On May 28, 1957 National League owners unanimously authorized baseball's expansion to the west coast. The Brooklyn Dodgers and New York Giants were approved to move their franchises to Los Angeles and San Francisco respectively.
Brooklyn Dodgers owner Walter O'Malley had been trying to get a new stadium built in Brooklyn to replace the 32,000 seat Ebbets Field that he felt his team had outgrown. His unsuccessful attempts to get the new stadium approvals led to meetings with Los Angeles officials, where over a series of secret discussions the plan to move baseball to California was hatched. San Francisco mayor George Christopher, hearing about the O'Malley meetings, arranged to meet with Giants owner Horace Stoneham. Stoneham's Giants were not drawing fans on a consistent basis and he felt that a move to the west coast would revitalize the franchise.
On May 28th their wishes were granted, with only two conditions placed on the deal.
1) One team could not go without the other. If one team backed out the deal was off.
2) Both teams had to make their announcements before October 1, 1957.
Unfortunately for New York baseball fans both conditions were met and their beloved teams were gone by the start of the 1958 season.
New York was left with no National League team until 1962 when the New York Mets began play in Queens.
As a side note, ever wonder why the Mets uniforms are orange and blue? To embrace the mourning Giants and Dodgers fan base the Mets took orange from the Giants and blue from the Dodgers. Who knows if it worked, but the effort and idea were appreciated.
In this picture Giants owner Horace Stoneham (third from left) listens to Dodgers owner Walter O'Malley (far left) as he discusses the potential move with NY mayor Rober Wagner (middle).
Dodgers fans try to keep their team in Brooklyn