The Congress are a natural evolution of more than 60 years of purely American music. With a spirit rooted just south of the Mason-Dixon Line, and now calling Denver — “The Queen City of the West” — their home, they’ve got enough soul, grit, and have spent enough time in the woodshed and on the road to call them pretty much whatever you want. But whatever words you think you need to describe their contribution to the American music tradition — save your breath. The Congress play Rock & Roll, soulfully. The band plays tonight at Shakdown Bar at the top of Bridge Street in Vail Village. The show starts at 10 p.m. and is $5 at the door.