Article 1 section 8 provides the enumerated power that specifically gives the Congress exclusive legislative authority in all maters whatsoever over the land in question.
Perhaps you could unpack your reasoning a little?
I’m not seeing anything in Article 1 Section 8 that allows the government to assert private property rights on grazing land.
Unless the whole area is one enormous post office :0)
I don’t see that. Please be more specific.
Nothing in Art 1 Sec 8 allows this at all.