The Enclave Clause as ruled by SCOTUS in Fort Leavenworth R. Co. v. Lowe, 114 U.S. 525, 531, 5 S.Ct. 995, 29 L.Ed. 264 (1885). I am aware of this as I was for a time, the acting Garrison NCOIC for Ft Leavenworth.
In 1885, the Supreme Court ruled that there were two additional ways in which the United States could acquire federal enclaves: (1) the states could “cede” legislative jurisdiction to the United States, and (2) the United States could “reserve” legislative jurisdiction at the time of statehood. The Supreme Court added that these “cessions” and “reservations” were not limited to Enclave Clause (”needful building”) purposes.
Since the land transferred to the US government per the Treaty of Guadalupe Hidalgo (Article II Section 2 Treaty clause) and since the State of Nevada ceded the lands to the US Government as part of their Constitution, the lands belong to the US Government as a federal enclave. Further, since the lands are part of the Lake Mead National Recreation Area and needful buildings have been built on that property, the US Government owns and controls the land per Article I Section 8 both by fact and by SCOTUS ruling.