Swaths of California are sweltering and things are only expected to get worse during the Fourth of July holiday week for parts of the United States, with nearly 90 million people under heat alerts. Forecasters say the torrid conditions are being caused by a ridge of high pressure just off the West Coast and a separate ridge that has spawned heat warnings and advisories from Kansas and Missouri to the Gulf Coast states. Just north of California’s capital, firefighters working in scorching conditions battled a fast-moving blaze Tuesday that forced the evacuation of some 13,000 people. Authorities have yet to say how many homes were destroyed.