The average price for a gallon of gasoline in Sonoma County hit the $4 mark on Saturday, largely because of the Monday night fire at the Chevron Corp. refinery in Richmond.
Statewide, the average price for a gallon of regular gas also broke the $4 barrier.
Analysts warned motorists not to expect any relief at the pump until after Labor Day.
The fire did not close the Richmond refinery but hampered production. The refiner is the state's third largest and a major producer for Southern California.
In the Santa Rosa area, the average on Saturday was $4.05, compared to $3.980 on Friday and $3.839 a week ago, according to the American Automobile Association's Northern California office.
A month ago, the Santa Rosa average was $3.701, compared to $3.790 a year earlier.
The average price of gasoline was $4.044 in California on Saturday, compared to $3.986 on Friday and $3.841 a week ago.
Nationwide, the average for a gallon of gas at the pump has climbed to $3.67, a rise of 34 cents since July 1.
Even before the fire, AAA officials said that prices were already being driven slowly up by tensions in the Middle East and by increased summertime travel.
Analysts say that the National Oceanic and Atmospheric Administration has forecast a more active than normal hurricane season, which could affect production in the Gulf of Mexico, which would also drive prices higher.