I am contending they no longer own it precisely BECAUSE it was part of the Territory of Utah, and was admitted to the Union as a State. As part of becoming a state, the entire territory went from being federally owned to being state owned (or at any rate it SHOULD have).
And when Utah was admitted as a state, Section 3, Clause 2 of the Enabling Act read: "That the people inhabiting said proposed State do agree and declare that they forever disclaim all right and title to the unappropriated public lands lying within the boundaries thereof; and to all lands lying within said limits owned or held by any Indian or Indian tribes; and that until the title thereto shall have been extinguished by the United States, the same shall be and remain subject to the disposition of the United States, and said Indian lands shall remain under the absolute jurisdiction and control of the Congress of the United States;" So what part of "forever disclaim all right and title" to public lands is unclear?