 that destroyed seven homes under construction.

The slide was not exactly a surprise - landslides are commonplace in San Diego County, certainly in North County.

When landslides destroyed homes and displaced residents in Oceanside and Carlsbad, it was during the rainy winter of 2005. Wednesday's event happened during a drought.

"Sometimes these things are kind of unpredictable," said Rex Baum, a research geologist for the U.S. Geological Survey. "There are cases where there's not an obvious cause."

Landslides happen when the soil that makes up a hillside is too weak to support itself, he said. While not citing a cause for Wednesday's event, the activities of man also can be to blame, Baum said.

Sometimes "cut and fill" excavation can weaken hillsides, he said.

Hawk told reporters Wednesday afternoon they had determined on Tuesday that a landslide was imminent. As a result, they began to knock on doors and deliver notices warning residents of the danger.

Early Wednesday, city geologists and building inspectors were back in the neighborhood when the ground gave way at about 9 a.m.

Ritzy Mt. Soledad, with views that extend across the county in all directions, was developed some 50 years ago on graded land. The area has had "a history of problems since the 1960s with movement," Hawk said. "The geology here seems to be playing a critical role."

He added, "The grading techniques (used at that time) would not be allowed today."

Southern California's fragile geology lends itself to landslides, and the steep slopes and canyons of North County can be just as susceptible to failure as those in La Jolla, officials say.

North County's most recent destructive landslides happened nearly three years ago on Arroyo Avenue and Comanche Drive in Oceanside, and La Costa Avenue and Agua Dulce Court in Carlsbad.

Lawsuits are still pending in the Oceanside slides, which some residents have blamed on leaking city water lines. Attorneys, who recently reached a settlement in the La Costa de Marbella condominium case, attributed the slides to a ruptured water line attached to a fire hydrant.

Previous landslides, an elevated water table and super-saturated soil also have also been cited by some as causes in North County's cases.

One consultant who evaluated the Oceanside landslides was Avram Ninyo of San Diego-based Ninyo and Moore Geotechnical Consultants, Inc.

"Geologic conditions vary from site to site," Ninyo said Wednesday. "That's why each site needs its own, independent evaluation."

Geologists perform such evaluations by studying aerial maps and photographs and by boring deep holes into which a geologist is lowered, Ninyo said.

"There's a lot of interpretation, evaluation and determination that takes place," he said.

On Wednesday, officials ordered Soledad Mountain Road closed indefinitely. A gaping chasm spanned the entire width of the broad boulevard and utility poles lay toppled or tilting nearby.

While the cause remains under investigation, Hawk noted the slide occurred near an upthrust of the Rose Canyon Fault.

According to the U.S. Geological Survey Web site, Southern California is prone to landslides because it straddles the San Andreas Fault, a major tectonic plate boundary. The region also is crossed with smaller faults. Moving tectonic plates push the landscape upward while gravity pulls it downward, and when gravity prevails, landslides can occur.

- Staff writer Adam Kaye contributed to this report. Contact him at (760) 901-4074 or akaye@nctimes.com.

On the Net:

A 2005 report by the U.S Geological Survey, "Southern California Landslides - An Overview," can be found at http://pubs.usgs.gov/fs/2005/3107

Soledad Mountain Road landslide

8:50 a.m. Wednesday

• 0 -- reported injuries.

• 9 - homes deemed entirely off-limits for entry.

• 52 - homes where residents can gain entry to retrieve essential belongings.

• 52 - residents evacuated.

• 111 - homes effected.

• 2 - Red Cross shelters, at Kate Sessions Park and La Jolla High School.

• 411 - SDG&E customers without power for much of Wednesday.

• 3 - major landslides reported on Mt. Soledad since 1961.

In 2005, landslides hit Oceanside, Carlsbad

January 2005: Arroyo/Comanche landslide in Oceanside - On Jan. 11, 2005, during a season of heavy rains, a neighborhood in eastern Oceanside was stunned when a hillside lined with homes began to slip. Over the next several days, tons of mud crept down the steep slope behind Arroyo Avenue, slowly pushing into the backyards of the homes below on Comanche Drive. On Arroyo, six homes were immediately evacuated as roofs began to slant, slabs began to crack and walls began to crumble.

By the time the slide ended, those homes were ruined and a dozen more on Comanche were damaged.

Homeowners on both streets sued the city and eventually each other, claiming that public infrastructure under Arroyo contributed to the slide. Attorneys for the city of Oceanside and a group of residents whose homes were destroyed or damaged agreed three weeks ago to appoint Mike Roberts as a mediator in the case. If they are unable to reach a settlement, the case will go to trial in April, attorney Patrick Catalano said Wednesday.

March 2005: La Costa de Marbella landslide in Carlsbad

In March 2005, the earth began moving beneath the La Costa de Marbella condominium complex on La Costa Avenue, bending walls, tearing apart a private roadway and buckling a stretch of sidewalk along the busy thoroughfare.

Eight damaged condos were condemned by the city within weeks of the discovery of the landslide, and homeowners sued both the city and their insurance companies.

The city of Carlsbad contended the slide was an act of nature, saying heavy rains during the winter of 2004-05 made the hillside soggy and caused it to start moving. Residents blamed a leaking city fire hydrant and poorly maintained water lines.

In July, city officials announced that they had reached a $12.5 million settlement with homeowners in the complex.

Attorney John Schroeder, who represented six of the people whose condos were condemned, said at that time that he thought the key to obtaining the agreement came when he learned that the city had replaced a leaking o-ring in a fire hydrant near the Marbella complex on March 2, 2005.

Nine days later, Schroeder said, the city returned to find a water pipe hooked to the hydrant had ruptured, leaking water into the hillside.

March 2005: Agua Dulce Court landslide in Carlsbad

Not long after the slide at the La Costa de Marbella complex, the earth began to move on nearby Agua Dulce Court, just east of the major Rancho Santa Fe Road commuter route.

The landslide threatened two homes when it was discovered in March 2005. When crews dug a mud wall away from the homes, the upper edge of the slide started to rapidly collapse, threatening Rancho Santa Fe Road.

The contractors tried several times to install a wall to hold the soil, but the moving mud twisted the metal rods that would have supported the wall. In an effort to reduce the water in the soggy hillside, and thus slow the slide, the city of Carlsbad drilled into the rocky hillside above and pumped water out for weeks.

The hillside eventually dried out and by the end of that year the homeowners had begun moving back into their homes.