The outage began just after 9 a.m., PG&E spokesman Brian Swanson said. Power was restored to those customers shortly after 10 a.m.
Most of the affected customers -- about 29,000 -- were in Walnut Creek. Lafayette, Pleasant Hill and Alamo each had about 2,000 customers affected, Swanson said.
Investigators are examining an East Bay substation in trying to determine the cause of the outage, Swanson said.