At times the issue of common law marriage arises in the context of divorcing parties, or separating parties, or those who need to establish a legal marriage relationship. Utah law on the subject is as follows:
30-1-4.5. Validity of marriage not solemnized.
(1) A marriage which is not solemnized according to this chapter shall be legal and valid if a court or administrative order establishes that it arises out of a contract between a man and a woman who:
(a) are of legal age and capable of giving consent;
(b) are legally capable of entering a solemnized marriage under the provisions of this chapter;
(c) have cohabited;
(d) mutually assume marital rights, duties, and obligations; and
(e) who hold themselves out as and have acquired a uniform and general reputation as husband and wife.
(2) The determination or establishment of a marriage under this section shall occur during the relationship described in Subsection (1), or within one year following the termination of that relationship. Evidence of a marriage recognizable under this section may be manifested in any form, and may be proved under the same general rules of evidence as facts in other cases.
These kinds of cases are generally tricky and are usually best brought with the assistance of an attorney.