I've seen these in a number of places in so. Idaho, usually on BLM land. There will be a string of white posts, about 5' tall and spaced maybe 1/4 to 1/2 mile apart. I don't know how far the line goes. They might be on flat ground or sometimes on some pretty steep terrain. They're nothing more than a steel post in the ground with a length of 4" PVC pipe over it. Originally I thought they might be for mining claims but I've never seen any mining activity anywhere near them.

“In a time of deceit telling the truth is a revolutionary act.”
― George Orwell

It's not over when you lose. It's over when you quit.