Thomas Henry CLARK, SR.

Sources:

Ancestral File
Pioneers and Prominent Men of Utah, p. 310, 810. Bio.
Mormon Pioneer Overland Database - LDS.org/churchhistory/
Pedigree Resource File
Ancestry World Tree
New.FamilySearch.org, Feb 2010
Grantsville, UT, Cemetery Index - Ancestry.com, parents listed

Notes:

                   PIONEERS AND PROMINENT MEN OF UTAH:
    - (Excerpt) Clark, Thomas H. (son of Thomas Clark).  Born May 7, 1805, Acton, Herefordshire, Eng.  (Came to Utah Oct. 10, 1852.  Married Charlotte Gayley (daughter of William Gayley), who was born Jan 27, 1803... Family home Grantsville, Utah.

PIONEER:
    Came to Utah 1852 with wife, children and family.  Unidentified pioneer company.

PARENT CONNECTION:
    Evidence of correct parentage comes from the Grantsville Cemetery Index.  Note that the mother's name on the death record in the index shows Mary Plain, rather than Sarah Plain.  While this does not place doubt in the ancestry, further research may help to clarify why the alternate name was given.