<PAGE>
 
                                                                   EXHIBIT 10.13

                           [RECORDERS APPEARS HERE]


                                           FOR RECORDER'S USE ONLY
                                                                  --------------


                              ASSIGNMENT OF LEASE
                              -------------------

     GENES, LTD,, a California Limited Partnership and its Successor , GENES
CAPITAL MANAGEMENT COMPANY, an Arizona Corporation, as assignor, for a valuable
consideration, the receipt of which is hereby acknowledged, does hereby assign
to I.T.E., LTD., an Arizona Limited Partnership, its interest, being the
interest of GENES, LTD., a California Limited Partnership as lessor in and under
that certain Assignment of Lease dated June 24, 1980 and recorded July 3, 1980
as Instrument No. 121237, Official Records of Riverside County Records, State of
California; being the interest of LAPAN LANDPLAN 72, a Limited Partnership, as
lessor in and under that certain lease date October 20, 1971, and recorded
November 23, 1971 as Instrument No, 134252, Official Records, Riverside County
Records, State of California,

Dated: 9/15/87
      --------------     

                                                           [SEAL APPEARS HERE]

                                                /s/ Signature appears here
                                           -------------------------------------
                                           Genes Capital Management Company,
                                           An Arizona Corporation
                                           By: Patricia Lapan, President

--------------------------------------------------------------------------------
STATE OF CALIFORNIA         )
                              ss. 
COUNTY OF ALAMEDA           )
         -------------------   

On September 15, 1987, before me, the undersigned, a Notary Public in and for 
   ------------------
said State, personally appeared Patricia Lapan known to me to be the ___________
                                --------------                       
President, of the corporation that executed the within instrument, and known to
be the persons who executed the within instrument on behalf of the corporation
therein named, and acknowledged to me that such corporation executed the within
instrument pursuant to its by-laws or a resolution of its board of directors.


WITNESS my hand and official seal.       [SEAL OF MARY A. MUSGROVE - NOTARY
                                          PUBLIC - CALIFORNIA ALAMEDA COUNTY
                                          APPEARS HERE]

Signature /s/ Mary A. Musgrove
         --------------------------
         Mary A. Musgrove
----------------------------------- 
     Name (Typed or Printed)
<PAGE>
 
                                 GROUND LEASE
                                 ------------

        THIS GROUND LEASE, made and entered into this 25TH day of June, 198O, by
and between GENES, Ltd. , a California limited partnership ("Lessor") and SUMMIT
HEALTH LTD., a California corporation ("Lessee");

                             W I T N E S S E T H:
                             - - - - - - - - - -

        WHEREAS, Lessor is the owner of certain real property more particularly
described in Exhibit "A" attached hereto, in the City of Hemet, County of
Riverside, State of California; and

        WHEREAS, Lessor desires to lease to Lessee and Lessee desires to hire
from Lessor such real property upon the covenants and subject to the conditions
set forth herein;

        NOW, THEREFORE, in consideration of the mutual covenants and promises
contained herein, the parties hereto agree as follows:

    1.  Lease. Lessor hereby leases to Lessee and Lessee hereby hires from
        -----                                                             
Lessor all of that certain real property located on Devonshire Avenue more
particularly described in Exhibit "A" attached hereto, for the term and pursuant
to all of the convenants agreements and conditions contained herein.

    2.  Term. The term of this lease shall commence as of the date hereof and
        ----
shall continue for a period of fifty (50) years thereafter.

    3.  Rental.
        ------

        (a) During the term hereof, Lessee will pay rent to Lessor at Lessor's
address for notices hereunder or at such ether place as Lessor may from time to
time notify lessee in writing,


                                      -1-
<PAGE>
 
in advance, on the first day of each and every calendar month, the sum of One
Thousand Two Hundred Dollars ($1,200.00) per month, for a period of twelve
months.

        (b) The basic rent shall be increased by three per cent (3%) for each
and every succeeding twelve (12) months. In order to avoid misunderstanding or
ambiguity, the monthly rent from month thirteen (13) through twenty four (24)
shall be One Thousand Two Hundred Thirty Six Dollars ($1,236.00), payable in
advance each and every month. The monthly rent for month number twenty five (25)
through thirty six (36) shall be One Thousand Two Hundred Seventy Three Dollars
and Eight Cents ($1.,273.08), payable monthly in advance. The monthly rent for
month number thirty seven (37) through forty eight (48) shall be One Thousand
Three Hundred Eleven Dollars and Twenty Seven Cents ($1,311.27), payable
monthly in advance. The rent for each succeeding twelve (12) month period shall
be increased by three percent (3%) of the rent paid the preceding twelve (12) 
months.

    4.  NET LEASE.
        --------- 

        (a) This lease is intended to be a Net Lease in that it is the intention
of the parties hereto that rent payable to the Lessor shall not be reduced by
any cost or charge whatsoever, and that all expenses and charges, whether for
upkeep, maintenance, insurance, taxes, utilities and other charges of a like
nature or type or otherwise, shall be paid by Lessee.

        (b) Lessee agrees that it will pay and discharge punctually, each and
every cost, expense and obligation of every kind and nature whatsoever, for the
payment of which Lessor is, or shall or may be or become, liable by reason of
its estate or interest in the leased premises, or any portion thereof, or by
reason of any rights or interest of Lessor in or under this lease,


                                      -2-
<PAGE>
 
or by reason of or in any manner connected with or arising out of the ownership,
possession, leasing, operations management, maintenance, alteration, repair,
rebuilding, use or occupancy of the leased premises, or by any other reason
whether similar or dissimilar to the foregoing, foreseen or unforeseen,
connected with or arising out of the leased premises or this lease; provided,
however, that nothing herein shall be construed as obligating Lessee to pay or
discharge any lien or encumbrance upon the leased premises existing as of the
date hereof or hereafter created by Lessor. Lessee further agrees that it will
pay and discharge punctually as and when the same shall become due and payable,
at least five (5) days before delinquency and without penalty, all real estate
taxes, taxes upon or measured by rents, personal property taxes, privilege
taxes, excise taxes, business and occupational license taxes, water charges,
sewer charges, assessments (including, but not limited to, assessments for
public improvements or benefits) and all other governmental taxes, impositions
and charges of every kind and nature whatsoever, whether or not now customary or
within the contemplation of the parties hereto and regardless of whether the
same shall be extraordinary or ordinary, general or special, unforeseen or
foreseen, or similar or dissimilar to any of the foregoing (each such tax, water
charge, sewer charge, assessment and other governmental imposition and charge
which Lessee is obligated to pay hereunder being herein sometimes termed "Tax"),
which, at any time during the term hereof, shall be or become due and payable by
Lessor or by Lessee, or by both Lessor and Lessee, and which shall be levied,
assessed or imposed:

         (1) upon or with respect to, or shall be or become liens upon, the
    leased premises or any portion thereof or

                                      -3-
<PAGE>
 
any interest of Lessor therein or under this lease; or

         (2) upon or against, or which shall be measured by, or shall be or
    become liens upon, any rents or rental income, as such, payable to or on
    behalf of Lessor, in connection with the leased premises or any interest of
    Lessor therein;

         (3) upon or with respect to the ownership, possession, leasing,
    operation, management, maintenance, alteration, repair, rebuilding, use or
    occupancy by Lessee of the leased premises or any portion thereof or any
    building or improvement located thereon; or

         (4) upon this transaction or any document to which Lessee is a party
    creating or transferring an interest or an estate in the leased premises; or

         (5) upon or against Lessor any interest of Lessor in the leased
    premises in any manner and for any reason whether similar or dissimilar to
    the foregoing;

under or by virtue of any present or future law, statute, ordinance, regulation
or other requirement of any governmental authority whatsoever, whether federal,
state, county, city, municipal or otherwise, it being the intention of the
parties hereto that, insofar as the same may lawfully be done, the provisions of
this Paragraph should be so construed to provide that the amount of rental
reserved to Lessor under Paragraph 3 of this lease shall be net to Lessor.

    (c) If by law any tax or assessment with respect to the leased premises is
payable, or may at the option of Lessee be paid, in installments, Lessee may,
whether or not interest shall accrue on the unpaid balance thereof, pay the
same, and any accrued interest or any unpaid balance thereof, in installments as
each installment becomes due and payable, but in any event

                                      -4-
<PAGE>
 
before any fine, penalty, interest or cost may be added thereto for nonpayment
of any installment or interest.

    (d) Lessee covenants to furnish to Lessor, at least once in each calendar
year during the term of this lease, a certificate of an authorized officer of
Lessee to the effect that all Taxes with respect to the leased premises have
been paid. If Lessee shall fail to pay and discharge any Tax when and as
required by this Paragraph, Lessor may, but shall not be obligated to, pay and
discharge such Tax.

    (e) Any provision in this lease to the contrary notwithstanding, Lessee
shall not be required to pay, discharge, or remove any Tax (including penalties
and interest) , upon or against the leased premises, or any part thereof, so
long as Lessee shall in good faith contest the same or the validity thereof by
appropriate legal proceedings, and shall give Lessor prompt notice in writing of
its intention to do so at least ten (10) days before any delinquency occurs, and
so long as said legal proceedings shall operate to prevent the collection of the
tax, assessment, forfeiture, lien or imposition so contested, and/or the sale of
the leased premises, or any part thereof, to satisfy the same. Pending any such
legal proceedings Lessor shall not have the right to pay, remove or discharge
such Tax thereby contested; provided Lessee shall, upon the written request of
Lessor, protect and indemnify Lessor against all loss, cost, expense and damage
resulting therefrom; and provided further, that if at any time payment of such
Tax shall become necessary to prevent the delivery of a tax deed conveying the
leased premises or any portion thereof because of nonpayment, then Lessor may,
but shall not be required to, pay the same in sufficient time to prevent the
delivery of such tax deed. In the event of any such contest, Lessee shall,

                                      -5-
<PAGE>
 
within five (5) days after the final determination thereof, adversely to
Lessee, pay and discharge the amounts involved in or affected by such contest,
together with any penalties, fines, interest, costs and expenses that may have
accrued thereon or that may result from any such action by Lessee. Any
proceeding or proceedings for contesting the validity or amount of any Tax or to
recover back any Tax paid by Lessee, may be brought by Lessee at Lessee s own
expense, in the name of Lessor or in the name of Lessee, or both, as Lessee may
deem advisable; provided, however, that if any such proceeding be brought by
Lessee, Lessee shall indemnify and save harmless Lessor against any and all
loss, cost or expense of any kind that may be imposed upon Lessor in connection
therewith.

    (f)  Notwithstanding any provision herein to the contrary:

         (1) Lessee shall not be obligated to pay any federal or state income or
    franchise tax that may be payable or chargeable to Lessor under the Internal
    Revenue Code or any other similar tax or charge that may be payable by or
    chargeable to Lessor, under any present or future law of the United States
    or any State thereof, or imposed by any other governmental agency, upon or
    imposed with respect to or measured by (aa) any income of Lessor unrelated
    to this lease and (bb) the rents reserved hereunder to the extent that the
    foregoing taxes are applicable to such rents and are similarly imposed upon
    the other ordinary non-rental income and profits of Lessor. Nor shall Lessee
    be obligated to pay any personal property tax levied upon or with respect to
    any personal property of Lessor, or any inheritance, transfer estate,
    succession or other similar tax or charge that may be payable under any
    present or future law of the United

                                      -6-
<PAGE>
 
    States or the State of California, or imposed by any political or taxing
    subdivision thereof, or by any other governmental agency, by reason of the
    devolution, succession, transfer, passing by inheritance, devise,
    acquisition or becoming effective of the right to possession and enjoyment
    of all or any part of the estate of Lessor in the premises or the leased
    premises, whether by descent, deed, testamentary provision, trust deed,
    gift, mortgage, or otherwise.

    5.  Insurance. Lessee shall (at its own cost and expense) keep and maintain
        ---------                                                              
in full force during the term hereof public liability insurance covering the
leased premises and Lessee s activities therein against claims for personal
injury and death in an amount of not less than Five Hundred Thousand Dollars
($500,000.) for injury or death of any one person, and One Million Dollars
($1,000,000.) for injury or death of all persons in any one accident, and not
less than Nine Hundred Thousand Dollars ($900,000.) property damage. Any and all
insurance policies carried pursuant to this paragraph shall name Lessor as an
additional insured thereunder, and shall be payable as the interests of Lessor
and Lessee may appear. Lessor and Lessee hereby agree that no insurer of any
interest of either shall have any right of subrogation against the other and
that any and all insurance policies carried by either on the leased premises or
any part thereof shall contain a full waiver of subrogation by the insurer
against the other and its assigns. Lessee shall furnish to Lessor a certificate
evidencing the fact that the insurance described in this paragraph has been
obtained and is in full force and effect, and that such insurance cannot be
cancelled without ten (10) days' prior notice to Lessor.

    6.  Compliance with Laws. Lessee shall promptly comply with
        --------------------                                   

                                      -7-
<PAGE>
 
all laws, ordinances, rules and regulations of all Federal, State, County and
Municipal Governments now in force or that may be enacted hereafter affecting
the leased premises or Lessee's use and occupancy thereof. Lessee shall have the
right, however, to contest any such law, ordinance, rule or regulation by
appropriate legal action; provided Lessee shall, upon the written request of
Lessor, protect and indemnify Lessor against all loss, cost, expense or damage
resulting therefrom;

    7.  Indemnification. Lessee covenants and agrees, at its own cost and
        ---------------                                                  
expense, to indemnify and save harmless Lessor from and against and all claims
whatsoever by or on behalf of any person, firm, corporation (including Lessee or
any subtenant of Lessee) or governmental authority, arising out of or in
connection with the occupation, use, possession, conduct or management of, or
any work or thing whatsoever done, in or about, or transactions of Lessee
concerning the leased premises, including, but without limitation, claims for
injury or death to persons and claims of damage to property (including the
leased premises or any part thereof, or any property of Lessee located within or
about the leased premises), whether or not caused by any latent or other defects
upon the leased premises; provided, however, that Lessee shall not be required
to indemnify Lessor for any damage or injury of any kind whatsoever arising out
of the negligence of Lessor, its agents, or employees.

    8.  Eminent Domain.
        -------------- 

        It is understood and agreed that in the event the whole of the leased
premises is taken by governmental authority or by any corporation, public or
private, under the right of eminent domain, this lease shall cease and come to
an end and all rights of Lessee thereunder shall terminate, except as
hereinafter

                                      -8-
<PAGE>
 
provided. In the event that only a part of the premises are taken, the rent
herein reserved shall be adjusted for the remainder of the leased premises so
that Lessee shall be required to pay for the balance of the term that portion of
rent herein reserved which is appropriate for the value of the part of the
leased premises remaining after condemnation. If there is not sufficient space
remaining to conduct the business of Lessee, the lease shall terminate. From the
proceeds of the condemnation award after trial, or as otherwise agreed upon with
the condemnation authority without trial, Lessor and Lessee shall receive
reimbursement as follows: Lessor shall receive the value attributable to the
real property and improvements thereon subject however, to the right of the
Lessee to receive the sum that may be apportioned to the Lessee for the value of
the leasehold estate and interest of the Lessee.

    9.  Default.
        ------- 

        (a) Should Lessee default in the performance of any convenant,
    agreement or condition herein contained with reference to the payment of
    rent, and such default continue for thirty (30) days after such default, or
    should Lessee default in the performance of any covenant, agreement or
    condition herein, other than the payment of rent, and such default
    continues, without diligent effort being made to cure it, for sixty (60)
    days after receipt by Lessee of written notice thereof from Lessor, Lessor
    may:

        (1) Re-enter the leased premises, with or without process of law and
    remove all persons therefrom; or

        (2) Declare the lease term ended and re-enter the leased premises,
    with or without process of law, and remove all persons therefrom.

                                      -9-
<PAGE>
 
          (b) The exercise by Lessor of such rights of re-entry shall entitle
Lessor to sublet the leased premises for the account of Lessee and to apply the
proceeds of such rentals against the rentals due under the Lease to Lessor from
Lessee.

          (c) None of the rights herein granted to Lessor in the event of a
default by Lessee shall prejudice any other legal remedies available to Lessor
other than those herein enumerated. (No act of the Lessor shall be deemed an act
terminating this lease or declaring this lease term ended unless written notice
is served upon the Lessee expressly setting forth therein that the Lessor elects
to terminate said lease or to declare the lease term ended.

          10. Right to Inspect. Lessee shall permit Lessor and/or its agents to
              ----------------
enter into and upon the leased premises at all reasonable times for the purpose
of inspecting the same or for the purpose of posting notices of non-liability
for alterations, additions, repairs or new construction.

          11. Independent Operation. Nothing in this lease shall cause Lessor in
              ---------------------
any way to be construed as a partner, joint venture, or associated in any way
with the Lessee in the operation of said premises, or subject Lessor to any
obligation, loss, charge or expense connected with or arising from the operation
or use of said premises or any part thereof. Lessee, in any case not resulting
from Lessor's act of negligence, will hold Lessor exempt and harmless from all
claims and liability for death or of injury to any person or damage to the
goods, wares or merchandise of any person, or claims of any person arising from
the use of the premises by Lessee in the conduct of Lessee's business, or from
the failure of Lessee to keep the premises in good condition and repair.

          Lessee agrees further to defend on behalf of and in the name

                                     -10-
<PAGE>
 
of Lessor against any claim or demand arising out of Lessee's use of the leased
premises or arising out of claimed injury to person or property upon or in the
leased premises, whether meritorious or otherwise, said obligation to include
the retention and payment of legal counsel and investigation costs from the
first notice that any claim or demand is to be or may be made.

          12. Attorneys' Fees. Should either party commence an action against 
              ---------------
the other to enforce any obligation hereunder, the pre-vailing party shall be
entitled to recover a reasonable attorney's fee from the other unless expressly
otherwise provided herein.

          13. Heirs, Successors and Assigns. Each and every covenant, agreement
              -----------------------------
and condition contained herein shall be binding upon and insure to the benefit
of each of the parties, its successors and assigns.

          14. Notices. All notices required to be given hereunder shall be in
              -------
writing. Such notices shall be sent by United States registered mail, postage
prepaid, addressed to Lessee; Summit Health LTD., 4070 Laurel Canyon Blvd.,
Studio City, Ca. 91604; and to Lessor: Genes, LTD, 1750 Scenic View Crt., San
Leandro, Ca. 94577.

          15. Termination and Quitclaim. Upon the termination of this lease,
              -------------------------
whether by the expiration of the term thereof or for any other reason as
provided in this lease, then all of Lessee's interest in and to said leased
premises shall revert to the Lessor, and the Lessee shall upon demand execute
and deliver a Quitclaim Deed in favor of the Lessor, quitclaiming and releasing
all its right, title and interest in and to the said premises, which exist by
virtue of landlord, tenant relationship.

          16. General Covenants. The invalidity of any portion of this lease
              -----------------
shall not prevent the remainder from being carried into effect. Whenever the
context of any provision shall require


                                     -11-
<PAGE>
 
it, the singular number shall be held to include the plural number, and vice
versa, and the use of any gender shall include any other or all genders. The
paragraph and section headings this lease contain are for convenience only, and
do not constitute a part of the provisions hereof. All exhibits to which
reference is made are deemed included in the lease whether or not actually
attached. No oral modification of, or amendment to, this lease shall be
effective, but this lease may be modified or amended by written agreement signed
by the Lessee and the Lessor. This lease binds, applies to and inures to the
benefit of, as the case may require, the respective heirs, executors,
administrators, successors and assigns of Lessor and Lessee.

          17. Execution of Documents. Lessee agrees to execute any and all
              ----------------------
documents which Lessor deems necessary in order to secure any financing or re-
financing; or for the purpose of recording any documents including but not
limited to a short form lease, an assignment, a conveyance or transfer of the
property or any document of any kind or nature so long as it does not interfere
with the rights of Lessee to the quiet and peaceful possession of the leased
premises for the full term hereof.

          Lessor agrees to cooperate with Lessee in the execution of any
documents which may be necessary for the Lessee's business purposes except that
Lessor shall not be required to subordinate its interest in the land for an
amount in excess of $750,000.00.

          18. Miscellaneous.
              -------------

              (a) The timeliness of the monthly rent which is payable in advance
and in accordance with the provisions of Paragraph 3, is of the essence to the
Lessor. In the event Lessee is unable for any reason to deliver the stipulated
rent to Lessor on or before the tenth (10) day of each and every month, the
Lessee shall be obligated to pay a late charge of One Hundred Dollars


                                     -12-
<PAGE>
 
($100.) which charge shall be in addition to the stipulated rent. This charge
shall be assessed for each and every month that said rent is not received on
time.

          (b) Upon the execution of this document, Lessee will deliver to Lessor
the sum of One Thousand Two Hundred Dollars ($l,200.00) for rents of the
premises from July 1, 1980 until July 31, 1980.

          IN WITNESS WHEREOF, the parties hereto have executed this instrument
in duplicate by proper persons thereunto duly authorized as of the day and year
first here and above written.


     LESSOR:       GENES, Ltd.,
                   A California Limited Partnership


                   By /s/ Pat Wahl
                     ----------------------------
                     Pat Wahl, General Partner
                                     

LESSEE: SUMMIT HEALTH LTD.                (CORPORATE SEAL)


                   By [SIGNATURE APPEARS HERE]
                     ---------------------------- 

                   By
                     ----------------------------


                                     -13-
<PAGE>
 
                               ADDENDUM TO LEASE
                               -----------------

          With respect to that certain Lease dated June 25, 1980 by and between
GENES, LTD , hereafter called "Lessor" and SUMMIT HEALTH LTD., hereafter called
"Lessee", there is one additional necessary provision. Since this provision may
be of transient nature, it is set forth here and below and shall be of no force
and effect at such time that the underlying obligation to Central Bank and/or
it's assigns is extinguished.

          Central Bank, originally known as Central Valley National Bank, is the
obligee under that certain Note secured by a Deed of Trust on the subject
property dated June 18, 1970. Under the terms of said Note, Central Bank is
entitled to additional interest in the amount of two per cent (2%) of the total
gross annual income received during the preceding calendar year from the
property described by the Deed of Trust. A copy of said 20 Note is attached
hereto as Exhibit "A".

          The Deed of Trust contains a provision for financial disclosure by the
Trustor. This provision is attached hereto as Exhibit "B".

          Lessee shall, upon request, provide any and all information required
by Central Bank in order to fulfill the obligations created by these
instruments. Lessor shall report the gross income from land rent and shall be
liable for the payment of the participation fee based upon the land rent 
received.

          At such time that Lessor repays the existing obligation in full, this
Addendum shall become null and void and the Lessee
<PAGE>
 
                                  EXHIBIT "A"

PARCEL 1:
--------

That portion of Lot 2 in Block 142 of the Lands of the Hemet Land Company, in
the County of Riverside, State of California, as per map recorded in Book 1 page
1-4 of Maps, in the office of the County Recorder of said County, described as
follows:

BEGINNING at a point on the center line of Devonshire Avenue, 165 feet East of
the intersection of the center line of San Jacinto Street with the center line
of Devonshire Avenue; THENCE South, parallel with the center line of San Jacinto
Street, 300 feet; THENCE East parallel with the center line of Devonshire
Avenue, 75 feet; THENCE North, parallel with the center line of San Jacinto
Street, 300 feet, to the center line of Devonshire Avenue; THENCE West, on the
center line of Devonshire Avenue, 75 feet, to the Point of Beginning;

EXCEPT the Southerly SO feet.

ALSO EXCEPT, that portion in Devonshire Avenue.


PARCEL 2:
--------

The Northerly 300 feet, measured from the center line of Devonshire Avenue, of
Lot 2, in Block 142 of the Lands of the Hemet Land Company, in the County of
Riverside, State of California, as per map recorded in Book 1 page 14 of Maps,
in the office of the County Recorder of said County.

EXCEPT the Easterly 345.20 feet;

ALSO EXCEPT the Westerly 240 feet, measured from the center line of San Jacinto
Street.

ALSO EXCEPT that portion in Devonshire Avenue;

ALSO EXCEPT that portion lying within Tehquitz Estates as per map recorded in
Book 42 page 91 of Maps, in the office of the County Recorder of said County.
<PAGE>
 
shall have not future reporting obligations.


Dated:      June 25, 1980

            LESSOR:       GENES, Ltd.,
                          A California Limited Partnership
                                                                     
                                                                       
                          By /s/ Pat Wahl
                            --------------------------------
                            Pat Wahl, General Partner

Dated: June 25, 1980

            LESSEE:       SUMMIT HEALTH LTD.
                  

                          By /s/ Signature appears here
                            -------------------------------

                          By
                            -------------------------------