[LETTERHEAD OF PILLSBURY MADISON & SUTRO LLP]
                                                                     Exhibit 5.1


                              December 4, 1996


Westamerica Bancorporation
1108 Fifth Avenue
San Rafael, CA 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 6,600,000 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 November
11, 1996, (the "Agreement"), among WABC, ValliCorp Holdings, Inc. ("ValliCorp"),
a Delaware corporation, and ValliWide Bank, a California banking corporation,
and a related Agreement and Plan 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 the use of our name under the caption "Legal Matters"
in the Registration Statement and in the Joint Proxy Statement/Prospectus
included therein.


                              Very truly yours,


                              /s/ Pillsbury Madison & Sutro LLP
[4743]