You could start educating yourself with 28 USC.
My research comes up with the following:
http://www.law.cornell.edu/uscode/text/43/1068
Note the several limitations
- up to 160 acres
- that it is up to the Sec Interior’s discretion
- that it must start no later than Jan 1 1901
- must have paid taxes levied by the State
From what I have read, even if Bundy did file a claim of adverse possession, he would only gain at most 160 acres (not the 600,000) and even that would be in jepardy as it is unlikely that the State of Nevada has assessed taxes due on that land.