Two utilities were sued Tuesday for the widespread destruction from last week's deadly mudslides that were caused when hillsides ravaged by California's largest-ever wildfire let loose in heavy rain.

An amended negligence lawsuit filed in Santa Barbara County Superior Court added the Montecito Water District to the suit that originally targeted only Southern California Edison.

The litigation was brought by three people injured or related to someone hurt, plus a business damaged in flash floods that devastated the coastal town of Montecito. At least twenty people were killed by mudslides and more than 350 homes were destroyed or damaged.

Crews continued to search Tuesday for three missing people, including a 2-year-old girl.

Seven people remained hospitalized a week after they were injured in the mudslides. Twenty-eight patients have been treated and released.

Transportation workers were blasting boulders and clearing other debris that littered U.S. Highway 101, the freeway linking Santa Barbara with Ventura. The route is not expected to reopen until Jan. 22, transportation officials said.

The suit claims an explosion or fire in one of SCE's transformers sparked the enormous Thomas Fire on the night of Dec. 4 in neighboring Ventura County, followed by another transformer fire nearly 6 miles (10 kilometers) away that was a second ignition point and that the two blazes merged. It further states that the Jan. 9 mudslides only occurred because vegetation that typically holds soil in place was burned in the blaze.

"Had SCE acted responsibly, the Thomas Fire could have been prevented," attorney Robert Curtis said in court papers. The utility failed to properly maintain power lines and transformers and safely trim tinder-dry vegetation around their equipment, the suit said.

Southern California Edison said it was premature to speculate on litigation related to the mudslides while the California Department of Forestry and Fire Protection continues to investigate the cause of the blaze.

"The devastating impact of the mudslides in Montecito has been tragic," Edison said in a statement, adding it was supporting the recovery effort and would attempt to restore power when it was safe to do so.

The water district is accused of not having an adequate shut-off valve system to stop the flow of water when a major water main burst in hills above Montecito. At least 8 million gallons of water from large storage tanks joined the rainfall that cascaded down the steep slopes toward the town, carrying boulders and trees that crushed cars and flattened homes.

The water district did not immediately respond to phone and email requests for comment.

Among other damages sought, the suit seeks an unspecified amount of money for property ruined, emotional distress and lost wages, as well as punitive damages.

"It's difficult to put a dollar value on property damage alone, much less the loss of life," said attorney Peter Bezek. "But I don't think it's an overestimation that damages could exceed $1 billion."

The number of single-family homes destroyed by the slides nearly doubled from last week to 115, according to a more accurate assessment Tuesday. But the number of damaged houses was lowered to 242.

That's a fraction of the more than 1,000 homes and buildings destroyed by the fire that burned out of control for more than a month, but the mudslide was far deadlier. The fire that scorched 440 square miles (1,140 square kilometers) was responsible for two deaths, officials said.

Several other fire lawsuits have been filed against Southern California Edison and other defendants in Ventura County. Other suits are also expected in the mudslides, with one law firm soliciting clients through a TV commercial airing in the Los Angeles market.

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Associated Press Writers Brian Melley and John Antczak contributed to this story.