<PAGE>   1
                                                                     EXHIBIT 3.1



                            SPIEKER PROPERTIES, INC.
                             ARTICLES SUPPLEMENTARY


        SPIEKER PROPERTIES, INC., a Maryland corporation, having its principal
office in the City of Baltimore, Maryland (the "Corporation"), hereby certifies
to the Maryland State Department of Assessments and Taxation that:

        FIRST: Pursuant to authority expressly vested in the Board of Directors
of the Corporation by the Charter of the Corporation, the Board of Directors has
duly reclassified 6,000,000 shares of the Common Stock (par value $.0001 per
share) of the Corporation into 6,000,000 shares of a class designated as Series
C Cumulative Redeemable Preferred Stock (par value $.0001 per share) of the
Corporation ("Series C Preferred Stock") and has provided for the issuance of
such shares.

        SECOND: The reclassification increases the number of shares classified
as Series C Preferred Stock from no shares immediately prior to the
reclassification to 6,000,000 shares immediately after the reclassification. The
reclassification decreases the number of shares classified as Common Stock (par
value $.0001 per share) from 660,500,000 shares immediately prior to the
reclassification to 654,500,000 shares immediately after the reclassification.

        THIRD: Subject in all cases to the provisions of Article NINTH of the
Charter of the Corporation with respect to Excess Stock, the following is a
description of the preferences, conversion and other rights, voting powers,
restrictions, limitations as to dividends, qualifications and terms and
conditions of redemption of Series C Preferred Stock of the Corporation:

               1.     DESIGNATION AND AMOUNT.

                      The designation of Series C Preferred Stock described in
        Article FIRST hereof shall be "Series C Cumulative Redeemable Preferred
        Stock (par value $.0001 per share)." The number of shares of Series C
        Preferred Stock to be authorized shall be 6,000,000. The Series A
        Preferred Stock, par value $.0001 per share ("Series A Preferred Stock")
        and the Series B Cumulative Redeemable Preferred Stock, par value $.0001
        per share ("Series B Preferred Stock"), of the Corporation rank on a
        parity as to dividends and amounts upon liquidation.

               2.     DIVIDENDS AND DIVIDEND PROVISIONS.

                      (a) Subject to the rights of series of Preferred Stock
        which may from time to time come into existence, holders of Series C
        Preferred Stock shall be entitled to receive, when and as declared by
        the Board of Directors, out of funds legally available for the payment
        of dividends, cumulative preferential cash dividends at the rate of
        $1.96875 per annum per share. Such dividends shall be cumulative from
        the date of original issue and shall be payable quarterly in arrears on
        the last day of January, April, July and October or, if not a business
        day, the next succeeding business day (each, a "Dividend Payment Date").
        The first dividend, which will be due on October 31, 1997, will be for
        less than a full quarter. Such first dividend and any dividend payable
        on Series C Preferred Stock for any partial dividend period will be
        computed on the basis of a 360-day year consisting of twelve 30-day
        months. Dividends will be payable to holders of record as they appear in
        the records of the Corporation at the close of business on the
        applicable record date, which shall be on such date designated by the
        Board of Directors of the Corporation for the payment of dividends that
        is not more than 50 nor less than 10 days prior to such Dividend Payment
        Date (each, a "Dividend Record Date").




                                      - 1 -



<PAGE>   2
                      (b) Dividends on Series C Preferred Stock will accrue
        whether or not the Corporation has earnings, whether or not there are
        funds legally available for the payment of such dividends and whether or
        not such dividends are declared. No interest, or sum of money in lieu of
        interest, shall be payable in respect of any dividend payment or
        payments on Series C Preferred Stock which may be in arrears. Holders of
        the Series C Preferred Stock will not be entitled to dividends in excess
        of the full cumulative dividends as described above.

                      (c) If, for any taxable year, the Corporation elects to
        designate as "capital gain dividends" (as defined in Section 857 of the
        Internal Revenue Code of 1986, as amended, or any successor revenue code
        or section (the "Code")) any portion (the "Capital Gains Amount") of the
        total distributions (as determined for federal income tax purposes) paid
        or made available for the year to holders of all classes of capital
        stock (the "Total Distributions"), then the portion of the Capital Gains
        Amount that shall be allocable to holders of Series C Preferred Stock
        shall be in the same portion that the Total Distributions paid or made
        available to the holders of Series C Preferred Stock for the year bears
        to the Total Distributions.

                      (d) If any shares of Series C Preferred Stock are
        outstanding, no dividends shall be declared or paid or set apart for
        payment on any shares of series of capital stock of the Corporation
        ranking, as to dividends, on a parity with or junior to Series C
        Preferred Stock for any period unless full cumulative dividends have
        been or contemporaneously are declared and paid or declared and a sum
        sufficient for the payment thereof set apart for such payments on shares
        of Series C Preferred Stock for all past dividend periods and the then
        current dividend period. When dividends are not paid in full (or a sum
        sufficient for such full payment is not set apart) upon the shares of
        Series C Preferred Stock and the shares of any other series of capital
        stock ranking on parity as to dividends with shares of Series C
        Preferred Stock, all dividends declared upon shares of Series C
        Preferred Stock and any other series of capital stock ranking on a
        parity as to dividends with Series C Preferred Stock shall be declared
        pro rata so that the amount of dividends declared per share on Series C
        Preferred Stock and such other series of capital stock shall in all
        cases bear to each other the same ratio that accrued dividends per share
        on Series C Preferred Stock and such other series of capital stock bear
        to each other.

                      (e) Except as provided in Section 2(d), unless full
        cumulative dividends on shares of Series C Preferred Stock have been or
        contemporaneously are declared and paid or declared and a sum sufficient
        for the payment thereof set apart for payment for all past dividend
        periods and the then current dividend period, no dividends (other than
        in shares of Common Stock or other capital stock ranking junior to
        Series C Preferred Stock as to dividends and amounts upon liquidation)
        shall be declared or paid or set aside for payment or other dividend
        shall be declared or made upon the shares of Common Stock, Class B
        Common Stock, Class C Common Stock, Series A Preferred Stock, Series B
        Preferred Stock or any other capital stock of the Corporation ranking
        junior to or on a parity with Series C Preferred Stock as to dividends
        or amounts upon liquidation, nor shall any shares of Common Stock, Class
        B Common Stock, Class C Common Stock, Series A Preferred Stock, Series B
        Preferred Stock or any other capital stock of the Corporation ranking
        junior to or on a parity with Series C Preferred Stock as to dividends
        or amounts upon liquidation be redeemed, purchased or otherwise acquired
        for any consideration (or any moneys be paid to or made available for a
        sinking fund for the redemption of any such capital stock) by the
        Corporation (except by conversion into or exchange for other capital
        stock of the Corporation ranking junior to Series C Preferred Stock as
        to dividends and amounts upon liquidation).




                                      - 2 -


<PAGE>   3
                      (f) Any dividend payment made on shares of Series C
        Preferred Stock shall first be credited against the earliest accrued but
        unpaid dividend due with respect to shares of Series C Preferred Stock
        which remains payable.

               3.     LIQUIDATION RIGHTS.

                      (a) Subject to the rights of series of Preferred Stock
        which may from time to time come into existence, upon any voluntary or
        involuntary liquidation, dissolution or winding up of the affairs of the
        Corporation, then, before any distribution or payment shall be made to
        the holders of any shares of Common Stock or any other class or series
        of capital stock of the Corporation ranking junior to Series C Preferred
        Stock in the distribution of assets upon any liquidation, dissolution or
        winding up of the affairs of the Corporation, the holders of shares of
        Series C Preferred Stock shall be entitled to receive out of assets of
        the Corporation legally available for distribution to stockholders,
        liquidation distributions in the amount of the liquidation preference of
        $25.00 per share, plus an amount equal to all dividends accrued and
        unpaid thereon. After payment of the full amount of the liquidating
        distributions to which they are entitled, the holders of shares of
        Series C Preferred Stock will have no right or claim to any of the
        remaining assets of the Corporation, including the Series A Preferred
        Stock and the Series B Preferred Stock. In the event that, upon any such
        voluntary or involuntary liquidation, dissolution or winding up of the
        affairs of the Corporation, the available assets of the Corporation are
        insufficient to pay the amount of the liquidation distributions on all
        outstanding shares of Series C Preferred Stock and the corresponding
        amounts payable on all shares of other classes or series of capital
        stock of the Corporation ranking on a parity with Series C Preferred
        Stock in the distribution of assets upon any liquidation, dissolution or
        winding up of the affairs of the Corporation ("Parity Stock"), then the
        holders of shares of Series C Preferred Stock and Parity Stock shall
        share ratably in any such distribution of assets in proportion to the
        full liquidating distributions to which they would otherwise be
        respectively entitled.

                      (b) A consolidation or merger of the Corporation with or
        into any other entity or entities, or a sale, lease, conveyance or
        disposition of all or substantially all of the assets of the Corporation
        or the effectuation by the Corporation of a transaction or series of
        related transactions in which more than 50% of the voting power of the
        Corporation is disposed of, shall not be deemed to be a liquidation,
        dissolution or winding up of the affairs of the Corporation within the
        meaning of this Section 3.

               4.     REDEMPTION.

                      (a) Shares of Series C Preferred Stock are not redeemable
        prior to October 10, 2002. On and after October 10, 2002, the
        Corporation at its option upon not less than 30 nor more than 90 days'
        written notice may redeem outstanding shares of Series C Preferred
        Stock, in whole or in part, at any time or from time to time, for cash
        at a redemption price of $25.00 per share, plus an amount equal to all
        dividends accrued and unpaid thereon to the date fixed for redemption,
        without interest. The redemption price of shares of Series C Preferred
        Stock (other than the portion thereof consisting of accrued and unpaid
        dividends) is payable solely out of proceeds from the sale of other
        capital stock of the Corporation, which may include Common Stock,
        Preferred Stock, depositary shares, interests, participations or other
        ownership interests in the Corporation however designated (other than
        debt securities converted into or exchangeable for capital stock), and
        any rights, warrants or options to purchase any thereof. Holders of
        shares of Series C Preferred Stock to be redeemed shall surrender such
        shares of Series C Preferred Stock at the place designated in such
        notice and shall be entitled to the redemption price and any accrued and
        unpaid dividends payable upon such redemption following such surrender.
        If fewer than all of the




                                      - 3 -


<PAGE>   4
        outstanding shares of Series C Preferred Stock are to be redeemed, the
        number of shares to be redeemed will be determined by the Corporation
        and such shares may be redeemed pro rata from the holders of record of
        such shares in proportion to the number of such shares held by such
        holders (with adjustments to avoid redemption of fractional shares) or
        by lot in a manner determined by the Corporation.

                      (b) Unless full cumulative dividends on all shares of
        Series C Preferred Stock and Parity Stock shall have been or
        contemporaneously are declared and paid or declared and a sum sufficient
        for the payment thereof set apart for payment for all past dividend
        periods and the then current dividend period, no shares of Series C
        Preferred Stock or Parity Stock shall be redeemed unless all outstanding
        shares of Series C Preferred Stock and Parity Stock are simultaneously
        redeemed; provided, however, that the foregoing shall not prevent the
        purchase or acquisition of shares of Series C Preferred Stock or Parity
        Stock pursuant to a purchase or exchange offer made on the same terms to
        holders of all outstanding shares of Series C Preferred Stock or Parity
        Stock, as the case may be. Furthermore, unless full cumulative dividends
        on all outstanding shares of Series C Preferred Stock and Parity Stock
        have been or contemporaneously are declared and paid or declared and a
        sum sufficient for the payment thereof set apart for payment for all
        past dividend periods and the then current dividend period, the
        Corporation shall not purchase or otherwise acquire directly or
        indirectly any shares of Series C Preferred Stock or Parity Stock
        (except by conversion into or exchange for shares of capital stock of
        the Corporation ranking junior to Series C Preferred Stock and Parity
        Stock as to dividends and amounts upon liquidation).

                      (c) Notice of redemption will be mailed at least 30 days
        but not more than 90 days before the redemption date to each holder of
        record of shares of Series C Preferred Stock at the address shown on the
        stock transfer books of the Corporation. Each notice shall state: (i)
        the redemption date; (ii) the number of shares of Series C Preferred
        Stock to be redeemed; (iii) the redemption price per share; (iv) the
        place or places where certificates for shares of Series C Preferred
        Stock are to be surrendered for payment of the redemption price; and (v)
        that dividends on shares of Series C Preferred Stock will cease to
        accrue on such redemption date. If fewer than all shares of Series C
        Preferred Stock are to be redeemed, the notice mailed to each such
        holder thereof shall also specify the number of shares of Series C
        Preferred Stock to be redeemed from each such holder. If notice of
        redemption of any shares of Series C Preferred Stock has been given and
        if the funds necessary for such redemption have been set aside by the
        Corporation in trust for the benefit of the holders of shares of Series
        C Preferred Stock so called redemption, then from and after the
        redemption date, dividends will cease to accrue on such shares of Series
        C Preferred Stock, such shares of Series C Preferred Stock shall no
        longer be deemed outstanding and all rights of the holders of such
        shares will terminate, except the right to receive the redemption price.

                      (d) The holders of shares of Series C Preferred Stock at
        the close of business on a Dividend Record Date will be entitled to
        receive the dividend payable with respect to such shares of Series C
        Preferred Stock on the corresponding Dividend Payment Date
        notwithstanding the redemption thereof between such Dividend Record Date
        and the corresponding Dividend Payment Date or the Corporation's default
        in the payment of the dividend due. Except as provided above, the
        Corporation will make no payment or allowance for unpaid dividends,
        whether or not in arrears, on shares of Series C Preferred Stock which
        have been called for redemption.

                      (e) Series C Preferred Stock will not be subject to any
        sinking fund or mandatory redemption, except as provided in Article
        NINTH of the Charter of the Corporation.




                                      - 4 -



<PAGE>   5
               5.     VOTING RIGHTS.

                      (a) Except as indicated in this Section 5, or except as
        otherwise from time to time required by applicable law, the holders of
        shares of Series C Preferred Stock will have no voting rights.

                      (b) If six quarterly dividends (whether or not
        consecutive) payable on shares of Series C Preferred Stock or any Parity
        Stock are in arrears, whether or not earned or declared, the number of
        directors then constituting the Board of Directors of the Corporation
        will be increased by two, and the holders of shares of Series C
        Preferred Stock, voting together as a class with the holders of shares
        of any other series of Parity Stock entitled to such voting rights (any
        such other series, the "Voting Preferred Stock"), will have the right to
        elect two additional directors to serve on the Corporation's Board of
        Directors at any annual meeting of stockholders or a properly called
        special meeting of the holders of Series C Preferred Stock and such
        other Voting Preferred Stock until all such dividends have been declared
        and paid or set aside for payment. The term of office of all directors
        so elected will terminate with the termination of such voting rights.

                      (c) The approval of a majority of the outstanding Series C
        Preferred Stock and all other series of Voting Preferred Stock similarly
        affected, voting as a single class is required in order to (i) enter
        into a share exchange that affects shares of Series C Preferred Stock or
        the Voting Preferred Stock, or consolidate with or merge the Corporation
        with or into any other corporation, unless in each such case each share
        of Series C Preferred Stock and Voting Preferred Stock remains
        outstanding without a material adverse change to its terms and rights or
        is converted into or exchanged for preferred stock of the surviving
        entity having preferences, conversion and other rights, voting powers,
        restrictions, limitations as to dividends, qualifications and terms or
        conditions of redemption thereof identical to that of a share of Series
        C Preferred Stock or the Voting Preferred Stock, or (ii) authorize,
        reclassify, create, or increase the authorized amount of any class of
        stock having rights senior to Series C Preferred Stock or the Voting
        Preferred Stock with respect to the payment of dividends or amounts upon
        liquidation, dissolution or winding up of the affairs of the
        Corporation. However, the Corporation may create additional classes of
        Parity Stock and capital stock ranking junior to Series C Preferred
        Stock as to dividends or amounts upon liquidation, dissolution or
        winding up of the affairs of the Corporation ("Junior Stock"), increase
        the authorized number of shares of Parity Stock and Junior Stock and
        issue additional series of Parity Stock and Junior Stock without the
        consent of any holder of Series C Preferred Stock.

                      (d) The approval of two-thirds of the outstanding Series C
        Preferred Stock and all other series of Voting Preferred Stock similarly
        affected, voting as a single class, is required in order to amend the
        Corporation's Articles Supplementary or Charter to affect materially and
        adversely the rights, preferences or voting power of the holders of
        shares of Series C Preferred Stock or the Voting Preferred Stock.

                      (e) Except as provided above and as required by law, the
        holders of Series C Preferred Stock are not entitled to vote on any
        merger or consolidation involving the Corporation, on any share exchange
        or on a sale of all or substantially all of the assets of the
        Corporation.




                                      - 5 -


<PAGE>   6
               6.     CONVERSION.

                      The shares of Series C Preferred Stock are not convertible
        into or exchangeable for any other property or securities of the
        Corporation, except that each share of Series C Preferred Stock is
        exchangeable into Excess Stock as provided in Article NINTH of the
        Charter of the Corporation.

               7.     STATUS OF REDEEMED OF REACQUIRED STOCK.

                      In the event any shares of Series C Preferred Stock shall
        be redeemed pursuant to Section 4 hereof or reacquired, the shares so
        redeemed or reacquired shall revert to the status of authorized but
        unissued shares of Series C Preferred Stock available for future
        issuance and reclassification by the Corporation.







                                      - 6 -



<PAGE>   7
        IN WITNESS WHEREOF, SPIEKER PROPERTIES, INC. has caused these presents
to be signed in its name and on its behalf by its Chief Financial Officer and
Executive Vice President and witnessed by its Secretary on October 8, 1997.



WITNESS:                                    SPIEKER PROPERTIES, INC.




  /s/ Sara H. Reynolds                      By:   /s/ Craig G. Vought
--------------------------------                --------------------------------
Sara H. Reynolds                                    Craig G. Vought
Secretary                                           Chief Financial Officer and
                                                    Executive Vice President


        THE UNDERSIGNED, Chief Financial Officer and Executive Vice President of
SPIEKER PROPERTIES, INC., who executed on behalf of the Corporation the Articles
Supplementary of which this certificate is made a part, hereby acknowledges in
the name and on behalf of said Corporation the foregoing Articles Supplementary
to be the corporate act of said Corporation and hereby certifies that the
matters and facts set forth herein with respect to the authorization and
approval thereof are true in all material respects under the penalties of
perjury.




                                                /s/ Craig G. Vought
                                                --------------------------------
                                                Craig G. Vought





                                      - 7 -