Montecito, California (CNN) Tens of thousands of Californians have evacuated their homes as a storm approaches and could bring "dangerous flash flooding, mud and debris flow" Friday.

Less than two months ago, they saw their houses buried in mud or surrounded by scorched hillsides.

On Thursday, more than 20,000 people in Goleta, Santa Barbara, Summerland and Carpinteria were ordered to evacuate their homes "out of an abundance of caution," Santa Barbara County Sheriff Bill Brown said.

Mark Olson was outside his home Thursday filling up bags with dirt from January's mudflows. He and some friends were putting the bags around the garage and setting other sacks to funnel water away from his property.

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