CAMP PENDLETON (AP) — Hundreds of firefighters spent the first day of Southern California’s 2004 fire season Monday battling three separate blazes that broke out in 100-degree heat and quickly blackened more than 2,000 acres.

One of the fires, in rolling hills south of Temecula in Riverside County, destroyed two buildings used by UC Riverside researchers. The buildings, a home and a facility for tagging birds and other research, was located in a particularly vulnerable, heavily forested area of a nature preserve.

“They are just totally burned to the ground. All that’s left is a couple of pieces of steel,” said Rick Cook, emergeny services coordinator for Riverside County.

The largest of the fires, near the Camp Pendleton Marine base, burned across about 1,500 acres. No structures were damaged and no injuries were reported.

The fire, which started Sunday in an artillery training area, was 30 percent contained Monday morning, with full containment expected Wednesday, said Camp Pendleton spokesman Staff Sgt. Jim Goodwin. The fire was headed east toward an area burned by a 2002 fire, which was expected to slow its progress, Goodwin said.

On Sunday, sheriff’s deputies asked 80 families to voluntarily leave their homes and go to an evacuation center set up by the Red Cross at Fallbrook High School. No mandatory evacuation orders had been issued, Goodwin said.

The fires all broke out Sunday, a day before the official start of Southern California’s 2004 fire season, which was declared three weeks earlier than last year because of concerns about dangerous conditions caused by a lack of rainfall and a tree-killing bark beetle infestation.

The fire near Temecula had burned across 750 acres and was 30 percent contained Monday morning, Vogt said.

“We are expecting hot, dry weather again with slight east winds, which will make the containment effort challenging,” he said.

The third fire, just east of Lake Elsinore, had burned across 350 acres and was about 70 percent contained Monday. About 340 firefighters were battling it, aided by water-dropping aircraft. One structure was burned but it was not a home, said Lorri Larson, spokeswoman for the Riverside County Fire Department.

One firefighter suffered heat stroke battling the blaze and another sprained an ankle. A third firefighter was reported injured from dehydration while working the Wolf Valley fire.

The fires began as Southern California was in the grip of a record-setting spring heat wave.

Hot weather records were set in at least 16 Southern California communities on Sunday, according to the National Weather Service. Temperatures in many areas ranged from the high 90s to the low 100s, with more of the same expected Monday.

Near Temecula, residents of about 100 homes closest to the fire had been advised to evacuate. The Red Cross set up a shelter for them at the Temecula Community Recreation Center.

Many of the homes closest to the flames were in Dorland Mountain Colony, a small artists retreat.

The causes of the three fires were under investigation.

Capt. Rick Vogt of the state Department of Forestry said authorities were hoping to question three motorcycle riders seen in the area of the fire near Temecula when it ignited Sunday afternoon. He wouldn’t say if they were believed to have started the blaze, but asked that anyone who saw the motorcyclists in the area of Anza Road and Via Pascal contact Riverside County authorities.