 Columbia Banking System Inc. COLB, -2.00 and Umpqua Holdings Corp. UMPQ, -0.67 announced Tuesday an all-stock merger deal that would bring together two West Coast regional banks with a combined market capitalization of about 7.7 billion and a combined more than 50 billion in assets. Under terms of the deal, Umpqua shareholders will receive 0.5968 Columbia Banking shares for each Umpqua share they own. 