Exhibit 4

Executed in
75 Counterparts
of which this is
Counterpart No. ___

IDAHO POWER COMPANY

TO

DEUTSCHE BANK TRUST COMPANY AMERICAS

AND

STANLEY BURG,

As Trustees under its Mortgage and Deed of Trust dated as of October 1, 1937.

_______________

Forty-second Supplemental Indenture
Dated as of May 1, 2007

TABLE OF CONTENTS[1]

                                                      Page                                    

Parties and Recitals........................................................................................................................... 1

ARTICLE I

Maximum amount of obligations to be secured by the indenture.......................................................... 5

ARTICLE II The Trustees

Acceptance of trust........................................................................................................................... 5
Recitals deemed made by the Company............................................................................................. 5

ARTICLE III Miscellaneous Provisions

Meanings of terms............................................................................................................................. 5
Ratification and Confirmation............................................................................................................. 5
Counterparts..................................................................................................................................... 5
Testimonium...................................................................................................................................... 6
Signatures and seals........................................................................................................................... 6
Acknowledgments............................................................................................................................. 8
Affidavits......................................................................................................................................... 11

 

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                                                                              i

SUPPLEMENTAL INDENTURE, dated as of the first day of  May, 2007, made and entered into by and between IDAHO POWER COMPANY, a corporation of the State of Idaho (successor by merger to Idaho Power Company, a corporation of the State of Maine, hereinafter sometimes called the "Maine Company"), whose address is 1221 West Idaho Street, Boise, Idaho 83702-5627 (hereinafter sometimes called the "Company"), party of the first part, and DEUTSCHE BANK TRUST COMPANY AMERICAS, formerly known as Bankers Trust Company, a corporation of the State of New York, whose post office address is 60 Wall Street, New York, New York  10005 (hereinafter sometimes called the "Corporate Trustee"), and Stanley Burg (hereinafter sometimes called the "Individual Trustee"), parties of the second part (the Corporate Trustee and the Individual Trustee being hereinafter together sometimes called the "Trustees"), as Trustees under the Mortgage and Deed of Trust dated as of October 1, 1937 hereinafter referred to; and

WHEREAS, the Maine Company has heretofore executed and delivered to the Trustees its Mortgage and Deed of Trust (hereinafter sometimes referred to as the "Original Indenture"), dated as of October 1, 1937, to secure the payment both of the principal of and interest and premium, if any, on all Bonds at any time issued and outstanding thereunder and to declare the terms and conditions upon which Bonds are to be issued thereunder; and

WHEREAS, the Maine Company was merged into the Company on June 30, 1989; and

WHEREAS, in order to evidence the succession of the Company to the Maine Company and the assumption by the Company of the covenants and conditions of the Maine Company in the Bonds and in the Original Indenture, as supplemented, contained, and to enable the Company to have and exercise the powers and rights of the Maine Company under the Original Indenture, as supplemented, in accordance with the terms thereof, the Company executed and delivered to the Trustees a Twenty-eighth Supplemental Indenture, dated as of June 30, 1989 (which supplemental indenture is hereinafter sometimes called the "Twenty-eighth Supplemental Indenture"); and

WHEREAS, said Twenty-eighth Supplemental Indenture was recorded in the records of the County of Elko, Nevada; the Counties of Baker, Grant, Harney, Malheur, Union and Wallowa, Oregon; the Counties of Ada, Adams, Bannock, Bear Lake, Bingham, Blaine, Boise, Bonneville, Butte, Camas, Canyon, Caribou, Cassia, Clark, Elmore, Gem, Gooding, Idaho, Jefferson, Jerome, Lemhi, Lincoln, Minidoka, Oneida, Owyhee, Payette, Power, Twin Falls, Valley and Washington, Idaho; the Counties of Lincoln and Sweetwater, Wyoming; and with the Secretary of State of Montana; and

WHEREAS, in accordance with the terms of the Original Indenture, the Maine Company or the Company has executed and delivered to the Trustees the following supplemental indentures in addition to the Twenty-eighth Supplemental Indenture:

Designation	Dated as of
First Supplemental Indenture	July 1, 1939
Second Supplemental Indenture	November 15, 1943
Third Supplemental Indenture	February 1, 1947
Fourth Supplemental Indenture	May 1, 1948
Fifth Supplemental Indenture	November 1, 1949
Sixth Supplemental Indenture	October 1, 1951
Seventh Supplemental Indenture	January 1, 1957
Eighth Supplemental Indenture	July 15, 1957
Ninth Supplemental Indenture	November 15, 1957
Tenth Supplemental Indenture	April 1, 1958
Eleventh Supplemental Indenture	October 15, 1958
Twelfth Supplemental Indenture	May 15, 1959
Thirteenth Supplemental Indenture	November 15, 1960
Fourteenth Supplemental Indenture	November 1, 1961
Fifteenth Supplemental Indenture	September 15, 1964
Sixteenth Supplemental Indenture	April 1, 1966
Seventeenth Supplemental Indenture	October 1, 1966
Eighteenth Supplemental Indenture	September 1, 1972
Nineteenth Supplemental Indenture	January 15, 1974
Twentieth Supplemental Indenture	August 1, 1974
Twenty-first Supplemental Indenture	October 15, 1974
Twenty-second Supplemental Indenture	November 15, 1976
Twenty-third Supplemental Indenture	August 15, 1978
Twenty-fourth Supplemental Indenture	September 1, 1979
Twenty-fifth Supplemental Indenture	November 1, 1981
Twenty-sixth Supplemental Indenture	May 1, 1982
Twenty-seventh Supplemental Indenture	May 1, 1986
Twenty-ninth Supplemental Indenture	January 1, 1990
Thirtieth Supplemental Indenture	January 1, 1991
Thirty-first Supplemental Indenture	August 15, 1991
Thirty-second Supplemental Indenture	March 15, 1992
Thirty-third Supplemental Indenture	April 1, 1993
Thirty-fourth Supplemental Indenture	December 1, 1993
Thirty-fifth Supplemental Indenture	November 1, 2000
Thirty-sixth Supplemental Indenture	October 1, 2001
Thirty-seventh Supplemental Indenture	April 1, 2003
Thirty-eighth Supplemental Indenture	May 15, 2003
Thirty-ninth Supplemental Indenture	October 1, 2003
Fortieth Supplemental Indenture	May 1, 2005
Forty-first Supplemental Indenture	October 1, 2006

                                                                             

each of which is supplemental to the Original Indenture (the Original Indenture and all indentures supplemental thereto together being hereinafter sometimes referred to as the "Indenture"); and

WHEREAS, the Original Indenture and said Supplemental Indentures (except said Fifteenth Supplemental Indenture) have each been recorded in the records of the County of Elko, Nevada; the Counties of Baker, Grant, Harney, Malheur, Union and Wallowa, Oregon; the Counties of Ada, Adams, Bannock, Bear Lake, Bingham, Blaine, Boise, Bonneville, Butte, Camas, Canyon, Caribou, Cassia, Clark, Elmore, Gem, Gooding, Idaho, Jefferson, Jerome, Lemhi, Lincoln, Minidoka, Oneida, Owyhee, Payette, Power, Twin Falls, Valley and Washington, Idaho; the Counties of Lincoln and Sweetwater, Wyoming; and with the Secretary of State of Montana; and

WHEREAS, the Maine Company or the Company has heretofore issued Bonds, under and in accordance with the terms of the Indenture in the following series and aggregate principal amounts:

                                                                             

Series	Principal Amount Issued	Principal Amount Outstanding
3-3/4% Series due 1967	$18,000,000	None
3-1/8% Series due 1973	18,000,000	None
2-3/4% Series due 1977	5,000,000	None
3% Series due 1978	10,000,000	None
2-3/4% Series due 1979	12,000,000	None
3-1/4% Series due 1981	15,000,000	None
4-1/2% Series due 1987