EXHIBIT 5.1
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                                  May 22, 1997

Westamerica Bancorporation
1108 Fifth Avenue
San Rafael, CA 94901

         Re: Registration Statement on Form S-8

Ladies and Gentlemen:

         With reference to the Registration Statement on Form S-8 to be filed by
Westamerica Bancorporation, a California corporation (the "Company"), with the
Securities and Exchange Commission under the Securities Act of 1933, relating to
132,429 shares of Common Stock of the Company issuable pursuant to the ValliCorp
Holdings, Inc. 1996 Auburn Continuation Stock Option Plan, the ValliCorp
Holdings, Inc. 1996 Auburn 1982 Incentive Continuation Stock Option Plan, the
ValliCorp Holdings, Inc. Directors' Stock Option Plan, and the ValliCorp
Holdings, Inc. Key Employees' Stock Option Plan, it is our opinion that such
shares of the Common Stock of the Company, when issued and sold in accordance
with the respective plans, will be legally issued, fully paid and nonassessable.

         We hereby consent to the filing of this opinion with the Securities and
Exchange Commission as Exhibit 5.1 to the Registration Statement.

                                           Very truly yours,



                                          /s/ PILLSBURY MADISON & SUTRO


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