The blaze was first reported just before 5 p.m.
Saturday in the area of Clayton Creek Road and Highway 29, according to the Associated Press.
The flames jumped a road Sunday and moved into the town of 1,200, where a post office, a winery, a Habitat for Humanity office and several other businesses were destroyed.
The high school is still unharmed, according to SFGate.com, but the sports fields were burned, and classes have been canceled indefinitely.
Suzie Blankenship, a spokeswoman for the California Department of Forestry and Fire Protection, told the AP the fire was spreading rapidly because of parched conditions brought on by California's historic drought.