San Francisco, CA-based UnionBanCal Corporation and its Union Bank subsidiary have entered into an agreement to acquire Pacific Capital Bancorp, the Santa Barbara, CA-headquartered owner of Santa Barbara Bank & Trust, for $46 per share in cash.

The acquisition remains subject to approval from banking regulators and other customary closing conditions and is expected to close in the final quarter of the year.

The firm said the purchase of Pacific Capital and its primary bank operations, Santa Barbara Bank & Trust, will expand its geographic footprint across “important areas” of the central coast, as well as strengthening Union Bank’s ability to serve customers through greater scale and distribution in markets including wealth management.

UnionBanCal also said the acquisition presents opportunities from expanded product offerings and cross-sell in business banking, wealth management and commercial and community banking, which is a source of “significant revenue.”

Pacific Capital’s book value is expected to increase “significantly” upon completion of the transaction, due to tax-related assets and an increase in the value of the loan portfolio.

UnionBanCal has assets of $89.7 billion, as of 31 December 2011, with 414 branches across California, Washington, Oregon, Texas and New York, as well as two international offices.

Pacific Capital has $5.9 billion in assets, and is the parent company of Santa Barbara Bank & Trust.