<SEC-DOCUMENT>0001127602-25-012796.txt : 20250430
<SEC-HEADER>0001127602-25-012796.hdr.sgml : 20250430
<ACCEPTANCE-DATETIME>20250430144809
ACCESSION NUMBER:		0001127602-25-012796
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20250429
FILED AS OF DATE:		20250430
DATE AS OF CHANGE:		20250430

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Wondeh Inez
		CENTRAL INDEX KEY:			0001898736
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-09383
		FILM NUMBER:		25894062

	MAIL ADDRESS:	
		STREET 1:		4550 MANGELS BLVD A-2M
		CITY:			FAIRFIELD
		STATE:			CA
		ZIP:			94534

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			WESTAMERICA BANCORPORATION
		CENTRAL INDEX KEY:			0000311094
		STANDARD INDUSTRIAL CLASSIFICATION:	NATIONAL COMMERCIAL BANKS [6021]
		ORGANIZATION NAME:           	02 Finance
		EIN:				942156203
		STATE OF INCORPORATION:			CA
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1108 FIFTH AVE
		CITY:			SAN RAFAEL
		STATE:			CA
		ZIP:			94901
		BUSINESS PHONE:		(707) 863-6000

	MAIL ADDRESS:	
		STREET 1:		4550 MANGELS BLVD
		STREET 2:		A-2Y
		CITY:			FAIRFIELD
		STATE:			CA
		ZIP:			94534-4082

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	INDEPENDENT BANKSHARES CORP
		DATE OF NAME CHANGE:	19830801
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-04-29</periodOfReport>

    <issuer>
        <issuerCik>0000311094</issuerCik>
        <issuerName>WESTAMERICA BANCORPORATION</issuerName>
        <issuerTradingSymbol>WABC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001898736</rptOwnerCik>
            <rptOwnerName>Wondeh Inez</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>WESTAMERICA BANCORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>4550 MANGELS BLVD A-2M</rptOwnerStreet2>
            <rptOwnerCity>FAIRFIELD</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94534</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-04-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>451</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>48.51</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>946</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>/s/ Kris Irvine, attorney-in-fact for Ms. Wondeh</signatureName>
        <signatureDate>2025-04-30</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
