1.  Marriage Record:

2a.  1850 Census Index/Images (online at Ancestry.com; Image #60 of 220):  Sacramento City, Sacramento Co., CA, p. 165B, 601/630, enumerated 22 Oct 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):

C P Huntington	29	M		Merchant		Conn
Danl Hammond	26	M		????		NY
Edw Shultz	32	M		"		"
David Hays	25	M		None		"
Jno C Trueman	21	M		Clerk		"
Alfred Robinson	28	M		"		Vt

2b.  1850 Census Index/Images (online at Ancestry.com; Image #13 of 46):  Town of Oneonta, Otsego Co., NY, p. 132B, 535/574, enumerated 9 Aug 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):

Mrs. Collis Huntington	26	F			2500	Connecticut
Mary Stodard	18	F				"

Mary is most likely Elizabeth's sister.

3.  1860 Census Images (online at Ancestry.com; Image #79 of 619):  Sacramento P.O., Second Ward in Sacramento, Sacramento Co., Ca, p. 79, PN 79, 696/635, enumerated 19 Jun 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):

C P Huntington	39	M		Merchant	18000	15000	Conn
Elizabeth S "	35	F					"
Chas Miller	22	M		Clerk			NY

4.  1870 Census Index/Images (online at Genealogy.com; Image #9 of 54):  New York City (Ward 21), New York Co., NY, Roll 1009 (Book 1), p. 390A, PN 9, 34/52, enumerated 22 Jul 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):

Huntington C P	50	M	W	Prest C P R R of Cal	10000	200,000	Connecticut
__________ Elizabeth S	47	F	W	At Home			Connecticut
__________ Clara E	9	F	W	At School			California
Hammond Scott	16	M	W	At School			California
Rogers Mary	?0	F	W	Cook			Ireland
Clarey Kate	30	F	W	Waitress			Ireland
Stoddard Hattie	18	F	W	At School			Connecticut
Heller? Mary	25	F	W	At Home			New York
Hammond Diomed?	33	F	W	At Home			New York
McCoy Andrew	30	M	W	Coachman			Ireland

5.  LDS.  Family Search: Census Records: 1880 United States (online at FamilySearch.org):

Census Place: New York, New York (Manhattan), New York City-Greater, New York
Source: FHL Film #1254880; NARA Film #T9-0880; Pg 414D
	Relation	Sex	Marr	Race	Age	Birthplace	Occupation	Fa	Mo
Collis P. HUNTINGTON	Self	M	M	W	58	CT	Vice Pres Pacific Rr	...	...
Elizabeth HUNTINGTON	Wife	F	M	W	57	CT	Keeping House	CT	CT
Clara E. HUNTINGTON	Dau	F	S	W	19	CA	At School	CT	CT
Jennie STODDARD	Niece	F	S	W	12	CA	At School	CT	CT
Annie WEBSTER	Other	F	S	W	40	MA	Housekeeper	MA	MA
Margrette CARROLL	Other	F	S	W	25	IRE	Servant	IRE	IRE
Annie LALLY	Other	F	S	W	35	IRE	Cook	IRE	IRE
Sarah MC SORLEY	Other	F	S	W	25	IRE	Servant	IRE	IRE

6.  1890 Census:  the 1890 Census Population Schedules were destroyed.

7.  1900 Census Index/Images (online at Genealogy.com; Image #3 of 31 — mis-indexed "Collie Huntington"):  2 Fifty-Seventh Street, Borough of Manhattan (19th Ward), New York City, New York County, NY, Roll 1115 (Book 2), p. 257A, SN 2, SD 1, ED 778, enumerated 2 Jun 1900, official enumeration date 1 Jun 1900 (extracted by Diana Gale Matthiesen):

1900:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).
1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	19	20	22	23	24	25	26	27
17	17	Huntington Collis	Head	W	M	Oct 1820	79	M	16			CT	CT	CT	Financere	0	Y	Y	Y	O	F	H
		__________ Arabela	Wife	W	F	Jun 1856	43	M	16	1	1	AL	MD	VA			Y	Y	Y
		[plus eleven servants*]

*three butlers, a footman, a cook, two maids, a laundress, a housekeeper, a fireman, and an elevator-man.
Arabella appears to be fibbing about her age and birthplace (she was born in 1852 in Virginia).

8.  1910 Census Index/Images (online at Genealogy.com):  can't find our widow, at least not as head-of-household.

9.  1920 

10.  Henry Hall, ed.  1895-96.  America's Successful Men of Affairs: an Encyclopedia of Contemporaneous Biography.  Vol. 1.  The New York Tribune, New York (online at Ancestry.com).  See biographical sketch of our subject. 

11.  Daniel Van Pelt.  c1898.  Leslie's History of the Greater New York. Vol. III: Encyclopedia of New York Biography and Genealogy.  Arkell Publ. Co., NY (online at HeritageQuest at Genealogy.com).  See biographical sketch of our subject. 

12.  Rossiter Johnson, ed.  1904.  Twentieth Century Biographical Dictionary of Notable Americans.  Vol. V.  The Biographical Society, Boston, MA (online at Ancestry.com).  See biographical sketch of our subject. 

13.  Anon.  1915.  The Huntington Family in America: a Genealogical Memoir of the Known Descendants of Simon Huntington from 1633 to 1915.  Huntington Family Assn., Hartford, CT (online at GenealogyLibrary.com).  See excerpt. 

14.  Rockwell D. Hunt, ed.  1932.  California and Californians.  Vol. 2.  Lewis Publ., Chicago (online at Ancestry.com).  On p. 331:

By this time there had been formed in California an anti-slavery party which, though not strong in numbers at first, contained on its roster many prominent names, such as Collis P. Huntington, Cornelius Cole, Mark Hopkins, Charles and Edwin B. Crocker, and Leland Stanford.  David C. Broderick, United States Senator 1857-59, also made his influence felt against the “slave oligarchy” that dominated the State politics of the time.

15.  Eric Howard.  1932.  "Collis P. Huntington."  Pages 76-77 in Rockwell D. Hunt, ed.  California and Californians.  Vol. 4.  Lewis Publ., Chicago (online at Ancestry.com). 

16.  Stephen Birmingham.  1982.  The Grande Dames.  Simon & Schuster, NY.

p.188

Few women in American history have managed to conceal their pasts as successfully as Arabella.  While passing as his "niece," she was the mistress of C.P. Huntington for nearly fifteen years. Collis Potter Huntington was the mastermind behind the enormous Central Pacific and Southern Pacific Railroads.  He was a man of stupendous wealth who kept his first wife so totally in the background that most people did not know he was married.

17.  George Childs Kohn, ed.  2001.  The New Encyclopedia of American Scandal.  Checkmark Books, NY.  Index at Ancestry.com indicates an entry for Collis P. HUNTINGTON.

18.  Biography: Collis Potter HUNTINGTON (online at the web site of the Huntington Family Association).