Commercial Bank, West Coast deal linked to common interests. (Commercial Bancorp.; West Coast Bancorp.)

The merger of West Coast Bancorp on the shores of the Pacific, and Commercial Bancorp in the heart of the Willamette Valley, came as no surprise to industry watchers who expected a union between the two for some time.

Three critical factors crystallized the deal: a new joint data processing center near Salem, recent expansions by both companies into suburban Portland, and a moment of crisis last summer in which a pair of small-town banks bonded.

The new $420 million bank holding company, announced Oct. 25, combines a profitable coastal community bank with historical links in commercial fishing to a land-locked lender in a growing region dominated by …