Here's Thom Hartmann on the subject:
My comment on Thom Hartmann's claims against Cliven Bundy:
... to exercise like Authority over all Places purchased by the Consent of the Legislature of the State in which the Same shall be, for the Erection of Forts, Magazines, Arsenals, dock-Yards, and other needful Buildings." Does that really cover 81% of Nevada? A reasonable-person, plain-language reading suggests it does not."
What constitutional provision provides for the federal government purchasing/owning 81% of Nevada, most of which percentage doesn't fall under "other needful Buildings"?
Is mile after mile of desert not used for Forts, Magazines, Arsenals, or dock-Yards really a "needful Building"? The Supreme Court says it is. I say that, that court should have said it isn't and should have expected an amendment to the Constitution before so much raw land could legally become land of the US government.
If there's another clause covering this, I'll stand better educated. It wouldn't be the first time. So, let me know.