Santa Barbara County says it made a clerical error when it released an earlier report that the number missing was 48.
It has previously put the figure at 17, with another 17 confirmed to have been killed and 28 hurt in the disaster which was triggered by heavy rain on Tuesday.
Hundreds of people are searching for survivors of the flash flooding and mudslides in Montecito, near Santa Barbara, which destroyed scores of homes and damaged more than 400.
Cars have been wrecked, there is thick muck and the mud is waist-deep in some areas - in a scene that Sheriff Bill Brown has likened to a First World War battlefield.
Rescue teams, using dogs and scanners, have been working up to 12 hours a day and risked stepping on nails or shattered glass, or being exposed to raw sewage, or dealing with leaking gas.
"A lot of the street signs are gone, the roads are impassable. It all has to be done on foot," said Dan Page who is part of the rescue teams.
Meanwhile, Santa Barbara County officials reportedly chose not to send an emergency alert to people's mobile phones warning of mudslides until the destructive floods had already begun.
For days, the county had issued repeated warnings via social media, news media and emails about the potential for mudslides.
But county emergency manager Jeff Gater said officials decided not to use the mobile push alert system, similar to an amber alert for abducted children, until 3.50am on Tuesday due to concern it might not be taken seriously.
It was unclear how many people actually got the alert.
But by then, tons of mud, trees, rocks and other debris were rolling down hills that had been burned in the largest fire on record in the state.
Montecito has a population of 9,000. Its residents include celebrities such as TV presenters Oprah Winfrey, whose home has suffered some damage, and Ellen DeGeneres.
DeGeneres said on her talk show that the town is a "tight-knit" community.
She said: "It's not just a wealthy community, it's filled with a lot of different types of people from all backgrounds.
"And there are families missing, there are people who are missing family members ... it's catastrophic."
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