Major Blackouts In Southern Calif.

Sweltering heat and the loss of key transmission lines Thursday forced power officials in Southern California to impose rolling blackouts, leaving as many as half a million people without power for about half an hour, officials said.

The California Independent System Operator, which operates the states's electric grid, declared a transmission emergency at 3:57 p.m., said ISO spokeswoman Stephanie McCorkle.

About 30 minutes later, power was being restored to people subjected to the blackouts, she said.

It marked one of the most serious disruptions since the power crisis in 2000 and 2001, in which high demand, high wholesale energy costs, transmission glitches and a tight supply caused widespread power problems.

The ISO ordered SoCal Edison to reduce demand Thursday throughout its region, prompting blackouts in areas of Fontana, La Puente, Cathedral City, Huntington Beach, Long Beach and Ontario, said Gil Alexander, a spokesman for the utility.

The situation was exacerbated by the sudden loss of key transmission lines from the Pacific Northwest, Alexander said.

Few problems were reported in communities struck by the blackouts.

SoCal Edison has about 13 million customers in more than 400 Southern California cities and communities.