I can’t seem to find anything in my copy of the Constitution, other than the District of Columbia, regarding ‘federal land’. Am I missing something?
Federal lands need to be absorbed by the States... obviously.
Check Article 1, Section 8, Clause 17
So: 35 of the 50 states were created by Congress out of pre-existing federal lands. Most of the federal estate today consists of lands the federal government has always owned and that were retained at the time of statehood. In addition, much smaller tracts have been purchased (or donated by private owners) over the years for various purposes. Many of the Civil War battlefields now owned and managed by the National Park Service, for example, were acquired by purchase and donation, but the acreage involved in such sites is dwarfed by the lands retained by the federal government at the time of statehood.
The real argument is whether the federal government should have deeded all public lands over to the various states at the time of statehood. This has never been done automatically. Remember that in the early federal period, the ongoing sale of federal lands to the public was a major source of federal revenues (along with tariffs). What happened in the 1880's, however, was that the arable lands had largely been sold, and the remaining federal estate was largely in the desert and mountain west (and later in Alaska) where yeoman agriculture was no longer the driving interest. Congress realized that timber, mining, and grazing interests were the primary drivers, and that huge tracts of federal lands were now being acquired for a song by large corporate interests, not the pioneer families of historical memory. Congress balked at selling millions of acres at a time to the robber barons, so it shifted to a leasing orientation.
Western lands advocates argue that these lands should be shifted to state ownership. That is a defensible argument, but it would take an act of Congress. These lands have always been federally owned.