REDDING, Calif. — An explosive wildfire raged through several Northern California communities, killing two firefighters and destroying dozens of homes after thousands of terrified residents fled in miles-long traffic jams. Flames that turned the sky orange swept through the communities of Shasta and Keswick before jumping the Sacramento River on Thursday and reaching Redding, a city of about 92,000 people and the largest in the region. The so-called Carr Fire is “taking down everything in its path,” said Scott McLean, a CalFire spokesman for the crews battling the blaze. Sixty-five structures had been destroyed, and 500 other buildings were threatened, fire officials said. A firefighter with the Redding Fire Department was killed in Shasta County, officials said Friday.