[1_Of_We]

Check Article 1, Section 8, Clause 17

[Bob]

I'm assuming you mean this portion:

...and to exercise like Authority 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;

That's one huge penumbra, or is that an emanation?

Does that seem anything close to what makes up federal land today? How much of that area is actually being used for its specific intended purposes?