Hundreds of people fled as the nearly 4-square-mile fire continued to grow despite more than 500 firefighters and a swarm of tanker planes and helicopters dousing the area.
Residents of hundreds of homes were asked to leave, but many are unoccupied vacation houses. No injuries had been reported.
The blaze had grown to more than 2,500 acres by early afternoon and was completely uncontained, according to the California Department of Forestry and Fire Protection. The flames produced thick smoke that could be seen miles away.
The mountain range separates Santa Cruz and Santa Clara counties, about 15 miles south of San Jose, and the rural area is dotted with homes.
At least 10 homes were destroyed, and three schools closed their doors Thursday, officials said.
Santa Clara and Santa Cruz county officials said hundreds of people evacuated, including 200 students from a summer camp. Some were being taken to an evacuation center in Watsonville set up by the Red Cross.
Heavy brush and timber and winds gusting up to 50 mph were complicating firefighting efforts. Officials estimated the fire would grow to nearly 16 square miles before being contained.
"The fuels are very heavy and dry from a pretty mild winter. With that wind added in as a factor, it's a pretty good recipe for fire," said Battalion Chief Mike Marcucci.
The blaze also circled Maymens Flat, a community of about seven homes overlooking the Pacific Ocean. Kenneth Kim, 66, stood on a ridge and peered through binoculars to see smoke coming from his home of 20 years.
"Oh, it's gone. It's smoldering," Kim said. "I feel very scared, mad and ... to start all over, I don't know how."
A separate round of evacuations was ordered in Southern California, where downpours Thursday triggered mudslides in three Orange County canyons scarred by last fall's wildfires.
Orange County Fire Authority Battalion Chief Kris Concepcion said some residents in Williams Canyon were unable to leave because of mud and debris flows. Some houses have been damaged.
Orange County Fire Authority Capt. Mike Blawn said evacuations were under way in three canyons; he didn't know how many people were covered by the order.
The area of the mudslides was charred last fall by a wildfire that burned 15 homes and about 44 square miles.
In Florida, a wildfire forced the evacuation of dozens of homes in the Deerhaven area north of Orlando. The blaze started Wednesday and has scorched more than 1,000 acres. It was 20 percent contained Thursday. The cause is not yet known.