SAN FRANCISCO (CBS SF) — San Francisco’s famous fog may be the culprit behind a power outage that left thousands of people in the dark on Sunday.

The outage was first reported around 9:30 a.m. in the city’s Richmond District and initially affected some 4,600 homes and businesses.

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A power pole at California St. and 16th Avenue had caught fire. A PG&E worker at the scene told KPIX that condensation from fog, possibly mixed with dirt and grime, likely caused an electrical arc.

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More than 600 customers were still without power late Sunday afternoon.