Exhibit 99.1

FOR IMMEDIATE RELEASE

October 17, 2008

Contacts: Melanie J. Dressel, President and

Chief Executive Officer

(253) 305-1911

Gary R. Schminkey, Executive Vice President

and Chief Financial Officer

(253) 305-1966

COLUMBIA BANKING SYSTEM FILES FORM S-3

SHELF REGISTRATION STATEMENT

TACOMA, Washington, October 17, 2008 — Columbia Banking System, Inc. (NASDAQ: COLB) (“Columbia”) announced today that it has filed a shelf registration statement on Form S-3 with the Securities and Exchange Commission (SEC). When declared effective by the SEC, the shelf registration statement will allow Columbia to raise capital from time to time, up to an aggregate of $100 million, through the sale of common and preferred stock. Specific terms and prices will be determined at the time of each offering under a separate prospectus supplement, which will be filed with the SEC at the time of the offering.

Melanie Dressel, President and Chief Executive Officer, said, “By filing this shelf registration, we are increasing our capital flexibility. It puts us in a position to take advantage of potential opportunities that we anticipate over the next several years.”

The registration statement on Form S-3 filed with the SEC has not yet become effective. Securities may not be sold nor may offers to buy be accepted prior to the time that the registration statement becomes effective. This news release does not constitute an offer to sell, or the solicitation of an offer to buy securities, nor shall there be any sale of securities in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification of the securities under the securities laws of that state.

About Columbia

Headquartered in Tacoma, Washington, Columbia Banking System, Inc. is the holding company of Columbia Bank, a Washington state-chartered full-service commercial bank. With the 2007 acquisitions of Mountain Bank Holding Company and Town Center Bancorp and the 2008 internal merger of its subsidiary, Bank of Astoria, into Columbia Bank, Columbia Banking System has 52 banking offices in Pierce, King, Cowlitz, Kitsap, Thurston and Whatcom counties in Washington State, and Clackamas, Clatsop, Tillamook and Multnomah counties in Oregon. Included in Columbia Bank are former branches of Mt. Rainier National Bank, doing business as Mt. Rainier Bank, with 5 branches in King and Pierce counties. Columbia Bank does business under the Bank of Astoria name at the Bank of Astoria’s former branches located in Astoria, Warrenton, Seaside and Cannon Beach in Clatsop County and in Manzanita in Tillamook County. More information about Columbia can be found on its website at www.columbiabank.com.

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Note Regarding Forward Looking Statements

This news release includes forward looking statements, which management believes are a benefit to shareholders. These forward looking statements describe management’s expectations regarding future events and developments such as future operating results, growth in loans and deposits, continued success of our style of banking and the strength of the local economy. The words “will,” “believe,” “expect,” “should,” and “anticipate” and words of similar construction are intended in part to help identify forward looking statements. Future events are difficult to predict, and the expectations described above are necessarily subject to risk and uncertainty that may cause actual results to differ materially and adversely. In addition to discussions about risks and uncertainties set forth from time to time in our filings with the SEC, factors that may cause actual results to differ materially from those contemplated by such forward looking statements include, among others, the following possibilities: (1) local and national economic conditions are less favorable than expected or have a more direct and pronounced effect on us than expected and adversely affect our ability to continue internal growth at historical rates and maintain the quality of our earning assets; (2) a continued decline in the housing/real estate market; (3) changes in interest rates significantly reduce interest margins and negatively affect funding sources; (4) deterioration of credit quality that could, among other things, increase defaults and delinquency risks in the Banks’ loan portfolios (5) projected business increases following strategic expansion activities are lower than expected; (6) competitive pressure among financial institutions increases significantly; (7) legislation or regulatory requirements or changes adversely affect the businesses in which we are engaged; and (8) our ability to realize the efficiencies we expect to receive from our investments in personnel, acquisitions and infrastructure

Source: Columbia Banking System, Inc.

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