Temecula, Calif. ? Southern California’s 2004 fire season opened Monday with firefighters battling blazes that covered nearly 5,000 acres and forced hundreds of people to evacuate.

The largest was a 2,500-acre fire in Riverside County. But five other blazes were scattered across Santa Barbara, Los Angeles and San Diego counties, as temperatures climbed to 100 degrees in some places.

Several firefighters among the thousands on the job were treated for injuries, including heatstroke, dehydration and smoke inhalation.

Authorities ordered a mandatory evacuation of several homes in the path of the Riverside County fire in the hills south of Temecula. They previously advised residents of about 100 homes to evacuate.

The blaze destroyed a home and a research facility used by researchers at the University of California, Riverside.

The start of the fire season was declared three weeks earlier than last year because of dry weather and a tree-killing bark beetle infestation.