Residents of most of the homes evacuated after a landslide were allowed to return home on Thursday, even as dozens of city workers monitored the area for signs of fresh slippage.

Residents of 75 of the 111 homes evacuated after Wednesday's slide, which destroyed at least two homes in the upscale La Jolla neighborhood, were allowed to go home Thursday morning, Mayor Jerry Sanders said.

Nine homes were unsafe and remained off limits and another 27 needed to be evaluated further before occupants can return, he said.

Police had spent the night making sure no one entered evacuated properties.

Sanders, who declared a state of emergency Wednesday, said the White House and the governor's office had called to offer aid.

"Just about everybody who could possibly help has offered to help us," Sanders said at a news conference.

Sanders said the city would hire a forensic geology firm to explore why the land gave way.

Officials said conditions were relatively stable Thursday.

"It's still shifting, but just very slightly," Police Sgt. Jim Schorr said. "Every once in a while there will be a little crumbling, but the majority of the movement has subsided."

The landslide cut a 50-yard-long chasm in a four-lane street and left a 20-foot-deep ravine overlooking Interstate 5 hundreds of feet below.

Just one day earlier, city officials had warned residents of four homes not to sleep in them because the land might give way. It wasn't clear if those residents heeded the warnings.

The neighborhood, which comprises many million-dollar homes, is in an area that has a history of landslides dating back to the 1960s.

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 fancy 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.

The city began noticing cracks on Soledad Mountain Road in July and water and gas main breaks in August. A water line in the neighborhood was replaced with an above-ground pipeline in September to avert damage from the moving earth.

Sanders defended the city against charges by some residents that it didn't do enough after noticing the street cracks in July.

"We have been working with people in the most immediately affected areas since July," Sanders said at a news conference. "We have contacted the most immediately affected people over and over and over again."

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

Rob Hawk, a city engineering geologist, said most movement had already occurred, but extra slippage is possible. "The current slide has basically come to a rest," Hawk said.

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, Hawk said.

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 four homes that now border the collapse, Hawk said.

The landslide sent earth sliding down into backyards of houses in the street below, Hawk said. "It is fairly well-defined and localized," Hawk said.

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