Utah Affirmative Defense: Unilateral mistake

[R]escission is available as a remedy for a unilateral mistake of fact. In doing so, we emphasized the following elements that must be established in order to obtain such relief:

1. The mistake must be of so grave a consequence that to enforce the contract as actually made would be unconscionable.
2. The matter as to which the mistake was made must relate to a material feature of the contract.
3. Generally the mistake must have occurred notwithstanding the exercise of ordinary diligence by the party making the mistake.
4. It must be possible to give relief by way of rescission without serious prejudice to the other party except the loss of his bargain. In other words, it must be possible to put him in status quo.

John Call Eng'g, Inc. v. Manti City Corp., 743 P.2d 1205, 1209-10 (Utah 1987).