Assuming a custodian account is opened in the State of Utah and the minor passes away, who would be the beneficiary to the funds. I've searched all over the Utah Code -- Statutes and Constitution found at utah.gov but I can't find anything.

You would haveto look toward the Utah Probate Code - it would be passed on the the rightful hiers. Look up 75-2-103 - Share of heirs other than surviving spouse.