A massive fire struck at the core of Chevron Corp’s large Richmond, California, refinery on Monday, spewing flames and a column of smoke into the air, threatening a prolonged outage that may increase prices of the costliest U.S. gasoline. The fire was contained, but not extinguished, according to the company. The fire has blazed for hours after it erupted at the refinery in a densely populated industrial suburb of San Francisco. Smoke could be seen billowing over the Bay Area and four train stations were shut.