The Santa Cruz fire flared just two weeks after another blaze two miles away scorched 4,200 acres and destroyed at least three dozen homes. Late Wednesday, mandatory evacuations were ordered for 500 residents in the heavily forested hills. Voluntary evacuations were in place for another 1,000 residents.

The fast-moving fire in the Bonny Doon area grew to more than 300 acres shortly after it broke out about 3 p.m. It could spread to as many as 1,000 acres before firefighters are able to slow down the flames, Battalion Chief Paul Van Gerwen said.

Hot temperatures, steady winds and tinder-dry vegetation created conditions exactly like those that fed the earlier blaze.

Those conditions also prevailed throughout the rest of Northern California, where hundreds of firefighters were deployed on fire lines from the North Coast wine country to the Central Valley.

For a second day, erratic wind gusts surprised firefighters who were overrun by flames.

Three firefighters were burned near Lincoln, about 35 miles northeast of Sacramento, when they were caught in a 65-acre grass fire burning in a dry rice field. Two of them had moderate to severe burns to their faces and arms, while the third was released from a hospital after treatment for minor facial burns.

The fire unexpectedly changed direction, trapping the firefighters and destroying two fire engines, said Bill Mendonca, battalion chief for the California Department of Forestry and Fire Protection.

Two are career firefighters from the state fire agency, while the third is a volunteer with the Placer County Fire Department. All three were taken to the University of California, Davis Medical Center regional burn center in Sacramento.

The burn center also was treating a 21-year veteran of the Sacramento Metro Fire Department who was injured on Tuesday while trying to protect a mobile home near a grass fire southeast of Sacramento.

“He's conscious, he's alert, his spirits are good,” Capt. Jeff Lynch, a spokesman for the department, said after surgery on the firefighter. “It's going to be several months of surgeries, rehabilitation.”

The captain suffered third-degree burns to his hands and second-degree burns to his arms. His two crew members were able to get inside their fire engine and escaped injury.

The injuries to four firefighters in less than 24 hours show just how fast and dangerous wind-whipped grass fires can be, said experts in fire behavior.

Those fires can give firefighters less time to react to sudden changes in wind direction, said Larry Hood, a fire behavior analyst with the U.S. Forest Service. Unlike brush or trees, the dead grass that carpets California's Central Valley after spring also responds to even the slightest drop in humidity.

“With those light, airy fuels, the fire behavior can change in a second,” Hood said.

This week's hot, dry north wind, gusting to 40 mph, turns the grass to tinder and can send embers sailing far ahead of the main fire. Flames, even in grass just a foot tall, can reach 4 to 6 feet high.

The extreme fire danger is expected to last through Thursday, with temperatures hitting 100 degrees throughout the Central Valley. Felix Garcia, a meteorologist with the National Weather Service in Sacramento, said winds are expected to decrease, which would help the firefighting efforts.

“Tomorrow looks like a much better day,” Garcia said.

That would be a relief to families who have been evacuated ahead of a 200-acre fire in Butte County near Chico, about 90 miles north of Sacramento.

Conditions already had improved from Tuesday, when wildfires damaged dozens of homes and thousands of acres across Northern California. Flames destroyed 32 homes in Stockton, 50 miles south of Sacramento, and 21 homes in Palermo, about 60 miles north of the state capital.

Other blazes were burning near the coast in Monterey and Sonoma counties, while firefighters had contained dozens of smaller fires.

About 12 Palermo-area residents spent Tuesday night at an evacuation center established at Oroville's Church of the Nazarene, church secretary Tina Brandt said.

“I grabbed a few pieces of clothing, my purse. My daughter grabbed her important papers and some clothing, whatever we could put in the car, and we left,” evacuee Debbie Buchman said Wednesday in a telephone interview from the shelter. “We were hoping we would still have a home when we got back, but we didn't.”

Buchman, her 21-year-old daughter and 4-year-old granddaughter were getting aid from church members and the Red Cross after losing their three-bedroom rural rented home to Tuesday's flames.

“The whole house was burnt to the ground, with everything we own,” Buchman said. “It's pretty rough.”

On Wednesday, the state activated contracts with private companies to use DC-10 and DC-7 air tankers. Seven air tankers and eight helicopters were dumping water and fire retardant on flare-ups.