WILDFIRE RESOURCE GUIDE: Protect your home and family
MOST POPULAR: Video, stories and more
SIGN-UP: Get breaking news sent to you from ABC7 News
Forest Service spokeswoman Vicki Collins says the blaze grew by 500 acres overnight and could become even more active Monday afternoon when highs could reach 98 degrees with 20-mph wind gusts.
The fire is burning in a remote area of the San Rafael Wilderness, about 25 miles east of Santa Maria.
No homes are threatened and no injuries are reported but a dozen campgrounds were evacuated after the fire erupted on Saturday.
Collins says about 600 firefighters aided by water-dropping aircraft are fighting the blaze in steep terrain. The fire is burning through 6-foot-tall chaparral that last burned in 1922.
The cause hasn't been determined.
MORE: ABC7's Bay Area wildfire resource guide and safety tips
FULL COVERAGE: Latest California wildfire headlines
Today's latest headlines | ABC7 News on your phone
Follow us on Twitter | Fan us on Facebook | Get our free widget
