<Page>

                                                      Registration No. 33-______
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8
                             Registration Statement
                        Under the Securities Act of 1933

                             WESTERN SIERRA BANCORP
             (Exact Name of Registrant as Specified in its Charter)

                     CALIFORNIA                           68-0390121
         -------------------------------               -------------------
         (State or Other Jurisdiction of                 (I.R.S. Employer
          Incorporation or Organization)               Identification No.)


       3350 COUNTRY CLUB DRIVE, SUITE 202, CAMERON PARK, CALIFORNIA 95682
                    (Address of Principal Executive Offices)

                       WESTERN SIERRA BANCORP 401KSOP PLAN
                            (Full Title of the Plans)

               GARY D. GALL, PRESIDENT AND CHIEF EXECUTIVE OFFICER
       3350 COUNTRY CLUB DRIVE, SUITE 202, CAMERON PARK, CALIFORNIA 95682
                     (Name and Address of Agent for Service)

                                 (530) 677-5600
          (Telephone Number, including Area Code, of Agent for Service)

                                    Copy to:
                            Gary Steven Findley, Esq.
                        Gary Steven Findley & Associates
              1470 North Hundley Street, Anaheim, California 92806
                                 (714) 630-7136

                          CALCULATION OF REGISTRATION FEE
<Table>
<Caption>
============================================================================================
Title of Each Class      Amount      Proposed Maximum       Proposed Maximum      Amount of
 Of Securities To         To Be       Offering Price           Aggregate        Registration
  Be Registered       Registered(a)    Per Share(b)          Offering Price          Fee
--------------------------------------------------------------------------------------------
<S>                  <C>             <C>                    <C>                 <C>
Common stock         100,000 Shares       $14.90               $1,490,000          $372.50
(No Par Value)
============================================================================================
</Table>

(a)      There are also registered hereby such indeterminate number of shares of
         common stock as may become issuable by reason of the operation of the
         anti-dilution or certain other provisions of the 401KSOP.

(b)      Estimated pursuant to Rule 457(h) solely for the purpose of computing
         the registration fee, utilizing $14.90 as the average of the bid and
         asked price of Western Sierra Bancorp's common stock as of August 2,
         2001.

================================================================================

<Page>

                                     PART II

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE

Western Sierra Bancorp (the "Registrant") hereby incorporates by reference the
documents listed below. All documents subsequently filed by the Registrant
pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Securities Exchange Act
of 1934 prior to the filing of a post-effective amendment which indicates that
all securities offered have been sold or which deregisters all securities then
remaining unsold, shall be deemed to be incorporated by reference herein and to
be a part hereof from the date of filing such documents.

(a)      The Registrant's annual report filed on Form 10-K for the year ended
         December 31, 2000.

(b)      The Registrant's quarterly reports filed on Form 10-Q for the quarter
         ended March 31, 2001.

(c)      The description of the Registrant's common stock is contained in its
         Registration Statement on Form S-4, file number 333-66675.

Any statement contained herein or in any document incorporated by reference
herein shall be deemed to be modified or superseded for purposes of this
Registration Statement to the extent that another statement contained herein or
in any other document subsequently filed, which also is incorporated by
reference herein, modifies or supersedes such statement. Any statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part of this Registration Statement.

ITEM 4.  DESCRIPTION OF SECURITIES

The Registrant's common stock is registered under Section 12 of the Exchange
Act.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL

Not Applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS

The Articles of Incorporation and Bylaws of the Registrant provide for
indemnification of agents including directors, officers and employees to the
maximum extent allowed by California law including the use of an indemnity
agreement. The Registrant's Articles further provide for the elimination of
director liability for monetary damages to the maximum extent allowed by
California law. The indemnification law of the State of California generally
allows indemnification in matters not involving the right of the corporation, to
an agent of the corporation if such person acted in good faith and in a manner
such person reasonably believed to be in the best interests of the corporation,
and in the case of a criminal matter, had no reasonable cause to believe the
conduct of such person was unlawful. California law, with respect to matters
involving the right of a corporation, allows indemnification of an agent of the
corporation, if such person acted in good faith, in a manner such person
believed to be in the best interests of the corporation and its shareholders;
provided that there shall be no indemnification for: (i) amounts paid in
settling or otherwise disposing of a pending

                                       2

<Page>

action without court approval; (ii) expenses incurred in defending a pending
action which is settled or otherwise disposed of without court approval; (iii)
matters in which such person shall have been adjudged to be liable to the
corporation unless and only to the extent that the court in which the proceeding
is or was pending shall determine that such person is entitled to be
indemnified; or (iv) other matters specified in the California General
Corporation Law.

The Registrant's Bylaws provide that the Registrant shall to the maximum extent
permitted by law have the power to indemnify its directors, officers and
employees. The Registrant's Bylaws also provide that the Registrant shall have
the power to purchase and maintain insurance covering its directors, officers
and employees against any liability asserted against any of them and incurred by
any of them, whether or not the Registrant would have the power to indemnify
them against such liability under the provisions of applicable law or the
provisions of the Registrant's Bylaws. Each of the directors and executive
officers of the Registrant has an indemnification agreement with the Registrant
that provides that the Registrant shall indemnify such person to the full extent
authorized by the applicable provisions of California law and further provide
advances to pay for any expenses which would be subject to reimbursement.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED

Not Applicable.

ITEM 8.  EXHIBITS

 5.1   Opinion re: Legality
23.1   Consent of Perry-Smith LLP

The Registrant has submitted and received a favorable determination letter from
the IRS for the 401KSOP.

ITEM 9.  UNDERTAKINGS

The undersigned Registrant hereby undertakes:

(1)      To file, during any period in which offers or sales are being made, a
         post-effective amendment to this Registration Statement:

         (i)      To include any prospectus required by Section 10(a)(3) of the
                  Securities Act of 1933;

         (ii)     To reflect in the prospectus any facts or events arising after
                  the effective date of the Registration Statement (or the most
                  recent post-effective amendment thereof) which, individually
                  or in the aggregate, represent a fundamental change in the
                  information set forth in the Registration Statement;

                                       3

<Page>

         (iii)    To include any material information with respect to the plan
                  of distribution not previously disclosed in the Registration
                  Statement or any material change to such information in the
                  Registration Statement;

         provided, however, that paragraphs (1)(i) and (1)(ii) do not apply if
         the Registration Statement is on Form S-3 or Form S-8 and the
         information required to be included in a post-effective amendment by
         those paragraphs is contained in periodic reports filed with or
         furnished to the Commission by the Registrant pursuant to Section 13 or
         Section 15(d) of the Securities Exchange Act of 1934 that are
         incorporated by reference in the Registration Statement.

(2)      That, for the purpose of determining any liability under the Securities
         Act of 1933, each such post-effective amendment shall be deemed to be a
         new registration statement relating to the securities offered therein,
         and the offering of such securities at that time shall be deemed to be
         the initial bona fide offering thereof.

(3)      To remove from registration by means of a post-effective amendment any
         of the securities being registered which remain unsold at the
         termination of the offering.

The undersigned Registrant hereby undertakes that, for purposes of determining
any liability under the Securities Act of 1933, each filing of the Registrant's
annual report pursuant to Section 13(a) or Section 15(d) of the Securities
Exchange Act of 1934 (and, where applicable, each filing of an employee benefit
plan's annual report pursuant to Section 15(d) of the Securities Exchange Act of
1934) that is incorporated by reference in the Registration Statement shall be
deemed to be a new registration statement relating to the securities offered
therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

Insofar as indemnification for liabilities arising under the Securities Act of
1933 may be permitted to directors, officers and controlling persons of the
Registrant pursuant to the foregoing provisions, or otherwise, the Registrant
has been advised that in the opinion of the Securities and Exchange Commission
such indemnification is against public policy as expressed in the Act and is,
therefore, unenforceable. In the event that a claim for indemnification against
such liabilities (other than the payment by the Registrant of expenses incurred
or paid by a director, officer or controlling person of the Registrant in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Act and will be governed by the final adjudication of
such issue.

                                       4

<Page>

                                   SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized in the City of Cameron Park, State of California, on August 3, 2001.

                                        WESTERN SIERRA BANCORP

                                        /s/ GARY D. GALL
                                        ----------------------------------------
                                        Gary D. Gall
                                        President & CEO

Pursuant to the requirements of the Securities Act of 1933, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.


<Table>
<S>                                                             <C>                                  <C>
 /S/ GARY D. GALL                                            ,  Director and Principal               August 3, 2001
-------------------------------------------------------------   Executive Officer
Gary D. Gall



 /S/ CHARLES W. BACCHI                                       ,  Chairman                              July 27, 2001
-------------------------------------------------------------
Charles W. Bacchi



 /S/ BARBARA L. COOK                                         ,  Director                              July 27, 2001
-------------------------------------------------------------
Barbara L. Cook



 /S/ LARY A. DAVIS                                           ,  Director                              July 30, 2001
-------------------------------------------------------------
Lary A. Davis



 /S/ WILLIAM J. FISHER                                       ,  Director                              July 27, 2001
-------------------------------------------------------------
William J. Fisher



 /S/ HOWARD JAHN                                             ,  Director                              July 27, 2001
-------------------------------------------------------------
Howard "Skip" Jahn
</Table>

                                       5

<Page>

<Table>
<S>                                                             <C>                                  <C>
 /S/ ALAN J. KLEINERT                                        ,  Director                              July 31, 2001
-------------------------------------------------------------
Alan J. Kleinert



 /S/ THOMAS MANZ                                             ,  Director                              July 27, 2001
-------------------------------------------------------------
Thomas Manz



 /S/ HAROLD S. PRESCOTT, JR.                                 ,  Director                              July 27, 2001
-------------------------------------------------------------
Harold S. Prescott, Jr.



 /S/ OSVALDO I. SCARIOT                                      ,  Director                              July 31, 2001
-------------------------------------------------------------
Osvaldo I. Scariot



 /S/ DAVID MERCK                                             ,  Principal Financial                  August 3, 2001
-------------------------------------------------------------   Officer
David Merck
</Table>

                                       6

<Page>


                                  EXHIBIT INDEX



 Exhibit
 NUMBER                                      DESCRIPTION
--------                   -----------------------------------------------

   5.1                     Opinion re: Legality

  23.1                     Consent of Perry-Smith LLP





                                       7
[{"type": "S-8", "sequence": "1", "filename": "a2055939zs-8.txt", "description": "S-8", "secsgml_size_bytes": 15501}]
{"company-data": {"conformed-name": "WESTERN SIERRA BANCORP", "cik": "0001072688", "assigned-sic": "6022", "irs-number": "680390121", "state-of-incorporation": "CA", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-66950", "film-number": "1698838"}, "business-address": {"street1": "3350 COUNTRY CLUB DRIVE", "street2": "SUITE 202", "city": "CAMERON PARK", "state": "CA", "zip": "95682", "phone": "5306775600"}, "mail-address": {"street1": "4011 PLAZA GOLDORADO", "city": "CAMERON PARK", "state": "CA", "zip": "95682"}}
Registration No. 33-______
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8
                             Registration Statement
                        Under the Securities Act of 1933

                             WESTERN SIERRA BANCORP
             (Exact Name of Registrant as Specified in its Charter)

                     CALIFORNIA                           68-0390121
         -------------------------------               -------------------
         (State or Other Jurisdiction of                 (I.R.S. Employer
          Incorporation or Organization)               Identification No.)

       3350 COUNTRY CLUB DRIVE, SUITE 202, CAMERON PARK, CALIFORNIA 95682
                    (Address of Principal Executive Offices)

                       WESTERN SIERRA BANCORP 401KSOP PLAN
                            (Full Title of the Plans)

               GARY D. GALL, PRESIDENT AND CHIEF EXECUTIVE OFFICER
       3350 COUNTRY CLUB DRIVE, SUITE 202, CAMERON PARK, CALIFORNIA 95682
                     (Name and Address of Agent for Service)

                                 (530) 677-5600
          (Telephone Number, including Area Code, of Agent for Service)

                                    Copy to:
                            Gary Steven Findley, Esq.
                        Gary Steven Findley & Associates
              1470 North Hundley Street, Anaheim, California 92806
                                 (714) 630-7136

                          CALCULATION OF REGISTRATION FEE
============================================================================================
Title of Each Class      Amount      Proposed Maximum       Proposed Maximum      Amount of
 Of Securities To         To Be       Offering Price           Aggregate        Registration
  Be Registered       Registered(a)    Per Share(b)          Offering Price          Fee
--------------------------------------------------------------------------------------------
Common stock         100,000 Shares       $14.90               $1,490,000          $372.50
(No Par Value)
============================================================================================
(a)      There are also registered hereby such indeterminate number of shares of
         common stock as may become issuable by reason of the operation of the
         anti-dilution or certain other provisions of the 401KSOP.

(b)      Estimated pursuant to Rule 457(h) solely for the purpose of computing
         the registration fee, utilizing $14.90 as the average of the bid and
         asked price of Western Sierra Bancorp's common stock as of August 2,
         2001.

================================================================================
PART II

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE

Western Sierra Bancorp (the "Registrant") hereby incorporates by reference the
documents listed below. All documents subsequently filed by the Registrant
pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Securities Exchange Act
of 1934 prior to the filing of a post-effective amendment which indicates that
all securities offered have been sold or which deregisters all securities then
remaining unsold, shall be deemed to be incorporated by reference herein and to
be a part hereof from the date of filing such documents.

(a)      The Registrant's annual report filed on Form 10-K for the year ended
         December 31, 2000.

(b)      The Registrant's quarterly reports filed on Form 10-Q for the quarter
         ended March 31, 2001.

(c)      The description of the Registrant's common stock is contained in its
         Registration Statement on Form S-4, file number 333-66675.

Any statement contained herein or in any document incorporated by reference
herein shall be deemed to be modified or superseded for purposes of this
Registration Statement to the extent that another statement contained herein or
in any other document subsequently filed, which also is incorporated by
reference herein, modifies or supersedes such statement. Any statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part of this Registration Statement.

ITEM 4.  DESCRIPTION OF SECURITIES

The Registrant's common stock is registered under Section 12 of the Exchange
Act.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL

Not Applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS

The Articles of Incorporation and Bylaws of the Registrant provide for
indemnification of agents including directors, officers and employees to the
maximum extent allowed by California law including the use of an indemnity
agreement. The Registrant's Articles further provide for the elimination of
director liability for monetary damages to the maximum extent allowed by
California law. The indemnification law of the State of California generally
allows indemnification in matters not involving the right of the corporation, to
an agent of the corporation if such person acted in good faith and in a manner
such person reasonably believed to be in the best interests of the corporation,
and in the case of a criminal matter, had no reasonable cause to believe the
conduct of such person was unlawful. California law, with respect to matters
involving the right of a corporation, allows indemnification of an agent of the
corporation, if such person acted in good faith, in a manner such person
believed to be in the best interests of the corporation and its shareholders;
provided that there shall be no indemnification for: (i) amounts paid in
settling or otherwise disposing of a pending

                                       2
action without court approval; (ii) expenses incurred in defending a pending
action which is settled or otherwise disposed of without court approval; (iii)
matters in which such person shall have been adjudged to be liable to the
corporation unless and only to the extent that the court in which the proceeding
is or was pending shall determine that such person is entitled to be
indemnified; or (iv) other matters specified in the California General
Corporation Law.

The Registrant's Bylaws provide that the Registrant shall to the maximum extent
permitted by law have the power to indemnify its directors, officers and
employees. The Registrant's Bylaws also provide that the Registrant shall have
the power to purchase and maintain insurance covering its directors, officers
and employees against any liability asserted against any of them and incurred by
any of them, whether or not the Registrant would have the power to indemnify
them against such liability under the provisions of applicable law or the
provisions of the Registrant's Bylaws. Each of the directors and executive
officers of the Registrant has an indemnification agreement with the Registrant
that provides that the Registrant shall indemnify such person to the full extent
authorized by the applicable provisions of California law and further provide
advances to pay for any expenses which would be subject to reimbursement.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED

Not Applicable.

ITEM 8.  EXHIBITS

 5.1   Opinion re: Legality
23.1   Consent of Perry-Smith LLP

The Registrant has submitted and received a favorable determination letter from
the IRS for the 401KSOP.

ITEM 9.  UNDERTAKINGS

The undersigned Registrant hereby undertakes:

(1)      To file, during any period in which offers or sales are being made, a
         post-effective amendment to this Registration Statement:

         (i)      To include any prospectus required by Section 10(a)(3) of the
                  Securities Act of 1933;

         (ii)     To reflect in the prospectus any facts or events arising after
                  the effective date of the Registration Statement (or the most
                  recent post-effective amendment thereof) which, individually
                  or in the aggregate, represent a fundamental change in the
                  information set forth in the Registration Statement;

                                       3
(iii)    To include any material information with respect to the plan
                  of distribution not previously disclosed in the Registration
                  Statement or any material change to such information in the
                  Registration Statement;

         provided, however, that paragraphs (1)(i) and (1)(ii) do not apply if
         the Registration Statement is on Form S-3 or Form S-8 and the
         information required to be included in a post-effective amendment by
         those paragraphs is contained in periodic reports filed with or
         furnished to the Commission by the Registrant pursuant to Section 13 or
         Section 15(d) of the Securities Exchange Act of 1934 that are
         incorporated by reference in the Registration Statement.

(2)      That, for the purpose of determining any liability under the Securities
         Act of 1933, each such post-effective amendment shall be deemed to be a
         new registration statement relating to the securities offered therein,
         and the offering of such securities at that time shall be deemed to be
         the initial bona fide offering thereof.

(3)      To remove from registration by means of a post-effective amendment any
         of the securities being registered which remain unsold at the
         termination of the offering.

The undersigned Registrant hereby undertakes that, for purposes of determining
any liability under the Securities Act of 1933, each filing of the Registrant's
annual report pursuant to Section 13(a) or Section 15(d) of the Securities
Exchange Act of 1934 (and, where applicable, each filing of an employee benefit
plan's annual report pursuant to Section 15(d) of the Securities Exchange Act of
1934) that is incorporated by reference in the Registration Statement shall be
deemed to be a new registration statement relating to the securities offered
therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

Insofar as indemnification for liabilities arising under the Securities Act of
1933 may be permitted to directors, officers and controlling persons of the
Registrant pursuant to the foregoing provisions, or otherwise, the Registrant
has been advised that in the opinion of the Securities and Exchange Commission
such indemnification is against public policy as expressed in the Act and is,
therefore, unenforceable. In the event that a claim for indemnification against
such liabilities (other than the payment by the Registrant of expenses incurred
or paid by a director, officer or controlling person of the Registrant in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Act and will be governed by the final adjudication of
such issue.

                                       4
SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized in the City of Cameron Park, State of California, on August 3, 2001.

                                        WESTERN SIERRA BANCORP

                                        /s/ GARY D. GALL
                                        ----------------------------------------
                                        Gary D. Gall
                                        President & CEO

Pursuant to the requirements of the Securities Act of 1933, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.
/S/ GARY D. GALL                                            ,  Director and Principal               August 3, 2001
-------------------------------------------------------------   Executive Officer
Gary D. Gall

 /S/ CHARLES W. BACCHI                                       ,  Chairman                              July 27, 2001
-------------------------------------------------------------
Charles W. Bacchi

 /S/ BARBARA L. COOK                                         ,  Director                              July 27, 2001
-------------------------------------------------------------
Barbara L. Cook

 /S/ LARY A. DAVIS                                           ,  Director                              July 30, 2001
-------------------------------------------------------------
Lary A. Davis

 /S/ WILLIAM J. FISHER                                       ,  Director                              July 27, 2001
-------------------------------------------------------------
William J. Fisher

 /S/ HOWARD JAHN                                             ,  Director                              July 27, 2001
-------------------------------------------------------------
Howard "Skip" Jahn
5
/S/ ALAN J. KLEINERT                                        ,  Director                              July 31, 2001
-------------------------------------------------------------
Alan J. Kleinert

 /S/ THOMAS MANZ                                             ,  Director                              July 27, 2001
-------------------------------------------------------------
Thomas Manz

 /S/ HAROLD S. PRESCOTT, JR.                                 ,  Director                              July 27, 2001
-------------------------------------------------------------
Harold S. Prescott, Jr.

 /S/ OSVALDO I. SCARIOT                                      ,  Director                              July 31, 2001
-------------------------------------------------------------
Osvaldo I. Scariot

 /S/ DAVID MERCK                                             ,  Principal Financial                  August 3, 2001
-------------------------------------------------------------   Officer
David Merck
6
EXHIBIT INDEX

 Exhibit
 NUMBER                                      DESCRIPTION
--------                   -----------------------------------------------

   5.1                     Opinion re: Legality

  23.1                     Consent of Perry-Smith LLP

                                       7