<PAGE>
                                                                   EXHIBIT 10.23

NOTWITHSTANDING ANY OTHER PROVISION OF THIS AGREEMENT, NO SHARES OF WESTERN
SIERRA BANCORP'S COMMON STOCK SHALL BE ISSUED PURSUANT HERETO UNLESS THE WESTERN
SIERRA BANCORP 1999 STOCK OPTION PLAN SHALL HAVE FIRST BEEN APPROVED BY THE
SHAREHOLDERS OF WESTERN SIERRA BANCORP.

                             WESTERN SIERRA BANCORP

                        INCENTIVE STOCK OPTION AGREEMENT

        This Incentive Stock Option Agreement (the "Agreement") is made and
entered into as of the 11th day of December, 2001, by and between Western Sierra
Bancorp, a California corporation (the "Bancorp"), and Kirk Dowdell
("Optionee");

        WHEREAS, pursuant to the Western Sierra Bancorp 1999 Stock Option Plan
(the "Plan"), a copy of which is attached hereto, the Board of Directors of the
Bancorp has authorized granting to Optionee an incentive stock option to
purchase all or any part of four thousand (4,000) authorized but unissued shares
of the Bancorp's common stock at the price of fifteen Dollars and ninety Cents
($15.90) per share, such option to be for the term and upon the terms and
conditions hereinafter stated;

        NOW, THEREFORE, it is hereby agreed:

        1. GRANT OF OPTION. Pursuant to said action of the Board of Directors,
the Bancorp hereby grants to Optionee the option to purchase, upon and subject
to the terms and conditions of the Plan which is incorporated in full herein by
this reference, all or any part of four thousand (4,000) shares of the Bancorp's
common stock (hereinafter called "stock") at the price of fifteen dollars and
ninety Cents ($15.90) per share, which price is not less than one hundred
percent (100%) of the fair market value of the stock (or not less than 110% of
the fair market value of the stock for Optionee-shareholders who own securities
possessing more than ten percent (10%) of the total combined voting power of all
classes of securities of the Bancorp) as of the date of action of the Board of
Directors granting this option.

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         2. EXERCISABILITY. This option shall be exercisable as to:

<TABLE>
<CAPTION>
            Number of Shares                        Vesting Date
            ----------------                     ------------------
<S>                                              <C>
                  800                                Immediate
                  800                            December 11, 2002
                  800                            December 11, 2003
                  800                            December 11, 2004
                  800                            December 11, 2005
</TABLE>

This option shall remain exercisable as to all vested shares until December 11,
2011 (but not later than ten (10) years from the date this option is granted)
unless this option has expired or terminated earlier in accordance with the
provisions hereof or in the Plan. Subject to paragraphs 4 and 5, shares as to
which this option becomes exercisable pursuant to the foregoing provision may be
purchased at any time prior to expiration of this option.

         3. EXERCISE OF OPTION. This option may be exercised by written notice
(substantially in the form as that which is attached as Exhibit A) delivered to
the Bancorp stating the number of shares with respect to which this option is
being exercised, together with (a) cash in the amount of the purchase price of
such shares, or (b) subject to applicable law, with the Bancorp's stock
previously acquired by Optionee and held by Optionee for a period of at least
six months. Notwithstanding the foregoing, in the event Optionee does exercise
the option by utilizing (b) above, Optionee should obtain tax advice as to the
consequences of such action. Not less than ten (10) shares may be purchased at
any one time unless the number purchased is the total number which may be
purchased under this option and in no event may the option be exercised with
respect to fractional shares. Upon exercise, Optionee shall make appropriate
arrangements and shall be responsible for the withholding of any federal and
state taxes then due.

         4. CESSATION OF EMPLOYMENT. Except as provided in Paragraphs 2 and 5
hereof, if

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Optionee shall cease to be an employee of the Bancorp or a subsidiary
corporation for any reason other than Optionee's death or disability [as defined
in Section 22(e)(3) of the Internal Revenue Code of 1986, as amended from time
to time (the "Code")], this option shall expire three (3) months thereafter.
During the three (3) month period this option shall be exercisable only as to
those installments, if any, which had accrued as of the date when Optionee
ceased to be an employee of the Bancorp or a subsidiary corporation.

         5. TERMINATION OF EMPLOYMENT FOR CAUSE. If Optionee's employment with
the Bancorp or a subsidiary corporation is terminated for cause, this option
shall expire thirty (30) days from the date of such termination. Termination for
cause shall include, but not be limited to, termination for malfeasance or gross
misfeasance in the performance of duties or conviction of a crime involving
moral turpitude, and, in any event, the determination of the Board of Directors
with respect thereto shall be final and conclusive.

         6. NONTRANSFERABILITY; DEATH OR DISABILITY OF OPTIONEE. This option
shall not be transferable except by will or by the laws of descent and
distribution and shall be exercisable during Optionee's lifetime only by
Optionee. If Optionee dies while serving as an employee of the Bancorp or a
subsidiary corporation, or during the three (3) month period referred to in
Paragraph 4 hereof, this option shall expire one (1) year after the date of
Optionee's death or on the day specified in Paragraph 2 hereof, whichever is
earlier. After Optionee's death but before such expiration, the persons to whom
Optionee's rights under this option shall have passed by will or by the laws of
descent and distribution or the executor or administrator of Optionee's estate
shall have the right to exercise this option as to those shares for which
installments had accrued under Paragraph 2 hereof as of the date on which
Optionee ceased to be an employee of the Bancorp or a subsidiary corporation.

         If Optionee terminates his or her employment because of disability (as
defined in Section 22(e)(3) of the Code), Optionee may exercise this option to
the extent he or she is entitled to do so at the date of termination, at any
time within one (1) year of the date of termination, or before the expiration
date specified in Paragraph 2 hereof, whichever is earlier.

<PAGE>
         7. EMPLOYMENT. This Agreement shall not obligate the Bancorp or a
subsidiary corporation to employ Optionee for any period, nor shall it interfere
in any way with the right of the Bancorp or a subsidiary corporation to reduce
Optionee's compensation.

         8. PRIVILEGES OF STOCK OWNERSHIP. Optionee shall have no rights as a
shareholder with respect to the Bancorp's stock subject to this option until the
date of issuance of stock certificates to Optionee. Except as provided in the
Plan, no adjustment will be made for dividends or other rights for which the
record date is prior to the date such stock certificates are issued.

         9. MODIFICATION AND TERMINATION. The rights of Optionee are subject to
modification and termination upon the occurrence of certain events as provided
in Sections 13 and 14 of the Plan.

         10. NOTIFICATION OF SALE. Optionee agrees that Optionee, or any person
acquiring shares upon exercise of this option, will notify the Bancorp not more
than five (5) days after any sale or other disposition of such shares.

         11. REPRESENTATIONS OF OPTIONEE. No shares issuable upon the exercise
of this option shall be issued and delivered unless and until the Bancorp has
complied with all applicable requirements of California and federal law and of
the Securities and Exchange Commission and the California Department of
Corporations pertaining to the issuance and sale of such shares, and all
applicable listing requirements of the securities exchanges, if any, on which
shares of the Bancorp of the same class are then listed. Optionee agrees to
ascertain that such requirements shall have been complied with at the time of
any exercise of this option. In addition, if the Optionee is an "affiliate" for
purposes of the Securities Act of 1933, there may be additional restrictions on
the resale of stock, and Optionee therefore agrees to ascertain what those
restrictions are and to abide by the restrictions and other applicable federal
and state securities laws.

         Furthermore, the Bancorp may, if it deems appropriate, issue stop
transfer instructions against any shares of stock purchased upon the exercise of
this option and affix to any certificate representing such shares the legends
which the Bancorp deems appropriate.

<PAGE>
         Optionee represents that the Bancorp, its directors, officers,
employees and agents have not and will not provide tax advice with respect to
the option, and Optionee agrees to consult with his or her own tax advisor as to
the specific tax consequences of the option, including the application and
effect of federal, state, local and other tax laws.

         12. NOTICES. Any notice to the Bancorp provided for in this Agreement
shall be addressed to it in care of its President or Chief Financial Officer at
its main office and any notice to Optionee shall be addressed to Optionee's
address on file with the Bancorp or a subsidiary corporation, or to such other
address as either may designate to the other in writing. Any notice shall be
deemed to be duly given if and when enclosed in a properly sealed envelope and
addressed as stated above and deposited, postage prepaid, with the United States
Postal Service. In lieu of giving notice by mail as aforesaid, any written
notice under this Agreement may be given to Optionee in person, and to the
Bancorp by personal delivery to its President or Chief Financial Officer.

         13. INCENTIVE STOCK OPTION. This Agreement is intended to be an
incentive stock option agreement as defined in Section 422 of the Code;
provided, however, that if the option shall fail to constitute an incentive
stock option for any reason, the option shall thereafter be governed by the
provisions of the Plan regarding nonqualified stock options.

IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of the
day and year first above written.

OPTIONEE                                 WESTERN SIERRA BANCORP

By                                       By
   ---------------------------------         -----------------------------------
   Kirk Dowdell                              Chuck Bacchi, Chairman

                                         By
                                             -----------------------------------
                                             Gary Gall, Pres/CEO

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                                    EXHIBIT A

                         NOTICE OF STOCK OPTION EXERCISE

Gary D. Gall
President and CEO
Western Sierra Bancorp
3350 Country Club Drive
Cameron Park, California 95682

Dear Mr. Gall:

Pursuant to my incentive stock option agreement dated _______________, I am
exercising my stock option to acquire ____________ shares of common stock of
Western Sierra Bancorp. I am also enclosing payment by means of (cash in the
amount of $_________, or ________ qualifying shares of Western Sierra Bancorp
having a fair market value) equal to the sum of the option exercise price.

I further acknowledge that Western Sierra Bancorp makes no representations as to
federal or state tax matters, and that I am to consult with my own tax attorney
or tax accountant for advice with respect to the exercise of my stock option and
the effect of the sale of the option shares. [(For executive officers of the
Bancorp or insiders of the Bancorp) I further acknowledge that I am an affiliate
or insider of Western Sierra Bancorp and that federal securities laws are
applicable to the exercise of the stock option and any subsequent sale of the
option shares including the applicability of the Securities Act of 1933 and Rule
144 (both dealing with the sale of shares by an affiliate). I agree to comply
with such securities laws and rules.]

                                         Sincerely,

                                         Kirk Dowdell