Utah Code § 57-2-10: Proof of execution -- How made.

The proof of the execution of any conveyance whereby real estate is conveyed or may be affected shall be:

(1) by the testimony of a subscribing witness, if there is one; or,

(2) when all the subscribing witnesses are dead, or cannot be had, by evidence of the handwriting of the party, and of a subscribing witness, if there is one, given by a credible witness to each signature.