(Bloomberg) -- - Steady winds fanned the flames of a wildfire in Southern California yesterday, expanding the destruction by 60 percent in one day.

The fire grew in size to 39,900 acres (15,960 hectares) last night from 24,000 acres on Oct. 26, Daniel McCarthy, a spokesman for the California Department of Forestry and Fire Protection's Riverside County Fire unit, said in an interview.

Firefighters were able to contain 25 percent of the blaze, up from 5 percent yesterday, McCarthy said, with a goal of encompassing more today.

``We're certainly hopeful,'' he said. ``The firefighters have had a positive result'' on containing the blaze.

About 2,078 firefighters from across the state, including prison inmate crews, were trying to bring the wildfire under control, he said. Yesterday 171 engines, 15 air tankers, 22 helicopters and 34 bulldozers were attacking the blaze. Police also looked for the person responsible for the blaze that killed four firefighters and seriously injured a fifth.

The U.S. National Weather Service issued a so-called red flag warning for southwestern California until 11 p.m. local time today because of low humidity, gusting winds of up to 45 miles an hour (72 kilometers per hour), and dry conditions, which can help a fire spread.

A reward for information leading to the arrest and conviction of the person or people responsible for setting the fire rose to $500,000 yesterday, McCarthy said.

``We want to let everyone know that we are searching for the arsonists, we will find them and we will punish them,'' California Governor Arnold Schwarzenegger said in San Francisco yesterday.

Hot, Dry Winds

The fire began at 1:12 a.m. local time Oct. 26 in ground brush in Cabazon, Riverside County, about 100 miles (161 kilometers) east of Los Angeles and about 20 miles west of Palm Springs. The blaze, dubbed the Esperanza fire, shot up the arid California hills and was spread by hot, dry winds.

The wildfire was deliberately set and constituted murder, the Riverside County Fire Department said.

The area affected was mainly uninhabited and included land to the east of Highway 79, south of Beaumont, Captain Don Camp, a spokesman for the California Department of Forestry and Fire Protection, said in a telephone interview yesterday.

Weather conditions this weekend focus on the strength of the winds, which are gusting 20 miles to 25 miles an hour, said Valerie MacAdam, a spokeswoman for the California Department of Forestry and Fire Protection's Riverside County Fire unit.

``The winds are pretty much controlling the fire,'' MacAdam said. ``With this type of fire, it tends to make its own wind conditions.''