The speaker announces a kind of song about empty places, "back of beyond" being a phrase for somewhere remote and far from anything. The first surprise is the detail chosen to prove the emptiness: not a lack of people or buildings, but the impossibility of finding a cow. It's a funny, down-to-earth measure of how far out we are.
The second half turns dreamier. In the desert, a flag would "need the wind," as if the cloth were waiting to be given a purpose. A miracle, the speaker suggests, might do no more for the night life than one hundred ants. That line is playful and a little deflating, since something as grand as a miracle is set beside a small crowd of insects.
The mood is quiet, wry and observant. The speaker doesn't seem unhappy about the emptiness. Instead there's affection for places where very little happens, and where small things, like ants, become the main event.