It's about a lot of things, but distilled to its essence, most of the people were there because of resentment against the government's ever expanding involvement in everyone's life. Key players in this drama included desert tortoises, generations of family grazing, state's rights, snipers tracking peaceful protestors, tiny "free speech" zones, and
maybe Harry Reid's shenanigans with a Chinese solar company that wanted the land. This map tells a small part of the story.

Consider it an angry white person's million man march (minus one or two people).
As a personal aside, I know someone who was there on Saturday. I haven't spoken to him yet but there's zero doubt that his patriotic fervor culminated in a hangover this morning from his Saturday night in Vegas.