Bush ordered federal agencies to assist firefighting efforts in Butte, Mendocino, Monterey, Santa Clara, Santa Cruz, Shasta and Trinity counties. A three-week-old blaze in Los Padres National Forest destroyed 16 buildings. It's 71 percent contained.
More than 150 fires in Butte and Mendocino counties are threatening about 2,000 homes.
The fires have spread a smoky haze over much of the San Francisco Bay area and Central Valley, prompting smog warnings.
Lightning set many of the fires and authorities say more lightning could be in store for the weekend.