<DOCUMENT>
<TYPE>EX-5.1
<SEQUENCE>3
<FILENAME>dex51.txt
<DESCRIPTION>OPINION OF JAMES J. THEISEN, ESQ
<TEXT>
<PAGE>

                                                                    EXHIBIT 5.1

                           UNION PACIFIC CORPORATION
                               1416 Dodge Street
                             Omaha, Nebraska 68179

                                                               October 30, 2001

Union Pacific Corporation
1416 Dodge Street
Omaha, NE 68179

Dear Ladies and Gentlemen:

   I am Senior Corporate Counsel of Union Pacific Corporation, a Utah
corporation (the "Company"), and I am familiar with the Registration Statement
on Form S-4 (the "Registration Statement") being filed by the Company with the
Securities and Exchange Commission under the Securities Act of 1933, as
amended, with respect to the shares of common stock, par value $2.50 per share,
of the Company (the "Issued Stock") issuable upon completion of the Company's
offer to exchange (the "Offer") in which each of the issued and outstanding
shares of common stock ("Motor Cargo Common Stock"), no par value, of Motor
Cargo Industries, Inc., a Utah corporation ("Motor Cargo"), may be exchanged
for the right to receive from the Company, at the election of the holder
thereof: (i) 0.26 of a share of Common Stock or (ii) $12.10 in cash in
accordance with the terms of the Agreement and Plan of Merger, dated as of
October 15, 2001, among Motor Cargo, the Company and Motor Merger Co., a Utah
corporation and wholly owned subsidiary of the Company (the "Merger Agreement").

   I, or attorneys under my supervision, have examined the Merger Agreement,
the Registration Statement, the Tender Offer Statement on Schedule TO and forms
of the letter of election and transmittal and other ancillary documents being
filed by the Company. I have examined such other documents and made such other
investigations as I have deemed necessary or advisable for purposes of this
opinion.

   Based thereon, I am of the opinion that the Issued Stock, when delivered in
exchange for shares of Motor Cargo Common Stock pursuant to the Offer will be
duly authorized, validly issued, fully paid and nonassessable.

   I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement. I also consent to the use of my name under the caption
"Legal Matters" in the prospectus contained in the Registration Statement.

                                          Very truly yours,

                                          /s/ James J. Theisen, Jr., Esq.


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</DOCUMENT>
