UnionBanCal Corp., parent to Union Bank, with 60 branches in San Diego, entered into a definitive agreement to purchase Pacific Capital Bancorp, a bank holding company based in Santa Barbara, for about $1.5 billion, the company said March 13.

The proposed purchase price of $46 for each share of PCB was a 60 percent premium to Pacific Capital’s stock price when the transaction was announced.

Pacific Capital, the parent firm to Santa Barbara Bank & Trust, has $5.9 billion in assets and 47 branches in the Central Coast part of the state.

Based in San Francisco, UnionBanCal Corp. has about $90 billion in assets and operates 414 branches in California, Washington, Oregon, Texas and New York, plus two international offices. It is a unit of Tokyo-based Mitsubishi UFJ Financial Group Inc.

UBC said Pacific Capital Bancorp’s tangible book value is expected to increase significantly upon the close of the transaction, during the fourth quarter of 2012, from tax-related assets and an increase in the value of the loan portfolio.

— Mike Allen