Firefighters struggling to contain a massive blaze in Southern California suffered a slight setback Friday when the winds fanned the nearly 24,000-acre fire, causing it to jump over a major highway in one spot.

Fire officials were hoping the so-called Esperanza fire, which has killed four firefighters and left one in critical condition, wouldn't cross Highway 79, since there's a landfill full of methane gas on the other side. Firefighters were digging in, trying to prevent further spread of the fire at the highway.

But at 2 p.m. ET, California Department of Forestry spokesman Becky Luther told FOX News that the fire had in fact made the jump. But firefighters were able to put out the flames in that spot. She said experts expected the strong winds, which are helping spread the fire, to continue at least until midnight tonight.

The wind-whipped wildfire, which authorities said was arson, raced across 15 miles of terrain in the region and was burning about 1,000 acres each hour. At one point, several hundred mountain residents took refuge with campers in a nearby RV park where crews could protect them.

About 400 RVs, with 800 to 1,000 people, had registered to spend the weekend for annual Halloween events, said Silent Valley ranger Charles Van Brunt. Officials said the visitors had enough food and water because they had prepared to be there for the weekend.

We need to be on our business today, folks. It's serious out there for at least the next 24 hours," Tim Chavez, a fire behavior analyst, said during a morning briefing of firefighters in Beaumont.

The Esperanza fire was 5 percent contained; 1,200 firefighters with 168 fire engines were battling it and building a fire line. Aiding the effort were 10 air tankers, including 15 helicopters and 10 air attack aircraft, the Riverside County fire department told FOX News. Meanwhile, 32 hand crews were using 27 bulldozers to help contain the blaze.

"We're going to be here, and we're going to hit it hard," said Riverside County fire Chief John Hawkins.

Authorities said a $500,000 reward would be offered for information leading to the arrest of the people who started the blaze. But they're not revealing why they think the fire was set on purpose.

"A deliberately set arson fire that leads to the death of anyone constitutes murder," Hawkins said.

Bill Peters, spokesman for the California Department of Forestry, said Friday on ABC's "Good Morning America that authorities "are certain because they came out with the cause fairly quickly ... I think they're going to hold the cause real close to the vest, if you will, because of the deaths."

In all, nearly 700 people were evacuated, Gov. Arnold Schwarzenegger told reporters.

Meanwhile, another fire sprung up in neighboring Orange County, about 50 miles southwest. There, firefighters were battling a brush fire that started overnight and forced the evacuation of about 140 people from a campground in the Cleveland National Forest near the city of Lake Elsinore, said Orange County Fire Capt. Steve Miller.

The blaze at the Lazy W Ranch campsite on Hot Springs Canyon, off the Ortega Highway, began as a structure fire and spread to the surrounding vegetation, Miller said. Between three and five acres have burned. Orange County firefighters have already responded to the blaze, and authorities have asked for 25 engines and aircraft to stop the fire's spread.

There have been no reports of injuries. This blaze is about 50 miles southwest of the Esperanza blaze that's blackened almost 38 square miles in the San Jacinto Mountains, about 30 miles west of Palm Springs. It destroyed 10 structures, including at least five homes. At one point, several hundred mountain residents took refuge with campers in a nearby RV park where crews could protect them.

"We had a lot of activity overnight," Peters said. He said winds, which he described as "squirrely," were still strong.

The Santa Ana winds are expected to continue through Saturday, and some could reach up to 60 mph. Winds Friday were expected to reach 15 to 25 mph. A "red flag warning" was in effect through Saturday night because of a mix of strong winds, low humidity and warm temperatures.

Fire officials were mourning the deaths of four U.S. Forest Service firefighters killed while attempting to protect a home close to where the fire began in Cabazon. The flames came so quickly the five-person crew had no time to retreat to its engine or use protective sheltering.

Killed were engine Capt. Mark Loutzenhiser, 44, of Idyllwild; engine operator Jess McLean, 27, of Beaumont; assistant engine operator Jason McKay, 27, of Phelan; and firefighter Daniel Hoover-Najera, 20, of San Jacinto. All were based in Alandale, a small community near Idyllwild.

Three of the firefighters died at the scene and two were taken to the hospital in critical condition. One died several hours later and the other had burns over 95 percent of his body, said Pat Boss, a U.S. Forest Service spokesman.

The surviving firefighter, Pablo Cerda, 23, of Fountain Valley, also had severe respiratory damage, according to Dr. Dev Gnanadev, a trauma surgeon at Arrowhead Regional Medical Center.

"Overall, the chances of survival are low when you have that bad of an injury," Gnanadev said.

Schwarzenegger on Thursday proclaimed a state of emergency for Riverside County and ordered flags to be flown at half staff at the State Capitol and all forestry and fire protection facilities throughout the state.

It was the deadliest wildfire in the United States since July 10, 2001, when four firefighters were killed in Washington's Okanogan National Forest.

Thursday's deaths brought to 19 the number of California firefighters killed in the line of duty over the past year, according to statistics kept by California Professional Firefighters, a lobbying organization.

U.S. Rep. Mary Bono, R-Calif., told FOX News Friday morning that there were three shelters in the region taking people in as they evacuate their homes.

At least one civilian suffered minor injuries and 200 people in the small, mountain communities of Poppet Flat and Twin Pines were forced to flee their homes, authorities said.

People in the Silent Valley Club RV Resort near Poppet Flat were unable to leave after firefighters closed the only road out of the community. TV footage showed vehicles racing through smoke and flames just before the road was closed.

Firefighters said it was safer to keep the people in the RV park because the blaze was stymied by a firebreak created years earlier around the area, said sheriff's Cpl. Todd Garvin.

"This is a safe haven here. That was cleared about six years ago and it still works. It's amazing," Garvin said.

Pillars of smoke that could initially be seen in the area were quickly blown away by the strong winds and at one point the scent of smoke could be detected as far away as San Diego, 80 miles south.

Timo Hargu, 61, said he rushed from his hilltop home with his two dogs after he looked out a window and saw the fire burning in a nearby valley.

"The whole thing was ablaze with flame," he said. "It was the most spectacular view. A terrible view, but spectacular."

The Associated Press contributed to this report.