Columbia Banking System (COLB) 8-K/A Completion of Acquisition or Disposition of Assets

EXHIBIT 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in the registration statements of Columbia Banking System, Inc. on Form S-3 (No. 333-206125), on Form S-8 (Nos. 333-195456, 333-187690, 333-160371, 333-160370, 333-125298 and 333-100420), and on Form S-4 (Nos. 333-216039) of our report dated March 13, 2017, relating to the consolidated financial statements of Pacific Continental Corporation and Subsidiary appearing in this Amendment No. 1 to the Current Report on Form 8-K/A of Columbia Banking System, Inc.

/s/ Moss Adams LLP

Portland, Oregon

December 18, 2017