EXHIBIT 5.1
                   [LETTERHEAD OF PILLSBURY MADISON & SUTRO]


                                                        September 8, 1994



Westamerica Bancorporation
1108 Fifth Avenue
San Rafael, California 94901

Ladies and Gentlemen:

     With reference to the Registration Statement on Form S-4 filed by
Westamerica Bancorporation, a California corporation ("WABC"), with the
Securities and Exchange Commission in connection with the registration under the
Securities Act of 1933, as amended, of 1,400,000 shares of WABC Common Stock, no
par value (the "Shares"), to be issued in connection with the merger
contemplated by the Agreement and Plan of Reorganization dated as of July 25,
1994, as amended (the "Agreement"), among WABC, PV Financial, a California
corporation, and Pacific Valley National Bank, a national banking association,
and a related Agreement of Merger (the "Merger Agreement," and collectively with
the Agreement, the "Agreements") which Agreements are described therein and
filed as an exhibit thereto:

     We are of the opinion that the Shares have been duly authorized and, when
issued in accordance with the Agreements, will be legally issued, fully paid and
nonassessable.

     We hereby consent to the filing of this opinion as Exhibit 5.1 to the
Registration Statement and to the use of our name under the caption "Legal
Matters" in the Registration Statement and in the Proxy Statement/Prospectus
included therein.

                                       Very truly yours,

                                       /s/ PILLSBURY MADISON & SUTRO