Once a startup establishes itself in San Francisco, you don’t see many of them moving into Silicon Valley, but Square is bucking that trend. This spring it’s opening up a satellite office at 5451 Great America Parkway in Santa Clara that will house up to 50 employees living in the South Bay. Square has been on growth tear lately, doubling in size to 800 employees in the past year (though it hasn’t reached 1,000 bodies it projected for the end of 2013). In October, It moved its HQ to a mammoth space at 1445 Market Street. Though it’s opening up new offices in NYC, Atlanta, Tokyo, Waterloo and now the Valley, it still has plenty of room to grow in SF where it can accommodate 2,000 people.