EXHIBIT 23(A) CONSENT OF INDEPENDENT ACCOUNTANTS We hereby consent to the incorporation by reference in the Joint Proxy Statement/Prospectus constituting part of this Registration Statement on Form S- 4 of Columbia Banking System, Inc. of our report dated January 22, 1997 appearing on page 35 of its Annual Report on Form 10-K for the year ended December 31, 1996. We also consent to the reference to us under the heading "Experts" in such Joint Proxy Statement/Prospectus. PRICE WATERHOUSE LLP Seattle, Washington September 4, 1997