At the tech art roundtable day 2 at GDC there were questions about USD, so here are some links to the artist resources mentioned:
Book of USD: Book of USD - Getting Started with Universal Scene Description (USD)
USD in 15 minutes: What is USD? (The basics of Pixar’s 3D file format in 15 minutes)
Would love to see any others that are more artist friendly, as usually all the resources on USD are only programmer/engineer friendly.