In Los Angeles, city engineers slapped red or yellow tags on more than 100 homes, rendering them temporarily uninhabitable or safe for only limited entry.
In tiny Glassell Park, a section of northern Los Angeles, hillside homes could be heard creaking and cracking, reports CBS News Correspondent Sandra Hughes.
Crews responded to 270 mudslides, some of which forced evacuations after crashing into homes, said Los Angeles Public Works Department Commissioner Janice Wood.
The damage spread south into Orange and San Diego counties — where dozens of homes were slipping or evacuated following landslides — and across the border into Tijuana, Mexico, where the Office of Civil Protection reported at least seven homes had collapsed and more than 150 people were evacuated.
Warnings have been placed on thousands of houses, Tijuana Civil Protection Director Humberto Garcia said, though some families don't want to leave for fear their belongings could be looted.
A house-sized boulder teetered above Pacific Coast Highway in Malibu, forcing the closure of a two-mile stretch of the well-worn road.
"CalTrans is going to put some explosives in the boulder and then try to blow it up in a controlled fashion, so we can get rid of the boulder and the threat to the homes down below," said Los Angeles County Supervisor Zev Yaraslovsky.
The only safe way in or out is by foot. UCLA heart surgeon Dr. Pervaiz Chaudry walked about three miles from Topanga Canyon.
"I haven't gone home for three days, so I don't know if my apartment is there," Chaudry said.
"It goes with the territory. It's not bad. We could go through with this," resident George Dekirmendjian told CBS station KCAL.
The record rains in Southern California have done heavy damage to the dairy industry, killing or sickening cows and leaving herds udder-deep in mud and cold water.
Many farmers are watching their cows die from exhaustion and exposure.
Dairy farmers said the drenching has cost the Southern California industry at least $38 million in lost milk production, dead and sickened animals, and damage to holding ponds and other flood-control features on their farms.
In many cases, the farmers are unable to do much to remove the standing water, because of strict environmental laws regulating dairy-farm runoff, which is usually fouled with manure.
"We have nowhere to go with the water, the ground is soaked. Our dairies aren't designed to deal with this," said Art Marquez, a third-generation dairy farmer in this community about 40 miles east of Los Angeles. Marquez has 2,000 cows at two dairies and said he has lost at least $2,000 a day to the rain over the past few weeks.
Everyone in the Los Angeles Public Works Department licensed to evaluate whether shifting ground had made homes uninhabitable was in the field, according to commissioner Janice Wood.
"If the janitor had a geotech license, he'd be out there today, too," she said.
City fire spokesman Brian Humphrey said some ambulance crews had been diverted to work as reconnaissance teams to spot signs of flooding and mudslides.
At least nine people died throughout the state during the six-day deluge that pushed rain totals to their highest level since Los Angeles was a small outpost in the desert.
In downtown, rainfall has reached 9.14 inches, bringing the total since July 1 to 34.36 inches — the most in Los Angeles since 1889-90. The record for a single year was set in 1883-84 at 38.18 inches. The yearly average is about 15 inches.
The calmer weather that began Wednesday was expected to continue into Thursday with some cloudy conditions, forecasters said.
Officials estimated that damage to roads and facilities in Los Angeles County alone reached $52.5 million since Jan. 1, with up to $10 million in damage caused by the latest storm.
On Monday, the heaviest day of rain, the Los Angeles Fire Department received nearly 2,000 calls — twice the normal amount, said spokesman Brian Humphrey.
In Ventura County, the small Santa Paula airport remained closed after more than 155 feet of runway crumbled into the rushing Santa Clara River. Mudslides forced Amtrak to suspend train service between Los Angeles and Santa Barbara through at least Thursday.
The wet weather has been quite an adjustment in a place known for eternal sunshine. People dodge puddles and scattered palm fronds in the streets, drive more slowly on the freeways, and even talk about the weather in a region that usually doesn't have any worth discussing.
"It's so depressing," said Stephanie Soechtig, 28, who runs a television production company from her Santa Monica home and hasn't able to walk her Chihuahua, Fellini, because of the relentless downpours. "We've been stuck inside all day. I feel like I'm going crazy."
The record rains have brought another concern: fire danger, reports Hughes. While the hills may look lush and beautiful now, fire officials fear what could happen next summer.
"If it does turn hot and dry again June, July, August with the Santa Ana winds that we get towards the fall, then the increased grasses, particularly in the lower elevations, could be real problematic for us," said Angeles National Forest supervisor Judy Noiron.