I stumbled across this interview with Josh where he talks about his muse, which he refers to as The Monster:
Feeding the Monster
Here's a snippet:
The monster is the invisible force that decides what you write about. Some people call it “The Muse,” but I’ve never found that to be a particularly apt description for a creature so voracious. This is no gossamer-clad maiden. I don’t know much about it, but I know that it lives deep in the synaptic jungle, its tail twitching lazily, its slow-breathing bulk heaving sulfurous sighs as it waits. You have to feed the monster everything you come across, be it books, music or movies, your friends and enemies and any other shiny baubles you find strewn in your path. You shovel everything you’ve got—a long-handled snow shovel works best—into its big toothy mouth, and it chews everything up and sighs once again. It never says “thank you,” and you don’t expect any gratitude, but once in a while the monster will taste something it really enjoys. When it does, you’ll notice a slight lift of its scaly brow and a narrowing of its keyhole pupils. It doesn’t give away much, but if you know your monster, that’s all you need to see.
This other article has a sample of lyrics from one of his best songs Thin Blue Line and a paragraph from Bright's Passage highlighting his ability to invoke images and emotions in his novel just as powerful as in his songs.
Bright's Passage by Josh Ritter
I will definitely be reading this in the near future.