FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person * THORSON JOHN A   2. Issuer Name and Ticker or Trading Symbol WESTAMERICA BANCORPORATION [WABC] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) SVP/Treasurer (Last) (First) (Middle) 3. Date of Earliest Transaction (Month/Day/Year) 04/01/2005 (Street)   4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 04/01/2005   F   1,066 (1) D $ 50.8289 3,200 (1) I Deferred Common Stock 04/01/2005   G V 415 D $ 0 415 (1) I by daughter RPT Common Stock 04/01/2005   G V 415 D $ 0 415 (1) I by daughter SRT Common Stock               3,006.2841 (1) (2) D   Common Stock               125.858 (3) I ESOP

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
THORSON JOHN A			SVP/Treasurer

Signatures

by: John "Robert" A Thorson		04/04/2005
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	The reporting person deferred delivery of 2,600 restricted performance shares vesting in January 2003 until March 31, 2005. The shares were held in a rabbi trust ("Deferred") until the prescheduled distribution. At the time of the distribution from the rabbi trust, 704 shares were delivered to the reporting person's direct account, 415 shares were gifted to each of two custodial accounts for minor children, and 1,066 shares were sold by the rabbi trust to pay the tax liability. Also, since the reporting person's last report, 1,570 restricted performance shares vesting 1/26/06 and reported as direct holdings until delivered, were delivered to the reporting person's deferred holdings.
(2)	Includes reinvested dividends as of 2/7/05.
(3)	Includes all contributions to Westamerica Bancorporation's Tax Deferred/Savings Plan (ESOP) through 3/31/05.

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