Document:

<PAGE>

                                                                 EXHIBIT 10.37.1

                              AMENDMENT NO. 4 TO
                              ------------------
                        PURCHASE AND SALE AGREEMENT AND
                        -------------------------------
                           JOINT ESCROW INSTRUCTIONS
                           -------------------------
                           AND SIDE LETTER AGREEMENT
                           -------------------------

          THIS AMENDMENT NO. 4 TO PURCHASE AND SALE AGREEMENT AND JOINT ESCROW
INSTRUCTIONS AND SIDE LETTER AGREEMENT (this "Amendment") is made and entered
                                              ---------
into and effective as of November 30, 1999, by and between KAISER VENTURES INC.,
a Delaware corporation and KAISER STEEL LAND DEVELOPMENT INC., a Delaware
corporation (collectively, "Seller"), and ONTARIO VENTURES I, LLC, a Delaware
                            ------
limited liability company ("Buyer").
                            -----

                                   RECITALS
                                   --------

          A.   WHEREAS, Buyer and Seller have entered into that certain Purchase
and Sale Agreement and Joint Escrow Instructions dated as of October 19, 1999 as
amended by that certain Amendment No. 1 to Purchase and Sale Agreement and Joint
Escrow Instructions and Side Letter Agreement dated as of November 2, 1999, by
that certain Amendment No. 2 to Purchase and Sale Agreement and Joint Escrow
Instructions and Side Letter Agreement dated as of November 12, 1999, and by
that certain Amendment No. 3 to Purchase and Sale Agreement and Joint Escrow
Instructions and Side Letter Agreement dated as of November 19, 1999
(collectively, the "Purchase Agreement"); and
                    ------------------

          B.   WHEREAS, pursuant to the Purchase Agreement, Buyer and Seller
have entered into that certain Side Letter Agreement dated as of October 19,
1999 which side letter was amended by the amendments to the Purchase Agreement
described in Recital A above (as amended, the "Side Letter Agreement"), the form
                                               ---------------------
of which was attached to the Purchase Agreement as Exhibit DD; and
                                                   ----------

          C.   WHEREAS, Buyer and Seller desire to again amend the Side Letter
Agreement and the Purchase Agreement, as more particularly set forth herein.

          NOW, THEREFORE, in consideration of the mutual covenants and
agreements herein contained and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, Buyer and Seller
hereby agree as follows:

                                   AGREEMENT
                                   ---------

     1.   The Purchase Agreement is hereby amended as follows:

          A.   The "Contingency Date" (as defined in Section 1.11 of the
Purchase

                                       1
<PAGE>

Agreement) shall be February 4, 2000; provided, however, that if Buyer does not
cancel Escrow prior to February 4, 2000, and if the sum of Seventy-Five Thousand
Dollars is therefore released to Seller as set forth in Section 3.1.2 below,
then the Contingency Date shall automatically be extended to March 6, 2000.

          B.   Section 3.1.2 of the Agreement is hereby revised to read in full
as follows:

               3.1.2   Disposition of Deposit. In the event this Agreement is
                       ----------------------
     terminated for any reason prior to 5:00 p.m. on December 16, 1999 or
     pursuant to Section 6.1 or 13 hereof, the Deposit (including all interest
     thereon) shall be fully refunded to Buyer by Escrow Holder.   On December
     17, 1999, Seventy-Five Thousand Dollars ($75,000) of the Deposit shall be
     released to Seller and become nonrefundable to Buyer, but shall be
     applicable to the Purchase Price.  The balance of the Deposit, including
     all interest thereon, shall be fully refundable to Buyer by Escrow Holder
     in the event that this Agreement is terminated for any reason prior to the
     Contingency Date.  On February 4, 2000, an additional Seventy-Five Thousand
     Dollars ($75,000) of the Deposit shall be released to Seller and become
     nonrefundable to Buyer, but shall be applicable to the Purchase Price.  The
     remaining balance of the Deposit, including all interest thereon, shall be
     fully refunded to Buyer by Escrow Holder in the event that this Agreement
     is terminated for any reason prior to the Contingency Date.  Following the
     Contingency Date, in the event this Agreement is terminated or the Close of
     Escrow fails to occur by reason of Buyer's default hereunder, the entire
     Deposit (including all interest thereon) shall be held by Escrow Holder for
     the benefit of Seller and paid to Seller pursuant to Section 6.2 hereof.
     In the event this Agreement is terminated by reason of Seller's default or
     the Close of Escrow fails to occur by reason of Seller's default hereunder,
     then the Deposit (including all interest thereon and including any portion
     of the Deposit which was released to Seller) shall be returned to Buyer.
     Upon the Close of Escrow, the entire Deposit (including all interest
     thereon) shall be paid to Seller and shall be credited towards the payment
     of the Purchase Price.

          C.   Section 14.1.3 is hereby added to the Purchase Agreement to read
in full as follows:

               14.1.3  Agreement Re Tamkin. Buyer and Seller have each received
                       -------------------
     a letter from lawyers representing the Tamkin entities asserting various
     claims.  During the term of this Agreement and if Buyer acquires the
     property as provided herein Buyer (and Buyer's members and their
     affiliates) and Seller each agree that none of them will enter into or
     propose a settlement with Tamkin Capital Partners, Jeffrey H. Tamkin and
     related parties arising out of Buyer's purchase of the Real Property
     without (i) trying to effect a settlement of all of their respective
     disputes with such entities, (ii) seeking and obtaining the consent

                                       2
<PAGE>

     of the other Party to any such settlement (which consent shall not be
     unreasonably withheld), and (iii) being certain that no such settlement
     would preclude the settling Party from being a witness on behalf of any
     non-settling Party; in the event that a Party desires to settle and the
     other Party does not consent to such settlement, the Party not consenting
     to the settlement shall thereafter advance and pay all costs and expenses
     of the defense, including but not limited to, all reasonable attorneys'
     fees, expert witness fees, and other similar items, of the Party desiring
     to settle the claims against it and the Party desiring not to settle shall
     indemnify and hold harmless the Party desiring to settle as to any amount
     or obligation that the Party desiring to settle may be obligated to pay or
     perform in excess of the amount or obligation for which the matter could
     have been settled.

          D.   Seller and Buyer hereby agree that Exhibits D, H, I, J, P, R, S,
T, U, V, W, X, AA and BB attached hereto shall be deemed final and shall be
attached to, deemed to be part of and included in the Purchase Agreement.

          E.   Exhibit O is hereby omitted from the Purchase Agreement and all
               ---------
reference to Exhibit O in the Side Letter Agreement and the Purchase Agreement
             ---------
shall hereinafter constitute references to Exhibit R.
                                           ---------

          F.   The date by which Buyer and Seller shall negotiate in reasonable
good faith to finalize the remaining provisions of Exhibits E, G, K, L, M, M-I,
Q, Y and CC and attach them to the Purchase Agreement shall be further extended
to February 4, 2000.  During the time between the date hereof and February 4,
2000, the Parties shall diligently use reasonable good faith to finalize such
Exhibits.  In the event that all of such Exhibits are not so agreed upon by such
date, then either Buyer or Seller may terminate the Purchase Agreement, in which
event the provisions of Section 4.7 thereto shall apply except that any portion
of the Deposit theretofore released to Seller shall not be refunded to Buyer.

          G.   Section 4.11 shall be added to the Purchase Agreement to read in
full as follows:

               4.11  Approval of Financial Abilities of Buyer. Seller shall
                     ----------------------------------------
     have until February 4, 2000 to satisfy itself as to the matters set forth
     in Section 4.10 of the Purchase Agreement.  If Seller is not satisfied as
     to such matters, then the Purchase Agreement shall be terminated, in which
     event the provisions of Section 4.7 of the Purchase Agreement shall apply
     except that any portion of the Deposit theretofore released to Seller shall
     not be refundable to Buyer.

          H.   Amendment to Section 4.9. Section 4.9 of the Purchase Agreement
               ------------------------
is hereby amended by extending the date by which Buyer and Seller shall
negotiate in good faith to finalize the IT Contract and performance bond
therefor or each of the Insurance Policies so that they are acceptable to Seller
to February 4, 2000.  In the event that all of such Insurance Policies,

                                       3
<PAGE>

the IT Contract and the performance bond therefor are not so agreed upon by such
date, then either Buyer or Seller may terminate the Purchase Agreement, in which
event the provisions of Section 4.7 thereto shall apply except that any portion
of the Deposit theretofore released to Seller shall not be refundable to Buyer.

     2.   No Other Amendments. Except as expressly amended hereby, the Purchase
          -------------------
Agreement and the Side Letter Agreement are unchanged and in full force and
effect.

                                       4
<PAGE>

     3.   Counterparts. This Amendment may be executed in counterparts, each of
          ------------
which shall be an original and all of which taken together shall constitute the
same instrument.

          IN WITNESS WHEREOF, the parties hereto have executed this Amendment as
of the dates written below.

BUYER:                        ONTARIO VENTURES I, LLC, a Delaware limited
-----                             liability company

                                  By:  LandBank Environmental Properties, LLC, a
                                       Delaware limited liability company, its
                                       Manager

                                       By:  LandBank, Inc., a Delaware
                                            corporation, its managing member

                                       By:  /s/ Stuart L. Miner
                                            ---------------------------
Date Executed:    12/17/99             Its: Principal
               --------------               ---------------------------

SELLER:                           KAISER VENTURES INC., a Delaware corporation
------

                                  By:  /s/ Terry L. Cook
                                       --------------------------------
Date Executed:    12/17/99        Its: Sr. Vice President
               --------------          --------------------------------

                                  KAISER STEEL LAND DEVELOPMENT INC., a Delaware
                                  corporation

                                  By:  /s/ Terry L. Cook
                                       --------------------------------
Date Executed:    12/17/99        Its: Vice President
               --------------          --------------------------------

                                       5
<PAGE>

RECEIVED AND ACCEPTED THIS ____ DAY OF __________________, 1999.

ESCROW HOLDER:

CHICAGO TITLE INSURANCE COMPANY

By:________________________
Its:_______________________

                                       6
<PAGE>

                              Exhibits Available
                              ------------------
                                  to the SEC
                                  ----------
                             Upon Written Request
                             --------------------

                                       7<PAGE>

                                                                 EXHIBIT 10.37.2

                              AMENDMENT NO. 5 TO
                              ------------------
                        PURCHASE AND SALE AGREEMENT AND
                       --------------------------------
                           JOINT ESCROW INSTRUCTIONS
                           -------------------------
                           AND SIDE LETTER AGREEMENT
                           -------------------------

          THIS AMENDMENT NO. 5 TO PURCHASE AND SALE AGREEMENT AND JOINT ESCROW
INSTRUCTIONS AND SIDE LETTER AGREEMENT (this "Amendment") is made and entered
                                              ---------
into and effective as of February 4, 2000, by and between KAISER VENTURES INC.,
a Delaware corporation and KAISER STEEL LAND DEVELOPMENT INC., a Delaware
corporation (collectively, "Seller"), and ONTARIO VENTURES I, LLC, a Delaware
                            ------
limited liability company ("Buyer").
                            -----

                                   RECITALS
                                   --------

          A.   WHEREAS, Buyer and Seller have entered into that certain Purchase
and Sale Agreement and Joint Escrow Instructions dated as of October 19, 1999 as
amended by that certain Amendment No. 1 to Purchase and Sale Agreement and Joint
Escrow Instructions and Side Letter Agreement dated as of November 2, 1999, by
that certain Amendment No. 2 to Purchase and Sale Agreement and Joint Escrow
Instructions and Side Letter Agreement dated as of November 12, 1999, by that
certain Amendment No. 3 to Purchase and Sale Agreement and Joint Escrow
Instructions and Side Letter Agreement dated as of November 19, 1999 and by that
certain Amendment No. 4 to Purchase and Sale Agreement and Joint Escrow
Instructions and Side Letter Agreement dated as of November 30, 1999
(collectively, the "Purchase Agreement"); and
                    ------------------

          B.   WHEREAS, pursuant to the Purchase Agreement, Buyer and Seller
have entered into that certain Side Letter Agreement dated as of October 19,
1999 which side letter was amended by the amendments to the Purchase Agreement
described in Recital A above (as amended, the "Side Letter Agreement"), the form
                                               ---------------------
of which was attached to the Purchase Agreement as Exhibit DD; and
                                                   ----------

          C.   WHEREAS, Buyer and Seller desire to again amend the Side Letter
Agreement and the Purchase Agreement, as more particularly set forth herein.

          NOW, THEREFORE, in consideration of the mutual covenants and
agreements herein contained and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, Buyer and Seller
hereby agree as follows:

                                   AGREEMENT
                                   ---------

     1.   Amendments.  The Purchase Agreement and Side Letter Agreement are
          ----------
hereby amended as follows:

                                       1
<PAGE>

          A.   The "Contingency Date" (as defined in Section 1.11 of the
Purchase Agreement) shall be extended further to March 6, 2000 and the sum of
Seventy-Five Thousand Dollars is therefore released to Seller as set forth in
Section 3.1.2.

          B.   The date by which Buyer and Seller shall negotiate in reasonable
good faith to finalize the remaining provisions of Exhibits E, G, K, L, M, M-I,
Q, Y and CC and attach them to the Purchase Agreement shall be further extended
to March 6, 2000. During the time between the date hereof and March 6, 2000, the
Parties shall diligently use reasonable good faith to finalize such Exhibits. In
the event that all of such Exhibits are not so agreed upon by such date, then
either Buyer or Seller may terminate the Purchase Agreement, in which event the
provisions of Section 4.7 thereto shall apply except that any portion of the
Deposit theretofore released to Seller shall not be refunded to Buyer.

          C.   Section 4.9 of the Purchase Agreement is hereby amended by
extending the date by which Buyer and Seller shall negotiate in good faith to
finalize the IT Contract and performance bond therefor or each of the Insurance
Policies so that they are acceptable to Seller to March 6, 2000. In the event
that all of such Insurance Policies, the IT Contract and the performance bond
therefor are not so agreed upon by such date, then either Buyer or Seller may
terminate the Purchase Agreement, in which event the provisions of Section 4.7
thereto shall apply except that any portion of the Deposit theretofore released
to Seller shall not be refundable to Buyer.

     2.   Buyer's Financial Abilities. Seller hereby confirms that it has
          ---------------------------
satisfied itself as to the Financial Abilities of Buyer set forth in Section
4.10 of the Purchase Agreement.

     3.   No Other Amendments. Except as expressly amended hereby, the Purchase
          -------------------
Agreement and the Side Letter Agreement are unchanged and in full force and
effect.

     4.   Counterparts. This Amendment may be executed in counterparts, each of
          ------------
which shall be an original and all of which taken together shall constitute the
same instrument.

          IN WITNESS WHEREOF, the parties hereto have executed this Amendment as
of the dates written below.

                                       2
<PAGE>

Buyer:                        ONTARIO VENTURES I, LLC, a Delaware limited
-----                             liability company

                                  By:  LandBank Environmental Properties, LLC, a
                                       Delaware limited liability company, its
                                       Manager

                                       By:  LandBank, Inc., a Delaware
                                            corporation, its managing member

                                            By:  /s/ Stuart L. Miner
                                                 -----------------------------
Date Executed:    02/10/00                  Its: Principal
               --------------                    -----------------------------

Seller:                           KAISER VENTURES INC., a Delaware corporation
------

                                  By:  /s/ Lee R. Redmond
                                       ---------------------------------------
Date Executed:    02/08/00        Its: Sr. Vice President
               --------------          ---------------------------------------

                                  KAISER STEEL LAND DEVELOPMENT INC., a Delaware
                                  corporation

                                  By:  /s/ Lee R. Redmond
                                       ---------------------------------------
Date Executed:     02/08/00       Its: Vice President
               ---------------         ---------------------------------------

RECEIVED AND ACCEPTED THIS ____ DAY OF _________________, 2000.

ESCROW HOLDER:

CHICAGO TITLE INSURANCE COMPANY

By:_______________________
Its:______________________

                                       3

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00004-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00004-of-00352.parquet"}]]