Rolling blackouts plagued California for the second straight day Tuesday, leaving nearly half a million homes and businesses from San Diego to the Oregon border without power. Traffic snarled, schools operated on natural light, and businesses throughout Silicon Valley closed as the crisis that crippled the state's power grid Monday struck again. Unseasonably warm temperatures, reduced electricity imports from the Pacific Northwest and power plant shutdowns prompted the outages, which began at 9:30 a.m.