The summer wildfire season in Southern California has barely begun and already hundreds of homes have been evacuated as flames have engulfed thousands of acres of San Gabriel Mountain foothills about 25 miles northeast of downtown Los Angeles.

Two major brush fires erupted Monday in Azusa and Duarte, two small cities located south of the Angeles National Forest, knocking out power and sparking a mandatory evacuation of about 600 homes, according to KTLA-TV in Los Angeles.

These seasonal fires have a significant economic impact annually. California Gov. Jerry Brown’s office estimated last fall that the latest fire season cost the state $212 million. The weekend after the estimate was released, 400 homes were destroyed in and around Middleton, California, adding to the financial toll.

San Gabriel Mountains Fires Duarte Azusa Cars head west on the 210 freeway in Pasadena, California, as heavy smoke from the Fish Fire and the Reservoir Fire is seen in the San Gabriel Mountains northeast of Los Angeles June 20, 2016. Photo: Robyn Beck/AFP/Getty Images

At least five other significant fires have started in California, New Mexico and Arizona in the past week that are still burning amid a sizzling heat wave in the Southwest. At least four hikers were killed in Arizona over the weekend because of heat exhaustion as temperatures in Phoenix touched 115 degrees Fahrenheit Monday, with little relief expected this week.

The two new major brush fires in California erupted within an hour of each other as temperatures in this drought-stricken part of the country touched 109 degrees.

Called the Reservoir Fire, one of them broke out at about 11:15 a.m. local time (2:15 p.m. EDT) near Azusa, and authorities believe it began when a car went off the road and ignited dry vegetation, according to KNBC-TV in Los Angeles. That fire quickly spread to at least 1,200 acres by mid-afternoon. “We have activated the emergency alarm,” Azusa police tweeted

Santa Barbara Fire California Wildfire Firefighters battle the expanding Sherpa Fire outside Santa Barbara, California, June 17, 2016. Photo: David McNew/AFP/Getty Images

Dubbed the Fish Fire, the second fire sprang into life within an hour in a canyon near Duarte. Its cause has yet to be determined. The two fires had claimed at least 3,500 acres by late afternoon and were still raging out of control despite firefighters’ efforts in the air and on the ground.

Three dams in the area are operating on contingency generators, according to the Los Angeles County Department of Public Works.

Meanwhile, NBC News reported Sunday there were at least five other ongoing wildfires, two in Southern California, two in New Mexico and one in Arizona. The largest outbreak was close to the Cibola National Forest, about 20 miles south of Albuquerque: It has scorched a minimum of 35,000 acres.

Sherpa Fire Santa Barbara Wildfire A firefighting BAe-146s jet drops fire retardant on the Sherpa Fire outside Santa Barbara, California, June 18, 2016. Photo: David McNew/AFP/Getty Images

Southern California has two fire seasons each year. The Santa Ana fire season runs between October and April as hot and dry westward winds blow out to sea, with fires more likely to strike coastal areas than anywhere else. The summer fire season runs from June to September.

A study published in the journal Environmental Research last September concluded that global climate change is making California drier and its fire seasons more intense.