How Wyoming engineers make snow plow itself

As we drove across the vastness of Wyoming on Interstate 80 last week, my kids and I were struck by the beauty of the landscape, the abundance of antelope and other wildlife, and most of all, the hundreds of miles of fences.

After driving through what seemed like hundreds of miles of giant windmills in Kansas and Colorado a couple of weeks before, we first thought that the fences might be banks of solar panels, similarly harnessing renewable energy resources. But before long, it became clear that the fences were simply made of wood, and not connected in any way that would keep animals in or out, even though cattle seemed to enjoy lying in their shade.

What were they? Why were they there?