On April 15, 1958, now 62 years ago, the SF Giants hosted the LA Dodgers in the first MLB game ever played on the West Coast.
Prior to 1958, the New York Giants and Brooklyn Dodgers, along with the Yankees, were rivals in New York City. That was the "Subway Series" of old, before the Subway Series of today between the Yankees and Mets.
Chris Landers of MLB.com wrote about the history of the two teams' moves to California. The Dodgers' owner at the time, Walt O'Malley, was exactly the kind of owner we'd recognize today: a real estate guy asking for someone else to help him pay for a new stadium.