That kind of shit has been going on here in Nevada for 30 years, google "Sagebursh Rebellion" and you'll get the history over it. One guy even tried to bomb a Fed courthouse here in Reno over it about 20 years ago.

Not sure about the particulars of this case, sometimes the taking of horses and cattle on Fed lands are really egragious and unjustified; otheritmes the ranchers are in the wrong and it just doesn't take much to get people whipped-up about it because they're already angry at Fed land managers. There's a lot of gray area and sometmes the Feds haven't enforced the rules or boundries and then suddenly people find out that the parcel they've been grazing on for 70 years has been off-limits for that whole time.