8-K

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported):

July 23, 2007

COLUMBIA BANKING SYSTEM, INC.

(Exact name of registrant as specified in its charter)

Washington

(State or other jurisdiction of incorporation)

0-20288	91-1422237
(Commission File Number)	IRS Employer Identification No.

1301 A Street

Tacoma, WA 98402

(Address of principal executive offices) (zip code)

Registrant’s telephone number, including area code: (253) 305-1900

(Former Name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligations of the registrant under any of the following provisions:

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act of (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act of (17 CFR 240.13e-4(c))

Item 2.01. Completion of Acquisition or Disposition of Assets

On July 23, 2007, Columbia Banking System, Inc. (“Columbia”) completed its two pending acquisitions. Columbia acquired Mountain Bank Holding Company (“MBHC”), a Washington corporation, and its subsidiary bank, Mt. Rainier National Bank, a national banking association headquartered in Enumclaw, Washington. Columbia also acquired Town Center Bancorp (“TWBC”), an Oregon corporation, and its subsidiary bank, Town Center Bank, a commercial bank headquartered in Portland, Oregon.

Under the terms of the merger agreement between Columbia and Mountain Bank Holding Company, MBHC merged with and into Columbia, and Mt. Rainier National Bank merged with and into Columbia State Bank. The acquisition was accomplished pursuant to a Plan and Agreement of Merger whereby shareholder of MBHC will receive a “unit” consisting of .4231 shares of Columbia common stock and cash in an amount of $11.25. Columbia will issue an aggregate of 993,932 shares of its common stock and pay a total of $26,428,106 to MBHC shareholders.

Under the terms of the merger agreement between Columbia and Town Center, TWBC merged with and into Columbia, and Town Center Bank merged with and into Columbia’s subsidiary, Columbia State Bank. The acquisition was accomplished pursuant to a Plan and Agreement of Merger pursuant to which shareholders of TWBC elected to receive a “unit” comprised of .3391 shares of Columbia common stock and cash in an amount of $9.382. Columbia will issue an aggregate of 704,839 shares of its common stock and pay a total of $19,501,021 to TWBC shareholders.

The Agreement between Columbia and MBHC was included as Appendix A to the Proxy Statement/Prospectus dated May 17, 2007, and the Agreement between Columbia and Town Center was included as Appendix A to the Proxy Statement/Prospectus dated June 13, 2007, previously filed by Columbia as part of its Registration Statement on Form S-4 with the Securities and Exchange Commission. A copy of the press release dated July 23, 2007, which is attached as Exhibit 99.1 is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits

(a) Financial statements – not applicable

(b) Pro forma financial information – not applicable

(c) Shell company transactions—not applicable

(d) Exhibits

99.1 Press Release dated July 23, 2007 announcing the closing of the transactions.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Dated: July 23, 2007	COLUMBIA BANKING SYSTEM, INC.
	By:	/s/ Melanie J. Dressel
		Melanie J. Dressel
		President and Chief Executive Officer

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EX-99.1

Exhibit 99.1

FOR IMMEDIATE RELEASE

July 23, 2007

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 COMPLETES ACQUISITIONS OF MOUNTAIN BANK

HOLDING COMPANY AND TOWN CENTER BANCORP

TACOMA, Washington—Columbia Banking System, Inc. (NASDAQ: COLB) (“Columbia”) today announced the completion of its acquisitions of Mountain Bank Holding Company, the parent company of Mt. Rainier National Bank, and Town Center Bancorp, the parent company of Town Center Bank. Shareholders of both organizations overwhelmingly approved the transactions, and all regulatory approvals have been received. With the completion of the mergers, Columbia’s total assets approach $3 billion, with 53 branches in nine counties in Washington and Oregon.

Melanie J. Dressel, President and Chief Executive Officer of Columbia said, “We are delighted to welcome Mt. Rainier and Town Center customers, employees and shareholders to the Columbia family. We are joining forces with two well-run, profitable organizations that have strong cultural similarities, talented management and employees, and the same dedication to the best possible customer service. As we expand our geographic footprint into adjacent markets, we are moving significantly closer to our goal of becoming a Pacific Northwest regional community bank.”

Effective today, Mt. Rainier National Bank has been merged into Columbia State Bank, a subsidiary of Columbia Banking System, and will do business as Mt. Rainier Bank. Mt. Rainier Bank has seven locations in Washington, including Enumclaw, Buckley, Black Diamond, Auburn, Maple Valley, Sumner, and Federal Way. Town Center Bank has been merged into Columbia State Bank, adding five Oregon locations in the North Clackamas and Northeast Portland area.

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About Columbia

Columbia Banking System, Inc. is a 53-branch Tacoma-based bank holding company whose wholly owned banking subsidiaries are Columbia Bank and Bank of Astoria. Columbia Bank is a Washington state-chartered full-service commercial bank; with completion of the mergers, Columbia Bank has 48 banking offices in Pierce, King, Cowlitz, Kitsap and Thurston counties in Washington State, and Clackamas and Multnomah counties in Oregon. Included in Columbia Bank are former branches of Mt. Rainier National Bank, doing business as Mt. Rainier Bank, with 7 branches in King and Pierce counties. Bank of Astoria, a federally insured commercial bank headquartered in Astoria, Oregon, operates four branches in Clatsop County: Astoria, Warrenton, Seaside and Cannon Beach; and one branch 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 Columbia’s management’s expectations regarding future events and developments such as Columbia’s continued growth. The words “goal,” “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 Columbia’s 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, national and international economic conditions are less favorable than expected or have a more direct and pronounced effect on Columbia than expected and adversely affect Columbia’s ability to continue its internal growth at historical rates and maintain the quality of its earning assets; (2) changes in interest rates reduce interest margins more than expected and negatively affect funding sources; (3) projected business increases following strategic expansion or opening or acquiring new branches are lower than expected; (4) costs or difficulties related to the integration of acquisitions are greater than expected; (5) competitive pressure among financial institutions increases significantly; (6) legislation or regulatory requirements or changes adversely affect the businesses in which Columbia is engaged.

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