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                                                           EXHIBIT 10.23


                      SUPPLEMENTAL RETIREMENT BENEFIT AGREEMENT


    THIS AGREEMENT (the "Agreement") is effective as of the 3rd day of August,
1990, by and between Morrison Knudsen Corporation, a Delaware corporation (the
"Company"), and ROBERT A. TINSTMAN (the "Executive").


                                      RECITALS:

    Company adopted the Morrison Knudsen Corporation Retirement Plan, effective
January 1, 1988 (the "Plan") for the benefit of its employees.  Company now
desires to provide for the payment of additional retirement benefits to
Executive so that his total retirement benefits can be determined without regard
to certain limitations imposed by law on the Plan.

    NOW, THEREFORE, it is agreed,


                                          I.
                               PURPOSE OF THE AGREEMENT

    1.01.  PURPOSE.  Company desires to recognize the value of Executive's
services to Company and to encourage his continued service with Company by
making adequate provision for his future retirement security.  This Agreement is
necessitated by certain compensation and benefit limitations imposed by the
Employee Retirement Income Security Act of 1974, as amended ("ERISA") and by
Sections 401(a)(17) and 415 of the Internal Revenue Code of 1986, as amended
(the "Code").


                                         II.
                              INCORPORATION OF THE PLAN

    2.01   PLAN.  The Plan, as amended through the date of adoption of this
Agreement, is attached hereto as Exhibit A and incorporated herein.  Any
amendment made to the Plan by Company shall be incorporated by reference as of
its effective date and form a part of this Agreement.  All capitalized terms
used in this Agreement shall have the meanings assigned to them under the Plan
unless otherwise provided herein.


                                         III.
                                  AMOUNT OF BENEFIT

    3.01   THE ADDITIONAL BENEFIT.  The benefit payable to Executive or his
beneficiary or beneficiaries under this Agreement (the "Additional Benefit")
shall be the actuarial equivalent of the excess, if any, of:


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    (a)    the Retirement Income benefit which would have been payable to
           Executive or his beneficiary or beneficiaries under the Plan, if the
           provisions of the Plan were administered without regard to the
           maximum retirement benefit limitation of Sections 415 of the Code
           and the maximum compensation limitation of Section 401(a)(17) of the
           Code,

    over

    (b)    the Retirement Income benefit which is, in fact, payable to
           Executive or his beneficiary or beneficiaries under the Plan.

    3.02   ACTUARIAL EQUIVALENT.  If the Additional Benefit is payable in any
form other than a 5-year certain and straight life annuity over the lifetime of
Executive, or if it commences at anytime prior to Executive's Normal Retirement
Date under the Plan, prior to payment, the Additional Benefit shall be adjusted
in accordance with the Plan's factors for determining actuarial equivalence in
the same manner that it would be adjusted if paid under the Plan.

    3.03   CONDITION FOR BENEFITS.  If Executive is not entitled to a benefit
under the Plan, Executive shall not be entitled to the Additional Benefit.


                                         IV.
                                 PAYMENT OF BENEFITS

    4.01   TERMINATION OF EMPLOYMENT.  Upon Executive's termination of
employment for any reason other than "Cause" (as defined in Section 4.02 below),
Executive or his beneficiary or beneficiaries shall be entitled to receive the
Additional Benefit in the same form and at the same time or times as benefits
are payable under the Plan.

    4.02   CAUSE DEFINED.  For purposes of Section 4.01 above, "Cause" shall
mean Executive's:  (i) conviction of any criminal violation involving
dishonesty, fraud or breach of trust; (ii) willful engagement in any misconduct
in the performance of his duties that materially injures Company, monetarily or
otherwise; (iii) performance of any act which, if known to Company's customers,
clients or stockholders would materially and adversely affect Company's
business; or (iv) willful and substantial nonperformance of assigned duties
(other than any such failure resulting from Executive's incapacity due to
physical or mental illness) which has continued after Company's Board of
Directors has given written notice of such nonperformance to Executive, which
notice specifically identifies the manner in which the Board of Directors
believes that Executive has not substantially performed his duties and which
indicates the Board of Directors intention to terminate Executive's employment
because of such nonperformance.  For purposes of clauses (ii) and (iv) of this
Section 4.02, no act or omission on Executive's part shall be deemed "willful"
if committed or omitted in good faith and with a reasonable belief his action
was in the best interest of Company.


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    4.03   APPROVAL OF COMPANY.  An election made by Executive under the Plan
with respect to the form, or the date for commencement of payment shall not
apply to the Additional Benefit, if any, unless approved in writing by the
Executive Compensation Committee of Company's Board of Directors (the
"Committee").


                                          V.
                                  EXECUTIVE'S RIGHTS

    5.01   UNSECURED OBLIGATION.  The Additional Benefit shall be a general,
unsecured obligation of Company.  Company's obligation under this Agreement
shall not (i) impose any obligation upon the Plan's Trust Fund, (ii) be paid
from the Plan's Trust Fund, or (iii) have any effect upon the Plan or the
payment of benefits from the Plan's Trust Fund.


                                         VI.
                                      AMENDMENT

    6.01   AMENDMENT.  This Agreement may be amended only by an instrument in
writing signed by the parties hereto.


                                         VII.
                              RESTRICTIONS ON ASSIGNMENT

    7.01   ALIENATION.  The interest of Executive or his beneficiary or
beneficiaries may not be sold, transferred, assigned or encumbered in any
manner, either voluntarily or involuntarily, and any attempt to so alienate,
sell, transfer, assign, pledge, encumber or charge the same shall be null and
void.  No benefit hereunder, before it is paid, shall be liable for or subject
to the debts, contracts, liabilities, engagements or torts of any person to whom
such benefits or funds are payable, nor shall it be subject to garnishment,
attachment or other legal or equitable process.


                                        VIII.
                                 NATURE OF AGREEMENT

    8.01   BENEFIT TRUST AGREEMENT.  Company shall attach this Agreement, as
amended from time to time, to Exhibit A, as amended from time to time, of the
Morrison Knudsen Corporation Benefit Trust Agreement ("Benefit Trust Agreement).

    8.02   UNFUNDED AGREEMENT.  Except in the case of a Potential Change in
Control (as defined in Section 1.13 of the Benefit Trust Agreement), Company
shall not be required to set aside any funds or other assets to be used to
satisfy its obligation under this Agreement.


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    8.03   NO SECURITY INTEREST.  It is the intent of Company and Executive
that the amounts, if any, set aside shall not create a "funded" trust within the
meaning of the Code or ERISA and that such amounts, if any, shall remain at all
times subject to the claims of Company's general creditors.  Accordingly,
Company shall not create a security interest in the amounts, if any, set aside
in favor of Executive or his beneficiary or beneficiaries, or any other
creditor.

    8.04   DISTRIBUTION UNDER BENEFIT TRUST AGREEMENT.  Distributions made
under the Benefit Trust Agreement to Executive or his beneficiary or
beneficiaries with respect to this Agreement shall, to the extent of such
distributions, satisfy Company's obligation under this Agreement.


                                         IX.
                                 CONTINUED EMPLOYMENT

    9.01   NO ENLARGEMENT OF RIGHTS.  This Agreement shall not be deemed to
constitute a contract of employment between the parties hereto, nor shall any
provision hereof be construed as restricting the right of Company to discharge
Executive or restrict the right of Executive to terminate his employment.


                                          X.
                 BINDING ON COMPANY, EXECUTIVES AND THEIR SUCCESSORS

    10.01  SUCCESSORS.  This Agreement shall be binding upon and inure to the
benefit of Company, its successors and assigns and Executive, his heirs,
executors, administrators and legal representatives.  If Company merges or
consolidates with any other corporation, the term "Company" as used in this
Agreement shall be deemed to refer to such successor or survivor corporation.


                                         XI.
                                   CLAIMS PROCEDURE

    11.01  CLAIMS PROCEDURE.  Except in the case where benefits are being paid
to Executive or his beneficiary or beneficiaries under the Benefit Trust
Agreement, the claims procedure set forth in the Plan shall govern any claim for
benefits under this Agreement; provided, however, wherever the term "Committee"
appears in the Plan, the term "Executive Compensation Committee of Company's
Board of Directors" shall be substituted therefor.  Where benefits are being
paid under the Benefit Trust Agreement, the claims procedure set forth in
Sections 4.02 and 7.03 of the Benefit Trust Agreement shall govern any claim
regarding such benefits.


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                                         XII.
                                    COMMUNICATIONS

    12.01  COMMUNICATIONS.  Any notice or communication hereunder shall be made
in writing and may either be delivered personally or sent by first class mail to
the most recent address provided by each party to the other in writing.


                                        XIII.
                                  GENERAL PROVISIONS

    13.01  UNCLAIMED BENEFIT.  Executive shall keep Company informed of his
current address and the current address of his beneficiary or beneficiaries.
Company shall not be  obligated to search for the whereabouts of Executive or
his beneficiary or beneficiaries.  If the location of Executive or his
beneficiary or beneficiaries is not made known to Company within three (3) years
after the date on which payment of Executive's benefit under this Agrement would
otherwise commence, then Company shall have no further obligation to pay any
benefit hereunder to Executive or his beneficiary or beneficiaries and
entitlement to such benefit shall lapse.

    13.02  GENDER AND NUMBER.  Words used in the masculine gender shall be
construed as though they were also used in the feminine gender in all cases
where they would so apply;  words used in the singular form, shall be construed
as though they were also used in the plural form in all cases where they would
so apply; words used in the plural form, shall be construed as though they were
also used in the singular form in all cases where they would so apply.

    13.03  WITHHOLDING TAXES.  To the extent required by law, Company may
withhold from any payments due hereunder all applicable federal, state or local
taxes.

    13.04  HEADINGS.  The headings and subheadings of this Agreement have been
inserted for convenience only and form no part of this Agreement.

    13.05  COUNTERPARTS.  This Agreement may be executed in any number of
counterparts, each of which shall be deemed to be an original, but all of which
together constitute but one instrument, which may be sufficiently evidenced by
any counterpart.

    13.06  GOVERNING LAW.  This Agreement shall be construed in accordance with
and governed by the laws of the State of Idaho.


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    IN WITNESS WHEREOF, Company and executive have executed this Agreement the
day and year first above written.



ATTEST:                                MORRISON KNUDSEN CORPORATION



/s/ Stephen G. Hanks                   BY:  /s/ Michael J. Shirley
-----------------------------------        -------------------------------
Stephen G. Hanks                            Michael J. Shirley



                                       EXECUTIVE

                                       /s/ Robert A. Tinstman
                                       -----------------------------------
                                       Robert A. Tinstman


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                                       EXHIBITS


                       THE REGISTRANT AGREES TO PROVIDE TO THE
                  SECURITIES AND EXCHANGE COMMISSION, UPON REQUEST,
                            COPIES OF THE EXHIBITS HERETO.


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