<PAGE>

                                                                    EXHIBIT 4.23

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              This Supplemental Indenture is, among, other things,
                             A MORTGAGE OF CHATTELS


                         Southern California Gas Company


                                       TO


                     Wells Fargo Bank, National Association
                        (formerly American Trust Company)
                                     TRUSTEE


                                ----------------


                             SUPPLEMENTAL INDENTURE
                   To original Indenture dated October 1, 1940


                                ----------------


                          DATED AS OF FEBRUARY 1, 1981



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<PAGE>

                                TABLE OF CONTENTS

                                                                            PAGE
                                                                            ----

PARTIES ...................................................................   1

RECITALS:
     Execution of Original Indenture and Supplements thereto ..............   1
     Recording of Original Indenture and Supplements thereto ..............   1
     Bonds heretofore issued ..............................................   3
     Creation of Series N, due 2001 .......................................   3
     Lien on After Acquired Property ......................................   3
     Purpose of Supplemental Indenture ....................................   4
     Fulfillment of conditions precedent ..................................   4
     Consideration and Authorization ......................................   5

GRANTING CLAUSES:
     Real property in California counties specified in Schedule A .........   6
     Plant, system and utilities in specified counties and elsewhere ......   6
     Other properties now or hereafter owned ..............................   7
     Excepted properties ..................................................   7

HABENDUM AND DECLARATION OF TRUST .........................................   8


                                   ARTICLE I.

               AMOUNT, FORM, NUMBERING, DENOMINATION, TRANSFER AND
                    EXCHANGE OF BONDS OF SERIES N, DUE 2001.

SECTION 1.01.  Authorized amount of bonds of Series N, due 2001 ...........   8

SECTION 1.02.  Bonds of Series N, due 2001; issuable as fully registered
                 bonds; form of registered bonds and certificate ..........   9

SECTION 1.03.  Exchangeability of bonds ...................................  14

SECTION 1.04.  Offices or agencies for payment, registration, transfer and
                 exchange of bonds of Series N, due 2001 ..................  15

SECTION 1.05.  Certain conditions as to transfer, etc., of bonds of
                 Series N, due 2001 .......................................  15
<PAGE>

                                       ii

                                                                            PAGE
                                                                            ----
                                   ARTICLE II
                INTEREST, MATURITY DATE, REDEMPTION, SINKING FUND
                          AND CERTAIN OTHER PROVISIONS.

SECTION 2.01.  Interest rate, maturity date and places and medium of
                 payment ..................................................  15

SECTION 2.02.  Redemption of bonds of Series N, due 2001 ..................  15

SECTION 2.03.  Sinking Fund for bonds of Series N, due 2001 ...............  17

SECTION 2.04.  Other provisions of bonds of Series N, due 2001 ............  17


                                  ARTICLE III.
                               SUNDRY PROVISIONS.

SECTION 3.01.  Trustee not responsible for recitals, recordation of
                 Supplemental Indenture as required by law ................  17

SECTION 3.02.  Date of Supplemental Indenture and bonds of Series N,
                 due 2001, are dates of identification ....................  18

SECTION 3.03.  Supplemental Indenture deemed to be part of Original
                 Indenture ................................................  18

SECTION 3.04.  Trustee accepts trusts on same terms expressed in Original
                 Indenture ................................................  18

SECTION 3.05.  Execution of Supplemental Indenture in counterpart .........  18

TESTIMONIUM ...............................................................  19

SIGNATURES AND SEALS ......................................................  19

ACKNOWLEDGMENTS ...........................................................  20

SCHEDULE A ................................................................  22
<PAGE>

                                       1

               This Supplemental Indenture is, among other things,

                             A MORTGAGE OF CHATTELS

      THIS SUPPLEMENTAL INDENTURE, dated as of February 1, 1981, made and
entered into in the City of Los Angeles, State of California by and between
SOUTHERN CALIFORNIA GAS COMPANY, a corporation duly organized and existing under
the laws of the State of California, and having its principal place of business
in the City of Los Angeles, State of California (hereinafter sometimes called
the "Corporation"), party of the first part, and WELLS FARGO BANK, NATIONAL
ASSOCIATION (formerly AMERICAN TRUST COMPANY), a national banking association
duly organized and existing under and by virtue of the laws of the United States
of America, and having its principal place of business in the City and County of
San Francisco, California (hereinafter sometimes called the "Trustee"), party of
the second part,

      W I T N E S S E T H :

      WHEREAS, the Corporation has executed and delivered to the Trustee a
certain Indenture (hereinafter sometimes called the "Original Indenture") dated
October 1, 1940, to secure bonds of the Corporation designated generally as its
"First Mortgage Bonds" to be issued from time to time in one or more series, any
of which series may vary from any other as to certain particulars specified in
Section 2.01 of the Original Indenture, and the Corporation has executed and
delivered to the Trustee Supplemental Indentures dated, respectively, as of July
1, 1947, May 1, 1948, June 1, 1950, April 1, 1952, August 1, 1955, June 1, 1956,
December 1, 1956, July 1, 1957, October 1, 1959, July 1, 1963, September 1,
1964, June 1, 1965, December 1, 1966, October 1, 1970, August 1, 1972, September
1, 1972, October 1, 1974, May 1, 1976, October 1, 1977 and November 1, 1979,
supplementing and amending the Original Indenture (the Original Indenture
together with this Supplemental Indenture and all other supplemental indentures
being herein collectively sometimes referred to as the "Indenture"); and

      WHEREAS, the Original Indenture and said Supplemental Indentures dated,
respectively, as of July 1 1947, May 1, 1948, June 1, 1950, April 1, 1952 and
August 1, 1955, are recorded in the office of the
<PAGE>

                                       2

County Recorder of each of the Counties listed below in the Official Records
thereof, as stated in said Supplemental Indenture dated as of June 1, 1956; said
Supplemental Indentures dated, respectively, as of June 1, 1956 and December 1,
1956, are so recorded as stated in said Supplemental Indenture dated as of July
1, 1957; said Supplemental Indenture dated as of July 1, 1957 is so recorded as
stated in said Supplemental Indenture dated as of October 1, 1959; said
Supplemental Indenture dated as of October 1, 1959 is so recorded as stated in
said Supplemental Indenture dated as of July 1, 1963; said Supplemental
Indenture dated as of July 1, 1963 is so recorded as stated in said Supplemental
Indenture dated as of September 1, 1964; said Supplemental Indenture dated as of
September 1, 1964 is so recorded as stated in said Supplemental Indenture dated
as of June 1, 1965; said Supplemental Indenture dated as of June 1, 1965 is so
recorded as stated in said Supplemental Indenture dated as of December 1, 1966;
said Supplemental Indenture dated as of December 1, 1966 is so recorded as
stated in said Supplemental Indenture dated as of October 1, 1970; said
Supplemental Indenture dated as of October 1, 1970 is so recorded as stated in
said Supplemental Indenture dated as of August 1, 1972; said Supplemental
Indenture dated as of August 1, 1972 is so recorded as stated in said
Supplemental Indenture dated as of September 1, 1972; said Supplemental
Indenture dated as of September 1, 1972 is so recorded as stated in said
Supplemental Indenture dated as of October 1, 1974; said Supplemental Indenture
dated as of October 1, 1974 is so recorded as stated in said Supplemental
Indenture dated as of May 1, 1976; said Supplemental Indenture dated as of May
1, 1976 is so recorded as stated in said Supplemental Indenture dated as of
October 1, 1977; said Supplemental Indenture dated as of October 1, 1977 so
recorded as stated in said Supplemental Indenture dated as of November 1, 1979;
and said Supplemental Indenture dated as of November 1, 1979 is recorded in the
offices of the County Recorders in the Counties of the State of California, as
follows:

  County               Reference                             Date
  ------               ---------                             ----
Fresno           Book 7403, Pages 838-867     Official Records  November 1, 1979
Imperial         Book 1443, Pages 92-123      Official Records  November 1. 1979
Kern             Book 5241, Pages 448-479     Official Records  November 1, 1979
Kings            Book 1161, Pages 263-294     Official Records  November 1, 1979
Los Angeles      Book 1979, 79-1236112        Official Records  November 2, 1979
<PAGE>

                                       3

  County               Reference                             Date
  ------               ---------                             ----
Orange           Book 13379, Pages 825-856    Official Records  November 1, 1979
Riverside        Book 1979, Page 234542       Official Records  November 2, 1979
San Bernardino   Book 9806, Pages 1046-1077   Official Records  November 2, 1979
San Diego        Book 1979, Pages 1963-1994   Official Records  November 1, 1979
San Luis Obispo  Vol, 2198, Pages 893-924     Official Records  November 1, 1979
Santa Barbara    Book 1979,79-51419           Official Records  November 1, 1979
Tulare           Vol. 3711, Pages 1-32        Official Records  November 1, 1979
Ventura          Book 5530, Pages 1-40        Official Records  November 2, 1979

      WHEREAS, bonds of the Corporation of eleven (11) series designated,
respectively, as its "First Mortgage Bonds, Series A, due 1982", First Mortgage
Bonds, Series B, due 1981", "First Mortgage Bonds, Series E, due 1988" "First
Mortgage Bonds, Series F, due 1989", "First Mortgage Bonds, Series G, due 1991",
"First Mortgage Bonds, Series H, due 1995", "First Mortgage Bonds, Series I, due
1997", "First Mortgage Bonds, Series J, due 1981", "First Mortgage Bonds, Series
K, due 1996", "First Mortgage Bonds, Series L, due 1997" and "First Mortgage
Bonds, Series M, due 1999", are outstanding as a part of the First Mortgage
Bonds referred to in the Original Indenture, each series of bonds, unless and
until the taking of further appropriate action by the Board of Directors of the
Corporation, being without limitation as to aggregate authorized principal
amount; and

      WHEREAS, pursuant to the provisions of Sections 2.01 and 2.02 of the
Original Indenture, the Board of Directors of the Corporation has, by resolution
duly adopted and delivered to the Trustee, created, as a part of the First
Mortgage Bonds referred to in the Original Indenture, a new series of bonds
designated "First Mortgage Bonds, Series N, due 2001" (herein sometimes called
"bonds of Series N"), to be of the form, terms. and provisions, provided in that
resolution and herein, which new series of bonds, unless and until the taking of
further appropriate action by the Board of Directors of the Corporation, is to
be without limitation as to aggregate authorized principal amount and of which
series bonds in the aggregate principal amount of $70,000 000 are to be
presently issued; and

      WHEREAS, it is provided in the Original Indenture that all the business,
franchises and properties, real, personal, and mixed, of every
<PAGE>

                                       4

kind and nature whatsoever and wheresoever situate, which might thereafter be
acquired by the Corporation, shall be as fully embraced within the lien thereof
as if said properties were owned by the Corporation at the date of the Original
Indenture and were particularly described therein and specifically conveyed
thereby, excepting certain properties expressly excepted by the provisions
thereof; and

      WHEREAS, subsequent to the execution of the Original Indenture the
Corporation has acquired properties hereinafter mentioned or referred to, all of
which properties, upon the acquisition thereof by the Corporation, became and
now are subject to the lien, operation and effect of the Original Indenture by
virtue of the after-acquired property clause or other clauses thereof; but the
Corporation, nevertheless, desires to execute, acknowledge, deliver and cause to
be recorded this Supplemental Indenture for the purposes, among others, of
expressly and specifically subjecting such after-acquired properties to the lien
of the Original Indenture as supplemented and of further assuring and confirming
the lien of the Original Indenture as supplemented on all of the properties of
every kind and character, whether real or personal and regardless of the date of
acquisition thereof by the Corporation, intended to be subjected to the lien
thereof; and

      WHEREAS, under the provisions of Sections 2.02 and 16.01 of the Original
Indenture the Corporation and the Trustee are authorized to execute and deliver
an indenture supplemental to the Original Indenture (i) to set forth the
particulars, permitted by Section 2.01 of the Original Indenture, as to which
the bonds of Series N are to vary from the bonds of the other series of said
First Mortgage Bonds, and (ii) for any purpose not inconsistent with the terms
of the Indenture; and

      WHEREAS, for and in consideration of the premises the Corporation
desires to execute this Supplemental Indenture; and

      WHEREAS, the making, executing, delivering and recording of this
Supplemental Indenture have been duly authorized by proper corporate action of
the Corporation; and

      WHEREAS, the execution and delivery of this Supplemental Indenture have
been authorized and approved by the Public Utilities Commission of the State of
California;
<PAGE>

                                       5

      NOW, THEREFORE, in consideration of the premises and of the sum of one
dollar ($1 ), lawful money of the United States of America, duly paid by the
Trustee to the Corporation, and of other good and valuable considerations,
receipt of which is hereby acknowledged, and of the fully registered in order
(a) to set forth or specify (i) the form of the fully registered bonds of Series
N and the form of the certificate to be endorsed on all bonds of said series,
and (ii) the terms and provisions of the bonds of Series N, including the
particulars thereof which vary from the bonds of the other series of said First
Mortgage Bonds, and (b) further to secure the payment of both the principal of
and interest on the bonds of the Corporation now or at any time hereafter
outstanding under the Original Indenture and/or any indenture supplemental
thereto, including specifically, but without limitation, all of said First
Mortgage Bonds now outstanding and said $70,000,000 aggregate principal amount
of bonds of Series N, according to their tenor and effect, and further to secure
the observance and performance of all of the covenants and conditions contained
in the Original Indenture agreements or in any indenture supplemental thereto,
and without in any way limiting the generality or effect of the Indenture
insofar as by any provision thereof any of the property therein or hereafter
described or referred to is now subject or intended to be subject to the lien
and operation thereof, but to such extent confirming such lien and operation,
the Corporation has executed and delivered this Supplemental Indenture and has
granted, bargained, sold, released, conveyed, mortgaged, assigned, transferred,
pledged, set over and confirmed, and does hereby grant, bargain, sell, release,
convey, mortgage, assign, transfer, pledge, set over and confirm unto Wells
Fargo Bank, National Association, the Trustee, and to its successor or
successors in the trust created by the Original Indenture and/or any indenture
supplemental thereto, and to its and their assigns, forever, with power of sale,
subject, to the extent applicable by the terms of the Indenture to any of the
properties hereinafter referred to or described, to the exceptions other than
with respect to exception (f) set forth on page 67 of the Original Indenture and
reading as follows: "(f) Any gas and/or oil acreage, gas and/or oil wells, gas
and/or oil reserves, or gas and/or oil leaseholds hereafter acquired by the
Corporation, or any property or equipment now or hereafter owned by the
Corporation and used for the development of gas and/or oil acreage or for the
drilling for or production of gas and/or oil from
<PAGE>

                                       6

such acreage"; which, exception (f) is by this granting clause hereby expressly
made inapplicable to certain parcels of property specified herein [and other
than as expressly provided in the granting clauses of said Supplemental
Indentures dated respectively as of June 1, 1956, July 1, 1957, October 1, 1959,
July 1, 1963, September 1, 1964, December 1, 1966, October 1, 1970, September 1,
1972, October 1, 1974, May 1, 1976, October 1, 1977 and November 1, 1979 with
respect to said exception (f) which is by said granting clauses expressly made
inapplicable to certain therein specified parcels of property], reservations,
conditions, terms and provisions provided in the Indenture with respect to
properties subject or intended to be subject thereto, all of the properties and
assets of the Corporation, real, personal and mixed, of every kind and
character, whether now or hereafter owned by the Corporation and wheresoever
situated, including, without in any way limiting or modifying the generality or
effect of the foregoing, all and singular, the following properties:

      FIRST: All of the lots, pieces and parcels of land and rights or interests
in real property situate in the Counties in the State of California,
specifically described and mentioned or enumerated in Schedule A attached
hereto, to which reference is hereby made and the same is made a part hereof
with the same force and effect as if the same were here set forth at length.

      SECOND: All and singular the plants, properties, equipment, real and
personal property, estates, interests, goodwill, generating, transmission,
feeding, storing, and distribution systems, and utilities of the Corporation
situate in the Counties of Fresno, Imperial, Kern, Kings, Los Angeles, Orange,
Riverside, San Bernardino, San Diego, San Luis Obispo, Santa Barbara, Tulare and
Ventura, and elsewhere, in the State of California, with all and singular the
franchises, ordinances, grants, easements, licenses, powers, immunities,
permits, privileges, appurtenances, tenements and other rights and property
thereunto appertaining or belonging, as the same now exist and as the same and
any and all parts thereof may hereafter exist or be improved, added to,
enlarged, extended or acquired in said counties or elsewhere in said state or
any other state or states.
<PAGE>

                                       7

      THIRD: All other property, real, personal and mixed, of every kind, nature
and description (including, without in any way limiting the effect of the
generality hereof; all facilities; all stocks, bonds and other securities from
time to time conveyed, assigned, transferred, mortgaged or pledged on behalf of
the Corporation, or with its consent, to the Trustee in the manner and for the
purposes as provided in the Indenture; all gas manufacturing plants, boilers,
engines, compressors, motors, pumps, generators, gasholders, tanks, appliances,
oil storage facilities, gas storage facilities, wells, buildings, structures,
plants, works and other improvements; all gas transmission and distributing
lines and systems; all meters and regulators and all other apparatus, machinery,
appliances, tools, furniture, fixtures, supplies, facilities and utilities and
other personal property; or any right or interest in any thereof; all business
and goodwill, rights, consents, franchises, ordinances, licenses, agreements,
contracts, permits, easements, rights of way, leases and leasehold interests;
powers, grants, privileges and immunities to construct, operate and maintain
lines and other facilities or properties for conveying gas or other commodities
or utilities for any purpose or purposes through, under and over public streets
or highways, or public or private places or property; all reversions,
remainders, tolls, incomes, revenues, earnings, rents, issues and profits of any
property, real, personal and mixed; and all other classes and types of property
described or refer red to in the Original Indenture, or any indenture
supplemental thereto), now or hereafter owned, held, possessed, acquired or
enjoyed by or in any manner conferred upon or appertaining to the Corporation,
including the interest of the Corporation in all leases now or hereafter owned
by it, together with all and singular the tenements, hereditaments, and
appurtenances belonging or in any way appertaining To each and every part of any
and all property subject or intended to be subject to the lien and operation of
the Original Indenture as supplemented, and the reversion and reversions,
remainder and remainders, tolls, incomes, revenues, earnings, rents, issues and
profits thereof.

      SAVING AND EXCEPTING, however, from the property hereby mortgaged,
conveyed in trust and/or pledged, all property, whether now owned by the
Corporation or hereafter acquired by it, expressly saved and excepted from the
lien of the Indenture and therein referred to as the "excepted property" (except
otherwise expressly provided in this Supplemental Indenture and any Supplemental
Indenture herein-
<PAGE>

                                       8

above mentioned, with respect to exception (f) of said "excepted property"),
unless and until, upon the occurrence of an event of default under the
Indenture, the Trustee, or any receiver appointed thereunder, shall take
possession of any or all of such excepted property.

      TO HAVE AND TO HOLD in trust with power of sale for the equal and
proportionate benefit and security of all holders of bonds of the Corporation,
now or hereafter outstanding under the Indenture as from time to time in effect,
and for the enforcement and payment of said bonds and interest thereon when
payable, and the performance of and compliance with the covenants and conditions
of the Indenture as from time to time in effect, without any preference,
distinction or priority as to lien or otherwise of any of said bonds over any
others thereof by reason of the difference in the time of the actual issue, sole
or negotiation thereof, or for any other reason whatsoever, except as otherwise
expressly provided in the Indenture as from time to time, in effect, so that
each and every such bond shall have the same lien and so that the principal and
interest of every such bond shall, subject to the terms thereof, be equally and
proportionately secured by said lien, as if such bond had been made, executed,
delivered, sold and negotiated simultaneously with the execution and delivery of
the Original Indenture.

      IT IS HEREBY COVENANTED, DECLARED, AND AGREED by and between the parties
hereto that all such bonds are issued, authenticated and delivered, or are to be
issued, authenticated and delivered, and that all property subject, or to become
subject, to the Original Indenture, including any indenture supplemental
thereto, is to be held, subject to the covenants, conditions, uses and trusts
therein set forth.

      It is hereby further stipulated and provided:


                                    ARTICLE I

                     AMOUNT, FORM, NUMBERING, DENOMINATION,
                         TRANSFER AND EXCHANGE OF BONDS
                             OF SERIES N, DUE 2001

      SECTION 1.01. The bonds of Series N may be issued at any time or from time
to time upon and subject to the terms and provisions of the Indenture. Unless
and until the taking of further appropriate action
<PAGE>

                                       9

by the Board of Directors of the Corporation the bonds of said Series shall be
without limitation as to aggregate authorized principal amount.

      SECTION 1.02. The bonds of Series N shall be issued only as fully
registered bonds without coupons. The fully registered bonds without coupons and
the certificate of authentication to be endorsed on all bonds of said Series,
shall be substantially in the following form:

         (FORM OF REGISTERED BOND WITHOUT COUPONS, SERIES N, DUE 2001)

                         SOUTHERN CALIFORNIA GAS COMPANY
            (Incorporated under the laws of the State of California)

                     FIRST MORTGAGE BOND, SERIES N, DUE 2001
                                      (15%)

NO. ____________                                                 $ ____________

      SOUTHERN CALIFORNIA GAS COMPANY, a corporation organized and existing
under the laws of the State of California (hereinafter called the "Corporation",
which term shall include any successor corporation, as defined in the Indenture
hereinafter referred to), for value received, hereby promises to pay to
____________, or registered assigns, the sum of _____________________ DOLLARS in
lawful money of the United States of America, on the first day of February,
2001, and to pay interest thereon to the registered owner hereof from the date
of this bond, at the rate of 15% per annum in like lawful money, payable
semi-annually, on the first days of February and August in each year, commencing
August 1, 1981, until the Corporation's obligation with respect to the payment
of such principal shall be discharged as provided Both in the Indenture
hereinafter mentioned. the principal of and interest on this bond will be paid
at the principal office of Wells Fargo Bank, National Association, or its
successor trustee under said Indenture, in the City and County of San Francisco,
State of California or at the main office of the Trustee in the City of Los
Angeles, or, at the option of the registered owner hereof, principal will be
paid at the office or agency of the Corporation in the City of New York, State
of New York.
<PAGE>

                                       10

      The provisions of this bond are continued on the reverse hereof and such
continued provisions shall for all purposes have the same effect as though fully
set forth at this place.

      IN WITNESS WHEREOF, SOUTHERN CALIFORNIA GAS COMPANY has caused this bond
to be signed in its corporate name by its President or a Vice-President and its
corporate seal to be hereto affixed and attested by its Secretary or in
Assistant Secretary.

      Dated as of ____________________, 19____

                                    SOUTHERN CALIFORNIA GAS COMPANY

                                    By
                                       ---------------------------------------
                                                  Vice President

(CORPORATE SEAL)

ATTEST:

---------------------------
        Secretary


                  (REVERSE SIDE-FORM OF REGISTERED BOND WITHOUT
                          COUPONS, SERIES N, DUE 2001)

      This bond is one of a duly authorized issue of bonds of the Corporation
(herein called the "bonds"), of the series hereinafter specified, all issued and
to be issued under and all equally and ratably secured by a mortgage and deed of
trust dated October 1, 1940, executed by the Corporation to Wells Fargo Bank,
National Association (formerly American Trust Company), as Trustee, to which
mortgage and deed of trust and all indentures supplemental thereto, including
Supplemental Indentures dated, respectively, as of July 1, 1947, August 1, 1955,
June 1, 1956, December 1, 1956, June 1, 1965, August 1, 1972 and May 1, 1976
(herein collectively referred to as the "Indenture"), refer-
<PAGE>

                                       11

ence is hereby made for a description of the property conveyed in trust,
mortgaged and pledged, the nature and extent of the security, the rights of the
registered owners of the bonds and of the Trustee or trustees in respect
thereof, the terms and conditions upon. which the bonds are, and are to be,
secured and the circumstances under which additional bonds may be issued. The
bonds may be issued for various principal sums, and may be issued in series,
which may mature at different times, may bear interest at different rates and
may otherwise vary as in the Indenture provided. This bond is one of a series
designated as the "First Mortgage Bonds, Series N, due 2001" (herein called
"bonds of Series N") of the Corporation, issued under and secured by the
Indenture.

      As provided in the Indenture, by any indenture or indentures supplemental
thereto executed by the Corporation and the Trustee and consented to by the
holders of not less than two-thirds (2/3) in principal amount of the bonds at
the time outstanding, and, in case one or more, but less than all, of the series
of bonds then outstanding are affected by such supplemental indenture, consented
to by the holders of at least two-thirds (2/3) in principal amount of the bonds
of such series so affected, the Indenture or any indenture supplemental thereto,
and the rights and obligations of the Corporation and the holders of bonds, may
be modified or altered from time to time, as provided in the Indenture;
provided, however, (a) that the right of any holder of any bond to receive
payment of the principal of and interest on such bond, on or after the
respective due dates expressed in such bond, or to institute suit for the
enforcement of any such payment on or after such respective dates, shall not be
impaired or affected by any such supplemental indenture without the consent of
such holder, and (b) that no such modification, or alteration shall reduce the
proportions of bondholders' consents required as aforesaid; such proportions to
be determined in each case as provided in the Indenture.

      The bonds of Series N are subject to redemption (a) at any time prior to
maturity at the option of the Corporation either as a whole or in part, or
through operation of the Renewal Fund, upon payment of the percentages of the
principal thereof as set forth in the table below under the heading "Regular
Redemption Price" during the respective 12 months' period beginning February 1,
in each of the years mentioned, or (b) by operation of the Sinking Fund upon
payment of the per-
<PAGE>

                                       12

centages of the principal thereof set forth below under the heading "Special
Redemption Price" during said periods. Notwithstanding the foregoing, none of
the bonds of Series N may be redeemed prior to February 1, 1986 directly or
indirectly from the proceeds of or in anticipation of any refunding operation
involving the incurring of debt which has an interest cost to the Corporation of
less than 15.094% per annum.

      Redemption Price           Redemption Price           Redemption Price
      ----------------           ----------------           ----------------
Year  Regular  Special     Year  Regular  Special     Year  Regular  Special
----  -------  -------     ----  -------  -------     ----  -------  -------
1981  115.00%      --      1988  109.49%  100.00%     1995  103.95%  100.00%
1982  114.22       --      1989  108.69   100.00      1996  103.16   100.00
1983  113.43       --      1990  107.90   100.00      1997  102,37   100.00
1984  112.64       --      1991  107.11   100.00      1998  101.58   100.00
1985  111.85       --      1992  106.32   100.00      1999  100.79   100.00
1986  111.06       --      1993  105.53   100.00      2000  100.00   100.00
1987  110.27   100.00%     1994  104.74   100.00

together in each case with accrued interest to the date fixed for redemption,
and upon notice given by publication once in each of three separate calendar
weeks in one daily newspaper printed in the English language of general
circulation in the Borough of Manhattan, City and State of New York, and in one
similarly printed daily newspaper of general circulation in the City and County
of San Francisco, California (the first of such publications to be not less than
thirty and not more than sixty days before the redemption date), or, notice of,
any such redemption may be mailed to the registered owners of the bonds to be
redeemed not less than thirty nor more than sixty days before the redemption
date, in lieu of such notice being given by publication, all subject to the
conditions and as more fully set forth in the Indenture, including (1) the
condition that failure to give notice of any such redemption by mail, if
required, or any defect therein or in the mailing thereof shall not affect the
validity of the proceedings for the redemption of any bonds so to be redeemed if
notice by publication, if required, is duly given and (2) the condition that, if
any notice of redemption of bonds shall state that it is subject to receipt by
or for the account of the Trustee on or before the date fixed for redemption of
moneys applicable to and sufficient for such redemption, such bonds shall not
become due and payable by virtue of such notice unless such moneys shall be held
by or for the account of the Trustee on or before the date fixed for redemp-
<PAGE>

                                       13

tion. If this bond or any portion hereof is called for redemption and payment
duly provided as specified in the Indenture, interest shall cease to accrue on
this bond or such portion hereof from and after the date fixed for such
redemption.

      The bonds are entitled to the benefits of the Sinking Fund and the Renewal
Fund as provided in the Indenture.

In case an event of default, as defined in the Indenture, shall occur, the
principal of all bonds then outstanding under the Indenture may be declared or
become due and payable upon the conditions and in the manner and with the effect
provided in the Indenture.

      This bond is transferable by the registered owner hereof at the office or
agency of the Corporation in said City and County of San Francisco, in said City
of Los Angeles, in the Borough of Manhattan, City of New York and in such other
place or places as the Corporation may designate at any time or from time to
time, and thereupon a new fully registered bond or bonds of said series, without
coupons, of authorized denomination or denominations, of a like aggregate
principal amount, will be issued to the transferee or transferees in exchange
for this bond; and at any of said offices or agencies fully registered bonds of
Series N without coupons, are exchangeable for a like aggregate principal amount
of other such fully registered bonds of authorized denominations; all in the
manner and subject to the conditions as provided in the Indenture.

      No recourse shall be had for the payment of the principal of or the
interest on this bond or for any claim based hereon or on the lndenture or any
indenture supplemental thereto, against any incorporator, stockholder, director
or officer, past, present or future, of the Corporation, or of any predecessor
or successor corporation, either directly or through the Corporation, or any
such predecessor or successor corporation, whether by virtue of any
constitution, statute or rule of law, or by the enforcement of any assessment or
penalty, or otherwise, all such liability being waived and released by every
registered owner hereof by the acceptance of this bond and as part of the
consideration for the issue hereof, and being likewise waived and released by
the terms of the Indenture.

      This bond shall not become valid or obligatory for any purpose or be
entitled to any benefit under the Indenture until Wells Fargo
<PAGE>

                                       14

Bank, National Association, or its successor as Trustee under the Indenture, or
an authenticating agent, shall have signed the form of certificate endorsed
hereon.

                     [FORM OF CERTIFICATE OF AUTHENTICATION]

                                   CERTIFICATE

      This bond is one of the bonds, of the series designated therein, described
in the within-mentioned Indenture.

        WELLS FARGO BANK,              or            BANKERS TRUST COMPANY,
     NATIONAL ASSOCIATION,
            Trustee                                   Authenticating Agent

By                                             By
   ----------------------------                   ----------------------------
       Authorized Officer                             Authorized Officer

      The bonds of Series N may contain or have imprinted thereon such
provisions or specifications not inconsistent with the Indenture as may be
required to comply with the rules of any stock exchange or any federal or state
authority or commission, or to comply with usage with respect thereto, and may
bear such other appropriate endorsements or notations as are authorized or
permitted by the Indenture.

      The fully registered bonds of Series N shall be issuable in denominations
of $1,000 and any integral multiple of $1,000 and shall be dated as provided in
paragraph 1 of Section 2.01 of the Original Indenture, The definitive bonds of
Series N shall be numbered in such manner as the Corporation shall at any time
or from time to time determine.

      SECTION 1.03. In the manner and subject to certain conditions and
limitations specified herein and in the Indenture, bonds of Series N may be
exchanged without a service charge for a like aggregate principal amount of such
bonds of Series N of other authorized denomination or denominations.
<PAGE>

                                       15

      SECTION 1.04. The Corporation shall maintain in the City and County of San
Francisco, and in the City of Los Angeles, State of California, and also in the
Borough of Manhattan, City of New York, State of New York, and in such other
place or places as the Corporation may designate at any time or from time to
time, an office or agency where bonds of Series N may be presented for payment,
registration, transfer and exchange as provided therein or in the Indenture.
Such office or agency in the City and County of San Francisco shall be the
principal office of the Trustee and such office or agency in the City of Los
Angeles shall be the main office of the Trustee in said City and such office or
agency in the Borough of Manhattan, City of New York shall be the principal
office of Bankers Trust Company unless and until the Corporation shall designate
another office or agency by notice in writing delivered to the Trustee.

      SECTION 1.05. No transfer or exchange of any bonds of Series N pursuant to
any of the provisions of this Article I shall be made except upon and in
accordance with all of the applicable terms, provisions and conditions of said
bonds and of the Indenture.


                                   ARTICLE II

                INTEREST, MATURITY DATE, REDEMPTION, SINKING FUND
                          AND CERTAIN OTHER PROVISIONS.

      SECTION 2.01. The bonds of Series N shall bear interest at the rate, shall
be expressed to mature as to principal, and shall be payable as to principal and
interest at such place or places and in such money, all as provided in the form
of such bonds set forth in Section 1.02 hereof and by the applicable provisions
of the Indenture.

      SECTION 2.02. The bonds of Series N shall be subject to redemption, either
in whole or in part, at the applicable redemption prices specified in said form
of bonds, upon notice, in the manner and otherwise upon the terms and conditions
and with the effect, as provided herein and by the applicable provisions of the
Indenture, which provisions of the Indenture are hereby modified and
supplemented, but only with respect to the bonds of Series N, as follows:
<PAGE>

                                       16

      (a) If at the time of publication or mailing of, or of otherwise giving,
any notice of redemption of any of the bonds of Series N the Corporation shall
not have deposited with the Trustee and/or irrevocably directed the Trustee to
apply, from moneys held by it available to be used for the redemption of bonds
of Series N, an amount in cash sufficient to redeem all of the bonds of Series N
called for such redemption, including accrued interest to the date fixed for
redemption, such notice shall state that it is subject to the receipt by the
Trustee on or before the date fixed for redemption of moneys applicable to and
sufficient for such redemption and that such notices shall be of no effect
unless such moneys are so received on or before such date.

      (b) The Trustee, upon request of the Corporation evidenced by a resolution
of its Board of Directors, shall, for and in behalf of and in the name of the
Corporation call for redemption of bonds of Series N provided that, if cash
sufficient for such redemption is not hold by the Trustee at the time of such
call, the notice shall state that it is subject to the receipt by the Trustee on
or before the date fixed for redemption of moneys applicable to and sufficient
for such redemption and that such notice shall, be of no effect unless such
moneys are so received on or before such date.

      (c) If bonds of Series N shall be called for redemption pursuant to a
notice containing the statement set forth in subparagraph (a) or subparagraph
(b) of this Section 2.02, the principal amount and premium, if, any, of such
bonds shall not become due and payable by virtue of such call or notice unless
on or before the date fixed for redemption the Corporation shall have
irrevocably deposited with the Trustee for the purpose of redeeming all of the
bonds of Series N called for redemption, including funds for the payment, of
accrued interest to the date fixed for redemption, and/or irrevocably directed
the Trustee to apply, from moneys held by it available. to be used for the
redemption of bonds of Series N an amount in cash sufficient to redeem all of
the bonds of Series N called for redemption, including funds for the payment of
accrued interest to the date fixed for redemption.
<PAGE>

                                       17

      Notwithstanding the foregoing, none of the bonds of Series N may be
redeemed prior to February 1, 1986 directly or indirectly from the proceeds of
or in anticipation of any refunding operation involving the incurring of debt
which has an interest cost to the Corporation of less than 15.094% per annum.

      SECTION 2.03. The bonds of Series N shall be entitled to the benefits of
the Renewal Fund as provided in the Indenture and shall also be entitled to
benefit, as hereinafter provided, under the Sinking Fund referred to in Section
8.01 of the Indenture. To provide for such benefit under said Sinking Fund, said
Section 8.01, as heretofore amended and now in effect, is hereby further amended
by adding thereto, immediately preceding the last paragraph thereof, a new
paragraph reading as follows:

            "The Corporation further covenants and agrees that, on or before
      April first in the year 1987 and in each year thereafter so long as any of
      the bonds of Series N are outstanding, it will pay to the Trustee, as a
      payment for that year to the Sinking Fund referred to in the first
      paragraph of this Section 8.01, the amount of $4,660,000, together with a
      payment at maturity of $4,760,000, on February 1, 2001, in respect of such
      series."

      SECTION 2.04. The bonds of Series N shall, except as in this Supplemental
Indenture otherwise expressly provided, be on the terms and provisions, and
shall represent such rights and be entitled to such benefits, as are applicable
thereto by the terms of the Indenture.


                                   ARTICLE III

                               SUNDRY PROVISIONS.

      SECTION 3.01. The recitals of fact contained herein shall be taken as the
statements of the Corporation, and the Trustee assumes no responsibility for the
correctness of the same. The Corporation hereby covenants and agrees that it
will cause this Supplemental Indenture to be kept recorded and/or filed as may
be required by law, in such manner and in such places as may be necessary fully
to preserve and protect the security of the bondholders and all of the rights of
the Trustee hereunder,
<PAGE>

                                       18

and that it will with all reasonable dispatch deposit with the Trustee
counterparts of this Supplemental Indenture bearing official notation or
endorsements showing such recordation and/or filing, or in case such
counterparts are not returned to the Corporation, furnish to the Trustee the
best official evidence of such recordation and/or filing reasonably obtainable
by the Corporation, or evidence of the taking of such other action, if any, but
the Trustee, subject to the provisions of Sections 14.02 and 14.03 of said
Original Indenture, shall in no wise be liable for any failure or omission in
this regard.

      SECTION 3.02. The date of this Supplemental Indenture and the date of the
bonds of Series N are intended as and for a date for the convenient
identification of this Supplemental Indenture and of the bonds of said series,
and are not intended to indicate that this Supplemental Indenture was executed
and delivered or that said bonds were executed, delivered or issued on said
date; it being hereby provided that this Supplemental Indenture may be executed
and delivered, and that said bonds may be executed, delivered or issued, either
on said date or before or after said date, and that this Supplemental Indenture
is in fact executed and delivered by each party hereto on the date of its
certificate of acknowledgment hereto attached.

      SECTION 3.03. This Supplemental Indenture shall be deemed to be part of
the Original Indenture, and the Corporation agrees to conform to and comply with
all and singular the terms, provisions, conditions and covenants set forth
therein and herein. This Supplemental Indenture shall be construed in connection
with and as a part of the Original Indenture, as heretofore amended and
supplemented.

      SECTION 3.04. It is further agreed that the Trustee accepts the trust
imposed upon it by this Supplemental Indenture, upon and subject to the same
terms and conditions as are expressed in Article XIV of the Original Indenture.

      SECTION 3.05. In order to facilitate the recording of this Supplemental
Indenture, the same may be executed in several counterparts, each of which so
executed shall be deemed to be an original, and such counterparts shall
collectively constitute one and the same instrument.
<PAGE>

                                       19

     IN WITNESS WHEREOF, Southern California Gas Company has caused this
Supplemental Indenture to be signed in its corporate name by its President or
one of its Vice Presidents, and its Secretary or one of its Assistant
Secretaries, and its corporate seal to be hereunto duly affixed, and Wells Fargo
Bank, National Association, in token of its acceptance of the trust hereby
established, has caused this Supplemental Indenture to be signed in its
corporate name by one of its Authorized Officers and its Secretary or one of its
Assistant Secretaries, and its corporate seal to be hereunto duly affixed, all
as of February 1, 1981.

                                       SOUTHERN CALIFORNIA GAS COMPANY

Attest:

/s/ H.E. GOODENOW                      By  /s/ G. DAVID WOOSLEY
-----------------------------             -------------------------------------
                 Secretary                                    Vice President

(SEAL)

                                       WELLS FARGO BANK, NATIONAL
Attest:                                   ASSOCIATION

/s/ R.T. MARAVILLA                     By  /s/  M.C. WELCH
-----------------------------             -------------------------------------
       Assistant Secretary                                Authorized Officer

(SEAL)
<PAGE>

                                       20

STATE OF CALIFORNIA,          )
                              )   ss.
COUNTY OF LOS ANGELES,        )


      On this 28th day of January, 1981, before me, FLORENCE B. FROST, a Notary
Public of the State of California, duly commissioned and sworn, personally
appeared G. DAVID WOOSLEY, known to me to be Vice President, and H. E. GOODENOW
known to me to be the Secretary, of SOUTHERN CALIFORNIA GAS COMPANY, one of the
corporations named in and which executed the foregoing instrument, known to me
to be the persons who executed the within instrument on behalf of said
Corporation, and acknowledged to me that said Corporation executed the same, and
acknowledged to me that said Corporation executed the within instrument pursuant
to its by-laws or a resolution of its board of directors.

      IN WITNESS WHEREOF, I have hereunto set my hand and affixed my official
seal the day and year in this certificate first above written.


                                             /s/ FLORENCE B. FROST
                                    -----------------------------------------
                                                FLORENCE B. FROST

                                    Notary Public of the State of California.

                                                                          (SEAL)
My Commission Expires August 14, 1983.
<PAGE>

                                       21

STATE OF CALIFORNIA           )
                              )   ss.
COUNTY OF LOS ANGELES,        )


      On this 28th day of January, 1981, before me, FLORENCE B. commissioned
FROST, a Notary Public of the State of California, duly commissioned and sworn,
personally appeared M. C. WELCH, known to me to be an Assistant Authorized
Officer, and R. T. MARAVILLA, known to me to be an Assistant Secretary, of WELLS
FARGO BANK, NATIONAL ASSOCIATION, a national banking association, one of the
corporations named in and which executed the foregoing instrument, known to, me
to be the persons who executed the within instrument on behalf of said
Corporation, and acknowledged to me that said Corporation executed the same, and
acknowledged to me that said Corporation executed the within instrument pursuant
to its by-laws or a resolution of its board of directors.

      IN WITNESS WHEREOF, I have hereunto set my hand and affixed my official
seal the day and year in this certificate first above written.


                                             /s/ FLORENCE B. FROST
                                    -----------------------------------------
                                                FLORENCE B. FROST

                                    Notary Public of the State of California.

                                                                          (SEAL)
My commission Expires August 14, 1983.
<PAGE>

                                       22

                                   SCHEDULE A

      Incorporated in and made a part of the Supplemental Indenture dated as of
February 1, 1981, by and between Southern California Gas Company and Wells Fargo
Bank, National Association, Trustee.

      The descriptive names or captions do not constitute a part of the property
descriptions, being used only for convenience of reference and identification.

The term "Grantor" as used hereinafter refers to the grantor of each parcel of
property hereinafter described to Southern California Gas Company.

                              COUNTY OF LOS ANGELES

      Those certain lots, pieces and parcels of land and other property, rights,
and estates situate in the County of Los Angeles, State of California, described
as follows:

                           General Offices and Garages

Parcel 1:

      Lot "A" of Tract 6004, in the City of Los Angeles, in the County of Los
Angeles, State of California, as per map recorded in Book 79, Page 12 of Maps,
in the Office of the County Recorder of said County.

Parcel 2:

      Lot 5 of H. F. SPENCER'S Subdivision of the North half of Block 57 of
ORD'S Survey, as per map recorded in Book 5, Page 35, of Miscellaneous
records of Los Angeles County, and that portion of Lot 4 of said H. F.
SPENCER'S Subdivision included within the following described lines:

      Beginning at the intersection of the Southeasterly line of said H. F.
SPENCER'S Subdivision with the Southeasterly prolongation of the Southwesterly
face of the Southwesterly wall of a four story brick building known as the Hotel
Stephens, said point of intersection being distant South 37 51' West along said
Southeasterly line of said H. F. SPENCER'S subdivision 195.81 foot from the
Southwesterly line of Eighth Street, 70 feet wide, as at present Established;
Thence South
<PAGE>

                                       23

37"51' West along said Southeasterly line of said H. F. SPENCER'S Subdivision
50.18 feet to the Northeasterly line of Tract No. 6004. as per map recorded in
Book 79 Page 12 of Maps, in the office of the County recorder of said county;
Thence North 52 08' West along said Northeasterly line 156.98 feet to the
Southeasterly line of a 20 foot alley running Northeasterly through said H. F.
SPENCER'S Subdivision; Thence North 37 49' East along said alley 50.25 feet to
the Southwesterly face of the Southwesterly wall of said four story brick
building; thence South 52 06'10" East along said Southwesterly face of said
Southwesterly wall of said four story brick building and along the Southeasterly
prolongation thereof, 157.00 feet to the point of beginning.

      EXCEPT that portion of Lot 5 of said H. F. SPENCER'S Subdivision
included within the following described lines:

      BEGINNING at the intersection of the Southeasterly line of said H. F.
SPENCER'S SUBDIVISION with the Southeasterly prolongation of the Southwesterly
face of the Southwesterly wall of a twelve story brick building known as the
HOTEL RITZ, said point of intersection being distant South 37 51' West along
said Southeasterly line of H. F. SPENCER'S Subdivision 145.72 feet from the
Southwesterly line of Eighth Street, 70 feet Wide, as at present established;
thence South 37 51' West along said Southeasterly line of H. F. SPENCER'S
Subdivision 50.09 feet to the Southeasterly prolongation of the Southwesterly
face of the Southwesterly wall of a four story brick building known as Hotel
Stephens; thence North 52 06'10" west along said last mentioned Southeasterly
prolongation and along said Southwesterly face of the Southwesterly wall of said
four story brick building 157.00 feet to the Southeasterly line of a 20 foot
alley running Northeasterly through said H. F. SPENCER'S Subdivision; thence
North 37 49' East along said alley, 50.03 feet to the Northwesterly prolongation
of said Southwesterly face of the Southwesterly wall of said twelve story brick
building; thence South 52 07'40" East along said Northwesterly prolongation and
along said Southwesterly face of the Southwesterly wall of said twelve story
brick building and along the Southeasterly prolongation thereof, 157.03 feet to
the point of beginning.
<PAGE>

                                       24

                                  Industry Base

Parcel A:

      Parcel 1 in the City of Industry, in the County of Los Angeles, State of
California, as shown on Parcel Map No. 167, filed in Book 138 Page 78 of Parcel
Maps, in the office of the County Recorder of said County.

Parcel B:

      An easement for ingress and egress over the easterly 20 feet of Parcel 2
in the City of Industry, in the County of Los Angeles, State of California, as
shown on Parcel Map No. 167, filed in Book 138 Page 78 of Parcel Maps, in the
office of the County Recorder of said County.

                               COUNTY OF RIVERSIDE

      Those certain lots, pieces and parcels of land and other property, rights,
and estates situate in the County of Riverside, State of California, described
as follows:

                               Hemet District Base

      Lot 515 of Romola Farms No. 6A, as shown by Map on file in Book 14 pages
63, 64 and 65 of Maps, Riverside County Records; EXCEPTING that portion as
described in that Deed to the State of California by Deed recorded February 14,
1962 in Book 3077 page 364 of official records and as Instrument No. 13971.

                            COUNTY OF SAN BERNARDINO

      Those certain lots, pieces and parcels of land and other property, rights,
and estates situate in the County of San Bernardino, State of California,
described as follows:

                              Needles Crossover R/W

      All that portion of the south one-half of the south one-half of the north
one-half and the north one-half of the north one-half of the south one-half both
of the above being of the northwest quarter of
<PAGE>

                                       25

the northwest quarter of Section 13, Township 9 North, Range 22 East, San
Bernardino Base and Meridian; lying west of River Road, being 100 feet wide per
official Records, Book 2909, Page 320, and recorded in the County Recorder's
Office of said County.

                                  Fontana Base

      The West 6 acres of the East 16 Acres of Farm Lot 732, according to map
showing subdivision of lands belonging to the Semi-Tropic Land and Water
Company, in the County of San Bernardino, State of California, as per Map
recorded in Book 11 Page 12 of Maps, in the office of the County Recorder of
said County.

      The area and distances of the above described property are computed to the
centers of the adjoining streets shown on said Map.