The CZU Lightning Complex of fires burning in San Mateo and Santa Cruz counties grew to 83,335 acres and was 29 percent contained as of Saturday morning, Cal Fire said.
One person has died and another person has been injured since the fires were sparked by lightning on Aug. 16.
Cal Fire said Saturday morning that the fires have destroyed 620 homes and 57 other structures. Another 10,207 are threatened.
The blazes have forced an estimated 45,000 residents to evacuate.