An explosive 25,000 acre wildfire is destroying entire communities 100 miles north of San Francisco

A massive wildfire is exploding across rural communities in Northern California, expanding to over 25,000 acres since it began Saturday afternoon.

It has sent more than 3,000 people racing out of the area, leaving behind their homes and towns, and sending four firefighters to the hospital with second-degree burns.

The fire erupted in Lake County, about 100 miles north of San Francisco, Saturday afternoon at 1:30 p.m., burning about 50 acres at its start. It quickly grew to 400 acres by 4:00 p.m. and reached 10,000 acres by 6:30 p.m. By late Saturday night, it had hit 25,000 acres.

The fire rapidly chewed through brush and trees parched from several years of drought, the California Department of Forestry and Fire Protection said. An unconfirmed number of structures were destroyed. Entire towns as well as residents along a 35-mile stretch of highway were evacuated.

The firefighters, all members of a helicopter crew, were airlifted to a hospital burn unit, where they were listed in stable condition, department spokesman Daniel Berlant said.

To the east, firefighters battled a blaze about 70 miles southeast of Sacramento that exploded to more than 101 square miles in four days, turning the grassy, tree-studded Sierra Nevada foothills an eerie white.

Crews increased containment to 15 percent despite a thick layer of smoke that kept air tankers and helicopters from flying Saturday.

The fire, which broke out on Wednesday, destroyed 86 homes, 51 outbuildings and was threatening about 6,400 more.

"I lost my business - it's all burned up - my shop, my house, 28 years of living," said Joe Thomas, who lives near the community of Mountain Ranch. "I got to start all over. It's depressing."

 Literally, entire streets of Middletown, California are on fire.

Mandatory evacuation orders have  been put out for a number of areas in Lake County, including Bottle Rock Road, High Valley Road, Hwy 175 Cobb, Hwy 29 Tubbs Lane (Calistoga, Napa County) to Hwy 29/Hwy 53 (Lower Lake, Lake County) Butts Canyon Road to Napa County Line, including Berreyssa Estates.

 Thomas, who runs a tractor dealership and repair business, said he and his wife grabbed papers, his work computer, photos and their four dogs. But they left a goat, five ducks, six rabbits and more than 30 chickens behind.

"I turned the pens open and turned them lose. I just couldn't gather them up," he said. "All we want to do is go home. It's miserable."

Gov. Jerry Brown declared a state of emergency, helping free up funding and resources in the firefight. More than 3,850 firefighters were assigned to the blaze, and more we expected to join the firefight. Its cause is under investigation.

Meanwhile, new evacuation orders were issued Saturday for the largest wildfire in the state, threatening to sweep through an ancient grove of Giant Sequoia trees. The fire, sparked by lightning on July 31, has charred 201 square miles, the U.S. Forest Service said.

Firefighters cleared brush around the Grant Grove and set prescribed burns to keep the flames from overrunning it. By Saturday, the backfiring and monitoring efforts appeared to have helped protect the treasured trees, the Fresno Bee reported.

The grove is named for the towering General Grant tree that stands 268 feet tall. There are dozens of Sequoia groves in the Sierra Nevada, and some trees are 3,000 years old.