EXHIBIT 23.8 [LETTERHEAD OF ARTHUR ANDERSEN LLP] CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS As independent public accountants, we hereby consent to the incorporation by reference in this S-4 registration statement (No. 33-57033), filed by Westamerica Bancorporation, of our reports dated February 4, 1994, included (or incorporated by reference) in North Bay Bancorp's 10-K for the year ended December 31, 1993 and to all references to our Firm included in this registration statement. /s/ ARTHUR ANDERSEN LLP San Francisco, California January 31, 1995