<PAGE>
 
                                                                    EXHIBIT 10.2


                                   CALMAT CO.

                             MASTER TRUST AGREEMENT

                            (EFFECTIVE JULY 1, 1996)

              (WACHOVIA BANK OF NORTH CAROLINA, N.A., "TRUSTEE")
<PAGE>
 
                               TABLE OF CONTENTS

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                                                                                                                                PAGE

<S>                                                                                                                             <C> 

RECITALS.....................................................................................................................   1

AGREEMENT....................................................................................................................   1

ARTICLE 1. -   DEFINITIONS...................................................................................................   1
        1.1  GENERAL.........................................................................................................   1
        1.2  OTHER DEFINITIONS...............................................................................................   3

ARTICLE 2. -   ESTABLISHMENT OF TRUST........................................................................................   4
        2.1  TRUST ESTABLISHED...............................................................................................   4
        2.2  COMMINGLED FUND.................................................................................................   4
        2.3  ALLOCATIONS AND SEGREGATED FUNDS................................................................................   4
        2.4  DISQUALIFIED PLANS..............................................................................................   5

ARTICLE 3. -   PORTFOLIOS AND INVESTMENT ADVISORS............................................................................   5
        3.1  PORTFOLIOS......................................................................................................   5
        3.2  INVESTMENT ADVISOR..............................................................................................   5
        3.3  COMMON, COLLECTIVE OR COMMINGLED FUNDS..........................................................................   5
        3.4  COMPANY STOCK FUNDS.............................................................................................   6
        3.5  REMOVAL OR RESIGNATION..........................................................................................   6
        3.6  ASSUMED INVESTMENT RESPONSIBILITY...............................................................................   6
        3.7  INVESTMENT POWERS...............................................................................................   6
        3.8  ALLOCATION OF GAINS OR LOSSES...................................................................................   7
        3.9  PARTICIPANT DIRECTED INVESTMENTS................................................................................   7

ARTICLE 4. -   POWERS AND DUTIES OF THE TRUSTEE..............................................................................   7
        4.1  GENERAL POWERS..................................................................................................   7
        4.2  SPECIFIC DUTIES.................................................................................................   7
        4.3  OTHER POWERS OF THE TRUSTEE.....................................................................................   8
        4.4  EMERGENCIES AND DELEGATES.......................................................................................  10
        4.5  TRUSTEE ACTIONS DURING TENDER OFFER.............................................................................  10
        4.6  TRUSTEE POWERS WITH RESPECT TO TENDER OFFER.....................................................................  13
        4.7  GROUP ANNUITIES.................................................................................................  13
        4.8  GENERAL DUTIES..................................................................................................  14
        4.9  GLOBAL CUSTODY..................................................................................................  14
        4.10 DISTRIBUTIONS...................................................................................................  15
        4.11 CASH RESERVES...................................................................................................  15

ARTICLE 5. -   CERTAIN DUTIES OF THE INVESTMENT COMMITTEE....................................................................  15
        5.1  GENERAL.........................................................................................................  15
        5.2  FIDUCIARY STANDARDS.............................................................................................  16

ARTICLE 6. -   TRUSTEE ACCOUNTING............................................................................................  16
        6.1  GENERAL TRUSTEE RESPONSIBILITIES................................................................................  16
        6.2  PERIODIC REPORT.................................................................................................  16
        6.3  APPROVAL OF ACCOUNTING..........................................................................................  17
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                                       i
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ARTICLE 7. -   TRUSTEE SUCCESSION....................................................................................   17
        7.1  RESIGNATION AND REMOVAL.................................................................................   17
        7.2  SUCCESSOR TRUSTEE.......................................................................................   17

ARTICLE 8. -   MISCELLANEOUS.........................................................................................   18
        8.1  WRITTEN DIRECTIONS......................................................................................   18
        8.2  ADVICE OF LEGAL COUNSEL.................................................................................   19
        8.3  SCOPE OF TRUSTEE RESPONSIBILITIES.......................................................................   19
        8.4  PARTIES TO JUDICIAL ACTIONS.............................................................................   19
        8.5  TRUSTEE FEES AND EXPENSES...............................................................................   19
        8.6  ALLOCATION OF FIDUCIARY RESPONSIBILITY..................................................................   20
        8.7  EXCLUSIVE PURPOSE RULE..................................................................................   20
        8.8  PARTIES' RELIANCE.......................................................................................   20
        8.9  NON-ALIENATION..........................................................................................   21

ARTICLE 9. -   ADOPTION OF AGREEMENT BY PLANS........................................................................   21

ARTICLE 10. -  AMENDMENT, TERMINATION AND INTERPRETATION.............................................................   21
        10.1 AMENDMENT...............................................................................................   21
        10.2 TERMINATION OF AGREEMENT AND TRUST......................................................................   22
        10.3 GOVERNING LAW...........................................................................................   22
        10.4 GENERAL INTERPRETATION..................................................................................   22

SCHEDULE A...........................................................................................................   24
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                                      ii
<PAGE>
 
                                  CALMAT CO.

                            MASTER TRUST AGREEMENT



     THIS MASTER TRUST AGREEMENT is made and entered into as of the _____ day of
June, 1996, by and between CALMAT CO. (the "Company"), and WACHOVIA BANK OF
NORTH CAROLINA, N.A. ("Wachovia" or the "Trustee").


                                   RECITALS:
                                   --------

     1.   The Company and certain of its subsidiaries and other affiliates have
adopted and maintain, for the exclusive benefit of certain of their employees,
plans that are intended to qualify under (S)401(a) of the Internal Revenue Code
of 1986, as amended (the "Code"). The Company desires to create a master trust
(the "Master Trust") to serve as the funding medium for certain of the
aforementioned plans and to appoint Wachovia as Trustee therefor. The Company
intends that the Master Trust qualify as a tax-exempt trust under (S)501(a) of
the Code.

     2.   This Master Trust Agreement is intended to effect the creation of the
Master Trust and to comply in all respects with the Employee Retirement Income
Security Act of 1974, as amended.

     3.   As of the date of the transfer of all assets which are attributable to
a plan subject to this Master Trust Agreement, this Master Trust Agreement shall
supersede the Trust Agreement previously established for such plan (the "Prior
Trust Agreements") and the Prior Trust Agreements shall have no further force or
effect.


                                   AGREEMENT
                                   ---------

     The Company and the Trustee do mutually covenant and agree as follows:


                                  ARTICLE 1.
                                  --------- 

                                  DEFINITIONS
                                  -----------

1.1  GENERAL.
     -------
     As a general rule, when a word or phrase is used in this Master Trust
Agreement with the initial letter capitalized, the word or phrase shall be given
the meaning ascribed to it in the Recitals or in this Section 1.1.
<PAGE>
 
      (a) "ADMINISTRATOR" - means the Company, the committee, or the individual
           -------------                                                       
or individuals which has the responsibility for administering each Plan.  The
Administrator shall be deemed for purposes of ERISA to be the Plan Administrator
and the named fiduciary for Plan administration.

      (b) "AFFILIATE" - means a subsidiary or affiliate of the Company.
           ---------                                                    

      (c) "BOARD OF DIRECTORS" - means the Board of Directors of the Company.
           ------------------                                                

      (d) "COMPANY STOCK" - means stock issued by the Company or any Affiliate
           -------------                                                      
that is a "qualifying employer security" within the meaning of (S) 407(d) (5) of
ERISA.

      (e) "COMPANY STOCK FUND" - means a Portfolio consisting, primarily, of
           ------------------                                               
Company Stock.

      (f) "COVERED INDIVIDUAL"  - means a participant, retired participant,
           ------------------                                               
vested former employee, surviving spouse, alternate payee, beneficiary or
contingent annuitant under the terms of the Plans.

      (g) "EFFECTIVE DATE" - means July 1, 1996, the date this Master Trust
           --------------                                                    
Agreement generally shall be effective . The effective date of the adoption of
the Master Trust Agreement by the Company or an Affiliate with respect to a
particular Plan shall be the date set forth with respect to the Plan on Schedule
A hereto.

      (h) "ERISA" - means the Employee Retirement Income Security Act of 1974,
           -----                                                              
as amended from time to time, and the regulations issued thereunder.

      (i) "EMPLOYER" - means the Company and each Affiliate that sponsors one or
           --------                                                             
more of the Plans.

     (j)  "INVESTMENT ADVISOR" - MEANS AN INVESTMENT MANAGER, AN
           ------------------                                   
Investment Trustee or, in those cases where the Investment Committee has assumed
investment responsibility for a Portfolio, the Investment Committee.

      (k) "INVESTMENT COMMITTEE"  -  means the committee, as constituted from
           --------------------                                            
time to time, which has the responsibility (i) for allocating the assets of the
Trust Fund among the Portfolios, (ii) for monitoring the diversification of any
investments of the Trust Fund, (iii) for assuring that no Plan violates any
provisions of ERISA limiting the acquisition or holding of securities or other
property of the Company and its Affiliates, (iv) for directing the investment of
a Portfolio, and (v) for the appointment and removal of Investment Advisors. The
Investment Committee shall consist of one or more members who shall be appointed
by the procedure

                                       2
<PAGE>
 
determined by the Board of Directors. Unless and until the Board of Directors
adopts a resolution providing otherwise, the Investment Committee shall be the
Finance Committee of the Board of Directors. The Investment Committee shall be
deemed, for purposes of ERISA, to be the named fiduciary for Plan investments.

      (l) "INVESTMENT MANAGER" - means, in accordance with (S)3(38) of ERISA, an
           ------------------                                                   
investment manager registered as an investment advisor under the Investment
Advisors Act of 1940, a bank as defined in that Act or an insurance company
qualified to manage, acquire or dispose of any asset of the Trust fund, which is
appointed by the Investment Committee to manage a Portfolio. The Trustee shall
have no responsibility to determine whether a person or entity acting as an
Investment Advisor meets or continues to meet this definition.

      (m) "INVESTMENT TRUSTEE" - means the Trustee appointed by the Investment
           ------------------                                                 
Committee to manage a Portfolio. The Investment Trustee must consent in writing
to its appointment.

      (n) "PLAN"  -  means each qualified plan satisfying the requirements of
           ----
(S)401(a) of the Code which has been adopted and is maintained by the Company or
by an Affiliated and for which this Master Trust Agreement has been adopted as
the funding medium in accordance with Section 9.  Each such Plan shall be
identified on Schedule A hereto which may be amended from time to time.

      (o) "PLAN ACCOUNT" - means the bookkeeping account maintained by the
           ------------                                                   
Trustee to record a Plan's interest in the Trust Fund.  The Plan Accounts are
bookkeeping accounts only.

      (p) "PORTFOLIO" - means one or more sub-accounts within the Master Trust,
           ---------                                             
each comprised of a portion of the assets of the Trust Fund. The number,
description and allocation of Portfolios shall be determined by the Investment
Committee as provided in Section 3 of this Master Trust Agreement.

      (q) "TRUST FUND" - means the assets of the trust under this Master Trust
           ----------                                                         
Agreement.

1.2  OTHER DEFINITIONS.
     ----------------- 

     Other definitions of terms of limited application are set within the
Sections to which such specialized definitions relate.

                                       3
<PAGE>
 
                                  ARTICLE 2.
                                  ----------

                             ESTABLISHMENT OF TRUST
                             ----------------------

2.1  TRUST ESTABLISHED.
     ----------------- 

     As of the Effective Date, the Company establishes with the Trustee, as a
funding medium for the Plans, a trust consisting of such sums of money or
property as from time to time shall be paid or transferred to the Trustee with
respect to the Plans, and such earnings, profits, increments, additions and
appreciation thereto and thereon as may accrue from time to time to be dealt
with in accordance with the terms of this Master Trust Agreement.

     Each Employer intends that this Trust shall constitute a part of its Plan
or Plans which will meet the requirements of ERISA and qualify under Code
(S)401(a), and thereby obtain tax exempt status under Code (S)501(a).

     The Trustee shall have no duty to collect or enforce payment to it of any
contributions, or to require any contributions to be made, and shall have no
duty to compute any amount to be paid to it nor to determine whether amounts
paid comply with the terms of a Plan.  The Trustee shall hold the Trust Fund
without distinction between principal and income.

2.2  COMMINGLED FUND.
     --------------- 

     The Trust Fund is made up of the assets of the Plans, which are being
commingled for investment purposes.  Although the assets of the Plans are being
commingled for investment purposes, each Plan shall continue to be separate plan
for all purposes, including (S) 414(1) of the Code.  Each separate Plan shall be
deemed to have an undivided interest in the Trust Fund except any such assets
required to be segregated by the provisions herein or by the provisions of the
Plan.  The interest of a Plan in the Trust Fund shall be used solely for the
benefit of the Covered Individuals of that Plan and to pay the expenses of that
Plan.  The portion of the Trust Fund attributable to one Plan may not be used
for the benefit of any other Plan.

2.3  ALLOCATIONS AND SEGREGATED FUNDS.
     -------------------------------- 

     The Trustee is directed to maintain a Plan Account for each Plan to record
the Plan's interest in the Trust Fund. If in the future the Trustee receives
written notice from the Investment Committee to segregate the assets
attributable to a Plan, the Trustee shall do so as soon thereafter as
practicable. Thereafter, the Trustee shall administer each such separate fund in
the manner provided in Article 4, or if so directed by the Investment Committee,
shall deliver the assets of any such separate fund to

                                       4
<PAGE>
 
such successor trustee or trustees as shall be designated by the Company.

2.4  DISQUALIFIED PLANS.
     ------------------ 

     In the event that the Internal Revenue Service determines that any Plan
hereunder is not a qualified plan within the meaning of (S) 401(a) of the Code,
and if such Plan is not amended so as to qualify under such section within the
period of time permitted by law for retroactive amendment of such Plan, then the
Company shall promptly direct the Trustee to segregate the assets of such Plan
pursuant to Section 2.3 above and, after making provision for the payment of
taxes and expenses, if any, attributable to such Plan, either direct the Trustee
to transfer such assets to a new trust established by the Company for that
purpose and/or, if permitted by the Plan and under applicable law, return all or
any part of such Plan to the Company or to an Affiliate.


                                  ARTICLE 3.
                                  ----------

                      PORTFOLIOS AND INVESTMENT ADVISORS
                      ----------------------------------

3.1  PORTFOLIOS.
     ---------- 

     The Trustee shall establish such number of Portfolios as the Investment
Committee from time to time may designate, to each of which shall be allotted
such assets of the Trust Fund as the Investment Committee shall designate.

3.2  INVESTMENT ADVISOR.
     ------------------ 

     The Investment Committee shall appoint an Investment Advisor for each
Portfolio. The Investment Advisor so appointed shall have the sole power and
duty to manage and direct the investment and reinvestment of the assets of such
Portfolio.   The Investment Advisor shall issue instructions to the Trustee in
writing, by facsimile, by electronic media or orally (to be followed promptly by
written confirmation) or in such manner as shall be agreed upon between the
Investment Advisor and the Trustee, subject to such guidelines and restrictions
as may be contained in the Plans, this Master Trust Agreement or any separate
agreement between the Investment Committee and such Investment Advisor.

3.3  COMMON, COLLECTIVE OR COMMINGLED FUNDS.
     -------------------------------------- 

     In the event that an Investment Advisor appointed hereunder is a bank or
trust company, the Investment Committee shall have full authority and discretion
to authorize such Investment Advisor to invest and reinvest all or any part of
its Portfolio in any common, collective or commingled trust fund maintained by
it as trustee for the investment of assets of trusts under plans which are
qualified

                                       5
<PAGE>
 
under (S) 401 (a) of the Code and exempt from taxation under (S) 501 (a) of the
Code.  The Trustee is authorized to enter into any and all agreements necessary
to accomplish these investments.  The Trustee shall have no liability for assets
held in a common, collective, or commingled fund (other than its own) invested
in accordance with this Section 3.3.

3.4  COMPANY STOCK FUNDS.
     ------------------- 

     One or more of the Portfolios may consist of Company Stock and such
Portfolio or Portfolios will occasionally be referred to in this Agreement as a
"Company Stock Fund" or the "Company Stock Funds".  Unless the Investment
Committee directs otherwise, the Investment Committee will be the Investment
Advisor for such Portfolio or Portfolios.  Pursuant to, and to the extent
provided in, Sections 4.5 and 4.6 of this Agreement and the provisions of any
applicable Plan, the Investment Committee hereby assigns to the Trustee the
responsibility for voting proxies and tendering Company Stock.  In performing
its duties with respect to a Company Stock Fund, the Trustee shall maintain the
strict confidentially of any instructions received from Covered Individuals in
accordance with the provisions of each relevant Plan.

3.5  REMOVAL OR RESIGNATION.
     ---------------------- 

     Upon removal or resignation of an Investment Advisor, and pending
appointment of a substitute Investment Advisor, the Trustee shall invest any
uninvested cash in interest bearing obligations having maturities of ninety days
OR. less, or in a common, collective or commingled fund comprised substantially
of such obligations, and shall not sell or liquidate any investments of the
Portfolio.

3.6  ASSUMED INVESTMENT RESPONSIBILITY.
     --------------------------------- 

     The Investment Committee, by giving written notice to the Trustee, may
assume investment responsibility for a Portfolio or for assets held in any cash
account maintained by the Trustee. With respect to assets or Portfolios over
which the Investment Committee has assumed investment responsibility, the
Trustee, acting only as directed by the Investment Committee, shall enter into
such agreements (including any agreement entering into a limited partnership, a
subtrust or a participation in real estate funds) as are necessary to facilitate
any investment. The Trustee shall not make any investment review of, or consider
the propriety of holding or selling, or vote any assets over which the
Investment Committee has assumed investment responsibility.

3.7  INVESTMENT POWERS
     -----------------

     With respect to each Portfolio, the Investment Advisor thereof (or with
respect to those assets or a cash account over which the

                                       6
<PAGE>
 
Investment Committee has assumed investment responsibility, the Investment
Committee) shall have the investment powers granted to the Trustee under
Sections 4.2 and 4.3, as limited by the agreement between the Investment
Committee and the Investment Advisor, as if all references therein to the
Trustee referred to the Investment Advisor (or Investment Committee).

3.8  ALLOCATION OF GAINS OR LOSSES.
     ----------------------------- 

     The income, expenses, gains, losses and investment appreciation or
depreciation with respect to a Portfolio shall be allocated to the Plan Accounts
of those Plans that have an interest in such Portfolio in accordance with such
written and nondiscriminatory rules and procedures as may be established by the
Trustee and approved by the Investment Committee from time to time. Unless the
Investment Committee indicates otherwise, each Plan shall have a proportional
interest in each Portfolio.

3.9  PARTICIPANT DIRECTED INVESTMENTS.
     -------------------------------- 

     If the terms of a Plan so permit, each Covered Individual in such Plan may
direct the investment of his accounts in any Portfolio established hereunder,
all  in accordance with the provisions of the relevant Plan.  The Investment
Committee or its designee shall inform the Trustee of the investment directions
of the Covered Individual made in accordance with the terms of such Plan, and
the Trustee shall transfer assets between and among the Portfolios to the extent
necessary to effectuate such instructions in accordance with the Plans.  The
Trustee shall not be liable for any loss resulting from such investments as are
authorized and directed by the Covered Individual or by the Investment Committee
pursuant to the directions of Covered Individuals.


                                  ARTICLE 4.
                                  ----------

                       POWERS AND DUTIES OF THE TRUSTEE
                       --------------------------------

4.1  GENERAL POWERS.
     --------------

     Pursuant to the terms of this Master Trust Agreement and ERISA, the Trustee
shall hold, manage as directed, care for and protect the assets of the Trust
Fund.  The Trustee shall maintain appropriate auditing and security safeguards
for the assets of the Trust Fund.

4.2  SPECIFIC DUTIES.
     --------------- 

     The Trustee shall have the following duties in respect of each Portfolio,
subject to the direction of the Investment Committee or
an Investment Advisor:   

                                       7
<PAGE>
 
     (a)  to receive and deliver securities and cash from and to purchasers,
sellers, brokers and their agents in accordance with the instructions of the
Investment Advisor;

     (b)  to collect interest and dividends, and the principal of called or
matured securities;

     (c)  to invest cash automatically in a short-term investment common trust
fund maintained by the Trustee, a commercial paper pooled note or such other
short-term instrument;

     (d)  to buy and sell fractional shares and rights as instructed by the
Investment Advisor;

     (e)  to give the Investment Advisor timely advice of each transaction
affecting the Portfolio, in writing, electronically, or by such other means as
may be mutually acceptable to the Trustee and the Investment Advisor;

     (f)  to render to the Investment Committee, and to the Investment Advisor,
such reports as the Investment Committee may from time to time require,
including a monthly valuation of each Portfolio, reports of transactions,
capital gains and losses, dividends, interest income, stock dividends, splits,
rights, offerings, calls on bonds, bonds maturing, quarterly investment review
valuation reports and annual summary accounting reports;

     (g)  to credit dividends and interest to the account of the Portfolio when
received, and process any required claims for such items;

     (h)  to cause securities to be reregistered in a manner satisfactory to the
Trustee; and

     (i)  to forward to the investment advisor proxy statements and other
notices received.

4.3  OTHER POWERS OF THE TRUSTEE.
     --------------------------- 

     Subject to the provisions of Article 3 and Section 4.2, and the directions
of the Investment Committee or an Investment Advisor, the Trustee also is
authorized and empowered:

     (a)  to sell, exchange, convey, transfer or otherwise dispose of any
property held by it, by private contract or at public auction, and the person
dealing with the Trustee shall not be bound to see to the application of any
money or property paid or delivered to the Trustee in connection with any such
sale or other disposition, or to inquire into the validity or propriety of any
such sale or other disposition;

                                       8
<PAGE>
 
     (b)  to exercise the voting rights of any stocks, bonds or other securities
except that the Trustee shall not vote or tender any Company Stock or other
employer securities to which any Covered Individual is entitled to direct the
vote under any Plan except in accordance with the instructions of the Covered
Individual and the provisions of the Plan; to give general or special proxies or
powers of attorney with or without power of substitution; to exercise any
conversion privileges, subscription rights or other options and to make any
payments incidental thereto; to consent to or otherwise participate in corporate
reorganizations or other changes affecting corporate securities and to delegate
discretionary powers and to pay any assessments or charges in connection
therewith; and generally to exercise any of the powers of an owner with respect
to stocks, bonds, securities or other property held in the Trust Fund;

     (c)  to make, execute, acknowledge and deliver any and all documents of
transfer and conveyance and any and all other instruments that may be necessary
or appropriate to carry out the powers herein granted;

     (d)  to register any security held in the Trust Fund administered hereunder
in its own name or in the name of a nominee and to hold any security in bearer
form, but the books and records of the Trustee shall at all times show that all
such securities are part of the trust administered hereunder;

     (e)  to employ suitable agents and counsel and to pay their reasonable
expenses and compensation;

     (f)  to compromise, arbitrate or otherwise adjust, settle or defend claims
in favor of or against the trust administered hereunder;

     (g)  to lend stock certificates or other securities held by the Trustee to
a broker-dealer registered under the Securities Exchange Act of 1934 or to a
bank and invest the collateral provided by such borrower pursuant to a written
agreement with the Investment Committee which satisfies the requirements of
Department of Labor Prohibited Transaction Exemption 81-6 or any successor or
additional exemption;

     (h)  to write options against any securities or other property held by the
Trustee or other forms of options directly related to any such options
outstanding as directed by the Investment Advisor;

     (i)  to invest in financial futures, to establish accounts with futures
commission merchants, to transfer assets to such futures commission merchants,
and to execute any and all documents or instruments and perform any and all
other acts necessary or appropriate to invest in financial futures as directed
by the Investment Advisor;

                                       9
<PAGE>
 
     (j)  to invest in savings accounts or certificates of deposit including
those of the Trustee;

     (k)  to invest, reinvest, or hold all or any part of a Portfolio in
"qualifying employer securities" or "qualifying employer real property", as such
terms are defined in Section 407(d) of ERISA;

     (1)  to lend money to Plan participants in accordance with the provisions
of a Plan;

     (m)  to invest all or any part of a Portfolio in any common, collective or
commingled fund maintained by a bank, specifically including but not by way of
limitation, the Plan of Wachovia Corporation Diversified Funds for Retirement
Trusts for the investment of assets of trusts for plans which are qualified
under (S) 401(a) and the trust is exempt from tax under (S) 501(a) of the Code;
during such period of time as an investment exists in such common, collective or
commingled trust, the trust document establishing such trust shall constitute a
part of this Master Trust; and

     (n)  to perform every act in the management of the Trust Fund that
individuals may perform in the management of like property owned by them free of
any trust and to exercise every power with respect to each item of property in
the Trust Fund, real and personal, which individual owners of like property can
exercise.

No enumeration of specific powers herein shall be construed as a limitation on
the general powers of the Trustee.

4.4  EMERGENCIES AND DELEGATES.
     ------------------------- 

     In case of any emergency, the Trustee may act in the absence of directions
from the Investment Advisor having the power and duty to direct the Trustee with
respect to the matter involved and shall incur no liability in so acting except
to the extent it fails to comply with the requirements of ERISA.

     By written notice to the Trustee, the Administrator, any Investment Advisor
or the Investment Committee may authorize the Trustee to act on matters in the
ordinary course of the business of the Trust or on specific matters upon the
signature of its delegate.

4.5  TRUSTEE ACTIONS DURING TENDER OFFER.
     ----------------------------------- 

     In the event of any transaction involving one or more offers to purchase
Company Stock which is evidenced by the filing of a Statement on Schedule 14D-l
with the Securities and Exchange Commission ("SEC") or any other similar
transaction (such transaction referred to herein as a "Tender Offer" and the
date of

                                       10
<PAGE>
 
filing with the SEC referred to herein as the "Filing Date"), paragraphs (a)
through (j) shall apply:

     (a)  Notwithstanding anything in the Plan to the contrary, after the Filing
Date --

          (i)  No option to receive cash instead of Company Stock under any of
     the Plans' distribution provisions shall be honored unless the
     Administrator otherwise directs, and the Company Stock portion of any
     distribution shall be limited to amounts of Company Stock credited, on or
     before the Filing Date, to the accounts of the Covered Individual in
     question; and

          (ii) No participant election to invest additional amounts in a Company
     Stock Fund shall be honored after the Filing Date. The portion of any
     account which otherwise would have been invested in a Company Stock Fund
     shall instead be invested in a fixed income fund as directed by the
     Investment Committee.

     (b)  The Company shall promptly, and at its own expense, engage the
services of an Outside Independent Plan Administrator ("OIPA") experienced in
administration of like plans.  The OIPA shall, on a standby basis, perform those
functions (and only those functions) which are set forth in paragraphs (c)
through (h) and which are necessary to preserve the strict confidentiality of
(i) the instructions received from Covered Individuals by the Trustee and (ii)
any other information which would reveal whether or not a Covered Individual's
accounts' proportionate share of a Company Stock Fund (such proportionate share
of any Company Stock Fund referred to herein as his "Company Stock Share") has
or has not been tendered.

     (c)  (i)  the trustee shall seek by mail confidential written instructions
     from each Covered Individual as to whether his Company Stock Share should
     be tendered pursuant to the Tender Offer.

          (ii) The Trustee shall distribute to each such Covered Individual, as
     soon as possible after the Filing Date, copies of all relevant material
     filed with the SEC with respect to the Tender Offer. The Trustee shall
     request that the filing party pay the reasonable expenses of the Trustee in
     connection therewith. The Trustee shall have the power to require that
     payment for such distribution of materials be made in advance, and in any
     event the Trustee shall be entitled to reimbursement out of the Trust Fund
     for its reasonable out-of-pocket expenses for services rendered in the
     performance of its responsibility and duties described in this Section

                                       11
<PAGE>
 
     (including any expenses not reimbursed by the filing party).

          (iii)  The identity of each covered individual and the amount of his
     Company Stock Share shall be determined from the list of Covered
     Individuals delivered to the Trustee by the Administrator or if an QIPA has
     previously been appointed under this Section and if the Administrator does
     not have such information because of the confidentiality rules contained
     herein, by that OIPA. The Administrator or QIPA, as applicable, shall take
     all such reasonable steps as may be necessary to provide the Trustee with
     information which is as current as possible.

     (d)  Each Covered Individual shall be entitled to instruct the Trustee,
with respect to his Company Stock Share, either

          (i)  to tender all (but not less than all) of such Company Stock
     Share, or

          (ii) not to tender any such Company Stock Share, and the Trustee shall
follow such instructions.

     (e)  The Trustee shall make such follow-up efforts, through additional
mailings, bulletins to be posted in areas where notices are normally posted by
the Company and otherwise, as it finds to be reasonable under the time
constraints and other circumstances at hand, to assure that materials referred
to in paragraph (c) have been received by Covered Individuals, and obtain
instructions from Covered Individuals, who have not otherwise responded to the
Trustee's request for instructions. The Company shall provide full cooperation
to the Trustee in this regard.

     (f)  If, after the Trustee has made the follow-up effort set out in
paragraph (e), a Covered Individual does not respond to the Trustee's request
for instructions, the nonresponding Covered Individual shall be deemed to have
made the election set out in paragraph (d) (ii).

     (g)  The Trustee shall make its own investment decision, as a fiduciary, as
to whether to tender the Company Stock Shares attributable to any forfeited and
unreallocated accounts.

     (h)  If some but less than all of the Covered Individuals' Company Stock
Shares are tendered and sold or exchanged by the Trustee, the QIPA shall
thereafter perform all functions with respect to all accounts as constituted on
or after the Filing Date. Records and administration for all contributions after
the Filing Date shall be maintained by the Administrator unless that duty has
also been delegated to the OIPA.

                                       12
<PAGE>
 
     (i)  At such time as events (e.q., termination of a Plan or placement of
                                  ----
all Plan assets in investments other than Company Stock) occur which obviate the
need for the OIPA in order to preserve confidentiality, the services of the OIPA
shall be terminated and, to the extent necessary to preserve confidentiality,
its records relating to the Plan shall be destroyed.

     (j)  The proceeds of the sale of any Company Stock sold by the Trustee
pursuant to an instruction from a Covered Individual in accordance with
paragraph (d) (i) shall be invested in accordance with the provisions of the
relevant Plan.

4.6  TRUSTEE POWERS WITH RESPECT TO TENDER OFFER.
     ------------------------------------------- 

     Except as provided in Section 4.5(g), the Trustee's functions under
Section 4.5 are and shall be solely custodial and ministerial. The Trustee shall
have no powers or duties with respect to a Tender Offer except as expressly set
forth in Section 4.5 and specifically shall have no power or duty --

     (a)  to manage or to control the assets of the Plan in connection with any
Tender offer (except as provided in Section 4.5(j));

     (b)  to evaluate any Tender Offer;

     (c)  to advise any Participant, as to the fairness or other features of a
Tender Offer;

     (d)  to tender or vote any Company Stock held under a Plan, except as
instructed by Covered Individuals; or

     (e)  to monitor or police the activities of the tendering entity or the
Company in promoting or resisting any Tender Offer; provided, however, that if
the Trustee becomes aware of any such activity which reasonably appears to the
Trustee to be coercive or misleading in any material way, the Trustee shall
promptly demand that the offending party take appropriate corrective action.
The Trustee shall, in the event of refusal or failure of such party to take such
corrective action as the Trustee reasonably finds appropriate, communicate with
Covered Individuals as to the matter.

4.7  GROUP ANNUITIES.
     --------------- 

     When and to the extent directed by the Investment Committee, the Trustee
shall invest all or a portion of the Trust Fund in a group annuity or guaranteed
investment contract issued by a legal reserve life insurance company.  The
Trustee may request and the Company shall provide an enforceable
indemnification against any losses, damages or expenses (including legal fees
and expenses of defense) incurred by the Trustee with respect to such
investment,

                                       13
<PAGE>
 
4.8  GENERAL DUTIES.
     -------------- 

     Notwithstanding any other provisions of this Master Trust Agreement, the
Trustee shall have the responsibility of discharging its duties with respect to
the Trust Fund solely in the interest of the Covered Individuals and for the
exclusive purpose of providing benefits under the Plans and defraying the
reasonable expense of administering the Trust Fund. The Trustee shall exercise
the care, skill,  prudence,  and diligence under the  circumstances  then
prevailing that a prudent man acting in a like capacity and familiar with such
matters would use in the conduct of an enterprise of a like character and with
like aims.  Moreover, the Trustee, to the extent it is responsible for
investment of the Trust Fund, shall diversify such investments so as to
minimize the risk of large losses, unless under the circumstances it is clearly
prudent not to do so, and shall administer the Trust Fund in accordance with the
terms and provisions of this Master Trust Agreement insofar as this Master Trust
Agreement is consistent with the provisions of applicable law.

4.9  GLOBAL CUSTODY.
     -------------- 

     The Trustee shall have no discretion, duty or responsibility with  respect
to  the  selection  or  supervision  of  foreign investments, including the
qualification of such investments as appropriate for the Trust Fund and shall
have no liability for the performance of such investments.

     The Trustee may utilize the services of a depository, sub-custodian, other
agents or sub-agents with respect to the custody and processing of foreign
investments. Such depository, sub-custodian and/or other agents or sub-agents
may be located in countries other than the United States and may in turn employ
additional sub-custodians and/or other agents and sub-agents who may be located
in countries other that the United States. At all times, Trustee shall maintain
the assets with an indicia of ownership in the United States.

     The Trustee shall bear no risk with respect to investment in foreign
securities related to investing in securities or the holding of cash denominated
in a currency other than that of the United States.

     The Trustee shall not be liable for any action taken, or any failure to
take any action required to be taken hereunder or otherwise to fulfill its
obligations hereunder (including without limitation the failure to receive or
deliver securities or the failure to receive or make any payment) in connection
with foreign investments in the event and to the extent that the taking of
action or such failure arises out of or is caused by any cause whatsoever beyond
its reasonable control.

                                       14
<PAGE>
 
     The Trustee shall exercise reasonable care in the selection and retention
of a depository, sub-custodians and/or other agents and sub-agents, but if the
Trustee has exercised reasonable care it shall otherwise have no
responsibilities for the performance of such depository, sub-custodians and/or
other agents and sub-agents with respect to foreign investments.  In the event
of claim or loss with respect to foreign investments, the Trustee will exercise
reasonable efforts to effect a recovery but does not guarantee the results.  The
cost and expense of its efforts will be charged to the Master Trust.  In no
event will the Trustee be liable for any claim or loss or related expense in
connection with the investment, custody and processing of foreign securities in
the absence of negligence or misconduct on the part of the Trustee itself.

4.10 DISTRIBUTIONS.
     -------------  

     The Trustee shall make distributions from the Trust Fund to such persons,
in such amounts, at such time and in such manner as the appropriate
Administrator from time to time shall direct in writing or in such other manner
as the parties may mutually agree. The Trustee shall have no responsibility (i)
to ascertain whether any direction received by the Trustee from an Administrator
in accordance with the preceding sentence is proper and in compliance with the
terms of a Plan or, (ii) to see to the application of any distribution.  The
Trustee shall not be liable for any distribution made in good faith without
actual notice or knowledge of the changed condition or status of any recipient.
If any distribution made by the Trustee is returned unclaimed, the Trustee shall
notify the Administrator and shall dispose of the distribution as the
Administrator shall direct.

4.11 CASH RESERVES.
     ------------- 

     Notwithstanding the provisions of Article 3, upon direction of the
Investment Committee, the Trustee shall retain all or any portion designated by
the  Investment Committee of  the  cash distributions  received  under  the
Plan  to  meet  anticipated requisitions or orders of the Investment Committee,
and shall invest such contributions temporarily in the manner referred to in
Section 4.2(c).


                                  ARTICLE 5.
                                  ----------

                  CERTAIN DUTIES OF THE INVESTMENT COMMITTEE
                  ------------------------------------------

5.1  GENERAL.
     -------

     The Investment Committee shall:

     (a)  anticipate the need for cash distribution pursuant to the terms of the
Plan and make such arrangements with each Investment

                                       15
<PAGE>
 
Advisor and the Trustee, or otherwise, as may be needed to provide cash
sufficient to satisfy such need;

     (b)  designate one or more individuals who shall have authority to give and
receive communications on behalf of the Investment Committee;

     (c)  cause each Investment Advisor to confirm oral instructions given to
the Trustee immediately thereafter in writing, electronically or in such other
manner as is mutually acceptable to the Trustee and the Investment Advisor;

     (d)  establish investment guidelines for the Trust Fund as a whole and for
each Portfolio so that investments are diversified to minimize the risk of large
losses, unless it is prudent not to do so under the circumstances, and

     (e)  designate the Investment Advisor, Trustee or other proper party to
exercise the voting rights of any stocks, bonds or other securities held in the
Trust.  Unless the Investment Committee reserves to itself or assigns to the
Trustee the power to exercise such voting rights, all voting rights will be
exercised by the Investment Advisor.  Such reservation or assignment shall be
made in the agreement appointing the Investment Advisor or in an addendum or
amendment thereto.

5.2  FIDUCIARY STANDARDS.
     -------------------- 

     The Investment Committee shall exercise all of its duties hereunder in
accordance with the fiduciary standards of ERISA.


                                  ARTICLE 6.
                                  ----------

                              TRUSTEE ACCOUNTING
                              ------------------

6.1  GENERAL TRUSTEE RESPONSIBILITIES.
     -------------------------------- 

     The Trustee shall maintain accounts of all receipts and disbursements,
including contributions, distributions, purchases, sales and other transactions
of the Trust Fund.  The accounts, and the books and records relating thereto,
shall be open to inspection and audit at all reasonable times by any person or
persons designated by the Investment Committee or entitled thereto under
ERISA.

6.2  PERIODIC REPORT.
     --------------- 

     Within thirty (30) days after the close of each fiscal year of the Trust
Fund and of any other period agreed upon by the Trustee and the Investment
Committee, the Trustee shall render to the Investment Committee a statement of
account for the Trust Fund for

                                       16
<PAGE>
 
the period commencing with the close of the last preceding period and a list
setting forth, as of the close of the current period, each asset of the Trust
Fund and its cost and fair market value. The Trustee shall determine fair market
value for each asset; provided, however, the Trustee shall rely conclusively
upon the determination of the issuing insurance company with respect to the fair
market value of each insurance contract and, when the Trustee determines that an
asset does not have a readily ascertainable fair market value, the Trustee may
rely upon the Investment Advisor of the Portfolio to which such asset is
allocated with respect to the determination of the fair market value of such
asset, and the Trustee shall have no responsibility with respect thereto.

6.3  APPROVAL OF ACCOUNTING.
     ---------------------- 

     An accounting of the Trustee may be approved by the Investment Committee by
written notice delivered to the Trustee or by failure to object to the
accounting by written notice delivered to the Trustee within six (6) months of
the date upon which the accounting was delivered to the Investment Committee.
The approval of an accounting shall constitute a full and complete discharge to
the Trustee as to all matters set forth in that accounting as if the accounting
had been settled by a court of competent jurisdiction in an action or proceeding
to which the Trustee, the Company and the Investment Committee were parties. In
no event shall the Trustee be precluded from having its accountings settled by a
judicial proceeding. Nothing in this Section shall relieve the Trustee of any
responsibility, or liability for any responsibility, under ERISA, including,
without limitation, any responsibility or liability arising from the misfeasance
or malfeasance of the Trustee.


                                  ARTICLE 7.
                                  ---------- 

                              TRUSTEE SUCCESSION
                              ------------------

7.1  RESIGNATION AND REMOVAL.
     ----------------------- 

     The Trustee may resign at any time by giving written notice to the
Investment Committee, or the Investment Committee may remove the  Trustee at any
time by giving written notice to the Trustee. Any such resignation or removal
shall be effective thirty (30) days after the date of the Trustee's resignation
or receipt of the notice of removal or at such earlier date as the Trustee and
the Investment Committee may agree.

7.2  SUCCESSOR TRUSTEE.
     ----------------- 

     In the case of the resignation or removal of the Trustee, the Investment
Committee shall within thirty  (30)  days appoint a successor Trustee, who shall
qualify as such by delivering a

                                       17
<PAGE>
 
written acceptance of the terms of the Master Trust Agreement to the Company,
the Employers, the Investment Committee and the retiring Trustee. As soon as
practicable thereafter, the retiring Trustee shall deliver the assets of the
Trust Fund to the successor Trustee but may reserve such reasonable amount as
the Trustee may deem necessary for outstanding and accrued charges against the
Trust Fund.

     The successor Trustee, and any successor to the trust business of the
Trustee by merger, consolidation or otherwise, shall have all of the powers
given the originally named Trustee except those contained in Section 4.2(j).
Except as otherwise provided in ERISA, no successor Trustee shall be personally
liable for any act or omission of any predecessor.  Except as otherwise
provided in ERISA, the receipt of the assets of the Trust Fund by the successor
Trustee and the approval of the Trust Fund by the successor Trustee and the
approval  of  the Trustee's  final  accounting by the Investment Committee in
the manner provided in Article 6 shall constitute a full and complete discharge
of the Trustee.

     Any corporation into which the Trustee may be merged or with which it may
be consolidated, or any corporation resulting from any merger or consolidation
to which the Trustee may be a party, or any Corporation succeeding to the
business of the Trustee or to which substantially all of the assets of the
Trustee may be transferred, shall be the successor of the Trustee hereunder
without the execution or filing of any paper and without any further action on
the part of the parties hereto, with like effect as if such successor trustee
had originally been named trustee herein; and in any such event, and except as
may be otherwise provided in ERISA, it shall not be necessary for the Trustee or
any successor Trustee to give notice to any person having an interest in this
Master Trust Agreement or in the Master Trust hereby created or in any of' the
property held by the Trustee hereunder and the requirements of any and all
statutes and laws (other than ERISA) that notice shall be given by the Trustee
in any such case are hereby waived.


                                  ARTICLE 8.
                                  ----------

                                 MISCELLANEOUS
                                 -------------

8.1  WRITTEN DIRECTIONS
     ------------------

     Any action required to be taken by the Company or any Affiliate shall be by
resolution of its Board of Directors or by written direction of such one or more
of its officers or agents as shall be designated by resolution of its Board of
Directors to act for the company or affiliate.   The trustee may rely upon a
certified copy of such a resolution filed with the trustee and shall have no
responsibility for any action taken by the trustee in accordance with any such
resolution or direction.

                                       18
<PAGE>
 
     The Company shall certify to the Trustee the names of the Administrators
and of the Investment Committee acting from time to time, and the Trustee shall
not be charged with knowledge of a change in the Administrators or in the
membership of the Investment Committee until so notified by the Company. Any
action required to be taken by the Administrators or the Investment Committee
shall be by written direction of such one or more of its members as shall be
designated to act.  The Trustee may rely upon an instrument of designation
signed by the Administrators  or  the  Investment Committee as provided and
filed with the Trustee and shall have no responsibility for any action taken by
the Trustee in accordance with any such written direction.

8.2  ADVICE OF LEGAL COUNSEL.
     -----------------------

     The Trustee may consult with legal counsel, who also may be counsel for the
Company, with respect to its responsibilities under this Master Trust Agreement
and shall be fully protected in acting or refraining from acting in reliance
upon the written advice of the Company's legal counsel.

8.3  SCOPE OF TRUSTEE RESPONSIBILITIES.
     --------------------------------- 

     In no event shall the terms of any Plan, either expressly or by
implication, be deemed to impose upon the Trustee any power or responsibility
other than those set forth in this Master Trust Agreement or in ERISA.  The
Trustee may assume, until advised to the contrary, that each Plan and the Trust
Fund is qualified under (S)401(a) and exempt from taxation under (S)501(a) of
the Code.  The Trustee shall be accountable for contributions made to a Plan and
included among the assets of the Trust Fund but shall have no responsibility to
determine whether the contributions comply with the provisions of the Plan or
ERISA.

8.4  PARTIES TO JUDICIAL ACTIONS.
     --------------------------- 

     In any judicial proceeding to settle the accounts of the Trustee, the
Company and the Investment Committee shall be the only necessary parties.  In
any other judicial proceeding with respect to the Trustee or the Trust Fund, the
Trustee, the Company and each affected Employer shall be the only necessary
parties.  No Covered Individual shall be entitled to any notice of process.  A
final judgment in any such proceeding shall be binding upon the parties to the
proceeding and all Covered Individuals.

8.5  TRUSTEE FEES AND EXPENSES.
     ------------------------- 

     The expenses incurred by the Trustee in the performance of its duties,
including fees for legal services rendered to the Trustee, such compensation to
the Trustee as may be agreed upon in writing from time to time by the Investment
Committee and the Trustee, and all other proper charges and disbursements of the
Trustee, shall be

                                       19
<PAGE>
 
paid from the assets of the Trust Fund unless the Company in its discretion
chooses to pay such expenses from its assets or unless otherwise specifically
provided in a Plan; provided, however, the foregoing is not intended to preclude
the Company from paying other proper expenses of administering and operating the
Plan and obtaining reimbursement from the assets of the Trust Fund.  All taxes
of any nature whatsoever that may be imposed under existing or future laws upon
or in respect of the Trust Fund or the income therefrom shall be paid from the
Trust Fund.

8.6  ALLOCATION OF FIDUCIARY RESPONSIBILITY.
     -------------------------------------- 

     The Company and the Affiliates have allocated fiduciary responsibility
among various persons in accordance with the terms of the Plans and this Master
Trust Agreement.  Except with respect to such fiduciary responsibility as is
allocated to the Trustee, the Trustee shall have no responsibility for any error
or loss that may result by reason of the exercise or non-exercise of that
fiduciary responsibility by the person to whom it is allocated.

     The Company shall indemnify the Trustee, directly from the Company's own
assets (including the proceeds of any insurance policy the premiums of which are
paid from the Company's own assets), from and against any and all claims,
demands, losses, damages, expenses (including, by way of illustration and not
limitation, reasonable attorneys' fees and other legal and litigation costs),
judgments and liabilities arising from, out of, or in connection with the
actions or omissions of the Company, any Affiliate, the Administrators, the
Investment Committee, the Investment Advisors, or any other fiduciary appointed
by any of the foregoing, expect when determined to be due to the Trustee's
negligence or willful misconduct and only to the extent consistent with ERISA.

8.7  EXCLUSIVE PURPOSE RULE.
     ---------------------- 

     No part of the Trust Fund shall be diverted to any purpose other than the
exclusive benefit of the Covered Individuals or, except as otherwise permitted
under the affected Plan and ERISA, shall be remitted to the Company or an
Affiliate.

8.8  PARTIES' RELIANCE.
     ----------------- 

     Any person dealing with the Trustee shall have no obligation to see to the
application of any money paid or property delivered to the Trustee or to inquire
into the provisions of this Master Trust Agreement of any Plan or into the
Trustee's authority thereunder or compliance therewith. Any such person may rely
upon the statement of the Trustee that the Trustee is acting in accordance with
this Master Trust Agreement.

                                       20
<PAGE>
 
8.9  NON-ALIENATION.
     -------------- 

     Except as may be permitted under any Plan or required under the Code or
ERISA, no interest of a Covered Individual in the Trust Fund, any Plan or
any distribution therefrom shall be subject to the claim of any creditor, any
spouse for alimony or support, or others,  or to  legal process;  and no such
interest may be voluntarily or involuntarily alienated or encumbered.


                                  ARTICLE 9.
                                  ----------

                        ADOPTION OF AGREEMENT BY PLANS
                        ------------------------------

     Any qualified plan satisfying the requirements of (S)401 (a) of the Code
which has been adopted and is maintained by the Company or an Affiliate may
become a Plan and use the Master Trust as a funding medium, provided the Trustee
and the Company approve such use.  To effect such arrangement the Board of
Directors of the sponsor of such a plan (or the Board of Trustees of a jointly
administered collectively bargained plan) shall adopt resolutions appointing the
Trustee as trustee for such plan, adopting the Master Trust Agreement and
specifying that the Master Trust shall serve as the funding medium for the plan.
The Company or Trustee may require any other reasonable procedures which it
deems helpful as condition for such a plan to become a Plan.  The name of each
Plan and the date it acquires Plan status hereunder shall be set forth on
Schedule A, attached hereto and made a part hereof.


                                  ARTICLE 10.
                                  -----------

                   AMENDMENT, TERMINATION AND INTERPRETATION
                   -----------------------------------------

10.1 AMENDMENT.
     --------- 

     The Company reserves the right at any tine and from time to time by action
of its Board of Directors or of the Investment Committee as its agent, to amend
any or all of the provisions of this Agreement by notice thereof in writing
delivered to the Trustee; provided, however, that no such amendment which
affects the rights, duties or responsibilities of the Trustee may be made
without its consent; and provided, further, that no such amendment shall
authorize or permit at any time, prior to the satisfaction of all liabilities
for benefits under a Plan, any part of the corpus or income of the Trust Fund
with respect to such Plan to be used for or diverted to purposes other than for
the exclusive benefit of Covered Individuals under such Plan and payment of
expenses of such Plan.

                                       21
<PAGE>
 
10.2 TERMINATION OF AGREEMENT AND TRUST.
     ---------------------------------- 

     This Master Trust Agreement shall terminate in its entirety when there is
no asset remaining in the Trust Fund.

     This Master Trust Agreement shall terminate with respect to a Plan by
action of the Company or an Affiliate responsible for making contributions with
respect to such Plan, by the Plan's loss of its qualified status under (S)401(a)
of the Code, by the Company's sale or dissolution of the Affiliate responsible
for making contributions to such Plan, or by the failure of a corporate
successor to the Company to elect to become a party to this Master Trust
Agreement.  Upon termination with respect to a Plan, the Trustee shall
distribute the portion of the Trust Fund allocated to such Plan in the manner
directed by the Investment Committee (which distribution may be in cash, in kind
or a combination thereof), as the Trustee and the Investment Committee shall
agree; provided, the Trustee shall be entitled to prior receipt of such rulings
and determinations from such administrative agencies as it may deem necessary or
advisable to assure itself that the distribution directed is in accordance with
law and will not subject the Trust Fund or the Trustee to liability; and,
provided further, the Trustee may reserve such reasonable amount as the Trustee
may deem necessary for outstanding and accrued fees, expenses and charges
against the portion of the Trust Fund allocated to such Plan. Nothing herein is
intended to prevent the Trustee from returning assets to the Company or an
Affiliate for a proper reversion under
ERISA.

10.3 GOVERNING LAW.
     ------------- 

     To the extent, if any, not governed by ERISA, the validity of this Master
Trust Agreement shall be determined by, and this Master Trust Agreement shall be
governed, administered, construed and enforced according to, the laws of the
State of California.  In case of any conflict between the provisions of any Plan
and of this Master Trust Agreement, the provisions of such Plan shall govern.

10.4 GENERAL INTERPRETATION.
     ---------------------- 

     The masculine pronouns include the feminine wherever used, and the feminine
include the masculine wherever used.  The singular includes the plural and the
plural the singular in all cases where such meanings would be appropriate.  The
headings of sections and subsections are included solely for convenience of
reference, and in the event of conflict between such headings and the text of
the Master Trust Agreement, the text shall control.

                                       22
<PAGE>
 
     IN WITNESS WHEREOF, the Company and the Trustee have caused their
respective duly authorized officers to execute this Master Trust Agreement all
as of the day and year first above written.

CALMAT CO.                                   ATTEST:

By: /s/ Paul Stanford                        By: _________________________
   ---------------------------------------
   Executive Vice President-Administration, 

Title:  General Counsel & Secretary          Title: ______________________
        ----------------------------------


WACHOVIA BANK OF NORTH CAROLINA, N.A.        ATTEST:

By: /s/ [Signature illegible]                By: /s/ [Signature illegible]
   ---------------------------------------      --------------------------

Title: Vice President                        Title: Assistant Secretary
      ------------------------------------         -----------------------   

                                       23
<PAGE>
 
                                  SCHEDULE A


<TABLE> 
<CAPTION> 
            Plan Name                                       Effective Date*
            ---------                                       ---------------
  <S>                                                       <C> 
  The Thrift and Profit Sharing                             July 1, 1996   
  Retirement Plan and The Money Purchase                                   
  Pension Plan for Employees of CalMat                                     
  Co.                                                                     
                                                                
  The CalMat Co. Hourly Retirement Plan                     July 1, 1996
  and Hourly Savings Plan
</TABLE> 


*Effective date of participation in Master Trust.

                                       24
<PAGE>
 
                                  SCHEDULE A

<TABLE>
<CAPTION>
PLAN NAME                                   EFFECTIVE DATE*
---------                                   ---------------
<S>                                         <C> 
THE THRIFT AND PROFIT SHARING                JULY 1, 1996
RETIREMENT PLAN AND THE MONEY PURCHASE
PENSION PLAN FOR EMPLOYEES OF CALMAT CO.

THE CALMAT CO. HOURLY RETIREMENT PLAN       JULY 1,1996
AND HOURLY SAVINGS PLAN

THE CALMAT CO. BARGAINING UNIT              JULY 1, 1996
RETIREMENT PLAN.
</TABLE>

*Effective date of participation in Master Trust.
<PAGE>
 
                            CALIFORNIA ALL-PURPOSE

                                ACKNOWLEDGMENT
--------------------------------------------------------------------------------


State of California           )
County of Los Angeles         )

On June 28, 1996, before me, Maureen A. Bayon, A Notary Public, personally
appeared Paul Stanford - Executive Vice President,

[x]  personally known to me

     OR                                              

[_]  proved to me on the basis of satisfactory evidence

to be the person whose name is subscribed to the within instrument and
acknowledged to me that he executed the same in his authorized capacity, and
that by his signature on the instrument the person, or the entity upon behalf of
which the person acted, executed the instrument.


WITNESS my hand and official seal.                [Notary Seal]


/s/ Maureen A. Bayon
---------------------------
Signature of Notary