Here is the details that led me to the previous post. I assumed Maria(h) L was a first spouse as she is old enough to have been in the 1850 family listing but isn't, but is co listed with him from 1856 to 1870. Was she a sister? Effie was born 1876/77 consistent with potential divorce / death of Maria L and marriage to Sarah J Huffman 25 Sep 1873. There is an unprovenced marriage between an Edwin Clark and Maria Richards in Ohio 1853. Can't prove its the same pair but its the closest thing I can come up with to explain who Maria L Clark is. See below for LDS listing.

1850
Edwin Clark
Age: 25
Estimated Birth Year: abt 1825
Birth Place: Virginia
Gender: Male
Home in 1850 (City,County,State): Harrison, Fayette, Indiana
Family Number: 207
Household Members: Name Age
James Clark 73
Eliza Clark 65
William Clark 30
Louisa Clark 28
Elizabeth Clark 26
Edwin Clark 25
Isaac Clark 23

1856
Edwin C Clark
Birth Year: abt 1828
Birth Place: Virginia
Gender: Male
Census Date: 1856
Residence State: Iowa
Residence County: Boone
Locality: Pleasant
Roll: IA_69
Line: 5
Family Number: 73
Household Members: Name Age
James Clark 79
Maria L Clark 24
Jane E Clark 12
John W Clark 34
Edwin C Clark 28

1860
Name: Edwin C Clark
Age in 1860: 35
Birth Year: abt 1825
Birthplace: Virginia
Home in 1860: Lexington, Lafayette, Missouri
Gender: Male
Post Office: Lexington
Household Members: Name Age
Jno W Clark 41
Edwin C Clark 35
Elizabeth J Clark 22
Maria L Clark 23
John W Johnson 35
Mary F Johnson 24
Florence Johnson 2
Johnny Johnson 1
James Carmac 27
J Sahlamer 50

1870
Name: Edwin M Clark
Birth Year: abt 1830
Age in 1870: 40
Birthplace: Virginia
Home in 1870: Grape Grove, Ray, Missouri
Race: White
Gender: Male
Household Members: Name Age
Edwin M Clark 40
John W Clark 45
Mariah L Clark 43
Elisabeth Clark 42
John T Smith 10

1880
Edwin C. Clark
Home in 1880: Bogart, Carroll, Missouri
Age: 55
Estimated Birth Year: abt 1825
Birthplace: Virginia
Spouse's Name: Sarah J. Clark
Father's birthplace: Virginia
Mother's birthplace: Virginia
Occupation: Farming
Marital Status: Married
Household Members: Name Age
Edwin C. Clark 55
Sarah J. Clark 25
Effie B. Clark 3
Edwin Clark 1

LDS Listing for Maria Richards and Edwin Clark
Name: Maria Richards
Birth: Abt 1827 - Conneaut, Ashtabula, Ohio
Death: 23 Mar 1916
Marriage: est 1848 - Conneaut, Ashtabula, Ohio
Parents: John Chauncey Richards, Fanny Hine
Spouse: Edwin Clark

FWIW
John R